DAMPING BEHAVIOR OF DYNAMICALLY CURED BUTYL RUBBER POLYPROPYLENE BLENDS

Dynamically cured blends of butyl rubber (IIR; isoprene-isobutylene ru bber) and anhydride-grafted polypropylene (PP) of various component ra tios and curative loadings were prepared by melt mixing. Evidence from dynamic mechanical analysis and phase-contrast microscopy suggested t hat these blends were heterogeneous, with the PP phase being continuou s. Damping characteristics of these blends in the temperature range of -60 to 0-degrees-C were strongly affected by a liquid-state relaxatio n peak of the IIR phase. It was observed that the presence of a contin uous PP phase tends to suppress the intensity of this characteristic l oss peak and shift it towards lower temperatures; on the other hand, t he crosslinking of IIR has little effect on the intensity of the broad loss peak but tends to shift it towards higher temperatures. These ob servations were interpreted in terms of effects of thermal misfit stre ss and crosslinking on the liquid-liquid transition of the IIR phase.