Prevention of Ozone Attack on Rubber by Use of Waxes

Abstract

Abstract The tendency for stretched rubber, when subjected to outdoor exposure, to form cracks perpendicular to the direction of stress was originally known as suncracking. The work of Newton showed that light was not necessary and identified ozone as the causative agent. That ozone is the principal factor there seems to be no doubt, but we cannot assert that it is the sole factor. Some test specimens, for example, have been found to crack in the shade, but not in the sun, and some investigators suspect that certain atmospheric pollutants may have a modifying effect. It has been known since 1881 that addition of wax to the rubber compound will provide protection against this type cracking. Garvey and Emmett found that oils or oil-like materials would also effect improvement, but by far the major portion of work has been done with petroleum waxes. The two broad classes of petroleum waxes are paraffin and microcrystalline. The value of the literature—and this applies to many fields other than ozone cracking—is sharply limited by the tendency to characterize waxes as either paraffin wax or microcrystalline wax. As a matter of fact, the composition of petroleum waxes is complex, so that there are large differences in composition between different paraffin waxes and different microcrystalline waxes, with resultant differences in their performance when added to rubber.