The effect of accelerated aging on the properties of nitrile butadiene rubber (NBR) O-rings

The degradation behaviors and mechanisms of nitrile butadiene rubber O-rings aged in air are investigated by accelerated aging tests at different temperatures. The compressive stress changes of nitrile butadiene rubber O-rings are monitored by using a self-designed test device during the degradation process. The aging samples under different conditions are evaluated by measuring attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, crosslinking density, compressive stress relaxation, weight loss, mechanical properties, and fracture morphology. The results demonstrate that the compressive stress declines with aging time, and the higher the temperature is, the faster the stress decreases. The ATR-FTIR results indicate that amide groups and hydroxyl groups are formed during the degradation process. The elevated temperature plays a significant role in the surface chemical changes. The changes in the crosslinking density of the samples could be attributed to the competition between crosslinking and chain scission, and the crosslinking mainly predominates in the aging process. The results of mechanical properties show that the tensile strength, elongation at break, and hardness of samples changes significantly with aging time and temperature. In addition, the fracture morphology observation reveals that the formation of a hardened brittle outer layer, voids, and agglomerates lead to a further decrease in mechanical properties. These results are very important for evaluating the lifetime of rubber O-rings and can be utilized to improve the stability and durability of sealing systems.