Novel Pulp Fibre Reinforced Thermoplastic Composites
The reinforcement potential of pulp fibres is presently not fully explored in thermoplastic composites. One of the reasons is that currently used processing methods comprise several severe thermomechanical steps inducing premature degradation of the fibres. Three pre-forming techniques were developed to prepare pulp fibre reinforced cellulose diacetate (CDA) pre-forms, namely filtration-forming, solvent impregnation, and commingling with polymer fibres. These techniques eliminate all thermomechanical steps, prior to final processing. The CDA polymer was nevertheless found to be very sensitive to the specific process histories relevant to each technique, contrary to the pulp fibres, whose size, shape, and mechanical properties were not affected by neither of the preforming processes. The tensile properties of composites compression moulded from solvent impregnated pre-forms were compared to those of ground china reed reinforced CDA. Whereas ground china reed particles were found to act merely as fillers increasing composite stiffness, a remarkable reinforcement effect was observed for the pulp fibre reinforced impregnated pre-forms. A combination of a stiffness increase by a factor 5.2 and a strength increase by a factor of 2.3 relative to the pure polymer was achieved, whereas in typical pulp fibre reinforced thermoplastics, the stiffness increase is frequently obtained at the expense of loss in strength. This work highlights the key factors which control the mechanical performance of pulp fibre reinforcements previously neglected in literature, and demonstrates the remarkable reinforcement potential of such renewable material. Furthermore, the properties achieved by optimising the extraction and processing steps indicate that pulp fibre reinforced thermoplastics composites are appropriate materials for load bearing applications.