Effects of crosslinking densities on mechanical properties of nitrile rubber composites in thermal oxidative aging environment

The effects of crosslinking densities on mechanical properties of nitrile rubber (NBR) composites before and after thermal oxidative aging are investigated. Tensile strengths of NBR composites are enhanced slightly at the initial aging stage, attributing to moderate increment of crosslinking densities. Continuous decrease with further aging is followed, resulting from over-crosslinking and uneven distribution of crosslinking densities. The digital image correlation method is explored for large-strain deformation measurement by displacement accumulation and establishing strain model, being promising in practical age detection and measurement of mechanical properties in complex environments. Compression sets are gradually increased with aging because of the destruction of the original crosslinking structures. The molecular chains fracture inhibits elastic recoveries of compressive NBR composites and results in residual deformation in thermo-oxidative and compressive environment after unloading. This study provides new ideas for exploring mechanical properties of rubber-based composites before and after thermal oxidative aging.