Thermally sprayable polyethylene coatings for marine environment
S.K. Singh a, S.P. Tambe a, V.S. Raja b, Dhirendra Kumar a,∗a Naval Materials Research Laboratory, Shil-Badlapur Road, P.O. Anandnagar, Ambernath 421506, India
b Corrosion Science and Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
Received 3 January 2007; accepted 26 July 2007
bstract
Application of organic coatings is one of the methods for protection of mild steel against corrosion. In the present work, low-density polyethyleneLDPE) has been used as binder for development of anticorrosive coating. Since non-polar characteristics of LDPE make its adhesion poor toost substrates, polar groups have been introduced in LDPE by grafting maleic acid (MAc) using reactive extrusion method. Grafted LDPE was
haracterized by chemical method, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermo-gravimetricnalysis (TGA), wide angle X-ray scattering (WAXS) and melt flow index (MFI). Grafted LDPE was pigmented with different pigments suchs red iron oxide, micaceous iron oxide (MIO), titanium dioxide (TiO2) and aluminium at three concentrations (i.e., 20, 30 and 40%). Theseompositions were applied on grit blasted mild steel specimen by flame spray technique. The coated specimens were evaluated for adhesiontrength and resistance to corrosion in salt spray, humidity and seawater. Red iron oxide-based composition showed better adhesion and corrosion
esistance compared to other compositions. Subsequently, corrosion resistance of red iron oxide-based compositions was studied by electrochemicalmpedance spectroscopy (EIS). The modified LDPE coating containing 30% red iron oxide showed higher resistance to corrosion compared to 20nd 40% red iron oxide-based compositions.
In the present age of industrialization, organic coatings could,n a way be considered valuable engineering materials since theyonstitute an integral part of any fabricated steel structure. Thepplication of organic coatings is one of the methods for steelrotection against corrosion [1,2].
The composition of most high-tech paint products includeetween 50 and 80% volatile organic compounds (VOCs) byass. These compounds (solvents and diluents) are necessary
o dissolve binders and dilute the paint. After drying, their emis-ion into the atmosphere reach practically incalculable levels [3].he coating industry has been seeking alternative technologies
hat are less polluting than the currently employed solvent-basedystems that cause the emission of volatile organic compounds.
he technologies based on powder coatings and thermal spray-
ng of polymeric coatings is ideally suited to meet the stringentnvironmental regulations curtailing the VOC emission.
Thermal spray organic coatings can be applied at relativelyow ambient temperatures. Since, these coatings are mostly ther-
oplastic, they can be repaired easily by remelting or applyingdditional material. These coatings can have excellent chemi-al resistance depending on polymer type. These coatings areuite resistant to damage caused by impact and abrasion [4].olyethylene, polypropylene, nylon, PVDF, poly ether–etheretone (PEEK), poly methyl methacrylate (PMMA) and ther-oplastic polyesters are some of the polymers, which can be
prayed by thermal spray process and can provide longer serviceife. Thermal spray eliminates the need for solvents and becausehe materials are processed in the form of powders and, in addi-ion, due to the high kinetic energy of thermal spray processes,he particle do not need to be fully molten in order to spreadut on the substrate surface [5]. The key attributes of the ther-al spray processes are that polymer coatings can be applied
nd repaired on-site and that the size of the part and coatinghickness are effectively unlimited. The coating application is a
ne step process and costly solvent disposal is eliminated [6].hermal spraying techniques like flame spray, high velocity oxy
uel (HVOF) and plasma spray have been used extensively forpraying of thermoplastic polymer coatings [5,7,8].
Earlier, in our work [9] we have modified LDPE with maleiccid by �-irradiation technique. But this technique has certainimitations such as bulk modification is difficult due to non-vailability of �-irradiation facility and reaction with monomeras to be carried out immediately after exposure to radiation.o overcome the above limitations, in the present work, LDPEas been modified by using reactive extrusion method and appli-ation of LDPE through thermal spray technique for corrosionrotection of mild steel substrate is examined. The work involvesrafting LDPE with maleic acid and examining the effect of dif-erent pigments such as red iron oxide, micaceous iron oxideMIO), titanium dioxide (TiO2) and aluminium on the corrosionesistance behaviour of thermally sprayed LDPE
. Experimental
.1. Materials
Low-density polyethylene (LDPE) powder, having averaged50) particle size of 267 �m, was obtained from IPCL (India).DPE powder was sieved in laboratory and powder having par-
icle size less than 200 �m was used for grafting. Maleic acidMAc) monomer used in the study, having 99.5% purity andelting point 136–141 ◦C, was supplied by S.D. Fine Chem
India) and was used in the as received condition. The initia-or, dicumyl peroxide (DCP), having 99% purity was obtainedrom ACROS Organics, USA and used in as received condi-ion. Chemical reagents used for titration were of either ARrade or they were standardized before use. The pigments usedn the study were obtained from M/s DuPont, USA and ZIGMAnternational (India).
.2. Reactive extrusion
The reactive extrusion process was carried out in a BRABEN-ER single screw extruder having 19.1 mm barrel diameter and/D ratio 25. The processing conditions were (a) temperaturerofile: 165, 170, 175 and 180 ◦C; (b) screw rotation: 50 rpm;c) torque: 10 N m and (d) processing time: 5 min. All the formu-ations were first mixed in a ceramic ball mill for approximatelyh and then fed through the extruder hooper.
.3. Grafting of MAc on LDPE
LDPE powder was mixed with maleic acid at 3, 5, 8 and 10%oncentration and 1% DCP was added in the composition. Theormulation processed by reactive extrusion was cryo-grinded,ransferred to hot distilled water and stirred for about 30 minnd filtered. Powder was washed thoroughly with hot water toemove any free maleic acid. Grafted LDPE powder (LDPE-g-
Ac) was dried under reduced pressure at 80 ◦C for 16 h beforeharacterization.
.4. Pigmentation of LDPE and grafted LDPE
Red iron oxide, MIO, titanium dioxide and aluminium pig-ents were used for pigmentation of LDPE and grafted LDPE
3
fi
c Coatings 60 (2007) 186–193 187
t 20, 30 and 40% (by weight) concentrations. The blends werextruded at 140 ◦C in single screw extruder at 50 rpm for 10 min.fter extrusion, blend was passed through a cryo-grinder to
chieve required particle size, suitable for flame spray appli-ation.
.5. Thermal spray application
LDPE, LDPE-g-MAc and pigmented compositions werepplied on mild steel specimens by Powderjet 86 PII′′ flamepray gun. The flame spray gun and powder feed unit PF 700ere supplied by M/s Metallizing Equipment Company Pvt.imited, Jodhpur (India). The gun was used both for preheat-
ng the substrate and spraying the coating. Acetylene and airere used, at a flow rate of 28 and 38 L/min, respectively,
o produce combustion flame. Compressed air (at 6.0 kg/cm2)as used to fluidize the powder and transport the powder fromowder feeder unit to the gun. The coating powder feed rateas kept at 12.0 g/min. Before application of coating, panelsere preheated to 70–80 ◦C. During application, coating tem-erature was controlled by varying the traverse interval of theame spray gun. Coating temperature was monitored continu-usly and as soon temperature reached to 190–200 ◦C, sprayingas stopped. The preheat temperature and final coating temper-
ture were measured using hand held non-contact thermometerInfrared thermometer, model no. IR-L-1000). The flame sprayun is moved across the substrate to deliver a succession ofolten droplets to build up a coating of required thickness. Pan-
ls were coated by flame spraying with one coat of LDPE andDPE-g-MAc at an average film thickness of 250 �m and pig-ented compositions were applied at an average film thickness
f 175 �m.
. Characterization
.1. Acid value and percent grafting
Acid value and percent grafting were determined by titratingrafted product. 0.5 g of grafted sample was dissolved in 40 mlf hot dichloro benzene (DCB), cooled to 80 ◦C and titrated withthanolic NaOH using thymol blue as indicator. The ethanolicaOH was standarised with benzoic acid. Acid value (Z) andercent grafting were calculated using following equations:
cid value (Z) = 56.1 × A × 0.1
B× 100 (1)
here A is the burette reading and B is the weight of sample (g):
cid equivalent (M) = 56.1 × 1000
Z(2)
rafting (wt.%) = 58
M − 58× 100 (3)
.2. Infrared spectroscopy
LDPE and grafted LDPE samples were converted into thinlms by hot pressing at 130 ◦C and were directly mounted on
1 rgani
tisceswof
%
wa
3
DA1
3
uMoabRa
3
grp
3
Iiots
3
Ltp
paab
3
flgoIthswtov
4
twpcroSaaos
Fcwhich is characteristics of carbonyls from carboxylic dimmeracids. The peak appeared at 1785 cm−1 is characteristic of anhy-dride carbonyl. Since maleic acid was grafted on LDPE byreactive extrusion, there is a possibility of conversion of acid
88 S.K. Singh et al. / Progress in O
he frame of spectrophotometer. FTIR spectra of films havingdentical thickness were recorded by employing a Perkin-Elmerpectrophotometer (Model 1600 series). The relative intensityhange (RIC) was measured by taking FTIR spectrum, at differ-nt intervals, of LDPE and LDPE-g-MAc films exposed to saltpray. The band characteristic of methylene groups (1367 cm−1)as taken as the reference band. The relative intensity changef the particular bands upon exposure to salt spray was obtainedrom the following expression [10]:
RIC =
(A1715A1367
)n days
−(
A1715A1367
)0 days(
A1715A1367
)0 days
× 100 (4)
here A1367 and A1715 are the absorption at 1367 and 1715 cm−1
nd n is the exposure period.
.3. Melt flow index
Melt flow index measurements were carried out as per ASTM-1238, using Tinius Olsen melt flow Indexer (Model MP600).s melting points of LDPE and LDPE-g-MAc are 102 and05 ◦C, respectively, measurements were carried out at 113 ◦C.
.4. Thermal properties
Melting points of polymeric powders were determined bysing a differential scanning calorimeter (TA Instruments,odel Q 100). DSC measurement was carried out with a ramp
f 10 ◦C/min maintained during heating scan under nitrogentmosphere. Thermal decomposition temperature was studiedy Thermo-Gravimetric Analyser (TA Instruments, Model Hi-es. TGA 2950) at a heating rate of 10 ◦C/min under nitrogentmosphere to a temperature of 800 ◦C.
.5. WAXS analysis
The WAXS measurement was done by X-ray wide angleoniometer (M/s Philips, Holland) at 50 kV, 120 mA using scanange of 5–35◦. The analysis was carried out on powdered sam-les of LDPE and LDPE-g-MAc.
.6. Adhesion strength
Adhesion strength was determined as per method described inndian Standard IS: 101 (pull-off method). The method was mod-fied by reducing the area of one dolly to facilitate the debondingf coating from one side. For each coating, five specimens wereested and average value of the data has been reported as adhesiontrength.
.7. Evaluation of anticorrosive property
The anticorrosive property of pigmented compositions ofDPE and LDPE-g-MAc was evaluated by assessing their resis-
ance to corrosion in salt spray, humidity cabinet and seawater aser method described in IS: 101. Clean and rust free mild steel
c Coatings 60 (2007) 186–193
anels of size 150 mm × 100 mm × 1.5 mm were grit blastednd coated by flame spraying with one coat of the compositionst an average film thickness of 175 �m. The edges were sealedy dipping the coated panels in molten wax before exposure.
.8. Electrochemical impedance spectroscopy (EIS)
EIS has been used to study the anticorrosive behaviour ofame sprayed 30% red iron oxide pigmented LDPE and LDPE--MAc coatings. The impedance measurements were carriedut using Gamry CMS 300 electrochemical impedance system.n this study, 3.5% NaCl solution was used as electrolyte andhe exposed sample area was 21.5 cm2. Three electrodes systemaving saturated calomel electrode (SCE) as reference electrode,ample as working electrode and platinum as counter electrodeas employed. A sine wave of 10 mV (RMS) was applied across
he cell. The measurements were made in the frequency rangef 50 kHz to 0.02 Hz. EIS study was carried out on samples afterarious exposure intervals.
. Results and discussion
Fig. 1 shows variation in percent grafting at different concen-rations of maleic acid. As expected, extent of grafting increasedith maleic acid concentration. Maximum grafting of 1.1 weightercent was observed for 10% maleic acid. Grafting was notarried out at higher concentrations of maleic acid because it iseported [11] that higher degree of grafting leads to higher degreef water absorption due to presence of excess carboxyl groups.ince the aim of the present work is to modify the LDPE fornticorrosive coating application and high water absorption willffect the service life of coating, LDPE-g-MAc having graftingf 0.9 weight percent was selected for pigmentation and furthertudy.
FTIR spectra of LDPE and LDPE-g-MAc are shown inig. 2. The peak corresponding to vibration stretching of thearbonyl group ( C O) in LDPE-g-MAc is about 1715 cm−1
Fig. 1. Effect of maleic acid concentration on grafting of LDPE.
S.K. Singh et al. / Progress in Organic Coatings 60 (2007) 186–193 189
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iTgabia
1omtsaFwTgeel
Lmog
D3cddr
TC
Fig. 3. DSC curves of (a) LDPE and (b) LDPE-g-MAc, 8% maleic acid.
MpHs
Grit blasted mild steel panels coated with LDPE, LDPE-g-MAc, titanium dioxide, red iron oxide, micaceous iron oxide(MIO) and aluminium pigmented LDPE and LDPE-g-MAc weretested for adhesion strength. It is seen that grafting of maleic
ig. 2. FTIR spectrum of (a) LDPE and (b) LDPE-g-MAc, 8% maleic acid.
nto anhydride due to heat treatment during extrusion [12,13].he anhydride peak (1785 cm−1) was absent in FTIR spectra ofrafted LDPE using irradiation method [9]. There are no peakst 1715 and 1785 cm−1 in the FTIR spectrum of LDPE as no car-onyl group exists in LDPE. The appearance of two new peaksn FTIR spectrum of LDPE-g-MAc confirms grafting of maleiccid onto LDPE.
To ascertain the observation that peak appearing at715 cm−1 in FTIR spectrum of LDPE-g-MAc is due to graftingf MAc, acid values of LDPE and LDPE-g-MAc were deter-ined. Higher acid value of LDPE-g-MAc (Table 1) compared
o LDPE indicated grafting of MAc onto LDPE. Further, FTIRpectra of maleic acid were recorded to confirm that the highercid value is not due to free maleic acid present in grafted LDPE.TIR spectra of free maleic acid show a peak at 1704 cm−1
hereas in case of LDPE-g-MAc peak appears at 1715 cm−1.his confirms that higher acid value of LDPE-g-MAc is due torafting of maleic acid. The grafting of MAc to LDPE is furtherstablished by melt flow index results, shown in Table 1. It isxpected that introduction of polar group in LDPE matrix willead to reduction in melt flow index due to hydrogen bonding.
DSC curves in Fig. 3 show melting points of LDPE andDPE-g-MAc at 102 and 105 ◦C, respectively. This change inelting point after grafting can be attributed to the presence
f polar carboxyl groups. However, the effect is small as therafting level is very low.
Fig. 4 gives TGA thermograms of LDPE and LDPE-g-MAc.ecomposition of LDPE and LDPE-g-MAc is seen to start at70 and 388 ◦C, respectively. Low grafting is not expected tohange much of the thermal degradation behavior. The large
ifference between the melting (i.e., 105 ◦C) and initial degra-ation temperatures (i.e., 388 ◦C) of LDPE-g-MAc makes thisesin suitable for flame spray application.
able 1omparative study of LDPE and LDPE-g-MAc
Polymer Acid value Melt flow index(g/10 min)
Adhesionstrength (MPa)
LDPE 0.6 2.16 5.4LDPE-g-MAc (8%
maleic acid)8.9 1.40 8.8
Fig. 4. TGA curves of (a) LDPE and (b) LDPE-g-MAc, 8% maleic acid.
Figs. 5 and 6 show WAXS spectra for LDPE and LDPE-g-Ac (8% maleic acid) samples. It is evident from the spectra that
eak intensity of the LDPE-g-MAc is lower than that of LDPE.owever, the crystallite size calculated from these spectra is
ame in both the cases.
Fig. 5. WAXS spectra of LDPE.
190 S.K. Singh et al. / Progress in Organic Coatings 60 (2007) 186–193
Fig. 6. WAXS spectra of LDPE-g-MAc, 8% maleic acid.
Table 2Adhesion strength of pigmented compositions
Coatings Adhesion strength (MPa)
Pigment content
20% 30% 40%
LDPE + red iron oxide 6.8 6.5 6.9LDPE-g-MAc + red iron oxide 9.2 9.6 9.8LDPE + MIO 7.0 6.0 6.6LDPE-g-MAc + MIO 7.5 7.9 7.8LDPE + titanium dioxide 7.3 7.5 7.3LDPE-g-MAc + titanium dioxide 8.2 8.9 8.9LL
cid enhances adhesion of LDPE to mild steel surface due tontroduction of polar groups in the polymer backbone (Table 1).ut no appreciable change in adhesion (Table 2) was observedue to incorporation of pigments in LDPE and grafted LDPE.owever, modified LDPE pigmented with red iron oxide showedaximum adhesion compared to other pigmented compositions.Grit blasted mild steel panels coated with titanium dioxide,
ed iron oxide, micaceous iron oxide (MIO) and aluminium pig-
ented compositions of LDPE and LDPE-g-MAc were exposed
o salt spray, humidity and seawater for thirteen weeks to eval-ate their resistance to corrosion. Results shown in Table 3ndicate that pigmentation has improved the corrosion resistance
MFLo
able 3nfluence of pigment content on corrosion resistance of coatings represented by 0–10
oatings Influence of pigments on corrosion resistanc
: severe corrosion; 10: no corrosion/no blistering.
ig. 7. Relative intensity change of IR bands in (a) LDPE; (b) LDPE-g-MAc.
f these two resins. Improved corrosion resistance of pigmentedDPE-g-MAc compared to pigmented LDPE may be attributed
o the better interaction between pigments and LDPE-g-MAcue to its polar nature, leading to compact film formation, thuseducing the ingress of ionic species towards the metal sub-trate. It can be seen from the results shown in Table 3 thatll the compositions have excellent resistance to corrosion inumidity conditions but slightly inferior performance in saltpray and seawater immersion conditions. The adverse effectn performance of LDPE and modified LDPE-based composi-ions may be attributed to the oxidation of LDPE in aqueous
edium [14]. Further, Henry et al. [15] have also reported thathe oxidation rate of polyolefins strongly depends on the pHf water and oxidation rate is higher in alkaline medium com-ared to inert or an acidic medium. Modification of LDPE byrafting maleic acid has been found to enhance the resistanceo oxidation, when exposed to salt spray. For this purpose freelms of LDPE and LDPE-g-MAc were exposed to salt spray and
heir FTIR spectrum was taken after different time intervals. Thehange in relative intensity of IR bands of LDPE and LDPE-g-
Ac was calculated in terms of %RIC. It is evident from the
ig. 7 that there is change in relative intensities of LDPE andDPE-g-MAc but the change is more prominent in the casef LDPE. The change in relative intensity may be attributed to
S.K. Singh et al. / Progress in Organic Coatings 60 (2007) 186–193 191
re an
st
tsotarpwbnptrooscppbahhmp
c39tawebi(
wcdpnstmottRttwbToetance and which decreases further with time indicates that thecoating has very high permeability and this coating will not givecorrosion protection for longer duration. The behaviour may be
Fig. 8. SEM of MIO pigment (a) befo
imultaneous formation and breakup of functional groups dueo oxidation of LDPE.
Red iron oxide and aluminium compositions, at all concen-rations, have shown very good resistance to corrosion in saltpray and seawater immersion tests. The improved performancef red iron oxide may be due to the fact that the proper wet-ing of pigment with resin (polar–polar interaction between resinnd pigment) has led to impervious film formation. One of theeasons for the unsatisfactory performance of titanium dioxideigmented compositions may be that in this study this pigmentas used alone. This pigment protects the surface by providing aarrier against the environment and generally is used in combi-ation with other pigments. Micaceous iron oxide pigment haslate type of shape and has a tendency to orient itself parallelo the substrate and thus, protects the surface from corrosion byeducing the ingress of corrosive species. The poor performancef MIO reported in this study is attributed to the destructionf its plate type of morphology (Fig. 8a and b) due to highhear force encountered by pigment particles during mixing andryo-grinding processes. In case of aluminium pigmented com-ositions, the lamellar shape and ductile nature of aluminiumigment have played a very significant role. It may be possi-le that due to high shear force encountered during extrusionnd cryo-grinding processes, the aluminium pigment particlesave flattened and aligned. These aligned aluminium particlesave helped in reducing the ingress of corrosive species. Thisay be the reason for good corrosion resistance of aluminium
igmented compositions.The EIS study of red iron oxide (at 20, 30 and 40%) pigmented
ompositions of LDPE and LDPE-g-MAc were carried out using.5% NaCl solution as electrolyte. The readings were taken after, 16, 23, and 26 days of exposure. Bode plots were recorded andhe impedance (Z) at 0.1 Hz was read from the plots and reporteds polarization resistance (Rp). The impedance measurementsere corrected to 21.5 cm2 area. The values were plotted against
xposure period and following observations were made. It cane seen from Fig. 9 that maro 20 (LDPE-g-MAc + 20% redron oxide) composition had high initial polarization resistanceRp > 109 � cm2) but after 16 days it has dropped significantly
Fo
d (b) after mixing and cryo-grinding.
ith time and approached the range of 106 � cm2 below whichorrosion protection is lost. Based on polarization resistanceata after 26 days it is anticipated that this coating will haveoor long-term corrosion protection. However, this feature isot reflected even after 13 weeks of exposure in salt spray andeawater immersion tests, where coating is showing good resis-ance to corrosion (Table 3). The Nyquist and Bode plots of
aro 30 (LDPE-g-MAc + 30% red iron oxide) up to 26 daysf exposure are shown in Figs. 10 and 11. This coating sys-em has outstanding barrier properties up to 26 days under theest conditions (Fig. 9). After 23 days, there is a small drop inp value from 4.3 × 1010 to 1.2 × 1010 � cm2, which indicates
hat pores are opening up and coating is becoming permeableo water and electrolyte but is still in the impedance range inhich long-term corrosion protection is provided. The sameehaviour was also noticed in exposure tests after 13 weeks.he third coating, i.e., maro 40 (LDPE-g-MAc + 40% red ironxide) has shown low impedance 106 � cm2 after 9 days ofxposure (Fig. 9). The low value of initial polarisation resis-
ig. 9. Effect of concentration of red iron oxide pigment on barrier propertiesf LDPE-g-MAc.
192 S.K. Singh et al. / Progress in Organic Coatings 60 (2007) 186–193
Fig. 10. Nquist plots of LDPE-g-MAc + 30% red iron oxide after (( ) 9 days;( ) 16 days; ( ) 23 days; ( ) 26 days). (For interpretation of the referencesto colour in this figure legend, the reader is referred to the web version of thearticle.)
Fig. 11. Bode plots of LDPE-g-MAc + 30% red iron oxide after (( ) 9 days;(ta
ais
o
Fo
Fdi
Riira2i(1htf1hd4omit is in protective zone (Rp > 10 � cm ), but the resistance has
) 16 days; ( ) 23 days; ( ) 26 days). (For interpretation of the referenceso colour in this figure legend, the reader is referred to the web version of therticle.)
ttributed to the high concentration of red iron oxide in the coat-ng. The exposure tests data does not confirm the findings of EIS
tudy.
The polarization resistance of pero 20 (LDPE + 20% red ironxide) after 9 days of exposure is 2.0 × 107 � cm2 (Fig. 12). The
ig. 12. Effect of concentration of red iron oxide pigment on barrier propertiesf LDPE.
dvt
Fdi
ig. 13. Nquist plots of LDPE + 30% red iron oxide after (( ) 9 days; ( ) 16ays; ( ) 23 days; ( ) 26 days). (For interpretation of the references to colourn this figure legend, the reader is referred to the web version of the article.)
p value of this coating has decreased with time and after 23 dayst has reached to 2.5 × 105 � cm2, this indicates that this coatings not suitable for long-term corrosion protection and due to thiseason further measurement was not carried out. The Nyquistnd Bode plots of pero 30 (LDPE + 30% red iron oxide) up to6 days of exposure are shown in Figs. 13 and 14. This coat-ng system has low impedance (compared to maro 30) initiallyFig. 12), which further dropped down to 2.5 × 108 � cm2 after6 days of exposure. With Rp value of 108 � cm2, this coatingas some permeability to water and electrolyte but is still inhe range in which corrosion protection is provided. The majoreature of this coating is that the impedance has stabilized after6 days and little further change, suggesting that after initialydration and related chemical changes, little or no change oreterioration has occurred. The impedance behaviour of pero0 is also shown in Fig. 12. The pero 40 (LDPE + 40% red ironxide) composition has shown impedance behaviour similar toaro 40 (Fig. 9) and in both cases after 9 days of exposure,
6 2
ropped down. This indicates that this system will also not pro-ide corrosion protection for longer period. This may be dueo the reason that at high loading of red iron oxide, corrosion
ig. 14. Bode plots of LDPE + 30% red iron oxide after (( ) 9 days; ( ) 16ays; ( ) 23 days; ( ) 26 days). (For interpretation of the references to colourn this figure legend, the reader is referred to the web version of the article.)
ehaviour of coating is governed by the porosity introduced inhe coating.
. Summary
Maleic acid was grafted to LDPE by reactive extrusionethod at different concentrations of maleic acid in presence of
nitiator. Maximum grafting of 1.1% was achieved at 10% maleiccid concentration. FTIR has shown generation of carboxylroup in grafted LDPE with 8% maleic acid, which led to an acidalue of 8.9. DSC and TGA studies showed shift in melting pointnd initial degradation temperature of grafted LDPE. GraftedDPE has shown higher adhesion strength than LDPE. EIS studyf red iron oxide pigmented compositions has shown that LDPE--MAc coating with 30% red iron oxide has superior resistanceo corrosion than coatings having 20 and 40% red iron oxide.
cknowledgements
The authors sincerely thank to Dr. J. Narayana Das, Direc-
or for his keen interest, constant encouragement and for givingermission to publish this paper. Assistance of Mr. N.G. Mal-ankar of this laboratory is gratefully acknowledged in carryingut FTIR analysis.
[
[
c Coatings 60 (2007) 186–193 193
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