Diffusion of Antioxidants in Rubber

Abstract

Abstract The study of the diffusion of polymers in order to determine the size and shape of the macromolecules in solutions has been the subject of numerous recent works. Considerably fewer studies have been devoted to the problem of the diffusion of low-molecular substances dissolved in polymers, and the existing works in this field refer principally to gas-polymer systems. It is also known that the rate of diffusion in polymers of solid and liquid low-molecular compounds governs in a number of cases the kinetics of processes of great practical importance. In particular, the kinetics of a process as important to the rubber industry as the oxidation of rubber is, to a large degree, related to the rate of diffusion of antioxidants and other soluble ingredients in the rubber. Rubber as a diffusion medium is distinguished from liquids and solid crystalline substances by certain properties which are governed by the characteristic heat movement of the macromolecules. Thus, Brün showed that Einstein's equation cannot be applied in the case of diffusion in rubber, and Barrer developed a theory of diffusion of gases in rubber, according to which the presence of an activation zone is necessary for the initial process of diffusion. The present study concerns the diffusion of certain solid antioxidants dissolved in rubber (phenyl-2-naphthylamine, dinaphthylamine, and dinaphthyl-phenylenediamine).