Properties of Hard Rubber. XIV. Influence of Some Ingredients on Surface Deterioration in Sunlight
Abstract Experiments have been made to find to what extent ingredients capable of reacting with sulfuric acid to form insoluble sulfates can prevent the loss of insulating properties of hard rubber on exposure to daylight. Hard rubbers containing small and large percentages of calcium and barium carbonates and litharge have been tested, along with a comparable unloaded material and one containing an inert filler, barium sulfate. In no case was there a substantial improvement. Although the basic fillers gave better results than the inert filler, the samples containing them were inferior to the unloaded sample. The partial recovery of insulating properties on removal from light after a low surface resistivity has been reached has been investigated. Appreciable recovery took place in all cases, but this was most marked with the sample containing calcium carbonate. It was anticipated that the basic ingredients examined would to some extent prevent the undesirable effects of acid forma- tion in cases where the exposure to light was not continuous or so severe as bright north daylight. Further experiments on this point are recommended. The value of benzidine as an ingredient which forms an insoluble sulfate was tested by treating the surface of hard rubber with aqueous and benzene solutions of this material. Appreciable improvement was observed in each case. Attempts to prepare vulcanizates containing benzidine or derivatives of it having the same protective effect were unsuccessful.