In situ modulus enhancement of polypropylene monofilament through blending with a liquid-crystalline copolyester

Abstract

An immiscible blend of poly(propylene) (PP) with a thermotropic liquid-crystalline polymer (TLCP, trade name Rodrun LC5000), a copolyester of 80/20 mol ratio of p-hydroxy benzoic acid and polyethylene terephthalate was prepared in a twin-screw extruder. The blend extrudate was fabricated as monofilament by using a single-screw extruder equipped with a fiber line. The as-spun filament was drawn at 120°C to enhance molecular orientation. Morphology, thermal, tensile, and dynamic mechanical properties of both as-spun and drawn monofilaments were investigated. Almost continuously long TLCP fibers dispersed in PP matrix were obtained in the composite as-spun monofilaments. The maximum modulus was found in 15 wt% TLCP/PP composite as-spun filament, an increase of about 2.4 times that of the as-spun neat PP. For the drawn filaments, the 10 wt% TLCP/PP composite showed a maximum modulus, an increase of about 1.5 times that of the drawn neat PP. The increase in to moduli was attributed not only to the reinforcement by TLCP fibrils with very high aspect ratio but also to the increases in PP crystallinity and molecular orientation through the drawing process. A remarkable improvement in the dynamic mechanical properties of the composite monofilaments was observed, especially in the high-temperature region.