Abstract
Abstract An apparatus is described for measuring the oxygen absorption of vulcanized rubber, either in darkness or under illumination from a controlled light source. The light and dark oxidation curves of four vulcanizates at temperatures of 60°, 65°, and 70° C are examined. Three of the four vulcanizates were protected by the incorporation, respectively, of 2 per cent phenyl-β-naphthylamine, 2 per cent mercaptobenzimidazole, and a mixture of 1 per cent each of the above substances. The dark reaction over 60 hours' duration was in all cases similar and could be represented by a standard equation. It is shown that the effects of PBN and MBI on the dark oxidation are clearly different throughout the temperature ranges. From a consideration of the initial reaction, the decay during storage of the initial oxidizability of the vulcanizates is shown. In oxidation under light from a relatively weak source at a given temperature, the total absorption is considered as the sum of the dark thermal oxidation appropriate to the temperature, and a light-activated absorption. The effect of the light is then shown to be similar in all cases, the rate of absorption due to light starting from zero and increasing through a maximum to a constant value. By comparison of these constant light rates, it is shown that PBN and MBI have little effect on the light-activated absorption of the control, but that the mixture (PBN, MBI) effectively reduces this absorption. The persistence or development of an enhanced dark rate after illumination is shown to depend on the period of illumination and the length of dark storage of the vulcanizate.
Published Version
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