Effect of Mixed Solvents on the Structure of Polyvinylidene Fluoride Flat Membrane in Thermally Induced Phase Separation Method

Polyvinylidene fluoride (PVDF) flat membrane was prepared by thermally induced phase separation (TIPS) method using a mixture of dimethyl phthalate (DMP) and dioctyl phthalate (DOP) as a diluent. The PVDF/DMP/DOP system phase separation was test by DSC, cross section structure of membrane was observed by SEM. The effect of polymer concentrations, cooling rate and coagulation bath temperature on the cross section structure of membrane and surface micro-structure were studied. Results showed that membrane pore size porosity and water flux decreased with the increase in polymer concentration. The membrane section by the dendritic structure transition of nodular structure eventually turned into a compact structure. Pore size and water flux increased with the increase in coagulation bath temperature. The spherulite structures of the cross section of the membrane reduced while the lacy structure increased cross section smoothing.