Degradation of Highly Elastic Polymers. VI. The Intermittent Chemo-Stress Relaxation of Crosslinked 1,5-Polyenes

Abstract

Abstract Measurements of the continuous stress relaxation of thiuram vulcanizates and intermittent stress relaxation of both sulfur and C—C crosslinked vulcanizates of natural rubber were discussed. These measurements were made in the presence of either oxygen or nitrogen at various temperatures both with and without sample pretreatment. The following conclusions were drawn: 1. Determination of the rate of continuous tension loss is not suitable for measuring the oxidative degradation of vulcanizates from 1,5 polyenes according to a stress relaxation method. The reason for this is that rheological processes superimpose themselves on the chemical reactions initiated by oxygen, cause a reduction in tension, and affect both the form of the relaxation curve and also the rate of tension loss. This is particularly noticeable in the case of vulcanizates containing polysulfide bonds. 2. It was possible, using intermittent stress relaxation and by choosing suitable temperatures and frequencies, to eliminate the influence of rheological processes and thus to measure only the rate of tension loss due to oxidative degradation.