Basic Reactions Occurring during Rubber Reclaiming. I. The Influence of Reclaiming Media, Antioxidant, and Defibering Agents on Vulcanized Natural Rubber at 195 Pounds Per Square Inch Gauge Pressure (196.6° C)

Abstract

Abstract The influence of surrounding atmosphere, antioxidant, and defibering agents at 196.6° C on the hydrocarbon of rubber was studied by subjecting a laboratory prepared, pure-gum, natural rubber compound to reclaiming in the absence of any reclaiming oils or chemicals. Data obtained on the amount of acetone and chloroform extracts and on the unsaturation of the reclaims and the chloroform extracts could therefore be interpreted in terms of the effect of the factors mentioned above on the rubber hydrocarbon and not as the effect of any chemicals added to the rubber to promote reclaiming. It was found that the effect of the surrounding atmosphere during reclaiming is the predominant factor in the reaction. Acidic surrounding atmospheres result in a slow and rather uniform rate of molecular breakdown and in the formation of small amounts of oxidation products. Apparently no secondary oxidative attack occurs at the double bonds. An open steam atmosphere provides the greatest amount of oxidized products and also a high initial molecular breakdown, followed by a slow progressive increase in it as the reclaiming periods are lengthened. A decrease in the unsaturation value of the acetone extracted reclaim indicates that secondary oxidative attack at the double bonds occurs at long reclaiming intervals. Alkaline reclaiming atmospheres provide little if any oxidation products and result in a very high initial rate of molecular breakdown. Longer reclaiming periods do not change further the amount of molecular breakdown. The very small amounts of oxygen necessary to promote the reclaiming reactions, the dependence of the course of these reactions on the acidity or alkalinity of the surrounding reclaiming media, together with the high initial rate of molecular breakdown reactions under conditions where such rate would be speeded up, permit the tentative explanation of these reactions on the basis of hydroperoxidic chain reactions. Further experiments along this line are being carried out.