Chemical Stress-Relaxation of Filled Vulcanizates under Large Cyclic-Deformation

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Abstract
The stress relaxation under cyclic deformation was used to elucidate the fatigue mechanism of carbon-black filled natural-rubber vulcanizates. Below 70°C the rate of stress relaxation of the filled vulcanizates depended on both extension ratio and frequency. Above 70°C it depended on the extension ratio only. The stress relaxation above 70°C is caused by the scission of both the primary bonds of polymer chains and bonds between polymer and carbon black. Below 70°C it is caused by the scission of the bonds between polymer chain and carbon black. However, at very small deformation above 70°C the mechanism of the stress relaxation of the filled system was the same as that of the unfilled system. The failure of the chemical bonds of polymer chains is involved, but not the failure of bonds between polymer and filler. The same relaxation mechanism may be operating in both air and nitrogen under the large deformation, because the amplitude dependence was the same.

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