STUDY ON TRIBOLOGICAL BEHAVIOR OF PLASMA-TREATED PEEK AND ITS COMPOSITES

In this paper, neat PEEK, PEEK-8%PTFE and PEEK-10%PTFE-10%graphite-10% carbon fibre have been treated by plasma to improve their tribological behaviour. The treatment gas was argon, and five different treatment parameters were selected. The range of plasma treatment time was 1.0-5.0 min, the range of voltage was 0.8-1.3 kV. Tribological experiments of sliding PEEK and its composites against a steel ring showed that the sliding friction coefficient mu and the specific wear rate w(s) decreased significantly, especially for the PEEK/steel rubbing pair. The mean friction coefficient <(mu)over bar>. dropped from 0.42 to 0.23 and the mean specific wear rate <(Ws)over bar> dropped from approximate to 10(-5) to approximate to 10(-6) (mm(3) N-1 m(-1)), i.e. a one order of magnitude decrease. It is also shown that mu and w(s) for different plasma treatments have different values. In general, a certain type of plasma treatment has been found to have the best results for all three specimens. The highest selected voltage of the equipment was 1.3 kV and the shortest treatment time was 1.0 min for this treatment. With scanning electron microscopy of polymeric wear debris it has been found that the wear mechanisms were different for treated and untreated specimens. Fourier transform reflection IR spectroscopic analysis of worn pin surfaces showed that the thermal degradations for treated and untreated specimens were also different. Differential scanning calorimetry analysis of worn pin top sections also showed that the crystallinity for treated specimen was smaller than that for untreated specimen. It is concluded that the improvement of tribological behaviour of PEEK and its composites after plasma surface treatment is due to cross-linking of PEEK and improvement of the interface strength of carbon fibre reinforced PEEK composites. The plasma treatment for polymers and their composites has potential application prospects.