Abstract
The dynamic mechanical properties of rubbers loaded with carbon black have been the subject of many investigations because of their importance in the performance of products, especially the energy dissipation, skid resistance, and other properties of vehicle tires. However, the important variables of frequency and temperature in oscillating deformations have usually been explored in fragmentary fashion. In particular, the degree to which these variables can be treated with frequency-temperature superposition appears to differ considerably depending on the type of compound investigated. In many cases, data have been insufficient to establish whether the essential criterion for superposition, namely, the same temperature dependence for all relaxation mechanisms, is satisfied. For this purpose, extensive measurements over wide ranges of closely spaced frequencies and temperatures are required. Such data are needed, in any case, to determine the responses of elements of a vehicle tire over the ranges of temperature and time scale to which they are subjected in use and to provide input information for thermo-mechanical modelling of power loss in tires. This paper is intended to be one of a series on dynamic mechanical properties of a variety of carbon black-loaded compounds over wide ranges of frequency and temperature. It describes results for a vulcanized butyl rubber loaded with a medium processing channel black, and the almost chemically identical linear polymer polyisobutylene loaded with a semireinforcing furnace black; these results are compared with previously published data for vulcanized butyl gum and pure polyisobutylene . The shear strain amplitude in these measurements is very small, of the order of 10−5 to 10−7, in a range of linear viscoelasticity as confirmed by sensitive tests, and thus the Mullins effect is avoided. The prominent dependence of viscoelastic properties on strain amplitude, as investigated by Payne and Watson and later workers, appears at considerably higher strains of 10−3 or more. Of course, the behavior in large deformations will be very different from that described here, but it is important to understand first the properties of the structure close to its equilibrium rest state.
