The Study On The Modification Of PVDF UF Membrane And Its Gel Mechanism

Due to its hydrophobicity, the application of PVDF membrane was limited. In this paper, poly(methyl methacrylate) (PMMA) and cellulose acetate (CA) were introduced to hydrophilize PVDF membrane by the way of blend. What's more, the control of membrane pore size and the theory of gel and phase separation were also investigated. Firstly, the optimum composition and conditions for preparing PVDF membrane were obtained by square-crossing test whose indications were the pure water flux, the rejection for BSA and membrane strength. The membrane was prepared with higher pure water flux of 200 mL/cm2·h and better rejection of more than 96% for BSA, When the casting membrane solution, which was with the content of polymer 17%, the content of additive (NMP) 3%,the blend ration of PVDF/PMMA/CA and DMF/CH3COOH respectively 8:1:1 and 8:2, gel in the tap water.Secondly, a new method controlling membrane pore size, the chemical way,was brought forward in the paper. And a conclusion was drawn: it contributed to the solvent out of the casting membrane solution and made phase separation take place instantaneously that glacial acetic acid reacted with Na2CO3. Then the narrow distribution of membrane pores size with 0.15～0.21(m could be obtained. In addition, the hydrophilicity of membrane was characterized by the contact angle and results showed that the hydrophilicity of blend membranes was close to that of PMMA membrane if PMMA was contained in casting solution though CA wasmore hydrophilic than PMMA. This was mainly resulted from the delamination gel which was proved by the ultrared ATR spectrum and photo of teared dry membrane.Finally, the phase graph of the optimum composition of PVDF/PMMA/CA system was simply studied. Results indicated that the theory of phase separation for PVDF/PMMA/CA system belonged to poor polymer nucleus growth and the membrane structure with finger state pore was gained at last.To sum up, the innovations in my paper mainly included the choice of PVDF/PMMA/CA, the studies on the control of pore size and the theory of delamination gel.