Preparation of microporous poly(vinylidene fluoride) membranes via phase inversion in supercritical CO2

Microporous poly(vinylidene fluoride) (PVDF) membranes were prepared from PVDF/N,N-dimethylacetamide (DMAC) solutions by using supercritical CO2 phase inversion process. As revealed by scanning electron microscope (SEM) and differential scanning calorimeter (DSC), the PVDF membranes exhibit morphological characteristics resulting from both liquid–liquid phase separation and crystallization, i.e., cellular pores surrounded by interlinked PVDF particulate crystallites. This indicates that both types of phase separation processes take place in the supercritical CO2 phase inversion process. The effects of pressure, temperature, and initial polymer concentration on the final membrane structures were investigated. We also investigated the effect of addition of poly(methyl methacrylate) (PMMA) in the casting dope on the PVDF membrane structure. The membrane structure changed significantly with the variation of PVDF/PMMA mass ratio in the casting dope as well as polymer concentration. It was found that the variation of temperature and pressure has a minor influence on the membrane structure.