Oxidation of Unvulcanized Rubber. Effect of Carbon Black

Abstract The effect of carbon black on the autocatalytic stage of oxidation of unvulcanized rubber is shown to be specific for the type of carbon, the reaction conditions, and the polymer. Carbon black is an effective antioxidant for cold rubber when the rubber is heated in air or oxygen. The effectiveness of carbon in inhibiting oxidation increases as the volatile content of the carbon increases. The special case of low loadings of highly oxidized carbons, which completely repress gelation during Banbury mixing, is of particular interest. The opposite behavior of carbon black during rubber gelation is observed when benzoyl peroxide is used as catalyst. With cold rubber, carbon black promotes gelation, while with natural rubber increased scission results. Alteration of any one of these variables produces profound changes in the course and extent of the oxidation reactions.