Abstract
Dynamic mechanical properties of polyisobutylene, butyl rubbers, Paracril, cisโ1,4โpolybutadiene, reinforced with EPC black, were determined in the temperature range โ150โ+170ยฐC., in the frequency range 2โ20 kcycles/sec. In the amorphous polymers, reinforcement causes an increase of sound velocity at any temperature, while the glass transition point T~g~ and the thermal coefficient of sound velocity dV/dT remain practically unchanged. Only at high temperatures, near the softening region, are lower values of the damping factor Q^โ1^/dT found for the filled samples, as compared with the corresponding unfilled ones. Addition of reinforcing carbon black to cisโ1,4โpolybutadiene causes an increase of sound velocity at any temperature, and a little shift of the maximum damping point toward lower temperatures. In the reinforced sample, the Q^โ1^ โ T curve, in the region of high dissipation, becomes more unsymmetrical, showing a flat region at temperatures just above the maximum. A comparison of the mechanical spectra of the unfilled vulcanized samples of cisโ1,4โpolybutadiene with those of the corresponding filled vulcanized ones (with the same sulfur content and the same heat treatment) shows a shift of the glass transition point and of the maximum damping toward lower temperatures with addition of the filler. The experimental results are discussed and the conclusion is drawn that neither structural changes nor appreciable variations of chain mobility are caused by addition of carbon black in the examined rubbers.