The Chemistry of Carbon Black and Reinforcement

Abstract In this discussion, we have indicated that carbon blacks display both chemical and catalytic activity which appear to be sufficient to radically alter the chemistry of vulcanization. Much of the chemical reactivity results in removal of molecules or reactive intermediates which might otherwise produce crosslinks. However, in some cases the chemical reactivity seems to be associated with catalytic activity. When carbon black is heated with rubber, as during hot mixing or during cure, the following types of reaction are considered possible: a) Alkylation (in a broad sense) of carbon black by rubber molecules. This would be a case of alkylation of an aromatic material by an olefin. b) Isomerization of the double bond structure of rubber molecules resulting in conjugation. c) Chemisorption of rubber molecules with dissociation—dehydrogenation—and chemical combination of the rubber-free radicals so formed with the carbon black surface or with themselves, a type of polymerization. Insofar as addition to carbon black is involved, the results of a) and c) are, for practical purposes, identical. During vulcanization, the action of carbon black will be dependent upon the nat