Relating Aging Effects on Physical and Viscoelastic Properties of Rubber to Fundamental Changes in Material Structure

Material chemists and engineers design elastomeric compounds to meet chemical and physical specifications dictated by the targeted application. There are often concerns for how these properties change over time. This study focused on the effects of thermal aging in air on NBR and HNBR elastomeric compounds. It was seen that when NBR compounds were heat aged in air for periods up to 1000 hrs. there was significant loss in elongation and corresponding increase tensile strength and hardness.

<span">The changes in physical properties correlated with a 6 to 8 % increase in cross link density that was measured using a technique involving material swell in MEK. Cross linking was seen to occur as early as 168 hrs. heat aging (100° C) .XPS (survey) analysis of the aged rubber showed significantly higher levels of oxygen on the surfaces of aged rubber compared to the control material. High resolution C1s scans showed approximately three times more C=O in aged surfaces compared to the un-aged rubber. The effect of aging appeared non- uniform, that more >C=0, >C=N were seen on the surface vs bulk of the aged rubber. SEM studies showed that the cut/tear pattern of rubber aged at 1000 hrs. was visibly different from that of the un-aged rubber