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Desalination,83(1991)343-360ElsevierSciencePublishersB.V.,AmsterdamTHESTIJDYOFMECHANISMOFORGANICADDITIVESACTIONINTHEPOLYSULFONEMEMBRANECASTINGSOLUTION*I-IOUTAI-PINGDONGSHENG-HUAZHENGLING-YINGDalianInstituteofChemicalPhysics,AcademiaSinica,P.O.Box110,Dalian(China)SUMMARYTheinteractionbetweenpolysulfone(PS)and71lowmolecularweightorganiccompoundswithdiffe-rentfunctionalgroupshavebeenstudiedbythegasliquidchromatography(GLC).Thefreeenergyofsolu-tionandheatofsolutionofthesecompoundstoPSpolymerhavebeenobtained,andthefreeenergyofsolutionhasbeencorrelatedtotheselectedorganicadditivesinPS-dimethylacetamide(DMAC)castingso-lutions.Accordingtothecloudpointandtherheo-logicalpropertiesofPS-DMRC-additivessolutions,aswellastheeffectofadditivesontheporesizeinthemembranesurface,themechanismoftheactionoforganiccompoundsinPSmembranecastingsolutionhasbeenproposed.Themodelsuggestedmaygiveasatisfactoryexplanationtotheexperimentalresults.INTRODUCTIONGernerallythemembranecastingsolutionconsistsofpolymer,solventandadditives.Whenthemembranematerialandrelevantsolventaredetermined,thenatureofadditivesisthemostactivefactoraffe-ctingthestructureandstateofcastingsolutions.Thestructureandperformanceofresultingmembranecanbecontrolledthroughselectingdif.$erentorga-nicadditivesaswellasthedifferentamountofadditives.Intheearlydayof609,thestudywasfocusedontheinorganicsaltadditives(l).Theroleofinorganicsaltadditivesincastingsolutionhasbeenconsideredasfollows:thesaltionshave*TheprojectissupportedbyNSFC343344changedtheinteractionbetweenthemacromoleculechainsandthesaltitselfhasgivenaplaceforporeformationduringgelation.Soonafterwardstheorganicadditiveshavebeenused.Inthestudytotheorganicadditivesaction(2-7)thedifferentexperimentalmethodshavebeenused.Theconclusionisthatthemembraneporousstructureoriginatedfromtwokindsofstructureofpolymermoleculesinthecastingsolution,i.e.thepolymernetworkandaggregatestructure.Theactionoforganicadditivesincastingsolutionhasbeenconsideredaffectingthepropertiesofpolymernetworkandaggregate.TheactionofPVPadditivesinPSmembranecastingsolu-tionhasbeenexpectedtocontroltheexchanerateofsolventandprecipitantduringgelation(8$.Thestudywasmainlyfocusedonthehighmolecu-larweightorganicadditivesinPScastingsolution,thereforethegoalofthisworkistostudytheactionoflowmolecularweightorganicadditives.Experimental1.GasliquidchromatographySP-2305GasChromatograph(BeijingAnalyticalInstrumentFactory)withthermalconductivelydetec-torwasusedinthisexperiment.Thecolumntempera-turewascontrolledwithin0.4OC.ThePSmaterial(ShanghaiZhangHongPlasticsFactory)wereusedasstationaryphasecoatedonthe80-100meshchromo-sorbViHMDSsupportwhichhasminimaladsorption.2.CloudpointmeasurementAccurateamountsofPSandDMACwereaddedin-toatitratebottletoobtaina10.00%homogeneousbinarysolutionbystirringatroomtemperaturefor8hours.Thenorganicadditivesweredrippedslowlyintothetitratebottleat25*C,andthecloudpointwasobserved.3.DeterminationofviscosityNDJ-79rollingtypeviscositymeter(TongJiUniversity)wasinstalledinadrybox.Therelativehumiditywascontrolledunder30%.Theviscosityatdifferenttemperatureswasobtained.4.Analyticalmethodsofmembraneporousstruc-tureJEM-1200EXtypetransmissionelectronmicros-copes(JapanElectronicCo.)andHVS-5GBhighvacuum345coatingfilminstrument(JapanHitachiCo.)wereus-edtodeterminemembraneporesizeanditsdistribu-tion.toDunchtheporesatDuringdeterminingthewaterpermeability,thepressurewasraisedto9Kg/Cm'first,thenthedataofwaterflux-wereobtainedunder3Kg/Cm'.ResultsandDiscussion1.TheselectionoforganicadditivesI;nPSmem-branecastingsolutionwithGLC(1)BlanktestofsupportThedeadretentionvolumesofsomeorganicsolutesonsupport(withoutpolymer)arelistedinTable1.Alltheorganicsolutestestedhavethesimi-larretentionvolumetothatofn-hexaneexceptace-ticacid.Thisshowsthesupporthaslowadsorptiontoorganicsolutes.TABLE1TheretentionvolumesofsomeorganiccompoundstoChromsorbWHMDSsupportOrganiccompoundIRetentionvolumes(ml/g)n-hexane8.00butyronitrile8.00pyridine8.00n-amylamine8.03porpylbenzene8.03n-butglalcohol8.03furfurylalcohol8.03aceticacid8.45T(column)240°C,F(carriergas)8ml/min.(2)RepetitionexperimentUnderthesameexperimentalconditions,theretentionvolumewasdeterminedintwocolumnswithdifferentamountofstationaryphase.TherelevantthermodynamicsfunctionATwasobtained.ThedataarelistedinTable2.Therelativedeviationwaslessthan5%.346TABLE2Freeenergy(LG)indifferentcolumnsOrganicco;ipoundDhUCbenzylalcoholdimethylform-amidecyclohexanolmethylethylketoneethyleneglycoltoluenenitroethanen-butylalcoholethyleneglycolmono-methyletherAC(KJmol-'(column1'aG(KJmol-'1(column2:-11.66-15.44-13.78-9.88-2.89-10.38-3.00FE-10.36-6.16-7.03$2.I;*;;.Z-10.86-5.97-6.67-3.94-5.84-11.44-14.81-13.46Relativedeviation(%I2.3(3)HeatofsolutionandfreeenergyofsolutionThepartitioncoefficientKDisdefinedasfollows:amountofsoluteinthestationaryphaseKD=(1)amountofsoluteinthemobilephase&cordingtoRef.(S)VRKD='v(2)c)WhereV0obtaineit=adjustedrqentionvolume,whichmaybefromthechromatogram,andVS=volumeofstationaryphase.Theheatofosolutionisgivenby:AHs=-R2'(3)b(WhereVg=adjusteds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