Preparation of PVDF hollow fiber membrane from a ternary polymer/solvent/nonsolvent system via thermally induced phase separation (TIPS) method

Porous poly (vinylidene fluoride) PVDF hollow fiber membranes were successfully prepared from a ternary system including PVDF, solvent and nonsolvent via thermally induced phase separation (TIPS) process. Glycerol triacetate (triacetin) as solvent and glycerol as nonsolvent were used in this study. The effect of nonsolvent concentration on polymer/solvent/nonsolvent phase diagram was studied. The addition of glycerol brought about the change of phase separation mechanisms from the solid-liquid phase separation (polymer crystallization) to liquid-liquid phase separation. Based on these results, hollow fiber membranes were fabricated. Effects of nonsolvent concentration, air gap distance and water bath temperature on morphology, water permeability, solute rejection and strength of fabricated membranes were studied. Using shorter air gap distance, higher bath temperature and higher glycerol concentration were effective to obtain higher water permeability. In another set of experiments, the effect of polymer extrusion temperature on morphology and permeability of the hollow fiber membrane was studied. It was observed that changing polymer extrusion temperature had different effects on membrane permeabilities for both membranes with crystalline and interconnected structures. In addition, the performance of membranes prepared from PVDF/triacetin/glycerol system was compared with that prepared from PVDF/triacetin system.