Surface Chemical Modification Of Poly(vinylidene Fluoride)Membrane And Its Application In Swage Treatment

In the 21st century,the protection of water resources has become a major problem,with the further development of industry,water pollution is becoming more and more serious,the application of membrane technology in water treatment has been proved effective.Polyvinylidene fluoride(PVDF)is a kind of membrane materials with excellent performance,such as good electrical properties,heat resistance,good mechanical properties,radiation resistance and chemical stability.It has become one of fluorine-containing polymer membrane materials at present.However,due to the obvious hydrophobicity of pure PVDF membrane,it limits its application in water treatment.Therefore,to explore the mechanism of membrane fouling and hydrophobic modification of PVDF membrane has become one of the focuses of water treatment workers.In this paper,the hydrophilic and antifouling properties of the modified PVDF membrane are studied by surface chemical modification.Firstly,KOH/CH3OH,KOH/KMnO4and KOH/KMnO4/TBAB three kinds of mixed liquid were used to modify the surface of the membrane.Through the analysis of the water flux and contact angle of the modified PVDF membrane the optimal alkali concentration,three kinds of processing time and temperature were determined.The best conditions of KOH/CH3OH mixed liquid are as follows:KOH concentration 5wt%,heating time 60min,heating temperature 60?.And the best conditions of KOH/KMnO4 and KOH/KMnO4/TBAB are as follows:KOH concentration 30wt%,heating time 30min,heating temperature 60?.Secondly,the properties of the three kinds of PVDF membrane under the optimum conditions of the above mixture are analyzed and compared.In the fourier transform infrared spectroscopy,it is found that the hydrophilic polar groups such as carbonyl group and hydroxyl group are successfully introduced into the modified membrane surface.At the same time,it is found that the membrane contact angle,water flux,water absorption,membrane fouling index(MFI)and bovine serum albumin(BSA)adsorption capacity are improved obviously.The contact angles of the modified PVDF membrane are significantly reduced from 110° to 75°,66°,62°.The water fluxes are greatly improved from 33L/(m2·h)to 95L/(m2·h),100L/(m2·h),110L/(m2·h).Water absorption rate is 4 to 10 times that of the original membrane.The MFI value decreases from 13.6 to 0.9067,0.8813 and 0.8709.The adsorption capacity of BSA decreases from 78.3?g/cm2 to 38.2?g/cm2,30.?g/cm2,27.6?g/cm2.Finally,there PVDF membranes before and after modification are used to treat the domestic sewage.Compare the treatment performances which showes that the removal efficiencies of turbidity,SS and COD are not significant,which are 89%?91%,93%?95%,73%?76%.The flux before and after modification showes a good linear relationship with t0.5?and the slopes of linear fitting are-2.8071,-4.0205,-4.1855,-4.4355.The linear slope of the modified membrane is obviously less than that of the original PVDF membrane,which indicates that the original PVDF membrane is more easily contaminated.And the rate of membrane fouling is reduced by modification.Using clean water to clean the polluted membranes,the recoveries rate of membrane water flux are 48%,69%,74%,80%,and the membrane resistance coefficients are 1.0625,0.4394,0.3514,0.25.The resistance coefficient of modified membrane is significantly less than that before modification,which indicates that the membrane fouling resistance is improved.