Solubility and Diffusion of Sulfur in Synthetic Elastomers

Abstract

Abstract 1. The rate of solution of sulfur in various elastomers during milling depends on the temperature of the elastomer, the solubility and rate of diffusion of sulfur in the elastomer, the particle size and type of sulfur used, and the degree of breakdown of the elastomer. 2. The relative heat build-up on the mill rolls for each elastomer after 30-minute milling increases in the order: natural crepe rubber, Butyl, Buna-S, Neoprene-GN, Perbunan, Hycar OR-15. Conclusions as to extent of cross-linkage, mutual attraction of the chain molecules, and plasticity are indicated from data of this type. 3. The solubility of sulfur in the several elastomers increases with the degree of mastication, as shown in the cases of natural crepe and Buna-S, until a limiting value is obtained. 4. The specific diffusion rate of sulfur through various elastomers was determined. These rates of diffusion decrease in the following order: natural crepe rubber, Buna-S (GR-S), Hycar OR-15, Butyl B-3. 5. In synthetic elastomers the change in sulfur solubility with increase in temperature is greater than in natural rubber, the solubility is less at room temperature, and the rates of diffusion are slower; therefore the possibilities of heterogeneous vulcanization with these elastomers are increased.