毕业设计外文文献翻译.docx

毕业设计外文文献翻译.docx

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毕业设计外文文献翻译

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,whileat6MPatheequilibriumisreachedin20hours.Thefasterdiffusionat6MPa