Mechanism of Oxidation of Rubber and Its Bearing on Accelerated Aging Tests Parts I And II

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Abstract
1. An apparatus is described for the measurement of the rate of oxidation of rubber at either constant pressure or constant volume. Provision is made for further additions of oxygen during the oxidation. 2. It was confirmed that the rate of oxidation of rubber is independent of the oxygen pressure. 3. The zero order reaction rate of oxidation varies with temperature according to the Arrhenius equation. 4. The depth of oxygen penetration decreases exponentially with temperature, and is reduced by low oxygen pressure, low oxygen permeability or by a fast rate of oxidation. 5. If the dimensions of the rubber sample are too large, or the temperature is too high, it is probable that only the outside layers of the rubber will undergo oxidation, and the low rate of oxidation observed will depend on the depth of oxygen penetration. 6. On exposure to light the propensity of the rubber for oxidation gradually increases, and the data suggest the slow attainment of a photostationary state between two opposing reactions, involving the formation of peroxide by light and disappearance by a dark reaction. 7. On removing light-activated rubber into the dark, the enhanced oxidation rate persists for a considerable time. 8. All specifications for accelerated aging tests should specify the importance of not exposing the samples to a bright light before submitting them to the aging operation. 9. The peroxide formed by the action of light can be destroyed by the action of heat in vacuo.

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