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ofstryacceptedAbstractTherefore,polypropylenesampleswithdifferentcomCompositesPartA36Theeffectsofthermalpropertiesofvariousfillersmagnetite,barite,copper,talc,glassfibresandstrontiumferriteinvariousproportionsonthecoolingbehaviourofpolypropylenematrixcompositesareinvestigatedinaninjectionmouldingprocess.Athermocoupleinthecavityofthemouldrecordsthetemperaturesatthesurfaceofthecompositeduringinjectionmoulding.Fromtheslopeofthecoolingcurvesthethermaldiffusivitiesofthecompositesareestimatedandcomparedwiththermaldiffusivitiesatroomtemperatureandelevatedtemperaturesmeasuredwithatransienttechnique.Thecoolingcurvesshowdifferentmergingsectionsaffectedbytheafterpressure,thediffusivityofthecompositeandthediffusivityofpolypropylenematrix.Thecoolingbehaviourdependsontheanisotropicthermaldiffusivityoftheusedcomposite,whichiscausedbythealignmentoffillermaterialduetotheinjectionmouldingprocessandtheinterconnectivityofthefillerparticles.Thethermaldiffusivityshowsthehighestvaluefor30voltalcfilledpolypropylene,whereastheshortestcoolingtimewasfoundfor35volcopperfilledpolypropylene.Theknowledgeofthesystematicvariationofthermaltransportpropertiesofcompositesduetodifferentfillermaterialandfillerproportionsallowstooptimizethemouldprocessandtocustomizetheheatflowproperties.Furthermore,thestronglyanisotropicthermaltransportpropertiesoftalcfilledpolypropyleneallowthedesignofcompositeswithapredefinedmaximumheatflowcapabilitytotransportheatinapreferreddirection.KeywordsA.Polymer–matrixcompositesPMCsB.ThermalpropertiesE.InjectionmouldingParticulatefiller1.IntroductionCommonlyusedplastics,suchaspolypropyleneandpolyamide,havealowthermalconductivity.However,newapplications,mainlyinautomotiveindustries,e.g.forsensorsoractuators,requirenewmaterialswithanenhancedorhighthermalconductivity1.Bytheadditionofsuitablefillerstoplastics,thethermalbehaviourofpolymerscanbechangedsystematicallyuptosignificanthigherthermaldiffusivityofO1.2mm2/sfrom0.2mm2/sforunfilledpolypropylene2,3.Suchfilledpolymerswithhigherthermalconductivitiesthanunfilledonesbecomemoreandmoreanimportantareaofstudybecauseofthewiderangeofapplications,e.g.inelectronicpackaging4–6.Thehigherthermalconductivitycanbeachievedbytheuseofasuitablefillersuchasaluminium1,carbonfibresandgraphite7,aluminiumnitrides6,8ormagnetiteparticles2.Also,thecoolingbehaviourinthemouldoftheinjectionmouldingmachineisinfluencedbythethermalpropertiesofthepolymerfillercomposite.However,publishedvaluesofthermalconductivitiesofthesamefillermaterialsindifferentpolymermatricesvarydrasticallyandacomparisonofdifferentmaterialsisdifficultoratleastimpossible2.CoolingbehaviourofparticleinjectionmouldingBerndWeidenfellera,,MichaelaInstituteofPolymerScienceandPlasticsProcessing,TechnicalUniversitybGeoForschungsZentrumPotsdam,Section4.1ExperimentalGeochemiReceived25June2004filledpolypropyleneduringprocessHo¨ferb,FrankR.SchillingbClausthal,Agricolastrasse6,D38678ClausthalZellerfeld,GermanyandMineralPhysics,Telegrafenberg,D14473Potsdam,Germany4July20042005345–351talcandSrFe12O19werepreparedbyextrusionandinjectionmouldingusingvariousvolumefractions0–50.MagnetiteandbaritearegenerallyusedtoincreasetheweightofKochStr.42,D38678ClausthalZellerfeld,Germany.Tel.C495323723708faxC495323723148.Emailaddressbernd.weidenfellertuclausthal.deB.Weidenfeller.Correspondingauthor.PresentaddressInstituteofMetallurgy,RobertmerciallyavailablefillersFe3O4,BaSO4,Cu,glassfibres,3.ExperimentalTalc,Mg3Si4O10OH2Strontiumferrite,SrFe12O19Copper,CuGlassfibresl111.76G0.00,l3310.69G1.35,a2.97,a3.00G0.10,a6.10G0.90l11401l1.2–1.51314152.01.51511PlateletIrregularIrregularFibre2.785.118.942.58aretesPartA362005345–3512.TheoreticalconsiderationsTheFourierlawofheattransportinonedimensionisgivenbyvTvtZav2Tvx21withtemperatureT,timet,positionxandthermaldiffusivitya.Inanhomogeneousbody,thermaldiffusivityaandthermalconductivitylareinterrelatedbyspecificdensityrpolypropylene,e.g.forbottleclosurescosmeticsindustry,cf.Ref.10,strontiumferriteisusedinpolymerbondedmagnets,glassfibresareusedforthereinforcementofmaterials,andtalcisanantiblockingagent.However,copperwaschosenasadditionalfillerbecauseofitshighthermalconductivitycomparedtotheothermaterials.Thethermalpropertiesoftheseinjectionmouldedsamplesandtheinjectionmouldingbehaviourwereinvestigatedandcorrelatedtotheamountandthekindoffillermaterial.Table1SelectedpropertiesoffillermaterialsMagnetite,Fe3O4Barite,BaSO4ThermalconductivityW/mKa4.61G0.42,a5.10,l119.7l112.07G0.02,l332.92G0.07,a1.72G0.04Reference1313Meanparticlediametermm91.5ParticleshapeIrregularIrregularDensityg/cm35.14.48adenotesmeasurementsonmonomineralicaggregates.Directionsofanisotropyandl33areparalleltothecrystallographicaxesa,bandc,respectively.B.Weidenfelleretal./Composi346andspecificheatcapacitycpaccordingtolZcpra2AssuminganinjectionmouldingprocesswithanisothermalfillingstageforapolymerwithatemperatureTPandaconstanttemperatureofthemouldTMaswellasatemperatureindependentthermaldiffusivitya,ananalyticalsolutionofEq.1resultsin9TZTMC4pðTPKTMÞXNnZ012nC1expKað2nC1Þ2p2ts2C26C27sinð2nC1ÞpxsC18C193InEq.3,sdenotesthewallthicknessoftheinjectionmouldedpartandTthetemperatureofthemouldingafter3.1.MaterialsTestmaterialsweresuppliedbyMinelcoB.V.TheNetherlands.MinelcoB.V.preparedincooperationwithRTPs.a.r.lFranceseveralpolypropylenePPcompoundswithvariousfillersFe3O4,BaSO4,Cu,glassfibres,talcandSrFe12O19inanextrusionprocesssimilartothatdescribedinRef.2.Thefillermaterialsarecommonlyusedmaterialsinindustrialproducts.Thefillerparticlesdonothaveatimetafterinjection.Neglectinghigherorderterms,Eq.3canbereducedforthepositionxZs/2toTZTMC4pðTPKTMÞexpKap2ts2C18C19C26C274Eq.4givesarelationbetweencoolingrateandthermaldiffusivityinaninjectionmouldingprocess,wherehighthermaldiffusivitiesresultinahighercoolingrateandshorterprocesscycles.specifiedbythethermalconductivitytensorl11,l22,l33,wherel11,l22surfacecoatingwhichcanaffectthermalproperties.SomeselectedpropertiesofthefillermaterialsarelistedinTable1.Fig.1.Photographoftheusedmouldfortheinjectionmouldingexperiments.Themouldconsistsofastandardtensiletestsampleandatestbarforthemeasurementofthermaldiffusivity.timecurvesthesameinjectionmouldingparametersforallcompositematerialswerechosen.Theusedinjectionmachine.ThepositionofthethermocouplefortemperaturemeasurementsisPartA362005345–3513473.2.ThermaldiffusivitymeasurementsThethermaldiffusivityofthepolymersismeasuredbyatransientmethod12,closelyrelatedtolaserflashexperiments11.Theusedtransienttechniqueisespeciallyoptimizedformeasurementsofpolyphaseaggregates.Atemperaturesignalistransferredtotheuppersideofthesampleandregisteredbyathermocouple.Thetransferredtemperaturesignalstartsathermalequilibrationprocessinthespecimen,whichisrecordedbyathermocoupleasthedifferencebetweensamplesrearsurfaceandaconstanttemperatureinafurnaceandwhichisusedfortheevaluationofthermaldiffusivity.Aleastsquaresalgorithmisusedtodeterminethethermaldiffusivity,whilevaryingsystematicallythethermaldiffusivityvalueinanespeciallyFig.2.Moldwithcavityforpreparingtestsamplesinaninjectionmouldingmarkedbyanarrow.B.Weidenfelleretal./Compositesdesignedfinitedifferencescheme.AdetaileddescriptionoftheapparatusisgivenbySchilling12.Theaccuracyofthemeasurementsofthepolyphaseaggregatesis3.Forthermaldiffusivitymeasurements,smallcylindersof10mmdiameterand5–6mmheightwerecutoutoftheinjectionmouldedrodscf.Fig.1.3.3.InjectionmouldingWithaninjectionmouldingmachineAllrounder320C600250,Arburg,Germanystandardsamplesformeasuringtensilepropertiestogetherwitharodforthermalmeasurementsof10mmdiameterand130mmlengthwerepreparedinonemouldcf.Fig.1.InthecavityofthetensiletestbarachromelalumelTypeKthermocouplewasapplied.Duringinjectionmouldingexperimentsthetemperaturewasrecordedevery0.5sbyadigitalmultimeterandstoredinapersonalcomputer.ThepositionofthethermocoupleatthesamplesurfaceanditspositioninthecavityoftheejectorareshowninFigs.1and2,respectively.Thethermocouplesubmergesapproximately0.2mmintomouldingparametersarelistedinTable2.TheresultantcharacteristictimesoftheinjectionmouldingcyclearetabledinTable3.4.ResultsanddiscussionInFig.3,thecoolingbehaviourofpolypropylenewithoutandwithvariousfractionsofmagnetitefillerarepresented.thecavity.Therefore,agoodthermalcontactbetweenpolymerandthermocoupleevenaftershrinkage10ofthemouldingisensured.Forabettercomparisonoftherecordedtemperature–Table3CharacteristictimesinoneinjectionmouldingcyclestartingwiththeinjectionofthepolymerintothecavityattimetiZK8.5suntiltheejectionofthemouldattfZ68sInjectiontimesK8.5–2Dwelltimes2–9Coolingtimes9–54Open/closetimeejectiontimes54–68Totalcycletimes76.5ThesetimesdefinethetimeaxisabscissaofFigs.3and6.Table2InjectionmouldingparametersduringpreparationofsamplerodsformeasurementsofthermaldiffusivitybytransienttechniqueMasspolymertemperature8C200Mouldtemperature8C20Cycletimes76.5Injectiontimes10.5Dosingtimes12.4Holdingpressuretimes7.0InjectionpressurePa6107ylenecompositeswithvariousfillerfractionsofFe3O4.ThesymbolsaremeasuredtesPartA362005345–351Atatimet0Z0sthetemperaturemeasuredbythethermocouplereachesamaximumvaluearound2008C.Withincreasingtimetheobservedtemperaturedecreases.AftertZ54sthemouldopensandthecoolingbehaviourrecordedwiththethermocouplechangesbecauseitisnolongerincontactwiththeinjectionmouldedmaterial.Duetothelargediameteroftherod,thetime54suntilthemouldisopenedandtheinjectionmouldedpartsareejectedischosenrelativelyhightoensurethatthepartsaresurelysolidified.ItcanbeseeninFig.3thattheslopeofthecurvechangessignificantlyaftertz9s,whichcorrespondstothetimeFig.3.Comparisonofcoolingcurvesofunfilledpolypropylenewithpolypropvaluesthelinesareregressionlinescf.text.B.Weidenfelleretal./Composi348wheretheafterpressureisremoved.Additionally,Fig.3pointsoutthatthecompositeinthecavitycoolsdownfasterwithincreasingmagnetitefraction.ToreachatemperatureofTZ608CatemperaturefarbelowthesolidificationofthesamplethepolypropyleneneedsinthedescribedexperimentatimeoftZ50.5s,whereascoolingtimeofpolypropylenewith50volFe3O4isreducedtotZ30.9scf.Table4.Thereducedcoolingtimeisingoodagreementwiththeincreasedthermaldiffusivityofmagnetitefilledcompositesduetothehighthermaldiffusivityoftheparticlescf.Table1whichleads,regardingEq.4,toanincreasedcoolingrate.ThetemperaturetimedependenceinFig.3doesnotfollowasimplelinearbehaviourexpectedfortemperature–timecurvesbyEq.4inalogarithmicplot.Onlyfortheunfilledpolypropylenethemeasuredvaluescanbefittedwithasinglestraightlinebetweenapproximately15and54s.Theslopeofthislineleadstoadiffusivityofaz0.21mm2/scf.Eq.4.Theothermeasuredcoolingcurvesofthepolypropylenemagnetitecompositesarefittedineachcasewithtwostraightlines,forthehightemperaturea1andlowtemperaturea2region.Thethermaldiffusivitiesestimatedfromtheslopesoftheregressionlinesarea115st40sz0.24mm2/sanda241st54sz0.19mm2/sforPPwith15volFe3O4,a112st33sz0.29mm2/sanda234st54sz0.19mm2/sforPPwith30volFe3O4,anda19st22sz0.33mm2/sanda228st54sz0.16mm2/sforPPwith50volFe3O4cf.Table5.Itisremarkablethatthecalculatedthermaldiffusivitiesa1ofthehighertemperaturepartsofthecoolingcurvesarealittlebitlowerthanthediffusivitiesmeasuredwiththetransienttechnique,whilethecalculatedthermaldiffusivitiesa2ofthelowertemperaturepartsofthecoolingcurvesmeetthemeasureddiffusivityvaluesTable4TimettocooldownapolypropylenefillercompositefromamasspolymertemperatureofTMZ200downto608CCompositeFillerfractionvoltfrom200to608CsPP050.5PPCFe3O41546.4PPCFe3O43040.5PPCFe3O44534.6PPCFe3O45034.9PPCBaSO41544.3PPCBaSO43040.7PPCBaSO44535.6PPCCu1540.5PPCCu3033.8PPCCu3529.0PPCglassfibres1546.0PPCglassfibres3041.8PPCglassfibres3540.8PPCtalc1545.7PPCtalc3042.5PPCSrFe12O193040.9ThecoolingismeasuredinsituwithinacavityofthemouldbyaKtypethermocouple.
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