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//-->.pos {position:absolute; z-index: 0; left: 0px; top: 0px;}Conductive eco-polymer composites: wearbehaviour of recycled polycarbonate/crushedrubber microparticlesR. Autay1, K. Elleuch1, K. Zribi2,3and J.-F. Feller*3Following an eco-design approach we have investigated the possible formulation of conductivepolymer composite (CPC) from recycled poly(carbonate) (PC) and crushed rubber microparticles(CR) for tribological applications. Particularly, the abrasive wear behaviour of CPC has beenstudied as a function of smooth surface treatments applied to rubber fillers to improve theiradhesion with the PC matrix. The effects of normal load, sliding velocity and treatments applied toCR on the wear rate and kinetics were investigated. Pin-on-disc tests carried out under waterlubrication show that the wear rate increases with the increase in load and sliding velocity.Moreover, among all surface treatments, the most effective to improve the interface quality andthus wear resistance was a stripping of rubber microparticles with methanol whereas flaming wasassumed to degrade filler surface and dichloromethane to swell the matrix. Additionally wearexperiments proved to be effective in evaluating the quality of PC/CR interface.Keywords:CPC, Abrasive wear, Wear rate, Kinetics of wear, Recycling, Eco-designIntroductionOwing to environmental issues it is a main concern touse plastics and composites having the lowest impact onnature as possible according to eco-design rules.1In fact,analysing the life cycle of such materials evidences thatthe use of recycled polymers in composite formulationsallows us to get rid of one of the most impacting step, i.e.polymerisation. Nevertheless, recycled polymers oftenhave degraded properties compared to their virginhomologues as their first processing quite systematicallycauses macromolecular chains breakage and conse-quently molar mass decrease.2Thus, two differentstrategies can be envisaged to reuse such engineeringpolymer wastes: target the same kind of application butthis requires regeneration by addition of a couplingagent or a chain extender to enhance mechanicalproperties, or find a new application that will be lessexigent from this point of view.3–6Electrically conduc-tive polymer composites (CPCs) obtained by blendingan insulating polymer matrix with conductive fillerslike carbon nanoparticles,7–13carbon micro andnanofibres11,14–17or metal micro and nanoparticles18,19give a good example of applications which do not needexceptional mechanical properties; on the other hand,Unit of Research Industrial Chemistry & Materials, National School ofEngineers, Sfax, Tunisia2Laboratory of Water, Energy & Environment, National School ofEngineers, Sfax, Tunisia3Smart Plastics Group, European University of Brittany (UEB), LIMATB-UBS, Lorient, France*Correspondingauthor, email jean-francois.feller@univ-ubs.fr1these materials have been studied by many groups fortheir smart functionalities.9,18,20,21In fact, they exhibitseveral interesting features due to their resistivity vari-ation with thermal,22–24mechanical12,25or chemicalsolicitations.23,24,26,27This versatility of CPC is used for‘intelligent’ applications such as self-regulated heatingapplications such as shielding,28,29switching11,19,23orvapour sensors.14,18,26,27Some of the last evolutions in the CPC field concernthe use of exclusion volumes to decrease the percol-ation threshold and control conductive pathwaysstructuring.30–34In a recent study, it was shown that CPCobtained by dispersing crushed tire rubber microparticlesinto recycled poly(carbonate) matrix (PC/CR) had veryattractive properties for smart applications24owing to theirsensitivity to environmental changes like temperature andvapour atmosphere. Nevertheless, it was also found thatthe development of these composites required taking careof the quality of PC/CR interface to prevent anydeterioration of their mechanical properties both at micro35and macro36scales. Among all different strategies experi-mented to improve adhesion between rubber fillers and PCmatrix solvent washing appeared to better than flaming andcoupling agents.37This was explained by a double effect ofsolvent: first a removal of oil and dust from particlessurface, and second a desorption of low molar masselastomer molecules from the reticulated network whichcould act as compatibilising agent. To go further intointerface characterisation and understanding of adhesionbetween filler and matrix, we have investigated wearproperties of PC/CR eco-composites.In fact, abrasive wear behaviour of polymer compo-sites has attracted lots of scientists due to its simpleßInstitute of Materials, Minerals and Mining 2011Published by Maney on behalf of the InstituteReceived 29 June 2010; accepted 30 October 2010DOI 10.1179/1743289811X12988633927952Plastics, Rubber and Composites2011VOL40NO3139Autay et al.Wear behaviour of conductive eco-polymer compositesapproach and ability to study surface characteristics insevere friction conditions in relation with the differentmechanical characteristics of the material.38–42Manymodels, which attempted to relate the abrasive wearresistance of polymers to other mechanical properties,have been examined43–45and it was shown that the wearbehaviour14,46differed depending upon the polymertype.Numerous studies have been carried out to investigatethe influence of test conditions on wear properties.47–58Some authors observed a decrease in wear rate withincreasing load in a number of materials and it wasassociated to the formation of ridges within the wearscar.46Others showed that its value will increase when theload increases to the limit load value because of thecritical surface energy of the polymer.59The effect ofsliding speed and load, on the friction and wear of glass-fibre-reinforced poly(ether imide), (20%) composite hasbeen studied,38it was reported that no unique trendbetween wear rate and speed can be expected. The sameauthors showed that the friction coefficient of unfilledPEI and PEI/PTFE composite decreased with increasingload; however, in the case of glass-fibre-reinforced PEI,the effect of load on wear differed with counterfaceroughness and no clear trend emerged. Liuet al.41reported that load is the most important factor in thewear of unfilled UHMWPE specimens; however, for thewear of filler reinforced UHMWPE composites, the roleof the load abates and the role of abrasive particle sizeincreases with the increase in filler particle size. On theother hand, sliding speed seems to have little effect on thetotal wear volume. Abrasive wear studies60of poly(arylether ketone) PAEK and their composites, against siliconcarbide (SiC) abrasive paper, showed that wear volumeincreases with the increase in load and sliding distance.Liuet al.61observed that wear loss of PA and UHMWPEblend is higher under dry-sliding conditions thanlubricated test conditions, and increases with load in-crease. Li and Bell,62showed that the mechanicalproperties and wear resistance of UHMWPE can beimproved by surface treatment with the active screenplasma nitriding technique. Zhanget al.63reported thattribological behaviour of plasma-treated PEEK and itscomposites was improved. Indumathiet al.64found thatcomparison of wear rates of treated and untreatedsamples under various loads revealed that cryo-treatmenttechnique has potential to increase the wear resistance ofsome polymers and their composites. Finally, Blanchetand Peng65reported that wear resistance of fluorinatedethylene propylene can be increased through electronirradiation treatment.The present paper investigates the ability of tribologicalexperiments to discriminate between different treatmentsapplied to crushed rubber microparticles to improve theiradhesion with a poly(carbonate) matrix. Additionally, it isof interest to produce information on wear behaviour,under variable normal load and sliding velocity, of suchnew polymer composites having low impact on environ-ment which proved to be suitable for smart applications.panel cuttings by Self-Signal company (derived fromMakrolon 3103 commercial grade of Bayer company)and of crushed tire rubber particles (CRs) from Delta-Gom company. PC wastes were just ground at roomtemperature to obtain millimetric pellets without anyadditional treatment whereas rubber millimetric particleswere milled in liquid nitrogen to reduce their diameterrange down to 140mm,w,315 mmafter sieving. The finemicrometric CR particles were then melt-mixed withmillimetric PC crushed pellets. The density of CRmeasured with a pycnometre wasd50?840.Two typesof surface treatments were carried out:(i) firstly, a flame treatment proceeded to oxidise theCR surface and obtain satisfactory level ofadhesion with poly(carbonate). This treatmentwas performed with a propane blowtorch. Theflame temperature was about 800uC and particleswere flamed during 1 min at a distance of20 cm.(ii) Second, a solvent washing with dichloromethaneor methanol was done to eliminate oil residues.Particles were dispersed in solution under sonica-tion and stirred at room temperature for 25 min.Then the particles were filtered and dried undervacuum at 40uC for 30 min to remove remainingsolvent.Main properties of PC can be found in Table 1,additional data concerning recycled polymers are givenelsewhere.1,24,35,36Blend processingPC/CR blends were melt-mixed in a BRABENDER 50EHT internal mixer with contra rotating blades drivenby WINMIX software. Polymers were dried undervacuum for 24 h at 90uC before processing. PC matrixand CR particles were mixed with a rotor speed ofV540rev min21at a temperature ofT5240uCfor10 min. These optimised blending conditions alloweda good dispersion of CR into PC. Just after mixing,blends were hot pressedTmould.5240uC,pmould.550bar,tmould.55min to provide 4 mm thick plates which werecooled down to room temperature in approximately15 min. Normalised samples of 10610 mm were cut outof plates with a small numerical milling machine. Theformulations used in this study were composed of 80%PC/20% untreated CR, 80% PC/20% flame treated CR,80% rPC/20% solvent treated CR.Wear testsAbrasion tests were conducted by the use of aMETKON Instruments machine that simulates a pin-on-disc configuration. The schematic illustration of thewear test apparatus is shown in Fig. 1 and describedelsewhere.61,60,66During abrasion experiments, polymersamples with dimensions of 1061064 mm wereTable 1 Characteristics(carbonate)ofvirginandvPCGlass transition temperatureTg/uCYoung modulusE/GPaStrain at breaker/%Stress at breaksr/MPaThermal conductivityl/Wm21K21Density (at 23uC)d1482.310065–700.211.2recycledrPC1491.95572……polyExperimentalMaterialsThe material used in this study is a blend of poly(carbonate) engineering wastes (rPC) from signalisation140Plastics, Rubber and Composites2011VOL40NO3Autay et al.Wear behaviour of conductive eco-polymer composites1 Pin-on-disc wear test configuration2 Evolution of wear rate with normal loadabraded against waterproof (grit grade 600) SiC paper,fixed on the rotating disc surface. The tests were carriedout at ambient temperature under water lubricatingcondition. A constant lubricant flow was used in orderto avoid rip of the abrasive paper especially in thebeginning of the wear test. Samples were brought intocontact with abrasive paper under constant normal load.The abrasive paper was changed before each test. Wearrate, computed from weight loss of sample and averagedon three separate tests, was measured at different timesby stopping the test. The wear rate (%) is calculated byequation (1)T~m{mtm(1)to sliding distance through equation (2)). These results arein agreement with those found by Shipway and Ngao46forpoly(methyl methacrylate) samples2pRvt(2)60whereR55cm,tis the time (s) andvis the rotation speed(rev min21).The application of a normal load of 40 N generates asignificant increase in the wear rate compared to aloading of 20 and 10 N; this evolution can be explainedby the heavy damage of PC matrix by ploughing andcutting action of abrasive particles at higher load. It wasnoticed that curves do not start from zero, then twoslopes are distinguished: the one with higher value,indicating a maximum speed of wear, located in theinterval of time (0–1 min) and the other lower value(thus a low wear speed) spread out over the remainingwear time. This phenomenon can be explained by thefact that the first contact of the material with virginabrasive paper (Fig. 3a) will generate necessarily amaximum tearing off of the material during the firstminute, then the active surface of the paper will becovered by an adherent layer (formed by wear debris,the area outlined in Fig. 3b) whose thickness increaseswith wear time. Moreover, most grains lose theirsharpness by crushing, some of them being torn off.This supports the reduction of wear speed and explainsthe decrease in wear kinetics with wear time, whateverthe loading.Figure 4 illustrates the effect of sliding velocity on thewear rate of CPC with untreated CR. It shows a linearincrease in wear rate with the increase in sliding velocityand a decrease in the kinetics of wear is noticed, in thecourse of the wear time, for all speeds. It should benoted that the heat accumulated in the wear processcauses thermal softening of the polymer, and repeatedsliding causes massive tearing and rupture of the surfacelayer. Indeed, the variation of the wear rate is moremarked for high sliding velocity values (220 or270 rev min21), which is in agreement with the resultsfound by Wang and Sliding54describing the effect ofsliding velocity on wear loss.d~wheremandmtare respectively mass of the samplebefore and after a timetof wear.An electronic scale with an accuracy of 1023g wasused to weigh samples. The abrasive wear test conditionsare detailed in Table 2.Microstructure characterisationMicrostructures of worn surfaces, for the various CPCs,were observed with different microscopes. Scanningelectronic microscopy observations were performed witha JEOL JSM-6031 after fracture of samples in liquidnitrogen and spray deposition onto the surface of a thingold layer. A LEICA DMLP optical microscope withLIDA software in episcopy mode and non-polarisedlight was used to observe worn surfaces of both paperand composite.Results and discussionEffect of test conditions on wear propertiesThe effect of normal load on wear rate of a CPC withuntreated CR is shown in Fig. 2. It can be seen that thewear rate increases linearly with sliding time (proportionalTable 2 Experimental conditions for abrasive wear testsLoad/NSliding velocity of disc/rev min21Sliding velocity of disc/m s21Testing time/minTesting length/mLubricant flowrate/m3s21Abrasive paper roughnessRa/mmAbrasive paper grit grade5, 10, 20, 4050, 170, 220, 2700.26, 0.89, 1.15, 1.411 to 615.7 to 508.92.166102530600Effect of CR treatment on CPC wear behaviourPreliminary tests were carried out under 5 N and50 rev min21(mild conditions) for four CPC onlydiffering by CR particles treatment.Plastics, Rubber and Composites2011VOL40NO3141Autay et al.Wear behaviour of conductive eco-polymer composites3anon-worn andbworn surface of abrasive paper (2006)4 Wear rate as a function of sliding velocity of abrasivedisc5 Wear rate of CPC as a function of type of appliedtreatmentAs shown in Fig. 5, the CPC with CR washed byCH2Cl2wears very quickly (wear rate equals to 100% atthe end of less than 2 min) and it presents the highestkinetics of wear. This fast degradation of the materialcan be explained by the absence of the adherent layerformed by wear debris on the counter face, unlike otherCPCs, which leads to the specimen being directly incontact with a clean abrasive surface; then the mechan-ism of wear changes and the wear loss increasessignificantly. Moreover, it is likely the dichloromethanewashing has partially swollen PC matrix changingsurface roughness and probably also degrading it. Thefast degradation of the CPC with CR washed by CH2Cl2makes the study reserved exclusively for the CPC thatshowed an abrasion resistance (CPC with CR flamedand washed with methanol).It should be noted that the results found for theevolution of wear properties with test conditions in thecase of the CPC with CR flamed or washed by methanolare similar to those found for CPC with untreated CR.Thus it can be concluded that 5 N load only makes itpossible to evidence the effect of washing solvent but notto compare the influence of other treatments.Figures 6 and 7 show that the CPC with flamed CRhas the lowest resistance to abrasive wear. However, theCPC with CR washed with methanol has always thelowest wear rate. It should be noted that washing withmethanol eliminates the residues of grease and any traceof moisture being able to generate chains breakage byhydrolysis for example or appearance of air bubbles inthe composite. This treatment was also found toimprove adhesion between PC and CR in another6 Wear rate of CPC as a function of applied treatmentunder high speedstudy,36in the same way flaming contributes althoughless importantly to the improvement of the interfacequality. Scanning electron and optical micrographs ofabraded surfaces under 10 N load and 50 rev min21sliding velocity (Figs. 8 and 9) show the presence ofporosities or internal cavities due probably to theimprisonment of air bubbles in the mixture and thepresence of a phenomenon of wrenching of CR particleswhich proves that treatments have no significantinfluence on the reduction of these phenomena. Inaddition, deep furrows in the abrading direction due tothe ploughing action by sharp abrasive particles areillustrated. It is pointed out that the furrows appear onlyunder severe tribological conditions and they arecharacteristics of abrasive wear.Figure 10 represents the evolution of the wear rate asa function of the applied loading for wear duration of142Plastics, Rubber and Composites2011VOL40NO3Autay et al.Wear behaviour of conductive eco-polymer composites7 Wear rate of CPC as a function of applied treatmentunder high load6 min. It is noted that the wear rate of various materialsmakes a remarkable jump at a loading of 40 N and moreparticularly the wear rate of CPC with flamed CRincreased more than those of others. Moreover, thecurves of kinetics of wear for the various materials(Fig. 11) show an abrupt increase in the kinetics of wearof the CPC with flamed CR while passing to a loading of40 N. The low wear resistance of flamed CR filled CPCis thought to result from its higher rigidity, i.e. Youngmodulus determined by tensile tests.36In fact, hetero-geneous materials with high rigidity can less easilyaccommodate slip, which will weaken their wearresistance. Additionally nanoindentation tests haveshown that CPC filled with flamed CR presented theaCPC with untreated CR;bCPC with CR washed withmethanol;cCPC with flamed CR9 Scanning electron micrograph of surfaces of wear afterwear test under 10 N load and 50 rev min21slidingvelocity (6200)lowest hardness and the weakest resistance to diamondindenter depression, which can be compared to theaction of silica grains on paper surface during weartests.35As the abrasive wear resistance is an increasinglinear function of the material’s hardness,67the wearrate increase was considered to be acceptable for flamedCR CPC, and then mechanical and wear rate results arein good agreement.ConclusionIn this study, wear experiments have been carried out(with a pin-on-disc test under water lubrication) toinvestigate the tribological behaviour of CPC obtainedaCPC with untreated CR;bCPC with CR washed withmethanol;cCPC with flamed CR8 Optical micrograph of surfaces of wear after wear testunder 10 N load and 50 rev min21sliding velocity(6200)10 Wear rate of CPC as a function of applied treatmentfort56min (V550 rev min21)Plastics, Rubber and Composites2011VOL40NO3143zanotowane.pl doc.pisz.pl pdf.pisz.pl hannaeva.xlx.pl