Study on the Mechanical Behavior of Nitrile Rubber Materials Under Thermal-Oil and Thermal–Oxidative Aging in Service Environments

Rubber sealing materials’ aging behavior under challenging circumstances, such as high temperatures, oxygen exposure, or oil immersion, significantly effects how well they seal and how long they last. In order to systematically examine nitrile rubber’s aging behavior and the evolution of mechanical properties under thermo–oxidative and thermo-oil conditions, this study used accelerated high-temperature aging tests. Test results indicate that in a hot-oil environment, the rubber exhibits significant swelling, with mass increasing by up to 9.96%. Hardness undergoes a non-monotonic change, first decreasing and then increasing. In contrast, under thermal-oxidative conditions, hardness increases continuously, exhibiting a marked rise after 7 days of aging at 125 °C. Mechanical property tests revealed a substantial increase in elastic modulus after thermal–oxygen aging. At 125 °C, the modulus rose from an initial 0.4128 MPa to 0.9626 MPa, representing an approximate 133% increase. The compression set reached 83.23% after 7 days of thermal–oxygen aging at 125 °C, compared to 66.89% under thermal-oil conditions. Infrared spectroscopy analysis further indicates enhanced nitro groups and alterations in other functional groups during aging, confirming oxidative chain scission and crosslinking reactions. This study provides quantitative experimental evidence for predicting the service life and optimizing the performance of nitrile rubber under severe environmental conditions.