Mild Stress Softening and Dynamic Properties of Rubber Vulcanizates

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Abstract
Mild, reversible stress softening of vulcanizates loaded with carbon blacks of widely different structures and reinforcing characteristics was investigated by means of a novel electronic variable shear amplitude dynamic tester. The instrument yields low frequency dynamic data for vulcanizates in the range of double strain amplitudes of 3×10−5 to 1.0, covering nearly five decades. Mild reversible stress softening (up to 100 per cent amplitude) in a variety of vulcanizates investigated is caused by a reversible thixotropic breakdown of transient carbon chains, which contribute to reinforcement by an energy dissipating mechanism. Persistent, “fused” carbon chains contribute to reinforcement by their beneficial influence on the crosslink density of the vulcanizate. Elastomer and carbon chains respond independently to stress.

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