Effect of solvent power on PVDF membrane polymorphism during phase inversion

Polyvinylidene fluoride (PVDF) membranes were prepared via the phase inversion method. The focus of this paper was put on the effects of four specific solvents with different solubility power including hexamethylphosphoramide (HMPA), trimethylphosphate (TMP), N,N-dimethylformamide (DMF) and triethylphosphate (TEP) on membrane polymorphism. Polymorphism of PVDF membranes was analyzed by wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) respectively. All results revealed that the dissolution of PVDF in different solvents had a great influence on the membrane crystalline phase. The well dissolved PVDF solution tended to form α phase during phase inversion process while the poorly dissolved PVDF solution favored the formation of β phase. Furthermore, a soft coagulation bath was used during the phase inversion process to enhance the filtration permeability of the PVDF membranes. The fouling resistance to protein and mechanical properties of the membranes were also investigated.

► PVDF membranes were prepared via the phase inversion method.
► PVDF membrane polymorphism is highly dependent on the solvent dissolving power.
► The well dissolved PVDF solution tended to form alpha phase.
► The poorly dissolved PVDF solution favored the formation of beta phase.