Reinforcement of Rubber by Fillers Tear Resistance

Abstract

Abstract The results of experimental studies on 1) the effect of reinforcing fillers on tear strength and on the roughness of the resultant torn surfaces, 2) the relative adhesion of rubber to fillers and 3) the effect of hysteresis on tear strength are critically examined. They show that the maximum reinforcing effect of fillers is only exhibited if sufficient time is allowed for their strengthening role to develop during tearing, and that under these conditions the tip of the growing tear is broader and the torn surface rougher. They also confirm that the surface or immediate environment of filler particles provide a region of relative weakness, and that failure takes place at the interfaces ahead of the advancing tear, the rupture path wandering from one internal flaw to another. In addition they show that the more reinforcing fillers adhere more strongly to the rubber. Further, for gum vulcanizates, it appears that there is a simple relationship between tearing energy and hysteresis and that rubbers with higher hysteresis possess higher tear strength. A synthesis of the results of these three investigations provides a qualitative picture of the role of reinforcing fillers in increasing the strength of rubbers. It appears that a process giving rise to sufficiently rapid relaxation of stress ahead of the tip of a growing tear can in principle result in broadening of the tip of the tear and lead to increased strength. It is considered that this type of process plays an important and sometimes dominant role in the reinforcement of rubbers by fillers or by crystallization, and provides a consistent and coherent mechanism which indicates a source of the roughening of rupture surfaces of filler reinforced rubbers and of their possible branching and knotty tearing.