Study On Surface Hydrophilic Modification Of Polyethersulfone Ultrafiltration Membrane Based On Tannic Acid And Carboxymethyl Chitosan

To improve the hydrophilicity of commercial polyethersulfone(PES)hollow fiber membrane,this paper aims to modify the surface of PES hollow fiber membrane,improve the water flux and better retention performance.In this experiment,tannic acid and carboxymethyl chitosan were used as modifiers,and commercial PES hollow fiber membrane was used as the bottom membrane by impregnation method.The effects of tannic acid(TA)and carboxymethyl chitosan(CMCS)addition in HCl-Tris buffer solution(p H=7.8)on the hydrophilic modification of membrane were investigated.At the same time,in order to further improve the membrane flux,N,N-dimethylacetamide(DMAC)was used to etch the bottom membrane PES to expand the membrane pores,and then the above modification was carried out to improve its filtration performance.First of all,in HCl-Tris buffer solution with p H=7.8,different mass of TA was added,and different TA concentration was configured.Then the surface of PES hollow fiber membrane was modified by impregnation method to prepare different TA-PES modified membranes.Then the effect of modification time on membrane modification was studied under the optimum TA.The results showed that with the increase of TA content,the water contact angle of the membrane gradually decreased,the hydrophilicity gradually increased,the flux first increased and then decreased,and the rejection rate of BSA did not change significantly.When the addition of TA was 0.05 g and the modification time was 7 h,the flux of the modified membrane reached the maximum.Compared with the original membrane 78.00 L/(m~2·h),the flux of the modified membrane increased to 105.65L/(m~2·h),and the retention rate reached 100.00%.Then,in order to improve the stability of TA,under the above conditions,different mass of CMCS and TA were added to the buffer solution,and then the original membrane was modified by impregnation method.With the modification time and the addition amount of CMCS as the research factors,a more hydrophilic TA-CMCS-PES modified hollow fiber membrane was prepared.The experiment showed that the amino group of CMCS interacted with TA hydroxyl by hydrogen bond,which prevented the oxidation of TA.With the increase of CMCS content,the water contact angle of the membrane further decreased.Compared with the original membrane,the flux first increased and then decreased;the optimal addition amount of CMCS was 0.025 g,and the optimal modification time was 6 h.The optimal flux of modified membrane reached 105.72L/(m~2·h),and the rejection rate reached 100.00%.Finally,the PES hollow fiber membrane was etched by DMAC,which was used as the pretreatment of the membrane.The optimal modification conditions of the above two steps(0.05 g TA-0.025 g CMCS-6 h)were selected to explore the influence of the amount of DMAC and the pretreatment time on the membrane modification,that is,the original membrane was treated by DMAC and then modified under the above conditions.The experiment showed that with the increase of DMAC concentration,the water contact angle of the membrane gradually increased,and the pore size gradually increased.Compared with the unmodified membrane,the membrane flux significantly increased,and its BSA rejection rate remained above 93.00%.At the same time,on the basis of the optimal DMAC concentration,the effect of pretreatment time of different bottom membranes on membrane performance was studied.The experimental results show that with the increase of pretreatment time,the water contact angle of the modified membrane increases gradually,the pore size increases first and then decreases,and the flux increases first and then decreases.When the pretreatment time is 20 min,the optimal membrane flux reaches120.84 L/(m~2·h),and the retention rate reaches 98.90%.