Damping behaviour of dynamically cured butyl rubber/polypropylene blends

Dynamically cured blends of butyl rubber (IIR; isoprene-isobutylene rubber) and anhydride-grafted polypropylene (PP) of various component ratios and curative loadings were prepared by melt mixing. Evidence from dynamic mechanical analysis and phase-contrast microscopy suggested that these blends were heterogeneous, with the PP phase being continuous. Damping characteristics of these blends in the temperature range of −60 to 0°C were strongly affected by a liquid-state relaxation peak of the IIR phase. It was observed that the presence of a continuous PP phase tends to suppress the intensity of this characteristic loss peak and shift it towards lower temperatures; on the other hand, the crosslinking of IIR has little effect on the intensity of the broad loss peak but tends to shift it towards higher temperatures. These observations were interpreted in terms of effects of thermal misfit stress and crosslinking on the liquid-liquid transition of the IIR phase.