The effect of annealing on the melt rheology of ternary PE/PA6/GF composites

Abstract

Ternary composites have been prepared by simultaneous extrusion of polyethylene (PE), polyamide-6 (PA6) and short glass fibre (GF) reinforcement. Two types of fibres – compatible either to the PA6 or to the PE phase – were used and this led to composites with distinctly different morphology and properties. The PA6-compatible fibres were interconnected by PA6 bridges and formed a continuous network within the matrix, whereas for the PE-compatible fibres such a network was not formed.The composites were annealed at temperatures above the melting points of both thermoplastic components and the changes of the rheological properties of their melts were monitored using small amplitude oscillatory flow. A substantial increase of the stiffness of the composites containing PA6-compatible fibres was observed after 2h annealing at 250°C. This higher level of stiffness was preserved during the consequent cooling down to 120°C. The effect of strain softening of the melts was studied by applying different strain amplitudes. The results of the rheological study were analysed using a recently developed theoretical model. The analysis confirmed the relation between the changes of the properties and the development of the morphology that was previously found by dynamic mechanical analysis in the solid state.