Poly(vinylidene fluoride) membranes prepared via nonsolvent induced phase separation combined with the gelation

Abstract In this work, we employed the nonsolvent induced phase separation (NIPS) combined with the gelation method to prepare poly(vinylidene fluoride) (PVDF) membranes. The mixture of N,N-dimethylformamide (DMF) and γ-Butyrolactone (γ-BL) was used as a solvent, and water was used as a nonsolvent. Membrane changed from a cellular to spherulitic morphologies simply by varying the mass ratio of DMF/γ-BL and the PVDF concentration. On quenching the casting solution (with 15 wt% PVDF concentration) in the water bath, the membrane had a uniformly cellular morphology, which resulted from a typical liquid–liquid (L-L) phase separation. At higher PVDF concentrations (≥20 wt%), membranes presented a spherulitic structure, arising from a solid–liquid (S-L) phase separation. The crystallization behavior and crystalline form of the PVDF membrane were identified by different scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR), respectively. For the 15 wt%-PVDF membrane gained from the mixed solvent with a mass ratio of DMF/γ-BL = 8/2, the highest tensile strength (7.3 MPa) and elongation at break (223%) was obtained.