Role of treatment to graphite particles to increase the thermal conductivity in controlling tribo-performance of polymer composites

Abstract

A novel type of graphite (thermographite) having higher thermal conductivity (TC) due to a patented treatment is commercialized recently. It was anticipated that such particles would be more effective in conducting away frictional heat generated on the tribo-surfaces leading to the enhanced performance. Hence two composites were developed based on high performance Polyarylether ketone (PAEK) (50% by wt) containing 30% short glass fibers (GF) and hexa-boron nitride (hBN) 10% apart from 10% graphite. First composite designated as CNG contained 10% natural graphite (NG) while the other designated as CTG contained 10% thermographite (TG). These were processed by identical method (twin screw extrusion followed by injection molding). The tribo-performance was evaluated in a pin on disc (mild steel) configuration under very high load and speeds. It was observed that both the composites exhibited excellent tribo-performance. However, CNG performed better than the CTG in all respects only under severe operating conditions. Under low PV conditions, difference was not clear. It showed lower friction coefficient, and wear rate as compared to CTG. CNG showed PVlimit value 96.6MPa-m/s which was decisively superior to CTG (91MPa-m/s). CNG could sustain higher speed (3.45m/s) than the CTG (3.25m/s) under 900N in spite of slightly lower TC. It was concluded that during treatment (patented by the company) TG has slightly distorted layer-lattice structure as compared to the natural graphite, which could be responsible for transferring less beneficial film under severe operating conditions. SEM and EDAX studies were conducted to understand wear mechanisms. Such composites with such high PVlimit values low, µ (0.04) and low wear rates (1×10−16m3/Nm) are not reported in the literature and may prove as ideal materials for dry bearings in harsh operative conditions.