Study of the Mechanism of Surface Deterioration of Ebonite and of Means of Preventing Deterioration

Abstract

Abstract Following up earlier work on the subject, experiments are reported showing that the deterioration of the surface resistivity of ebonite caused by a particular quantity of light increases with decreasing intensity of illumination, and from the results of exposures to different types of radiation it is concluded that the surface temperature of the ebonite during exposure is the most important variable causing this difference. The observed effects are explained by assuming that sulfurous acid is produced as an intermediate product in the deterioration, and that this may either decompose to sulfur dioxide and water, or oxidize to sulfuric acid. If the former reaction is favored by a rise in temperature, the observed influence of intensity and type of illumination, and also the changes in resistivity after ceasing exposure can be explained. Possible methods of preventing or reducing deterioration are discussed, and it is concluded that application of an opaque surface coating, possibly incorporating a suitable basic material to neutralize any acid formed, is the only method likely to be really effective. This method is not possible in many cases. Incorporation of a suitable antioxidant (sym, di-β-naphthyl-para-phenylenediamine was the best of those tested) reduced the rate of deterioration. Where surface coating is impracticable, the use of an antioxidant might be considered, although improvement of resistance to deterioration by a factor of more than three has not so far been achieved by this means.