-材料成型與控制工程專(zhuān)業(yè)畢業(yè)設(shè)計(jì)外文文獻(xiàn)翻譯-固態(tài)微孔丙烯腈丁二烯苯乙烯泡沫塑料

PAGE畢業(yè)設(shè)計(jì)外文文獻(xiàn)譯文及原文學(xué)生：學(xué)號(hào)：院（系）：機(jī)電工程學(xué)院專(zhuān)業(yè)：材料成型與控制工程指導(dǎo)教師：2011年6月PAGE6Solid-StateMicrocellularAcrylonitrile-Butadiene-StyreneFoamsSUMMARYMicrocellularABSfoamsareanovelfamilvofmaterialswiththepotentialtosignificantlyreducematerialcostsinanumberofapplicationsthatcurrentlyusesolidpolymer.ABSfoamswereproducedusingcarbondioxideinasolid-stateprocess.SolubilityanddiffusivityofC02inABSwasmeasured,andthelatterwasfoundtodependsignificantlyonthegasconcentration.Theusefulrangeofprocess-spaceforABS-CO2wascharacterized.ClosedcellABSfoamswereproducedwithdensitiesrangingfrom1.03g/cm3(almostcompletelysolid)to0.09g/cm3.ItwasdeterminedthattherearemanydifferentprocessingconditionsthatcanproducemicrocellularABSfoamsthathavethesamedensity.Thecellnucleationdensitywasoftheorderof10cellspercm3,andtheaveragecellsizesobservedrangedfrom0.5umto5.6um.INTRODUCTIONABS(Acrylonitrile-butadiene-styrene)hasgrowntobecomeoneofthemostwidelyusedthermoplasticintheworldbecauseofthewiderangeofavailableproperties.easeofprocessing,andagoodbalancebetweenpriceandperformance.ABSisanamorphouscopolymeralloy,withacrylonitrilebringingchemicalresistanceandheatstability,butadienebringingtoughness,andstyreneprovidinggoodprocessingcharacteristics.Thesequalitiesprovideanexcellentengineeringthermoplasticthatisusedforawiderangeofproducts,includingcomputerhousings,automotiveinteriors,appliances,andbuildingmaterials.Inmanyapplications,thesolidABScanbereplacedbyrelativelyhighdensitymicrocellularfoams,sincethepropertiesofsolidABSarenotfullyutilized.Currently,theonlyprocessthancanproducefoamssuitableforthincross-sectionsisthesolid-statemicrocellularprocessoriginallydevelopedatMITasawaytoproducehighstrengthpolymerfoamswhichcanreducetheamountofmaterialusedinmanufacturedproducts.Thisprocessproducesfoamswithaverylargenumberofverysmallcells,typicallyontheorderof10umdiameter,andthusthephase"microcellularfoams"wascoined.Thebatchmicrocellularprocesshastwostages.Inthefirststageathermoplasticsampleisplacedinapressurevesselwhichisthenpressurizedwithanon-reactinggas.Carbondioxideandnitrogenaretypicallyusedasthefoamingagentsbecauseoftheirlowcostandhighsolubilityinmostpolymers.Thepolymersampleabsorbsthegasuntilanequilibriumgasconcentrationisreached.Atthispoint.thesampleisremovedfromthepressurevessel.Inthesecondstageofthemicrocellularprocessthesampleisheated,typicallyinahotbath,toinducefoaming.Thetemperatureofthehotbathisintheneighbourhoodoftheglasstransitiontemperatureofthepolymer,andthusthepolymerremainsinasolid,orrubberystate,wellbelowthemeltingpoint,duringtheentireprocess.Todistinguishthesefoamsfromthecommonfoamsmadefrompolymermelts,theyaredescribedas"solidstate"foams.Theprocessdescribedaboveisabatchprocessusedtoproducerelativelysmallamountsoffoamspecimensatatime.Theproductioncapabilityofthesolid-statemicrocellularfoamshasincreasedwiththedevelopmentofthesemi-continuousprocess.Inthesemi-continuousprocessthesheetofpolymerplacedinthepressurevesselisreplacedwitharollofpolymerwhichhasagaspermeablematerialrolledupinittoallowgastodiffuseintotheentiresurfaceoftheroll.Thepolymerrollandgaspermeablematerialarefirstseparated,andthenthepolymersheetisdrawnthroughahotbathtofoam,andacoldbathifnecessarytoquenchthestructure.Microcellularfoamscanbeproducedwithawiderangeofdensitiesandwithanintegralskid.Duetotheirpotentialasanovelfamilyofmaterials,anumberofpolymer-gassystemshavebeenexploredinrecentyears,includingpolystyrene,polycarbonate,PET,PETC,andPVC.InthispaperwepresentadetailedexperimentalcharacterizationoftheABS-C02system,andexploretheeffectsofkeyprocessparametersonthemicrostructure.EXPERIMENTALCommerciallyavailableCycolacGPX3700ABS,manufacturedbyGeneralElectricwasusedinthisstudy.Allofthespecimenswereproducedfrom1.5mmthicksheetwithnaturalcolour.Theunprocessedmaterialhasadensityof1.04g/cm3,andaglasstransitionstemperatureofabout116℃.SolubilityanddiffusivitymeasurementsSpecimenswerecutfrom1.5mmthicksheettodimensionsof2.5x2.5cm.Eachsamplewasthensaturatedinapressurevesselat26.7℃(80°F)controlledto±1℃.Thetemperatureandpressureusedtosaturatethespecimenswillbereferredtoasthesaturationtemperatureandsaturationpressurerespectively.Thesaturationpressurewascontrolledtowithin±35kPa(±5psi).Thesampleswereperiodicallyremovedfromthepressurevesselandweighedonaprecisionbalancewithaccuracyof±10ugtodeterminetheamountofgasabsorbed.Becausetheamountofgasabsorbedbythesampleswasontheorderof10mg,thismethodprovidedsufficientaccuracy.Desorptionmeasurementsweremadefromfullysaturatedsamples.AfterreachingequilibriumC02concentration,thesampleswereallowedtodesorbtheC02whileheldat26.7℃(80°F)andatmosphericpressure.Duringthedesorptionexperiments,thesampleswereweighedonaprecisionbalancetodeterminetheremainingC02concentration.FoamsamplepreparationandcharacterizationSampleswerecuttodimensionsof2.5cm×2.5cmandsaturatedinapressurevesselmaintainedat26.7±1℃(80°F)untilanequilibriumCO2concentrationwasreached.Thetimerequiredtoreachequilibriumwasdeterminedfromthesorptionmeasurementsdiscussedabove.Aftersaturation.allspecimenswereallowedtodesorbgasforfiveminutespriortofoaming.Thesamedesorptiontime,5minutes,wasusedforallspecimenstoensurethattheintegralunfoamedskinthicknesswasnegligiblysmall.Afterdesorption,thesampleswerefoamedbyheatinginaglycerinbathforalengthoftimethatwillbereferredtoasthefoamingtime.Thetemperatureoftheglycerinbathusedtofoamthespecimenswillbereferredtoasthefoamingtemperature.Allsampleswerefoamedforfiveminutes.Oncethefoamingtimehadelapsed,thefoamedspecimenswereimmediatelyquenchedinawaterbathmaintainedatroomtemperature.Specificvaluesofthesaturationpressures,foamingtemperatures,andfoamingtimeswillbediscussedlater.Afterfoaming,thesampleswereimmersedinliquidnitrogenandthenfracturedtoexposetheinternalmicrostructure.ThefracturedsurfacesweremadeconductivebydepositionofAu-Pdvapourandthenstudiedunderascanningelectronmicroscope(SEM).AllSEMmicrographsweretakenalongthecentre-lineofthesample. DeterminationofcellsizeandcellnucleationdensityTheaveragecellsize,cellsizedistribution,andnumberofbubblesperunitvolumeoffoamweredeterminedbySaltikov'smethoddescribedindetailbyUndenvood.Saltikov'smethodallowsthecharacteristicsofathreedimensionaldistributionofspherestobeestimatedfromatwodimensionalimage,suchasamicrograph.Previouslyitwasassumedthatthefractureplanepassedthroughthecentreofallbubblesinamicrograph,introducingasmallerrorintheestimationoftheaveragecellsize.cellsizedistribution,andcellnucleationdensity.Inaddition,itwasalsoassumedpreviouslythatthenumberofbubblesperunitvolume(i.e.bubbledensity)couldbedeterminedbycubingthelinedensity.Saltikov'smethodprovidesamorerobustprocedureforestimatingthebubbledensity,andisapplicabletoawiderrangeofmicrostructures.Saltikov'smethodwasimplementedbydigitizinganSEMmicrographwithapproximately200bubbles,andusingNlHlmagetodeterminetheareasofthebubbles.NIHImageisapublicdomainimageprocessingandanalysisprogramdevelopedattheResearchServicesBranch(RSB)oftheNationallnstituteofMentalHealth(NIMH),partoftheNationalInstitutesofHealth(NIH).ThemeanbubblediameterandstandarddeviationsreportedinthispaperarebasedonthelognormaldistributionproposedbySaltikov.Thecellnucleationdensitywasdeterminedbyamethoddescribedpreviouslyandisthenumberofbubblesthatnucleatedineachcm3ofunfoamedpolymer.ThevolumefractionofthebubbleswastakentobetheareafractionofthebubblesinamicrographassuggestedbyUnderwood.Thedensityofeachsamplewasdeterminedbytheweightdisplacementmethod,ASTMD792.RESULTSANDDISCUSSIONThesolubilityanddiffusivityofC02inABSFigure1showsthegassorptionofCO2into1.5mmthickABSsheetsubjectedtosaturationpressuresof350kPa,1MPa,2MPa,3MPa,4MPa,5MPa,and6MPaatasaturationtemperatureof26.7℃(80°F).TheCO2concentrationinmggas/gpolymerisplottedvstime.Overtime,theconcentrationofCO2increaseswithinthepolymeruntilthepolymerabsorbsnomoregasandcanbeconsideredsaturated.Asexpected,theconcentrationofgasatequilibriumincreasesasthesaturationpressureisincreased.FortheABSformulationstudiedhere,equilibriumconcentrationsashighas150mgC02/gpolymerwereachievedatasaturationpressureof6MPa.Figure1alsoshowsthatthediffusionofCO2inABSisFigure1Sorptioncurvesfor1.5mmthickABSinCO2at26.7℃(8O°F),andpressuresrangingfrom350kPato6MPa.Increasingsaturationpressuresresultinshortersaturationtimesandhigherequilibriumconcentrationsdependentongaspressure.Weseethatittakesapproximately50hourstoreachequilibriumatasaturationpressureof3MPa,whileat6MPatheequilibriumisreachedin20hours.Thefasterdiffusionat6MPaisaresultofeffectiveTgofthegas-polymersystemapproachingthesaturationtemperatureof26.7℃.ThisisevidentfromFigure5where,for6MPasaturation.theonsetofbubblenucleationisaround27°C.TheequilibriumconcentrationinmilligramsofC02pergrampolymerisplottedinFigure2asafunctionofthesaturationpressure.ThesetofpointsinFigure2definethesorptionisothermfor26.7℃.UsuallythisisothermcanbecharacterizedusingtheDualModeSorptionModel.Inthissystemat26.7℃however,astraightlinepassingthroughtheoriginrepresentsallofthedataaccurately,andthereforeHenry'sLawcanbeusedtopredicttheequilibriumconcentrationatagivensaturationpressure:C=HPs(1)whereCistheequilibriumgasconcentration,mg/g;HisHenry'sLawconstant(orsolubility),mg/g..MPa;andPsisthesaturationpressure,MPa.Figure2SorptionisothermforC02inABSat26.7℃(80°F).Notethatequilibriumconcentrationincreaseslinearlywithsaturationpressureandthelinearregressionpassesthroughtheorigin,indicatingHenry'sLawisvalidforawiderangeofpressuresinthissystemFigure2showsthatHenry'sLawisvalidforallofthesaturationpressuresexplored.FromaleastsquaresfitofthedatainFigure2,theHenry'sLawconstantwasdeterminedtobe25.0mg/g.MPaforasaturationtemperatureof26.7℃.Figure3showsdesorptionresultsforABSat26.7℃.wherethefractionofthegasremainingfromthefullysaturatedconditionisplottedasafunctionoftime.TherateofdesorptionseeninFigure5isafunctionoftheinitialC02concentration;increasingsaturationpressure(orequivalentlytheequilibriumconcentration)resultsinafasterrateofdesorption.ThisbehaviourisconsistentwithourobservationsfromFigure1wherehighersaturationpressuresledtosignificantlylowersorptiontimes.Theaveragediffusioncoefficient,D,canbeestimatedfromFigure1usingthesolutionofthediffusionequationforaplanesheet.Thisdiffusioncoefficientisanaverageovertheentirerangeofgasconcentrationsexperiencedbythesample,andisgivenby:(2)Figure3Desorptioncurvesfor1.5mmABSat26.7℃andatmosphericconditions.Thegasconcentrationisgivenasafractionoftheinitialconcentration.Ahigherinitialsaturationpressureresultsinafasterdesorptionwheretisthesorptiontime,1isthethicknessofthesheet,and(t/12)1/2isthevalueoft/12whenhalfoftheequilibriumamountofgashasbeenabsorbed.Table1presentstheapproximatetimetoreachsaturation,andtheaveragediffusioncoefficientsforC02inABSfordifferentgaspressures.Weseethatthediffusioncoefficientsrangefrom2.14x10-8cm2/secforsaturationat350kPato19.2x10-8cm2/secat6.0MPa.Asaresultofthisconcentrationdependentdiffusivity,thesaturationtimedecreases(seeTable1)withincreasingsaturationpressure.fromabout120hoursat350kPatoabout8hoursat6.0MPa.Conditionsforsteady-statestructureTheobjectiveofthisportionofthestudywastodeterminethefoamingtimerequiredtoproduceABSfoamswithasteady-state,orequilibrium,density.Fromtheinstantasaturatedsampleisplacedintheglycerinbath,thebulkdensityofthespecimendecreasesataneverdecreasingrateuntilasteadysatevalueisachieved.Afterthefoamdensityhasreachedsteady-state,thedensitystopsdecreasing.Foragivenspecimenthickness,thetimerequiredtoreachsteady-stateisafunctionofthesaturationpressureandtemperature,andfoamingtemperature.Inthisexperiment,samplesweresaturatedwithC02maintainedat350kPa(50.8psi)and22℃,andfoamedat120℃forvariouslengthsoftime.Thelowestgaspressurewaschosenforthisexperimentsoastofindthelongesttimeneededtoachievesteady-statestructure.ThefoamdensityasafunctionoffoamingtimeisplottedinFigure4.Recallthatthedensityoftheoriginal.unfoamedABSwas1.04g/cm3.Figure4showsthatittakesapproximately300seconds(5min)toreachsteady-stateintheABS-C02systemforthegivenprocessingconditions.Sincemostotherprocessingconditionswillreachanequilibriumfoamdensityfasterthanattheseconditions,weusedafoamingtimeof300secondsforallexperimentsinthisstudy.Inaddition.Figure4showsthatatafoamingtemperatureof120℃,theoriginaldensityisreducedbyapproximately50%duringthe300secondsoffoaming.Figure4Plotoffoamdensityasafunctionoffoamingtime,showingthatafoamingtimeofapproximately300secondsisrequiredtoreachequilibriumintheABS-C02system.Samplesweresaturatedat350kPa,allowedtodesorbfor5minutes,thenfoamedat120°CTheeffectofsaturationpressureandfoamingtemperatureToexploretheeffectoffoamingtemperatureandsaturationpressureonmicrostructure,samplesweresaturatedatdifferentpressuresandthenfoamedoverarangeoftemperatures.Afterthesampleshadbeenproduced,thefoamdensity,averagecellsize,cellsizedistribution,andcellnucleationdensityweredetermined.Figure5showsaplotoftherelativedensity(densityofthefoamdividedbythedensityofthesolidmaterial)asafunctionoffoamingtemperatureforthesaturationpressuresexplored.AwiderangeofrelativedensitiescanbeproducedintheABS-C02system.Foamscanbeproducedwithrelativedensitiesfrom0.99(i.e.almostfullydense)toaslowas0.09.Inaddition,mostdensitiescanbeproducedbyusingmorethanoneprocessingcondition.Inotherwords,differentsaturationconditionsandfoamingtemperaturescanbeusedtoproducethesamedensityfoam.Similartoothermicrocellularsystems,Figure5showsthatfoamingcanoccurinABSattemperaturessignificantlybelowtheglasstransitiontemperatureoftheunsaturatedmaterialduetoplasticizingofthepolymermatrixbytheabsorbedC02.Asthesaturationpressureisincreased,theeffectiveglasstransitiontemperaturedrops,allowingfoamstobeproducedFigure5ProcessspacefortheABS-CO2,system,showingaplotoftherelativedensityasafunctionoffoamingtemperatureforsaturationpressuresfrom350kPato6MPa.Allsamplesweresaturatedat26.7℃.allowedtodesorbforfiveminutesbeforefoaming,thenfoamedforfiveminutes.Theusefulpartoftheprocessspaceliestotheleftoftheminimumdensityforagivengaspressureatlowertemperatures.Atasaturationpressureof6MPa.Figure5showsthatfoamingispossibleatapproximately27℃,justaboveroomtemperature.TherelativedensityofmicrocellularABSisaffectedstronglybythefoamingtemperature.Asthefoamingtemperatureincreases,therelativedensitydecreasesinnearlinearproportion.Thefactthatrelativedensitydecreasesnearlylinearlywithfoamingtemperatureisagreatprocessingadvantage.allowingprecisecontroloverthisvitalfoamproperty.Asthefoamingtemperatureincreases,thefoamdensityreachesaminimum,andcanstarttoincreasewithincreasingtemperature.At5MPa,Figure5showsthatusingfoamingtemperatureshigherthan100℃producesfoamswithahigherrelativedensity.At140℃,forexample,arelativedensityofapproximately0.8isproduced,significantlyhigherthantherelativedensityof0.3producedatafoamingtemperatureof100℃.Athighertemperature,thecellsbegintocollapseleadingtoadenserstructure.Foamsproducedatthesehighertemperaturesaretypicallyofpoorquality,with1to2mmblistersonthesurface.ThisminimuminthedensityversusfoamingtemperaturecanbeobservedatseveralothergaspressuresinFigure5.Figure6showsSEMsoffourdifferentmicrocellularABSfoams.Thefirsttwoimages,AandB,demonstratethelargeeffectofsaturationpressureonfoamdensityandcellsize.Figure6AandBwereproducedwithdifferentsaturationpressures,3and6MParespectively,butthesamefoamingtemperatureof70℃.ThefoamsinAandBhaverelativedensitiesof0.70and0.42respectively.Thecellsizesvaryfromapproximately5umforAtolessthan1umforB.ImagesCandDinFigure6showtwofoamsproducedfromthesamesaturationpressure,350kPa,butfoamedatdifferenttemperatures,105and120℃.Thefoamshaverelativedensitiesof0.88forCand0.31forDandshowmarkedlydifferentfoamstructures.Table2presentstheresultsofthescanningelectronmicrographanalysis,andshowsitispossibletoproducemicrocellularABSfoamswithawiderangeofcellularproperties.NotallfoamsweresuitableforanalysisusingSaltikov'smethod.Tobesuitableforanalysis,thefoamstructureshouldhavesphericalcells,andthecellsmustbedistinctinthemicrograph.Forexample,inFigure6imagesAandCcanbeanalyzed,whileBandDcannot.ThusthetestpressuresandfoamingtemperaturesnotreportedinTable2aretheconditionsthatproducedcellsnotsuitableforaSaltikovanalysis.ThemeasuredaveragecelldiametersinTable2varyfrom5.58pmto0.54pm,andthecellnucleationdensityrangesfrom4.0x1010to1.8x1013cellspercm3.MicrocellularABSfoamsgenerallyhavesmallcellsizesandhighcellnucleationdensities.Figure6MicrographsoffourdifferentmicrocellularABSfoams.AandBweresaturatedatdifferentpressures,3MPaand6MParespectively,butwerefoamedatthesametemperature,70℃.CandDwerebothsaturatedatthesamepressure,350kPa,butwerefoamedatdifferenttemperatures,105and120℃,respectively.AllsampleswereallowedtodesorbforfiveminutesbeforebeingfoamedforfiveminutesCONCLUSIONSProcessingconditionshavebeenpresentedforproducingsolid-statemicrocellularABSfoamsusingcarbondioxideastheblowingagent.Itwasfoundthat,atagiventemperature,therateofC02sorptionanddesorptioninABSisdependentonthegasconcentration.ItwasalsodiscoveredthattheABS-C02systemexhibitedauniquemicrostructurewitharelativelynarrowdistributionofbubblesizes.Anexperimentalinvestigationofthemajorprocessingvariables,foamingtime,saturationpressure,andfoamingtemperatureyieldedseveralinsightsintotheprocessingbehaviouroftheABS-C02system.Itwasdeterminedthatittakesamaximumofapproximately300secondsforfoamgrowthtocomplete.Itwasalsodeterminedthat,forallsaturationpressuresexplored,foamdensitydecreasesnearlylinearlywithincreasingfoamingtemperatureuntilaminimumdensityisreached.Foamswithdensitiesrangingfrom0.09g/cm3toalmostfullydense,1.03g/cm3wereproduced.TheusefulrangeofprocessspacefortheABS-C02systemwasestablished.ACKNOWLEDGEMENTSThisresearchwasprimarilysupportedbytheUniversityofWashington-IndustryCellularCompositesConsortium.PartialsupportwasprovidedbyNationalScienceFoundationGrantMSS9114840.Thissupportisgratefullyacknowledged.1.BrisimitzakisA.C.,Styrenicresins-ABS,ModernPlastics,68,(1991),85-86；2.MartiniJ.E..SuhN.P.andWaldmanF.A.,TheProductionandAnalysisofMicrocellularThermoplasticFoams,SocietyofPlasticsEngineersTechnicalPapers,XXVIII,(1982),674-676；3.KumarV.andSchirmerH.G.,Semi-continuousProductionofSolidStatePETFoams,SocietyofPlasticsEngineersTechnicalpapers,XLI,(1995),2189-2192；4.KumarV.andSchirmerH.G.,ASemi-continuousProcesstoProduceMicrocellularFoams,USPatent5,684.055(1997)；5.KumarV.andWellerJ.E.,AModelfortheUnfoamedSkinonMicrocellularFoams.PolymerEngineeringandScience,34,(1994),169-173；6.KumarV.andWellerJ.E.,ProductionofMicrocellularPolycarbonateUsingCarbonDioxideforBubbleNucleation,JournalofEngineeringforIndustry,116.(1994).413-420；7.HandaV.P..WongB.,ZhangZ.,KumarV.,EddyS.andKhemaniK.,SomeThermodynamicandKineticPropertiesoftheSystemPETG-C02,andMorphologicalCharacteristicsoftheC02-BlownPETGFoams,PolymerEngineeringandScience,39,(1999),55-61；8.KumarV.andStolarczukP.J.,MicrocellularPETFoamsproducedbytheSolidStateProcess,SocietyofPlasticsEngineersTechnicalPapers.XLII,(1996).1894-1899；9.KumarV.andWellerJ.E.,AProcesstoProduceMicrocellularPVC,InternationalPolymerProcessing,7,(1993),73-80；10.ShimboM.,BaldwinD.F.andSuhN.P.,Polym.Eng.Sci.,35,(1995),1387；11.ParkC.B.andSuhN.P.,Polym.Eng.Sci.,36,(1996),34；12.ColliasD.I.,BairdD.G.andBorggreveR.J.M.,Polymer,25,(1994),3978；13.UnderwoodE.E..QuantitativeStereology,Adison-Wesley,Reading,Massachusetts,(1970)；14.MichaelsA.S.,ViethW.R.andBarrieJ.A.,SolutionofGasesinPolyethyleneTerephthalate,JournalofAppliedPhysics,34,(1963),1-12；15.CrankJ..TheMathematicsofDiffusion,OxfordUniversityPress,NewYork(1975)。固態(tài)微孔丙烯腈丁二烯苯乙烯泡沫塑料摘要ABS微孔泡沫材料在目前許多所使用的固體高分子材料中，有著降低材料成本潛質(zhì)的新穎材料。ABS泡沫成型時(shí)，在其固化過(guò)程中使用二氧化碳，ABS中的二氧化碳溶解度和擴(kuò)散系數(shù)被檢測(cè)，其中后者被認(rèn)為更依賴(lài)于氣體濃度。適用于ABS-二氧化碳材料空間有用的范圍進(jìn)行了表征。閉孔泡沫材料制作的ABS密度由1.03g╱cm3（幾乎完全固體）到0.09g/cm3.據(jù)測(cè)定，有許多不同的加工條件，可以生產(chǎn)具有相同的密度的ABS微孔泡沫材料。泡核密度是10個(gè)/cm3，并且所觀察的泡孔大小范圍為0.5微米到5.6微米。簡(jiǎn)介由于用途廣泛、易于加工，并且性價(jià)比高等特性，ABS（丙烯腈丁二烯苯乙烯）已經(jīng)發(fā)展成為世界上最廣泛使用的熱塑性材料。ABS是一種無(wú)定形共聚物，丙烯腈使合金具有耐化學(xué)性和熱穩(wěn)定性，丁二烯帶來(lái)韌性，并提供良好的加工特性苯乙烯。這些品質(zhì)提供優(yōu)良的工程熱塑性塑料，是一個(gè)廣泛的產(chǎn)品，包括電腦外殼，汽車(chē)內(nèi)飾，家電，建筑用料。在許多應(yīng)用中，相對(duì)高密度的微孔泡沫可代替ABS，因?yàn)楣腆wABS的特性沒(méi)有得到充分利用。目前，唯一能產(chǎn)生合適比薄截面泡沫的過(guò)程，是最初在麻省理工學(xué)院固態(tài)微孔開(kāi)發(fā)的過(guò)程，作為一種生產(chǎn)高強(qiáng)度復(fù)合泡沫材料，可以在制造產(chǎn)品時(shí)降低原材料的使用量。這個(gè)過(guò)程產(chǎn)生了很多很小的微孔泡沫塑料，通常泡孔直徑為10微米，因此，“微孔發(fā)泡”，因此“微孔發(fā)泡”的相就形成了。批處理微孔過(guò)程有兩個(gè)階段。在第一階段的一種熱塑性樣本被放置在一個(gè)壓力容器，然后是與非反應(yīng)氣體加壓。二氧化碳和氮由于其成本低、溶解度高，故通常用作大多數(shù)聚合物的發(fā)泡劑。該聚合物樣品吸收氣體，直到達(dá)到氣體濃度平衡。在這時(shí)。該樣本是從壓力容器中取出。第二階段過(guò)程中，微孔樣品通常在一個(gè)熱水澡中加熱，促使試樣減少發(fā)泡。熱浴的溫度是在聚合物的玻璃化轉(zhuǎn)變溫度附近，因而聚合物仍處于固體或橡膠態(tài)，然而在整個(gè)過(guò)程中溫度遠(yuǎn)低于熔點(diǎn)。為了區(qū)別于這些泡沫和由共同聚合物融化制成的泡沫，它們被稱(chēng)為“固態(tài)”泡沫。上面描述的過(guò)程是在一個(gè)批次中，生產(chǎn)相對(duì)少量的泡沫標(biāo)本過(guò)程。該固態(tài)微孔泡沫生產(chǎn)能力增加與半連續(xù)工藝開(kāi)發(fā)。在半連續(xù)過(guò)程中的聚合物負(fù)債表中的壓力容器置于被替換的聚合物卷其中有一個(gè)透氣材料卷在它允許氣體擴(kuò)散到了整個(gè)軋輥表面。該聚合物輥和透氣材料是第一次分離，然后聚合物表是通過(guò)一個(gè)熱水澡發(fā)泡繪制和冷水浴如果需要淬火的結(jié)構(gòu)。微孔泡沫可生產(chǎn)為具有廣泛的密度和不可分割的打滑材料。由于其作為一種新型材料的種類(lèi)，近年來(lái)大量的高分子氣體系統(tǒng)已經(jīng)在開(kāi)始探討，包括聚苯乙烯，聚碳酸酯，PET，PETC和PVC。本文提出了一種對(duì)ABS-C02系統(tǒng)的詳細(xì)實(shí)驗(yàn)表征，并探討對(duì)組織的關(guān)鍵工藝參數(shù)的影響。實(shí)驗(yàn)市場(chǎng)上可以買(mǎi)到的由通用電氣公司制造的CycolacGPX3700ABS用在了這項(xiàng)研究。所有的標(biāo)本做成了1.5毫米厚的板材自然的色彩。未經(jīng)處理的材料具有密度為1.04g╱cm3，它的玻璃轉(zhuǎn)變溫度約為116℃。溶解度和擴(kuò)散系數(shù)的測(cè)量標(biāo)本被切成從1.5毫米厚、尺寸為2.5×2.5厘米的板材。每個(gè)樣品隨后后放于飽和的溫度控制在26.7℃±1℃（80°F）之間的壓力容器里。溫度和壓力容器用飽和的標(biāo)本通常稱(chēng)為飽和溫度和飽和壓。飽和壓力控制在±35千帕（±5磅）。對(duì)樣品進(jìn)行了定期從壓力容器取出并用精度為±10ug精密天平稱(chēng)重，以確定氣體的吸收量。由于氣體吸收的樣本量在10毫克級(jí)別，這種方法提供了足夠的精度。完全飽和的樣本采用脫附測(cè)量了。當(dāng)二氧化碳濃度達(dá)到平衡后，在26.7℃（80°F）和大氣壓下，樣品開(kāi)始脫附二氧化碳。在脫附實(shí)驗(yàn)中，在精密天平上稱(chēng)量樣品確定剩余二氧化碳濃度。泡沫樣品制備和表征樣品切成尺寸為2.5厘米×2.5厘米，使它在26.7±1℃（80°F）的壓力容器中，直到二氧化碳濃度達(dá)到平衡點(diǎn)時(shí)讓它飽和。確定達(dá)到平衡需要的時(shí)間從上面討論的吸附測(cè)量。飽和后，所有標(biāo)本開(kāi)始在發(fā)泡前五分鐘脫附氣體。所有的標(biāo)本也同樣解吸5分鐘，以確保整體未發(fā)泡的表面厚度很薄。解吸后，將樣品在一個(gè)泡沫的時(shí)間長(zhǎng)度，將被稱(chēng)為發(fā)泡時(shí)間甘油浴加熱。甘油浴的溫度下使用發(fā)泡標(biāo)本將被稱(chēng)為發(fā)泡溫度。所有樣品均發(fā)泡五分鐘。一旦發(fā)泡時(shí)間已經(jīng)過(guò)去了，在泡沫標(biāo)本立即淬火溫度保持在室溫水浴。特定值的飽和壓力，發(fā)泡溫度，發(fā)泡時(shí)間將在后面討論。發(fā)泡后，將樣品在液氮中浸泡，然后破碎，露出內(nèi)部的微觀結(jié)構(gòu)。表面的裂縫進(jìn)行了導(dǎo)電由金鈀氣相沉積，然后在掃描電子顯微鏡（SEM）研究。所有的SEM照片被帶到沿著中心的樣線。測(cè)定泡孔大小和泡核密度平均泡孔大小，泡孔大小分布，和每單位體積的泡沫氣泡數(shù)量由Saltikov的方法確定，并由安德伍德詳細(xì)地描述了。Saltikov的方法允許一個(gè)三球體三維分布的特點(diǎn)，從二維圖像如鏡，估算。以前有人認(rèn)為，斷裂面通過(guò)在一個(gè)顯微所有泡沫的中心，在引進(jìn)的平均細(xì)胞大小的估計(jì)，誤差小。細(xì)胞大小分布，細(xì)胞的成核密度。此外，還假設(shè)以前的每單位容積（即泡沫密度）氣泡數(shù)目可以由刺線密度決定的。Saltikov的估算方法提供一個(gè)更強(qiáng)大的泡沫密度的程序，并適用于更廣泛的微觀結(jié)構(gòu)。Saltikov的方法是實(shí)施數(shù)字化，約200氣泡一SEM照片，并利用北大嶼山公路圖片以確定泡沫的領(lǐng)域。NIH圖像是一個(gè)公共領(lǐng)域的圖像處理和分析方案在研究服務(wù)處（RSB）的心理健康中心（NIMH）衛(wèi)生研究院（NIH）國(guó)家機(jī)構(gòu)組成部分的國(guó)家學(xué)會(huì)發(fā)展。氣泡的平均直徑在本文報(bào)道標(biāo)準(zhǔn)偏差是根據(jù)Saltikov對(duì)數(shù)正態(tài)分布提出的。泡核密度的泡孔是由前面介紹的方法確定的，是在每立方厘米未發(fā)泡的聚合物泡沫核數(shù)。氣泡的體積分?jǐn)?shù)經(jīng)顯微氣泡的面積比例是由安德伍德提出的。每個(gè)樣品的密度是由重量法確定的，ASTMD792。結(jié)果與討論ABS中的二氧化碳的溶解度和擴(kuò)散系數(shù)圖1顯示成1.5毫米厚的ABS受到飽和度為350千帕的壓力，兆帕，2MPA，為3MPa，4MPa的，5MPa和6MPa，并在溫度26.7℃（80°F）條件下的飽和。表中的二氧化碳?xì)怏w吸附在氣體毫克/克聚合物CO2濃度隨時(shí)間繪制。隨著時(shí)間的推移，內(nèi)的高分子聚合物的二氧化碳濃度增加，直到?jīng)]有更多的吸收氣體，可認(rèn)為是飽和了。正如所料，氣體的飽和壓力平衡濃度的增加會(huì)增加。對(duì)于ABS研究制定在這里，只要150mg/gC02聚合物高濃度達(dá)到平衡，在6兆帕飽和壓力。圖1還表明，在ABS中的二氧化碳?xì)怏w是隨氣體壓力擴(kuò)散。我們看到，它需要大約50小時(shí)達(dá)到飽和的3兆帕壓力平衡，而在6兆帕的平衡是20小時(shí)到達(dá)。在6兆帕更快的擴(kuò)散是氣體聚合物系統(tǒng)Tg接近飽和溫度26.7℃一種有效的結(jié)果。從圖5的地方看出這是顯而易見(jiàn)的，，6兆帕飽和、泡核的發(fā)病??是在27°C。在每克聚合物C02毫克平衡濃度是繪制在圖2作為飽和壓力的功能。該點(diǎn)在圖2設(shè)置定義的吸附等溫線為26.7℃。通常，在這個(gè)系統(tǒng)，這等溫線的特點(diǎn)可以用在26.7℃雙模式吸附模型。然而，直線通過(guò)原點(diǎn)的消失代表著所有的數(shù)據(jù)準(zhǔn)確，因此亨利定律可以用于預(yù)測(cè)在給定的平衡濃度飽和壓力：C=HPs(1)其中，C為平衡氣體濃度，mg/G，H是亨利定律常數(shù)（或溶解度），毫克/g..MPa和Ps為飽和壓力，MPa。圖2顯示，亨利定律是飽和的壓力都有效探索。從最小二乘圖2中的數(shù)據(jù)擬合，亨利定律常數(shù)被確定為25.0毫克/飽和溫度為26.7℃g.MPa。圖3顯示在26.7℃脫附為ABS的結(jié)果。凡從完全飽和的條件是剩余的氣體比例繪制成時(shí)間的函數(shù)。對(duì)解吸率圖5所示是一個(gè)初始二氧化碳濃度的功能;日趨飽和壓力（或等價(jià)的平衡濃度）在解吸速度更快的結(jié)果。這種現(xiàn)象是由圖1，其中高飽和壓力導(dǎo)致吸附時(shí)間大大降低我們的意見(jiàn)是一致的。平均擴(kuò)散系數(shù)，D，可估計(jì)從圖1使用了平面板材的擴(kuò)散方程的解。這種擴(kuò)散系數(shù)比由經(jīng)驗(yàn)豐富的氣體樣品平均濃度全部范圍，并為：(2)其中T為吸附時(shí)間，1是圖紙的厚度，（t/12）1/2是t/12值時(shí)，氣體的平衡量的一半已被吸收。表1給出的大致時(shí)間達(dá)到飽和，而在ABSC02不同氣體壓力平均擴(kuò)散系數(shù)。我們看到，在350千帕飽和，擴(kuò)散系數(shù)范圍從2.14x10-8cm2/sec至19.2x10-8cm2/sec在6.0MPa。由于這種濃度依賴(lài)性擴(kuò)散的結(jié)果，飽和時(shí)間減少（見(jiàn)表1）隨著飽和壓力。從350千帕約120小時(shí)，在6.0兆帕約8小時(shí)。穩(wěn)態(tài)條件結(jié)構(gòu)這一部分的研究目標(biāo)是確定發(fā)泡生產(chǎn)出穩(wěn)定的狀態(tài)ABS泡沫所需的時(shí)間，或平衡，密度。從瞬間飽和樣品放置在甘油浴，試樣的體積密度減小，直至達(dá)到穩(wěn)定沙爹值在不斷下降率。后泡沫密度已達(dá)到穩(wěn)定狀態(tài)，密度停止下降。對(duì)于給定的試樣厚度，所需要的時(shí)間達(dá)到穩(wěn)定狀態(tài)是一個(gè)飽和的壓力和溫度的函數(shù)，和發(fā)泡溫度。在這個(gè)實(shí)驗(yàn)中，樣品在350kPa（50.8磅）和22℃的C02保持飽和，并在120℃發(fā)泡的時(shí)間長(zhǎng)短不一。最低氣壓是選擇了這個(gè)實(shí)驗(yàn)，以尋找所需的時(shí)間最長(zhǎng)的達(dá)到穩(wěn)態(tài)結(jié)構(gòu)。作為一種發(fā)泡泡沫密度是時(shí)間的函數(shù)繪制在圖4?；叵胍幌?，原來(lái)的密度。未發(fā)泡的ABS為1.04g/cm3。圖4表明，大約需要300秒（5分鐘），以達(dá)到在ABS-C02系統(tǒng)的穩(wěn)態(tài)給定加工條件。由于大多數(shù)其他加工條件將達(dá)到一個(gè)平衡泡沫密度高于在這種情況下，我們?cè)谶@項(xiàng)研究中使用的所有實(shí)驗(yàn)的300秒發(fā)泡時(shí)間。此外。圖4顯示，在120℃發(fā)泡溫度，密度是原來(lái)的約50％的發(fā)泡過(guò)程中減少了300秒。飽和壓力和發(fā)泡溫度的影響探討發(fā)泡溫度和飽和壓力對(duì)微觀結(jié)構(gòu)的影響，在不同的樣品飽和壓