Preparation of PVDF-HFP Microporous Membranes via the Thermally Induced Phase Separation Process

Abstract

The thermally induced phase separation (TIPS) process was employed to prepare poly (vinylidene fluoride-co-hexafluoropropylene; PVDF-HFP) microporous membranes using sulfolane as the diluent. The phase diagram of the PVDF-HFP/sulfolane system was drawn and analyzed. The effects of polymer content in casting solution and cooling rate on the cross-sectional morphology, crystallinity, crystal structure, and porous structure of the resulting membranes were investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and a mercury porosimeter, respectively. The mechanical properties of the membranes were evaluated by tensile tests. It was found that a solid-liquid phase separation occurred in the PVDF-HFP/sulfolane system. Spherulites and "net-shaped" structures coexisted in the obtained membranes. Polymer content and cooling rates had some influences on the crystallinity, porous structure, and mechanical properties of the membranes, but no influence on the polymer crystal structure of the membranes.

High-Throughput Characterization of Novel PVDF/Acrylic Polyelectrolyte Semi-Interpenetrated Network Proton Exchange Membranes

“…PVDF is an extensively studied semicrystalline polymer known for the complex polymorphism of its crystalline phase. − There are at least four known PVDF crystal phases: namely, α (phase II), β (phase I), γ (phase III), and δ (phase IV or polar phase II), which are dependent on numerous factors, including mechanical and thermal history as well as processing conditions. Furthermore, it is known that the use of a comonomer such as HFP can disrupt the ordering of the PVDF chains, thus reducing its degree of crystallinity. ,, The degree of crystallinity and type of crystalline phase of PVDF can affect its bulk properties (e.g., mechanical strength, glass transition, and melting temperatures) as well as its interaction with other polymers (e.g., miscibility, phase separation). Information about crystallinity of the different PVDF grades can be obtained directly from their corresponding XRD spectra shown in Figure A.…”

Crystalline polymorphism in poly(vinylidenefluoride) membranes

“…In PVDF-co-HFP copolymers, the β phase was formed at low temperature, and it transformed from β phase to α and γ phases at a high temperature (120-130 °C), which is below its melting point 159 °C [59]. However, for (PVDFco-HFP) membranes prepared via TIPS using sulfolane as the diluent, the α crystalline phase was formed regardless of polymer content or cooling rate [104].…”

A study on fabrication of PVDF-HFP/PTFE blend membranes with controllable and bicontinuous structure for highly effective water-in-oil emulsion separation

“…To date, few literatures report PVDF-HFP membranes fabricated via thermally induced phase separation (TIPS) method. Ji et al 19 and Cui et al 20,21 prepared PVDF-HFP membranes for lithium ion battery via TIPS method. Cao et al 22 fabricated the PVDF-HFP porous membrane by supercritical CO 2 extraction of DBP template from PVDF-HFP/DBP lm.…”