Analysis of Cure Characteristics on Cross-Link Density and Type, and Viscoelastic Properties of Natural Rubber

The interrelation of degree and type of cross-linking and viscoelastic properties of sulfur-cured natural rubber (NR) vulcanizates was investigated by altering accelerator concentration, cure time, and cure temperature. Constants C 1 and C 2 from the Mooney-Rivlin equation were given via stress-strain measurement to estimate the cross-link density, cross link type, and effectiveness of forming cross-links, coupled with a thiol-amine chemical probe technique. The dynamic mechanical properties, such as storage modulus, damping behavior, and variation of the glass transition temperature, were found to be not necessarily dependent on the overall cross-link density but were a function of the percentage proportion of cross-link types generated in the NR compounds; these were varied by the compounding and curing conditions. The effects were explained based on desulfuration and decomposition reactions of the cross-links; these are also associated with additional heat built up during vulcanization.