Preparation of high strength poly(vinylidene fluoride) porous membranes with cellular structure via vapor-induced phase separation

The preparation of poly(vinylidene fluoride) (PVDF) membranes with high mechanical strength via vapor-induced phase separation (VIPS) is still a great challenge. In this study, high strength PVDF membranes with cellular pore structure are successfully prepared by comprehensively regulating the process parameters such as the dissolution temperature (Td), vapor temperature (Tv) and exposure time (t) during the VIPS process, as well as the membrane-forming parameter i.e. mass fraction of PVDF polymer. The effects of these parameters on microstructure and performances of the PVDF membranes are systematically investigated. In the investigated ranges of t from 0.67min to 20 min, the membranes with cellular structure are obtained at both elevated Td and Tv of 65 °C, relative humidity of 70%RH and mass fraction of 15 wt% PVDF. All the PVDF membranes with cellular structure prepared at elevated Td and Tv of 65 °C exhibit high mechanical properties, and the tensile stress at break (σ*) and tensile strain are higher than 2.5 MPa and 15%, respectively. The PVDF membrane prepared at t of 0.5 min has a critical structure and shows the maximum σ* of 4.0 MPa and tensile strain of 33%, respectively. It is expected that the results provide a valuable guidance for the design and fabrication of membranes from semi-crystalline polymer with desirable performances.