Stress relaxation of peroxide and sulfur vulcanizates of natural rubber

Abstract

Abstract The stress relaxation behavior of peroxide and sulphur vulcanized natural rubber has been investigated using a relaxometer of new design. The peroxide vulcanizates do not degrade significantly in vacuo and degrade by an exponential decrease in stress with time in oxygen. The vulcanizates from the two sulfur recipes used give stress relaxation in vacuo and more rapid relaxation in oxygen. A theoretical analysis provides the shape of stress–time curves anticipated for various modes of network degradation. The present data and other published results are consistent with a mechanism of scission at the crosslinks and not at random along the chains. The peroxide vulcanizates are interpreted as decaying by a first‐order scission of crosslinks and the sulfur vulcanizates by first‐order scission of two types of crosslink. The uncertainties still present in interpreting stress relaxation data are discussed.