Benzyl triphenyl phosphonium chloride as an additive for polyvinylidene fluoride: Melt rheology, crystallization, and electrical properties

Abstract

The β phase of polyvinylidene fluoride (PVDF) crystals is polar and has very good piezoelectric and dielectric properties as compared with the nonpolar α phase. Benzyl triphenyl phosphonium chloride (BTPC) has been previously shown to directly nucleate the β phase from melt, instead of α phase, and is an additive of practical importance. Different amounts of BTPC were melt mixed into PVDF using a micro twin screw extruder to study the rheology of the blends using oscillatory and steady shear viscometry. Data at different temperatures were found to superimpose onto a master curve using time‐temperature superposition. The complex viscosity and steady shear viscosity increased significantly upon addition of 0.5% BTPC and decreased slightly with further addition of BTPC. The storage modulus exhibited a plateau at low frequencies indicating structure formation in the melt on addition of BTPC. The horizontal shift factors derived from the time‐temperature superposition were found to follow an Arrhenius temperature dependence and the flow activation energy for each blend was obtained. Pure PVDF and PVDF films with 1% and 3% BTPC were melt extruded using a laboratory twin screw extruder. The film containing 3% of BTPC gave the highest fraction of β phase crystals (75%). Small angle light scattering results showed that the size of spherulites decreased with increase in the weight fraction of BTPC. The dielectric constant and conductivity of the films at low frequencies increased significantly with concentration of BTPC, as did the dielectric loss and AC electrical conductivity. POLYM. ENG. SCI., 54:2420–2429, 2014. © 2013 Society of Plastics Engineers