JOURNAL OFC O M P O S I T EM AT E R I A L SArticle

Studies on woven century fiberpolyester composites

K Raja Narender Reddy1, DKN Rao2, K Gopala Kishan Rao3 andKamal K Kar4

Abstract

Treated and untreated woven century fiber (CF) composites are investigated for evaluating their flexural, tensile, and

impact strengths, Barcol hardness, glass transition temperature, thermal resistance, and water absorption properties.

Scanning electron microscopy study revealed a brittle fracture for treated fiber composite, while significant fiber pull-out

is observed for the untreated fiber composite. Higher tensile and hardness properties, higher glass transition and thermal

decomposition temperatures, and low water absorption properties are obtained for alkaline-treated composites.

Enhanced interface bonding due to improved adhesion has helped in the formation of covalent bonds at the fiber–

matrix interface, resulting in superior tensile, thermal, and water absorption properties of the treated fiber composite.

Flexural and impact properties are higher for untreated fiber composite. This is due to the weak fiber–matrix interface

and a differential strain in fiber and matrix. The weak interface has provided an energy absorbing mechanism and

enhanced the impact energy absorption capacity. The tensile strength of CF composite is very much comparable with

that of sisal fiber composite. The tensile and flexural properties are higher for the woven CF composites than those of

short CF composites. But the impact properties are superior for short fiber composites compared to the woven fiber

composites. Increased number of interfaces for the short fiber composites has contributed for the cushioning effect and

an enhanced energy absorbing mechanism. Water absorption properties have improved for the treated fiber composites

due to formation of a strong interface.

Keywords

Natural fiber composites, surface treatment, mechanical properties, differential scanning calorimetry, thermogravimetric

analysis, scanning electron microscopy

Introduction

With growing interest on use of ecofriendly materials inall areas of human activity, the development of biode-gradable composite materials using natural fibers is asolution par excellence. In fact, the Ford MotorCompany1 was using natural fiber composites since1930s. Composites made of thermoplastic or thermo-setting matrices are widely used for interiors of aircraftand automobiles, casings of electronic gadgets anddomestic appliances, panels in building construction,bicycles, sports goods, etc. In order to get better per-formance of these materials, it is important to havegood interface bonding between the fiber and thematrix. To overcome the difficulty associated with thehydrophobic nature of the resin, the hydrophilic natureof the natural fiber, the fibers are subjected to chemical

treatments such as NaOH, KOH, LiOH, and acetyla-tion, wherein the lignin and hemicelluloses will dissolveand expose the OH groups and modify the crystalstructure of the fibers.2 These treatments will alterthe microfibril angle and enhance the mechanicalproperties. Porosity, surface tension, wetting, and

1Department of Mechanical Engineering, Kakatiya Institute of Technology

& Science, Warangal, India2Vivekananda Institute of Technology & Science, Karimnagar, India3Central Instrumentation Centre, Kakatiya University, Warangal, India4Advanced Nanoengineering Materials Laboratory, Indian Institute of

Technology, Kanpur, India

Corresponding author:

DKN Rao, Vivekananda Institute of Technology & Science, Karimnagar

505 001, India

Email: dr_dknrao@yahoo.co.in

Journal of Composite Materials

46(23) 2919–2933

! The Author(s) 2012

Reprints and permissions:

sagepub.co.uk/journalsPermissions.nav

DOI: 10.1177/0021998311434789

jcm.sagepub.com

adhesion properties of the fibers are further improvedthrough treatments such as silane, maleic anhydridepolypropylene, and acetic anhydride. Several plantfibers such as banana, hemp, cellulose, henequen,wheat straw, ramie, jute, pineapple, okra, kenaf, andsisal are used for making natural fiber composites.3–10

Treatments on sisal fibers10–16 such as mercerization,permanganate, benzoylation, polymethyl methacrylate,and admicellar polymerization have improved interfa-cial adhesion and enhanced the tensile, flexural, andimpact strengths, dynamic mechanical behavior, waterabsorption, electrostatic charge, thermal stability,dielectric constant, and ac conductivity of sisal fiberpolyester composites. Storage modulus, loss modulus,and damping factor have increased with each treatmentand decreased with increase in fiber content.

Century (Agave americana) fiber has drawn attentionfrom several researchers because of their large leaflength, leaf biomass, fiber length, fineness, density,and high strength. Century fibers (CFs) have greatpotential for reinforcement in composites as well asfor textiles and geotextiles.17–19 The fibers are tradition-ally used for ropes, cordage, and mats. Bessadoket al.20,21 reported that treatments such as acetic anhy-dride, styrene, acrylic acid, and maleic anhydride, haveimproved the wetting and adhesion properties of thefibers and significantly increased the moisture resis-tance, breaking strength, and breaking strain. Oudianiet al.22,23 found that retting of leaves in sea water hasproduced fine fibers with fairly low lignin content(2.12%) compared to other natural fibers (2.4%).However, the fibers produced by manual extractionhave the lowest density and highest crystallinity(51.2%). Treatments with lower concentrations haveproduced the fibers stronger than the untreated fibers,while treatments with high concentration (>2% w/v)have produced weaker fibers. It was noted by Thamaeand Baillie24 that fibers produced from conventionalboiling of leaves and mercerization have doubled theinterfacial shear strength and improved the tensile andthermal properties of the fibers. Mylsamy andRajendran25,26 have found that the alkali treatment offibers has improved the tensile, flexural, impact, waterabsorption, machinability, dynamic mechanical, as wellas thermo mechanical properties.26 They have notedthat 3-mm long fibers have fairly good bonding withepoxy matrix when compared to those made of 5- and7-mm long fibers. A discontinuous A. americana fiber-reinforced epoxy composite table has been built and theconceptual design and fabrication has been presentedby Mylsamy and Rajendran.27

The study of recent literature suggests that the workon woven CF composites is very apt. Results obtainedfor treated and untreated woven fiber century compos-ites are compared with the recent results of Mylsamy

and Rajendran26 for short CF composites. It was a nat-ural selection by the authors to choose the CFs becauseof the fibers’ fine features. This study has been a part ofthe first authors’ major Project on the selection of bestfibers to promote cultivation of such plants for socio-economic reasons. Flexural, tensile, and impactstrengths, Barcol hardness, glass transition tempera-ture, thermal degradation, and water absorption prop-erties of the treated and untreated woven CFcomposites are presented in this article. Results arealso compared with sisal fiber composites and also theshort fiber century composites. Differential scanningcalorimetry (DSC) and thermogravimetric analysis(TGA) are done for thermal analysis, and fracturebehavior is observed through scanning electron micros-copy (SEM). These studies will establish a database onthe properties of woven CF polyester composites.Components for non-structural applications, such asequipment casings and panels in construction industryas wood substitute can be molded using polyestermatrix and with thermoplastic matrices, such as,polypropylene, the interiors of automobiles, parts ofdomestic appliances, bicycle parts, and sports goods,can be produced.

Experimental

Century fiber

CFs are produced from leaves by retting process. Theleaves are cut and dried to allow the watery substanceto evaporate and then soaked in still water for 15 days.The fermented soft greenish substance is washed thor-oughly and the fibers are peeled off the leaves andwashed and dried in shady place. The length of thefibers is between 100 and 123 cm and the size rangesbetween 150 and 300mm.

Alkali treatment

For chemical treatment, the dried fibers are soaked in2% NaOH solution for 24 h at room temperature. Thefibers are washed thoroughly with distilled water toremove NaOH. These treated fibers are dried at roomtemperature for 24 h. CFs are generally coarse and havebecome soft upon treatment.

Preparation of composites

Uni-directional mats are prepared on an indigenousweaving set-up using treated and untreated fibers. Thesize of the mat is 440� 440mm2 with a density of0.542 kg/m2. General purpose isopthalic polyesterresin is procured from M/s Sakthi Fiber Glass,Chennai, India. As additives, 2% methyl ethyl ketone

2920 Journal of Composite Materials 46(23)

peroxide and 2% cobalt napthanate are used. Waxpolish and polyvinyl alcohol (PVA) are used as releas-ing agents. CF composites (cfc) are fabricated in anopen mold process between two thick glass plates.The laminates are prepared with fiber resin ratio byweight equal to 1:6. A thin coat of PVA is applied onthe contacting surfaces of the plates to act as releasingsurfaces. The resin mix is poured on the plate andwoven fiber mat is placed and then rolled for properwetting and release of entrapped air. Another half ofthe resin is poured and spread over the mat and otherglass plate is placed on it. The laminate is kept under aload of around 1000N for 24 h. Then, the laminate ispost-cured at room temperature for another 24 h. Twotypes of composites, one with treated fiber and theother with untreated fiber are made. They are referredin this article as: cfc-t (CF composite-treated) and cfc-ut (CF composite-untreated).

Flexural test, flexural strength, and flexural modulus

Flexural properties are evaluated as per ASTM D-790through three-point bend test on compression testingmachine at a cross-head speed of 1.25mm/min, sup-plied by Hydraulic and Engineering Instruments, NewDelhi. The size of the specimen is 32� 12.7mm2. Thespecimen was freely supported and the maximum loadapplied in the middle of the specimen. The flexuralmodulus is calculated from the slope of the initial por-tion of the load–deflection curve.

Flexural strength. Flexural strength is the maximumstress in the outer surface of the specimen at themoment of break. When the homogeneous elastic mate-rial is tested with three-point system, the maximumstress occurs at the midpoint. This stress is evaluatedfor any point on the load–deflection curve usingEquation (1).

�f ¼3PL

2bd2ð1Þ

where �f is the stress in the outer specimen at midpoint(MPa), P the load at a given point on the load–deflec-tion curve (N), L the support span (mm), b the width ofbeam tested (mm), and d the depth of beam tested(mm).

Flexural modulus. Flexural modulus or modulus of elas-ticity in bending is a measure of the stiffness during theinitial part of the bending process. Flexural modulus isthe ratio of stress to corresponding strain within theelastic limit. A tangent line is drawn to the steepestinitial straight line portion of the load–deflection

curve, and flexural modulus is calculated usingEquation (2).

EB ¼L3m

4bd3ð2Þ

where, EB; the modulus of elasticity in bending (MPa),L the support span (mm), m the slope of the tangent tothe initial straight line portion of the load–deflectioncurve, N/mm of deflection, b the width of the specimen(mm), and d the depth of specimen (mm).

Tensile test, tensile strength, and tensile modulus

The tensile test is conducted on an electronic tensiletesting machine Zwick/Roell Z010-10KN-UTM at across-head speed of 3mm/min and a gage length of50mm. Standard Type IV dumbbell-shaped specimensare used as per ASTM D-638. The values of tensilestrength and tensile modulus are obtained from theload–deflection values by taking the maximum loadresisted up to the point of fracture and the correspond-ing strain.

Morphology

The fractured surfaces of the treated and untreatedfiber composites during tensile test are studied bySEM using EVOMA15 Smart SEM.

Impact strength

Notched impact performance of the composite is eval-uated as per ASTM D-256 using Izod impact suppliedby PSI Sales Pvt. Ltd., New Delhi. The size of the sam-ples is 12� 60mm2. The test specimen was supportedby a vertical cantilever beam and the specimen brokenby the swing of the pendulum. This method elaboratesthe determination of the resistance to breakage by flex-ural shock. Five specimens are tested and the averagevalue of impact strength is considered.

Barcol hardness

Standard test method ASTM D-2583-75 is used to findindentation hardness of the composite through Barcolimpresser model no. 934-1. This test employs a hard-ened steel truncated cone indenter having an angle of20� with a flat tip at 0.157mm diameter. Five specimenswere tested and the average value is taken.

Differential scanning calorimetry

Composites exhibit changes in material properties suchas volume, enthalpy, heat capacity, thermal expansion,

Reddy et al. 2921

and tensile modulus as the material is heated throughglass transition temperature, Tg and it goes from glassto rubbery state. DSC is performed with the help ofMettler using Star SW 8.1 analyzer to measure Tg.The temperature is programmed in the range 25–300�C with a heating rate of 10�C/min in nitrogenatmosphere with a flow rate of 30mL/min.

Thermogravimetric analysis

TGA curves are used to determine the thermal degra-dation and thermal stability of the polymeric material.Thermal decomposition is observed in terms of loss ofglobal mass using TA Instrument TGAQ50 V20.10Build 36 thermogravimetric analyzer. The temperaturechange is controlled from room temperature to 800�Cat a heating rate of 20�C/min. A high-purity nitrogenstream was continuously passed into the furnace at aflow rate of 60mL/min at room temperature and atmo-spheric pressure. Before starting each run, nitrogen isused to purge the furnace for 30min to establish aninert environment to prevent any unwanted oxidativedecomposition.

Water absorption

Water absorption tests are conducted on rectangularspecimens of dimension 76.2� 25.4mm2 size as perASTM D-570. The samples are conditioned by heatingin an oven at 50�C for 24 h and then cooling to roomtemperature. The weights of the samples are taken byShimadzu Electronic Balance with readability of0.001 g. All the samples are immersed in double distilledwater for 24 h at room temperature. Reconditioning isdone by keeping them once again in the oven for 24 hrsat 50�C. Percentage increase in weight of the specimenduring immersion is obtained from the ratio of increasein average weight of the conditioned specimen afterimmersion in water for 24 h and the average weight of

reconditioned specimen calculated nearest to 0.01%.The amount of soluble matter lost is given by thedecrease in weight of the specimen after reconditioning.

Results and discussion

Flexural properties

The flexural strength of the composite is determinedbased on the maximum bending load at failure usingEquation (1). It can be seen from Table 1 that cfc-ut hasthe highest flexural strength. The weak fiber–matrixinterface in cfc-ut has been advantageous in creatinga differential strain in the matrix and fiber. This hasallowed the stretching and bending simultaneouslythat prevented the kind of brittle fracture and resultedin highest flexural strength of 188MPa. For cfc-ut, theslope of the load–deflection curve is large and the speci-men could withstand a highest load of 175N. For cfc-t,the slope is small and the specimen could withstandonly 50N, as shown in Figure 1. The chemical treat-ment has dissolved the lignocelluloses, and the fibersbecame thin and soft resulting in a very flexible lami-nate for the treated fibers, while the cfc-ut specimen hasbeen rigid. Prolonged exposure of the fiber during treat-ment has weakened the fiber surfaces and reduced thestiffness property of the composite. This pattern ofresults confirms the statement by Reid et al.9 thatincreased concentrations will damage the fiber surfaceand reduce the mechanical properties. In the presentcase, the alkali treatment was given for 24 h whichhas reduced the strength of the fibers. Similarly,Pothan et al.11 have reported that the flexural strengthhas reduced upon NaOH treatment for woven sisalfiber composites. Results of the present solution arealso compared with those of short fiber century epoxycomposite reported by Mylsamy and Rajendran.26 Incase of short fiber-treated century/epoxy composite(T3EC), the highest flexural strength is only 58MPa

Table 1. Mechanical properties of CF composites

Property cfc-t cfc-ut resin T3ECa UT3ECb

Flexural strength (MPa) 99 188 136 58 54

Flexural modulus (MPa) 17,544 39,814 7191 3500 3250

Ultimate tensile strength (MPa) 47 42 39 23.5 23

Tensile modulus (MPa) 682 615 399 257 235

Impact strength (J/m) 48� 6 71� 1 5 134 117

Barcol hardness 60 59.5 56 – –

Density (g/cm3) 1.3 1.2 1.27 – –

Glass transition temperature (Tg),�C 79.56 77.97 73.4 – –

Note: aT3EC-treated 3-mm size short fiber epoxy composite.26

bUT3EC-untreated 3-mm size short fiber epoxy composite.26

2922 Journal of Composite Materials 46(23)

for treated fiber composite and for untreated fiber com-posite, it is 54MPa. In this case, the treatment has notsignificantly influenced the strength property. The pre-sent treated woven CF composite with polyester matrixhas produced nearly twice the flexural strength com-pared to that of the short-fiber epoxy compositewhich is equal to 99MPa. Due to the long and contin-uous fibers, the woven fiber composite has shown theproperty of better load sharing than in the case of shortfiber composites. For neat resin, the flexural strength is

equal to 136MPa and the flexural modulus is7191MPa. In case of short fiber composite, it can beseen that all the properties are higher for the treatedfiber composite. This reflects on the effect of variationin fiber–matrix interfaces in the long and short fibercomposites. These variations have contributed for dif-ferent values of flexural strength. Results indicate thatfor flexural load applications, the long untreated fibercomposites are advantageous. The modulus of elasticityfor bending is calculated using Equation (2) as per

Figure 2. Specific flexural strength of CF composites.

Figure 1. Load–deflection diagram for flexural test on CF composites.

Reddy et al. 2923

ASTM D-790. The values of flexural modulus are listedin Table 1. For the treated fiber composite, the flexuralmodulus is equal to 17,544MPa and for the untreatedfiber composite, it is equal to 39,814MPa. Specific flex-ural strength and specific flexural modulus values of thecomposites and the neat resin are highly rational forcomparison with each other and they are obtained bytaking into account the variation in the density of thespecimens. These values are shown in Figures 2 and 3.The specific flexural strength is equal to 76.6MPa/g/cm3 for cfc-t, for cfc-ut, it is equal to 156.6MPa/g/cm3, and for neat resin, it is equal to 108MPa/g/cm3.Similarly, the specific flexural modulus is equal to13.5GPa/g/cm3 for cfc-t, while it is equal to 33GPa/g/cm3 for cfc-ut and for neat resin, it is equal to5.6GPa/g/cm3.

Tensile properties

Unlike in the case of flexural properties, the tensileproperties have increased for composite with treatedfibers. The strong interface due to increased adhesionbetween the fiber and the matrix as a result of chemicaltreatment has produced a positive effect on tensileproperties. The stress–strain diagram for tensile loadingis shown in Figure 4. Except for the initial part of thecurves, the cfc-t, cfc-ut, and neat resin have followedthe linear Hooke’s law. The ultimate tensile strength ofcfc-t is 47MPa and it is equal to 42MPa for cfc-ut. Forneat resin, it is equal to 39MPa, as shown in Table 1.The tensile modulus of cfc-t is equal to 682 and615MPa for cfc-ut, while it equal to 399MPa forneat resin. Pothan et al.11 have reported a similar

trend of increase in tensile modulus for treated wovensisal fiber composites.15 The tensile strength of wovensisal fiber composite was equal to 45� 3MPa and thetensile modulus was 5.8� 0.4GPa. The tensile strengthobtained for the present woven CF composites is quitecomparable with that of sisal fiber composite and thetensile modulus of CF composites is less by an order of10. Unidirectional CF mats are used in this study andthe sisal fiber mats are bidirectional. The effect of direc-tion of fibers in the weaving pattern has contributed forthe variation in the tensile modulus of the composite,while it has not made significant on the tensile strength.The tensile strength depends only on the cross-sectionof the specimen, while the longitudinal fibers and thematrix will resist the tensile load. But the tensile mod-ulus depends on the stress and strain of the member.The strain occurring in bidirectional sisal fiber speci-men is small compared to that of CF composite speci-men with the unidirectional mat. Elongation of thespecimen with bidirectional sisal fiber mat is resistedby both the longitudinal as well as the transversefibers that are connected through the resin matrix.Only longitudinal fibers and the matrix will resist elon-gation in tensile loading of CF composites. Hence, thestrain is more in case of the present CF composites,while it is less for sisal fiber composites, as reportedby Pothan et al.11 This justifies the higher tensile mod-ulus of the bidirectional sisal fiber composites and thelower value of tensile modulus for CF composites.Further, higher modulus in bidirectional composites isalways useful for resistance to higher impact loads. Incase of short fiber century (A. americana) epoxy com-posite,26 the sample with treated 3-mm long fibers has a

Figure 3. Specific flexural modulus of CF composites.

2924 Journal of Composite Materials 46(23)

tensile strength of 23.5MPa and for untreated fibercomposite, it is equal to 23MPa. Although this varia-tion is small, the tensile modulus has increased signifi-cantly which is equal to 257MPa for the T3ECcompared to that of 235MPa for UT3EC. This increaseis due to enhanced interfacial adhesion because of thealkali treatment of the fibers which resulted in brittlefracture. The effect of chemical treatment on flexuralproperties is very significant, while the tensile propertiesare not affected significantly which can be noted from

the values given in Table 1. The specific tensile strengthand specific tensile moduli for cfc-t, cfc-ut, and neatresin are shown in Figures 5 and 6, respectively. Forcfc-t, the specific ultimate strength is equal to36.5MPa/g/cm3 and for cfc-ut, it is equal to34.7MPa/g/cm3, while it is equal to 30.5MPa/g/cm3

for neat resin. The specific tensile modulus is equal to526MPa/g/cm3 for cfc-t; for cfc-ut, it is equal to511MPa/g/cm3 and for neat resin, it is equalto 315MPa/g/cm3. This increase in tensile modulus

Figure 5. Specific tensile strength of CF composites.

Figure 4. Load–deflection diagram for tensile test on CF composites.

Reddy et al. 2925

can be attributed to the change in the intrinsic structureand crystallinity of the fibers and the reduction inmicrofibril angle of the fibers associated with chemicaltreatment.

Morphology

The SEM micrographs of the fractured surfaces of thetreated and untreated specimens are shown in Figures 7

and 8, respectively. Alkali treatment has dissolved thelignin and hemicelluloses, thus forming straight serra-tions on the fiber surface that can be seen clearly inFigure 7, while such lines are absent on the surface ofthe untreated fiber in Figure 8. Similar rough fibersurface morphology was reported in case of sisalfibers due to alkali treatment.11 Microholes areformed on the fiber surface due to dissolution oflignin on the fiber surface. This surface modification

Figure 7. SEM image of fractured treated CF composite.

Figure 6. Specific tensile modulus of CF composites.

2926 Journal of Composite Materials 46(23)

has increased the interaction between fibers and theresin and improved the fiber–matrix adhesion, resultingin a sharp, brittle fracture for the treated fiber compos-ite. There are traces of fiber pull-out observed in Figure8 for the untreated fiber composite which indicate aweak interface bonding. Pothan et al.11 have reportedvoids in the tensile failure surfaces of alkali treated sisalfiber composites and such voids are not present for CFcomposites. However, for untreated fiber composites,

long fibers at the fracture surface are seen for bothsisal fiber composites as well as for the present CFcomposites.

Impact strength

For treated CF composite, the impact strength isequal to 48 J/m, while for untreated fiber composite,it has the highest value equal to 71 J/m. In case of neat

Figure 8. SEM image of fractured untreated CF composite.

Figure 9. Impact strength of CF composites.

Reddy et al. 2927

resin, the impact strength is very low equal to 5 J/m.The treated fiber composites have lower impactstrength as a consequence of higher interface adhe-sion, resulting in lack of energy absorption mechanismin the composite. The impact strength is much less forneat resin due to complete absence of fibers for theshock absorbing mechanism. However, the resultsreported by Mylsamy and Rajendran26 for shortfiber epoxy composites with 3, 7, and 10mm fibersshow that the composite with treated fibers of 3mmhas given the highest impact strength of 134 J/m andthe untreated 3mm fiber composite has given 120 J/m.The impact strength has reduced with increase inlength of the fiber from 7 to 10mm. The fiberscould transmit the energy of impact into the epoxymatrix through increased number of interfaces ratherthan through lesser numbers of long interfaces. Thehigher impact strength in case of 3-mm long shortfiber composite is due to the increased number ofinterfaces with random orientations which increasedthe cushioning effect, resulting in higher energyabsorption. However, for the present woven fibercomposites, the adhesion was more and the cushioningeffect is reduced due to lack of energy absorptionmechanism. The values of impact strength for differentcomposites, cfc-t, cfc-ut, and neat resin are shown inFigure 9.

Barcol hardness

Using the Barcol impressor, the Barcol hardness isdetermined for the treated CF composite which isequal to 60 and it is 59.5 for untreated fiber

composite, while it is equal to 56 for neat resin, asgiven in Table 1.

DSC analysis

DSC analysis is done in nitrogen atmosphere of 30mL/min with a heating rate of 10�C/min between 25� and300�C. Results for composites and the neat resin areshown in Table 1. For amorphous solid like the fibercomposite, a state of transition occurs due to change inheat capacity from hard brittle state to soft rubberystate. For composite with treated fibers, the glass tran-sition temperature (Tg) is 79.56�C with a heat flow of�0.956 mw/min and at a heat capacity of �0.0956 mw/�C. Similarly, for composite with untreated fibers, theglass transition temperature is 77.97�C with a heat flowof �0.479 mw/min and at a heat capacity of �0.0479mw/�C. For neat resin, Tg is observed at 73.4�C with aheat flow of �0.625 mw/min and at a heat capacity of�0.0625 mw/�C. These peaks indicate the glass transi-tion temperature and increase in Tg, representing areduction of mobility of the polymer backbone due toformation of chemical bond between the resin and thematrix. Higher Tg of treated fiber composite indicateshigher thermal stability compared to the untreated fibercomposite and neat resin.

Thermogravimetric analysis

TGA of the composites and the neat resin are presentedin Figure 10. Thermal decomposition of each sampletook place in a programmed temperature range25–800�C. The neat resin showed only one stage

Figure 10. TGA thermograms of treated and untreated CF composite and neat resin.

2928 Journal of Composite Materials 46(23)

of weight loss process. This has a transition tempera-ture from 340�C to 417�C, and it is clear that the peaktransition temperature has occurred at 401�C. Theweight loss and residual weight of neat resin for theTGA are found to be 91% and 3%, respectively.Thermogravimetric curves show that the thermal stabil-ity of the composites is found to be higher than that ofthe neat resin. Beginning of decomposition took placeat 260�C for both treated and untreated fiber compos-ites and for neat resin, it is at 340�C. However, thedecomposition has ended at 475�C for treated fibercomposite, while it occurred at 463�C and 417�C foruntreated fiber composite and neat resin, respectively.The results are listed in Table 2. Therefore, the thermalstability of the treated fiber composite is higher com-pared to untreated fiber composite. Lower percentagelosses are obtained for treated fiber composite. Higherthermal stability of treated fiber composites is due toimproved fiber/matrix interaction as a result of addi-tional intermolecular bonding between fiber and the

matrix. This is also evident from the lower weight lossat different temperatures.

Water absorption

Treated fiber composite has absorbed less water com-pared to that of untreated fiber composite. Treatmentof CFs with NaOH for 24 h has made the fibers lesshydrophilic and decreased the water absorption capac-ity by 13.45%. The moisture absorption behavior ofvarious composites is shown in Figure 11. The percent-age of water absorption for cfc-t composite is 2.25 andfor cfc-ut, it 2.6, while it is equal to 0.5 for neat resin.There is a decrease in water absorption in case of trea-ted fiber composite. As the fibers are hydrophilic innature, they absorbed water during immersion, andloss of matter has been observed upon reconditioning.The percentage loss of soluble matter during immersionafter reconditioning the specimens is shown in Figure12. In case of cfc-t, due to fiber surface treatment, there

Figure 11. Moisture absorption behavior of CF composites.

Table 2. Thermogravimetric analysis of CF composites and resin

Transition temperature (�C)

% weight loss at

transition temperature

Residual weight

(%) at 460�C

Beginning of

decomposition

Maximum

decomposition

End of

decomposition

Cfc-t 225 405 430 23 3

Cfc-ut 200 390 424 26 3

resin 340 401 417 60 3

Reddy et al. 2929

is absolutely no loss of soluble matter, whereas for cfc-ut, there is 0.34% loss of soluble matter and for neatresin, the loss is 0.04%. Absorption of water by ligno-cellulose material has rendered the formation of hydro-gen bonds between water and hydroxyl groups of cel-lulose, hemi-cellulose, and lignin in the cell wall,2

causing the swelling of the composite. This has resultedin increase in width and reduction in the length of thecomposite. Less water is absorbed by treated fiber

composite which is due to replacement of hydrophilicOH groups of fiber by more hydrophobic ester groupsor otherwise due to formation of a protective layer atthe interface which prevented water molecules frompenetrating into the cell wall. The moisture absorptionbehavior for long-time immersion up to 1200 h is shownin Figure 13. It can be noted that there is a gradualincrease in water absorption for both cfc-t and cfc-ut,and the state of saturation has occurred at around

Figure 13. Moisture absorption behavior of CF composites for long-time immersion.

Figure 12. Soluble matter lost for CF composites.

2930 Journal of Composite Materials 46(23)

700 h. At saturation, the maximum moisture absorp-tion values for cfc-t and cfc-ut composites are 7.75%and 6.8%, respectively, and for neat resin, a maximumabsorption of 2.16% has occurred at 1000 h. The thick-ness, width, and the length of neat resin have slightlyincreased due to long-time immersion, the results ofwhich are shown in Figures 14–16. For the treatedfiber composite, there is an increase in thickness by8.7% and width by 4%. During this period, the

thickness and width of untreated fiber composite haveincreased by 9.42% and 3.17%, respectively, while thelength has slightly decreased by 1.36% for untreatedfiber composite and 0.4% for treated fiber composite.The percentage reduction in length for treated fibercomposite for 1200 h of immersion in water was verysmall and nearly constant at 0.4%. It confirms that thetreated fiber composites are stable in moist environ-ment. However, the increase in thickness of the

Figure 14. Change in thickness of CF composites for long-time immersion.

Figure 15. Change in width of CF composites for long-time immersion.

Reddy et al. 2931

untreated fiber composites was considerable as thefibers have swollen, resulting an increase in both thick-ness and width and a decrease in length.

Conclusions

Mechanical, thermal, and water absorption behavioursof woven treated and untreated fiber composites werestudied. Absence of fiber pull-out and a brittle fractureindicate good interface bonding in treated fiber com-posite. This has resulted in higher tensile and hardnessproperties, low water absorption, high glass transitiontemperature, and higher decomposition temperature.Higher flexural strength and flexural modulus andhigh impact strength are obtained for untreated CFcomposite. Alkali treatment has improved the fiber–matrix adhesion and enhanced the interface strengththat has positively influenced the tensile, water absorp-tion, and thermal properties except the flexural andimpact properties. Fiber pull-out in case of untreatedfiber composites indicates a weak fiber–matrix interfaceand was helpful for the increased flexural strength andflexural modulus. The long untreated fibers with weakinterface have provided a suitable energy absorptionmechanism for increased impact strength. The authorshave compared the present results with the latest resultson sisal fiber composites11 and Century (A. Americana)short fiber composites26 available in the literature. Thiscomparison has brought good insights about the trendof the results upon chemical treatment and reduced theflexural and impact properties in sisal fiber compositesThe short fiber composites are good for impact loadingonly but for all other properties, long woven fiber

composites are better. The formation of covalentbond at the fiber–matrix interface in treated fiber com-posite has resulted in increased glass transition temper-ature and higher thermal resistance. TGA gave higherdecomposition temperature and low weight loss. Thewater absorption properties have improved for the trea-ted fiber composite. It has also reduced the moistureabsorption capacity due to the formation of protectivelayer in the fiber–matrix interface and also preventedthe loss of soluble matter.

Funding

This research received no specific grant from any fundingagency in the public, commercial, or not-for-profit sectors.

Acknowledgments

Financial support by A.P. State Council for Science andTechnology (APCOST), Warangal Regional Centre,Hyderabad, India, vide letter APCOST/wgl/s&t/SPP/2007-

2008 dated 31.3.2008 is gratefully acknowledged.

Conflict of interests

None declared.

References

1. Mougin G, Magnum M and Eikelenberg N. Natural-fiberscomposites for the automotive industry: challenges, solu-

tions and applications. Int J Mater Prod Technol 2009;36(1–4): 176–188.

2. John MJ and Anandjiwala RD. Recent developments inchemical modification and characterization of natural

fiber-reinforced composites. Polym Compos 2008; 29(2):

187–207.

Figure 16. Change in length of CF composites for long-time immersion.

2932 Journal of Composite Materials 46(23)

3. Cordeiro N, Gouveia C and John MJ. Investigation of

surface properties of physico-chemically modified natural

fibers using inverse gas chromatography. Ind Crops Prod

2011; 33(1): 108–115.4. d’Almeida A, Calado V, Barreto D and d’Almeida J.

Effect of surface treatments on the dynamic mechanical

behavior of piassava fiber-polyester matrix composites. J

Therm Anal Calorim 2011; 103(1): 179–184.5. Rosa IMD, Kenny JM, Puglia D, Santulli C and Sarasini

F. Morphological, thermal and mechanical characteriza-

tion of okra (Abelmoschus esculentus) fibers as potential

reinforcement in polymer composites. Compos Sci

Technol 2010; 70(1): 116–122.

6. Siregar JP, Salit MS, Rahman MZA and Dahlan KZHM.

Thermogravimetric analysis (TGA) and differential

scanning calorimetric (DSC) analysis of pineapple leaf

fiber (PALF) reinforced high impact polystyrene

(HIPS) composites. Pertanika J Sci Technol 2011; 19(1):

161–170.7. Rashdi AAA, Salit MS, Abdan K and Megat MMH.

Water absorption behavior of kenaf reinforced unsatu-

rated polyester composites and its influence on their

mechanical properties. Pertanika J Sci Technol 2010;

18(2): 433–440.8. Rassmann S, Reid RG and Paskaramoorthy R. Effects of

processing conditions on the mechanical and water

absorption properties of resin transfer moulded kenaf

fiber reinforced polyester composite laminates.

Composites Part A 2010; 41(11): 1612–1619.

9. Reid RG, Asumani OML and Paskaramoorthy R. The

effect on the mechanical properties of kenaf fibre rein-

forced polypropylene resulting from alkali–silane surface

treatment. In: Ferreira AJM (ed.) 16th International con-

ference on composite structures ICCS16, Porto, Portugal,

28–30 June 2011.10. Towo AN and Ansell MP. Fatigue evaluation and

dynamic mechanical thermal analysis of sisal fiber–ther-

mosetting resin composites. Composites Sci Technol 2008;

68(3–4): 925–932.

11. Pothan LA, Mai YW, Thomas S and Li RKY. Tensile

and flexural behavior of sisal fabric/polyester textile com-

posites prepared by resin transfer molding technique. J

Reinf Plast Compos 2008; 27(16–17): 1847–1866.12. Sreekumar PA, Redouan S, Marc SJ, Nathalie L,

Kuruvilla J, Unnikrishnan G, et al. What’s the effect of

chemical treatment on dynamic mechanical properties of

sisal fiber-reinforced polyester composites fabricated by

resin transfer molding. Compos Interfaces 2008; 15(2–3):

263–279.13. Sreekumar PA, Saiah R, Saiter JM, Leblanc N, Kuruvilla

J, Unnikrishnan G, et al. Dynamic mechanical properties

of sisal fiber reinforced polyester composites fabricated

by resin transfer molding. Polym Compos 2009; 30(6):768–775.

14. Sangthong S, Pongprayoon T and Yanumet N.

Mechanical property improvement of unsaturated poly-ester composite reinforced with admicellar-treated sisalfibers. Composites Part A 2009; 40(6–7): 687–694.

15. Annapurna P and Bisoyi DK. Dielectric and impedance

spectroscopy studies on sisal fiber-reinforced polyestercomposite. J Mater Sci 2010; 45: 5742–5748.

16. Oladele IO, Omotoyinbo JA and Adewara JOT.

Investigating the effect of chemical treatment on the con-stituents and tensile properties of sisal fiber. J MinerMater Character Eng 2010; 9(6): 569–582.

17. Msahli S, Sakli F and Drean J-Y. Study of textile poten-tial of fibers extracted from Tunisian Agave americana L.AUTEX Res J 2006; 6(1): 9–13.

18. Zwane PE, Masarirambi MT, Magagula NT, DlaminiAM and Bhebhe E. Exploitation of Agave americana L.plant for food security in Swaziland. Am J Food Nutr2011; 1(2): 82–88. http://www.scihub.org/AJFN.

19. Davis SC, Dohleman FG and Long SP. The globalpotential for Agave as biofuel feedstock. GCBBioenergy 2011; 3: 68–78.

20. Bessadok A, Marais S, Roudesli S, Lixon C and MetayerM. Influence of chemical modifications on water-sorptionand mechanical properties of Agave fibers. Composites

Part A 2008; 39(1): 29–45.21. Bessadok A, Langevin D, Gouanve F, Chappey C,

Roudesli S and Maris S. Study of water sorption on mod-ified Agave fibers. Carbohydr Polym 2009; 76(1–2):

74–85.22. Oudiani AE, Chaabouni Y, Msahli S and Sakli F.

Physico-chemical characterization and tensile mechanical

properties of Agave americana L. fibers. J Text Inst 2009;100(5): 430–439.

23. Oudiani AE, Chaabouni Y and Sakli F. Mercerization of

Agave americana L. fibers. J Text Inst 2011; iFirst: 1–10.24. Thamae T and Baillie C. Influence of fiber extraction

method, alkali and silane treatment on the interface of

Agave americana waste HDPE composites as possibleroof ceilings in Lesotho. Compos Interfaces 2007; 14(7–9): 821–836.

25. Mylsamy K and Rajendran I. Influence of fiber length on

the wear behavior of chopped Agave americana fiber rein-forced epoxy composites. Tribol Lett 2011; 44(1): 75–80.

26. Mylsamy K and Rajendran I. Influence of alkali treat-

ment and fiber length on mechanical properties of shortAgave fiber reinforced epoxy composites. Mater Des2011; 32(8–9): 4629–4640.

27. Mylsamy K and Rajendran I. Conceptual design and fab-rication of a table using discontinuous Agave Americanafiber reinforced epoxy composite. Int J Acad Res 2010;2(1): 165–171.

Reddy et al. 2933