The influence of processing variables on the mechanical properties of injection molded pregenerated microcomposites

Abstract

This work was concerned with addressing how injection molding process variables affected the final mechanical properties of composite materials based on poly(ethylene terephthalate) (PET) reinforced with pregenerated thermotropic liquid crystalline polymer (TLCP) fibrils, where the TLCP had a higher melting point than the PET. These composites, referred to as pregenerated microcomposites, were produced using a two step processing scheme. First, a novel dual extrusion process was used to spin strands of PET reinforced with continuous lengths of TLCP fibrils. Second, these composite strands were subsequently chopped into pellets and injection molded below the melt processing temperature of the TLCP but above that of the matrix. This allowed the high modulus TLCP fibrils generated in the spinning step to be retained in the final injection molded samples. The influence of several injection molding variables on the final composite properties was examined, including the injection molding temperature and the type of diluting matrix used. These variables were shown to affect the final mechanical properties of the composites, with the best mechanical properties being achieved using low injection molding temperatures and poly(butylene terephthalate) as the diluting resin.