PreparationandCharacterizationofPolysulfonePolyvin

Desalination,70(1966)265-275265ElsevierSciencePublishersB.V.,Amsterdam-PrintedinTheNetherlandsPREPARATIONANDCHARACTERIZATIONOFPOLYSULFONE-POLYVINYLPYRROLIDONEBASEDMEMBRANES.S.MUNARIl,A.BOTTINOl,G.CAPANNELL12,P.MORETTIlandP.PETITBONI1InstituteofIndustrialChemistry,UniversityofGenoa,CorsoEuropa30,I-16132Genoa(Italy)2InstituteofIndustrialChemistry,UniversityofMessina,ContradaPapardo,I-98100Messina(Italy)SUMMARYMicroporouspolysulfonemembraneswerepreparedfromcastingsolutionsofpolysulfone,solventandpolyvinylpyrrolidoneasadditive.Themembraneswerecharacterizedbyscanning-electronmicroscopeobservations,porositymeasurementsandultrafiltrationtests.Theeffectofuolyvinvlpvrrolidoneanditsmolecularweightontheviscosityofthecastingsolutionsandthepropertiesofthemembranesisdiscussed.INTRODUCTIONBecauseofitschemicalresistanceandthermalstabilitypolysulfone(PS)isextensivelyusedformembranepreparation[1,2].PSmembranesarepreparedbyphaseinversionprocess.N,N-dimethylacetamide,N,N-dimethylformamide,dimethylsulfoxideandN-methyl-2-pyrrolidonearegenerallyusedassolvents.Duetothelowmolecularmassofthepolymer,PSsolutionsarecharacterizedbylowviscositiesandconsequently,aredifficulttocast.Toovercomethisproblemitiscommonpracticetoaddpolyvinylpyrrolidone(PVP)tothePSsolution[1,3-81.ThishydrosolublepolymerdissolvesinthesolventsmentionedaboveandiscompatiblewithPS[3].InspiteofthewideuseofPVPasadditive,fewpapers[3,5-71supplyinformationontheinfluenceofconcentrationandmolecularmassonthepropertiesofthemembranes.Wehaverecentlystartedaresearchtoincreaseknowledgeonthissubject.Inthispaperthestructure,ultrafiltrationperformanceandporosityofPS/PVPbasedmembranesarediscussedwithrespecttothebothPS/PVPratiointhesolutionandthemolecularmassoftheadditive.EXPERIMENTALMaterialandsolutionsPolysulfone(UDELP-3500)wassuppliedbyAmocoChemicals.Polyvinyl-pyrrolidonewithnominalaveragemolecularmass(Mw)of25,000(25K)and750,000(750K),respectively,wereobtainedbyServa.ReagentgradeN,N-OOll-9164/88/$03.5001968ElsevierSciencePublishersB.V.266dimethylacetamide(DMA)wasusedforthepreparationofbothbinarysolutionsofPSinDMAandternarysolutionscontainingboththepolymers.Viscositiesweremeasuredat20°CwithaBrookfieldLVTDviscometer.MembranepreparationMembraneswerepreparedfromasolutioncontaining15gofPSin85gofsolventandfromternarysolutionsobtainedbyaddingto100gof15wt%binarysolutionincreasingamountsofPVP.Solutionswerepouredontoasmoothglassplateandcastusingaknifewithagateof350wtocontrolthemembranethickness.Castsolutionswereallowedtostandfor30spriortoimmersioninwaterat4OC.After10minthemembraneswereremovedfromthebathandleachedfor48hunderrunningwaterpriortocharacterization.Alltheoperationswerecarriedoutat20°Cand60%relativehumidity.MembranecharacterizationScanningElectronMicroscopeobservationsMembraneswerefirstdriedwithaBalzersUnioncriticalpointdryer,thenfracturedatliquidnitrogentemperaturetoobtaincross-sectionsthataftercoatingwithgoldbymeansofaBalzersUnionsputteringdevicewereobservedwithaCambridgeStereoscan250MK2scanningelectronmicroscope(SEM).TopandbottomsurfacesofdriedandgoldcoatedspecimenswerealsoexaminedwithSEM.PorositymeasurementsMembraneporositywasevaluatedat20°Cthroughcombinedbubblepressureandsolventpermeabilitymeasurementst-9-111performedwithapermoporosimeter[12,13].Wetmembraneswerekeptovernightinanaqueousphaseobtainedfromthedemixingat20°Cofamixtureofisobutanol,metanolandwaterinvolumetricratio15:7:25.Thealcoholrichphase,theviscosityofwhichat20°Cwasn=3.4mPa.s,wasusedtodisplacetheaqueousphasefromthemembrane.Theinterfacialtensionbetweenthetwophaseswas6=0.35mPa.mat20°C.UltrafiltrationtestsWetmembranesweretestedfor2hinalaboratoryscalepilotplantwithanaqueoussolutionofamixtureofdextranssuppliedbyPharmaciawithnominalaveragemolecularmassof10,000,40,000,110,000and500,000respectively,withaweightratio1.13:1.08:0.87:1.Theoperatingconditionswere:200KPa,40°Cand5m-s-lrecirculationrate.Theconcentrationofthefeedsolutionwas2%(wt/v)andwaskeptconstantbyrecyclingbothpermeate267andretentate.Permeatefluxwasmeasuredafter30-60min,andattheendofthetest.Permeatesampleswerecollectedatthesametimestomeasurethedextranconcentration,andmolecularmassdistribution.ThesampleswereanalyzedusingaWaters-MilliporehighpressureliquidchromatographequippedwiththreecolumnsToyoSodaTSKPW-6000,PW4000andPW3000andadifferentialrefractometer.Thedextranretentionwascalculatedasfollows:RXq(1-Cp/Cf)*100wereCpandCfaredextranconcentrationsinthepermeateandinthefeed,respectively.Molecularmassdistributionwasobtainedbythedirectcalibrationmethod[14]usingauniversalcalibrationcurveobtainedwithpolyethtyleneglicolsofnarrowmolecularmassdistribution,suppliedbyPolyscience.RESULTSANDDISCUSSIONTheadditionofPVPtoPSsolutionsgreatlyalteratestheviscosityandthehigherthemolecularmassofPVPthehighertheincreaseofviscosity.bPvP(dFig.1EffectoftheadditionofPVP25K(a)andPVP750K(b)to15wt.%PSsolutioninDMAontheviscosityoftheresultingternarysolution.268TheeffectoftheadditionofPVP25Kand750Kto15wt.%PSsolutioninDMAontheviscosityoftheresultingternarysolutionsisreportedinFigure1.Asaconsequenceofth