ofstryacceptedAbstractTherefore,polypropylenesampleswithdifferentcom-Composites:PartA36Theeffectsofthermalpropertiesofvariousfillers(magnetite,barite,copper,talc,glassfibresandstrontiumferrite)invariousproportionsonthecoolingbehaviourofpolypropylenematrixcompositesareinvestigatedinaninjectionmouldingprocess.Athermocoupleinthecavityofthemouldrecordsthetemperaturesatthesurfaceofthecompositeduringinjectionmoulding.Fromtheslopeofthecoolingcurvesthethermaldiffusivitiesofthecompositesareestimatedandcomparedwiththermaldiffusivitiesatroomtemperatureandelevatedtemperaturesmeasuredwithatransienttechnique.Thecoolingcurvesshowdifferentmergingsectionsaffectedbytheafterpressure,thediffusivityofthecompositeandthediffusivityofpolypropylenematrix.Thecoolingbehaviourdependsontheanisotropicthermaldiffusivityoftheusedcomposite,whichiscausedbythealignmentoffillermaterialduetotheinjectionmouldingprocessandtheinterconnectivityofthefillerparticles.Thethermaldiffusivityshowsthehighestvaluefor30vol%talcfilledpolypropylene,whereastheshortestcoolingtimewasfoundfor35vol%copperfilledpolypropylene.Theknowledgeofthesystematicvariationofthermaltransportpropertiesofcompositesduetodifferentfillermaterialandfillerproportionsallowstooptimizethemouldprocessandtocustomizetheheatflowproperties.Furthermore,thestronglyanisotropicthermaltransportpropertiesoftalcfilledpolypropyleneallowthedesignofcompositeswithapredefinedmaximumheatflowcapabilitytotransportheatinapreferreddirection.Keywords:A.Polymermatrixcomposites(PMCs)；B.Thermalproperties；E.Injectionmoulding；Particulatefiller1.IntroductionCommonlyusedplastics,suchaspolypropyleneandpolyamide,havealowthermalconductivity.However,newapplications,mainlyinautomotiveindustries,e.g.forsensorsoractuators,requirenewmaterialswithanenhancedorhighthermalconductivity1.Bytheadditionofsuitablefillerstoplastics,thethermalbehaviourofpolymerscanbechangedsystematicallyuptosignificanthigherthermaldiffusivityofO1.2mm2/sfrom0.2mm2/sforunfilledpolypropylene2,3.Suchfilledpolymerswithhigherthermalconductivitiesthanunfilledonesbecomemoreandmoreanimportantareaofstudybecauseofthewiderangeofapplications,e.g.inelectronicpackaging46.Thehigherthermalconductivitycanbeachievedbytheuseofasuitablefillersuchasaluminium1,carbonfibresandgraphite7,aluminiumnitrides6,8ormagnetiteparticles2.Also,thecoolingbehaviourinthemouldoftheinjectionmouldingmachineisinfluencedbythethermalpropertiesofthepolymer-fillercomposite.However,publishedvaluesofthermalconductivitiesofthesamefillermaterialsindifferentpolymermatricesvarydrasticallyandacomparisonofdifferentmaterialsisdifficultoratleastimpossible2.CoolingbehaviourofparticleinjectionmouldingBerndWeidenfellera,*,MichaelaInstituteofPolymerScienceandPlasticsProcessing,TechnicalUniversitybGeoForschungsZentrumPotsdam,Section4.1ExperimentalGeochemiReceived25June2004；filledpolypropyleneduringprocessHoferb,FrankR.SchillingbClausthal,Agricolastrasse6,D-38678Clausthal-Zellerfeld,GermanyandMineralPhysics,Telegrafenberg,D-14473Potsdam,Germany4July2004(2005)345351talcandSrFe12O19)werepreparedbyextrusionandinjectionmouldingusingvariousvolumefractions(050%).Magne-titeandbaritearegenerallyusedtoincreasetheweightofKoch-Str.42,D-38678Clausthal-Zellerfeld,Germany.Tel.:C49-5323-723708；fax:C49-5323-723148.E-mailaddress:bernd.weidenfellertu-clausthal.de(B.Weidenfeller).*Correspondingauthor.Presentaddress:InstituteofMetallurgy,Robert-merciallyavailablefillers(Fe3O4,BaSO4,Cu,glassfibres,3.ExperimentalTalc,Mg3Si4O10OH2Strontiumferrite,SrFe12O19Copper,CuGlassfibresl11:1.76G0.00,l33:10.69G1.35,a:2.97,a:3.00G0.10,a:6.10G0.90l11:401l:1.21.51314152.01.51511PlateletIrregularIrregularFibre2.785.118.942.58aretes:PartA36(2005)3453512.TheoreticalconsiderationsTheFourierlawofheattransportinonedimensionisgivenbyvTvtZav2Tvx2(1)withtemperatureT,timet,positionxandthermaldiffusivitya.Inanhomogeneousbody,thermaldiffusivityaandthermalconductivitylareinterrelatedbyspecificdensityrpolypropylene,e.g.forbottleclosures(cosmeticsindustry,cf.Ref.10),strontiumferriteisusedinpolymerbondedmagnets,glassfibresareusedforthereinforcementofmaterials,andtalcisananti-blockingagent.However,copperwaschosenasadditionalfillerbecauseofitshighthermalconductivitycomparedtotheothermaterials.Thethermalpropertiesoftheseinjectionmouldedsamplesandtheinjectionmouldingbehaviourwereinvestigatedandcorrelatedtotheamountandthekindoffillermaterial.Table1SelectedpropertiesoffillermaterialsMagnetite,Fe3O4Barite,BaSO4Thermalconduc-tivity(W/(mK)a:4.61G0.42,a:5.10,l11:9.7l11:2.07G0.02,l33:2.92G0.07,a:1.72G0.04Reference1313Meanparticlediam-eter(mm)91.5ParticleshapeIrregularIrregularDensity(g/cm3)5.14.48adenotesmeasurementsonmonomineralicaggregates.Directionsofanisotropyandl33areparalleltothecrystallographicaxesa,bandc,respectively.B.Weidenfelleretal./Composi346andspecificheatcapacitycpaccordingtolZcpra(2)AssuminganinjectionmouldingprocesswithanisothermalfillingstageforapolymerwithatemperatureTPandaconstanttemperatureofthemouldTMaswellasatemperatureindependentthermaldiffusivitya,ananalyticalsolutionofEq.(1)resultsin9TZTMC4pTPKTM!XNnZ012nC1expKa2nC12p2ts2C26C27sin2nC1pxsC18C19(3)InEq.(3),sdenotesthewallthicknessoftheinjectionmouldedpartandTthetemperatureofthemouldingafter3.1.MaterialsTestmaterialsweresuppliedbyMinelcoB.V.(TheNetherlands).MinelcoB.V.preparedincooperationwithRTPs.a.r.l(France)severalpolypropylene(PP)compoundswithvariousfillers(Fe3O4,BaSO4,Cu,glassfibres,talcandSrFe12O19)inanextrusionprocesssimilartothatdescribedinRef.2.Thefillermaterialsarecommonlyusedmaterialsinindustrialproducts.Thefillerparticlesdonothaveatimetafterinjection.Neglectinghigherorderterms,Eq.(3)canbereducedforthepositionxZs/2toTZTMC4pTPKTMexpKap2ts2C18C19C26C27(4)Eq.(4)givesarelationbetweencoolingrateandthermaldiffusivityinaninjectionmouldingprocess,wherehighthermaldiffusivitiesresultinahighercoolingrateandshorterprocesscycles.specifiedbythethermalconductivitytensor(l11,l22,l33),wherel11,l22surfacecoatingwhichcanaffectthermalproperties.SomeselectedpropertiesofthefillermaterialsarelistedinTable1.Fig.1.Photographoftheusedmouldfortheinjectionmouldingexperiments.Themouldconsistsofastandardtensiletestsampleandatestbarforthemeasurementofthermaldiffusivity.timecurvesthesameinjectionmouldingparametersforallcompositematerialswerechosen.Theusedinjectionmachine.ThepositionofthethermocouplefortemperaturemeasurementsisPartA36(2005)3453513473.2.ThermaldiffusivitymeasurementsThethermaldiffusivityofthepolymersismeasuredbyatransientmethod12,closelyrelatedtolaser-flashexperi-ments11.Theusedtransienttechniqueisespeciallyoptimizedformeasurementsofpolyphaseaggregates.Atemperaturesignalistransferredtotheuppersideofthesampleandregisteredbyathermocouple.Thetransferredtemperaturesignalstartsathermalequilibrationprocessinthespecimen,whichisrecordedbyathermocoupleasthedifferencebetweensamplesrearsurfaceandaconstanttemperatureinafurnaceandwhichisusedfortheevaluationofthermaldiffusivity.Aleastsquaresalgorithmisusedtodeterminethethermaldiffusivity,whilevaryingsystematicallythethermaldiffusivityvalueinanespeciallyFig.2.Moldwithcavityforpreparingtestsamplesinaninjectionmouldingmarkedbyanarrow.B.Weidenfelleretal./Composites:designedfinite-differencescheme.AdetaileddescriptionoftheapparatusisgivenbySchilling12.Theaccuracyofthemeasurementsofthepolyphaseaggregatesis3%.Forthermaldiffusivitymeasurements,smallcylindersof10mmdiameterand56mmheightwerecutoutoftheinjection-mouldedrods(cf.Fig.1).3.3.InjectionmouldingWithaninjectionmouldingmachine(Allrounder320C600-250,Arburg,Germany)standardsamplesformeasuringtensilepropertiestogetherwitharodforthermalmeasure-mentsof10mmdiameterand130mmlengthwerepreparedinonemould(cf.Fig.1).Inthecavityofthetensiletestbarachromelalumel(TypeK)thermocouplewasapplied.Duringinjectionmouldingexperimentsthetemperaturewasrecordedevery0.5sbyadigitalmultimeterandstoredinapersonalcomputer.ThepositionofthethermocoupleatthesamplesurfaceanditspositioninthecavityoftheejectorareshowninFigs.1and2,respectively.Thethermocouplesubmergesapproximately0.2mmintomouldingparametersarelistedinTable2.TheresultantcharacteristictimesoftheinjectionmouldingcyclearetabledinTable3.4.ResultsanddiscussionInFig.3,thecoolingbehaviourofpolypropylenewithoutandwithvariousfractionsofmagnetitefillerarepresented.thecavity.Therefore,agoodthermalcontactbetweenpolymerandthermocoupleevenaftershrinkage10ofthemouldingisensured.ForabettercomparisonoftherecordedtemperatureTable3CharacteristictimesinoneinjectionmouldingcyclestartingwiththeinjectionofthepolymerintothecavityattimetiZK8.5suntiltheejectionofthemouldattfZ68sInjectiontime(s)K8.52Dwelltime(s)29Coolingtime(s)954Open/closetimeejectiontime(s)5468Totalcycletime(s)76.5Thesetimesdefinethetimeaxis(abscissa)ofFigs.3and6.Table2InjectionmouldingparametersduringpreparationofsamplerodsformeasurementsofthermaldiffusivitybytransienttechniqueMass(polymer)temperature(8C)200Mouldtemperature(8C)20Cycletime(s)76.5Injectiontime(s)10.5Dosingtime(s)12.4Holdingpressuretime(s)7.0Injectionpressure(Pa)6!107ylenecompositeswithvariousfillerfractionsofFe3O4.Thesymbolsaremeasuredtes:PartA36(2005)345351Atatimet0Z0sthetemperaturemeasuredbythethermocouplereachesamaximumvaluearound2008C.Withincreasingtimetheobservedtemperaturedecreases.AftertZ54sthemouldopensandthecoolingbehaviourrecordedwiththethermocouplechangesbecauseitisnolongerincontactwiththeinjectionmouldedmaterial.Duetothelargediameteroftherod,thetime(54s)untilthemouldisopenedandtheinjectionmouldedpartsareejectedischosenrelativelyhightoensurethatthepartsaresurelysolidified.ItcanbeseeninFig.3thattheslopeofthecurvechangessignificantlyaftertz9s,whichcorrespondstothetimeFig.3.Comparisonofcoolingcurvesofunfilledpolypropylenewithpolypropvalues；thelinesareregressionlines(cf.text).B.Weidenfelleretal./Composi348wheretheafterpressureisremoved.Additionally,Fig.3pointsoutthatthecompositeinthecavitycoolsdownfasterwithincreasingmagnetitefraction.ToreachatemperatureofTZ608Catemperaturefarbelowthesolidificationofthesamplethepolypropyleneneedsinthedescribedexper-imentatimeoftZ50.5s,whereascoolingtimeofpolypropylenewith50vol%Fe3O4isreducedtotZ30.9s(cf.Table4).Thereducedcoolingtimeisingoodagreementwiththeincreasedthermaldiffusivityofmagnetitefilledcompositesduetothehighthermaldiffusivityoftheparticles(cf.Table1)whichleads,regardingEq.(4),toanincreasedcoolingrate.ThetemperaturetimedependenceinFig.3doesnotfollowasimplelinearbehaviourexpectedfortemperaturetimecurvesbyEq.(4)inalogarithmicplot.Onlyfortheunfilledpolypropylenethemeasuredvaluescanbefittedwithasinglestraightlinebetweenapproximately15and54s.Theslopeofthislineleadstoadiffusivityofaz0.21mm2/s(cf.Eq.(4).Theothermeasuredcooli