Chemical cleaning and membrane aging of poly(vinylidene fluoride) (PVDF) membranes fabricated via non-solvent induced phase separation (NIPS) and thermally induced phase separation (TIPS)

Abstract

Poly(vinylidene fluoride) (PVDF) is one of the most used membrane materials in the water industries, and the PVDF membrane can be fabricated majorly through non-solvent induced phase separation (NIPS) and thermally induced phase separation (TIPS). The differences in membrane aging of NIPS-PVDF and TIPS-PVDF remain unclear. In this study, the agings of commercially available NIPS-PVDF and TIPS-PVDF membranes were investigated in the pilot-scale MBRs experiment as well as in the batch soaking tests. The raw PVDF powders in different crystalline polymorphs were also subjected to aging tests to examine the relation between PVDF polymorphous structure and aging. The results showed that the NIPS-PVDF membrane experienced more severe aging in the pilot-scale MBR experiment in comparison with the TIPS-PVDF membrane. Acid aging dislodged and eliminated the additives in the membrane, but did not attack the PVDF. NIPS-PVDF membrane was the dominant β PVDF phase, which was more susceptible to dehydrochlorination in alkaline oxide aging. The thin top layer in the asymmetric structure of the NIPS-PVDF membrane resulted in its vulnerability against alkaline oxide aging. The α PVDF phase and the symmetric structure of the TIPS-PVDF membrane contributed to its greater stability in alkaline oxide aging. Overall, the results can provide a basis for selecting a chemical cleaning strategy for PVDF membranes, and for improving the anti-aging characteristics of the PVDF in the membrane fabrication.