Swelling and Network (Crosslink) Density of Carbon Black-Filled Natural Rubber Vulcanizates

Abstract

Abstract The method cited by W. Kuhn and coworkers for the determination of network densities on the basis of a thermal analysis of swollen samples has been applied to unfilled and carbon black-filled natural rubber vulcanizates. The results with unfilled rubber on the basis of the new method are in the expected correlation with the measurements of the degree of swelling and the modulus of elasticity. From the results with carbon black-filled samples it is probable that an inhomogeneously crosslinked system is formed under the influence of the filler. It is concluded that there are regions of high network density adjacent to regions of low density. Consequently, the degree of swelling, referred solely to the rubber portion, is to be considered a mean value in the case of filled vulcanizates from which the network density cannot be deduced without additional measurement.