Formation of an Interconnected Lamellar Structure in PVDF Membranes with Nanoparticles Addition via Solid-Liquid Thermally Induced Phase Separation

Novel microporous membranes were prepared via thermally induced solid-liquid (S-L) phase separation of mixtures containing poly(vinylidene fluoride) (PVDF)/diphenyl ketone (DPK)/nanoparticles [ such as montmorillonite (MMT) and polytetrafluoroethylene (PTFE)] in diluted systems with a mass ratio of 29.7/70/0.3 wt %. The crystallization and melting characteristics of these diluted systems were investigated by polarizing optical microscopy (POM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and wide angle X-ray diffraction (WAXD). The nanoparticle structure and the interaction between PVDF chains and nanoparticle surfaces determined the crystallization behavior and morphology of the PVDF membrane. The addition of MMT and PTFE had a significant nucleation enhancement on the crystallization of PVDF accompanied by S-L phase separation during the thermally induced phase separation (TIPS) process. It was observed that an interconnected lamellar structure was formed in these two membranes, leading to a higher tensile strength compared with that of the reference membrane without nanoparticles addition. Additionally, addition of MMT facilitates the fiber-like beta phase crystal formation, resulting in the highest elongation at break. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 2715-2723, 2013