Crystallization behavior of PVDF in PVDF-DMP system via thermally induced phase separation

The crystallization behavior of PVDF (poly (vinylidene) fluoride) in FVDF-dimemylphthalate(DMP) system was investigated in the liquid-liquid (L-L) phase separation region, solid-liquid (S-L) phase separation region and different quenching conditions via thermally induced phase separation (TIPS). Differential scanning calorimetry (DSC) indicated the crystallinity of PVDF in FVDF-DMP system increased in the early stage of phase separation and polymer-rich phase crystallized completely in the late stage of phase separation. The scanning electron microscopy (SEM) showed the different quenching temperatures had effects on the spherulite size of polymer rich phase and the ultimate membrane structure in the different phase separation regions. The wide angle X-ray diffraction (WAXD) was used to quantify the crystal structure of PVDF in PVDF-DMP system. The α-phase PVDF was obtained when the system quenched to different temperatures above 40°C, and the area of diffraction peaks changed when quenching temperatures changed. While the β-phase PVDF was formed when PVDF-DMP system was quenched form liquid nitrogen and crystallized for 24 h in 25°C water bath.