The effect of ZnCl2 on the formation of polysulfone membrane

journalofMEMBRANESCIENCEELSEVIERJournalofMembraneScience119(1996)59-64TheeffectofZnC12ontheformationofpolysulfonemembraneSueRyeonKima,KewHoLeeb,MuShikJhona,*aCenterforMolecularScienceandDepartmentofChemistry,KoreaAdvancedInstituteofScienceandTechnology,373-1,Kusung-Dong,Yusung-Gu,Taejon,305-701,SouthKoreaAdvancedPolymerDivision,KoreaResearchInstituteofChemicalTechnology,P.O.Box107,Daedeog-Danji,Taejeon,305-343,SouthKoreaReceived3November1995;accepted19March1996AbstractInthepreparationofultrafiltrationmembranes,theeffectoftheadditionofZnC12inacastingsolution,polysulfone(PSf)/N-methylpyrrolidone(NMP)solution,wasinvestigatedonthemembraneperformance.PSfisanunchargedpolymer,butPSf/NMPwithZnC12showedanelectroviscousbehavior.Theadditionof3wt%ZnC1ztoPSfinducedaredshiftof3cm-1inthe1152.2cm-1peakwhichwasassignedtoasymmetricvibrationalstretchingbecauseofZnC12interactedwithPSfchain.TheadditionofZnC12increasedthereducedviscosityanddecreasedthecriticalconcentration,resultingfromtheassociationbetweenextendedchains.ThePSf/NMPsolutionwithZnC12requiredlesswaterfortheprecipitationpointthansaltlesssolutiondid.ItwasobservedthattheadditionofZnC12increasedtherejectionrateandloweredthemolecularweightcut-off(MWCO)ofPSfmembrane.Keywords:Polysulfone;ZnCI2;Castingsolution;Reducedviscosity1.IntroductionDuetoitsmechanicalstrength,thermostabilityandstabilityagainstchemicals,polysulfone(PSf)hasbeenwidelyusedasamembranematerial.ThestructureofPSfmembranepreparedbyphaseinver-sionisasymmetric[1-3].Itisimportanttocharacter-izetheskinlayeroftheasymmetricmembranebe-causethestructureandpropertyoftheskinlayerdeterminethemembraneperformance[4].Smolderetal.[5]suggestedthatthecharacteristicoftheskinlayerisinfluencedbythestructureofthecastingsolutionbecauseoftherapidexchangeofsolvent*Correspondingauthor.andnonsolventwhenacastingsolutionisimmersedinacoagulationbathcontaininganonsolvent.Smidetal.[6]foundthattheminimalskinthicknessofthemembraneisreducedwhenahigherintrinsicviscos-ityofthepolymerisused,leadingtoade