The Influence of Processing Conditions on the Mechanical Behaviour of Uhmwpe/Ha and Pmma/Ha Composites

Abstract

Polymer based composites reinforced with hydroxylapatite (HA) are a promising alternative for plasma-sprayed coated metals used in dental and orthopaedic implants. Two systems already in clinical application are polyethylene (PE) and polymethylmethacrylate (PMMA) filled with HA, for which the relationship between processing conditions and mechanical performance has not been sufficiently evaluated. This work is an attempt to correlate processing, morphology and performance, in order to optimise the mechanical behaviour of these materials. Composites reinforced with HA and talc (in volumetric fractions up to 30%) were produced by injection and compression moulding under a wide range of processing conditions. The injection moulding programme included the variation of the temperature profile along the plasticating barrel, the mould temperature, the flow rate and the holding time. For compression moulding, the effects of mould temperature, pressure and time were analysed. The morphology of the mouldings produced was characterised. It was possible to identify quantitative microstructural parameters (e.g., the thickness of the moulding skin) to explain the dependence of the mechanical performance (tensile, flexure and impact) of the composites on the respective processing conditions. The effect of molecular and filler orientation is also qualitatively discussed.