Enhancement of Mechanical Properties and Wear Resistance of Epoxy: Glass Fiber, Basalt Fiber, Polytetrafluoroethylene and Graphite

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1 Enhncement of Mechnicl Properties nd Wer Resistnce of Epoxy: Glss Fier, Bslt Fier, Polytetrfluoroethylene nd Grphite B. S. Knthrju 1, B. Suresh 2 * Aville online t Indin Journl of Advnces in Chemicl Science S1 (2016) Indin Journl of Advnces in Chemicl Science 1 Deprtment of Mechnicl Engineering, Don Bosco Institute of Technology, Bengluru, Krntk, Indi. 2 Deprtment of Mechnicl Engineering, The Ntionl Institute of Engineering, Mysuru, Krntk, Indi. Received 25 th Mrch 2016; Revised 11 th My 2016; Accepted 12 th My 2016 ABSTRACT Enhncements of mechnicl properties nd wer resistnce of epoxy using i-directionl fiers (E-glss nd slt) nd fillers nmely polytetrfluoroethylene (PTFE) nd grphite hs een systemticlly investigted in this study. Fier reinforced epoxy (G-B/E) filled with PTFE nd grphite (2%, 4%, nd 6%) were fricted using hnd lyup technique followed y compression molding. Interlminr sher strength, tensile, nd flexurl properties were determined to evlute the effectiveness of PTFE nd grphite fillers on the mechnicl properties. The dry sliding wer ehvior ws ssessed y using pin on disc pprtus under different lods nd different sliding distnces. Results show tht oth fillers improved the mechnicl properties, nd the improvement is more pronounced with the incorportion of grphite filler. The enhnced performnce of filler filled G-B/E composites is due to etter dhesion nd good dispersion of prticultes in the epoxy mtrix providing incresed surfce re for strong interfcil interction nd etter lod trnsfer. The wer test results indicte tht ddition of PTFE nd grphite in G-B/E hyrid composites hve significnt influence on wer ehvior under vried sliding distnce/ lods. Further, it ws found tht PTFE filled G-B/E composites exhiited lower specific wer rte s compred to unfilled nd grphite filled G-B/E hyrid composites. In ddition, scnning electron microscopy imges of the mechnicl test filed specimens of selected specimens hve lso een reported. The most importnt concept of this pper is to strength the importnce of integrting fiers nd functionl fillers in the design of wer resistnt polymer mtrix composites. Key words: G-B/E composites, Fillers, Mechnicl properties, Wer, Scnning electron microscopy. 1. INTRODUCTION Over the pst decdes, polymer mtrix composites re mde nd most widely used for structurl pplictions in the erospce, utomotive, nd chemicl industries, nd in providing lterntives to trditionl metllic mterils [1]. The fetures tht mke composites so promising s industril nd engineering mterils re their high specific strength, high specific stiffness, nd opportunities to tilor mteril properties through the control of fier nd mtrix compositions. Composites re developed for superior mechnicl strength nd this ojective often conflicts with the simultneous chievement of superior wer resistnce [2]. As result of this, these mterils re found to e used in mechnicl components such s gers, cms, wheels, impellers, rkes, clutches, conveyors, trnsmission elts, ushes, nd erings. In most of these services, the components re sujected to triologicl loding conditions, where the likelihood of wer filure ecomes greter. *Corresponding Author: E-mil: suresh2004@yhoo.co.in Phone: Bslt is nturl mteril tht is found in volcnic rocks. When used s (continuous) fiers, slt cn reinforce new rnge of composites. It cn lso e used in comintion with other reinforcements (e.g., slt/ cron). Since deep studies on this mteril re only recent, in the lst 10 yers, numer of reserchers hs een investigting properties nd ehvior of vrious composites mde of continuous or short slt fiers [3-8]. The dvntges mke slt fiers promising lterntive to glss fiers s reinforcing the mteril in composites when considering tht the price of slt fiers lies etween tht of E nd S-glss nd tht it is continuously dwindling s new mrket opportunities [9]. Therefore, over the lst yer s slt fiers hve een studied extensively s reinforcement in thermosetting mtrices [10-12]. Fiore et l. [13] demonstrte the fesiility of use of slt fiers in sustitution of glss one. To this im, hyrid composites were mnufctured y mens of ply sustitution techniques nd tested y three-point 107

2 ending nd tensile tests. Moreover, this solution ws then pplied to nvl ulkhed demonstrting tht, considering costs, environment impct, nd mechnicl performnces, this kind of mteril could sustitute the trditionl glss fier composites in nvl ppliction. De Ros et l. [14] confirmed tht using the stronger slt fier t the top nd ottom of the glss lminte improved the post-flexurl strength of the hyrids. However, it is difficult to trnsfer the conclusions from one hyrid to the other, s there is currently no theoreticl frmework ville to ssess the importnce of the vrious mteril prmeters. Aprt from fier reinforced composites, the composites mde from oth fier/filler reinforcement performed well in mny prcticl situtions. The use of fillers in the mtrix provide incresing lod withstnding cpility, reduced coefficient of friction, improved wer resistnce, nd therml properties. The question of why fiers nd fillers usully improve the wer resistnce of polymer mtrix hs een the suject of intense study in recent yers Zhng et l. [15] studied dry sliding friction nd wer ehvior of PEEK nd PEEK/SiC composite nd concluded tht the influences of SiC fillers in the composite effectively reduce the plough nd the dhesion etween the two reltive sliding prts. Suresh et l. [16] descried the role of SiC nd grphite on friction nd slide wer chrcteristics in glss-epoxy composites y dding them seprtely. They stted tht the influence of these inorgnic fillers hs significnt role in reducing friction nd exhiited etter wer resistnce properties. This study focuses on the evlution of the mechnicl nd dry sliding wer ehvior of glss-slt hyrid fier reinforced epoxy composite with nd without fillers such s grphite nd polytetrfluoroethylene (PTFE) (2, 4, nd 6 wt.% ech). 2. EXPERIMENTAL 2.1. Mterils Two types of reinforcement used in the present study re slt frics, 360 g/m 2, plin-weve (wrp 5F/10 mm, weft 5F/10 mm), tex 330, from Nickunj Pvt. Limited, nd E-Glss fric, 360 g/m 2, plinweve (wrp 5F/10 mm, weft 5F/10 mm), tex 330 (Suntech Fiers Ltd.). The mtrix used is n epoxy (LY556) is ifunctionl one tht is diglycidyl ether of isphenol-a, nd the high-temperture hrdener HT972 is solid, romtic mine, viz., 4,4 -dimino diphenyl methne. The resin nd hrdeners were kindly supplied y M/s. Huntsmn Advnced Mterils, Mumi. The wt.% of glss nd slt fiers in the formultions ws vried nd is listed in Tle Preprtion of Composite Lmintes The epoxy resin is mixed with the hrdener in the rtio 100:28 y weight. Dry hnd ly-up technique is employed to produce the composites. The stcking procedure consists of plcing glss nd slt fric one ove the other with the resin mix well spred etween the frics to otin hyrid fier reinforced composites. A porous Teflon film is plced on the completed stck. To ensure uniform thickness of the smple spcer of size 3 mm is used. The mold pltes hve relese gent smered on them. The whole ssemly is pressed in hydrulic press t pressing temperture nd pressure of 100 C nd 0.5 MP. The lminte so prepred hs size 500 mm 500 mm 3 mm ws kept it in hot ir oven t temperture of 120 C for 2 h. To prepre the prticulte filled fier reinforced composites grphite nd PFTE powder (verge prticle size of out 10 µm) is mixed with known weighed quntity of epoxy resin Mechnicl nd Wer Chrcteriztion Tensile testing ws performed ccording to ASTM D 638 using universl testing mchine (Klpk Instruments). The test ws conducted t crosshed speed of 2.5 mm/min t room temperture. Flexurl (three-point ending) test ws crried out ccording to ASTM D790. The verge of t lest five mesurements of ech lminte smple is reported here. The crosshed speed ws mintined t 2.5 mm/min. The interlminr sher strength (ILSS) ws evluted in ccordnce to ASTM D A spn-to-depth rtio of 4:1 nd cross-hed speed of 2.5 mm/min were used. A pin-on-disc wer test pprtus ws used for the dry sliding wer experiments (s per ASTMG-99 stndrd). The test ws conducted on trck of 50 mm Tle 1: Weight percentge of mtrix, fier, nd filler of prepred composites. Smple code Mtrix wt. % Fier wt. % Filler wt. % G E (Glss) B E (Bslt) GB E (50 Glss GB E+2 Gr (50 Glss GB E+4 Gr (50 Glss GB E+6 Gr (50 Glss GB E+2 PTFE (50 Glss GB E+4 PTFE (50 Glss GB E+6 PTFE (50 Glss PTFE: Polytetrfluoroethylene 2 grphite 4 grphite 6 grphite 2 PTFE 4 PTFE 6 PTFE 108

3 dimeter for specified test durtion, pplied lod, nd sliding velocity. The surfce of the specimen ws perpendiculr to the contct surfce. The surfces of oth the specimen nd the disc were clened with soft pper soked in cetone efore the test. The initil nd finl weights of the specimen were mesured y using n electronic digitl lnce with n ccurcy of g. The difference etween the initil nd finl weights is the mesure of weight loss. The weight loss ws then converted into wer volume using the mesured density dt. The specific wer rte prmeter provides more comprehensive mesure of the wer loss chrcteristics of the mterils. less volume of fier nd more void formtion in the composites. Flexurl (3-point ending) tests were performed to check the effect of two different filler prticles on the stiffness nd strength of composites. Figure 2 shows the lod-deflection curves of ll the prepred smples under flexurl loding. From Tle 2, it is oserved tht GB-E composites showing higher flexurl strength compred to pure slt reinforced composites nd lower s compred to pure glss fier composite. This cn e explined y the 3. RESULTS AND DISCUSSION 3.1. Mechnicl Chrcteriztion Figure 1 shows typicl tensile lod versus displcement curves of glss fier, slt fier, nd unfilled nd filled hyrid (glss-slt) fier reinforced epoxy composites. Here, the lod linerly incresed with incresing displcement until reching filure of ll the smples. From the result, it is oserved tht slt fric type shows n increse of 5% of the tensile strength when compred with glss fric reinforced composites. Hyridiztion of glss nd slt fier (GB-E) showed the tensile strength of MP, which is out 13.5% nd 8.5% higher thn the plin glss nd plin slt fier reinforced composites s listed in Tle 2. This is due to positive hyridiztion etween glss nd slt nd lso the etter interfcil onding etween the fier nd mtrix. Further incorportion of grphite prticles into GB-E composite increses the tensile strength nd modulus. This my e due to good prticle dispersion nd strong polymer/filler interfce dhesion for effective stress trnsfer. However, increse in ddition of grphite nd PTFE content up to 6% weight to the composites the tensile strengths nd modulus is found to e less this is due to more filler mteril in the composites dmges mtrix continuity, Figure 1: Typicl lod s function of displcement of G-E, B-E nd unfilled nd filled GB-E composites. Figure 2: Typicl lod s function of deflection of G-E, B-E nd unfilled nd filled GB-E composites. Tle 2: Mechnicl properties of prepred composites. Composites Tensile strength MP Tensile modulus GP Flexurl strength MP Flexurl modulus GP G E B E GB E GB E+2 Gr GB E+4 Gr GB E+6 Gr GB E+2 PTFE GB E+4 PTFE GB E+6 PTFE ILSS: Inter lminr sher strength, PTFE: Polytetrfluoroethylene ILSS MP 109

4 fct tht filure in slt lmintes tkes plce in the compressed hlf section, while in glss lmintes, the whole section is involved in the frcture process up to the tensile fce. Similr ehvior ws lso oserved y Wittek nd Tnimoto [17]. The GB-E with grphite prticle composites showed rpid lod rise, the highest mximum lod, nd ctstrophic filure. This mens tht the composite filed in rittle mnner. On the other hnd, the GB-E showed slow lod rise, lrge yield displcement, nd the lowest mximum lod. This ehvior suggests tht the composite filed in ductile mnner ecuse of the high elongtion property of slt fier. From the otined result, it is lso oserved tht ddition of oth grphite nd PTFE filler prticles enhnces the flexurl strength of GB-E composites. Flexurl strength of GB-E lmintes incresed y 34%, 36%, nd 30% for incorportion of 2%, 4%, nd 6% grphite prticles nd lso it is incresed y 13%, 24%, nd 8% for incresing wt.% of PTFE in GB-E composites. Grphite prticles filled GB-E composite showed the highest improvement in flexurl strength from ll the smples. The incresed flexurl properties signify tht grphite prticles were homogeneously dispersed in the epoxy mtrix. Tle 2 shows tht ILSS of GB-E composite is higher thn tht of pure glss nd slt fier reinforced composites. This confirms tht good ond exists etween the two different fiers nd epoxy resin. Further with the incorportion of grphite prticles in GB-E composite increses the ILSS, ut in contrst decrese in ILSS hs een oserved with increse in PTFE prticles. It shows the etter grphite prticles dispersion in the epoxy mtrix. From mong the smples, GB-E+2Gr showed the est result in the improvement of ILSS Wer Anlysis Figures 3 nd 4 show the wer volume s function of sliding distnce for unfilled GB-E nd Gr nd PTFE filled GB-E composites t different lods. Figure 5 is histogrm showing specific wer rte (Ko) of unfilled GB-E nd Gr nd PTFE filled GB-E composites t higher lod. The wer dt revel tht the wer volume tends to increse ner linerly with incresing sliding distnce nd strongly depends on the pplied lod for ll the composites tested. It ws oserved tht the wer performnce is improved for GB-E composite due inclusion of fillers nmely Gr nd PTFE. However, the wer performnce of PTFE filled GB-E composite showed higher sliding wer resistnce. Among the composites studied, the wer resistnce trend occurred in the order: PTFE-GB-E > Gr-GB-E > GB E for two different lods of 10 nd 20 N. The vritions in Figure 3: Wer volume loss of unfilled nd grphite filled GB-E smples t () 10 N nd () 20 N. Figure 4: Wer volume loss of unfilled nd polytetrfluoroethylene filled GB-E smples t () 10 N nd () 20 N. Figure 5: Vrition in specific wer rte ginst sliding distnce of unfilled GB-E nd filled GB-E composites t 20 N. 110

5 the specific wer rte with sliding distnce t 20 N lod re shown in Figure 5 nd, respectively. The specific wer rte decreses with incresing sliding distnce ut increses with increse in pplied lod. The results reveled higher sliding nture of GB-E composite compred to prticulte filled GB-E specimens. The phenomenon of decrese in specific wer rte is due to the nture of microprticles used. In this study, GB-E composite ws fricted y hnd ly-up technique followed y compression molding chrcterized y the resin rich top lyer. Sliding wer tests were performed on s cst surfce of the composite without disturing its originl surfce. Thus, in the initil stge of sliding, mtrix is in contct with steel disc nd hs less hrdness compred to tht of hrdened steel, resulting in severe mtrix dmge nd the rte of mteril removl is very high. Similrly, when glss nd slt fiers re in contct with steel disc i-directionl fiers provide etter resistnce to the process of sliding. For the purpose of comprison, the specific wer rte of ll the smples hs een shown in Figure 5 nd. It is seen tht the specific wer rte for ll the smples is high t lower sliding distnce nd low for higher sliding distnce. This is ttriuted to the fct tht t lower sliding distnce low modulus mtrix ws exposed nd t higher sliding distnce high modulus fier ws exposed to wer. These exposed fiers, ecuse of their high hrdness vlues, provide etter resistnce ginst the sliding. Thus, the rte t which the mteril is removed with respect to the sliding distnce decreses. Higher wer volume ws noticed for GB-E composites compred to prticulte filled GB-E composites. This is ecuse the hrd cermic prticles hve high specific modulus compred to glss nd slt fier nd possesses higher hrdness. The fillers such s Gr nd PTFE ws oserved to e eneficil to wer performnce nd 4wt.% PTFE filler filled GB-E composites shows etter wer resistnce compred to unfilled nd filled GB-E composites t two different lods Frctogrphy The scnning electron microscopy (SEM) microgrphs in Figure 6 nd nd Figure 7 nd showed the tensile frctured surfce of GB-E nd GB-E+2Gr composite systems, respectively. The frcture is due to delmintion etween the lyers of the composite smples nd fier-pull out (Figure 6). The SEM microgrph shown in Figure 6 indictes rittle frcture filure mechnism ecuse s evident from the clen fiers on frctured surfces. Other importnt filure mechnisms of composites such s fier frcture nd fier-mtrix deonding re lso oserved in SEM microgrph (Figure 6). SEM chrcteriztion of the GB-E+2Gr frctured surfce (Figure 7 nd ) confirmed the presence of grphite prticles on the surfce of slt nd in the epoxy mtrix showing the elementl components of grphite. This is qulittive indiction of greter interfcil strength etween the fier filler nd the mtrix (Figure 7). 4. CONCLUSIONS Some importnt conclusions of this investigtion re: The incorportion of micron-sized fillers improves the mechnicl properties such s tensile strength/ modulus nd flexurl strength/modulus of GB-E composite. The improvement is more pronounced with the comined ddition of grphite microfiller into the GB-E system The improved results re otined with 2 wt.% nd 6 wt.% of grphite filler loding in respect of tensile nd flexurl properties of GB-E composites. The tensile nd flexurl strengths show n increse of 5%, nd 35%, respectively Figure 6: Scnning electron microscopy imges of tensile frctured surfce of GB-E smples: () At 50 mgnifiction; nd () At 2000 mgnifiction. Figure 7: Scnning electron microscopy imges of tensile frctured surfce of GB-E+2Gr smples: () At 50 mgnifiction; nd () At 2000 mgnifiction. 111

6 s compred to unfilled GB-E composite. The enhncements in mechnicl properties re ttriuted to the good dispersion of prticultes in the epoxy mtrix which led to high surfce re for strong interfcil onding, nd etter lod ering from hyrid fiers Specific wer rte incresed with pplied lod t lower rding distnce nd decresed with incresing rding distnce. PTFE filled GB-E composite showed etter wer resistnce s compred to tht of unfilled GB-E nd Gr filled GB-E composites The wer volume ws less in the composite mteril with 4% PTFE filler s compred to tht of grphite. Higher specific wer resistnce (30%) ws noticed for PTFE-GB-E composite thn GB-E composite, due to high strength nd good luricting chrcteristics of filler. 5. REFERENCES 1. L. Chng, Z. Zhng, L. Ye, K. Friedrich, (2007) Triologicl properties of epoxy nnocomposites III chrcteristics of trnsfer films, Wer, 262: W. G. Stchowik, W. A. Btchelor, (2005) Engineering Triology, 3 rd ed. Amsterdm, Boston: Elsevier, p J. Sim, C. Prk, D. Y. Moon, (2005) Chrcteristic of slt fire s strengthening mteril for concrete structures, Composites Prt B: Engineering, 36(6-7): S. Crmignto, I. M. De Ros, F. Srsini, M. Vlente, (2009) Chrcteristion of slt fire reinforced vinylpolyester composite: An overview. In: Proceedings of 2 nd Interntionl Conference on Innovtive Nturl Fire Composites for Industril Applictions, Rome. 5. A. N. Liskovski, Y. L. Tsyuly, A. A. Medvedyev, (2001) Yrns of slt continuous fiers. In: Proceedings of the Fier Society, Rleigh, NC, USA. 6. J. M. Prk, W. G. Shin, D. J. Yoon, (1999) A study of interfcil spects of epoxy-sed composites reinforced with dul slt nd SiC fiers y mens of the frgmenttion nd coustic emission techniques, Composites Science nd Technology, 59(3): S. Mtko, P. Ann, G. Mrosi, A. Szep, S. Keszei, T. Czigny, K. Posloskei, (2003) Use of rective surfctnts in slt fier reinforced polypropylene composites, Mcromoleculr Symposi, 202: T. Czigány, (2005) Bslt fier reinforced hyrid polymer composites. Mterils Science Forum, : T. Czigány, J. Vd, K. Pölöskei, (2005) Bslt fier s reinforcement of polymer composites, Period Polytechnic Mechnicl Engineering, 49: S. Öztürk, (2005) The effect of fire content on the mechnicl properties of hemp nd slt fire reinforced phenol formldehyde composites, Journl of Mterils Science, 40: T. Czigány, K. Pölöskei, J. K. Kocsis, (2005) Frcture nd filure ehvior of slt fier mt-reinforced vinylester/epoxy hyrid resins s function of resin composition nd fier surfce tretment, Journl of Mterils Science, 40: W. Mingcho, Z. Zuogung, L. Yuin, L. Min, S. Zhijie, (2008) Chemicl durility nd mechnicl properties of lkli-proof slt fier nd its reinforced epoxy composites, Journl of Reinforced Plstics nd Composites, 27: V. Fiore, G. Di Bell, A. Vlenz, (2011) Glss-slt/epoxy hyrid composites for mrine pplictions. Mterils Design, 32: I. M. De Ros, F. Mrr, G. Pulci, C. Sntulli, F. Srsini, J. Tirillò, M. Vlente, (2011) Postimpct mechnicl chrcteristion of E-glss/ slt woven fric interply hyrid lmintes, Express Polymer Letters, 5(5): G. Zhng, H. Lio, H. Li, C. Mteus, J. M. Bordes, C. Coddet, (2006) On dry sliding friction nd wer ehvior of PEEK nd PEEK/ SiC-composite cotings, Wer, 260: B. Suresh, G. Chndrmohn, Siddrmih, P. Smpthkumrn, S. Seethrmu, (2007) Threeody rsive wer ehviour of cron nd glss fier reinforced epoxy composites, Mterils Science nd Engineering: A, 443: T. Wittek, T. Tnimoto, (2008) Mechnicl properties nd fire retrdncy of idirectionl reinforced composite sed on iodegrdle strch resin nd slt fires, Express Polymer Letters, 2:

7 *Biliogrphicl Sketch Mr. B. S. Knthrju otined his chelor degree in Mechnicl Engineering nd Mster Degree in Mechnicl Engineering specilized in product design nd mnufcturing from Visvesvry technologicl University (VTU) in the yer 2009 nd 2011 respectively. Presently he is working s Assistnt Professor in Mechnicl Engineering for Don Bosco Institute of Technology, Bnglore, ffilited to VTU, Belgvi, Krntk, Indi. Further, he is pursuing his PhD Degree under Visvesvry technologicl University (VTU), Belgvi, Krntk in the field of polymer composites. Dr B Suresh is Professor of the Deprtment of Mechnicl Engineering, The Ntionl Institute of Engineering, Mysuru since 1990 nd is currently the Den, Reserch & Development, Hed, Centre for Composite Mterils Reserch. He otined Diplom (1983) in ME from CPC Polytechnic, nd otined his B.E from NIE, Mysuru (1987) ffilited to UoM Mysuru, M. Tech in Mchine Dynmics (1995) from IIT Mdrs nd PhD (2007) from PSG College of Technology, ffilited to Ann University, Chenni. Reserch Interest includes Mterils science, Microstructure-property reltionships, Light weight PMCs, Nturl fiers -Composites, Frcture toughness, Wer, Arsion, Erosion, Mnufcturing Techniques-High Performnce Composites, Design with Composites, Nnocomposites. 113