Combination of Rubber and Carbon Black on Cold Milling

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Abstract
Although the structure of carbon black is imperfectly known, x-ray analysis has shown it to consist of layers of condensed rings of carbon atoms. Unsaturation and discontinuities in the layers are likely to provide sites for attack of free radicals, and thus make carbon black a radical acceptor of a special polyfunctional type. Assuming combination of rubber radicals and carbon black, a particle could terminate more than one sheared rubber chain. Furthermore, rubber chains attached to a carbon black particle could also undergo scission by shear and be terminated by combination with other particles. The result anticipated from this picture is a network of rubber and carbon black held together by chemical bonds. In rubber solvents, such a network would be insoluble and merely become swollen gel. Insolubilization of rubber on milling with carbon black has been reported on occasion, but the evidence is not sufficiently extensive to draw reliable conclusions as to its cause. This paper reports a systematic investigation of the occurrence of rubber-carbon black gel on cold milling. This gel has been shown to form, and the conditions for its formation and its properties have been interpreted as strong evidence for the above hypothesis of chemical-bond attachment of rubber and carbon black.
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