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.
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