Stress relaxation in rubbers containing reinforced fillers

Abstract

Stress relaxation in rubber stocks containing various fillers was measured at room temperature, and an empirical equation found for relating decrease in tension, ft, over a period of time from 0.1 sec. to 6 months, namely: where f1.0 is force after 1 min. of relaxation, n is the relaxation rate of material (by definition) and t is time in minutes. Raw rubbers were examined under compression, and cured rubbers were tested under tension. In both cured and raw butadiene rubbers, stress relaxation was found to be a viscous-controlled process. In raw rubbers, reinforcing carbon blacks decrease the rate of relaxation, while in cured rubbers the effect of carbon black is very small. However, in swollen (to VR = 0.25), cured rubbers, the rate of relaxation increases with increasing carbon black loading, indicating a slippage and/or breakage of some carbon black-polymer attachments.