Influence of hydraulic oil on degradation behavior of nitrile rubber O-rings at elevated temperature

The degradation of nitrile rubber O-rings exposed to hydraulic oil and air were investigated by adopting accelerated aging test. The chemical structures and mechanical properties of the aged samples were evaluated by measuring attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, crosslinking density, weight loss, mechanical properties and fracture morphology. The ATR-FTIR results indicate that chemical structure changed significantly due to loss of additives and oxidation reactions. Hydraulic oil and temperature played a critical role in surface chemical changes. The crosslinking density changes were attributed to the competition between crosslinking and chain scission. The mechanical test results show that there existed large differences in changes of mechanical properties for samples under different conditions, which correlated to loss of fillers, the changes in crosslinking density and the formation of defects. Additionally, the fracture morphologies demonstrate that the formation of hardened brittle outer layer, voids and agglomerates also promoted the decrease in mechanical properties.