The effect of thermo-oxidation on the continuous stress relaxation behavior of nitrile rubber

Continuous stress relaxation of nitrile rubber (NBR) was characterized in air and N2 at high temperatures (125 °C and 165 °C). Stress increase (“rebound”) after decay was observed in air, but not in N2. Chemical structure, crosslinking density and hardness investigations were carried out to gain insights into the underlying mechanism that governs such behavior. Results indicate that at later stage thermo-oxidative crosslinking prevailed over chain scission causing stress rebound. The effect of atmosphere, temperature and original strain on the stress relaxation is also discussed.