Tribological behaviour of acrylonitrile-butadiene rubber under thermal oxidation ageing

Acrylonitrile–butadiene rubber (NBR) is an important tribological material that is often used in dynamic sealing pairs (as rubber/metal seal-pairs), but often degrades prematurely because of thermal oxidation ageing. In this work, NBR seals were exposed to an accelerated thermal ageing atmosphere at different temperatures and time periods, and the aged NBRs were evaluated for their mechanical properties, tribological behaviour, and energy dissipation. The results showed that thermal oxidation ageing has a substantial effect on rubber properties. The hardness and bulk modulus of rubber increased, whereas its tensile strength and tear strength decreased remarkably with increasing ageing temperature and time. The evolution trends of rubber ageing can be divided into three regions (A, B, and C) according to different ageing degrees (high elastic state, weakened elastic state, and hardening state). The damage mechanism of each region is obviously different. The wear mechanism gradually changes from adhesive wear to abrasive wear, or fatigue and abrasive wear. Although the average wear rate decreases with the increase of ageing parameters, mechanical properties, such as viscoelasticity, fracture resistance, and tear resistance, were severely reduced or even disappeared. The adhesion and hysteresis characteristics of the rubber during friction were remarkably disturbed because of their ageing degradation. Therefore, different energy dissipation characteristics in friction were presented for various aged rubbers