Study In Modification Of PVDF Membrane With Zwitterionic Polymers And Membrane's Anti-fouling Performance

The situation of environment pollution and shortage of water resources has created a bottleneck problem for the world's sustainable economic development.Water treatment technology is of particularly importance.Advanced membrane technology has become one of the effective means to solve the issue and contribute to sustainable economy,and has received wide attention around the world,due to its high separation efficiency,low energy consumption,small foot print,easy to integrate with other technology without polluting the environment.Poly?vinylidene fluoride??PVDF?membrane is commonly used because of its advantages of high mechanical strength and good chemical stability.However,pure PVDF membrane has low surface energy,and is highly hydrophobic,it is easy to be polluted by many organic pollutants,such as proteins,etc.,resulting in a rapid decline in membrane performance.Therefore,improving the hydrophilicity of PVDF membrane is necessary to increase the membrane's ability against oganic pollution.Amphiphilic polymer additive not only provides the advantage of hydrophilic property,but also can overcome the disadvantage of some small hydrophilic polymer additive that may leach out during the application of wastewater treatment,and thus has become a research focus in recent years for membrane study.The zwitterionic polymer can form hydration layer on membrane surface simultaneously through hydrogen bonding and electrostatic effect,due to its both cationic and anionic groups,which makes the hydration layer more stable,as well as provides strong steric effect resisting pollutants attachment.Therefore,the main research purpose of this study is to desig and synthesize a new zwitterionic polymer of the structure of PMMA_x-b-PSBMA_y or P?MMA_x-r-SBMA_y?,as an additive to blend it with PVDF to prepare modified membranes.The additive/PVDF blend membranes were obtained by the immersion precipitation method.The effect of additive ratio and coagulation bath on the structure performance of the prepared membrane was investigated.When the ratio of additives and PVDF was at 1:9,coagulation bath was pure water,PMMA_x-b-PSBMA_y/PVDF blend membranes reached the smallest water contact angle of70.57°,with?G^TOT at-22.35 mJ/m².For the filtration of two types of different charged protein solutions?BSA and LYZ?,the relative flux recovery rate were 77.48%and 58.82%,respectively,the rejection rate of BSA and LYZ being 100%and 59.7%respectively.The results showed that the prepared zwitterionic additives improved the ability of the membranes to protein pollution.Relative to the protein LYZ,the modified membranes in this study showed better perfoamance for filtrating BSA protein solution.The result is consistent with the prodiction of the XDLVO theory to a large extent.In order to further improve the anti-fouling properties and hydrophilicity of the membrane in this study,the zwitterionic additives was prepared by random polimerization,as P?MMA_x-r-SBMA_y?,to increase the content of SBMA in the additive,and thus the SBMA content in the prepared membrane's surface and internal structure.According to the different monomer ratio used were obtained in the synthesis,two additives named r-poly1 and r-poly2,respectively,were obtained and then blend with PVDF to obtain modified membranes.It was found that porosity increased to 97.13%and 54.74%from 10.33%after adding the additives.When the blend ratio of r-poly2 and PVDF was 1:9,and coagulation bath contained 15%solvent,the membrane has achieved the best protein resistance:during the filtration of the protein solutions,the relative flux decrease rate,relative flux recovery rate and protein reject rate were 65%,100%and 96.5%respectively.When filtered hexadecane solution,the relative flux decrease rate,relative flux recovery rate and oil rejection rate of the membrane modified were 67.5%,100%,98.76%.The study demonstrated that P?MMA_x-r-SBMA_y?greatly improved the membrane property resistance of protein fouling,and can be an good additives for PVDF membrane modification to filter protein and oil in studies.Synthesizing two kinds of additives by different methods and blended them with PVDF,the result illustrated that membranes with P?MMAx-r-SBMAy?had better hydrophilicity.when the blend ratio of additive and PVDF was 1:9,coagulation bath was pure water,the water contact angle of modified membranes were 55.42°?r-poly1,H1?and 70.57°?M2?,respectivily.Under the optimum film forming's condition,the zwitterionic additives was prepared by random polimerization can better improve the membrane property resistance of protein fouling by camparing RFD,RFR and BSA rejection rate of membranes.