Surface Hydrophilicity and Structure of Hydrophilic Modified PVDF Membrane by Nonsolvent Induced Phase Separation and Their Effect on Oil/Water Separation Performance

The hydrophilic polyvinylidene fluoride (PVDF) material was prepared by ozone-induced grafting polymerization of acrylic acid on PVDF chains, and used for preparing oil/water separation ultrafiltration membranes by the nonsolvent induced phase separation method. The effect of membrane casting conditions was studied, and the results showed that N-methyl-2-pyrrolidone (NMP) present in the coagulation bath affected the membrane surface hydrophilicity as well as the membrane structure, and that casting solution concentration and air exposure time affected pore size but had little influence on surface hydrophilicity. The effect of material hydrophilicity and pore size was investigated, and the results indicated that improvement in hydrophilicity not only increased water flux itself, but also enabled high oil retention of membranes with larger pore sizes which had much higher water flux. The highest flux for the membranes with kerosene retention over 90% can reach over 300 L/m(2)h. The membranes showed good reusability under simple back flush.