Preparation And Characterization Of Solvent Resistant Nanofiltration Membrane Based On Polyvinylidene Fluoride

Solvent resistant nanafiltration(SRNF)process,which possesses advantages of high efficiency,low energy consumption and simple operation,shows very promising prospect in many fields,like the textile,paper,pharmaceutical,petrochemistry.Recently,developing high performance polymer solvent resistance nanofiltration membrane with low cost becomes one of the central topics in the field of membrane separation.Polyvinylidene fluoride(PVDF)as a kind of polymer,which owns advantages of high mechanical strength,strong chemical stability and good film forming ability,is an ideal option for solvent resistant nanofiltration membrane.In this study,to improve stability and selectivity of PVDF nanofiltration membrane,the PVDF membranes were modified by simple crosslinking with polyvinylpyrrolidone(PVP)and further investigated in SRNF system.After crosslinking,the separation performance,stability and antifouling performance of the membrane were greatly improved.The relationship between membranes morphology and their performance was further clarified by studying their forming process,crosslinking mechanism and microstructure.The detailed results are as following:(1)The PVDF nanofiltration membranes were prepared by immersion precipitation phase inversion method.The morphology of membrane was tuned by changing the concentration of PVDF in the casting solution(14 wt%,17 wt%,20 wt% and 23 wt%).With increasing the concentration of PVDF in the casting solution,the membranes became thicker,the porosity and the number of macropores in the supporting layer decreased,the retention rate of solute increased and the permeation flux on solvent decreased,enhance of membranes selectivity.(2)To further enhance the separation performance and the solvent stability of PVDF nanofiltration membrane,the PVDF membranes were further crosslinked by PVP.Compared with the original PVDF nanofiltration membrane,the stability of the modified membrane was improved,the rejection was obviously increased,and the permeation flux was decreased.For example,the membranes prepared from 23 wt% of PVDF solutions showed a rejection rate of32.7% to 93.5% on Rose Bengal in acetone solution before and after crosslinking respectively.To note that: the membranes showed greatly improved stability in THF after crosslinking,the crosslinked membrane showed more than 95% rejection on Rose Bengal in THF,showing very good prospect in SRNF.(3)The antifouling performance of PVDF nanofiltration membrane was studied as well.Bovine serum albumin(BSA)with concentration of 1mg/mL was selected as solute.The flux recovery rate of pure water was measured.The concentration of PVDF in the casting solution was 23 wt%,the rejection rate of 1 mg/mL BSA increased from 88.8% before crosslinking to98.8% after crosslinking,showing a high selectivity.Compared with the original PVDF nanofiltration membrane,the flux recovery rate of the modified membrane was increased,and the antifouling performance of the modified membrane was enhanced,with have a good prospect for development.