The viscosity reducing effects of very low concentrations of a thermotropic copolyester in a matrix of HDPE

Abstract

AbstractA thermotropic liquid crystalline polymer (TLCP), denoted as TLCP(1), was used as a processing aid for high density polyethylene (HDPE). The TLCP was a copolyester of hydroxybenzoic acid, hydroquinone and sebacic acid and was blended with HDPE to give 0.2, 0.5 and 2 wt% TLCP(1) blends. At a temperature of 185°C, when TLCP(1) is in the nematic regime, the processing window for HDPE was increased tenfold from a maximum shear rate of 100 s−1 for pure HDPE to 1170 s−1 for a 2 wt% TLCP(1) blend. There were large viscosity reductions of between 85% and 90% compared with the pure HDPE when the blended material was used at a wall shear stress value of approximately 2.4 × 105 Pa. This viscosity reduction was attributed to the TLCP(1) droplets changing shape from spheres to slender fibrils under shear flows.