Synergistic Friction and Wear of Ternary Blends of Polyetheretherketone, Polyetherimide and a Thermotropic Liquid Crystalline Polymer at Elevated Temperatures©

The dry sliding friction and wear behavior of ternary blends of polyetheretherketone (PEEK), polyetherimide (PEI) and a thermotropic liquid crystalline polymer (TLCP) was investigated as a function of operating temperature. Friction and wear measurements were performed at selected temperatures within the range of 20 degrees to 250 degrees C. The specific systems investigated consisted of binary PEEK/PEI 85/15 and 70/30 isotropic thermoplastic matrices and a thermotropic liquid crystalline copolyester acting as the reinforcing phase. Although individually both PEEK/PEI matrices and the TLCP were seen to undergo catastrophic tribological failure at their respective glass transition temperatures (T-g), the ternary PEEK/PEI/TLCP blends were able to maintain sliding at temperatures well in excess of the T-g of their constituent phases. This synergistic behavior is explained in terms of TLCP reinforcement and PEEK cold-crystallization. In the ternary blends investigated, PEI exhibits miscibility with both PEEK and the TLCP, a mutually immiscible pair of polymers. In view of this, PEI was expected to enhance, via blend compatibilization, mechanical properties and ultimately, tribological performance at high temperatures. Comparison of the tribological performance of PEEK/PEI/TLCP and PEEK/TLCP blends indicated otherwise however The sliding friction and wear mechanisms of the PEEK/PEI/TLCP blends are described in relation to their microstructures. The effects of TLCP concentration and thermal transitions on mechanical properties and tribological performance are also discussed.