The effect of hydrocarbon ageing on the mechanical properties, apparent crosslink density and CO₂ diffusion of a hydrogenated nitrile butadiene rubber (HNBR)

The effect of ageing in a sweet oil environment on the tensile properties, apparent crosslink density, CO₂ diffusion and Shore hardness of a typical carbon black reinforced hydrogenated nitrile butadiene rubber (HNBR) is presented. Different ageing conditions yielded materials with different properties, attributed to varying degrees of apparent crosslinking. These results showed that, with increasing apparent crosslink density, tensile stiffness and hardness increased, while CO₂ diffusivity and saturation swelling in chloroform decreased. The relationships between these properties suggests that geometry independent tests (such as solvent swelling) may be performed on parts retrieved from service in order to predict properties (such as tensile stiffness or gas diffusion) which cannot normally be measured on retrieved parts due to geometrical constraints.