Correlation of injection moulding parameters with mechanical and morphological aspects of natural fibre reinforced thermoplastics

Abstract

The mechanical behaviour of fibre reinforced composites depends – amongst other things – on the morphological structure. This in turn is greatly affected by the processing conditions. In this study a 10 weight % flax fibre reinforced high density polyethylene composite is prepared by extrusion compounding followed by injection moulding. The effect of injection temperature, speed and rotational screw speed on the morphology of fibres and matrix are studied and related to the tensile and impact behaviour of the composites. Results indicate that fibre length is easily affected by all parameters under consideration. Whereas a higher injection temperature allows the preservation of fibre length, an excessive increase in temperature, however, leads to their thermal degradation. Increased injection and rotational speeds further introduce excessive shear stresses on the fibre, causing their breakage, similarly leading to reduced mechanical performance. Matrix structure is mainly affected by the injection temperature, where its increase leads to the reduction in the degree of crystallinity and thus also a decrease in tensile strength. Other processing parameters prove to have minor effect on matrix morphology.