Stress-Softening and reinforcement of rubber

Abstract

The first part of the paper is concerned with stress-softening in rubber vulcanizates. Recent theories are briefly discussed and results are presented to demonstrate the authors' theory that the phenomenon of stress-softening in filled vulcanizates is due to the gum phase of the composite. A simple model demonstrating stress-softening effects is also presented. Following the authors' earlier work on the importance of hysteresis in determining the strength of rubber vulcanizates, in the second part of the paper, they apply this work to filler-loaded vulcanizates. It is found that when data are expressed independently of time and temperature, unfilled and filled results can be unified by the use of a simple hydrodynamic correction factor. On the other hand, when data are expressed in terms of time or temperature, an order of magnitude is obtained between the gum and filler-loaded vulcanizate results. The meaning of this anomaly is discussed and the authors' own conclusions on the most likely type of model for the reinforcement of rubbers is presented.