Synergistic manipulation of the polymorphic structure and hydrophilicity of PVDF membranes based on the in-situ esterification reaction to prepare anti-fouling PVDF membranes

Abstract

Improving the content of polar crystal phase and the hydrophilicity of PVDF membranes are proved the efficient ways to improve the enduringly anti-fouling ability of PVDF membranes. But synergistic manipulating the polymorphic structure and hydrophilicity of PVDF membranes is rarely reported so far. In this paper, the in-situ esterification reaction between styrene-maleic anhydride (SMA) and meglumine (MG) during nonsolvent induced phase separation (NIPS) process is found to simultaneously manipulate the polymorphic structure and hydrophilicity of PVDF membranes. The water contact angle of membranes is largely reduced from 95.8° to 31.2° with the increase in the MG adding amounts, proving that the hydrophilicity of PVDF membranes is notably improved. Moreover, the β-phase content is improved as the MG adding amounts increase due to the enhanced interactions between the –OH groups and the –CF₂ groups of PVDF through hydrogen bonds. As a result, a highly hydrophilic PVDF membrane with >90 % β-phase content is obtained. The durable antifouling testing reveals that the PVDF blend membranes possess lower flow decline ratio and higher flux recovery ratio compared with the virgin PVDF membranes, thus exhibiting better antifouling ability. The synergistic manipulation of hydrophilicity and crystalline phase of PVDF membranes might offer a paradigm shift in the design of high-performance separation membranes.