Thermomechanical properties and tribological behaviour of CaCO3 whisker-reinforced polyetheretherketone composites

Abstract

The thermal expansion properties, dynamic mechanical properties, and related tribological properties of polyetheretherketone (PEEK) composites filled with 0–25 wt.% content of calcium carbonate (CaCO3) whisker were investigated. The composite specimens were prepared by compression moulding. Thermomechanical analysis (TMA) was performed to determine linear coefficients of thermal expansion (CTE). Dynamic mechanical thermo-analysis (DMTA) was employed within the temperature range of 25–300 °C. Tribological testing of composites in dry wear mode against a carbon steel ring was carried out on a MM200 block-on-ring apparatus. All specimens show a large change in CTE at glass transition temperature ( Tg), but CTEs of CaCO3/PEEK composites at temperatures below and above Tg are much lower than pure PEEK. For 25 per cent CaCO3/PEEK the average CTE in the temperature range of 25–120 °C is about half lower than PEEK. CaCO3 whisker shows a significant effect on the dynamic stiffness at low and high temperatures. The increase of whisker content contributes to a rise to the storage modulus. CaCO3-whisker-filled PEEK composites exhibit considerably lower friction coefficient and wear rate than pure PEEK. With an increase in CaCO3 whisker contents, coefficient of friction of PEEK composites continuously decreases, while the specific wear rate shows minima for 15 per cent CaCO3 whisker inclusion with an approximate seven times improvement in comparison with PEEK. The improved tribological performance of CaCO3/PEEK composites is ascribable to the reinforcing effectiveness of CaCO3 whisker, which contributes to increase the thermal stability, stiffness, and load-carrying capacity of PEEK composites in terms of counteracting the effects of thermal softening and adhesion during the friction process.