PreparationandpropertiesofPVDFPVAhollowfibermembra

PreparationandpropertiesofPVDF/PVAhollowfibermembranesNanaLi,ChangfaXiao⁎,ShulinAn,XiaoyuHuTheKeyLaboratoryofHollowFiberMembraneMaterialsandMembraneProcess,MinistryofEducation,TianjinPolytechnicUniversity,Tianjin300160,ChinaabstractarticleinfoArticlehistory:Accepted17October2008Availableonline6November2009Keywords:PVDF/PVAhollowfibermembraneHydrophilicityMechanicalpropertyInterfacemicrovoidFluxRejectionratioOnprincipleofpolymerblendphaseseparation,PVDF/PVAhollowfibermembraneswerepreparedusingphaseinversionmethod.Themembranemorphologyandperformancevariedwiththeblendingratio.ThePVDF/PVAblendsshowedincompatibilitybytheresultsofdynamicmechanicalanalysis(DMA)andinfraredattenuatedtotalreflection(FTIR-ATR)samplingtechnique.Basedonburstingpressureandtensilestrengthsresults,wesuggestthatthemechanicalpropertiesofPVDF/PVAblendmembranesareworsethanthatofPVDFmembrane.PVAcanimprovethehydrophilicityofPVDF/PVAhollowfibermembranes,whichcouldbeilluminatedbythedecreaseincontactangle,theincreaseinequilibriumwatercontent(EWC)andthevarietyindynamicmoistureregain.ThepurewaterfluxincreaseswhiletherejectionratiodecreaseswithPVAcontentincreasing.Moreover,PVAcanimprovetheanti-foulingpropertyofPVDF/PVAhollowfibermembranes,whichcouldbeilluminatedbytheresultofincreasecoefficientofresistance.©2009ElsevierB.V.Allrightsreserved.1.IntroductionAsasemi-crystallinepolymer,poly(vinylidenefluoride)(PVDF)isfitformembranematerialduetoitsexcellentchemicalresistance,physicalandthermalstability,highstrengthandflexibility[1,2].However,thehydrophobicityofPVDFremainsaproblemandlimitsitsapplication,thus,hydrophilicmodificationofPVDFmembranesisoneofthehotspotsinmembranescience[3–5].Blendingisoftenusedtochangethepropertiesofpolymericmaterials[6].BlendsofPVDF/PEG,PVDF/PMMA,PVDF/PAN,PVDF/Nylon6,PVDF/SPS,PVDF/PVAc,PVDF/CA,PVDF/PEOandPVDF/PUhavebeenusedinthepreparationofultrafiltrationmembranes[7–17].Itiswellknownthatpoly(vinylalcohol)(PVA)isoneofthepolymericmaterialsformakingultrafiltrationmembranes.Itpos-sessesgoodhydrophilicityandotheradvantages[18].SomepapershaveindicatedthatPVAisapolymermisciblewithPVDF[19–21],andahighdegreeofintermolecularinteractionpresentsbetweenPVDFandPVAchains[22].AlthoughbothmiscibilityandmorphologyofPVDF/PVAblendshavebeenextensivelystudied,theeffectofblend-ingwithPVAonthepropertiesofPVDFmembranehasnotbeenreportedyet.Inthisstudy,PVDF/PVAblendhollowfibermembraneswerepreparedusingphaseinversionmethod.BlendingwithPVAcannotonlyimprovethehydrophilicityofPVDFmembrane,butalsoformtheinterfacemicrovoidthroughpolymerblendphaseseparation.Themorphologyandperformanceofthesemembraneswereinvestigatedbyusingdynamicmechanicalanalysis(DMA),scanningelectronmicroscope(SEM),ultraredinfraredattenuatedtotalreflection(FTIR-ATR)andcontactanglegoniometer.2.Experimental2.1.MaterialsThePVDF(W#1300)kindlyprovidedbyKurehaChemicalIndustryCo.,Ltd.,wasdriedfor24hinavacuumovenpriortouse.ThePVA(2099)waspurchasedfromShanxiSanweiCo.,Ltd.,whichwasrinsedanddriedpriortouse.Reagent-gradedimethylsulfoxide(DMSO)andpolyethyleneglycol(PEG)ofmolecularweight600suppliedfromTianjinFuchenChemicalReagentPlantwereusedwithoutfurtherpurification.2.2.PreparationofPVDF/PVAhollowfibermembranesThehollowfibermembraneswerepreparedwiththephaseinversionmethod.ThePVAwaswashedthoroughlyinwaterandthendriedinthevacuumovenforapproximately48hat50°Ctoremoveitswatercontent.ThePVDFwasdrieddirectlyinthevacuumovenforapproximately20hat90°Ctoremoveitswatercontent.Then,thespinningsolutionswerepreparedbydissolvingpolymerinDMSOatvariousblendingratiosofPVDF/PVA/PEG.Thetotalpolymercontentwas20wt.%,andPEGcontentwas6wt.%.Afterstirringstronglyfor12hat95°C,theresultinghomogeneoussolutionwastransferredtoastainlesssteelreservoirandwasthendegassedovernightat70°Cundervacuum.Thehollowfiberspinningapparatusanddetailspinningprocedureshavebeendescribedelsewhere[23].Inspinning,thespinneretwiththeDesalination250(2010)530–537⁎Correspondingauthor.DepartmentofMaterialsScience,TianjinPolytechnicUniversity,Tianjin,China.Tel.:[phone].E-mailaddress:[e-mail](C.Xiao).0011-9164/$–seefrontmatter©2009ElsevierB.V.Allrightsreserved.doi:10.1016/j.desal.2008.10.027ContentslistsavailableatScienceDirectDesalinationjournalhomepage:ficediameterof2.0mmandtheinnertubediameterof1.2mmwasused.Thefiberswerespunbythewetprocess(air-gap=20cm).Thetemperatureofenvironmentwas20°Candrelativehumiditywas65%.Thetake-upvelocitywas7–8m/min.Thesolutionextrusionratewasintherange2–2.5mL/minandtheinternalcoagulantflowratewasintherange2–2.5mL/min.Waterwasusedasinternalcoagulationbathandexternalcoagulationbathforallspinningruns.Thepreparedhollowfiberswereimmersedinfreshwaterforatleast2daysandthenexamined.ThePVDF/PVA(90/10,80/20,70/30wt/wt)hollowfibermembraneswerelabeledasPVDF9,PVDF8,andPVDF7respectively.BeforeSEMtests,weputtheresultingmembranesinglycerol–watersolutions(3partsglycerolto2partswater)andthendriedinair,whichcanretaintheporousstructure.Beforethemeasurementsofcontactangleandmechanicalpropertytests,weputtheresultingmembranesinavacuumfor