Zwitterionic Polymer Coating Modified Polyethersulfone Ultrafiltration Membrane To Improve Antifouling Capacity

Membrane separation technology is being widely used in chemical and food industries,water treatment,ultra-pure water preparation and other fields due to its high separation efficiency,low energy consumption,and no environmental pollution and so on.However,the fouling on membrane surfaces caused by the attachment of foulants(including inorganic,organie,and biological substances)is the most difficult problem.Protein adsorption and microbial cell adhesion are the main source of biofouling,which may account for 50-90%of the fouling and are difficult to eradicate from the membrane,since microorganism can grow on the membrane surface to form biofilm with a few initial colonies.Therefore,anti-biofouling on membrane has becoming a hot spot of research.The introduction of strongly hydrophilic zwitterion polymer to membrane surface is a common and effective method.Surface grafting can form a stable coating good antifouling performance.However,there quirement for specific reaction group on the membrane,and/or complicated reaction process limit its application.On the other hand,surface coating is the simplest method,the coating often immobilized on membrane by hydrogen bonds or van der Waals force,result in coating loss during filtration.In this dissertation,inspired by the universal adhesion of mussel mimetic polydopamine(PDA)and the excellent antifouling property of cell outer membrane phosphorylcholine zwitterion functionality,copolymer PMEN was synthesized by copolymerization with methacryloyloxyethylphosphorylcholine and p-nitrophen-oxyethylmethacrylate.Dopamine was coupled at the p-nitrophenoxyethyl group of PMEN to prepare PMEND.Three strategies were investigated for coating the phosphorylcholine zwitterion polymers on a commercial PES,ultrafiltration membrane(PESUM).Finally,PDA intermediated and PMEN permeated coupling method in aqueous solution was optimized,which could be used to form the zwitterion coating on other membrane and surfaces.The main work 1s as follows:Three kinds of PMEND polymers were prepared and adhered on PDA precoated PESUM from aqueous solutions.With the assistance of the PDA intermediate layer,the PMEND polymers could adhered on the PESUM/PDA surface stably when the content of catechol in the PMEND is more than 20%in unit.The anti-fouling performance of the modified ultrafiltration membrane was improved obviously,and the flux recovery ratio of PESUM/PDA/PMEND-73 was reached to 89%after three cycles of BSA protein pollution experiment.In addition,the modified membrane is powerful in removing oil from emulsions,and 99.99%or more of oil is removed from the oil-water emulsion at a concentration of 80,000 ppm.PMEN polymers bearing 10,20,and 30 unit percent of p-nitrophenoxyethyl active ester groups(labeled as PMEN91,PMEN82 and PMEN73)were synthesized with monomers of methacryloyloxyethylphosphorylcholine and p-nitrophenoxyethyl methacrylate.The PMEN was anchored on the surface of PESUM-PDA by amidation coupling with the PDA amino groups.Experiment results show that the grafting method can significantly improve the coating stability of PMEN91.However,the best anti-fouling performance is limited,as the flux recovery ratio is only 83%after three cycles of BSA fouling test.An optimized method of surface grafting was proposed.PDA solution and PMEN solution were permeated into the small pores of ultrafiltration membrane under pressure.Thus,both the membrane surface and the inner surface of the small pores could be grafted with PDA-PMEN coating,result in increased amount of PMEN immobilized on the membrane.This method improved the rejection ratio of the protein and enhanced the antifouling performance of the modified membrane.The PESUM-PDA-PMEN91(w/P)samples showed flux recovery ratios of 100%and 96%after two and three cycles of BSA contamination tests,respectively.Protein adhesion and bacterial adhesion results showed that PMEN antifouling coating could effectively reduce the adhesion of biological contaminants on the surface.Stability test results showed that the coating could be stabble in most ultrafiltration conditions for practical application.