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1、NucleationinFoamExtrusionS.T.LEESealedAirCorporation301MayhillSt.SaddleBrook,NewJersey07663ABSTRACT:Nucleationresultsarepresentedforpolyethylenesheetextru-sionwhileusingvolatilecarbondioxidewithanynucleatingagent.Sincetheex-trusionpressuremustexceedth
2、esystempressure,mechanicalsuperheatwascalculatedfromtheprocessingpressure.Theexperimentalresultsshowadiffer-entdistributionfromtheconventionalnucleationpredictions,basedoneitherchemicalsuperheatormechanicalsuperheat.Alsonotedwastheshearenergydependenc
3、e.Variousnucleationmechanismsarediscussedtoaddresstheen-ergyroleplayedbyshearinfoamextrusion.INTRODUCTIONoamextrusionhaslongbeenusedasaneffectiveandeconomicFwayinproducingqualitylow-densityproductsintheareaofinsula-tion,energyabsorption,andprotection[
4、1].Sincethepolymer’sperfor-manceandweightratiodoesnotappeartofollowalinearrelationshipwithdensityforcellularproducts[2],foamproductscanbedeveloped,notonlytogreatlyenlargethepropertywindow,buttousethepolymertoitsfullest.Anichemarkethasbeenandcontinuest
5、obedevelopedforthermoplasticfoams.Extrusionitselfinvolvescomplexthermaltransfersamidpolymerphasechangestomatchthethermoplasticpolymer’snatureforoptimalproduct.Thescrewrotation,ingeneral,generatesmechanicalenergytofacilitatemeltingandsheartoenhanceblen
6、dingofaheterogeneoussys-Thisrevisedpaperwaspresentedinitsoriginalformatthe58thAnnualTechnicalCon-ference(ANTEC’00)heldinOrlando,FL,May7–11,2000andthecopyrightisheldbytheSocietyofPlasticsEngineers.JOURNALOFCELLULARPLASTICSVolume37—May20012211530-7999/0
7、1/030221-10$10.00/0DOI:10.1106/HUMM-B95K-TUQ9-LKTDDownloadedfromcel.sagepub.comatPRINCETONUNIVLIBRARYonJanuary18,2016222S.T.LEEtemordissolutionofgasphaseinfoamextrusion.Whenthegasphaseisdissolvedinthemelttofoama“homogeneous”solution,itsviscosityandmel
8、tingpointaredepressed,duetothepresenceofgasinthepolymer.Asthestablemeltsolutiongoesthroughawedgeddie,foamingoccursasaresultofpressuredropinducedsupersaturation.Thegassaturatedpoly-mericfoambeginsthereplacementofgasbyairthroughnaturaldiffu-sion
