Layered morphology and bending fracture behavior of moulded composites of thermotropic liquid crystalline polymer and polyamide 6 containing epoxy component

Abstract

Layered morphology of moulded composites of thermotropic liquid crystalline polymer (LCP) and polyamide 6 (PA6) containing an epoxy component and their bending strengths were studied as a function of epoxy fraction. Injection-moulding of a thin composite plaque from extruded LCP/PA6 pellets at a temperature below the melting point of the LCP fibrils generated a multi-layered structure; while the surface skin layer with a thickness of 65–120 μm indicated a transverse orientation, the sub-skin layer was oriented in the flow direction and arc-curved flow traces featured in the core layer. Such microstructural orientations in the respective layers were more or less observed for any composite plaques with varying fractions of epoxy. The plaques containing 4.8 vol.% epoxy exhibited superior bending strength and large fracture strain. With an increase of epoxy fraction above 2.4 vol.%, the geometry of LCP domains changed from fibrillar to lamella-like shapes, which caused a shear-mode fracture. An analysis of the bending strength of the composite plaques on the basis of a symmetric layered model beam suggested that an epoxy component addition could alter not only the layer thickness but also the elastic moduli and strengths of the respective layers.