The Influence of Certain Accelerators on the Aging of Rubber

Among the accelerators which are at present on the market two are very much used, viz., diphenylguanidine as an accelerator of medium activity, and tetramethylthiouram disulfide as a rapid accelerator. Diphenylguanidine is used most of the time in proportions between 0.5 to 1 per cent, based on the rubber, and with about 3 per cent of sulfur. Tetramethylthiouram disulfide is used in proportions of between 0.2 and 0.5 per cent, based on the rubber, with about 1.8 per cent of sulfur. In this way “nervy” mixtures are obtained which have excellent physical properties; but it must be recognized that these two accelerators are, each in its class, the ones which impart to mixtures the poorest aging qualities. For example, the mixture: Pale crepe 100 Zinc oxide 5 Sulfur 3 Palm oil 1 Stearic acid 0.5 Diphenylguanidine 0.7 vulcanized 1 hour at 3 kilograms pressure, i. e., under conditions which lead to the best physical properties for the proportions used, was investigated.