Influence of silaned nano SiO2 on impact properties of carbon fiber.docx
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Influence of silaned nano SiO2 on impact properties of carbon fiber.docx
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InfluenceofsilanednanoSiO2onimpactpropertiesofcarbonfiber
InfluenceofsilanednanoSiO2onimpactpropertiesofcarbonfiberreinforcedpolyethylenecomposites
RongLiu
SchoolofMechanical&ElectronicEngineering,HainanUniversity,Hainan878805,P.R.China
Abstract
SilanednanoSiO2wasusedtoimprovetheadhesionpropertiesofcarbonfiber/polyethylene(CF/PE)composites.ThenanoSiO2weretreatedbysilaneunderdifferentdischargetime.Andthechangesonthesurfacepropertiesofthetreatedanduntreatedcompositeswerestudiedbyimpact,threepointbendingtestsandscanningelectronmicroscope(SEM)analysis.ThemeasurementshowedthatCFincreasesfracturetoughnesswiththeincreaseofCFcontent.WhiletoomuchhighcontentofCFdidnotfurthercausetheincreaseofthetoughnessofCF/PEcomposite.Theimpactstrengthofsilanedspecimensisstillhigherthanthoseoftheunsilanedones.Themodifiedcompositewiththegoodmatrix/fiberadhesionpossessed20%higherinterlaminarshearstrengthscomparedtothecompositehavingweakinterface.
Keywords:
SiO2;CF/PE;toughness
1.Introduction
Duringthelastdecade,considerableattentionwaspaidtoinorganic–organichybridmaterialsbecausetheirsolidstatepropertiescouldbetailoredinrelationtothenatureandrelativecontentoftheirconstitutivecomponents.Low-volumeadditions(1–5wt.%)ofhighlyanisotropicnanoparticles,suchaslayeredsilicates,providepropertyenhancementwithrespecttotheneatpolymerthatarecomparabletothoseachievedbyconventionalloadings(15–40wt.%)oftraditionalfillers.Besides,uniquevalueaddedpropertiesnotnormallypossiblewithtraditionalfillersarealsoobserved,suchasenhancedstrength,electricalconductivity,electrostaticdischarge,remote-actuatedshaperecoveryandablationresistance[1-3].
Inotherpublications,fracturetoughnesswasimprovedbyaddingsphericalnanoparticlesinwhichqualitynano-dispersioniseasiertoachieve[4,5].Filler/matrixinteractionandachievingqualitydispersionseemtobethekeyfactorsforfracturetoughnessenhancementfornano-scalefillers.
Oneofthemajorconcernsindesigningcompositestructuresistheirsusceptibilitytoimpactloading.Fiber-reinforcedpolymer-matrixcompositesareknowntobehighlysusceptibletointernaldamagecausedbytransverseloads,evenunderlow-velocityimpacts[6,7].Thecompositescanbedamagedonthesurfaceaswellasbeneaththesurfacewithrelativelylightimpactscausingbarely-visibleimpactdamage,whilethesurfacemayappeartobeundamagedtovisualinspection.Fortheeffectiveuseoffiber-reinforcedpolymer-matrixcompositesforhigh-performanceapplications,understandingthecausesfortheformationofsuchdamageunderlow-velocityimpactandimprovingthedamage-resistancecharacteristicsofthecompositesareimportantconsiderationswhichhavebeenthetopicofextensiveresearchforthelastfewyears.Reviewarticlesontheimpactbehaviourofpolymer-matrixcompositescoveringcon-tactlaws,impactdynamics,stressanalysis,damagemechanics,post-impactresidualpropertycharacterizationanddamage-resistanceimprovementsareavailableintheliterature[8,9].Manyresearchpublicationsareavailableontheimpactbehaviourofpolymer-matrixcompositescoveringspecificaspects[10,11].
Matrixdeformationandmicro-cracking,interfacialdebonding,laminasplitting,delamination,fiberbreak-ageandfiberpull-outarethepossiblemodesoffailureincompositessubjectedtoimpactloading.Eventhoughfiberbreakageistheultimatefailuremode,thedamagewouldinitiateintheformofmatrixcracking/laminasplittingandwouldleadtodelamination.Damage-freecompositesarenecessaryfortheireffectiveuse[12].
Inthiswork,SiO2istreatedbysilaneinordertoimprovethesurfacepropertiesofcarbonfiber.ThepurposeofthisworkistostudytheimpactpropertiesofthePEcompositesfilledwithsurfacemodifiedCF.SomeinsightsintotheimpactfracturemechanismsofthePEcompositearealsogiven.
2.Experimental
2.1Materials
Highdensitypolyethylene(HDPE)[Tg:
85℃,Tm:
130℃,p:
0.95gcm-3andMw:
125,000gmol-1],wereallMerck(Germany)productsandusedaspurchased.
Forthepresentinvestigation,thereinforcementmaterialswerecontinuouspolyacrylonitrile(PAN)-basedcarbonfibersmanufacturedbyShanghaisxcarbonTechnologyCo.Ltd.
Thesilane(KH550)wasdissolvedinethanolbeforeuse.Theparticlesofnano-SiO2weredispersedinethanolandsubjectedtoultrasonicagitationfor15min,thesilanesolutionwasthenintroducedandtheultrasonictreatmentcontinuedfor1h.
2.2Compositepreparation
PEsampleswerefirstdissolvedin40mLofxyleneinathreeneckedflask.RequiredamountofCFwasaddedintotheabovesolution.Indolewasalsodissolvedin10mLofxyleneandaddedintothesameflask.Thereactionmixturewaswashedwithdistilledhotwaterseveraltimes,anddriedinavacuumovenat70℃for24h.
2.3Impactandthreepointbending(TPB)tests
ACharpyunnotchedimpactstrengthtestwascarriedoutonapendulumimpacttester(ModelPH125,Amsler&Co.,Schaffhouse,Switzerland)withacapacityof0.98J.Thetestspanwas20mm,measuredbetweenthetwospecimensupports.
Thespecimenswereimpactedonthenarrow1mmsurface,withthelineofimpactmidwaybetweenthesupports,andthedirectionofblownormaltotheplaneofreinforcement.
AnINSTRON4206electromechanicalmachinewasusedtoimplementthethreepointbendingtest.
3.Resultsanddiscussion
3.1impactstrength
Fig.1TheimpactstrengthofCF/PEcompositewithCFcontent
TheresultsoffracturetoughnessmeasurementsareshowninFig1.AsseeninthisFig,CFincreasesfracturetoughnesswiththeincreaseofCFcontent.WhiletoomuchhighcontentofCFdidnotfurthercausetheincreaseofthetoughnessofCF/PEcomposite.BasedontheresultsshowninFig1,itcanbeexpectedthatcompositesmadeusingCFshowimprovedinterlaminarfracturetoughness.
Fig.2TheimpactstrengthofCF/PEcompositefilledwithSiO2withandwithouttreatment
TostudytheeffectofsilanednanoSiO2modificationontoughnessimprovementoffinalcompositeagainstthroughthicknesscracks,theresultsofimpactstrengthversusSiO2contentfornotchedtestspecimensarereportedinFig2.Itisinterestingthatallsamplesfracturedthroughthicknessandincreaseinmodifiercontentledtoincreasedimpactstrength.WhilesimilartypeofimpacttestwasusedtoevaluateimpactstrengthofCFmodifiedPEcomposites,revealednosignificantimprovementinimpactstrengthofthecomposite(Fig1).ThiscanbeattributedtothefactthatthePEusedinthatparticularinvestigationwasnotductileenoughtobetoughenedbyCFmodification.Thisiswhynoobviousimprovementinimpactstrengthofthecompositewasobserved.ThecontributionoffibersinabsorbingtheimpactenergyisnotinfluencedeffectivelybyCFmodification.Inaddition,Fig2showsthatimpactstrengthofsilanedspecimensarestillhigherthanthoseoftheunsilanedones.Themodifiedcompositewiththegoodmatrix/fiberadhesionpossessed20%higherinterlaminarshearstrengthscomparedtothecompositehavingweakinterface.ThereforeonemayconcludethatsilanedSiO2modificationimprovescrackinitiationenergyofthecomposites.
Themechanicalbenefitofthesenanoscalematerialsappearstoincreaseasstressintensitydecreases.Theyarenotcapableofhinderingcrackpropagation(fracturetoughness)onceacrackbeginstoadvance,buttheirnano-scaledimensionsenablethemtobetterinteractwiththematrixbeforeacriticalcrackisinitiated.Inaddition,SiO2maintaintheirhighaspectratiopost-processing.
Thisallowsforadelayincrazeformationandcoalescencepriortocrackinitiation.CFsdonotpresentanaspectratiowhichfavoursastronginteractionwiththematrix,reducingcreepimprovement.Ontheotherhand,thelargersizeoftheCFsallowsthemtoslowthegrowthofthecrackbydeflection,pull-outandcrackbridgingmechanisms.WhenanadvancingcrackispresentedwithaCF,itisdeflectedfollowingtheCF/matrixinterface,eventuallyleadingtothepulloutofthefilament.ThesurfacemodificationwassaidtohelpinexfoliatingagglomerationsandstrengtheningSiO2–matrixinteractions.
TheeffectofSiO2additiononthefailurebehaviorofCF/PEisillustratedbytheSEMmicrographshowninFig.3.Fiberpull-outisstillevidentonthefractureplaneandnoPEmatrixappearstoadheretothefibersurface.TheductilefailureofthePEmatrixchangestoabrittleonethatisassociatedwithsomelimitedcrazing.Thecrazeremnantsonthefracturesurfaceareclearlyvisible.Thus,itcanbeexpectedthat,duringthefractureprocess,theresistancetocrackpropagationwillbereducedmarkedlyandthesamplesfailinamorebrittlemanner.
(a)
(b)
(c)
Fig.3TheimpactfracturemorphologyofCF/SiO2/PEcomposite
Asseen,plasticdeformationsattheplasticzoneofmodifiedresinsareaccompaniedbystresswhitening.ThesizeofstresswhiteningincreaseswithincreasingtheSiO2content;suchthatin5vol%specimen,itexpandstothewholesurfaceinfrontofthecracktip(Fig.3a).ThedifferenceinthedamagezonesizesseeninFig.3isinagreementwithfracturetoughnessdatareportedinFig2.
TheflatandalmostfeaturelessimageseeninFig.3aindicatesthetypicalbrittlefractureofneatPE.Ontheotherhand,theroughfracturesurfaceof3vol%specimenseeninFig.3bshowsthesignificantamountofplasticdeformationoccurredinthismaterialpriortofracture.Itisfoundthatcavitationisaprerequisiteformassivesheardeformationofthematrix.Thelatterisknownasthemainsourceofenergyabs
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