提高乙烯-乙烯醇共聚物(EVOH)交联效率的方法

(EVOH)1LiuMeihua1,ZhangWanxi1,LiHaihong1,DengPengyang21DepartmentofMaterialScience,JilinUniversity,Changchun(130025)2ChangchunInstituteofAppliedchemistry,ChineseAcademyofScience,Changchun(130022)E-mail：[e-mail]dphysicalpropertiesofethylene-vinylalcoholcopolymer(EVOH)crosslinkedbyenhancedradiationhavebeenstudiedthroughvariousmethods.Itwasfoundthatthemosteffectiveagentforirradiationcrosslinkingwastriallylisocyanurate(TAIC)amongfourkindsofpolyfunctionalmonomers.65.6%gelcontentwereformedforEVOH-44(contentofethyleneis44mol%)at200kGywith5%TAIC,butforEVOH-32(contentofethyleneis32mol%),only37.4%gelcontentwereformedunderthesameconditions.ThisresultshowedthatthemorethecontentofethyleneunitscomprisedinEVOH,theeasierthechemicalbondscouldbeformedbetweendifferentmolecularchains.Tensilestrengthandelasticmodulusincreasedaftercrosslinkingathightesttemperature.Keywords:EVOH;Polyfunctionalmonomers;Radiation-crosslinking1.IntroductionEthylene-vinylalcoholcopolymers(EVOH)areconstructedbyrandomsequencinghydrophobicethylene(E)andhydrophilicvinylalcohol(V)monomericunits.ThepropertiesofEVOHvarydrasticallywiththecopolymercomposition[1].WhenthecontentofEunitsisbelow50mol%,EVOHhasoutstandinggas-barrierpropertiesunderdryconditionscomparedtootherpolymericmaterials[2].SoEVOHisusedwidelyinvariousfieldssuchasfoodpacking,gasolinetanks[3].Anditisexpectedtoworkwellasoneofsoftmaterialsforecologybecauseofnoemissionofpoisonousgasuponincineration.However,EVOHishygroscopicandtheabsorbedwaterinitlowersitsglasstransitiontemperature[4].Consequently,EVOHlosesmuchofitsabilitytoinhibitoxygendiffusion,whichisundesirableinfoodpackaging.Introducingcrosslinkingbondsbetweenpolymermoleculesbychemicalorradiationtreatmentsisapowerfulmethodtoreducethehygroscopicity.Butfewstudieshavebeenonthissubject.Inourpreviousstudy[5],wefoundthatneatEVOHwasdifficulttoradiationcrosslinkingwhenthecontentofethylenewaslessthan50mol%,becausedegradationoccurredinthepartofvinylalcohol.Thegelationdoseincreasedfromabout30kGyofHDPEto400kGyforEVOH-89(contentofethyleneis89mol%)whilethevaluewas800kGyforEVOH-44andabout1800kGyforEVOH-32byCo-60irradiatedinvacuumatroomtemperature.JustlikePVAcanbeirradiatedcrosslinkinginsolution[6],theefficiencyofradiationinducedcrosslinkingofEVOH-44wasfoundtobeincreasedas10%waterexistent[4].Butitisn’tstillveryclearaboutcrosslinkingeffectofEVOHonphysicalpropertiestillnow.Inthispaper,enhancementradiationcrosslinkingofEVOHandtreatmentconditionsforthemosteffectiveintroductionofcrosslinkingagentwerestudied.AndthemechanicalpropertiesofcrosslinkingEVOHwerealsoinvestigatedforthefirsttime.2.Experiment2.1MaterialTheEVOHcopolymers–E151(EVOH-44)andF101(EVOH-32)usedinthisworkwere1ThisarticleissupportedbytheNationalEducationDepartment'sfundforthedoctorprogram(20040183007)(DMAc)andabsolutealcoholusedinextractionexperimentwasfromBeijingChemicalPlant.Thepolyfunctionalmonomers-DiethyleneGlycolDiacrylate(DEGDA)、NeopentylGlycolDiacrylate(NPGDA)wereobtainedfromOrientOrganicChemicalPlant,China,andTAICwasfromLaiyuChemistryCo.Ltd.2.2ThemixtureofEVOHwithpolyfunctionalmonomersTwokindsofEVOHwereblendedwithdifferentpolyfunctionalmonomersusingPolylabSystemofHaake(RHEOMIX-600P),theblendtemperaturewas185and200forEVOH℃℃-44andEVOH-32mixturesamples,respectively.Alltheblendtimewas5minutes.ThemixtureratiosofDEGDAandNPGDAwithEVOH-44were1wt/wt%,2wt/wt%,3wt/wt%and5wt/wt%.AndthemixtureratiosofTAICwithEVOH-44andEVOH-32were1wt/wt%,2wt/wt%,3wt/wt%,5wt/wt%,7wt/wt%,and10wt/wt%.2.3IrradiationThesamplesweremoldedtoform1mmthicksheetsusingplatevulcanizingpress.TheworkingtemperaturesofEVOH-44andEVOH-32blendwere185℃and245℃,respectivelyandtheholdingtimewereall5minutes.Thesampleswereirradiatedbyelectronbeamandtheradiationdosewere50kGy,100kGy,200kGy,300kGyand600kGyrespectivelyatroomtemperature.Thedoseratewas600Gy/sec.2.4DeterminationofgelfractionThesamplescoveredwithnickel-meshwereextractedbyDMAcinaSokhletapparatusfor24h,andthentheyweredriedtoaconstantweightinvacuumat80afterwashingwithalcohol.℃Thegelfractionwascalculatedbyfollowingformula:10100%WGW=×WhereGisthegelfraction(%),1Wand0Wisthemassofthesamplesafterandbeforeexaction,respectively.2.5MechanicalpropertiesTensilestrength,elongationatbreakandelasticmodulusofthesamplesirradiatedatdifferentdosesweretestedwithanInstronuniversaltestinginstrument(INSTRON1121).Theextensionrateis50mm/minatroomtemperature(20)and200mm/minathightemperature(200).℃℃3.ExperimentResultsandAnalysis3.1SelectionthecrosslinkingagentFourkindsofpolyfunctionalmonomersweremixedwithEVOH-44andirradiatedbyelectronbeam,andtheirgelfractionswerelistedinTable1.Theresultsshowedthatthecrosslinkingnetworkwasformedinallmixturesamplesat100kGy.AmongthefourkindsofcrosslinkingagentstheTAICwasthemosteffectiveone.43.3%ofgelfractionwasobtainedat50kGywhe