Chemorheological Study on Natural Rubber Vulcanizates

Abstract

Chemical stress relaxation studies were carried out in air and in vacuo (0.001 mmHg) on two natural rubber vulcanizates: one cured by dicumyl peroxide and the other by tetramethylthiuram disulfide. These are believed to produce carbon–carbon cross-links and carbon–sulfur–carbon cross-links respectively.Chemical stress relaxation in air showed that oxidative scissions along the main chains were major causes of stress decay for each vulcanizate. The stress decay curves for both vulcanizates were nearly the same in air.Chemical stress decay in vacuo for the two samples was slower than that in air. The network with carbon–sulfur–carbon cross-links showed more rapid decay in vacuo than the network with carbon–carbon cross-links. Analysis of the effect of cross-link density on the decay curves in vacuo indicates that the cleavage was at the network junctures for the network with carbon–sulfur–carbon cross-links and the cleavage was along the main chains for the network with carbon–carbon closs-links.