Evaluation of sealability for aged rubber seals by spin–spin relaxation time

This paper presents the applicability of proton spin–spin relaxation time, T2, for the evaluation of the degradation of sealability for rubber seals. So far, compression set (CS) has been utilized to evaluate the degree of degradation of rubber seals. However, the reliability of CS for thin rubber seals is relatively low. Therefore, in this paper, we investigated the applicability of T2 as a parameter for the quantitative evaluation of the degradation of sealability instead of CS. The correlations between T2 and cross-link density, plasticizer concentration and CS for two acrylonitrile butadiene rubber (NBR) samples were discussed. The samples have different compounds and shapes: plate and O-ring. We exposed them to air and nitrogen atmospheres at high temperatures of 60, 80 and 100 °C for up to 33,000 h. The short spin–spin relaxation time, T2S, was shortened with aging and correlated well with the cross-link density, plasticizer concentration and CS, regardless of the atmosphere. These results revealed that T2S is a useful parameter for the quantitative evaluation of the degradation of sealability.