Study On Improving Hydrophilicity Of Polysulfone Ultrafiltration Membranes By Blending With Sulfobetaine Polyimide

Membrane fouling,which is caused by the inherently hydrophobic characteristics of polysulfone(PSf),dramatically decreases the membrane performance and lifetime,and represents a major roadblock for membrane applications.Thus,many efforts have devoted to improving membrane hydrophilicity and filtration properties with its modifications,however,many studies showed that the improvement of membrane antifouling property was mostly implemented at the sacrifice of other performances.In this study,we report the preparation and properties of PSf ultrafiltration membranes with sulfobetaine polyimides(PIs)as blending additive.Three molecular weights sulfobetaine PIs were synthesized and blended with PSf to fabricate ultrafiltration membranes via non-solvent induced phase separation process.Three different molecular weights sulfobetaine PIs with hydrophobic PI moity and two sulfobetaine end group were synthesized using 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride and 2,2’-dimethyl-4,4’-methylenedianiline as monomers,3-(dimethylamino)-1-propylamine and 1,3-propane sultone as blocking agents.The stability and compatibility of amphiphilic PIs in membrane matrix were effectively enhanced due to the strong interactions between PSf and hydrophobic chains of the amphiphilic PIs.Antifouling membranes with high pure water flux(PWF)and bovine serum albumin(BSA)rejection were prepared by blending with sulfobetaine PIs and polyethylene glycol(PEG).It was proved that membrane hydrophilicity,porosity and antifouling properties were significantly enhanced due to the introduction of sulfobetaine PIs.And the finger like pores of membrane became shorter and more uniform.Experimental results indicated that the addition of sulfobetaine polyimides substantially promoted the overall performance of polysulfone membranes,such as PWF(270 L/(m2 h)),BSA rejection(95.2%),anti-protein adsorption and antibacterial.During the preparation of the membrane,the hydrophilic segments of the additive extend toward the surface of the membrane,and the hydrophobic structure is embedded in the film matrix to improve the stability in the film and ensure that it is not eluted in the aqueous environment.Antifouling membranes with high mechanical strength and high thermal stability were prepared by blending with the highest molecular weight sulfobetaine PI.When the addition amount of the additive was 1.35%,the glass transition temperature of the blended membrane increased to 202 oC,and the PWF and BSA rejection could still be maintained at 200 L/(m2 h)and 98% respectively after soaking in water at 90 °C for 3 hours.The mechanical strength of the membrane can be ensured by adding the sulfobetaine PI additive,and the production cost could be reduced by reducing the amount of PSf.