Effect of fibre volume content on the mechanical performance of natural fibre reinforced thermoplastic composites

Natural fibre thermoplastic composites may be manufactured using a film stacking process, where fibre-preforms and matrix films are stacked alternately. The process has shown great potential due to the high flexibility referring to the stacking sequence and the using of simple tooling concepts, which may easily be scaled for industrial applications. As impregnation takes place through-the-thickness, the flow length is short and of particular interest when thermoplastic processing due to the high melt viscosities, particularly important when working with natural fibres and relatively low temperatures. In this study, flax fibres were impregnated by various thermoplastic matrix materials suitable to being processed at lower temperatures. Here we aim to study the impregnation of the natural fibres by varying the provided amount of matrix material within the film stacking process. Impregnation trials showed interesting potential of reducing the content of matrix material. This leads to a reduced thickness of the composite whilst maintaining the structural load bearing capability due to the unchanged presence of the fibre material. Starting from a fibre volume content of 50 % we demonstrate an increase it up to 77 %. Whilst we note no effect on the strength, we observed notable improvement in the flexural moduli.