材料成型与控制工程专业设计外文文献翻译固态微孔丙烯腈丁二烯苯乙烯泡沫塑料本科毕业论文.docx
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材料成型与控制工程专业设计外文文献翻译固态微孔丙烯腈丁二烯苯乙烯泡沫塑料本科毕业论文.docx
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材料成型与控制工程专业设计外文文献翻译固态微孔丙烯腈丁二烯苯乙烯泡沫塑料本科毕业论文
毕业设计
外文文献译文及原文
学生:
学号:
院(系):
机电工程学院
专业:
材料成型与控制工程
指导教师:
2011年6月8日
Solid-StateMicrocellularAcrylonitrile-Butadiene-StyreneFoams
SUMMARY
MicrocellularABSfoamsareanovelfamilvofmaterialswiththepotentialtosignificantlyreducematerialcostsinanumberofapplicationsthatcurrentlyusesolidpolymer.ABSfoamswereproducedusingcarbondioxideinasolid-stateprocess.SolubilityanddiffusivityofC02inABSwasmeasured,andthelatterwasfoundtodependsignificantlyonthegasconcentration.Theusefulrangeofprocess-spaceforABS-CO2wascharacterized.ClosedcellABSfoamswereproducedwithdensitiesrangingfrom1.03g/cm3(almostcompletelysolid)to0.09g/cm3.ItwasdeterminedthattherearemanydifferentprocessingconditionsthatcanproducemicrocellularABSfoamsthathavethesamedensity.Thecellnucleationdensitywasoftheorderof10cellspercm3,andtheaveragecellsizesobservedrangedfrom0.5umto5.6um.
INTRODUCTION
ABS(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.
EXPERIMENTAL
CommerciallyavailableCycolacGPX3700ABS,manufacturedbyGeneralElectricwasusedinthisstudy.Allofthespecimenswereproducedfrom1.5mmthicksheetwithnaturalcolour.Theunprocessedmaterialhasadensityof1.04g/cm3,andaglasstransitionstemperatureofabout116℃.
Solubilityanddiffusivitymeasurements
Specimenswerecutfrom1.5mmthicksheettodimensionsof2.5x2.5cm.Eachsamplewasthensaturatedinapressurevesselat26.7℃(80°F)controlledto±1℃.Thetemperatureandpressureusedtosaturatethespecimenswillbereferredtoasthesaturationtemperatureandsaturationpressurerespectively.Thesaturationpressurewascontrolledtowithin±35kPa(±5psi).Thesampleswereperiodicallyremovedfromthepressurevesselandweighedonaprecisionbalancewithaccuracyof±10ugtodeterminetheamountofgasabsorbed.Becausetheamountofgasabsorbedbythesampleswasontheorderof10mg,thismethodprovidedsufficientaccuracy.
Desorptionmeasurementsweremadefromfullysaturatedsamples.AfterreachingequilibriumC02concentration,thesampleswereallowedtodesorbtheC02whileheldat26.7℃(80°F)andatmosphericpressure.Duringthedesorptionexperiments,thesampleswereweighedonaprecisionbalancetodeterminetheremainingC02concentration.
Foamsamplepreparationandcharacterization
Sampleswerecuttodimensionsof2.5cm×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.
Determinationofcellsizeandcellnucleationdensity
Theaveragecellsize,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.
RESULTSANDDISCUSSION
ThesolubilityanddiffusivityofC02inABS
Figure1showsthegassorptionofCO2into1.5mmthickABSsheetsubjectedtosaturationpressuresof350kPa,1MPa,2MPa,3MPa,4MPa,5MPa,and6MPaatasaturationtemperatureof26.7℃(80°F).TheCO2concentrationinmggas/gpolymerisplottedvstime.Overtime,theconcentrationofCO2increaseswithinthepolymeruntilthepolymerabsorbsnomoregasandcanbeconsideredsaturated.Asexpected,theconcentrationofgasatequilibriumincreasesasthesaturationpressureisincreased.FortheABSformulationstudiedhere,equilibriumconcentrationsashighas150mgC02/gpolymerwereachievedatasaturationpressureof6MPa.Figure1alsoshowsthatthediffusionofCO2inABSis
Figure1Sorptioncurvesfor1.5mmthickABSinCO2at26.7℃(8O°F),andpressuresrangingfrom350kPato6MPa.Increasingsaturationpressuresresultinshortersaturationtimesandhigherequilibriumconcentrations
dependentongaspressure.Weseethatittakesapproximately50hourstoreachequilibriumatasaturationpressureof3MPa,whileat6MPatheequilibriumisreachedin20hour
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