Evaluation of the Tribological Properties of Polyimide and Poly(amide-imide) Polymers in a Refrigerant Environment

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Abstract
The tribological properties of three grades of polyimide (PI) and one grade of poly(amide-imide) (PAI) polymers are evaluated in a tetrafluoroethane (HFC-134a) environment. Friction coefficient, wear, and interface surface morphology are evaluated at temperatures of 20° and 120°C, sliding velocities from 0.127 to 3.75 m/s, contact pressures from 1.72 to 13.8 MPa, and counterface surface roughness of 0.06 and 0.40 μ Ra. Tests were conducted under dry or boundary lubricated conditions. Limited testing indicate that the polymers under study do not chemically degrade in HFC-134a environment. For the polymer grades tested, the combination of graphite and FIFE as filler materials provide the best wear characteristics in this environment. As expected, the environmental temperature has a strong effect on both the friction coefficient and the wear. Under boundary lubricated conditions, the presence of a liquid lubricant provides one order of magnitude lower wear compared to the wear obtained in dry sliding conditions. Results from tests conducted in air, argon, and HFC-134a show that the tribological properties of the polymers tested do not seem to be significantly influenced by the environment.