Dynamic Mechanical and Electrical Properties of Vulcanizates at Elongations up to Sample Rupture

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Abstract
Dynamic properties of vulcanizates have been measured at small and large extensions, up to specimen rupture, by means of a modified Rheovibron. The influence of temperature, frequency, and amplitude on the dynamic moduli has been determined for a number of SBR samples, uncharged or charged with silica or carbon black. A study has been made of the dynamic Mullins effect (stress-softening) and of dynamic stress-relaxation for various charged and uncharged samples. Electrical conductivity has been determined simultaneously with dynamic properties for carbon-black loaded elastomers. The gradual reformation of a previously destroyed secondary filler network could be followed quantitatively in rate and magnitude at very low frequencies. It appears that at small deformations a secondary, reversible filler network plays an important part in the dynamic properties of the vulcanizates. At intermediate deformations, however, this network has been eliminated. Conductance data of carbon-black loaded vulcanizates indicate a phenomenon of orientation of anisometric aggregates. At still higher deformations irreversible changes are observed, pointing to a rupture in filler—elastomer bonds as well as of elastomer chains, two experimentally distinguishable phenomena.

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