Abstract
The fundamental reaction of vulcanization is the combination of a vulcanizing agent with rubber. The kinetics of this reaction is expressed by smooth curves. Simultaneously with the combining of the vulcanizing agent, in fact as a result of it, changes take place in a number of physical and chemical properties of rubber—solubility, modulus, tensile strength, and other indexes. Unlike the kinetics of combination of the vulcanizing agent, the changes in these properties are most often represented by curves having a maximum or minimum which characterizes the phenomenon of optimum vulcanization. The extreme form which curves of changes of physical and chemical properties of rubber assume during vulcanization can be explained, in our opinion, by the fact that, during vulcanization, there is a competition between opposing reactions, of which one set are reactions of structure formation (i.e., increase of the molecular weight and the intensity of intermolecular reaction), and the others are destruction reactions. Thus, during vulcanization under factory conditions, at least two reactions take place: (1) the reaction between rubber and sulfur, and (2) the reaction between rubber and molecular oxygen introduced into the vulcanization mix by milling with the ingredients. The amount of oxvgen present here in moles approaches the molar concentration of sulfur.