Preparation and characterization of compatible PVDF/PPTA blends by in situ polymerization for separation membrane materials

Poly(p-phenylene terephtalamide) (PPTA) reinforcing blends are of great scientific interest, however the thermodynamic difference of the components make them incompatible with inferior physical-chemical properties. In this work, with the aim of exploring novel separation membrane materials, PPTA/poly(vinylidene fluoride) (PVDF) reinforcing blends were prepared by a novel reactive blending technique of in situ polymerization (method І), and the conventional solution blending (method Π), respectively. The effects of these two methods on polymers compatibility were investigated and compared through ATR-FTIR, XRD, XPS and FESEM characterization. Thermal stability, surface hydrophilicity and mechanical properties were measured through TG, water contact angle (WCA) and tensile measurements. It was found that stronger intermolecular interaction especially hydrogen bonds between polymer components in in-situ blends prevented PVDF from crystallization and a continuous phase configuration appeared. However, slution blends showed an obvious two-phase structure in FESEM observation which varied from a spherical crystallization of PVDF at low PPTA content to a fibrous-like crystallization of PPTA at high PPTA concentration. Solution blends showed lower hydrophilicity which was attributed to the PPTA crystallization and its perpendicular uniplanar orientation along blend film surface. In-situ blends exhibited higher tensile strength which was due to the better polymers compatibility between the rigid reinforced PPTA molecules and flexible PVDF matrix. The PPTA/PVDF in-situ blend is a promising candidate for the high-performance separation membrane material.