Processing and properties of composites based on high density polyethylene and thermotrophic liquid crystalline polymers

Abstract

This research was concerned with the processing and properties of composites of high density polyethylene (HDPE) and thermotropic liquid crystalline polymers (TLCPs). Strands of HDPE reinforced with TLCPs were generated using a novel dual extruder mixing technique. It was shown that the strength and modulus of the strands improved with increased strand drawing. Post-processing of the blended strands was done by means of compression and injection molding. It was observed that when the fiber aspect ratio dropped, the composite mechanical properties decreased. When pregenerated fibrils were maintained during injection molding at temperatures above the matrix melting point, but below the TLCP melting point, microcomposites were obtained. Microcomposites generated at the lowest temperatures had higher tensile properties than found for in situ composites and similar to glass reinforced HDPE. At 170°C the pregenerated fibers were no longer deformed during injection molding and high aspect ratio fibrils were maintained. The fiber orientation and addition of a compatibilizer were also studied. This study shows it is possible to extrusion blend HDPE with TLCPs and by optimizing the post-processing conditions, to obtain microcomposites with better properties than in situ composites.