Preparation of microporous poly(VDF-co-HFP) membranes by template-leaching method

The copolymer of vinylidene fluoride and hexafluoro propylene, poly(VDF-HFP), and the terpolymer of vinylidene fluoride, tetrafluoro ethylene, and hexafluoro propylene, poly(VDF-TEF-HFP), were solution blended at first to form dense composite films. Then, 90% acetone aqueous solution was used to leach out the terpolymer in the film at 5 °C. By varying the fraction of terpolymer in the blend and the leaching condition, microporous membranes with different porous morphology were produced, as revealed by SEM imaging. When the terpolymer content in the blend was lower than 30 wt%, low porosity (e.g., 24%) asymmetric membranes were obtained. On the other hand, when the terpolymer content approached 50%, skinless membranes with uniform pore distribution (pore size, ca. 1 μm) were produced. These skinless membranes demonstrate high tensile strengths (∼6 MPa) and water fluxes (3000-8000 LMH) that are potentially applicable to micro-filtration operations. Furthermore, crystallinities of the membranes were determined both by X-ray diffractometry and differential scanning calorimetry. Both methods indicated crystallinity near 24%, typical of poly(VDF-HFP) polymer in different forms.