| Membrane separation technology has been widely applied to the treatment of wastewater due to its high separation efficiency and relatively low energy consumption as well as it could be operated at room temperatures etc.Polyvinylidene fluoride(PVDF)is a kind of ideal membrane material because of its high mechanical strength,good thermal resistance and chemical stability.While its low surface energy and strong hydrophobicity make it easy to interact with the pollutants in the water to cause the fouling and function decreased of membrane,eventually restricting the development of membrane separation technology.It is generally accepted that the hydrophilic modification of membranes could improve their anti-fouling performance,and has been a hot spot in membrane separation field recently.Novel amphiphilic copolymers including P(St_x-co-MAA_y)and P(St_x-co-MAA)-g-fPEG_y were designed and synthesized in this study,and blend them with PVDF respectively by the method of phase inversion to prepare modified membranes.Factors such as the percentage of hydrophilic and hydrophobic segments,blend ratio of additives and PVDF,coagulation bath temperature and post-processing methods are carried on the structure and property of membranes.The results showed that the development of the macroporous structure of the membrane which modified by P(St_x-co-MAA_y)as an additive decreased its mechanical strength;And the increase of MAA group ratio in molecular could improve the hydrophilicity of the modified membrane.When the blending ratio of P(St1-co-MAA1)and PVDF was 1:9 and 2:8,and the coagulation temperature was 50 ?,the modified membranes(H1 and H2)had better hydrophilicity,their water contact angles were 62.10° and 62.63°respectively.In addition,the adsorption experiment of BSA showed that H1 and H2 had the minimum adsorption quantity of BSA,only 18% and 21% of the pure PVDF.The filtration experiments of BSA solution and hexadecane emulsion indicated that the addition of P(St_x-co-MAA_y)made the pure water flux of membranes improved,the relative flux decline of modified membranes reduced and the relative flux recovery increased.Therefore,H1 had the best anti-fouling performance.In order to further enhance the hydrophilicity and anti-fouling property of membranes,we used P(St_x-co-MAA_y)and fPEG which has hydrophilic flexible chain segment as reactants by esterification to synthesize a novel tri-block amphiphilic copolymer called P(St_x-co-MAA)-g-fPEG_y,and then used it as an additive to modify PVDF.The results showed that the modified membrane(M3)presented best hydrophilicity and fouling resistance when the ratio of P(St1-co-MAA)-g-fPEG1 and PVDF was 1:9 and the temperature of coagulation bath was 50 ?.Meanwhile the contact angle of water was 48.80°and the contact angle under water of oil is 160.66°.Compared with the H1,M3 has lower static adsorption to BSA.In the BSA solution and hexadecane emulsion filtration experiments,the initial water flux of the M3 is far higher than H1,after filtering BSA solution,the relative flux decline was 46.0%,less than 75.0% of the H1.After filtering the hexadecane emulsion the relative flux decline was 57.7%,higher than 37.0% of the H1,but the flux value is higher than the H1,the relative flux recovery of M3 was higher than the H1,its fouling resistance is better.At the same time,the membrane filtration experiments of humic acid results showed that the modified membranes have excellent anti-fouling property to natural organic matter. |
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