The reaction of ozone with surfaces of natural rubber, and its dependence upon strain

The progressive reaction of ozone with surfaces of natural rubber ( cis ‐polyisoprene) has been studied by means of replica electron microscopy. Unstrained rubber suffered surface degradation at a rate consistent with the predictions of a theory of diffusion with simultaneous chemical reaction. In strained surfaces the rate of ozone penetration was appreciably greater, but this is attributed to physical rather than chemical causes. Sites of preferred reaction (etch pits) were observed in both strained and unstrained specimens, the former also displaying oriented fissure systems. The origin of these features is explained in terms of Griffith's criterion and it is necessary to postulate, in the unstrained specimens, pre‐existing surface strains. The relation of the microscopic etch and fissure patterns to macroscopic ozone cracks is briefly discussed.