High performance polymer composites - Influence of processing technique on the fiber length and performance properties

High performance polymer composites, (especially short fiber reinforced) have gained immense importance in the field of tribo-materials, especially for dry bearings. Among various key parameters controlling the final performance, the processing technique is the one, which is least investigated. Injection molding leads to a uniform dispersion and distribution of fibers but at the cost of an excessive reduction in the aspect ratio of fibers. Compression molding of short fibers retains their aspect ratio to a greater extent, but at the cost of inefficient dispersion of fibre strands. Interestingly, both the factors viz. High aspect ratio of fibers and excellent dispersion are important for deciding the performance of composites. In this work, two composites (Poly aryl ether ketone - 50 wt%, short glass fibres (length - 3 mm)- 30 wt % and synthetic graphite - 20 wt%) were molded by injection (I) and compression (C) molding. These were triboinvestigated in adhesive and abrasive wear modes in identical conditions. Based on thermal degradation of composites at 600 degrees C, the final fibre length was observed as 200-300 mu m and 1.5 mm for I and C composites respectively. Both the composites showed low specific wear rate (K-0) (similar to 10(-16)m(3)/Nm) and coefficient of friction (mu) (similar to 0.03-0.05). Similarly, for abrasive wear, K-0 and mu were observed similar to 10(-10) m(3)/Nm and similar to 0.5-0.7 respectively. mu of I composite was lower in all conditions. The composite C was superior to the I in wear performance in adhesive wear, but not in abrasive wear. Worn surface analysis was done to understand the wear mechanisms.