Preparation and Characterization of the Polyimide-MoS₂/PTFE Composite with High Strength and Self-Adaptive Lubricating Performance in Air and Vacuum

Abstract

Polyimide (PI)-MoS 2 /poly(tetrafluoroethylene) (PTFE) composites are prepared using the hot press molding technique at 380 °C and 100 MPa. As the composition is PI-12.5 wt % MoS 2 -2.5 wt % PTFE, the composite possesses both high strength and excellent self-adaptive lubricating performance in air and vacuum. The average strength/modulus of compression and bending is 183.36 MPa/2.41 GPa and 151.93 MPa/3.98 GPa, respectively. PTFE is primarily transferred to form a continuous transfer film on the counterpart, which makes the coefficient of friction in both air and vacuum smaller than 0.20 at the initial stage. With the wastage of PTFE at the track, MoS 2 and PI gradually become dominant for the oriented shear layer in vacuum, which further decreases the coefficient of friction below 0.05. Nevertheless, from the beginning to the end, the transfer of PTFE is more firm in air, which causes PTFE to be the dominant component at the friction interface, resulting in the coefficient of friction below 0.2 for the whole stage. In the mechanism, PTFE is not negatively influenced by water because of its nonpolar and inertial essence, while MoS 2 and polar PI are sensitive to oxygen and water, which can restrain the slide within the shear layer and transfer film or between them. Additionally, original flake-like PTFE particles transform to spherulites due to recrystallization during the sintering process, which is beneficial for the enhancement of both strength and self-lubricating performance. The characteristics of this composite, i.e., wear performance, surface, friction interface, microstructure, mechanical performance, and applications in engineering, are systematically studied.