Effects of medium phases on the thermal degradation of hydrogenated nitrile rubber O-rings under compression

The degradation of hydrogenated nitrile rubber O-rings under exposure to either air or hydraulic oil under compression were investigated at elevated temperatures. The physical and chemical changes of the samples aged for various durations were studied by measuring the weight, compression set, tensile strength, elongation at break, crosslinking density, fracture morphology, and attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy. The results indicate that the weight decreased with exposure time and temperature and that weight loss was greater in oil. Crosslinking and chain scission both occurred during the aging process. The significant changes in the mechanical properties indicate that more severe degradation occurs in air. The fracture morphologies results show that the fracture surfaces aged in oil become rougher and have more defects. The ATR–FTIR results demonstrate that the hydroxyl groups were formed in air and oil, while carboxyl groups were only generated in air.