PVDF体系浸没沉淀相转化的两步成膜机理的探讨(7)

　第1期左丹英等:PVDF体系浸没沉淀相转化的两步成膜机理的探讨　 35 　

Researchontwo-stepsformationmechanismofPVDF

membranebyimmersionprecipitation

ZUODanying,XUYouyi,ZOUHantao

1

2

1

(1.DeparmentofPolymerScienceandEngineering,WuhanUniversityofScience,Hubei430073,China;2.InstituteofPolymerScience,,China)Abstract:Phaseseparationbehaviorsoftheskintwo-stepsmembrane-formingmechanismforPVDF/DMAcimmersingtheharshwatercoagulationbath.Thetheofcastingsolutionscontrolledthedemixingoftoplayer.highergradually,thePVDFcrystallizationbecamemoreimpor2tant,andtheofthetoplayerwastransformedfromtheinstantaneousliquid-liquid(L-L)demixingtothesolid-liquid(S-L)demixing.Sothemembraneuppersurfacevariedfromaporousstructuretoadensesurface.Inthecontrolofkinetics,L-Ldemixinghappenedinthesublayer.Thedemixingtimeandsublayerstructureswereaffectedbythethermodynamicsanddiffusion.WithPVDFconcentrationin2creasing,thePVDFcrystallizationbecamemoreandmoredominant,andthediffusionrateofsolventandnon2solventreduced,thenthedemixingtimebecamelonger,andtheinstantaneousL-LdemixingwaschangedtothedelayedL-Ldemixinginsublayer.Therefore,themacrovoidstructuresinmembranesdecreased,andthesponge-likestructuresincreasedwithaincrementofPVDFcrystallinity.

Keywords:PVDFasymmetricalmembrane;two-stepsmembraneformationmechanism;thermodynamics;phaseseparation(上接第18页)

Anewapproachtodeterminetheperiodofonline

backwashinultrafiltrationoperation

LIUWenfeng,YANGFenglin,LIULifen,YEMaosheng,

FUZhimin,XIAOZhenhua,MENGJun

(KeyLaboratoryofIndustrialEcologyandEnvironmentalEngineering,MOE,SchoolofEnvironmentandBiologicalScienceandTechnology,DalianUniversityofTechnology,Dalian116024,China)Abstract:Thediscretedataanalyzingmethodwasused-slopechangepointanalysistoanalyzethechangesofultrafiltrationpermeatefluxwithoutbackwash,acriticaltimet1ofthefoulinginultrafiltrationprocesswasob2tainedfromthedataanalysis,whichguidesthedeterminationofoptimalperiodofonlinebackwashinultrafiltra2tionoperationtheoretically.Thenaseriesoftestunderdifferentbackwashperiodswascarriedout,andanotheroptimalonlinebackwashperiodt2wasobtainedalsobyslopechangepointanalysis,whichwasinagreementwiththefirstcalculatedcriticaltimet1.Thustheexperimentalresultsupportsthisdataanalysisapproachtode2terminetheoptimalperiodofonlinebackwash,whichhassignificantvalueinguidingpracticalultrafiltrationop2erations.

Keywords:ultrafiltration;onlinebackwash;backwashperiod;slopechangepointanalysis

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