Penetration of Aromatic Hydrocarbons into Natural Rubber

Abstract

An investigation of organic solvents penetrating into and out of natural rubber (NR) vulcanisates as a function of time was conducted with respect to degree of swelling and deswelling, diffusion characteristics and mechanical properties. The natural rubber was vulcanised using different techniques to obtain various types of crosslinking; these included flexible and rigid sulphur, peroxide and mixed linkages. Stress-strain measurement was utilised to determine the overall crosslink density and the mechanical properties of the rubber. The degree of swelling and deswelling was conclusively related to the flexibility and mobility of polymer chains, size of the penetrant, temperature, and desulphuration and decomposition reactions of the crosslinks. Before and after equilibrium swelling overall degree of swelling was affected by the penetrant characteristics, whereas during the equilibrium state the degree of swelling was influenced by the types of crosslinks present in the rubber vulcanisates. The reduction in mechanical properties during swelling was due to the conversion of mechanical energy into an activation energy, this being used to achieve the penetration of the solvents into the polymer network. The property recovery after deswelling involved stress relaxation of the polymer network.