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Alumina-FilledPolystyreneMicro-andNanocompositesPreparedbyMeltMixingwithandWithoutLatexPrecompounding:StructureandPropertiesS.Siengchin,1J.Karger-Kocsis,1R.Thomann21InstituteforCompositeMaterials(InstitutfurVerbundwerkstoffeGmbH),KaiserslauternUniversityofTechnology,ErwinSchrodingerStr.,D-67663Kaiserslautern,Germany2InstitutfurMakromolekulareChemieundFreiburgerMaterialforschungszentrum,Albert-Ludwigs-UniversitatFreiburg,Stefan-Meier-Str.31,D-79104Freiburg,GermanyReceived2December2006;accepted4March2007DOI10.1002/app.26505Publishedonline16May2007inWileyInterScience().ABSTRACT:Aluminallerswereincorporatedinpoly-styrene(PS)in4.5wt%bymeltblendingwithandwith-outlatexprecompounding.Latexprecompoundingwasusedforthelatex-mediatedpredispersionofthealuminaparticles.TherelatedmasterbatchwasproducedbymixingPSlatexwithwaterdispersibleboehmitealuminainvari-ousparticlesizesfollowedbydrying.ThedispersionofthealuminainthePSwasstudiedbytransmissionandscanningelectronmicroscopy(TEMandSEM,respec-tively).ThemechanicalandthermomechanicalpropertiesofthePScompositesweredeterminedinuniaxialtensile,dynamic-mechanicalthermalanalysis(DMTA),andshort-timecreeptestsperformedatvarioustemperatures.Inaddition,themeltowofthecompositeswascharacter-izedinaplate/platerheometer.ItwasfoundthatdirectmeltmixingofthealuminawithPSresultedinmicro-,whereasthemasterbatchtechniqueinnanocomposites.Thestiffnessandresistancetocreep(summarizedinmas-tercurves)ofthenanocompositeswereimprovedcom-paredtothoseofthemicrocomposites.Thepropertiesofthecompositeswereupgradedbydecreasingnominalsizeofthewaterdispersiblealumina.Thepreparationtech-niqueandthesizeofthealuminaparticlesaffectedthetensilestrength,meltviscosity,andheatdistortiontemper-atureinlesserextentthanthestiffnessandthuscompli-ancedata.?2007WileyPeriodicals,Inc.JApplPolymSci105:29632972,2007Keywords:polystyrene;nanocomposite;creep;structure-propertyrelations;thermalproperties;stiffnessINTRODUCTIONNowadays,greateffectsareundertakentoimprovethemechanical,thermal,andotherproperties(e.g.,ameresistance,barrierproperties,electricconduc-tivity)ofpolymersusingllersofvariousshapefac-tors,whichmaybedispersedonnanoscaleintheresultingcomposites.Forthemodicationofpolysty-rene(PS),forexample,metaloxides,1,2organophilicmodiedlayeredsilicates,314andsingleandmulti-wallcarbonnanotubes1517werealreadytried.Itwasrecognizedearlierthatthepreparationtechniqueofthenanocompositeshasastrongimpactonthedis-persionofthenanoparticles.Onedifferentiatesusu-allybetweeninsitupolymerization,meltblending,andsolution/dispersionpreparationtechniques.18Thelattergroupingalsocoversthelatexcompound-ing/latexcoagulationmethods.Majorbenetsofthelatexroutearelistedbelow.Itisnoteworthythatfortheproductionofrubbernanocomposites,thela-texcoagulationisalreadywidelyused.1922Manypolymersareproducedbysuspensionandemulsionpolymerizationsinaqueousmedia.Therelatedsuspension,emulsions,orlatices(forrubbers)canbeeasymodiedwithwaterswellableorwaterdispersi-bleparticles.Waterswellableareforexampleseverallayeredsilicates(montmorillonites,bentonites)bear-ingintergalleryNa1ions.Viahydrationoftheinter-gallerycationsintercalatedandexfoliatedstructurescanbeachieved.Amongthewaterdispersiblecom-merciallyavailablenanollers,aluminashouldbementioned.Toproducenanocompositesusingaque-ousdispersions,slurriesarenotonlyanaffordablemethod(noorganophilicmodicationisneededforthellers)butarealsoassociatedwithreducedhealthhazard.Recallthattheparticlesintroducedareinmicronrangeandbecomenanoscaledonlyintheaqueousmedia.Inthefollow-upsteps(coagulation,dryingetc.),thenanoparticlesareembeddedinthepolymer,whichguaranteeseasyhandlingandmini-mizedhealthrisk.Apartfromrubbers,1922thisla-tex-routeisfollowedforvariouspolymers,includingPS,2328toproducevariousnanocomposites.Thereisafurtherscienticbeautywiththisapproach:itispossibletoproducemicro-andnanocompositesusingCorrespondenceto:J.Karger-Kocsis(kargerivw.uni-kl.de).JournalofAppliedPolymerScience,Vol.105,29632972(2007)VVC2007WileyPeriodicals,Inc.thesamecomponents(e.g.Ref.28).Thisisverystraightforwardtogureoutwhetherananoeffectexistsandwhatisitsinuenceonthematerialper-formance.Waterdispersiblealumina,offeredbythecompanySasol,werealreadyincorporatedinthermoplastics,2931thermosets,32andeveninthermoplasticrubbers,33however,usuallyaftertheirorganophilicmodica-tion.Inpristineform,aluminananoparticlesweredis-persedinpolyurethanerubberthroughlatexcom-pounding.34Notethatthealuminaparticlesremaininaggregates(micron-sized)whenintroducedinpoly-mersbymeltblending.TheaimofthisworkwastoproducePS/aluminamicro-andnanocompositesandtostudytheirprop-erties.Afurtheraimofthisworkwastochecktheeffectofthemeanparticlesizeofthewaterdispersi-blealumina.Microcompositeswereproducedbydirectmeltblending(incorporationofthealuminapowderinthePSmeltduringkneading),whereasnanocompositesbyacombinedmethod.Inthelattercase,thealuminaparticlesweredispersedinanaque-ousPSlatexpriortoitsdryingandincorporationinthePSbymeltblending(referredtomasterbatchtech-nique).EXPERIMENTALMaterialsandpreparationofcompositesTwotypesofwaterdisperableboehmitealumina(Disperal1P2andDispal111N7-80ofSasolGmbH,Hamburg,Germany)servedasllers.Theirspecica-tionsarelistedinTableI.PSlatexwith50wt%drycontent(BaystalSX1160)wassuppliedbyPolymerLatexGmbH(Marl,Germany).GranulatedPS(Poly-styrol158KGlasklar,BASF,Ludwigshafen,Germany)wasutilizedaspolymericmatrixforallcompositesystems.Itsvolumetricmeltowrate(MVRat2008C/5kg)was3cm3/10min.ThePS/aluminananocompositeswerepreparedbytwomethods:(a)directmeltcompoundingand(b)meltcompoundingusingamasterbatchproducedfromPSlatexcontainingaluminaparticle(master-batchtechnique).ThemolecularcharacteristicsofthePSsinlatexandgranulateformswerenotdeter-mined;however,theyweresimilaraccordingtosuppliersinformation.Thealuminacontentinthecorrespondingcompositeswassetfor4.5wt%.Meltmixingoccurredinlaboratorykneader(Type50ofBrabender,Duisburg,Germany)atT51808Candrotorspeedof60rpm.Thealuminapowder(directmethod)oralumina-containingPSmasterbatch(mas-terbatchtechnique)wasintroducedaftermeltmastication(granulates1driedlatex)for2min.Thedurationofthemeltmixingforbothdirectandmas-terbatchtechniqueswas6min.Themasterbatchwasproducedasfollows.First,anaqueousaluminaslurry(10wt%)waspreparedatambienttemperaturethroughmechanicalstirringfor30min.Then,thePSlatexwasintroducedinthisslurryandstirredforfurther30min.Theresultingslurrywaspouredinaframedglassplateanddriedfor48hatroomtemperature(RT)andfor12hat608C.Notethatthisconditiondoesnotproduceavoid-freelmfromPSlatexastheglasstransitiontemperature(Tg)ofPSismuchhigherthanRT.How-ever,avoid-freelmwasnoprerequsiteowingtothesubsequentmeltmixingprocess.Forreferencepur-pose,aPScontaining25wt%PSfromthelatexwasselected.Thiscompositionconsidersthelatex-derivedPScontentofthecomposites.ThecompoundsaftermeltmixingintheBrabenderkneaderwerecompressionmoldedin1-mmthicksheetsatT51808Cusingahotpress(EP-Stanzteil,Wallenhorst,Germany).CharacterizationofthealuminadispersionThedispersionofaluminainthePSmicro-andnano-compositeswasassessedbytransmissionandscan-ningelectronmicroscopy(TEMandSEM,respec-tively).TEMmeasurementswerecarriedoutwithaZeissLEO912Omegatransmissionelectronmicro-scopic(Oberkochen,Germany),applyinganaccelera-tionvoltageof120keV.Thinsections(?50nm)werecutatRTwithaDiatomediamondknifeusinganUltracutEmicrotome(ReichertandJung,Vienna,Austria).ThedispersionstateofthealuminaparticleswasstudiedbySEM,too.Here,thefracturesurfacesofthetensileloadedspecimensweresubjectedtoSEMinspectioninaJSM5400deviceofJeol(Tokyo,Japan).ThesurfacesweregoldcoatedpriortoSEMperformedat25kVaccelerationvoltage.TestingDynamic-mechanicalthermalanalysis(DMTA)wasmadeinsinglecantilevermodeat0.110Hzfrequen-TABLEISpecicationoftheWaterDispersibleBoehmiteAluminasasDeliveredbySasolGermanyGmbHCharacteristics/TypeDisperal1P2Dispal111N7-80Al2O3(%)7280Na2O(%)0.0020.002NO3(%)4.00.1Loosebulkdensity(g/L)850620Specicsurfacearea(m2/g)260100Meanpowderparticlesize(lm)4540Meandispersedparticlesizeinwater(nm)252202964SIENGCHINETAL.JournalofAppliedPolymerScienceDOI10.1002/appciesusingaQ800apparatus(TAInstruments,NewCastle).Thestoragemodulus(E0)alongwithmechan-icallossfactor(tand)wasdeterminedasafunctionofthetemperature(T52508C11308C).Thestrainappliedwas0.01%.Testswererunintheabovetem-peratureandfrequencyrangesbyincreasingthetem-peraturestepwiseby38Candequilibratingthespeci-menateachtemperaturefor5minpriortostartwiththefrequencysweep(setfor0.1,1,and10Hz,respec-tively).Thesampledimensionswere1033533mm3(width3length3thickness).Short-timecreeptestsweremadeintensilemodeatdifferenttemperaturesusingtheaboveDMAappara-tus.Thecreepandrecoverablecomplianceweredeterminedasafunctionofthetime(tcreep530minandtrecovery5120min).Thetensilestressappliedwas4MPa(at0.5%strain).Thiswasderivedfromatestseriescheckingthepresenceoflinearisochronousdeformation.Thespecimensdimensionswere933530.4mm3(width3length3thickness).TogetaclearerpictureonthecreepresponseofthePS/aluminacomposites,thetime-temperaturesuper-positionprinciplewasadoptedforshort-termcreeptestsperformedatvarioustemperatures.Thetensilestressappliedherewas3MPa.Thetemperaturede-pendenceofthecreepresponseofthePSanditscom-positeswasstudiedintherangefrom20to758C.Inthistemperaturerange,isothermaltestswererunonthesamespecimenbyincreasingthetemperaturestepwiseby58C.Priortothecreepmeasurement(du-ration15min),thespecimenwasequilibratedfor5minateachtemperature.Theheatdistortiontemperature(HDT)wasdeter-minedinthreepointbendingmodeusingthesameDMTAdevice.Thestressappliedwas0.46MPaandtheheatingratewassetfor28C/min(similartoASTMD648).Thesampledimensionswere6031233mm3(width3length3thickness).Inaddition,tensiletestswereperformedondumb-bell-shapedspecimens(S3AtypeaccordingtoDIN53504)onaZwick1474universaltestingmachine(Ulm,Germany).TestswererunatRTwithv52mm/mincrossheadspeedandtherelatedmodulus,strengthandelongationatbreakvaluesweredeter-mined.Acontrolledstrainrheometer(ARESofRheometricScientic,NJ,USA)wasutilizedinparallelplatecon-guration(diameteroftheplate:25mm)tomeasurethemeltrheologyofthePSanditscompositesatT51808C.Oscillatoryshearmeasurementswereper-formedoneachsamplebysettingthestrainampli-tudefor1%.Thiswasderivedfromastrainsweeptestseriescheckingthepresenceofthelinearvisco-elasticregion.Thegapbetweentheplateswas2mm.RESULTSANDDISCUSSIONAluminadispersionThecompositesheetsproducedbythemasterbatchtechniqueweremoretranslucentatthesamethick-nessthanthosepreparedbydirectmeltblending(Figure1).Thisisthersthintforthedifferenceinthedispersionstageofthealuminaparticlesinthecorrespondingcomposites.TEMpicturestakenfromthedirectmeltcom-poundedPScompositesevidencethepresenceoflarge,microscaleaggregatesofthealuminaparticles.Theyarethuscorrectlyreferredtomicrocomposites.TheonlydifferencebetweenP2and11N7-80particlesisthatthelatterisalsodispersedinsmalleraggre-gatesinthePSmatrixcf.Fig.2(b)bycontrasttoP2cf.Fig.2(a).CharacteristicTEMpicturestakenfromthecompositesproducedbythemasterbatchtech-niqueinFigure3showthatthealuminaparticlesarenanoscaleddispersedinthem.OnecanalsorecognizeFigure1MacrophotographsshowingthedifferenceinthetransparencybetweenPS/P2compositesatthesamethickness(51.1mm)producedbythemasterbatchtech-nique(a)anddirectmeltcompounding(b).Colorgurecanbeviewedintheonlineissue,.Figure2TEMpicturesfromthePS/aluminamicrocom-positesproducedbymeltblendingwithP2(a)and11N7-80(b)alumina,respectively.ALUMINA-FILLEDPSMICRO-ANDNANOCOMPOSITES2965JournalofAppliedPolymerScienceDOI10.1002/appthatthesizeoftheprimaryparticlesismuchsmallerforP2thanfor11N7-80,whichisinharmonywiththedatainTableI.Ontheotherhand,theparticlesarestillaggregatedintherelatednanocomposites(cf.Fig.3).ThereasonforthisaggregationisduetothePSla-texmediateddispersionofthealuminainthePS.Byreducingthecompoundingtemperaturewhencom-biningthePSwiththedriedPS/aluminafromthela-tex(masterbatch)itcouldbeshownthatthealuminaparticlesarelocatedintheboundarylayerbetweenthePSlatexparticles(cf.Fig.4).Thisndingisinanalogywithresultsreportedonpristineclaymodi-ednaturalrubberlattices.19,22ThealuminaparticlesbecomefurtherdispersedmostlyowingtoshearforcesinthefusedPSduringcompounding.SEMpicturestakenfromthefracturesurfacesoftensileloadedspecimensgivefurtherinsightinthealuminadispersion.Thisisduetothelargerview-eldinSEMcomparedtoTEM.Figure5comparesthefracturesurfacesofthePS/P2compositespro-duceddifferently.SecondarycrackingduetothelargeparticlescausingmicroductiledeformationofthePSisobviousforthemicrocompositescf.Fig.5(a).Theonsetofsecondarycracking,manifestinginacharacteristicdimplepattern,suggeststhatthealu-minaparticlesinthenanocompositearehomogene-ouslydispersedcf.Fig.5(b).ThesamestatementholdsforthePScompositeswithcoarsealuminapar-ticles(cf.Fig.6).BycomparingFigures5(a)and6(a)onemayconcludethatthe11N7-80particlesarebet-terdispersedthroughdirectmeltblendinginthePSmatrixthantheP2particles.PropertiesDMTAresponseFigure7depictsthestoragemodulus(E)andme-chanicallossfactor(tand)asafunctionoftempera-tureforthecompositescontaining4.5wt%ofalu-minaparticlesproducedbyvariousmethods.NotethatincorporationofaluminaparticlesinPSresultedinapronouncedstiffnessenhancementbelowtheTg.ThisreinforcingeffectwasaccompaniedwithashiftintheTgtowardshighertemperature.Thiscanbeassignedtotheformationofaninterphasewithreducedmolecularmobility.ItisverysurprisingthattheintensityoftheTgrelaxationincreasesbyaddingaluminaasusuallytheoppositetrendoccurs.Thismaybelinkedwithsomeconstrainteffectsinthecompositesforwhichtheauthorshavenoexplana-tion.Figure7alsoshowsthatthestiffnessofthecom-Figure3TEMpicturesfromthePS/aluminananocompo-sitesproducedbymasterbatchtechniquewithP2(a)and11N7-80(b)alumina,respectively.Figure4TEMpicturestakenfromthePS/P2nanocom-positesproducedbythemasterbatchtechniquebysettingthetemperatureofthecompoundingforT51658C.Figure5SEMpicturesfromthefracturesurfacesofthePS/P2compositesproducedbydirectblending(a)andmasterbatchtechnique(b),respectively.2966SIENGCHINETAL.JournalofAppliedPolymerScienceDOI10.1002/apppositeisgovernedbytheirproduction(yieldingmicro-andnanocomposites,respectively)andpracti-callynotinuencedbytheprimaryparticlesizeofthealumina.Recallthatunderprimaryparticlesizethatoneachievableinwaterslurryismeant(cf.TableI).ThestiffnessofPS/aluminacompositeswhichwerepreparedbydirectcompoundingwasalwaysinferiortothoseproducedbythemasterbatchtech-nique.Anattemptwasmadetoapplythetime-tem-peraturesuperpositionprincipletotheDMTAdatameasuredinfunctionofbothtemperature(T52508C11308C)andfrequency(f50.110Hz).MastercurvesinformofEversusfrequencywereproducedbysuperimoposingthestoragemodulusversusfrequencytracesusingthetime-temperaturesuperpositionprinciple.Areferencetemperature(T05708C)wasusedforthissuperpositionprocess.Notethattherelatedshiftfactor(aT)isgiven:aT?E0?T?E0?T0?(1)TheshiftfactorsarelinkedwithtemperatureviatheWilliams-Landel-Ferry(WLF)equati