Migration of Extender Oil in Natural and Synthetic Rubber

Abstract

Abstract The migration of oil, and in particular, the migration of extender oils in rubber is being studied through the use of radioactive isotopes. Techniques have been developed for uniform carbon-14 labelling of the aromatic-polar fractions of extender oils by Friedel-Crafts reaction and for the uniform labelling of the paraffinic fraction by methylene diradicals generated during photolysis of diazomethane-C14. These techniques formed the basis for a comparative study of the diffusion rates of aromatic and polar, and paraffinic, fractions of a highly aromatic and a paraffinic extender oil in several rubbers which represent a wide range in type of polymeric structure. Faster diffusion rates of both aromatic and polar, and paraffinic fractions, were observed in polybutadiene and natural rubber than in SBR, EPT, and polychloroprene. In most rubbers, paraffinic materials migrated appreciably faster than aromatic and polar fractions. Experiments using Firestone flex blocks indicated that oil migration rates are higher under simulated working conditions than when the sample is subjected to heat treatment alone. Diffusion coefficients for the migrating fractions were calculated from an appropriate solution of the basic differential equation of diffusion using modern computer techniques. The methods which have been developed are suitable for fundamental studies to gain more insight into the mechanisms of diffusion. These experimental methods are also suitable for use in practical studies of oil migration under actual or simulated working and environmental conditions. Ultimately sufficient information should be obtained to permit an accurate prediction of the performance of an extender oil in selected rubbers on the basis of the physical properties of the oil and a quantitative knowledge of the major molecular types present in the oil.