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1022010116711815(2010)220546204ScienceTechnologyandEngineeringVol110No12Jan12010Z2010Sci1Tech1Engng16(,266071),,,6,33%50%TQ327;A2009106Nylonisthemostpopularengineeringplasticsjustinvirtueoftheattractiveproperties.Carbonfiber2rein2forcedcomposite(CFRP)isakindofhighperformancematerialusedinhigh2technologyfields,suchastheaerospaceandautomobileindustries,aswellasinsportinggoods.Shortcarbonfiber2reinforcedpolymerexpandstheapplicationinvariousengineeringfieldtoformaveryimportantclassoftribo2materials.Despiteitslowermechanicalpropertiesincomparisonwithcon2tinuousfiber2reinforcedpolymers,shortcarbonfiber2reinforcedthermoplasticsisveryattractiveowingtotheiradvantagesofeasyfabrication,economyandbet2termechanicalpropertiescomparedwithpurepoly2mers[1,2].Fiber2matrixadhesionisveryimportantforme2chanicalpropertiesofCFRP.Itiswellacceptedthattheadhesioncanbeenhancedbysurfacetreatmentofcarbonfiber.Inordertoachievethepurpose,lotsofmethodshavebeendeveloped,suchasoxidation,coat2ing,andgraftingreaction.Generally,oxidationisabettermethodoftreatment.Itmayetchfibersurfacesandgeneratehydroxylandcarbonylgroups,whichmayreacteasilywithmatrices,andincreasethesurfaceen2ergy.Theoxidationmethodsusedforcarbonfibersur2facesincludeoxidationinvariousplasma[3,4],gas2phaseoxidation[5,6],anodization[79],electrochemicaloxida2tioninvariouselectrolytes[10,11],gamma2rayorneutronradion[12]andwetchemicalmethods[13]suchasboilinginsulfuricacid,phosphoricacid,ornitricacid,etc.Inthestudy,inordertomanufactureCFRPcon2tinuously,CFRPwerepreparedbytwin2screwextru2der.WeresearchintotheeffectofnitricacidontheCFbySEMphotographandtheeffectofCFoncrystalliza2tionperformanceofCFRPbyDSCcurve.1Experimental1.1MaterialsNylon6resin(PA6)issuppliedbytheChinaPet2rochemicalBaLingCompanyLtd.Thecarbonfiber(CF)issuppliedbyGuangweiCompanyLtd.1.2PreparationofCFCFiscutto5mmeach,andthenthesurfaceistreatedwith65wt%nitricacidin80Cwaterbathfor2h.Finallythefibersarewashedwithdistilledwater2,:6toeliminatetheexcessofreagents.1.3PreparationofsamplesbyextrudeDriedPA6isfirstmixedwiththeshort2cutCF.Theblendswith5wt%CFcontentarethenfedintotheextruderundertherequiredconditions,afterwardsarepelletized.Finallythedriedpelletswereinjectedintostandardsamples.1.4CharacterizationTensilestressandtensilemodulusaremeasuredac2cordingtoISO11841983usinganelectronictensiletester.NotchedimpactstrengthismeasuredaccordingtoISO1791982.surfacemorphologyareexaminedwithaSEM(JSM6390LV)ofJapaneseJeolCompa2nyrunningatanacceleratingvoltageof20kV.2Resultsanddiscussion2.1Surfacemorphologyanalysisofsinglecarbonfiber(a)untreated(b)treatedbynitricacid2oxidationFigure1surfacemorphologyofcarbonfiberFigure1showstheSEMphotographofsurfaceofuntreatedCFandnitricacid2oxidationtreatedCF.Itcanbeseenthatsurfaceofnitricacid2oxidationtreatedCFhasmorelegiblegroovesthanthatofuntreatedcar2bonfiber,whichisprobableduetonitricacidscorro2siononcarbonfiber.Therefore,itistobeexpectedthatnitricacidcanleadtothemicroetchcrackforma2tiononcarbonfibersurfacewhichenhancessurfaceroughnessresultinginimprovedmechanicalpropertiesofthecomposites[6].Thesemicroetchformationscananchormatrixandenchancecarbonfiber2matrixinterfa2cialstrength.2.2Fracturesurfacemorphologyanalysisofsample(a)(b)Figure2fracturesurfacemorphologyoftreatedcarbonfiberreinforcedpolymer(T2CFRP)ofsample.(atdif2fentmagnificationlevels)carbonfiber.Infigure2(a),itcantbeobservedthepullouteffectofcarbonfiber.Itindicatesthatfiber2matrixdebondingissupressed,whichotherwisewouldinduceprematureaccumulationofdamageleadingtofailure.74510Intherepresentativeimage(figure2(b))ofthebreakageregion,itispossibletoclearlyobservethereisamoreamountofadherentpolymeronthesurfaceofcarbonfiber.Thesesuggestthegoodmatrix2carbonfi2beradhesionandtheadhesivesuccessintheinterfacewhencarbonfiberisfractured.ItcanmakeCFeffec2tivelyundertaketensilestresswhencompositegotten2silestressandenhancemechanicalpropertiesofPA6matrix.2.3Mechanicalpropertiesofpureresinandcompos2iteTable1PhysicalpropertyofpureresinandcompositePropertyC1C2C3Tensilestrength/MPa66.274.278.4Tensilemodulus/MPa159119442472Notchedimpactstrength/kJm-212.814.816.9Yieldelongation/%13.38.114.95C1:purenylon6.C2:5wt%untreatedcarbonfiberreinforcednylon6composite.C3:5wt%treatedcarbonfiberreinforcednylon6composite.Intable1,itcanbeseenthatmechanicalporper2tiesofCFRP,comparedwiththatofC1,isobviouslyin2creased,while,mechanicalpropertiesofC3isbetterthanthatofC2.Especially,tensilemodulsofC3boostscomparedwiththatofC2by33%andpurePA6by50%.Itisexplainedthatcarbonfibercanwellworkedintakingonstressincomposite,moreover,treatedcar2bonfiberworkedbetterthanuntreatedcarbonfiberintakingonstressincomposite.Consequently,itillustra2tedthattreatingcarbonfiberbynitricacidcanbetterenhancedmechaniaclporpertiesofCFRP.3Conclusions(1)Nitricacidcaneffectivelychangsurfacemor2phologyofCFandenchancsurfaceroughness.(2)CFtreatedbynitricacidcomparedwithun2treatedCFmayhavebetterinterfacebondingwithPA6matrix.(3)tensilestrengthandtensilemoudleofcompos2iteareenhancedby33%and50%respectively.References1BijweJ,I