Research ArticleEffect of Hygrothermal Aging on the Mechanical Properties ofFluorinated and Nonfluorinated Clay-Epoxy Nanocomposites
Salah U Hamim and Raman P Singh
School of Mechanical and Aerospace Engineering College of Engineering Architecture and TechnologyOklahoma State University Stillwater OK 74078 USA
Correspondence should be addressed to Raman P Singh ramansinghokstateedu
Received 11 April 2014 Revised 31 July 2014 Accepted 1 August 2014 Published 29 October 2014
Academic Editor Miguel A Esteso
Copyright copy 2014 S U Hamim and R P SinghThis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited
Hydrophilic nature of epoxy polymers can lead to both reversible and irreversiblepermanent changes in epoxy upon moistureabsorption The permanent changes leading to the degradation of mechanical properties due to combined effect of moistureand elevated temperature on EPON 862 Nanomer I28E and Somasif MAE clay-epoxy nanocomposites are investigated in thisstudy The extent of permanent degradation on fracture and flexural properties due to the hygrothermal aging is determined bydrying the epoxy and their clay-epoxy nanocomposites after moisture absorption Significant permanent damage is observed forfracture toughness and flexural modulus while the extent of permanent damage is less significant for flexural strength It is alsoobserved that permanent degradation in Somasif MAE clay-epoxy nanocomposites is higher compared to Nanomer I28E clay-epoxy nanocomposites Fourier transform infrared (FTIR) spectroscopy revealed that both clays retained their original chemicalstructure after the absorption-desorption cycle without undergoing significant changes Scanning electron microscopy (SEM)images of the fracture surfaces provide evidence that SomasifMAE clay particles offered very little resistance to crack propagation incase of redried specimens when compared to Nanomer I28E counterpart The reason for the observed higher extent of permanentdegradation in Somasif MAE clay-epoxy system has been attributed to the weakening of the filler-matrix interface
1 Introduction
Epoxy polymers are very important class of advancedmateri-als Their main distinction from other types of polymers liesin their densely crosslinked molecular structure This cross-linking leads to a number of favorable thermal and mechan-ical properties including high strength and modulus highcreep resistance high glass transition temperature lowshrinkage and better chemical resistanceThese properties inconjunction with ease of processing have made epoxy resinsan attractive choice for use in many engineering compo-nents and structures They have found huge applications inaerospace automotive packaging coating andmicroelectricindustries In recent years researchers have developed andinvestigated polymer nanocomposites based on awide varietyof micro-nanoscale fillers including clay particles [1ndash6]aluminum particles [7] TiO
2particles [8] graphenes [9 10]
carbon nanotubes [11ndash13] and halloysites [4 14] to improve
the mechanical properties of epoxy polymers Among thevarious reinforcements large aspect ratio layered silicates orclays are especially attractive for enhancing the barrier pro-perties and hence can be used to improve the resistance tomoisture degradation
Epoxy polymers are characteristically hydrophilic whichmeans that they have strong affinity towards water Thisnature of epoxy resins makes them susceptible to high mois-ture absorption in general depending on the nature of theepoxy resin the equilibrium moisture uptake can be in therange of 1ndash7 [15] Absorbed moisture usually degradesthe functional structural and mechanical properties of thepolymer matrix [4 16ndash19] It has been reported that mechan-ical and thermal properties of epoxy-based systems areseverely affected by moisture absorption in comparisonto other matrix materials such as bismaleimide (BMI)polyetheretherketone (PEEK) and cyanate ester [20]
Hindawi Publishing CorporationInternational Scholarly Research NoticesVolume 2014 Article ID 489453 13 pageshttpdxdoiorg1011552014489453
2 International Scholarly Research Notices
Water absorption into a polymer matrix leads to changein both chemical and physical characteristics and affects themechanical properties through different mechanisms such asplasticization crazing hydrolysis and swelling Plasticizationis the most important physical change that occurs throughthe interaction of the water molecules with polar groups inthe matrix which can severely depress the glass transitiontemperature [12 18 21ndash24] For example high moistureabsorption capability of TGDDMDDS epoxy resin whichis about 7wt reduces the system Tg from 260∘C to 130∘C[25ndash27] In general for most epoxy systems Tg is reduced by20∘C1 wt of moisture intake [28] The decrease in modulusof epoxy has also been reported to be due to plasticizationaccording to several studies [29ndash32] Other studies showedthat the decrease in modulus resulted from crazing [33ndash35] where the absorbed water acted as a crazing agentcontinuously decreasing the mechanical strength of epoxieswith exposure time in water [34] This was supported bySEM micrographs of epoxies which have shown cavitiesand fractured fibrils that could be explained by a moistureinduced crazingmechanism [33]The aforementioned chem-ical changes mainly include chain scission and hydrolysis[22 36] Plasticization is considered reversible upon dryingwhile other effects of moisture absorption are irreversible
In recent years effect of moisture absorption on themechanical properties of neat epoxy and clay-epoxy nano-composite has been frequently studied Zhao and Li reportedthat tensile strength and modulus decreased for bothneat epoxy and nanocomposites upon moisture absorptionwhile the tensile strain increased significantly for mois-ture absorbed samples Although failure occurred in brittlemanner effect of plasticization was found in SEM imageswhich showed shear yielding for both neat epoxy andnanocomposite samples after being exposed to moisture[37] Similar degradation in mechanical properties has beenreported by Glaskova and Aniskevich [38] Alamri and Lowreported lower flexural strength and modulus for halloysitenanoclay and nanosilicon carbide nanocomposites as a resultof moisture absorption [4] Al-Qadhi et al studied the effectof moisture absorption on the tensile properties of clay-epoxy nanocomposites and found that tensile strength andmodulus decrease as a result of water uptake [24] Wang et alinvestigated the effect of hydrothermal degradation onmechanical properties such as tensile strength modulus andfracture toughness with immersion duration [39] ForDGEBA epoxy systems fracture toughness and moduluswere not influencedmuchwith immersion time while tensilestrength decreased for nanocomposites Tensile and flexuralproperties of nanoclay reinforced composite laminates andCNT reinforced nanocomposites have also been found to beaffected adversely as a result of moisture absorption [12 40]According to the study conducted by Buck et al at elevatedtemperature combination ofmoisture and sustained load sig-nificantly reduced ultimate tensile strength of E-glassvinyl-ester composite materials [41] A study on elastic modulusof epoxy polymer after absorption-desorption cycle showedrecovery of property from wet condition although modulusremained at a lower value than the as-prepared samples
for lower filler volume For higher volume fraction of rein-forcement elastic modulus improved to a value which wasmore than the elastic modulus of the as-prepared samples[19] Phua et al also reported recovery of tensile propertiesafter refrying OMTT-PBS nanocomposites A similar studyconducted by Ferguson and Qu showed recovery of elasticproperties from moisture saturated state after a desorptioncycle [42] However dersquoN eve and Shanahan did not observeany recovery of elastic modulus after absorption-desorptioncycle at elevated temperature [22] It is evident from thepublished works that moisture absorption can severely altermechanical properties of epoxies by decreasing the elasticmodulus [12 29 33] tensile strength [3 12] shear modulus[30 31] flexural strength and flexural modulus [40 43] yieldstress and ultimate stress [32] as water uptake increases
Most of the research on polymer-clay nanocompositeshas been mainly focused on investigating the effect of mois-ture absorption on mechanical properties such as elasticmodulus and tensile strength Although fracture toughnessis a very important property for these nanocomposites asthese are used in various structural applications the effectsof moisture absorption on fracture toughness of polymer-clay nanocomposites have not been studied extensivelyDurability of polymerclay nanocomposites is still neededto be studied in depth particularly for hygrothermal agingin which the degradation of the mechanical properties andloss of integrity of these nanocomposites occur from thesimultaneous action of moisture and temperature This studyon clay-epoxy nanocomposites was designed to investigatethe effect of hygrothermal aging on mechanical properties ofthese nanocomposites Two different clay particles were usedto investigate the effect of clay structure on the permanentproperty changes due to hygrothermal aging A drying cyclewas employed to quantify the recovery of the propertiesafter hygrothermal aging This was helpful to understandthe extent of permanent degradation that occurred by thecombined application of elevated temperature and moistureMechanical properties in terms of fracture toughness flex-ural strength and flexural modulus are the properties thatwere studied Scanning electron microscopy and Fouriertransform spectroscopy were conducted to further elucidatethe underlying fracture mechanisms of these preconditionedspecimens
2 Materials and Characterization
The epoxy resin used for this study is EPON 862 which is adiglycidyl ether of bisphenol FThe curing agent used for thisresin systemwas amoderately reactive low viscosity aliphaticamine curing agent Epikure 3274 Both of these chemi-cals were supplied by Miller-Stephenson Chemical Com-pany Inc Dunbury Connecticut Two structurally differentclay particles were used as reinforcement Nanomer I28Eis a surface modified montmorillonite based layered silicate(Nanocor Inc Arlington Heights IL) modified with aquaternary amine (trimethyl stearyl) Somasif MAE (Co-OpChemical Co Japan) which was the other clay particle usedfor this study is a synthetic mica modified with dimethyl
International Scholarly Research Notices 3
Table 1 Structure of the studied clay particles
Clay StructureNanocor I28E (Na)
119910(Al2minus119910
Mg119910)(Si4O10)(OH)
2119899H2O
025 lt 119910 lt 06
Somasif MAE (Na)2119909(Mg)3minus119909(Si4O10)(F119886OH1minus119886)
2119899H2O
015 lt 119909 lt 05
08 lt 119886 lt 10
dihydrogenated tallow ammonium chloride Table 1 showsthe structural composition of the clay particles used in thisstudy
21 Sample Preparation Epoxy was preheated to 65∘C beforedesired amount of clay was introduced and mixed usingmechanical mixer for 12 hours To reduce the viscosityof the mixture and to facilitate mixing temperature wasmaintained at 65∘C using a hot plate for the entire durationof mixing The mixture was then degassed for around 30minutes to remove any entrapped air bubbles Bubble-freemixture of clay and epoxy was then shear-mixed using ahigh-speed shear disperser (T-25 ULTRA TURRAX IKAWorks Inc North Carolina USA) for 30 minutes Duringthis process temperature was maintained at 65∘C using anice bath Subsequently the mixture was then degassed untilit was completely bubble-free Curing agent was added tothe mixture at 100 40 weight ratio and carefully hand-mixed to avoid introduction of any air bubble After it wasproperly mixed the final slurry containing epoxy and claywas poured into an aluminum mold and cured at roomtemperature for 24 hours followed by postcuring at 121∘Cfor 6 hours The final sample had a nominal dimension of17780mmtimes15250mmtimes1270635mm To study the effectof loading percentage the weight fraction of the clay in thenanocomposite was varied from 05 to 20
22 Environmental Preconditioning After specimens werecut into the final required dimension according to the ASTMstandards D5045 and D790 they were subjected to degrada-tion Specimens from each nanocomposite were taken andsubmerged in purified deionized boiling water for 24 hoursWater saturated specimens were dried in an oven at 110∘C for6 hours to remove moisture from the samples leaving onlypermanent degradation in the form of bonded water
intensity factor 119870Ic was determined by single edge notchbend (SENB) test as per the ASTM D5045 on univer-sal testing machine (Instron 5567 Norwood MA) in adisplacement-controlled mode with fixed crosshead speed of10mmmin Nominal dimension for the SENB test sampleswas 6730mm times 1520mm times 635mm A notch was cre-ated using precision diamond saw (MK-370 MK DiamondProducts Inc Torrance CA USA) and afterwards a sharpprecrack with ratio of 045 lt 119886119882 lt 055 was created by
tapping a fresh razor blade into the notch At least 5 speci-mens were tested for every condition Fracture toughness forthe specimens was calculated in terms of critical stress inten-sity factor 119870Ic The crack length 119886 was measured using anoptical microscope (Nikon L150) which has a traveling platewith graduations
119870Ic =119875
119861radic119882
119891(
119886
119882
) (1)
where 119875 = maximum applied force (N) 119861 = thickness ofthe specimen (mm)119882 = width of the specimen (mm) and119891(119886119882) = geometry factor and it is given by the followingequation
119891(
119886
119882
) =
3 (119878119882)radic119886119882
2 (1 + 2 (119886119882)) (1 minus 119886119882)
32
times [199 minus (
119886
119882
)(1 minus
119886
119882
)
times(215 minus 393 (
119886
119882
) + 27(
119886
119882
)
2
)]
(2)
where 119878 = support span (mm) and 119886 = length of the precrack(mm)
24 Flexural Strength and Flexural Modulus DeterminationFlexural strength and flexural modulus were determinedusing three-point bend (3PB) test according to ASTM D790on universal testing machine (Instron 5567 Norwood MA)The nominal dimension for the flexural test specimens was5590mmtimes1270mmtimes635mmThe crosshead speed for thetest was calculated using (3) The crosshead speed was foundto be 135mmmin Consider
119877 =
119885119871
2
6119889
(3)
where 119877 = rate of crosshead motion (mmmin) 119871 = supportspan (mm) 119889 = depth of beam (mm) and 119885 = rate ofstraining of the outer fiber (mmmmmin) = 001The flexural strength and flexural modulus were calculatedusing the following equations respectively
(MPa) 119875max = maximum load on the load-deflection curve(N) 119871 = support span (mm) 119887 = width of beam tested (mm)119889 = depth of beam tested (mm) and119898 = slope of the tangentto the initial straight-line portion of the load-deflection curve(Nmm of deflection)
25 Fracture Surface Morphology Surface morphology of thefractured specimens from SENB tests was observed using
4 International Scholarly Research Notices
Table 2 Weight changes in samples after preconditioning
scanning electron microscopy (Hitachi S-4800 FESEMDallas TX) As polymer materials are nonconductive toelectrons all fracture surfaces were sputtered with gold-palladium alloy before SEM imaging
26 Fourier Transform Infrared Spectroscopy FTIR spectros-copy measurements were performed using ATR-FTIR spec-trometer (Nicolet iS10 Waltham MA) using 64 scans at aresolution of 20 cmminus1 Each spectrum was recorded from4000 to 500 cmminus1 at room temperature Spectrawere analyzedusing OriginPro 90 (OriginLab Northampton MA)
3 Results and Discussions
31 Gravimetric Measurements Table 2 shows the relativeweight changes that occurred in the specimens after 24 hoursof boiling water absorption and 6 hours of high temperaturedesorption cycle For the studied material systems percent-age weight gain after absorption cycle showed no change asa function of clay loading percentage This observation wasdifferent from the findings reported by Glaskova and Aniske-vich for clay-epoxy nanocomposites [44] According to theirstudy moisture absorption was found to have increasedslightly with the increase of clay weight percentage Contrar-ily Alamri and Low reported decreasingmoisture absorptionwith increasing clay weight percentage [4] The reason whya different clay-epoxy nanocomposite system behaves differ-ently in moisture absorption test is still not clear and furtherinvestigation is required to understand it In this studyalthough both clays are structurally different the observedpercentage weight gain for both nanocomposite systems wasfound approximately to be the same These two observationsled to the conclusion that moisture diffusion process pri-marily depended on the polymer system under investigationMoisture desorption data showed that most of the absorbedwater is free water which can be driven out of the system bydrying For neat epoxy the amount of retained water afterdesorption cycle is less compared to the nanocompositesThis is possibly due to the fact that presence of clay hinderedthe moisture diffusion process in and out of the epoxypolymers An increasing trend in the amount of retainedmoisture for higher clay loading nanocomposites also sup-ported the aforementioned statement Amount of water
retained after the desorption cycle has been found to bealmost similar for both clay-epoxy nanocomposite systems
32 Fracture Toughness The critical stress intensity factorsas a function of clay loading percentage for Nanomer I28Eand Somasif MAE clay-epoxy nanocomposites are shown inFigure 1119870Ic values for the as-prepared samples are also listedas a reference
Critical stress intensity factor 119870Ic increased 28 for theas-prepared 05 wt Nanomer I28E clay-epoxy nanocom-posite compared to neat epoxy The reason behind thisobservation can be attributed to the layered structure of theclay Clay in a polymer material physically blocks bifurcatesand deflects the crack path compelling the crack to travellonger path which in turn results in higher toughness in aclay-polymer nanocomposite The toughening effect of clayon epoxy polymer started to decrease with any additionalclay reinforcement This is a common behavior for severaltypes of epoxy-clay nanocomposites and has been reportedin previous studies conducted on clay-epoxy nanocomposites[3 6 45 46] Depending on the processing technique andepoxy-clay interaction there is an optimum weight percent-age for which the property enhancement can be maximizedAny further addition of clay negates the positive effect byforming agglomerates due to improper exfoliation of the clayplatelets and thus results in stress concentration forcing thematerial to fail at lower loads For moisture saturated epoxy-clay nanocomposites119870Ic was found to be lower compared tothe as-prepared nanocomposite samples for all the NanomerI28E nanocomposites As water molecules diffuse into thenanofiller-epoxy interface debonding and weakening of theinterface occur resulting in poor stress transfer between thefiller and the epoxy matrix [43 47 48] Redried neat EPON862 free of void-filling water showed 29 reduction infracture toughness compared to the as-prepared neat EPON862 samples Addition of 05 wt of clay resulted in 16reduction in fracture toughness when compared to the as-prepared samples which was significantly less compared to29 reduction of neat epoxy For 20 wt Nanomer I28Eclay-epoxy nanocomposite redried samples were found to betougher than the as-prepared samples However the standarddeviation of the as-prepared sample was much higher whichcould possibly mean that the dried and the as-preparedsamples have no difference in toughness
International Scholarly Research Notices 5
06
08
1
12
14
16
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
Frac
ture
toug
hnes
sK
Ic(M
Pamiddotm
12
)
(a)
06
08
1
12
14
16
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
Frac
ture
toug
hnes
sK
Ic(M
Pamiddotm
12
)
(b)
Figure 1 Critical stress intensity factor 119870Ic as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxynanocomposites
For the as-prepared and moisture saturated samplesSomasif MAE nanocomposites showed comparable trend infracture toughness data clay reinforcement successfullyimproved the baseline epoxy properties andmoisture absorp-tion degraded the mechanical properties for all clay percent-ages However the permanent degradation after absorption-desorption cycle was found to be more prominent in the caseof Somasif MAE clay nanocomposites compared to NanomerI28E clay nanocomposites The recovery of property after6 hours of drying was negligible for Somasif MAE claynanocomposites whereas Nanomer I28E nanocompositesshowed significant recovery of property after drying Thedifference in property recovery of these two clay-epoxynanocomposites can be attributed to the structural differ-ences of the two clay particles and has been further investi-gated through SEM and FTIR technique
33 Flexural Properties Flexural modulus for the neat epoxyand clay-epoxy nanocomposites was determined from 3PBtest and has been plotted against clay loading percentage inFigure 2 for Nanomer I28E and Somasif MAE clay Flexuralmodulus increased almost linearly for both clays as a functionof clay loading percentage According to previous studieson epoxy polymers incorporation of hard substance suchas clay in polymer matrix results in higher modulus [49]When a load is applied on epoxy the polymer chains slidepast each other and deform This deformation is higher inless crosslinked structures compared to higher crosslinkedstructures Once layered silicates such as clay particles are
introduced in a polymer system it restricts the motion of thepolymer chain sliding and makes the matrix less pliable Asthe clay content increases it is more difficult for the polymerchains to untangle and move This increase in restriction ofpolymer chains is responsible for the increase in modulus asthe clay percentage increases
For the hygrothermally conditioned specimens themod-ulus is lower compared to the as-prepared specimens Thisbehavior observed is mostly due to the presence of waterinside the epoxy system which increases the ductility of theepoxy system Water acts as an effective plasticizer and candiffuse into the nanofiller-polymer interface and weaken thebonding between them [40 43] Presence of water in epoxysystem also results in an increase in free volume throughrupture of hydrogen bonding between polymer chains whichincreases the chain mobility and eases the segmental motionwhen a load is applied to the composite [50] These physicalchanges can be attributed to the observed lower modulus forwater absorbed specimens Other mechanisms affecting thepolymer such as hydrolysis and chain scission may also beresponsible for lowering the modulus Once hydrolysis andchain scission take place less bonding between the polymersmakes it more deformable resulting in lower modulus foraged samples [22 36 51] The effect of hygrothermal agingwas more severe in neat epoxy than in the nanocompositesFor neat EPON 862 flexural modulus decreased 20 afterhygrothermal aging whereas it was only 13 and 11 for05 wt of Nanomer I28E and Somasif MAE clay-epoxynanocomposites respectively In addition to being hard
6 International Scholarly Research Notices
24
26
28
3
32
34
36
38Fl
exur
al m
odul
us (G
Pa)
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(a)
24
26
28
3
32
34
36
38
Flex
ural
mod
ulus
(GPa
)Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(b)
Figure 2 Flexural modulus as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
substance clay particles have very high aspect ratioThe highaspect ratio of the clay platelets provides resistance againstpolymer chain mobility in a water absorbed ductile polymerleading to the observed lower degradation of flexural modu-lus values in comparison to neat polymer
For Nanomer I28E clay-epoxy samples conditioned at110∘C for 6 h recovery of flexural modulus was observedOnce redried free water residing in the microvoids wasevaporated and the effect of plasticizationwas not prominentanymore As a result the ductility of the polymer reducedand the recovery of mechanical properties from moistureabsorbed state occurred Nevertheless in case of SomasifMAE clay-epoxy samples modulus recovery was negligibleafter the desorption cycle Due to the structural differencebetween the two clay particles it is possible that the interfaceof Somasif MAE clay-epoxy is being more affected by thehygrothermal degradation than the Nanomer I28E clay-epoxy interface
Flexural strengths for the epoxy and clay-epoxy nano-composites were determined using three-point bend (3PB)test and are plotted against clay loading percentage in Figure 3for Nanomer I28E and Somasif MAE clay Figure 3 showsthat the addition of Nanomer I28E clay provided negligibleimprovement in flexural strength compared to neat epoxyThe maximum improvement in flexural strength was foundto be less than 10 for both clay-epoxy systems from the baseflexural strength of neat epoxy Similar observation has beenreported in the literature where addition of nanoclay parti-cles did not significantly improve the flexural strength of thesystem [52] Furthermore when 20 wt of clay is added to
the nanocomposite flexural strength value dropped to alower value than the neat epoxy Increasing the amount ofnanoparticles more than a certain amount has been found toreduce the flexural strength in earlier studies [53] It can alsobe observed that moisture absorbed nanocomposites showedsignificant reduction in flexural strength For 10 wt of I28Eclay-epoxy nanocomposites reduction in flexural strengthdue to hygrothermal aging is 32 Reduction in flexuralstrength of nanocomposites after moisture absorption hasbeen previously reported in the literature [4 43 54ndash56]and has been attributed to the degradation of interfaceregion which in turn reduces stress transfer between thenanofiller and the matrix For redried samples as most of themoisture is driven out of the system and plasticization effectwas minimal flexural strength for these samples recoveredalmost fully For instance flexural strength recovers to 95of its original value for 10 wt of Nanomer I28E clay-epoxynanocomposite
Almost similar trendwas observed for SomasifMAEclay-epoxy nanocomposites where addition of clay did not changethe property significantly and after 24 h of hygrothermalaging property decreased to a lower value compared to theas-prepared samples However the severity of degradationwas much less in both clay-epoxy systems compared to neatepoxy system Well dispersed high aspect ratio clay plateletshave the capability of crack deflection and crack arrestingwhich can lead to the observed higher flexural strength in wetclay-epoxy samples in comparison to neat epoxy samples [4857] For redried nanocomposites similar trend was observedfor both material systems and it was found that flexural
International Scholarly Research Notices 7
60
70
80
90
100
110
120Fl
exur
al st
reng
th (M
Pa)
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(a)
60
70
80
90
100
110
120
0 05 1 15 2 25
Flex
ural
stre
ngth
(MPa
)Clay loading (wt)
As-isMoist
Redried
minus05
(b)
Figure 3 Flexural strength as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
200 120583m
(a)
100 120583m
(b)
Figure 4 Scanning electron micrographs of neat epoxy polymer (a) as-prepared and (b) redried
strength recovers almost fully In this study flexural strengthhas not been largely affected by the addition of clay intothe epoxy This may as well mean that flexural strength hasbeen primarily governed by the flexural strength of the epoxyAs the strength of neat epoxy was marginally affected bythe absorption-desorption cycle so did the strength of clay-epoxy nanocomposites
34 Scanning Electron Microscopy (SEM) The scanning elec-tron micrographs of the fracture surface of tested neat epoxyand clay-epoxy nanocomposites are shown in Figures 4ndash8SEM micrograph of the fracture surface of the as-preparedneat polymer (Figure 4(a)) showed characteristic brittle fail-ure with a smooth fracture surface This mirror-like fracture
surface is an indication of poor fracture toughness of epoxyand has been reported in previous studies conducted onepoxy polymers [6] For the redried neat epoxy specimen(Figure 4(b)) a network of microcracks throughout thefracture surface is found For TGDDM-DDS system Morganet al observed similar behavior [58] According to their studyabsorbedmoisture enhances craze initiation and propagationin polymer which can result in the formation of microcracksor fibrils in the polymer system In this study lower fracturetoughness for dried neat polymer compared to unagedneat polymer can be attributed to the formation of thesemicrocracks
The SEMmicrographs of clay incorporated epoxy systemsshowed significantly rougher fracture surface compared to
8 International Scholarly Research Notices
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 5 Scanning electronmicrographs of the crack growth region for 05 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 6 Scanning electron micrographs of the crack growth region for 05 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
International Scholarly Research Notices 9
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 7 Scanning electronmicrographs of the crack growth region for 15 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 8 Scanning electron micrographs of the crack growth region for 15 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
10 International Scholarly Research Notices
the neat polymer Clay if present in a system physicallyblocks and slows down the crack propagation and the result-ing fracture surface of the nanocomposite shows river-markings instead of smooth fracture surface found in the neatpolymer These river-markings provide clear indication ofthe enhanced toughening mechanism in polymeric materialsdue to clay incorporation and support the observed higherfracture toughness for clay-epoxy nanocomposites comparedto the neat epoxy polymer Fracture surfaces of nanofillerreinforced polymer nanocomposites showing higher surfaceroughness have been reported in prior studies [4 6 59]Comparing the fracture surfaces of the as-preparedNanomerI28E and Somasif MAE nanocomposite systems (Figures5(a) 6(a) 7(a) and 8(a)) it was observed that the as-preparedSomasif MAE clay nanocomposite has considerably lessamount of river-markings which is indicative of poor tough-ening in Somasif MAE clay nanocomposites This obser-vation supported the difference of critical stress intensityfactor measured for these two nanocomposite systems Pooradhesion between Somasif MAE clay and epoxy resulted inless energy requirement during new surface formation whichcan be attributed as the reason of these nanocompositesshowing less fracture toughness than Nanomer I28E claynanocomposites for the same clay loading percentage
Fracture surface of moisture absorbed Nanomer I28Eclay nanocomposites (Figures 5(b) and 7(b)) showed lessnumber of river-markings (ie lower critical stress intensityfactor) than the as-prepared nanocomposites SEM micro-graph of Somasif clay-epoxy nanocomposites (Figures 6(b)and 8(b)) showed the presence of shear leaps As shearyielding requires less energy to form new surface moistureabsorbed specimens had lower fracture toughness than theas-prepared specimens Although shear yielding was foundto be the principle mechanism of failure in these specimenssome form of crack bifurcation and crack pinning was alsopresent in these fracture surfaces
Fracture surface micrographs of redried Nanomer I28Enanocomposites (Figures 5(c) and 7(c)) showed more rough-ness than themoisture absorbed specimens indicating higherfracture energy absorbance for these specimensMicrographsof redried Somasif MAE clay-epoxy samples (Figures 6(c)and 8(c)) showed significantly less rough fracture surfacethan the redried Nanomer I28E samples It is important tonote that these redried Somasif MAE clay-epoxy fracturesurfaces showed very little resistance against the crack prop-agation even after most of the water was driven out of thesystemThis observation led to the speculation that absorbedmoisture could have weakened the interface of the SomasifMAE clay particles and the epoxy matrix The replacementof ndashOH (hydroxyl) groups from the octahedral layer of theclay by the ndashF (fluorine) groups makes the Somasif MAE clayparticles muchmore hydrophobic compared to the NanomerI28E clay particlesThe higher hydrophobicity of the SomasifMAE clay particles could have exerted an additional forceon the moisture absorbed interface and weakened the bondbetween the clay particles and the epoxy chains This mighthave in turn resulted in the poor adhesionless fractureenergy absorption in the redried Somasif MAE clay-epoxynanocomposites
0
005
01
015
02
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
Figure 9 FTIR spectra for neat epoxy polymer before and afterabsorption-desorption cycle
35 Fourier Transform Infrared (FTIR) Spectroscopy FTIRspectra of the as-prepared and redried neat epoxy are shownin Figure 9 From the FTIR spectra it was evident that asa result of the absorption-desorption cycle the epoxy under-went some permanent chemical changes These chemicalchanges were probably due to the hydrolysis and chainscission mechanism The drying cycle used in this studyremoved most of the water that was absorbed by the polymersystem and it was believed that the remaining water (onlyabout 7 of the total moisture uptake) is chemically boundto the polymer system FTIR spectra (Figure 7) showed bandat 3200ndash3400 cmminus1 which is characteristic OH stretching ofthe hydroxyl group However significant difference was notobserved for the bands at 3200ndash3400 cmminus1
Figure 10 shows the FTIR spectra for Nanomer I28E andSomasif MAE clay powder before and after the absorption-desorption cycle Both clays showed characteristic SindashO peakin the 990 cmminus1 region Nanomer I28E clay showed anotherpeak at 915 cmminus1 region which is characteristic AlndashOH peakIn Somasif MAE the OH groups present in the corner ofthe octahedral layer of Nanomer I28E were substituted withF which explains the absence of the peak at 915 cmminus1 Bothclays in as-is condition showed 3200ndash3400 cmminus1 band forhydroxyl groups However the band was weaker in case ofSomasif MAE compared to Nanomer I28E clay because ofthe hydrophobic nature of the Somasif MAE clay It wasinteresting to note that the overall changes the clay powdersunderwent as a result of absorption-desorption cycle arefairly small and can be considered as insignificant
International Scholarly Research Notices 11
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
(a)
As-isRedried
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
Abso
rban
ce
Wavenumber (cmminus1)
(b)
Figure 10 FTIR spectra for clay particles before and after absorption-desorption cycle (a) Nanomer I28E and (b) Somasif MAE
4 Conclusion
Property deterioration due to moisture absorption has beenone of the most important areas of interest in polymerresearch for the last few years To be used as structural mater-ials it is of utmost importance to understand the reversibleand irreversible changes occurring in polymeric materials asa result of moisture absorption This study was conducted toelucidate the effect of moisture absorption on the mechan-ical properties of clay reinforced epoxy polymers Fracturetoughness flexural strength and flexural modulus weredetermined for two different clay-epoxy nanocompositesfollowing the ASTM standards The effects of hygrothermalaging and subsequent redrying on the mechanical prop-erties of these polymer nanocomposites were investigatedAfter removing the free water by drying the irreversibleeffect or the permanent damage due to hygrothermal agingon the clay-epoxy nanocomposite systems was determinedIrrespective of the clay reinforcement type all the studiedproperties were degraded due to hygrothermal aging Severalphysical and chemical changes such as interface weaken-ing hydrolysis and chain scission are responsible for theobserved effect The permanent damage or degradation wassevere in case of fracture toughness and flexural modulusFlexural strength of both systems was relatively unaffectedby the absorption-desorption cycle Permanent damage wasfound to be the highest for Somasif MAE clay reinforcedspecimens between two clay-epoxy nanocomposite systemsAfter studying the SEM micrographs of the fracture sur-faces it was speculated that moisture absorption had highernegative impact on the interface of Somasif MAE clay andepoxy matrix compared to the other clay-epoxy system
The hydrophobic nature of the Somasif MAE clay due tothe presence of ndashF (fluorine) in the structure may havecreated additional tension between the polymer crosslinksin presence of moisture FTIR spectra of the clay particlestreated with the same absorption-desorption cycle providedproof that both nanoparticles undergo minimal chemicalchange and retain their respective original chemistry Thisobservation makes the aforementioned speculation moreplausible Although incorporation of clay in epoxymatrix didnot fully stop the degradation it had positive effects to someextent It was observed that the studied properties in generalwere less severely degraded for clay-epoxy nanocompositescompared to neat epoxy samples Therefore clay particlescould be successfully used to reinforce polymer materials toreduce the severity of property deterioration caused by themoisture absorption However the chemistry between theclay particles and polymer matrix and more specifically thechemical structure of the clay particles should be carefullyconsidered to attain the best possible resistance against theproperty deterioration
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this work is fundedin part or fully by a Grant through the Oklahoma Nan-otechnology Applications Project (ONAP) (Grant no O9-20)
12 International Scholarly Research Notices
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
Water absorption into a polymer matrix leads to changein both chemical and physical characteristics and affects themechanical properties through different mechanisms such asplasticization crazing hydrolysis and swelling Plasticizationis the most important physical change that occurs throughthe interaction of the water molecules with polar groups inthe matrix which can severely depress the glass transitiontemperature [12 18 21ndash24] For example high moistureabsorption capability of TGDDMDDS epoxy resin whichis about 7wt reduces the system Tg from 260∘C to 130∘C[25ndash27] In general for most epoxy systems Tg is reduced by20∘C1 wt of moisture intake [28] The decrease in modulusof epoxy has also been reported to be due to plasticizationaccording to several studies [29ndash32] Other studies showedthat the decrease in modulus resulted from crazing [33ndash35] where the absorbed water acted as a crazing agentcontinuously decreasing the mechanical strength of epoxieswith exposure time in water [34] This was supported bySEM micrographs of epoxies which have shown cavitiesand fractured fibrils that could be explained by a moistureinduced crazingmechanism [33]The aforementioned chem-ical changes mainly include chain scission and hydrolysis[22 36] Plasticization is considered reversible upon dryingwhile other effects of moisture absorption are irreversible
In recent years effect of moisture absorption on themechanical properties of neat epoxy and clay-epoxy nano-composite has been frequently studied Zhao and Li reportedthat tensile strength and modulus decreased for bothneat epoxy and nanocomposites upon moisture absorptionwhile the tensile strain increased significantly for mois-ture absorbed samples Although failure occurred in brittlemanner effect of plasticization was found in SEM imageswhich showed shear yielding for both neat epoxy andnanocomposite samples after being exposed to moisture[37] Similar degradation in mechanical properties has beenreported by Glaskova and Aniskevich [38] Alamri and Lowreported lower flexural strength and modulus for halloysitenanoclay and nanosilicon carbide nanocomposites as a resultof moisture absorption [4] Al-Qadhi et al studied the effectof moisture absorption on the tensile properties of clay-epoxy nanocomposites and found that tensile strength andmodulus decrease as a result of water uptake [24] Wang et alinvestigated the effect of hydrothermal degradation onmechanical properties such as tensile strength modulus andfracture toughness with immersion duration [39] ForDGEBA epoxy systems fracture toughness and moduluswere not influencedmuchwith immersion time while tensilestrength decreased for nanocomposites Tensile and flexuralproperties of nanoclay reinforced composite laminates andCNT reinforced nanocomposites have also been found to beaffected adversely as a result of moisture absorption [12 40]According to the study conducted by Buck et al at elevatedtemperature combination ofmoisture and sustained load sig-nificantly reduced ultimate tensile strength of E-glassvinyl-ester composite materials [41] A study on elastic modulusof epoxy polymer after absorption-desorption cycle showedrecovery of property from wet condition although modulusremained at a lower value than the as-prepared samples
for lower filler volume For higher volume fraction of rein-forcement elastic modulus improved to a value which wasmore than the elastic modulus of the as-prepared samples[19] Phua et al also reported recovery of tensile propertiesafter refrying OMTT-PBS nanocomposites A similar studyconducted by Ferguson and Qu showed recovery of elasticproperties from moisture saturated state after a desorptioncycle [42] However dersquoN eve and Shanahan did not observeany recovery of elastic modulus after absorption-desorptioncycle at elevated temperature [22] It is evident from thepublished works that moisture absorption can severely altermechanical properties of epoxies by decreasing the elasticmodulus [12 29 33] tensile strength [3 12] shear modulus[30 31] flexural strength and flexural modulus [40 43] yieldstress and ultimate stress [32] as water uptake increases
Most of the research on polymer-clay nanocompositeshas been mainly focused on investigating the effect of mois-ture absorption on mechanical properties such as elasticmodulus and tensile strength Although fracture toughnessis a very important property for these nanocomposites asthese are used in various structural applications the effectsof moisture absorption on fracture toughness of polymer-clay nanocomposites have not been studied extensivelyDurability of polymerclay nanocomposites is still neededto be studied in depth particularly for hygrothermal agingin which the degradation of the mechanical properties andloss of integrity of these nanocomposites occur from thesimultaneous action of moisture and temperature This studyon clay-epoxy nanocomposites was designed to investigatethe effect of hygrothermal aging on mechanical properties ofthese nanocomposites Two different clay particles were usedto investigate the effect of clay structure on the permanentproperty changes due to hygrothermal aging A drying cyclewas employed to quantify the recovery of the propertiesafter hygrothermal aging This was helpful to understandthe extent of permanent degradation that occurred by thecombined application of elevated temperature and moistureMechanical properties in terms of fracture toughness flex-ural strength and flexural modulus are the properties thatwere studied Scanning electron microscopy and Fouriertransform spectroscopy were conducted to further elucidatethe underlying fracture mechanisms of these preconditionedspecimens
2 Materials and Characterization
The epoxy resin used for this study is EPON 862 which is adiglycidyl ether of bisphenol FThe curing agent used for thisresin systemwas amoderately reactive low viscosity aliphaticamine curing agent Epikure 3274 Both of these chemi-cals were supplied by Miller-Stephenson Chemical Com-pany Inc Dunbury Connecticut Two structurally differentclay particles were used as reinforcement Nanomer I28Eis a surface modified montmorillonite based layered silicate(Nanocor Inc Arlington Heights IL) modified with aquaternary amine (trimethyl stearyl) Somasif MAE (Co-OpChemical Co Japan) which was the other clay particle usedfor this study is a synthetic mica modified with dimethyl
International Scholarly Research Notices 3
Table 1 Structure of the studied clay particles
Clay StructureNanocor I28E (Na)
119910(Al2minus119910
Mg119910)(Si4O10)(OH)
2119899H2O
025 lt 119910 lt 06
Somasif MAE (Na)2119909(Mg)3minus119909(Si4O10)(F119886OH1minus119886)
2119899H2O
015 lt 119909 lt 05
08 lt 119886 lt 10
dihydrogenated tallow ammonium chloride Table 1 showsthe structural composition of the clay particles used in thisstudy
21 Sample Preparation Epoxy was preheated to 65∘C beforedesired amount of clay was introduced and mixed usingmechanical mixer for 12 hours To reduce the viscosityof the mixture and to facilitate mixing temperature wasmaintained at 65∘C using a hot plate for the entire durationof mixing The mixture was then degassed for around 30minutes to remove any entrapped air bubbles Bubble-freemixture of clay and epoxy was then shear-mixed using ahigh-speed shear disperser (T-25 ULTRA TURRAX IKAWorks Inc North Carolina USA) for 30 minutes Duringthis process temperature was maintained at 65∘C using anice bath Subsequently the mixture was then degassed untilit was completely bubble-free Curing agent was added tothe mixture at 100 40 weight ratio and carefully hand-mixed to avoid introduction of any air bubble After it wasproperly mixed the final slurry containing epoxy and claywas poured into an aluminum mold and cured at roomtemperature for 24 hours followed by postcuring at 121∘Cfor 6 hours The final sample had a nominal dimension of17780mmtimes15250mmtimes1270635mm To study the effectof loading percentage the weight fraction of the clay in thenanocomposite was varied from 05 to 20
22 Environmental Preconditioning After specimens werecut into the final required dimension according to the ASTMstandards D5045 and D790 they were subjected to degrada-tion Specimens from each nanocomposite were taken andsubmerged in purified deionized boiling water for 24 hoursWater saturated specimens were dried in an oven at 110∘C for6 hours to remove moisture from the samples leaving onlypermanent degradation in the form of bonded water
intensity factor 119870Ic was determined by single edge notchbend (SENB) test as per the ASTM D5045 on univer-sal testing machine (Instron 5567 Norwood MA) in adisplacement-controlled mode with fixed crosshead speed of10mmmin Nominal dimension for the SENB test sampleswas 6730mm times 1520mm times 635mm A notch was cre-ated using precision diamond saw (MK-370 MK DiamondProducts Inc Torrance CA USA) and afterwards a sharpprecrack with ratio of 045 lt 119886119882 lt 055 was created by
tapping a fresh razor blade into the notch At least 5 speci-mens were tested for every condition Fracture toughness forthe specimens was calculated in terms of critical stress inten-sity factor 119870Ic The crack length 119886 was measured using anoptical microscope (Nikon L150) which has a traveling platewith graduations
119870Ic =119875
119861radic119882
119891(
119886
119882
) (1)
where 119875 = maximum applied force (N) 119861 = thickness ofthe specimen (mm)119882 = width of the specimen (mm) and119891(119886119882) = geometry factor and it is given by the followingequation
119891(
119886
119882
) =
3 (119878119882)radic119886119882
2 (1 + 2 (119886119882)) (1 minus 119886119882)
32
times [199 minus (
119886
119882
)(1 minus
119886
119882
)
times(215 minus 393 (
119886
119882
) + 27(
119886
119882
)
2
)]
(2)
where 119878 = support span (mm) and 119886 = length of the precrack(mm)
24 Flexural Strength and Flexural Modulus DeterminationFlexural strength and flexural modulus were determinedusing three-point bend (3PB) test according to ASTM D790on universal testing machine (Instron 5567 Norwood MA)The nominal dimension for the flexural test specimens was5590mmtimes1270mmtimes635mmThe crosshead speed for thetest was calculated using (3) The crosshead speed was foundto be 135mmmin Consider
119877 =
119885119871
2
6119889
(3)
where 119877 = rate of crosshead motion (mmmin) 119871 = supportspan (mm) 119889 = depth of beam (mm) and 119885 = rate ofstraining of the outer fiber (mmmmmin) = 001The flexural strength and flexural modulus were calculatedusing the following equations respectively
(MPa) 119875max = maximum load on the load-deflection curve(N) 119871 = support span (mm) 119887 = width of beam tested (mm)119889 = depth of beam tested (mm) and119898 = slope of the tangentto the initial straight-line portion of the load-deflection curve(Nmm of deflection)
25 Fracture Surface Morphology Surface morphology of thefractured specimens from SENB tests was observed using
4 International Scholarly Research Notices
Table 2 Weight changes in samples after preconditioning
scanning electron microscopy (Hitachi S-4800 FESEMDallas TX) As polymer materials are nonconductive toelectrons all fracture surfaces were sputtered with gold-palladium alloy before SEM imaging
26 Fourier Transform Infrared Spectroscopy FTIR spectros-copy measurements were performed using ATR-FTIR spec-trometer (Nicolet iS10 Waltham MA) using 64 scans at aresolution of 20 cmminus1 Each spectrum was recorded from4000 to 500 cmminus1 at room temperature Spectrawere analyzedusing OriginPro 90 (OriginLab Northampton MA)
3 Results and Discussions
31 Gravimetric Measurements Table 2 shows the relativeweight changes that occurred in the specimens after 24 hoursof boiling water absorption and 6 hours of high temperaturedesorption cycle For the studied material systems percent-age weight gain after absorption cycle showed no change asa function of clay loading percentage This observation wasdifferent from the findings reported by Glaskova and Aniske-vich for clay-epoxy nanocomposites [44] According to theirstudy moisture absorption was found to have increasedslightly with the increase of clay weight percentage Contrar-ily Alamri and Low reported decreasingmoisture absorptionwith increasing clay weight percentage [4] The reason whya different clay-epoxy nanocomposite system behaves differ-ently in moisture absorption test is still not clear and furtherinvestigation is required to understand it In this studyalthough both clays are structurally different the observedpercentage weight gain for both nanocomposite systems wasfound approximately to be the same These two observationsled to the conclusion that moisture diffusion process pri-marily depended on the polymer system under investigationMoisture desorption data showed that most of the absorbedwater is free water which can be driven out of the system bydrying For neat epoxy the amount of retained water afterdesorption cycle is less compared to the nanocompositesThis is possibly due to the fact that presence of clay hinderedthe moisture diffusion process in and out of the epoxypolymers An increasing trend in the amount of retainedmoisture for higher clay loading nanocomposites also sup-ported the aforementioned statement Amount of water
retained after the desorption cycle has been found to bealmost similar for both clay-epoxy nanocomposite systems
32 Fracture Toughness The critical stress intensity factorsas a function of clay loading percentage for Nanomer I28Eand Somasif MAE clay-epoxy nanocomposites are shown inFigure 1119870Ic values for the as-prepared samples are also listedas a reference
Critical stress intensity factor 119870Ic increased 28 for theas-prepared 05 wt Nanomer I28E clay-epoxy nanocom-posite compared to neat epoxy The reason behind thisobservation can be attributed to the layered structure of theclay Clay in a polymer material physically blocks bifurcatesand deflects the crack path compelling the crack to travellonger path which in turn results in higher toughness in aclay-polymer nanocomposite The toughening effect of clayon epoxy polymer started to decrease with any additionalclay reinforcement This is a common behavior for severaltypes of epoxy-clay nanocomposites and has been reportedin previous studies conducted on clay-epoxy nanocomposites[3 6 45 46] Depending on the processing technique andepoxy-clay interaction there is an optimum weight percent-age for which the property enhancement can be maximizedAny further addition of clay negates the positive effect byforming agglomerates due to improper exfoliation of the clayplatelets and thus results in stress concentration forcing thematerial to fail at lower loads For moisture saturated epoxy-clay nanocomposites119870Ic was found to be lower compared tothe as-prepared nanocomposite samples for all the NanomerI28E nanocomposites As water molecules diffuse into thenanofiller-epoxy interface debonding and weakening of theinterface occur resulting in poor stress transfer between thefiller and the epoxy matrix [43 47 48] Redried neat EPON862 free of void-filling water showed 29 reduction infracture toughness compared to the as-prepared neat EPON862 samples Addition of 05 wt of clay resulted in 16reduction in fracture toughness when compared to the as-prepared samples which was significantly less compared to29 reduction of neat epoxy For 20 wt Nanomer I28Eclay-epoxy nanocomposite redried samples were found to betougher than the as-prepared samples However the standarddeviation of the as-prepared sample was much higher whichcould possibly mean that the dried and the as-preparedsamples have no difference in toughness
International Scholarly Research Notices 5
06
08
1
12
14
16
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
Frac
ture
toug
hnes
sK
Ic(M
Pamiddotm
12
)
(a)
06
08
1
12
14
16
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
Frac
ture
toug
hnes
sK
Ic(M
Pamiddotm
12
)
(b)
Figure 1 Critical stress intensity factor 119870Ic as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxynanocomposites
For the as-prepared and moisture saturated samplesSomasif MAE nanocomposites showed comparable trend infracture toughness data clay reinforcement successfullyimproved the baseline epoxy properties andmoisture absorp-tion degraded the mechanical properties for all clay percent-ages However the permanent degradation after absorption-desorption cycle was found to be more prominent in the caseof Somasif MAE clay nanocomposites compared to NanomerI28E clay nanocomposites The recovery of property after6 hours of drying was negligible for Somasif MAE claynanocomposites whereas Nanomer I28E nanocompositesshowed significant recovery of property after drying Thedifference in property recovery of these two clay-epoxynanocomposites can be attributed to the structural differ-ences of the two clay particles and has been further investi-gated through SEM and FTIR technique
33 Flexural Properties Flexural modulus for the neat epoxyand clay-epoxy nanocomposites was determined from 3PBtest and has been plotted against clay loading percentage inFigure 2 for Nanomer I28E and Somasif MAE clay Flexuralmodulus increased almost linearly for both clays as a functionof clay loading percentage According to previous studieson epoxy polymers incorporation of hard substance suchas clay in polymer matrix results in higher modulus [49]When a load is applied on epoxy the polymer chains slidepast each other and deform This deformation is higher inless crosslinked structures compared to higher crosslinkedstructures Once layered silicates such as clay particles are
introduced in a polymer system it restricts the motion of thepolymer chain sliding and makes the matrix less pliable Asthe clay content increases it is more difficult for the polymerchains to untangle and move This increase in restriction ofpolymer chains is responsible for the increase in modulus asthe clay percentage increases
For the hygrothermally conditioned specimens themod-ulus is lower compared to the as-prepared specimens Thisbehavior observed is mostly due to the presence of waterinside the epoxy system which increases the ductility of theepoxy system Water acts as an effective plasticizer and candiffuse into the nanofiller-polymer interface and weaken thebonding between them [40 43] Presence of water in epoxysystem also results in an increase in free volume throughrupture of hydrogen bonding between polymer chains whichincreases the chain mobility and eases the segmental motionwhen a load is applied to the composite [50] These physicalchanges can be attributed to the observed lower modulus forwater absorbed specimens Other mechanisms affecting thepolymer such as hydrolysis and chain scission may also beresponsible for lowering the modulus Once hydrolysis andchain scission take place less bonding between the polymersmakes it more deformable resulting in lower modulus foraged samples [22 36 51] The effect of hygrothermal agingwas more severe in neat epoxy than in the nanocompositesFor neat EPON 862 flexural modulus decreased 20 afterhygrothermal aging whereas it was only 13 and 11 for05 wt of Nanomer I28E and Somasif MAE clay-epoxynanocomposites respectively In addition to being hard
6 International Scholarly Research Notices
24
26
28
3
32
34
36
38Fl
exur
al m
odul
us (G
Pa)
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(a)
24
26
28
3
32
34
36
38
Flex
ural
mod
ulus
(GPa
)Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(b)
Figure 2 Flexural modulus as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
substance clay particles have very high aspect ratioThe highaspect ratio of the clay platelets provides resistance againstpolymer chain mobility in a water absorbed ductile polymerleading to the observed lower degradation of flexural modu-lus values in comparison to neat polymer
For Nanomer I28E clay-epoxy samples conditioned at110∘C for 6 h recovery of flexural modulus was observedOnce redried free water residing in the microvoids wasevaporated and the effect of plasticizationwas not prominentanymore As a result the ductility of the polymer reducedand the recovery of mechanical properties from moistureabsorbed state occurred Nevertheless in case of SomasifMAE clay-epoxy samples modulus recovery was negligibleafter the desorption cycle Due to the structural differencebetween the two clay particles it is possible that the interfaceof Somasif MAE clay-epoxy is being more affected by thehygrothermal degradation than the Nanomer I28E clay-epoxy interface
Flexural strengths for the epoxy and clay-epoxy nano-composites were determined using three-point bend (3PB)test and are plotted against clay loading percentage in Figure 3for Nanomer I28E and Somasif MAE clay Figure 3 showsthat the addition of Nanomer I28E clay provided negligibleimprovement in flexural strength compared to neat epoxyThe maximum improvement in flexural strength was foundto be less than 10 for both clay-epoxy systems from the baseflexural strength of neat epoxy Similar observation has beenreported in the literature where addition of nanoclay parti-cles did not significantly improve the flexural strength of thesystem [52] Furthermore when 20 wt of clay is added to
the nanocomposite flexural strength value dropped to alower value than the neat epoxy Increasing the amount ofnanoparticles more than a certain amount has been found toreduce the flexural strength in earlier studies [53] It can alsobe observed that moisture absorbed nanocomposites showedsignificant reduction in flexural strength For 10 wt of I28Eclay-epoxy nanocomposites reduction in flexural strengthdue to hygrothermal aging is 32 Reduction in flexuralstrength of nanocomposites after moisture absorption hasbeen previously reported in the literature [4 43 54ndash56]and has been attributed to the degradation of interfaceregion which in turn reduces stress transfer between thenanofiller and the matrix For redried samples as most of themoisture is driven out of the system and plasticization effectwas minimal flexural strength for these samples recoveredalmost fully For instance flexural strength recovers to 95of its original value for 10 wt of Nanomer I28E clay-epoxynanocomposite
Almost similar trendwas observed for SomasifMAEclay-epoxy nanocomposites where addition of clay did not changethe property significantly and after 24 h of hygrothermalaging property decreased to a lower value compared to theas-prepared samples However the severity of degradationwas much less in both clay-epoxy systems compared to neatepoxy system Well dispersed high aspect ratio clay plateletshave the capability of crack deflection and crack arrestingwhich can lead to the observed higher flexural strength in wetclay-epoxy samples in comparison to neat epoxy samples [4857] For redried nanocomposites similar trend was observedfor both material systems and it was found that flexural
International Scholarly Research Notices 7
60
70
80
90
100
110
120Fl
exur
al st
reng
th (M
Pa)
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(a)
60
70
80
90
100
110
120
0 05 1 15 2 25
Flex
ural
stre
ngth
(MPa
)Clay loading (wt)
As-isMoist
Redried
minus05
(b)
Figure 3 Flexural strength as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
200 120583m
(a)
100 120583m
(b)
Figure 4 Scanning electron micrographs of neat epoxy polymer (a) as-prepared and (b) redried
strength recovers almost fully In this study flexural strengthhas not been largely affected by the addition of clay intothe epoxy This may as well mean that flexural strength hasbeen primarily governed by the flexural strength of the epoxyAs the strength of neat epoxy was marginally affected bythe absorption-desorption cycle so did the strength of clay-epoxy nanocomposites
34 Scanning Electron Microscopy (SEM) The scanning elec-tron micrographs of the fracture surface of tested neat epoxyand clay-epoxy nanocomposites are shown in Figures 4ndash8SEM micrograph of the fracture surface of the as-preparedneat polymer (Figure 4(a)) showed characteristic brittle fail-ure with a smooth fracture surface This mirror-like fracture
surface is an indication of poor fracture toughness of epoxyand has been reported in previous studies conducted onepoxy polymers [6] For the redried neat epoxy specimen(Figure 4(b)) a network of microcracks throughout thefracture surface is found For TGDDM-DDS system Morganet al observed similar behavior [58] According to their studyabsorbedmoisture enhances craze initiation and propagationin polymer which can result in the formation of microcracksor fibrils in the polymer system In this study lower fracturetoughness for dried neat polymer compared to unagedneat polymer can be attributed to the formation of thesemicrocracks
The SEMmicrographs of clay incorporated epoxy systemsshowed significantly rougher fracture surface compared to
8 International Scholarly Research Notices
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 5 Scanning electronmicrographs of the crack growth region for 05 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 6 Scanning electron micrographs of the crack growth region for 05 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
International Scholarly Research Notices 9
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 7 Scanning electronmicrographs of the crack growth region for 15 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 8 Scanning electron micrographs of the crack growth region for 15 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
10 International Scholarly Research Notices
the neat polymer Clay if present in a system physicallyblocks and slows down the crack propagation and the result-ing fracture surface of the nanocomposite shows river-markings instead of smooth fracture surface found in the neatpolymer These river-markings provide clear indication ofthe enhanced toughening mechanism in polymeric materialsdue to clay incorporation and support the observed higherfracture toughness for clay-epoxy nanocomposites comparedto the neat epoxy polymer Fracture surfaces of nanofillerreinforced polymer nanocomposites showing higher surfaceroughness have been reported in prior studies [4 6 59]Comparing the fracture surfaces of the as-preparedNanomerI28E and Somasif MAE nanocomposite systems (Figures5(a) 6(a) 7(a) and 8(a)) it was observed that the as-preparedSomasif MAE clay nanocomposite has considerably lessamount of river-markings which is indicative of poor tough-ening in Somasif MAE clay nanocomposites This obser-vation supported the difference of critical stress intensityfactor measured for these two nanocomposite systems Pooradhesion between Somasif MAE clay and epoxy resulted inless energy requirement during new surface formation whichcan be attributed as the reason of these nanocompositesshowing less fracture toughness than Nanomer I28E claynanocomposites for the same clay loading percentage
Fracture surface of moisture absorbed Nanomer I28Eclay nanocomposites (Figures 5(b) and 7(b)) showed lessnumber of river-markings (ie lower critical stress intensityfactor) than the as-prepared nanocomposites SEM micro-graph of Somasif clay-epoxy nanocomposites (Figures 6(b)and 8(b)) showed the presence of shear leaps As shearyielding requires less energy to form new surface moistureabsorbed specimens had lower fracture toughness than theas-prepared specimens Although shear yielding was foundto be the principle mechanism of failure in these specimenssome form of crack bifurcation and crack pinning was alsopresent in these fracture surfaces
Fracture surface micrographs of redried Nanomer I28Enanocomposites (Figures 5(c) and 7(c)) showed more rough-ness than themoisture absorbed specimens indicating higherfracture energy absorbance for these specimensMicrographsof redried Somasif MAE clay-epoxy samples (Figures 6(c)and 8(c)) showed significantly less rough fracture surfacethan the redried Nanomer I28E samples It is important tonote that these redried Somasif MAE clay-epoxy fracturesurfaces showed very little resistance against the crack prop-agation even after most of the water was driven out of thesystemThis observation led to the speculation that absorbedmoisture could have weakened the interface of the SomasifMAE clay particles and the epoxy matrix The replacementof ndashOH (hydroxyl) groups from the octahedral layer of theclay by the ndashF (fluorine) groups makes the Somasif MAE clayparticles muchmore hydrophobic compared to the NanomerI28E clay particlesThe higher hydrophobicity of the SomasifMAE clay particles could have exerted an additional forceon the moisture absorbed interface and weakened the bondbetween the clay particles and the epoxy chains This mighthave in turn resulted in the poor adhesionless fractureenergy absorption in the redried Somasif MAE clay-epoxynanocomposites
0
005
01
015
02
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
Figure 9 FTIR spectra for neat epoxy polymer before and afterabsorption-desorption cycle
35 Fourier Transform Infrared (FTIR) Spectroscopy FTIRspectra of the as-prepared and redried neat epoxy are shownin Figure 9 From the FTIR spectra it was evident that asa result of the absorption-desorption cycle the epoxy under-went some permanent chemical changes These chemicalchanges were probably due to the hydrolysis and chainscission mechanism The drying cycle used in this studyremoved most of the water that was absorbed by the polymersystem and it was believed that the remaining water (onlyabout 7 of the total moisture uptake) is chemically boundto the polymer system FTIR spectra (Figure 7) showed bandat 3200ndash3400 cmminus1 which is characteristic OH stretching ofthe hydroxyl group However significant difference was notobserved for the bands at 3200ndash3400 cmminus1
Figure 10 shows the FTIR spectra for Nanomer I28E andSomasif MAE clay powder before and after the absorption-desorption cycle Both clays showed characteristic SindashO peakin the 990 cmminus1 region Nanomer I28E clay showed anotherpeak at 915 cmminus1 region which is characteristic AlndashOH peakIn Somasif MAE the OH groups present in the corner ofthe octahedral layer of Nanomer I28E were substituted withF which explains the absence of the peak at 915 cmminus1 Bothclays in as-is condition showed 3200ndash3400 cmminus1 band forhydroxyl groups However the band was weaker in case ofSomasif MAE compared to Nanomer I28E clay because ofthe hydrophobic nature of the Somasif MAE clay It wasinteresting to note that the overall changes the clay powdersunderwent as a result of absorption-desorption cycle arefairly small and can be considered as insignificant
International Scholarly Research Notices 11
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
(a)
As-isRedried
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
Abso
rban
ce
Wavenumber (cmminus1)
(b)
Figure 10 FTIR spectra for clay particles before and after absorption-desorption cycle (a) Nanomer I28E and (b) Somasif MAE
4 Conclusion
Property deterioration due to moisture absorption has beenone of the most important areas of interest in polymerresearch for the last few years To be used as structural mater-ials it is of utmost importance to understand the reversibleand irreversible changes occurring in polymeric materials asa result of moisture absorption This study was conducted toelucidate the effect of moisture absorption on the mechan-ical properties of clay reinforced epoxy polymers Fracturetoughness flexural strength and flexural modulus weredetermined for two different clay-epoxy nanocompositesfollowing the ASTM standards The effects of hygrothermalaging and subsequent redrying on the mechanical prop-erties of these polymer nanocomposites were investigatedAfter removing the free water by drying the irreversibleeffect or the permanent damage due to hygrothermal agingon the clay-epoxy nanocomposite systems was determinedIrrespective of the clay reinforcement type all the studiedproperties were degraded due to hygrothermal aging Severalphysical and chemical changes such as interface weaken-ing hydrolysis and chain scission are responsible for theobserved effect The permanent damage or degradation wassevere in case of fracture toughness and flexural modulusFlexural strength of both systems was relatively unaffectedby the absorption-desorption cycle Permanent damage wasfound to be the highest for Somasif MAE clay reinforcedspecimens between two clay-epoxy nanocomposite systemsAfter studying the SEM micrographs of the fracture sur-faces it was speculated that moisture absorption had highernegative impact on the interface of Somasif MAE clay andepoxy matrix compared to the other clay-epoxy system
The hydrophobic nature of the Somasif MAE clay due tothe presence of ndashF (fluorine) in the structure may havecreated additional tension between the polymer crosslinksin presence of moisture FTIR spectra of the clay particlestreated with the same absorption-desorption cycle providedproof that both nanoparticles undergo minimal chemicalchange and retain their respective original chemistry Thisobservation makes the aforementioned speculation moreplausible Although incorporation of clay in epoxymatrix didnot fully stop the degradation it had positive effects to someextent It was observed that the studied properties in generalwere less severely degraded for clay-epoxy nanocompositescompared to neat epoxy samples Therefore clay particlescould be successfully used to reinforce polymer materials toreduce the severity of property deterioration caused by themoisture absorption However the chemistry between theclay particles and polymer matrix and more specifically thechemical structure of the clay particles should be carefullyconsidered to attain the best possible resistance against theproperty deterioration
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this work is fundedin part or fully by a Grant through the Oklahoma Nan-otechnology Applications Project (ONAP) (Grant no O9-20)
12 International Scholarly Research Notices
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
Somasif MAE (Na)2119909(Mg)3minus119909(Si4O10)(F119886OH1minus119886)
2119899H2O
015 lt 119909 lt 05
08 lt 119886 lt 10
dihydrogenated tallow ammonium chloride Table 1 showsthe structural composition of the clay particles used in thisstudy
21 Sample Preparation Epoxy was preheated to 65∘C beforedesired amount of clay was introduced and mixed usingmechanical mixer for 12 hours To reduce the viscosityof the mixture and to facilitate mixing temperature wasmaintained at 65∘C using a hot plate for the entire durationof mixing The mixture was then degassed for around 30minutes to remove any entrapped air bubbles Bubble-freemixture of clay and epoxy was then shear-mixed using ahigh-speed shear disperser (T-25 ULTRA TURRAX IKAWorks Inc North Carolina USA) for 30 minutes Duringthis process temperature was maintained at 65∘C using anice bath Subsequently the mixture was then degassed untilit was completely bubble-free Curing agent was added tothe mixture at 100 40 weight ratio and carefully hand-mixed to avoid introduction of any air bubble After it wasproperly mixed the final slurry containing epoxy and claywas poured into an aluminum mold and cured at roomtemperature for 24 hours followed by postcuring at 121∘Cfor 6 hours The final sample had a nominal dimension of17780mmtimes15250mmtimes1270635mm To study the effectof loading percentage the weight fraction of the clay in thenanocomposite was varied from 05 to 20
22 Environmental Preconditioning After specimens werecut into the final required dimension according to the ASTMstandards D5045 and D790 they were subjected to degrada-tion Specimens from each nanocomposite were taken andsubmerged in purified deionized boiling water for 24 hoursWater saturated specimens were dried in an oven at 110∘C for6 hours to remove moisture from the samples leaving onlypermanent degradation in the form of bonded water
intensity factor 119870Ic was determined by single edge notchbend (SENB) test as per the ASTM D5045 on univer-sal testing machine (Instron 5567 Norwood MA) in adisplacement-controlled mode with fixed crosshead speed of10mmmin Nominal dimension for the SENB test sampleswas 6730mm times 1520mm times 635mm A notch was cre-ated using precision diamond saw (MK-370 MK DiamondProducts Inc Torrance CA USA) and afterwards a sharpprecrack with ratio of 045 lt 119886119882 lt 055 was created by
tapping a fresh razor blade into the notch At least 5 speci-mens were tested for every condition Fracture toughness forthe specimens was calculated in terms of critical stress inten-sity factor 119870Ic The crack length 119886 was measured using anoptical microscope (Nikon L150) which has a traveling platewith graduations
119870Ic =119875
119861radic119882
119891(
119886
119882
) (1)
where 119875 = maximum applied force (N) 119861 = thickness ofthe specimen (mm)119882 = width of the specimen (mm) and119891(119886119882) = geometry factor and it is given by the followingequation
119891(
119886
119882
) =
3 (119878119882)radic119886119882
2 (1 + 2 (119886119882)) (1 minus 119886119882)
32
times [199 minus (
119886
119882
)(1 minus
119886
119882
)
times(215 minus 393 (
119886
119882
) + 27(
119886
119882
)
2
)]
(2)
where 119878 = support span (mm) and 119886 = length of the precrack(mm)
24 Flexural Strength and Flexural Modulus DeterminationFlexural strength and flexural modulus were determinedusing three-point bend (3PB) test according to ASTM D790on universal testing machine (Instron 5567 Norwood MA)The nominal dimension for the flexural test specimens was5590mmtimes1270mmtimes635mmThe crosshead speed for thetest was calculated using (3) The crosshead speed was foundto be 135mmmin Consider
119877 =
119885119871
2
6119889
(3)
where 119877 = rate of crosshead motion (mmmin) 119871 = supportspan (mm) 119889 = depth of beam (mm) and 119885 = rate ofstraining of the outer fiber (mmmmmin) = 001The flexural strength and flexural modulus were calculatedusing the following equations respectively
(MPa) 119875max = maximum load on the load-deflection curve(N) 119871 = support span (mm) 119887 = width of beam tested (mm)119889 = depth of beam tested (mm) and119898 = slope of the tangentto the initial straight-line portion of the load-deflection curve(Nmm of deflection)
25 Fracture Surface Morphology Surface morphology of thefractured specimens from SENB tests was observed using
4 International Scholarly Research Notices
Table 2 Weight changes in samples after preconditioning
scanning electron microscopy (Hitachi S-4800 FESEMDallas TX) As polymer materials are nonconductive toelectrons all fracture surfaces were sputtered with gold-palladium alloy before SEM imaging
26 Fourier Transform Infrared Spectroscopy FTIR spectros-copy measurements were performed using ATR-FTIR spec-trometer (Nicolet iS10 Waltham MA) using 64 scans at aresolution of 20 cmminus1 Each spectrum was recorded from4000 to 500 cmminus1 at room temperature Spectrawere analyzedusing OriginPro 90 (OriginLab Northampton MA)
3 Results and Discussions
31 Gravimetric Measurements Table 2 shows the relativeweight changes that occurred in the specimens after 24 hoursof boiling water absorption and 6 hours of high temperaturedesorption cycle For the studied material systems percent-age weight gain after absorption cycle showed no change asa function of clay loading percentage This observation wasdifferent from the findings reported by Glaskova and Aniske-vich for clay-epoxy nanocomposites [44] According to theirstudy moisture absorption was found to have increasedslightly with the increase of clay weight percentage Contrar-ily Alamri and Low reported decreasingmoisture absorptionwith increasing clay weight percentage [4] The reason whya different clay-epoxy nanocomposite system behaves differ-ently in moisture absorption test is still not clear and furtherinvestigation is required to understand it In this studyalthough both clays are structurally different the observedpercentage weight gain for both nanocomposite systems wasfound approximately to be the same These two observationsled to the conclusion that moisture diffusion process pri-marily depended on the polymer system under investigationMoisture desorption data showed that most of the absorbedwater is free water which can be driven out of the system bydrying For neat epoxy the amount of retained water afterdesorption cycle is less compared to the nanocompositesThis is possibly due to the fact that presence of clay hinderedthe moisture diffusion process in and out of the epoxypolymers An increasing trend in the amount of retainedmoisture for higher clay loading nanocomposites also sup-ported the aforementioned statement Amount of water
retained after the desorption cycle has been found to bealmost similar for both clay-epoxy nanocomposite systems
32 Fracture Toughness The critical stress intensity factorsas a function of clay loading percentage for Nanomer I28Eand Somasif MAE clay-epoxy nanocomposites are shown inFigure 1119870Ic values for the as-prepared samples are also listedas a reference
Critical stress intensity factor 119870Ic increased 28 for theas-prepared 05 wt Nanomer I28E clay-epoxy nanocom-posite compared to neat epoxy The reason behind thisobservation can be attributed to the layered structure of theclay Clay in a polymer material physically blocks bifurcatesand deflects the crack path compelling the crack to travellonger path which in turn results in higher toughness in aclay-polymer nanocomposite The toughening effect of clayon epoxy polymer started to decrease with any additionalclay reinforcement This is a common behavior for severaltypes of epoxy-clay nanocomposites and has been reportedin previous studies conducted on clay-epoxy nanocomposites[3 6 45 46] Depending on the processing technique andepoxy-clay interaction there is an optimum weight percent-age for which the property enhancement can be maximizedAny further addition of clay negates the positive effect byforming agglomerates due to improper exfoliation of the clayplatelets and thus results in stress concentration forcing thematerial to fail at lower loads For moisture saturated epoxy-clay nanocomposites119870Ic was found to be lower compared tothe as-prepared nanocomposite samples for all the NanomerI28E nanocomposites As water molecules diffuse into thenanofiller-epoxy interface debonding and weakening of theinterface occur resulting in poor stress transfer between thefiller and the epoxy matrix [43 47 48] Redried neat EPON862 free of void-filling water showed 29 reduction infracture toughness compared to the as-prepared neat EPON862 samples Addition of 05 wt of clay resulted in 16reduction in fracture toughness when compared to the as-prepared samples which was significantly less compared to29 reduction of neat epoxy For 20 wt Nanomer I28Eclay-epoxy nanocomposite redried samples were found to betougher than the as-prepared samples However the standarddeviation of the as-prepared sample was much higher whichcould possibly mean that the dried and the as-preparedsamples have no difference in toughness
International Scholarly Research Notices 5
06
08
1
12
14
16
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
Frac
ture
toug
hnes
sK
Ic(M
Pamiddotm
12
)
(a)
06
08
1
12
14
16
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
Frac
ture
toug
hnes
sK
Ic(M
Pamiddotm
12
)
(b)
Figure 1 Critical stress intensity factor 119870Ic as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxynanocomposites
For the as-prepared and moisture saturated samplesSomasif MAE nanocomposites showed comparable trend infracture toughness data clay reinforcement successfullyimproved the baseline epoxy properties andmoisture absorp-tion degraded the mechanical properties for all clay percent-ages However the permanent degradation after absorption-desorption cycle was found to be more prominent in the caseof Somasif MAE clay nanocomposites compared to NanomerI28E clay nanocomposites The recovery of property after6 hours of drying was negligible for Somasif MAE claynanocomposites whereas Nanomer I28E nanocompositesshowed significant recovery of property after drying Thedifference in property recovery of these two clay-epoxynanocomposites can be attributed to the structural differ-ences of the two clay particles and has been further investi-gated through SEM and FTIR technique
33 Flexural Properties Flexural modulus for the neat epoxyand clay-epoxy nanocomposites was determined from 3PBtest and has been plotted against clay loading percentage inFigure 2 for Nanomer I28E and Somasif MAE clay Flexuralmodulus increased almost linearly for both clays as a functionof clay loading percentage According to previous studieson epoxy polymers incorporation of hard substance suchas clay in polymer matrix results in higher modulus [49]When a load is applied on epoxy the polymer chains slidepast each other and deform This deformation is higher inless crosslinked structures compared to higher crosslinkedstructures Once layered silicates such as clay particles are
introduced in a polymer system it restricts the motion of thepolymer chain sliding and makes the matrix less pliable Asthe clay content increases it is more difficult for the polymerchains to untangle and move This increase in restriction ofpolymer chains is responsible for the increase in modulus asthe clay percentage increases
For the hygrothermally conditioned specimens themod-ulus is lower compared to the as-prepared specimens Thisbehavior observed is mostly due to the presence of waterinside the epoxy system which increases the ductility of theepoxy system Water acts as an effective plasticizer and candiffuse into the nanofiller-polymer interface and weaken thebonding between them [40 43] Presence of water in epoxysystem also results in an increase in free volume throughrupture of hydrogen bonding between polymer chains whichincreases the chain mobility and eases the segmental motionwhen a load is applied to the composite [50] These physicalchanges can be attributed to the observed lower modulus forwater absorbed specimens Other mechanisms affecting thepolymer such as hydrolysis and chain scission may also beresponsible for lowering the modulus Once hydrolysis andchain scission take place less bonding between the polymersmakes it more deformable resulting in lower modulus foraged samples [22 36 51] The effect of hygrothermal agingwas more severe in neat epoxy than in the nanocompositesFor neat EPON 862 flexural modulus decreased 20 afterhygrothermal aging whereas it was only 13 and 11 for05 wt of Nanomer I28E and Somasif MAE clay-epoxynanocomposites respectively In addition to being hard
6 International Scholarly Research Notices
24
26
28
3
32
34
36
38Fl
exur
al m
odul
us (G
Pa)
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(a)
24
26
28
3
32
34
36
38
Flex
ural
mod
ulus
(GPa
)Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(b)
Figure 2 Flexural modulus as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
substance clay particles have very high aspect ratioThe highaspect ratio of the clay platelets provides resistance againstpolymer chain mobility in a water absorbed ductile polymerleading to the observed lower degradation of flexural modu-lus values in comparison to neat polymer
For Nanomer I28E clay-epoxy samples conditioned at110∘C for 6 h recovery of flexural modulus was observedOnce redried free water residing in the microvoids wasevaporated and the effect of plasticizationwas not prominentanymore As a result the ductility of the polymer reducedand the recovery of mechanical properties from moistureabsorbed state occurred Nevertheless in case of SomasifMAE clay-epoxy samples modulus recovery was negligibleafter the desorption cycle Due to the structural differencebetween the two clay particles it is possible that the interfaceof Somasif MAE clay-epoxy is being more affected by thehygrothermal degradation than the Nanomer I28E clay-epoxy interface
Flexural strengths for the epoxy and clay-epoxy nano-composites were determined using three-point bend (3PB)test and are plotted against clay loading percentage in Figure 3for Nanomer I28E and Somasif MAE clay Figure 3 showsthat the addition of Nanomer I28E clay provided negligibleimprovement in flexural strength compared to neat epoxyThe maximum improvement in flexural strength was foundto be less than 10 for both clay-epoxy systems from the baseflexural strength of neat epoxy Similar observation has beenreported in the literature where addition of nanoclay parti-cles did not significantly improve the flexural strength of thesystem [52] Furthermore when 20 wt of clay is added to
the nanocomposite flexural strength value dropped to alower value than the neat epoxy Increasing the amount ofnanoparticles more than a certain amount has been found toreduce the flexural strength in earlier studies [53] It can alsobe observed that moisture absorbed nanocomposites showedsignificant reduction in flexural strength For 10 wt of I28Eclay-epoxy nanocomposites reduction in flexural strengthdue to hygrothermal aging is 32 Reduction in flexuralstrength of nanocomposites after moisture absorption hasbeen previously reported in the literature [4 43 54ndash56]and has been attributed to the degradation of interfaceregion which in turn reduces stress transfer between thenanofiller and the matrix For redried samples as most of themoisture is driven out of the system and plasticization effectwas minimal flexural strength for these samples recoveredalmost fully For instance flexural strength recovers to 95of its original value for 10 wt of Nanomer I28E clay-epoxynanocomposite
Almost similar trendwas observed for SomasifMAEclay-epoxy nanocomposites where addition of clay did not changethe property significantly and after 24 h of hygrothermalaging property decreased to a lower value compared to theas-prepared samples However the severity of degradationwas much less in both clay-epoxy systems compared to neatepoxy system Well dispersed high aspect ratio clay plateletshave the capability of crack deflection and crack arrestingwhich can lead to the observed higher flexural strength in wetclay-epoxy samples in comparison to neat epoxy samples [4857] For redried nanocomposites similar trend was observedfor both material systems and it was found that flexural
International Scholarly Research Notices 7
60
70
80
90
100
110
120Fl
exur
al st
reng
th (M
Pa)
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(a)
60
70
80
90
100
110
120
0 05 1 15 2 25
Flex
ural
stre
ngth
(MPa
)Clay loading (wt)
As-isMoist
Redried
minus05
(b)
Figure 3 Flexural strength as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
200 120583m
(a)
100 120583m
(b)
Figure 4 Scanning electron micrographs of neat epoxy polymer (a) as-prepared and (b) redried
strength recovers almost fully In this study flexural strengthhas not been largely affected by the addition of clay intothe epoxy This may as well mean that flexural strength hasbeen primarily governed by the flexural strength of the epoxyAs the strength of neat epoxy was marginally affected bythe absorption-desorption cycle so did the strength of clay-epoxy nanocomposites
34 Scanning Electron Microscopy (SEM) The scanning elec-tron micrographs of the fracture surface of tested neat epoxyand clay-epoxy nanocomposites are shown in Figures 4ndash8SEM micrograph of the fracture surface of the as-preparedneat polymer (Figure 4(a)) showed characteristic brittle fail-ure with a smooth fracture surface This mirror-like fracture
surface is an indication of poor fracture toughness of epoxyand has been reported in previous studies conducted onepoxy polymers [6] For the redried neat epoxy specimen(Figure 4(b)) a network of microcracks throughout thefracture surface is found For TGDDM-DDS system Morganet al observed similar behavior [58] According to their studyabsorbedmoisture enhances craze initiation and propagationin polymer which can result in the formation of microcracksor fibrils in the polymer system In this study lower fracturetoughness for dried neat polymer compared to unagedneat polymer can be attributed to the formation of thesemicrocracks
The SEMmicrographs of clay incorporated epoxy systemsshowed significantly rougher fracture surface compared to
8 International Scholarly Research Notices
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 5 Scanning electronmicrographs of the crack growth region for 05 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 6 Scanning electron micrographs of the crack growth region for 05 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
International Scholarly Research Notices 9
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 7 Scanning electronmicrographs of the crack growth region for 15 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 8 Scanning electron micrographs of the crack growth region for 15 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
10 International Scholarly Research Notices
the neat polymer Clay if present in a system physicallyblocks and slows down the crack propagation and the result-ing fracture surface of the nanocomposite shows river-markings instead of smooth fracture surface found in the neatpolymer These river-markings provide clear indication ofthe enhanced toughening mechanism in polymeric materialsdue to clay incorporation and support the observed higherfracture toughness for clay-epoxy nanocomposites comparedto the neat epoxy polymer Fracture surfaces of nanofillerreinforced polymer nanocomposites showing higher surfaceroughness have been reported in prior studies [4 6 59]Comparing the fracture surfaces of the as-preparedNanomerI28E and Somasif MAE nanocomposite systems (Figures5(a) 6(a) 7(a) and 8(a)) it was observed that the as-preparedSomasif MAE clay nanocomposite has considerably lessamount of river-markings which is indicative of poor tough-ening in Somasif MAE clay nanocomposites This obser-vation supported the difference of critical stress intensityfactor measured for these two nanocomposite systems Pooradhesion between Somasif MAE clay and epoxy resulted inless energy requirement during new surface formation whichcan be attributed as the reason of these nanocompositesshowing less fracture toughness than Nanomer I28E claynanocomposites for the same clay loading percentage
Fracture surface of moisture absorbed Nanomer I28Eclay nanocomposites (Figures 5(b) and 7(b)) showed lessnumber of river-markings (ie lower critical stress intensityfactor) than the as-prepared nanocomposites SEM micro-graph of Somasif clay-epoxy nanocomposites (Figures 6(b)and 8(b)) showed the presence of shear leaps As shearyielding requires less energy to form new surface moistureabsorbed specimens had lower fracture toughness than theas-prepared specimens Although shear yielding was foundto be the principle mechanism of failure in these specimenssome form of crack bifurcation and crack pinning was alsopresent in these fracture surfaces
Fracture surface micrographs of redried Nanomer I28Enanocomposites (Figures 5(c) and 7(c)) showed more rough-ness than themoisture absorbed specimens indicating higherfracture energy absorbance for these specimensMicrographsof redried Somasif MAE clay-epoxy samples (Figures 6(c)and 8(c)) showed significantly less rough fracture surfacethan the redried Nanomer I28E samples It is important tonote that these redried Somasif MAE clay-epoxy fracturesurfaces showed very little resistance against the crack prop-agation even after most of the water was driven out of thesystemThis observation led to the speculation that absorbedmoisture could have weakened the interface of the SomasifMAE clay particles and the epoxy matrix The replacementof ndashOH (hydroxyl) groups from the octahedral layer of theclay by the ndashF (fluorine) groups makes the Somasif MAE clayparticles muchmore hydrophobic compared to the NanomerI28E clay particlesThe higher hydrophobicity of the SomasifMAE clay particles could have exerted an additional forceon the moisture absorbed interface and weakened the bondbetween the clay particles and the epoxy chains This mighthave in turn resulted in the poor adhesionless fractureenergy absorption in the redried Somasif MAE clay-epoxynanocomposites
0
005
01
015
02
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
Figure 9 FTIR spectra for neat epoxy polymer before and afterabsorption-desorption cycle
35 Fourier Transform Infrared (FTIR) Spectroscopy FTIRspectra of the as-prepared and redried neat epoxy are shownin Figure 9 From the FTIR spectra it was evident that asa result of the absorption-desorption cycle the epoxy under-went some permanent chemical changes These chemicalchanges were probably due to the hydrolysis and chainscission mechanism The drying cycle used in this studyremoved most of the water that was absorbed by the polymersystem and it was believed that the remaining water (onlyabout 7 of the total moisture uptake) is chemically boundto the polymer system FTIR spectra (Figure 7) showed bandat 3200ndash3400 cmminus1 which is characteristic OH stretching ofthe hydroxyl group However significant difference was notobserved for the bands at 3200ndash3400 cmminus1
Figure 10 shows the FTIR spectra for Nanomer I28E andSomasif MAE clay powder before and after the absorption-desorption cycle Both clays showed characteristic SindashO peakin the 990 cmminus1 region Nanomer I28E clay showed anotherpeak at 915 cmminus1 region which is characteristic AlndashOH peakIn Somasif MAE the OH groups present in the corner ofthe octahedral layer of Nanomer I28E were substituted withF which explains the absence of the peak at 915 cmminus1 Bothclays in as-is condition showed 3200ndash3400 cmminus1 band forhydroxyl groups However the band was weaker in case ofSomasif MAE compared to Nanomer I28E clay because ofthe hydrophobic nature of the Somasif MAE clay It wasinteresting to note that the overall changes the clay powdersunderwent as a result of absorption-desorption cycle arefairly small and can be considered as insignificant
International Scholarly Research Notices 11
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
(a)
As-isRedried
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
Abso
rban
ce
Wavenumber (cmminus1)
(b)
Figure 10 FTIR spectra for clay particles before and after absorption-desorption cycle (a) Nanomer I28E and (b) Somasif MAE
4 Conclusion
Property deterioration due to moisture absorption has beenone of the most important areas of interest in polymerresearch for the last few years To be used as structural mater-ials it is of utmost importance to understand the reversibleand irreversible changes occurring in polymeric materials asa result of moisture absorption This study was conducted toelucidate the effect of moisture absorption on the mechan-ical properties of clay reinforced epoxy polymers Fracturetoughness flexural strength and flexural modulus weredetermined for two different clay-epoxy nanocompositesfollowing the ASTM standards The effects of hygrothermalaging and subsequent redrying on the mechanical prop-erties of these polymer nanocomposites were investigatedAfter removing the free water by drying the irreversibleeffect or the permanent damage due to hygrothermal agingon the clay-epoxy nanocomposite systems was determinedIrrespective of the clay reinforcement type all the studiedproperties were degraded due to hygrothermal aging Severalphysical and chemical changes such as interface weaken-ing hydrolysis and chain scission are responsible for theobserved effect The permanent damage or degradation wassevere in case of fracture toughness and flexural modulusFlexural strength of both systems was relatively unaffectedby the absorption-desorption cycle Permanent damage wasfound to be the highest for Somasif MAE clay reinforcedspecimens between two clay-epoxy nanocomposite systemsAfter studying the SEM micrographs of the fracture sur-faces it was speculated that moisture absorption had highernegative impact on the interface of Somasif MAE clay andepoxy matrix compared to the other clay-epoxy system
The hydrophobic nature of the Somasif MAE clay due tothe presence of ndashF (fluorine) in the structure may havecreated additional tension between the polymer crosslinksin presence of moisture FTIR spectra of the clay particlestreated with the same absorption-desorption cycle providedproof that both nanoparticles undergo minimal chemicalchange and retain their respective original chemistry Thisobservation makes the aforementioned speculation moreplausible Although incorporation of clay in epoxymatrix didnot fully stop the degradation it had positive effects to someextent It was observed that the studied properties in generalwere less severely degraded for clay-epoxy nanocompositescompared to neat epoxy samples Therefore clay particlescould be successfully used to reinforce polymer materials toreduce the severity of property deterioration caused by themoisture absorption However the chemistry between theclay particles and polymer matrix and more specifically thechemical structure of the clay particles should be carefullyconsidered to attain the best possible resistance against theproperty deterioration
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this work is fundedin part or fully by a Grant through the Oklahoma Nan-otechnology Applications Project (ONAP) (Grant no O9-20)
12 International Scholarly Research Notices
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
scanning electron microscopy (Hitachi S-4800 FESEMDallas TX) As polymer materials are nonconductive toelectrons all fracture surfaces were sputtered with gold-palladium alloy before SEM imaging
26 Fourier Transform Infrared Spectroscopy FTIR spectros-copy measurements were performed using ATR-FTIR spec-trometer (Nicolet iS10 Waltham MA) using 64 scans at aresolution of 20 cmminus1 Each spectrum was recorded from4000 to 500 cmminus1 at room temperature Spectrawere analyzedusing OriginPro 90 (OriginLab Northampton MA)
3 Results and Discussions
31 Gravimetric Measurements Table 2 shows the relativeweight changes that occurred in the specimens after 24 hoursof boiling water absorption and 6 hours of high temperaturedesorption cycle For the studied material systems percent-age weight gain after absorption cycle showed no change asa function of clay loading percentage This observation wasdifferent from the findings reported by Glaskova and Aniske-vich for clay-epoxy nanocomposites [44] According to theirstudy moisture absorption was found to have increasedslightly with the increase of clay weight percentage Contrar-ily Alamri and Low reported decreasingmoisture absorptionwith increasing clay weight percentage [4] The reason whya different clay-epoxy nanocomposite system behaves differ-ently in moisture absorption test is still not clear and furtherinvestigation is required to understand it In this studyalthough both clays are structurally different the observedpercentage weight gain for both nanocomposite systems wasfound approximately to be the same These two observationsled to the conclusion that moisture diffusion process pri-marily depended on the polymer system under investigationMoisture desorption data showed that most of the absorbedwater is free water which can be driven out of the system bydrying For neat epoxy the amount of retained water afterdesorption cycle is less compared to the nanocompositesThis is possibly due to the fact that presence of clay hinderedthe moisture diffusion process in and out of the epoxypolymers An increasing trend in the amount of retainedmoisture for higher clay loading nanocomposites also sup-ported the aforementioned statement Amount of water
retained after the desorption cycle has been found to bealmost similar for both clay-epoxy nanocomposite systems
32 Fracture Toughness The critical stress intensity factorsas a function of clay loading percentage for Nanomer I28Eand Somasif MAE clay-epoxy nanocomposites are shown inFigure 1119870Ic values for the as-prepared samples are also listedas a reference
Critical stress intensity factor 119870Ic increased 28 for theas-prepared 05 wt Nanomer I28E clay-epoxy nanocom-posite compared to neat epoxy The reason behind thisobservation can be attributed to the layered structure of theclay Clay in a polymer material physically blocks bifurcatesand deflects the crack path compelling the crack to travellonger path which in turn results in higher toughness in aclay-polymer nanocomposite The toughening effect of clayon epoxy polymer started to decrease with any additionalclay reinforcement This is a common behavior for severaltypes of epoxy-clay nanocomposites and has been reportedin previous studies conducted on clay-epoxy nanocomposites[3 6 45 46] Depending on the processing technique andepoxy-clay interaction there is an optimum weight percent-age for which the property enhancement can be maximizedAny further addition of clay negates the positive effect byforming agglomerates due to improper exfoliation of the clayplatelets and thus results in stress concentration forcing thematerial to fail at lower loads For moisture saturated epoxy-clay nanocomposites119870Ic was found to be lower compared tothe as-prepared nanocomposite samples for all the NanomerI28E nanocomposites As water molecules diffuse into thenanofiller-epoxy interface debonding and weakening of theinterface occur resulting in poor stress transfer between thefiller and the epoxy matrix [43 47 48] Redried neat EPON862 free of void-filling water showed 29 reduction infracture toughness compared to the as-prepared neat EPON862 samples Addition of 05 wt of clay resulted in 16reduction in fracture toughness when compared to the as-prepared samples which was significantly less compared to29 reduction of neat epoxy For 20 wt Nanomer I28Eclay-epoxy nanocomposite redried samples were found to betougher than the as-prepared samples However the standarddeviation of the as-prepared sample was much higher whichcould possibly mean that the dried and the as-preparedsamples have no difference in toughness
International Scholarly Research Notices 5
06
08
1
12
14
16
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
Frac
ture
toug
hnes
sK
Ic(M
Pamiddotm
12
)
(a)
06
08
1
12
14
16
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
Frac
ture
toug
hnes
sK
Ic(M
Pamiddotm
12
)
(b)
Figure 1 Critical stress intensity factor 119870Ic as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxynanocomposites
For the as-prepared and moisture saturated samplesSomasif MAE nanocomposites showed comparable trend infracture toughness data clay reinforcement successfullyimproved the baseline epoxy properties andmoisture absorp-tion degraded the mechanical properties for all clay percent-ages However the permanent degradation after absorption-desorption cycle was found to be more prominent in the caseof Somasif MAE clay nanocomposites compared to NanomerI28E clay nanocomposites The recovery of property after6 hours of drying was negligible for Somasif MAE claynanocomposites whereas Nanomer I28E nanocompositesshowed significant recovery of property after drying Thedifference in property recovery of these two clay-epoxynanocomposites can be attributed to the structural differ-ences of the two clay particles and has been further investi-gated through SEM and FTIR technique
33 Flexural Properties Flexural modulus for the neat epoxyand clay-epoxy nanocomposites was determined from 3PBtest and has been plotted against clay loading percentage inFigure 2 for Nanomer I28E and Somasif MAE clay Flexuralmodulus increased almost linearly for both clays as a functionof clay loading percentage According to previous studieson epoxy polymers incorporation of hard substance suchas clay in polymer matrix results in higher modulus [49]When a load is applied on epoxy the polymer chains slidepast each other and deform This deformation is higher inless crosslinked structures compared to higher crosslinkedstructures Once layered silicates such as clay particles are
introduced in a polymer system it restricts the motion of thepolymer chain sliding and makes the matrix less pliable Asthe clay content increases it is more difficult for the polymerchains to untangle and move This increase in restriction ofpolymer chains is responsible for the increase in modulus asthe clay percentage increases
For the hygrothermally conditioned specimens themod-ulus is lower compared to the as-prepared specimens Thisbehavior observed is mostly due to the presence of waterinside the epoxy system which increases the ductility of theepoxy system Water acts as an effective plasticizer and candiffuse into the nanofiller-polymer interface and weaken thebonding between them [40 43] Presence of water in epoxysystem also results in an increase in free volume throughrupture of hydrogen bonding between polymer chains whichincreases the chain mobility and eases the segmental motionwhen a load is applied to the composite [50] These physicalchanges can be attributed to the observed lower modulus forwater absorbed specimens Other mechanisms affecting thepolymer such as hydrolysis and chain scission may also beresponsible for lowering the modulus Once hydrolysis andchain scission take place less bonding between the polymersmakes it more deformable resulting in lower modulus foraged samples [22 36 51] The effect of hygrothermal agingwas more severe in neat epoxy than in the nanocompositesFor neat EPON 862 flexural modulus decreased 20 afterhygrothermal aging whereas it was only 13 and 11 for05 wt of Nanomer I28E and Somasif MAE clay-epoxynanocomposites respectively In addition to being hard
6 International Scholarly Research Notices
24
26
28
3
32
34
36
38Fl
exur
al m
odul
us (G
Pa)
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(a)
24
26
28
3
32
34
36
38
Flex
ural
mod
ulus
(GPa
)Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(b)
Figure 2 Flexural modulus as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
substance clay particles have very high aspect ratioThe highaspect ratio of the clay platelets provides resistance againstpolymer chain mobility in a water absorbed ductile polymerleading to the observed lower degradation of flexural modu-lus values in comparison to neat polymer
For Nanomer I28E clay-epoxy samples conditioned at110∘C for 6 h recovery of flexural modulus was observedOnce redried free water residing in the microvoids wasevaporated and the effect of plasticizationwas not prominentanymore As a result the ductility of the polymer reducedand the recovery of mechanical properties from moistureabsorbed state occurred Nevertheless in case of SomasifMAE clay-epoxy samples modulus recovery was negligibleafter the desorption cycle Due to the structural differencebetween the two clay particles it is possible that the interfaceof Somasif MAE clay-epoxy is being more affected by thehygrothermal degradation than the Nanomer I28E clay-epoxy interface
Flexural strengths for the epoxy and clay-epoxy nano-composites were determined using three-point bend (3PB)test and are plotted against clay loading percentage in Figure 3for Nanomer I28E and Somasif MAE clay Figure 3 showsthat the addition of Nanomer I28E clay provided negligibleimprovement in flexural strength compared to neat epoxyThe maximum improvement in flexural strength was foundto be less than 10 for both clay-epoxy systems from the baseflexural strength of neat epoxy Similar observation has beenreported in the literature where addition of nanoclay parti-cles did not significantly improve the flexural strength of thesystem [52] Furthermore when 20 wt of clay is added to
the nanocomposite flexural strength value dropped to alower value than the neat epoxy Increasing the amount ofnanoparticles more than a certain amount has been found toreduce the flexural strength in earlier studies [53] It can alsobe observed that moisture absorbed nanocomposites showedsignificant reduction in flexural strength For 10 wt of I28Eclay-epoxy nanocomposites reduction in flexural strengthdue to hygrothermal aging is 32 Reduction in flexuralstrength of nanocomposites after moisture absorption hasbeen previously reported in the literature [4 43 54ndash56]and has been attributed to the degradation of interfaceregion which in turn reduces stress transfer between thenanofiller and the matrix For redried samples as most of themoisture is driven out of the system and plasticization effectwas minimal flexural strength for these samples recoveredalmost fully For instance flexural strength recovers to 95of its original value for 10 wt of Nanomer I28E clay-epoxynanocomposite
Almost similar trendwas observed for SomasifMAEclay-epoxy nanocomposites where addition of clay did not changethe property significantly and after 24 h of hygrothermalaging property decreased to a lower value compared to theas-prepared samples However the severity of degradationwas much less in both clay-epoxy systems compared to neatepoxy system Well dispersed high aspect ratio clay plateletshave the capability of crack deflection and crack arrestingwhich can lead to the observed higher flexural strength in wetclay-epoxy samples in comparison to neat epoxy samples [4857] For redried nanocomposites similar trend was observedfor both material systems and it was found that flexural
International Scholarly Research Notices 7
60
70
80
90
100
110
120Fl
exur
al st
reng
th (M
Pa)
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(a)
60
70
80
90
100
110
120
0 05 1 15 2 25
Flex
ural
stre
ngth
(MPa
)Clay loading (wt)
As-isMoist
Redried
minus05
(b)
Figure 3 Flexural strength as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
200 120583m
(a)
100 120583m
(b)
Figure 4 Scanning electron micrographs of neat epoxy polymer (a) as-prepared and (b) redried
strength recovers almost fully In this study flexural strengthhas not been largely affected by the addition of clay intothe epoxy This may as well mean that flexural strength hasbeen primarily governed by the flexural strength of the epoxyAs the strength of neat epoxy was marginally affected bythe absorption-desorption cycle so did the strength of clay-epoxy nanocomposites
34 Scanning Electron Microscopy (SEM) The scanning elec-tron micrographs of the fracture surface of tested neat epoxyand clay-epoxy nanocomposites are shown in Figures 4ndash8SEM micrograph of the fracture surface of the as-preparedneat polymer (Figure 4(a)) showed characteristic brittle fail-ure with a smooth fracture surface This mirror-like fracture
surface is an indication of poor fracture toughness of epoxyand has been reported in previous studies conducted onepoxy polymers [6] For the redried neat epoxy specimen(Figure 4(b)) a network of microcracks throughout thefracture surface is found For TGDDM-DDS system Morganet al observed similar behavior [58] According to their studyabsorbedmoisture enhances craze initiation and propagationin polymer which can result in the formation of microcracksor fibrils in the polymer system In this study lower fracturetoughness for dried neat polymer compared to unagedneat polymer can be attributed to the formation of thesemicrocracks
The SEMmicrographs of clay incorporated epoxy systemsshowed significantly rougher fracture surface compared to
8 International Scholarly Research Notices
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 5 Scanning electronmicrographs of the crack growth region for 05 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 6 Scanning electron micrographs of the crack growth region for 05 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
International Scholarly Research Notices 9
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 7 Scanning electronmicrographs of the crack growth region for 15 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 8 Scanning electron micrographs of the crack growth region for 15 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
10 International Scholarly Research Notices
the neat polymer Clay if present in a system physicallyblocks and slows down the crack propagation and the result-ing fracture surface of the nanocomposite shows river-markings instead of smooth fracture surface found in the neatpolymer These river-markings provide clear indication ofthe enhanced toughening mechanism in polymeric materialsdue to clay incorporation and support the observed higherfracture toughness for clay-epoxy nanocomposites comparedto the neat epoxy polymer Fracture surfaces of nanofillerreinforced polymer nanocomposites showing higher surfaceroughness have been reported in prior studies [4 6 59]Comparing the fracture surfaces of the as-preparedNanomerI28E and Somasif MAE nanocomposite systems (Figures5(a) 6(a) 7(a) and 8(a)) it was observed that the as-preparedSomasif MAE clay nanocomposite has considerably lessamount of river-markings which is indicative of poor tough-ening in Somasif MAE clay nanocomposites This obser-vation supported the difference of critical stress intensityfactor measured for these two nanocomposite systems Pooradhesion between Somasif MAE clay and epoxy resulted inless energy requirement during new surface formation whichcan be attributed as the reason of these nanocompositesshowing less fracture toughness than Nanomer I28E claynanocomposites for the same clay loading percentage
Fracture surface of moisture absorbed Nanomer I28Eclay nanocomposites (Figures 5(b) and 7(b)) showed lessnumber of river-markings (ie lower critical stress intensityfactor) than the as-prepared nanocomposites SEM micro-graph of Somasif clay-epoxy nanocomposites (Figures 6(b)and 8(b)) showed the presence of shear leaps As shearyielding requires less energy to form new surface moistureabsorbed specimens had lower fracture toughness than theas-prepared specimens Although shear yielding was foundto be the principle mechanism of failure in these specimenssome form of crack bifurcation and crack pinning was alsopresent in these fracture surfaces
Fracture surface micrographs of redried Nanomer I28Enanocomposites (Figures 5(c) and 7(c)) showed more rough-ness than themoisture absorbed specimens indicating higherfracture energy absorbance for these specimensMicrographsof redried Somasif MAE clay-epoxy samples (Figures 6(c)and 8(c)) showed significantly less rough fracture surfacethan the redried Nanomer I28E samples It is important tonote that these redried Somasif MAE clay-epoxy fracturesurfaces showed very little resistance against the crack prop-agation even after most of the water was driven out of thesystemThis observation led to the speculation that absorbedmoisture could have weakened the interface of the SomasifMAE clay particles and the epoxy matrix The replacementof ndashOH (hydroxyl) groups from the octahedral layer of theclay by the ndashF (fluorine) groups makes the Somasif MAE clayparticles muchmore hydrophobic compared to the NanomerI28E clay particlesThe higher hydrophobicity of the SomasifMAE clay particles could have exerted an additional forceon the moisture absorbed interface and weakened the bondbetween the clay particles and the epoxy chains This mighthave in turn resulted in the poor adhesionless fractureenergy absorption in the redried Somasif MAE clay-epoxynanocomposites
0
005
01
015
02
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
Figure 9 FTIR spectra for neat epoxy polymer before and afterabsorption-desorption cycle
35 Fourier Transform Infrared (FTIR) Spectroscopy FTIRspectra of the as-prepared and redried neat epoxy are shownin Figure 9 From the FTIR spectra it was evident that asa result of the absorption-desorption cycle the epoxy under-went some permanent chemical changes These chemicalchanges were probably due to the hydrolysis and chainscission mechanism The drying cycle used in this studyremoved most of the water that was absorbed by the polymersystem and it was believed that the remaining water (onlyabout 7 of the total moisture uptake) is chemically boundto the polymer system FTIR spectra (Figure 7) showed bandat 3200ndash3400 cmminus1 which is characteristic OH stretching ofthe hydroxyl group However significant difference was notobserved for the bands at 3200ndash3400 cmminus1
Figure 10 shows the FTIR spectra for Nanomer I28E andSomasif MAE clay powder before and after the absorption-desorption cycle Both clays showed characteristic SindashO peakin the 990 cmminus1 region Nanomer I28E clay showed anotherpeak at 915 cmminus1 region which is characteristic AlndashOH peakIn Somasif MAE the OH groups present in the corner ofthe octahedral layer of Nanomer I28E were substituted withF which explains the absence of the peak at 915 cmminus1 Bothclays in as-is condition showed 3200ndash3400 cmminus1 band forhydroxyl groups However the band was weaker in case ofSomasif MAE compared to Nanomer I28E clay because ofthe hydrophobic nature of the Somasif MAE clay It wasinteresting to note that the overall changes the clay powdersunderwent as a result of absorption-desorption cycle arefairly small and can be considered as insignificant
International Scholarly Research Notices 11
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
(a)
As-isRedried
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
Abso
rban
ce
Wavenumber (cmminus1)
(b)
Figure 10 FTIR spectra for clay particles before and after absorption-desorption cycle (a) Nanomer I28E and (b) Somasif MAE
4 Conclusion
Property deterioration due to moisture absorption has beenone of the most important areas of interest in polymerresearch for the last few years To be used as structural mater-ials it is of utmost importance to understand the reversibleand irreversible changes occurring in polymeric materials asa result of moisture absorption This study was conducted toelucidate the effect of moisture absorption on the mechan-ical properties of clay reinforced epoxy polymers Fracturetoughness flexural strength and flexural modulus weredetermined for two different clay-epoxy nanocompositesfollowing the ASTM standards The effects of hygrothermalaging and subsequent redrying on the mechanical prop-erties of these polymer nanocomposites were investigatedAfter removing the free water by drying the irreversibleeffect or the permanent damage due to hygrothermal agingon the clay-epoxy nanocomposite systems was determinedIrrespective of the clay reinforcement type all the studiedproperties were degraded due to hygrothermal aging Severalphysical and chemical changes such as interface weaken-ing hydrolysis and chain scission are responsible for theobserved effect The permanent damage or degradation wassevere in case of fracture toughness and flexural modulusFlexural strength of both systems was relatively unaffectedby the absorption-desorption cycle Permanent damage wasfound to be the highest for Somasif MAE clay reinforcedspecimens between two clay-epoxy nanocomposite systemsAfter studying the SEM micrographs of the fracture sur-faces it was speculated that moisture absorption had highernegative impact on the interface of Somasif MAE clay andepoxy matrix compared to the other clay-epoxy system
The hydrophobic nature of the Somasif MAE clay due tothe presence of ndashF (fluorine) in the structure may havecreated additional tension between the polymer crosslinksin presence of moisture FTIR spectra of the clay particlestreated with the same absorption-desorption cycle providedproof that both nanoparticles undergo minimal chemicalchange and retain their respective original chemistry Thisobservation makes the aforementioned speculation moreplausible Although incorporation of clay in epoxymatrix didnot fully stop the degradation it had positive effects to someextent It was observed that the studied properties in generalwere less severely degraded for clay-epoxy nanocompositescompared to neat epoxy samples Therefore clay particlescould be successfully used to reinforce polymer materials toreduce the severity of property deterioration caused by themoisture absorption However the chemistry between theclay particles and polymer matrix and more specifically thechemical structure of the clay particles should be carefullyconsidered to attain the best possible resistance against theproperty deterioration
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this work is fundedin part or fully by a Grant through the Oklahoma Nan-otechnology Applications Project (ONAP) (Grant no O9-20)
12 International Scholarly Research Notices
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
Figure 1 Critical stress intensity factor 119870Ic as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxynanocomposites
For the as-prepared and moisture saturated samplesSomasif MAE nanocomposites showed comparable trend infracture toughness data clay reinforcement successfullyimproved the baseline epoxy properties andmoisture absorp-tion degraded the mechanical properties for all clay percent-ages However the permanent degradation after absorption-desorption cycle was found to be more prominent in the caseof Somasif MAE clay nanocomposites compared to NanomerI28E clay nanocomposites The recovery of property after6 hours of drying was negligible for Somasif MAE claynanocomposites whereas Nanomer I28E nanocompositesshowed significant recovery of property after drying Thedifference in property recovery of these two clay-epoxynanocomposites can be attributed to the structural differ-ences of the two clay particles and has been further investi-gated through SEM and FTIR technique
33 Flexural Properties Flexural modulus for the neat epoxyand clay-epoxy nanocomposites was determined from 3PBtest and has been plotted against clay loading percentage inFigure 2 for Nanomer I28E and Somasif MAE clay Flexuralmodulus increased almost linearly for both clays as a functionof clay loading percentage According to previous studieson epoxy polymers incorporation of hard substance suchas clay in polymer matrix results in higher modulus [49]When a load is applied on epoxy the polymer chains slidepast each other and deform This deformation is higher inless crosslinked structures compared to higher crosslinkedstructures Once layered silicates such as clay particles are
introduced in a polymer system it restricts the motion of thepolymer chain sliding and makes the matrix less pliable Asthe clay content increases it is more difficult for the polymerchains to untangle and move This increase in restriction ofpolymer chains is responsible for the increase in modulus asthe clay percentage increases
For the hygrothermally conditioned specimens themod-ulus is lower compared to the as-prepared specimens Thisbehavior observed is mostly due to the presence of waterinside the epoxy system which increases the ductility of theepoxy system Water acts as an effective plasticizer and candiffuse into the nanofiller-polymer interface and weaken thebonding between them [40 43] Presence of water in epoxysystem also results in an increase in free volume throughrupture of hydrogen bonding between polymer chains whichincreases the chain mobility and eases the segmental motionwhen a load is applied to the composite [50] These physicalchanges can be attributed to the observed lower modulus forwater absorbed specimens Other mechanisms affecting thepolymer such as hydrolysis and chain scission may also beresponsible for lowering the modulus Once hydrolysis andchain scission take place less bonding between the polymersmakes it more deformable resulting in lower modulus foraged samples [22 36 51] The effect of hygrothermal agingwas more severe in neat epoxy than in the nanocompositesFor neat EPON 862 flexural modulus decreased 20 afterhygrothermal aging whereas it was only 13 and 11 for05 wt of Nanomer I28E and Somasif MAE clay-epoxynanocomposites respectively In addition to being hard
6 International Scholarly Research Notices
24
26
28
3
32
34
36
38Fl
exur
al m
odul
us (G
Pa)
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(a)
24
26
28
3
32
34
36
38
Flex
ural
mod
ulus
(GPa
)Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(b)
Figure 2 Flexural modulus as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
substance clay particles have very high aspect ratioThe highaspect ratio of the clay platelets provides resistance againstpolymer chain mobility in a water absorbed ductile polymerleading to the observed lower degradation of flexural modu-lus values in comparison to neat polymer
For Nanomer I28E clay-epoxy samples conditioned at110∘C for 6 h recovery of flexural modulus was observedOnce redried free water residing in the microvoids wasevaporated and the effect of plasticizationwas not prominentanymore As a result the ductility of the polymer reducedand the recovery of mechanical properties from moistureabsorbed state occurred Nevertheless in case of SomasifMAE clay-epoxy samples modulus recovery was negligibleafter the desorption cycle Due to the structural differencebetween the two clay particles it is possible that the interfaceof Somasif MAE clay-epoxy is being more affected by thehygrothermal degradation than the Nanomer I28E clay-epoxy interface
Flexural strengths for the epoxy and clay-epoxy nano-composites were determined using three-point bend (3PB)test and are plotted against clay loading percentage in Figure 3for Nanomer I28E and Somasif MAE clay Figure 3 showsthat the addition of Nanomer I28E clay provided negligibleimprovement in flexural strength compared to neat epoxyThe maximum improvement in flexural strength was foundto be less than 10 for both clay-epoxy systems from the baseflexural strength of neat epoxy Similar observation has beenreported in the literature where addition of nanoclay parti-cles did not significantly improve the flexural strength of thesystem [52] Furthermore when 20 wt of clay is added to
the nanocomposite flexural strength value dropped to alower value than the neat epoxy Increasing the amount ofnanoparticles more than a certain amount has been found toreduce the flexural strength in earlier studies [53] It can alsobe observed that moisture absorbed nanocomposites showedsignificant reduction in flexural strength For 10 wt of I28Eclay-epoxy nanocomposites reduction in flexural strengthdue to hygrothermal aging is 32 Reduction in flexuralstrength of nanocomposites after moisture absorption hasbeen previously reported in the literature [4 43 54ndash56]and has been attributed to the degradation of interfaceregion which in turn reduces stress transfer between thenanofiller and the matrix For redried samples as most of themoisture is driven out of the system and plasticization effectwas minimal flexural strength for these samples recoveredalmost fully For instance flexural strength recovers to 95of its original value for 10 wt of Nanomer I28E clay-epoxynanocomposite
Almost similar trendwas observed for SomasifMAEclay-epoxy nanocomposites where addition of clay did not changethe property significantly and after 24 h of hygrothermalaging property decreased to a lower value compared to theas-prepared samples However the severity of degradationwas much less in both clay-epoxy systems compared to neatepoxy system Well dispersed high aspect ratio clay plateletshave the capability of crack deflection and crack arrestingwhich can lead to the observed higher flexural strength in wetclay-epoxy samples in comparison to neat epoxy samples [4857] For redried nanocomposites similar trend was observedfor both material systems and it was found that flexural
International Scholarly Research Notices 7
60
70
80
90
100
110
120Fl
exur
al st
reng
th (M
Pa)
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(a)
60
70
80
90
100
110
120
0 05 1 15 2 25
Flex
ural
stre
ngth
(MPa
)Clay loading (wt)
As-isMoist
Redried
minus05
(b)
Figure 3 Flexural strength as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
200 120583m
(a)
100 120583m
(b)
Figure 4 Scanning electron micrographs of neat epoxy polymer (a) as-prepared and (b) redried
strength recovers almost fully In this study flexural strengthhas not been largely affected by the addition of clay intothe epoxy This may as well mean that flexural strength hasbeen primarily governed by the flexural strength of the epoxyAs the strength of neat epoxy was marginally affected bythe absorption-desorption cycle so did the strength of clay-epoxy nanocomposites
34 Scanning Electron Microscopy (SEM) The scanning elec-tron micrographs of the fracture surface of tested neat epoxyand clay-epoxy nanocomposites are shown in Figures 4ndash8SEM micrograph of the fracture surface of the as-preparedneat polymer (Figure 4(a)) showed characteristic brittle fail-ure with a smooth fracture surface This mirror-like fracture
surface is an indication of poor fracture toughness of epoxyand has been reported in previous studies conducted onepoxy polymers [6] For the redried neat epoxy specimen(Figure 4(b)) a network of microcracks throughout thefracture surface is found For TGDDM-DDS system Morganet al observed similar behavior [58] According to their studyabsorbedmoisture enhances craze initiation and propagationin polymer which can result in the formation of microcracksor fibrils in the polymer system In this study lower fracturetoughness for dried neat polymer compared to unagedneat polymer can be attributed to the formation of thesemicrocracks
The SEMmicrographs of clay incorporated epoxy systemsshowed significantly rougher fracture surface compared to
8 International Scholarly Research Notices
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 5 Scanning electronmicrographs of the crack growth region for 05 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 6 Scanning electron micrographs of the crack growth region for 05 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
International Scholarly Research Notices 9
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 7 Scanning electronmicrographs of the crack growth region for 15 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 8 Scanning electron micrographs of the crack growth region for 15 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
10 International Scholarly Research Notices
the neat polymer Clay if present in a system physicallyblocks and slows down the crack propagation and the result-ing fracture surface of the nanocomposite shows river-markings instead of smooth fracture surface found in the neatpolymer These river-markings provide clear indication ofthe enhanced toughening mechanism in polymeric materialsdue to clay incorporation and support the observed higherfracture toughness for clay-epoxy nanocomposites comparedto the neat epoxy polymer Fracture surfaces of nanofillerreinforced polymer nanocomposites showing higher surfaceroughness have been reported in prior studies [4 6 59]Comparing the fracture surfaces of the as-preparedNanomerI28E and Somasif MAE nanocomposite systems (Figures5(a) 6(a) 7(a) and 8(a)) it was observed that the as-preparedSomasif MAE clay nanocomposite has considerably lessamount of river-markings which is indicative of poor tough-ening in Somasif MAE clay nanocomposites This obser-vation supported the difference of critical stress intensityfactor measured for these two nanocomposite systems Pooradhesion between Somasif MAE clay and epoxy resulted inless energy requirement during new surface formation whichcan be attributed as the reason of these nanocompositesshowing less fracture toughness than Nanomer I28E claynanocomposites for the same clay loading percentage
Fracture surface of moisture absorbed Nanomer I28Eclay nanocomposites (Figures 5(b) and 7(b)) showed lessnumber of river-markings (ie lower critical stress intensityfactor) than the as-prepared nanocomposites SEM micro-graph of Somasif clay-epoxy nanocomposites (Figures 6(b)and 8(b)) showed the presence of shear leaps As shearyielding requires less energy to form new surface moistureabsorbed specimens had lower fracture toughness than theas-prepared specimens Although shear yielding was foundto be the principle mechanism of failure in these specimenssome form of crack bifurcation and crack pinning was alsopresent in these fracture surfaces
Fracture surface micrographs of redried Nanomer I28Enanocomposites (Figures 5(c) and 7(c)) showed more rough-ness than themoisture absorbed specimens indicating higherfracture energy absorbance for these specimensMicrographsof redried Somasif MAE clay-epoxy samples (Figures 6(c)and 8(c)) showed significantly less rough fracture surfacethan the redried Nanomer I28E samples It is important tonote that these redried Somasif MAE clay-epoxy fracturesurfaces showed very little resistance against the crack prop-agation even after most of the water was driven out of thesystemThis observation led to the speculation that absorbedmoisture could have weakened the interface of the SomasifMAE clay particles and the epoxy matrix The replacementof ndashOH (hydroxyl) groups from the octahedral layer of theclay by the ndashF (fluorine) groups makes the Somasif MAE clayparticles muchmore hydrophobic compared to the NanomerI28E clay particlesThe higher hydrophobicity of the SomasifMAE clay particles could have exerted an additional forceon the moisture absorbed interface and weakened the bondbetween the clay particles and the epoxy chains This mighthave in turn resulted in the poor adhesionless fractureenergy absorption in the redried Somasif MAE clay-epoxynanocomposites
0
005
01
015
02
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
Figure 9 FTIR spectra for neat epoxy polymer before and afterabsorption-desorption cycle
35 Fourier Transform Infrared (FTIR) Spectroscopy FTIRspectra of the as-prepared and redried neat epoxy are shownin Figure 9 From the FTIR spectra it was evident that asa result of the absorption-desorption cycle the epoxy under-went some permanent chemical changes These chemicalchanges were probably due to the hydrolysis and chainscission mechanism The drying cycle used in this studyremoved most of the water that was absorbed by the polymersystem and it was believed that the remaining water (onlyabout 7 of the total moisture uptake) is chemically boundto the polymer system FTIR spectra (Figure 7) showed bandat 3200ndash3400 cmminus1 which is characteristic OH stretching ofthe hydroxyl group However significant difference was notobserved for the bands at 3200ndash3400 cmminus1
Figure 10 shows the FTIR spectra for Nanomer I28E andSomasif MAE clay powder before and after the absorption-desorption cycle Both clays showed characteristic SindashO peakin the 990 cmminus1 region Nanomer I28E clay showed anotherpeak at 915 cmminus1 region which is characteristic AlndashOH peakIn Somasif MAE the OH groups present in the corner ofthe octahedral layer of Nanomer I28E were substituted withF which explains the absence of the peak at 915 cmminus1 Bothclays in as-is condition showed 3200ndash3400 cmminus1 band forhydroxyl groups However the band was weaker in case ofSomasif MAE compared to Nanomer I28E clay because ofthe hydrophobic nature of the Somasif MAE clay It wasinteresting to note that the overall changes the clay powdersunderwent as a result of absorption-desorption cycle arefairly small and can be considered as insignificant
International Scholarly Research Notices 11
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
(a)
As-isRedried
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
Abso
rban
ce
Wavenumber (cmminus1)
(b)
Figure 10 FTIR spectra for clay particles before and after absorption-desorption cycle (a) Nanomer I28E and (b) Somasif MAE
4 Conclusion
Property deterioration due to moisture absorption has beenone of the most important areas of interest in polymerresearch for the last few years To be used as structural mater-ials it is of utmost importance to understand the reversibleand irreversible changes occurring in polymeric materials asa result of moisture absorption This study was conducted toelucidate the effect of moisture absorption on the mechan-ical properties of clay reinforced epoxy polymers Fracturetoughness flexural strength and flexural modulus weredetermined for two different clay-epoxy nanocompositesfollowing the ASTM standards The effects of hygrothermalaging and subsequent redrying on the mechanical prop-erties of these polymer nanocomposites were investigatedAfter removing the free water by drying the irreversibleeffect or the permanent damage due to hygrothermal agingon the clay-epoxy nanocomposite systems was determinedIrrespective of the clay reinforcement type all the studiedproperties were degraded due to hygrothermal aging Severalphysical and chemical changes such as interface weaken-ing hydrolysis and chain scission are responsible for theobserved effect The permanent damage or degradation wassevere in case of fracture toughness and flexural modulusFlexural strength of both systems was relatively unaffectedby the absorption-desorption cycle Permanent damage wasfound to be the highest for Somasif MAE clay reinforcedspecimens between two clay-epoxy nanocomposite systemsAfter studying the SEM micrographs of the fracture sur-faces it was speculated that moisture absorption had highernegative impact on the interface of Somasif MAE clay andepoxy matrix compared to the other clay-epoxy system
The hydrophobic nature of the Somasif MAE clay due tothe presence of ndashF (fluorine) in the structure may havecreated additional tension between the polymer crosslinksin presence of moisture FTIR spectra of the clay particlestreated with the same absorption-desorption cycle providedproof that both nanoparticles undergo minimal chemicalchange and retain their respective original chemistry Thisobservation makes the aforementioned speculation moreplausible Although incorporation of clay in epoxymatrix didnot fully stop the degradation it had positive effects to someextent It was observed that the studied properties in generalwere less severely degraded for clay-epoxy nanocompositescompared to neat epoxy samples Therefore clay particlescould be successfully used to reinforce polymer materials toreduce the severity of property deterioration caused by themoisture absorption However the chemistry between theclay particles and polymer matrix and more specifically thechemical structure of the clay particles should be carefullyconsidered to attain the best possible resistance against theproperty deterioration
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this work is fundedin part or fully by a Grant through the Oklahoma Nan-otechnology Applications Project (ONAP) (Grant no O9-20)
12 International Scholarly Research Notices
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
Figure 2 Flexural modulus as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
substance clay particles have very high aspect ratioThe highaspect ratio of the clay platelets provides resistance againstpolymer chain mobility in a water absorbed ductile polymerleading to the observed lower degradation of flexural modu-lus values in comparison to neat polymer
For Nanomer I28E clay-epoxy samples conditioned at110∘C for 6 h recovery of flexural modulus was observedOnce redried free water residing in the microvoids wasevaporated and the effect of plasticizationwas not prominentanymore As a result the ductility of the polymer reducedand the recovery of mechanical properties from moistureabsorbed state occurred Nevertheless in case of SomasifMAE clay-epoxy samples modulus recovery was negligibleafter the desorption cycle Due to the structural differencebetween the two clay particles it is possible that the interfaceof Somasif MAE clay-epoxy is being more affected by thehygrothermal degradation than the Nanomer I28E clay-epoxy interface
Flexural strengths for the epoxy and clay-epoxy nano-composites were determined using three-point bend (3PB)test and are plotted against clay loading percentage in Figure 3for Nanomer I28E and Somasif MAE clay Figure 3 showsthat the addition of Nanomer I28E clay provided negligibleimprovement in flexural strength compared to neat epoxyThe maximum improvement in flexural strength was foundto be less than 10 for both clay-epoxy systems from the baseflexural strength of neat epoxy Similar observation has beenreported in the literature where addition of nanoclay parti-cles did not significantly improve the flexural strength of thesystem [52] Furthermore when 20 wt of clay is added to
the nanocomposite flexural strength value dropped to alower value than the neat epoxy Increasing the amount ofnanoparticles more than a certain amount has been found toreduce the flexural strength in earlier studies [53] It can alsobe observed that moisture absorbed nanocomposites showedsignificant reduction in flexural strength For 10 wt of I28Eclay-epoxy nanocomposites reduction in flexural strengthdue to hygrothermal aging is 32 Reduction in flexuralstrength of nanocomposites after moisture absorption hasbeen previously reported in the literature [4 43 54ndash56]and has been attributed to the degradation of interfaceregion which in turn reduces stress transfer between thenanofiller and the matrix For redried samples as most of themoisture is driven out of the system and plasticization effectwas minimal flexural strength for these samples recoveredalmost fully For instance flexural strength recovers to 95of its original value for 10 wt of Nanomer I28E clay-epoxynanocomposite
Almost similar trendwas observed for SomasifMAEclay-epoxy nanocomposites where addition of clay did not changethe property significantly and after 24 h of hygrothermalaging property decreased to a lower value compared to theas-prepared samples However the severity of degradationwas much less in both clay-epoxy systems compared to neatepoxy system Well dispersed high aspect ratio clay plateletshave the capability of crack deflection and crack arrestingwhich can lead to the observed higher flexural strength in wetclay-epoxy samples in comparison to neat epoxy samples [4857] For redried nanocomposites similar trend was observedfor both material systems and it was found that flexural
International Scholarly Research Notices 7
60
70
80
90
100
110
120Fl
exur
al st
reng
th (M
Pa)
Clay loading (wt)
As-isMoist
Redried
minus05 0 05 1 15 2 25
(a)
60
70
80
90
100
110
120
0 05 1 15 2 25
Flex
ural
stre
ngth
(MPa
)Clay loading (wt)
As-isMoist
Redried
minus05
(b)
Figure 3 Flexural strength as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
200 120583m
(a)
100 120583m
(b)
Figure 4 Scanning electron micrographs of neat epoxy polymer (a) as-prepared and (b) redried
strength recovers almost fully In this study flexural strengthhas not been largely affected by the addition of clay intothe epoxy This may as well mean that flexural strength hasbeen primarily governed by the flexural strength of the epoxyAs the strength of neat epoxy was marginally affected bythe absorption-desorption cycle so did the strength of clay-epoxy nanocomposites
34 Scanning Electron Microscopy (SEM) The scanning elec-tron micrographs of the fracture surface of tested neat epoxyand clay-epoxy nanocomposites are shown in Figures 4ndash8SEM micrograph of the fracture surface of the as-preparedneat polymer (Figure 4(a)) showed characteristic brittle fail-ure with a smooth fracture surface This mirror-like fracture
surface is an indication of poor fracture toughness of epoxyand has been reported in previous studies conducted onepoxy polymers [6] For the redried neat epoxy specimen(Figure 4(b)) a network of microcracks throughout thefracture surface is found For TGDDM-DDS system Morganet al observed similar behavior [58] According to their studyabsorbedmoisture enhances craze initiation and propagationin polymer which can result in the formation of microcracksor fibrils in the polymer system In this study lower fracturetoughness for dried neat polymer compared to unagedneat polymer can be attributed to the formation of thesemicrocracks
The SEMmicrographs of clay incorporated epoxy systemsshowed significantly rougher fracture surface compared to
8 International Scholarly Research Notices
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 5 Scanning electronmicrographs of the crack growth region for 05 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 6 Scanning electron micrographs of the crack growth region for 05 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
International Scholarly Research Notices 9
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 7 Scanning electronmicrographs of the crack growth region for 15 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 8 Scanning electron micrographs of the crack growth region for 15 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
10 International Scholarly Research Notices
the neat polymer Clay if present in a system physicallyblocks and slows down the crack propagation and the result-ing fracture surface of the nanocomposite shows river-markings instead of smooth fracture surface found in the neatpolymer These river-markings provide clear indication ofthe enhanced toughening mechanism in polymeric materialsdue to clay incorporation and support the observed higherfracture toughness for clay-epoxy nanocomposites comparedto the neat epoxy polymer Fracture surfaces of nanofillerreinforced polymer nanocomposites showing higher surfaceroughness have been reported in prior studies [4 6 59]Comparing the fracture surfaces of the as-preparedNanomerI28E and Somasif MAE nanocomposite systems (Figures5(a) 6(a) 7(a) and 8(a)) it was observed that the as-preparedSomasif MAE clay nanocomposite has considerably lessamount of river-markings which is indicative of poor tough-ening in Somasif MAE clay nanocomposites This obser-vation supported the difference of critical stress intensityfactor measured for these two nanocomposite systems Pooradhesion between Somasif MAE clay and epoxy resulted inless energy requirement during new surface formation whichcan be attributed as the reason of these nanocompositesshowing less fracture toughness than Nanomer I28E claynanocomposites for the same clay loading percentage
Fracture surface of moisture absorbed Nanomer I28Eclay nanocomposites (Figures 5(b) and 7(b)) showed lessnumber of river-markings (ie lower critical stress intensityfactor) than the as-prepared nanocomposites SEM micro-graph of Somasif clay-epoxy nanocomposites (Figures 6(b)and 8(b)) showed the presence of shear leaps As shearyielding requires less energy to form new surface moistureabsorbed specimens had lower fracture toughness than theas-prepared specimens Although shear yielding was foundto be the principle mechanism of failure in these specimenssome form of crack bifurcation and crack pinning was alsopresent in these fracture surfaces
Fracture surface micrographs of redried Nanomer I28Enanocomposites (Figures 5(c) and 7(c)) showed more rough-ness than themoisture absorbed specimens indicating higherfracture energy absorbance for these specimensMicrographsof redried Somasif MAE clay-epoxy samples (Figures 6(c)and 8(c)) showed significantly less rough fracture surfacethan the redried Nanomer I28E samples It is important tonote that these redried Somasif MAE clay-epoxy fracturesurfaces showed very little resistance against the crack prop-agation even after most of the water was driven out of thesystemThis observation led to the speculation that absorbedmoisture could have weakened the interface of the SomasifMAE clay particles and the epoxy matrix The replacementof ndashOH (hydroxyl) groups from the octahedral layer of theclay by the ndashF (fluorine) groups makes the Somasif MAE clayparticles muchmore hydrophobic compared to the NanomerI28E clay particlesThe higher hydrophobicity of the SomasifMAE clay particles could have exerted an additional forceon the moisture absorbed interface and weakened the bondbetween the clay particles and the epoxy chains This mighthave in turn resulted in the poor adhesionless fractureenergy absorption in the redried Somasif MAE clay-epoxynanocomposites
0
005
01
015
02
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
Figure 9 FTIR spectra for neat epoxy polymer before and afterabsorption-desorption cycle
35 Fourier Transform Infrared (FTIR) Spectroscopy FTIRspectra of the as-prepared and redried neat epoxy are shownin Figure 9 From the FTIR spectra it was evident that asa result of the absorption-desorption cycle the epoxy under-went some permanent chemical changes These chemicalchanges were probably due to the hydrolysis and chainscission mechanism The drying cycle used in this studyremoved most of the water that was absorbed by the polymersystem and it was believed that the remaining water (onlyabout 7 of the total moisture uptake) is chemically boundto the polymer system FTIR spectra (Figure 7) showed bandat 3200ndash3400 cmminus1 which is characteristic OH stretching ofthe hydroxyl group However significant difference was notobserved for the bands at 3200ndash3400 cmminus1
Figure 10 shows the FTIR spectra for Nanomer I28E andSomasif MAE clay powder before and after the absorption-desorption cycle Both clays showed characteristic SindashO peakin the 990 cmminus1 region Nanomer I28E clay showed anotherpeak at 915 cmminus1 region which is characteristic AlndashOH peakIn Somasif MAE the OH groups present in the corner ofthe octahedral layer of Nanomer I28E were substituted withF which explains the absence of the peak at 915 cmminus1 Bothclays in as-is condition showed 3200ndash3400 cmminus1 band forhydroxyl groups However the band was weaker in case ofSomasif MAE compared to Nanomer I28E clay because ofthe hydrophobic nature of the Somasif MAE clay It wasinteresting to note that the overall changes the clay powdersunderwent as a result of absorption-desorption cycle arefairly small and can be considered as insignificant
International Scholarly Research Notices 11
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
(a)
As-isRedried
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
Abso
rban
ce
Wavenumber (cmminus1)
(b)
Figure 10 FTIR spectra for clay particles before and after absorption-desorption cycle (a) Nanomer I28E and (b) Somasif MAE
4 Conclusion
Property deterioration due to moisture absorption has beenone of the most important areas of interest in polymerresearch for the last few years To be used as structural mater-ials it is of utmost importance to understand the reversibleand irreversible changes occurring in polymeric materials asa result of moisture absorption This study was conducted toelucidate the effect of moisture absorption on the mechan-ical properties of clay reinforced epoxy polymers Fracturetoughness flexural strength and flexural modulus weredetermined for two different clay-epoxy nanocompositesfollowing the ASTM standards The effects of hygrothermalaging and subsequent redrying on the mechanical prop-erties of these polymer nanocomposites were investigatedAfter removing the free water by drying the irreversibleeffect or the permanent damage due to hygrothermal agingon the clay-epoxy nanocomposite systems was determinedIrrespective of the clay reinforcement type all the studiedproperties were degraded due to hygrothermal aging Severalphysical and chemical changes such as interface weaken-ing hydrolysis and chain scission are responsible for theobserved effect The permanent damage or degradation wassevere in case of fracture toughness and flexural modulusFlexural strength of both systems was relatively unaffectedby the absorption-desorption cycle Permanent damage wasfound to be the highest for Somasif MAE clay reinforcedspecimens between two clay-epoxy nanocomposite systemsAfter studying the SEM micrographs of the fracture sur-faces it was speculated that moisture absorption had highernegative impact on the interface of Somasif MAE clay andepoxy matrix compared to the other clay-epoxy system
The hydrophobic nature of the Somasif MAE clay due tothe presence of ndashF (fluorine) in the structure may havecreated additional tension between the polymer crosslinksin presence of moisture FTIR spectra of the clay particlestreated with the same absorption-desorption cycle providedproof that both nanoparticles undergo minimal chemicalchange and retain their respective original chemistry Thisobservation makes the aforementioned speculation moreplausible Although incorporation of clay in epoxymatrix didnot fully stop the degradation it had positive effects to someextent It was observed that the studied properties in generalwere less severely degraded for clay-epoxy nanocompositescompared to neat epoxy samples Therefore clay particlescould be successfully used to reinforce polymer materials toreduce the severity of property deterioration caused by themoisture absorption However the chemistry between theclay particles and polymer matrix and more specifically thechemical structure of the clay particles should be carefullyconsidered to attain the best possible resistance against theproperty deterioration
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this work is fundedin part or fully by a Grant through the Oklahoma Nan-otechnology Applications Project (ONAP) (Grant no O9-20)
12 International Scholarly Research Notices
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
Figure 3 Flexural strength as a function of clay loading (a) Nanomer I28E and (b) Somasif MAE clay-epoxy nanocomposites
200 120583m
(a)
100 120583m
(b)
Figure 4 Scanning electron micrographs of neat epoxy polymer (a) as-prepared and (b) redried
strength recovers almost fully In this study flexural strengthhas not been largely affected by the addition of clay intothe epoxy This may as well mean that flexural strength hasbeen primarily governed by the flexural strength of the epoxyAs the strength of neat epoxy was marginally affected bythe absorption-desorption cycle so did the strength of clay-epoxy nanocomposites
34 Scanning Electron Microscopy (SEM) The scanning elec-tron micrographs of the fracture surface of tested neat epoxyand clay-epoxy nanocomposites are shown in Figures 4ndash8SEM micrograph of the fracture surface of the as-preparedneat polymer (Figure 4(a)) showed characteristic brittle fail-ure with a smooth fracture surface This mirror-like fracture
surface is an indication of poor fracture toughness of epoxyand has been reported in previous studies conducted onepoxy polymers [6] For the redried neat epoxy specimen(Figure 4(b)) a network of microcracks throughout thefracture surface is found For TGDDM-DDS system Morganet al observed similar behavior [58] According to their studyabsorbedmoisture enhances craze initiation and propagationin polymer which can result in the formation of microcracksor fibrils in the polymer system In this study lower fracturetoughness for dried neat polymer compared to unagedneat polymer can be attributed to the formation of thesemicrocracks
The SEMmicrographs of clay incorporated epoxy systemsshowed significantly rougher fracture surface compared to
8 International Scholarly Research Notices
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 5 Scanning electronmicrographs of the crack growth region for 05 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 6 Scanning electron micrographs of the crack growth region for 05 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
International Scholarly Research Notices 9
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 7 Scanning electronmicrographs of the crack growth region for 15 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 8 Scanning electron micrographs of the crack growth region for 15 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
10 International Scholarly Research Notices
the neat polymer Clay if present in a system physicallyblocks and slows down the crack propagation and the result-ing fracture surface of the nanocomposite shows river-markings instead of smooth fracture surface found in the neatpolymer These river-markings provide clear indication ofthe enhanced toughening mechanism in polymeric materialsdue to clay incorporation and support the observed higherfracture toughness for clay-epoxy nanocomposites comparedto the neat epoxy polymer Fracture surfaces of nanofillerreinforced polymer nanocomposites showing higher surfaceroughness have been reported in prior studies [4 6 59]Comparing the fracture surfaces of the as-preparedNanomerI28E and Somasif MAE nanocomposite systems (Figures5(a) 6(a) 7(a) and 8(a)) it was observed that the as-preparedSomasif MAE clay nanocomposite has considerably lessamount of river-markings which is indicative of poor tough-ening in Somasif MAE clay nanocomposites This obser-vation supported the difference of critical stress intensityfactor measured for these two nanocomposite systems Pooradhesion between Somasif MAE clay and epoxy resulted inless energy requirement during new surface formation whichcan be attributed as the reason of these nanocompositesshowing less fracture toughness than Nanomer I28E claynanocomposites for the same clay loading percentage
Fracture surface of moisture absorbed Nanomer I28Eclay nanocomposites (Figures 5(b) and 7(b)) showed lessnumber of river-markings (ie lower critical stress intensityfactor) than the as-prepared nanocomposites SEM micro-graph of Somasif clay-epoxy nanocomposites (Figures 6(b)and 8(b)) showed the presence of shear leaps As shearyielding requires less energy to form new surface moistureabsorbed specimens had lower fracture toughness than theas-prepared specimens Although shear yielding was foundto be the principle mechanism of failure in these specimenssome form of crack bifurcation and crack pinning was alsopresent in these fracture surfaces
Fracture surface micrographs of redried Nanomer I28Enanocomposites (Figures 5(c) and 7(c)) showed more rough-ness than themoisture absorbed specimens indicating higherfracture energy absorbance for these specimensMicrographsof redried Somasif MAE clay-epoxy samples (Figures 6(c)and 8(c)) showed significantly less rough fracture surfacethan the redried Nanomer I28E samples It is important tonote that these redried Somasif MAE clay-epoxy fracturesurfaces showed very little resistance against the crack prop-agation even after most of the water was driven out of thesystemThis observation led to the speculation that absorbedmoisture could have weakened the interface of the SomasifMAE clay particles and the epoxy matrix The replacementof ndashOH (hydroxyl) groups from the octahedral layer of theclay by the ndashF (fluorine) groups makes the Somasif MAE clayparticles muchmore hydrophobic compared to the NanomerI28E clay particlesThe higher hydrophobicity of the SomasifMAE clay particles could have exerted an additional forceon the moisture absorbed interface and weakened the bondbetween the clay particles and the epoxy chains This mighthave in turn resulted in the poor adhesionless fractureenergy absorption in the redried Somasif MAE clay-epoxynanocomposites
0
005
01
015
02
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
Figure 9 FTIR spectra for neat epoxy polymer before and afterabsorption-desorption cycle
35 Fourier Transform Infrared (FTIR) Spectroscopy FTIRspectra of the as-prepared and redried neat epoxy are shownin Figure 9 From the FTIR spectra it was evident that asa result of the absorption-desorption cycle the epoxy under-went some permanent chemical changes These chemicalchanges were probably due to the hydrolysis and chainscission mechanism The drying cycle used in this studyremoved most of the water that was absorbed by the polymersystem and it was believed that the remaining water (onlyabout 7 of the total moisture uptake) is chemically boundto the polymer system FTIR spectra (Figure 7) showed bandat 3200ndash3400 cmminus1 which is characteristic OH stretching ofthe hydroxyl group However significant difference was notobserved for the bands at 3200ndash3400 cmminus1
Figure 10 shows the FTIR spectra for Nanomer I28E andSomasif MAE clay powder before and after the absorption-desorption cycle Both clays showed characteristic SindashO peakin the 990 cmminus1 region Nanomer I28E clay showed anotherpeak at 915 cmminus1 region which is characteristic AlndashOH peakIn Somasif MAE the OH groups present in the corner ofthe octahedral layer of Nanomer I28E were substituted withF which explains the absence of the peak at 915 cmminus1 Bothclays in as-is condition showed 3200ndash3400 cmminus1 band forhydroxyl groups However the band was weaker in case ofSomasif MAE compared to Nanomer I28E clay because ofthe hydrophobic nature of the Somasif MAE clay It wasinteresting to note that the overall changes the clay powdersunderwent as a result of absorption-desorption cycle arefairly small and can be considered as insignificant
International Scholarly Research Notices 11
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
(a)
As-isRedried
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
Abso
rban
ce
Wavenumber (cmminus1)
(b)
Figure 10 FTIR spectra for clay particles before and after absorption-desorption cycle (a) Nanomer I28E and (b) Somasif MAE
4 Conclusion
Property deterioration due to moisture absorption has beenone of the most important areas of interest in polymerresearch for the last few years To be used as structural mater-ials it is of utmost importance to understand the reversibleand irreversible changes occurring in polymeric materials asa result of moisture absorption This study was conducted toelucidate the effect of moisture absorption on the mechan-ical properties of clay reinforced epoxy polymers Fracturetoughness flexural strength and flexural modulus weredetermined for two different clay-epoxy nanocompositesfollowing the ASTM standards The effects of hygrothermalaging and subsequent redrying on the mechanical prop-erties of these polymer nanocomposites were investigatedAfter removing the free water by drying the irreversibleeffect or the permanent damage due to hygrothermal agingon the clay-epoxy nanocomposite systems was determinedIrrespective of the clay reinforcement type all the studiedproperties were degraded due to hygrothermal aging Severalphysical and chemical changes such as interface weaken-ing hydrolysis and chain scission are responsible for theobserved effect The permanent damage or degradation wassevere in case of fracture toughness and flexural modulusFlexural strength of both systems was relatively unaffectedby the absorption-desorption cycle Permanent damage wasfound to be the highest for Somasif MAE clay reinforcedspecimens between two clay-epoxy nanocomposite systemsAfter studying the SEM micrographs of the fracture sur-faces it was speculated that moisture absorption had highernegative impact on the interface of Somasif MAE clay andepoxy matrix compared to the other clay-epoxy system
The hydrophobic nature of the Somasif MAE clay due tothe presence of ndashF (fluorine) in the structure may havecreated additional tension between the polymer crosslinksin presence of moisture FTIR spectra of the clay particlestreated with the same absorption-desorption cycle providedproof that both nanoparticles undergo minimal chemicalchange and retain their respective original chemistry Thisobservation makes the aforementioned speculation moreplausible Although incorporation of clay in epoxymatrix didnot fully stop the degradation it had positive effects to someextent It was observed that the studied properties in generalwere less severely degraded for clay-epoxy nanocompositescompared to neat epoxy samples Therefore clay particlescould be successfully used to reinforce polymer materials toreduce the severity of property deterioration caused by themoisture absorption However the chemistry between theclay particles and polymer matrix and more specifically thechemical structure of the clay particles should be carefullyconsidered to attain the best possible resistance against theproperty deterioration
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this work is fundedin part or fully by a Grant through the Oklahoma Nan-otechnology Applications Project (ONAP) (Grant no O9-20)
12 International Scholarly Research Notices
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
Figure 5 Scanning electronmicrographs of the crack growth region for 05 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
300 120583m
(a)
300 120583m
(b)
300 120583m
(c)
Figure 6 Scanning electron micrographs of the crack growth region for 05 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
International Scholarly Research Notices 9
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 7 Scanning electronmicrographs of the crack growth region for 15 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 8 Scanning electron micrographs of the crack growth region for 15 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
10 International Scholarly Research Notices
the neat polymer Clay if present in a system physicallyblocks and slows down the crack propagation and the result-ing fracture surface of the nanocomposite shows river-markings instead of smooth fracture surface found in the neatpolymer These river-markings provide clear indication ofthe enhanced toughening mechanism in polymeric materialsdue to clay incorporation and support the observed higherfracture toughness for clay-epoxy nanocomposites comparedto the neat epoxy polymer Fracture surfaces of nanofillerreinforced polymer nanocomposites showing higher surfaceroughness have been reported in prior studies [4 6 59]Comparing the fracture surfaces of the as-preparedNanomerI28E and Somasif MAE nanocomposite systems (Figures5(a) 6(a) 7(a) and 8(a)) it was observed that the as-preparedSomasif MAE clay nanocomposite has considerably lessamount of river-markings which is indicative of poor tough-ening in Somasif MAE clay nanocomposites This obser-vation supported the difference of critical stress intensityfactor measured for these two nanocomposite systems Pooradhesion between Somasif MAE clay and epoxy resulted inless energy requirement during new surface formation whichcan be attributed as the reason of these nanocompositesshowing less fracture toughness than Nanomer I28E claynanocomposites for the same clay loading percentage
Fracture surface of moisture absorbed Nanomer I28Eclay nanocomposites (Figures 5(b) and 7(b)) showed lessnumber of river-markings (ie lower critical stress intensityfactor) than the as-prepared nanocomposites SEM micro-graph of Somasif clay-epoxy nanocomposites (Figures 6(b)and 8(b)) showed the presence of shear leaps As shearyielding requires less energy to form new surface moistureabsorbed specimens had lower fracture toughness than theas-prepared specimens Although shear yielding was foundto be the principle mechanism of failure in these specimenssome form of crack bifurcation and crack pinning was alsopresent in these fracture surfaces
Fracture surface micrographs of redried Nanomer I28Enanocomposites (Figures 5(c) and 7(c)) showed more rough-ness than themoisture absorbed specimens indicating higherfracture energy absorbance for these specimensMicrographsof redried Somasif MAE clay-epoxy samples (Figures 6(c)and 8(c)) showed significantly less rough fracture surfacethan the redried Nanomer I28E samples It is important tonote that these redried Somasif MAE clay-epoxy fracturesurfaces showed very little resistance against the crack prop-agation even after most of the water was driven out of thesystemThis observation led to the speculation that absorbedmoisture could have weakened the interface of the SomasifMAE clay particles and the epoxy matrix The replacementof ndashOH (hydroxyl) groups from the octahedral layer of theclay by the ndashF (fluorine) groups makes the Somasif MAE clayparticles muchmore hydrophobic compared to the NanomerI28E clay particlesThe higher hydrophobicity of the SomasifMAE clay particles could have exerted an additional forceon the moisture absorbed interface and weakened the bondbetween the clay particles and the epoxy chains This mighthave in turn resulted in the poor adhesionless fractureenergy absorption in the redried Somasif MAE clay-epoxynanocomposites
0
005
01
015
02
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
Figure 9 FTIR spectra for neat epoxy polymer before and afterabsorption-desorption cycle
35 Fourier Transform Infrared (FTIR) Spectroscopy FTIRspectra of the as-prepared and redried neat epoxy are shownin Figure 9 From the FTIR spectra it was evident that asa result of the absorption-desorption cycle the epoxy under-went some permanent chemical changes These chemicalchanges were probably due to the hydrolysis and chainscission mechanism The drying cycle used in this studyremoved most of the water that was absorbed by the polymersystem and it was believed that the remaining water (onlyabout 7 of the total moisture uptake) is chemically boundto the polymer system FTIR spectra (Figure 7) showed bandat 3200ndash3400 cmminus1 which is characteristic OH stretching ofthe hydroxyl group However significant difference was notobserved for the bands at 3200ndash3400 cmminus1
Figure 10 shows the FTIR spectra for Nanomer I28E andSomasif MAE clay powder before and after the absorption-desorption cycle Both clays showed characteristic SindashO peakin the 990 cmminus1 region Nanomer I28E clay showed anotherpeak at 915 cmminus1 region which is characteristic AlndashOH peakIn Somasif MAE the OH groups present in the corner ofthe octahedral layer of Nanomer I28E were substituted withF which explains the absence of the peak at 915 cmminus1 Bothclays in as-is condition showed 3200ndash3400 cmminus1 band forhydroxyl groups However the band was weaker in case ofSomasif MAE compared to Nanomer I28E clay because ofthe hydrophobic nature of the Somasif MAE clay It wasinteresting to note that the overall changes the clay powdersunderwent as a result of absorption-desorption cycle arefairly small and can be considered as insignificant
International Scholarly Research Notices 11
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
(a)
As-isRedried
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
Abso
rban
ce
Wavenumber (cmminus1)
(b)
Figure 10 FTIR spectra for clay particles before and after absorption-desorption cycle (a) Nanomer I28E and (b) Somasif MAE
4 Conclusion
Property deterioration due to moisture absorption has beenone of the most important areas of interest in polymerresearch for the last few years To be used as structural mater-ials it is of utmost importance to understand the reversibleand irreversible changes occurring in polymeric materials asa result of moisture absorption This study was conducted toelucidate the effect of moisture absorption on the mechan-ical properties of clay reinforced epoxy polymers Fracturetoughness flexural strength and flexural modulus weredetermined for two different clay-epoxy nanocompositesfollowing the ASTM standards The effects of hygrothermalaging and subsequent redrying on the mechanical prop-erties of these polymer nanocomposites were investigatedAfter removing the free water by drying the irreversibleeffect or the permanent damage due to hygrothermal agingon the clay-epoxy nanocomposite systems was determinedIrrespective of the clay reinforcement type all the studiedproperties were degraded due to hygrothermal aging Severalphysical and chemical changes such as interface weaken-ing hydrolysis and chain scission are responsible for theobserved effect The permanent damage or degradation wassevere in case of fracture toughness and flexural modulusFlexural strength of both systems was relatively unaffectedby the absorption-desorption cycle Permanent damage wasfound to be the highest for Somasif MAE clay reinforcedspecimens between two clay-epoxy nanocomposite systemsAfter studying the SEM micrographs of the fracture sur-faces it was speculated that moisture absorption had highernegative impact on the interface of Somasif MAE clay andepoxy matrix compared to the other clay-epoxy system
The hydrophobic nature of the Somasif MAE clay due tothe presence of ndashF (fluorine) in the structure may havecreated additional tension between the polymer crosslinksin presence of moisture FTIR spectra of the clay particlestreated with the same absorption-desorption cycle providedproof that both nanoparticles undergo minimal chemicalchange and retain their respective original chemistry Thisobservation makes the aforementioned speculation moreplausible Although incorporation of clay in epoxymatrix didnot fully stop the degradation it had positive effects to someextent It was observed that the studied properties in generalwere less severely degraded for clay-epoxy nanocompositescompared to neat epoxy samples Therefore clay particlescould be successfully used to reinforce polymer materials toreduce the severity of property deterioration caused by themoisture absorption However the chemistry between theclay particles and polymer matrix and more specifically thechemical structure of the clay particles should be carefullyconsidered to attain the best possible resistance against theproperty deterioration
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this work is fundedin part or fully by a Grant through the Oklahoma Nan-otechnology Applications Project (ONAP) (Grant no O9-20)
12 International Scholarly Research Notices
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
Figure 7 Scanning electronmicrographs of the crack growth region for 15 wtNanomer I28E clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
200 120583m
(a)
200 120583m
(b)
200 120583m
(c)
Figure 8 Scanning electron micrographs of the crack growth region for 15 wt Somasif MAE clay-epoxy nanocomposites (a) as-prepared(b) moisture absorbed and (c) redried
10 International Scholarly Research Notices
the neat polymer Clay if present in a system physicallyblocks and slows down the crack propagation and the result-ing fracture surface of the nanocomposite shows river-markings instead of smooth fracture surface found in the neatpolymer These river-markings provide clear indication ofthe enhanced toughening mechanism in polymeric materialsdue to clay incorporation and support the observed higherfracture toughness for clay-epoxy nanocomposites comparedto the neat epoxy polymer Fracture surfaces of nanofillerreinforced polymer nanocomposites showing higher surfaceroughness have been reported in prior studies [4 6 59]Comparing the fracture surfaces of the as-preparedNanomerI28E and Somasif MAE nanocomposite systems (Figures5(a) 6(a) 7(a) and 8(a)) it was observed that the as-preparedSomasif MAE clay nanocomposite has considerably lessamount of river-markings which is indicative of poor tough-ening in Somasif MAE clay nanocomposites This obser-vation supported the difference of critical stress intensityfactor measured for these two nanocomposite systems Pooradhesion between Somasif MAE clay and epoxy resulted inless energy requirement during new surface formation whichcan be attributed as the reason of these nanocompositesshowing less fracture toughness than Nanomer I28E claynanocomposites for the same clay loading percentage
Fracture surface of moisture absorbed Nanomer I28Eclay nanocomposites (Figures 5(b) and 7(b)) showed lessnumber of river-markings (ie lower critical stress intensityfactor) than the as-prepared nanocomposites SEM micro-graph of Somasif clay-epoxy nanocomposites (Figures 6(b)and 8(b)) showed the presence of shear leaps As shearyielding requires less energy to form new surface moistureabsorbed specimens had lower fracture toughness than theas-prepared specimens Although shear yielding was foundto be the principle mechanism of failure in these specimenssome form of crack bifurcation and crack pinning was alsopresent in these fracture surfaces
Fracture surface micrographs of redried Nanomer I28Enanocomposites (Figures 5(c) and 7(c)) showed more rough-ness than themoisture absorbed specimens indicating higherfracture energy absorbance for these specimensMicrographsof redried Somasif MAE clay-epoxy samples (Figures 6(c)and 8(c)) showed significantly less rough fracture surfacethan the redried Nanomer I28E samples It is important tonote that these redried Somasif MAE clay-epoxy fracturesurfaces showed very little resistance against the crack prop-agation even after most of the water was driven out of thesystemThis observation led to the speculation that absorbedmoisture could have weakened the interface of the SomasifMAE clay particles and the epoxy matrix The replacementof ndashOH (hydroxyl) groups from the octahedral layer of theclay by the ndashF (fluorine) groups makes the Somasif MAE clayparticles muchmore hydrophobic compared to the NanomerI28E clay particlesThe higher hydrophobicity of the SomasifMAE clay particles could have exerted an additional forceon the moisture absorbed interface and weakened the bondbetween the clay particles and the epoxy chains This mighthave in turn resulted in the poor adhesionless fractureenergy absorption in the redried Somasif MAE clay-epoxynanocomposites
0
005
01
015
02
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
Figure 9 FTIR spectra for neat epoxy polymer before and afterabsorption-desorption cycle
35 Fourier Transform Infrared (FTIR) Spectroscopy FTIRspectra of the as-prepared and redried neat epoxy are shownin Figure 9 From the FTIR spectra it was evident that asa result of the absorption-desorption cycle the epoxy under-went some permanent chemical changes These chemicalchanges were probably due to the hydrolysis and chainscission mechanism The drying cycle used in this studyremoved most of the water that was absorbed by the polymersystem and it was believed that the remaining water (onlyabout 7 of the total moisture uptake) is chemically boundto the polymer system FTIR spectra (Figure 7) showed bandat 3200ndash3400 cmminus1 which is characteristic OH stretching ofthe hydroxyl group However significant difference was notobserved for the bands at 3200ndash3400 cmminus1
Figure 10 shows the FTIR spectra for Nanomer I28E andSomasif MAE clay powder before and after the absorption-desorption cycle Both clays showed characteristic SindashO peakin the 990 cmminus1 region Nanomer I28E clay showed anotherpeak at 915 cmminus1 region which is characteristic AlndashOH peakIn Somasif MAE the OH groups present in the corner ofthe octahedral layer of Nanomer I28E were substituted withF which explains the absence of the peak at 915 cmminus1 Bothclays in as-is condition showed 3200ndash3400 cmminus1 band forhydroxyl groups However the band was weaker in case ofSomasif MAE compared to Nanomer I28E clay because ofthe hydrophobic nature of the Somasif MAE clay It wasinteresting to note that the overall changes the clay powdersunderwent as a result of absorption-desorption cycle arefairly small and can be considered as insignificant
International Scholarly Research Notices 11
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
(a)
As-isRedried
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
Abso
rban
ce
Wavenumber (cmminus1)
(b)
Figure 10 FTIR spectra for clay particles before and after absorption-desorption cycle (a) Nanomer I28E and (b) Somasif MAE
4 Conclusion
Property deterioration due to moisture absorption has beenone of the most important areas of interest in polymerresearch for the last few years To be used as structural mater-ials it is of utmost importance to understand the reversibleand irreversible changes occurring in polymeric materials asa result of moisture absorption This study was conducted toelucidate the effect of moisture absorption on the mechan-ical properties of clay reinforced epoxy polymers Fracturetoughness flexural strength and flexural modulus weredetermined for two different clay-epoxy nanocompositesfollowing the ASTM standards The effects of hygrothermalaging and subsequent redrying on the mechanical prop-erties of these polymer nanocomposites were investigatedAfter removing the free water by drying the irreversibleeffect or the permanent damage due to hygrothermal agingon the clay-epoxy nanocomposite systems was determinedIrrespective of the clay reinforcement type all the studiedproperties were degraded due to hygrothermal aging Severalphysical and chemical changes such as interface weaken-ing hydrolysis and chain scission are responsible for theobserved effect The permanent damage or degradation wassevere in case of fracture toughness and flexural modulusFlexural strength of both systems was relatively unaffectedby the absorption-desorption cycle Permanent damage wasfound to be the highest for Somasif MAE clay reinforcedspecimens between two clay-epoxy nanocomposite systemsAfter studying the SEM micrographs of the fracture sur-faces it was speculated that moisture absorption had highernegative impact on the interface of Somasif MAE clay andepoxy matrix compared to the other clay-epoxy system
The hydrophobic nature of the Somasif MAE clay due tothe presence of ndashF (fluorine) in the structure may havecreated additional tension between the polymer crosslinksin presence of moisture FTIR spectra of the clay particlestreated with the same absorption-desorption cycle providedproof that both nanoparticles undergo minimal chemicalchange and retain their respective original chemistry Thisobservation makes the aforementioned speculation moreplausible Although incorporation of clay in epoxymatrix didnot fully stop the degradation it had positive effects to someextent It was observed that the studied properties in generalwere less severely degraded for clay-epoxy nanocompositescompared to neat epoxy samples Therefore clay particlescould be successfully used to reinforce polymer materials toreduce the severity of property deterioration caused by themoisture absorption However the chemistry between theclay particles and polymer matrix and more specifically thechemical structure of the clay particles should be carefullyconsidered to attain the best possible resistance against theproperty deterioration
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this work is fundedin part or fully by a Grant through the Oklahoma Nan-otechnology Applications Project (ONAP) (Grant no O9-20)
12 International Scholarly Research Notices
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
the neat polymer Clay if present in a system physicallyblocks and slows down the crack propagation and the result-ing fracture surface of the nanocomposite shows river-markings instead of smooth fracture surface found in the neatpolymer These river-markings provide clear indication ofthe enhanced toughening mechanism in polymeric materialsdue to clay incorporation and support the observed higherfracture toughness for clay-epoxy nanocomposites comparedto the neat epoxy polymer Fracture surfaces of nanofillerreinforced polymer nanocomposites showing higher surfaceroughness have been reported in prior studies [4 6 59]Comparing the fracture surfaces of the as-preparedNanomerI28E and Somasif MAE nanocomposite systems (Figures5(a) 6(a) 7(a) and 8(a)) it was observed that the as-preparedSomasif MAE clay nanocomposite has considerably lessamount of river-markings which is indicative of poor tough-ening in Somasif MAE clay nanocomposites This obser-vation supported the difference of critical stress intensityfactor measured for these two nanocomposite systems Pooradhesion between Somasif MAE clay and epoxy resulted inless energy requirement during new surface formation whichcan be attributed as the reason of these nanocompositesshowing less fracture toughness than Nanomer I28E claynanocomposites for the same clay loading percentage
Fracture surface of moisture absorbed Nanomer I28Eclay nanocomposites (Figures 5(b) and 7(b)) showed lessnumber of river-markings (ie lower critical stress intensityfactor) than the as-prepared nanocomposites SEM micro-graph of Somasif clay-epoxy nanocomposites (Figures 6(b)and 8(b)) showed the presence of shear leaps As shearyielding requires less energy to form new surface moistureabsorbed specimens had lower fracture toughness than theas-prepared specimens Although shear yielding was foundto be the principle mechanism of failure in these specimenssome form of crack bifurcation and crack pinning was alsopresent in these fracture surfaces
Fracture surface micrographs of redried Nanomer I28Enanocomposites (Figures 5(c) and 7(c)) showed more rough-ness than themoisture absorbed specimens indicating higherfracture energy absorbance for these specimensMicrographsof redried Somasif MAE clay-epoxy samples (Figures 6(c)and 8(c)) showed significantly less rough fracture surfacethan the redried Nanomer I28E samples It is important tonote that these redried Somasif MAE clay-epoxy fracturesurfaces showed very little resistance against the crack prop-agation even after most of the water was driven out of thesystemThis observation led to the speculation that absorbedmoisture could have weakened the interface of the SomasifMAE clay particles and the epoxy matrix The replacementof ndashOH (hydroxyl) groups from the octahedral layer of theclay by the ndashF (fluorine) groups makes the Somasif MAE clayparticles muchmore hydrophobic compared to the NanomerI28E clay particlesThe higher hydrophobicity of the SomasifMAE clay particles could have exerted an additional forceon the moisture absorbed interface and weakened the bondbetween the clay particles and the epoxy chains This mighthave in turn resulted in the poor adhesionless fractureenergy absorption in the redried Somasif MAE clay-epoxynanocomposites
0
005
01
015
02
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
Figure 9 FTIR spectra for neat epoxy polymer before and afterabsorption-desorption cycle
35 Fourier Transform Infrared (FTIR) Spectroscopy FTIRspectra of the as-prepared and redried neat epoxy are shownin Figure 9 From the FTIR spectra it was evident that asa result of the absorption-desorption cycle the epoxy under-went some permanent chemical changes These chemicalchanges were probably due to the hydrolysis and chainscission mechanism The drying cycle used in this studyremoved most of the water that was absorbed by the polymersystem and it was believed that the remaining water (onlyabout 7 of the total moisture uptake) is chemically boundto the polymer system FTIR spectra (Figure 7) showed bandat 3200ndash3400 cmminus1 which is characteristic OH stretching ofthe hydroxyl group However significant difference was notobserved for the bands at 3200ndash3400 cmminus1
Figure 10 shows the FTIR spectra for Nanomer I28E andSomasif MAE clay powder before and after the absorption-desorption cycle Both clays showed characteristic SindashO peakin the 990 cmminus1 region Nanomer I28E clay showed anotherpeak at 915 cmminus1 region which is characteristic AlndashOH peakIn Somasif MAE the OH groups present in the corner ofthe octahedral layer of Nanomer I28E were substituted withF which explains the absence of the peak at 915 cmminus1 Bothclays in as-is condition showed 3200ndash3400 cmminus1 band forhydroxyl groups However the band was weaker in case ofSomasif MAE compared to Nanomer I28E clay because ofthe hydrophobic nature of the Somasif MAE clay It wasinteresting to note that the overall changes the clay powdersunderwent as a result of absorption-desorption cycle arefairly small and can be considered as insignificant
International Scholarly Research Notices 11
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
As-isRedried
Abso
rban
ce
Wavenumber (cmminus1)
(a)
As-isRedried
0
02
04
06
08
1
12
500 1000 1500 2000 2500 3000 3500 4000
Abso
rban
ce
Wavenumber (cmminus1)
(b)
Figure 10 FTIR spectra for clay particles before and after absorption-desorption cycle (a) Nanomer I28E and (b) Somasif MAE
4 Conclusion
Property deterioration due to moisture absorption has beenone of the most important areas of interest in polymerresearch for the last few years To be used as structural mater-ials it is of utmost importance to understand the reversibleand irreversible changes occurring in polymeric materials asa result of moisture absorption This study was conducted toelucidate the effect of moisture absorption on the mechan-ical properties of clay reinforced epoxy polymers Fracturetoughness flexural strength and flexural modulus weredetermined for two different clay-epoxy nanocompositesfollowing the ASTM standards The effects of hygrothermalaging and subsequent redrying on the mechanical prop-erties of these polymer nanocomposites were investigatedAfter removing the free water by drying the irreversibleeffect or the permanent damage due to hygrothermal agingon the clay-epoxy nanocomposite systems was determinedIrrespective of the clay reinforcement type all the studiedproperties were degraded due to hygrothermal aging Severalphysical and chemical changes such as interface weaken-ing hydrolysis and chain scission are responsible for theobserved effect The permanent damage or degradation wassevere in case of fracture toughness and flexural modulusFlexural strength of both systems was relatively unaffectedby the absorption-desorption cycle Permanent damage wasfound to be the highest for Somasif MAE clay reinforcedspecimens between two clay-epoxy nanocomposite systemsAfter studying the SEM micrographs of the fracture sur-faces it was speculated that moisture absorption had highernegative impact on the interface of Somasif MAE clay andepoxy matrix compared to the other clay-epoxy system
The hydrophobic nature of the Somasif MAE clay due tothe presence of ndashF (fluorine) in the structure may havecreated additional tension between the polymer crosslinksin presence of moisture FTIR spectra of the clay particlestreated with the same absorption-desorption cycle providedproof that both nanoparticles undergo minimal chemicalchange and retain their respective original chemistry Thisobservation makes the aforementioned speculation moreplausible Although incorporation of clay in epoxymatrix didnot fully stop the degradation it had positive effects to someextent It was observed that the studied properties in generalwere less severely degraded for clay-epoxy nanocompositescompared to neat epoxy samples Therefore clay particlescould be successfully used to reinforce polymer materials toreduce the severity of property deterioration caused by themoisture absorption However the chemistry between theclay particles and polymer matrix and more specifically thechemical structure of the clay particles should be carefullyconsidered to attain the best possible resistance against theproperty deterioration
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this work is fundedin part or fully by a Grant through the Oklahoma Nan-otechnology Applications Project (ONAP) (Grant no O9-20)
12 International Scholarly Research Notices
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
Figure 10 FTIR spectra for clay particles before and after absorption-desorption cycle (a) Nanomer I28E and (b) Somasif MAE
4 Conclusion
Property deterioration due to moisture absorption has beenone of the most important areas of interest in polymerresearch for the last few years To be used as structural mater-ials it is of utmost importance to understand the reversibleand irreversible changes occurring in polymeric materials asa result of moisture absorption This study was conducted toelucidate the effect of moisture absorption on the mechan-ical properties of clay reinforced epoxy polymers Fracturetoughness flexural strength and flexural modulus weredetermined for two different clay-epoxy nanocompositesfollowing the ASTM standards The effects of hygrothermalaging and subsequent redrying on the mechanical prop-erties of these polymer nanocomposites were investigatedAfter removing the free water by drying the irreversibleeffect or the permanent damage due to hygrothermal agingon the clay-epoxy nanocomposite systems was determinedIrrespective of the clay reinforcement type all the studiedproperties were degraded due to hygrothermal aging Severalphysical and chemical changes such as interface weaken-ing hydrolysis and chain scission are responsible for theobserved effect The permanent damage or degradation wassevere in case of fracture toughness and flexural modulusFlexural strength of both systems was relatively unaffectedby the absorption-desorption cycle Permanent damage wasfound to be the highest for Somasif MAE clay reinforcedspecimens between two clay-epoxy nanocomposite systemsAfter studying the SEM micrographs of the fracture sur-faces it was speculated that moisture absorption had highernegative impact on the interface of Somasif MAE clay andepoxy matrix compared to the other clay-epoxy system
The hydrophobic nature of the Somasif MAE clay due tothe presence of ndashF (fluorine) in the structure may havecreated additional tension between the polymer crosslinksin presence of moisture FTIR spectra of the clay particlestreated with the same absorption-desorption cycle providedproof that both nanoparticles undergo minimal chemicalchange and retain their respective original chemistry Thisobservation makes the aforementioned speculation moreplausible Although incorporation of clay in epoxymatrix didnot fully stop the degradation it had positive effects to someextent It was observed that the studied properties in generalwere less severely degraded for clay-epoxy nanocompositescompared to neat epoxy samples Therefore clay particlescould be successfully used to reinforce polymer materials toreduce the severity of property deterioration caused by themoisture absorption However the chemistry between theclay particles and polymer matrix and more specifically thechemical structure of the clay particles should be carefullyconsidered to attain the best possible resistance against theproperty deterioration
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this work is fundedin part or fully by a Grant through the Oklahoma Nan-otechnology Applications Project (ONAP) (Grant no O9-20)
12 International Scholarly Research Notices
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
and NASA Experimental Program to Stimulate CompetitiveResearch (EPSCOR) (Grant no NNXO9AP68A)
References
[1] X Kornmann L A Berglund J Sterte and E P GiannelisldquoNanocomposites based on montmorillonite and unsaturatedpolyesterrdquo Polymer Engineering and Science vol 38 no 8 pp1351ndash1358 1998
[2] E P Giannelis ldquoPolymer layered silicate nanocompositesrdquoAdvanced Materials vol 8 no 1 pp 29ndash35 1996
[3] Y J Phua W S Chow and Z A Mohd Ishak ldquoThe hydrolyticeffect of moisture and hygrothermal aging on poly(butylenesuccinate)organo-montmorillonite nanocompositesrdquo PolymerDegradation and Stability vol 96 no 7 pp 1194ndash1203 2011
[4] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nano-filler reinforced epoxy nano-compositesrdquoMaterials amp Design vol 42 pp 214ndash222 2012
[5] C Kaynak G I Nakas and N A Isitman ldquoMechani-cal properties flammability and char morphology of epoxyresinmontmorillonite nanocompositesrdquo Applied Clay Sciencevol 46 no 3 pp 319ndash324 2009
[6] S R Lim andW S Chow ldquoFracture toughness enhancement ofepoxy by organo-montmorilloniterdquo Polymer Plastics Technol-ogy and Engineering vol 50 no 2 pp 182ndash189 2011
[7] R P Singh M Zhang and D Chan ldquoToughening of a brittlethermosetting polymer effects of reinforcement particle sizeand volume fractionrdquo Journal of Materials Science vol 37 no4 pp 781ndash788 2002
[8] C B Ng L S Schadler and R W Siegel ldquoSynthesis and mech-anical properties of TiO
2-epoxy nanocompositesrdquo Nanostruc-
tured Materials vol 12 no 1 pp 507ndash510 1999[9] M-Y Shen T-Y Chang T-H Hsieh et al ldquoMechanical prop-
erties and tensile fatigue of grapheme nanoplatelets reinforcedpolymer nanocompositesrdquo Journal of Nanomaterials vol 2013Article ID 565401 9 pages 2013
[10] J R Potts D R Dreyer C W Bielawski and R S RuoffldquoGraphene-based polymer nanocompositesrdquo Polymer vol 52no 1 pp 5ndash25 2011
[11] A Allaoui S Bai H M Cheng and J B Bai ldquoMechanical andelectrical properties of aMWNTepoxy compositerdquoCompositesScience and Technology vol 62 no 15 pp 1993ndash1998 2002
[12] S G Prolongo M R Gude and A Urena ldquoWater uptake ofepoxy composites reinforced with carbon nanofillersrdquo Compos-ites A Applied Science and Manufacturing vol 43 no 12 pp2169ndash2175 2012
[13] O Starkova S Chandrasekaran L A S A Prado F Tolle RMulhaupt and K Schulte ldquoHydrothermally resistant thermallyreduced graphene oxide andmulti-wall carbon nanotube basedepoxy nanocompositesrdquo Polymer Degradation and Stability vol98 no 2 pp 519ndash526 2013
[14] Y Tang S Deng L Ye et al ldquoEffects of unfolded and inter-calated halloysites onmechanical properties of halloysite-epoxynanocompositesrdquo Composites A Applied Science and Manufac-turing vol 42 no 4 pp 345ndash354 2011
[15] C Soles and A Yee ldquoA discussion of the molecular mechanismsof moisture transport in epoxy resinsrdquo Journal of PolymerScience Part B-Polymer Physics vol 38 pp 792ndash802 2000
[16] P S Theocaris E A Kontou and G C Papanicolaou ldquoTheeffect of moisture absorption on the thermomechanical proper-ties of particulatesrdquo Colloid amp Polymer Science vol 261 no 5pp 394ndash403 1983
[17] P S Theocaris G C Papanicolaou and E A Kontou ldquoInterre-lation between moisture absorption mechanical behavior andextent of boundary interface in particulate compositesrdquo Journalof Applied Polymer Science vol 28 no 10 pp 3145ndash3153 1983
[18] A Ishisaka and M Kawagoe ldquoExamination of the time-water content superposition on the dynamic viscoelasticity ofmoistened polyamide 6 and epoxyrdquo Journal of Applied PolymerScience vol 93 no 2 pp 560ndash567 2004
[19] K Aniskevich T Glaskova and Y Jansons ldquoElastic and sorp-tion characteristics of an epoxy binder in a composite duringits moisteningrdquoMechanics of Composite Materials vol 41 no 4pp 341ndash350 2005
[20] E Wolff ldquoMoisture effects on polymer matrix compositesrdquoSampe Journal vol 29 pp 11ndash19 1993
[21] C Carfagna A Apicella and L Nicolais ldquoEffect of the pre-polymer composition of amino-hardened epoxy resins on thewater sorption behavior and plasticizationrdquo Journal of AppliedPolymer Science vol 27 no 1 pp 105ndash112 1982
[22] B dersquo Neve and M E R Shanahan ldquoWater absorption by anepoxy resin and its effect on the mechanical properties andinfra-red spectrardquo Polymer vol 34 no 24 pp 5099ndash5105 1993
[23] K K Aniskevich T I Glaskova A N Aniskevich and Y AFaitelson ldquoEffect ofmoisture on the viscoelastic properties of anepoxy-clay nanocompositerdquoMechanics of Composite Materialsvol 46 no 6 pp 573ndash582 2011
[24] M Al-Qadhi N Merah Z Gasem N Abu-Dheir and BAbdul Aleem ldquoEffect of water and crude oil on mechanicaland thermal properties of epoxy-clay nanocompositesrdquoPolymerComposites vol 35 pp 318ndash326 2014
[25] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart I the nature of water in epoxyrdquo Polymer vol 40 no 20 pp5505ndash5512 1999
[26] J Mijovic and K-F Lin ldquoThe effect of hygrothermal fatigueon physicalmechanical properties and morphology of neatepoxy resin and graphiteepoxy compositerdquo Journal of AppliedPolymer Science vol 30 no 6 pp 2527ndash2549 1985
[27] J Zhou and J P Lucas ldquoHygrothermal effects of epoxy resinPart II variations of glass transition temperaturerdquo Polymer vol40 no 20 pp 5513ndash5522 1999
[28] WWWright ldquoThe effect of diffusion of water into epoxy resinsand their carbon-fibre reinforced compositesrdquo Composites vol12 no 3 pp 201ndash205 1981
[29] M P Zanni-Deffarges and M E R Shanahan ldquoDiffusion ofwater into an epoxy adhesive comparison between bulk behav-iour and adhesive jointsrdquo International Journal of Adhesion andAdhesives vol 15 no 3 pp 137ndash142 1995
[30] M Zanni-Deffarges and M Shanahan ldquoBulk and interphaseeffects in aged structural jointsrdquo Journal of Adhesion vol 45 pp245ndash257 1994
[31] R A Jurf and J R Vinson ldquoEffect of moisture on the staticand viscoelastic shear properties of epoxy adhesivesrdquo Journal ofMaterials Science vol 20 no 8 pp 2979ndash2989 1985
[32] M M Abdel Wahab A D Crocombe A Beevers and KEbtehaj ldquoCoupled stress-diffusion analysis for durability studyin adhesively bonded jointsrdquo International Journal of Adhesionand Adhesives vol 22 no 1 pp 61ndash73 2002
[33] R J Morgan J E OrsquoNeal and D B Miller ldquoThe structuremodes of deformation and failure and mechanical propertiesof diaminodiphenyl sulphone-cured tetraglycidyl 441015840 diamin-odiphenyl methane epoxyrdquo Journal of Materials Science vol 14no 1 pp 109ndash124 1979
International Scholarly Research Notices 13
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
[34] M G Lu M J Shim and S W Kim ldquoEffects of moisture onproperties of epoxy molding compoundsrdquo Journal of AppliedPolymer Science vol 81 no 9 pp 2253ndash2259 2001
[35] M G McMaster and D S Soane ldquoWater sorption in epoxythin filmsrdquo IEEE Transactions on Composi tes Hybrids aandManufacturing Technology vol 12 no 3 pp 373ndash386 1989
[36] G Z Xiao M Delamar and M E R Shanahan ldquoIrreversibleinteractions between water and DGEBADDA epoxy resinduring hygrothermal agingrdquo Journal of Applied Polymer Sciencevol 65 no 3 pp 449ndash458 1997
[37] H Zhao and R K Y Li ldquoEffect of water absorption on themechanical and dielectric properties of nano-alumina filledepoxy nanocompositesrdquo Composites A Applied Science andManufacturing vol 39 no 4 pp 602ndash611 2008
[38] T Glaskova and A Aniskevich ldquoMoisture effect on deforma-bility of epoxymontmorillonite nanocompositerdquo Journal ofApplied Polymer Science vol 116 no 1 pp 493ndash498 2010
[39] L Wang K Wang L Chen C He L Wang and Y ZhangldquoHydrothermal effects on the thermomechanical properties ofhigh performance epoxyclay nanocompositesrdquo Polymer Engi-neering and Science vol 46 no 2 pp 215ndash221 2006
[40] H Alamri and I M Low ldquoEffect of water absorption on themechanical properties of nanoclay filled recycled cellulose fibrereinforced epoxy hybrid nanocompositesrdquo Composites A App-lied Science and Manufacturing vol 44 no 1 pp 23ndash31 2013
[41] S E Buck D W Lischer and S Nemat-Nasser ldquoThe durabilityof E-glassvinyl ester composite materials subjected to environ-mental conditioning and sustained loadingrdquo Journal of Compos-ite Materials vol 32 no 9 pp 874ndash892 1998
[42] T P Ferguson and J Qu ldquoElastic modulus variation due tomoisture absorption and permanent changes upon redrying inan epoxy based underfillrdquo IEEE Transactions on Componentsand Packaging Technologies vol 29 no 1 pp 105ndash111 2006
[43] H N Dhakal Z Y Zhang and M O W Richardson ldquoEffectof water absorption on the mechanical properties of hempfibre reinforced unsaturated polyester compositesrdquo CompositesScience and Technology vol 67 no 7-8 pp 1674ndash1683 2007
[44] T Glaskova and A Aniskevich ldquoMoisture absorption byepoxymontmorillonite nanocompositerdquo Composites Scienceand Technology vol 69 no 15-16 pp 2711ndash2715 2009
[45] Kusmono M W Wildan and Z A Mohd Ishak ldquoPreparationand properties of clay-reinforced epoxy nanocompositesrdquo Inter-national Journal of Polymer Science vol 2013 Article ID 6906757 pages 2013
[46] S C Zunjarrao R Sriraman and R P Singh ldquoEffect of pro-cessing parameters and clay volume fraction on the mechanicalproperties of epoxy-clay nanocompositesrdquo Journal of MaterialsScience vol 41 no 8 pp 2219ndash2228 2006
[47] H J Kim and D W Seo ldquoEffect of water absorption fatigueonmechanical properties of sisal textile-reinforced compositesrdquoInternational Journal of Fatigue vol 28 no 10 pp 1307ndash13142006
[48] A Athijayamani M Thiruchitrambalam U Natarajan and BPazhanivel ldquoEffect of moisture absorption on the mechanicalproperties of randomly oriented natural fiberspolyester hybridcompositerdquoMaterials Science and EngineeringA vol 517 no 1-2pp 344ndash353 2009
[49] X Kornmann H Lindberg and L A Berglund ldquoSynthesis ofepoxy-clay nanocomposites Influence of the nature of the cur-ing agent on structurerdquo Polymer vol 42 no 10 pp 4493ndash44992001
[50] L Vertuccio A Sorrentino L Guadagno et al ldquoBehavior ofepoxy composite resins in environments at high moisture con-tentrdquo Journal of Polymer Research vol 20 no 6 article 178 2013
[51] W Tham Z Mohd Ishak and W Chow ldquoWater absorptionand hygrothermal aging behaviors of SEBS-g-MAH toughenedpoly(lactic acid)halloysite nanocompositesrdquo Polymer-PlasticsTechnology and Engineering vol 53 no 5 pp 472ndash480 2014
[52] VMortazaviMAtaiM Fathi S Keshavarzi N Khalighinejadand H Badrian ldquoThe effect of nanoclay filler loading on theflexural strength of fiber-reinforced compositesrdquo Journal ofDental Research vol 9 no 3 pp 273ndash280 2012
[53] R L Bowen ldquoEffect of particle shape and size distribution in areinforced polymerrdquo Journal of theAmericanDental Associationvol 69 pp 481ndash495 1964
[54] N Abacha M Kubouchi K Tsuda and T Sakai ldquoPerfor-mance of epoxy-nanocomposite under corrosive environmentrdquoExpress Polymer Letters vol 1 no 6 pp 364ndash369 2007
[55] F U Buehler and J C Seferis ldquoEffect of reinforcement andsolvent content on moisture absorption in epoxy compositematerialsrdquo Composites A Applied Science and Manufacturingvol 31 no 7 pp 741ndash748 2000
[56] J H Lee K Y Rhee and J H Lee ldquoEffects of moistureabsorption and surface modification using 3-aminopropyl-triethoxysilane on the tensile and fracture characteristics ofMWCNTepoxy nanocompositesrdquo Applied Surface Science vol256 no 24 pp 7658ndash7667 2010
[57] A Dorigato A Pegoretti and M Quaresimin ldquoThermo-mech-anical characterization of epoxyclay nanocomposites as matri-ces for carbonnanoclayepoxy laminatesrdquo Materials Scienceand Engineering A vol 528 no 19-20 pp 6324ndash6333 2011
[58] R J Morgan J E Orsquoneal and D L Fanter ldquoThe effect ofmoisture on the physical and mechanical integrity of epoxiesrdquoJournal of Materials Science vol 15 no 3 pp 751ndash764 1980
[59] H Alamri and I M Low ldquoMicrostructural mechanical andthermal characteristics of recycled cellulose fiber-halloysite-epoxy hybrid nanocompositesrdquo Polymer Composites vol 33 no4 pp 589ndash600 2012
