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1. The removal of chemisorbed oxygen from channel black and furnace black, without alteration of the underlying carbon surface, results in only minor effects in reinforcement potential regardless of the curative system employed, whether polar or free radical. 2. When the underlying carbon surface is changed by heat treatment to a state of lower energy, a significant decrease in the reinforcing ability of the carbon black results. 3. Different types of oxygen functional groups added to the carbon surface produce similar effects upon rubber properties. 4. These effects are limited to retardation of cure rate in sulfur curing systems. Only small effects of any kind are produced in the natural rubber-peroxide system. 5. The net conclusion to be drawn is that combined oxygen on the carbon surface plays a relatively minor role in the chemical effect of carbon black upon reinforcement; the nature of the carbon surface itself is of primary importance.

Previous investigations have shown a large difference between the amount of rubber insolubilized by carbon black in dilute solvent systems and in standard mill mixes. The purpose of this study, after reconciling these extremes, was to evaluate the role of adsorption in the insolubilization of rubber in mill-mixed compounds. An adsorption test was employed which eliminated the solvent effect of the dilute system and the mastication effect in mill mixing. Results showed that carbon black, depending on the temperature and atmosphere conditions imposed on the rubber carbon films, represses the scission, cross-linking, and gelation reactions of GR-S X-478. This repressive effect is ascribed to the adsorption and inactivation by the carbon black of the oxidized intermediates through which these various reactions proceed. The magnitude of this effect was found to vary with the type, loading, and surface chemistry of the carbon. This approach not only offers promise as a means for predicting the behavior of carbon black in rubber compounds, but also, because of its applicability to the study of all rubber-carbon systems, offers possibilities of providing additional information on the mechanism of the carbon-rubber bond.

All commercial tread grade carbon blacks, may be classified on the basis of electron microscope surface area and oil absorption. Similar industry wide grade classification on the basis of iodine number, tinting strength and oil absorption is considerably less reliable. However, among the blacks of individual carbon black suppliers, reasonably good classification of the tread grades is possible on the basis of these latter three carbon properties.