Reinforcement of Rubber by Carbon Black

The mechanism by which carbon black reinforces elastomers is one of the most interesting problems of modern technology and still a subject of much speculation. The effect itself was discovered by S. C. Mote of the India-Rubber, Gutta-Percha and Telegraph Works Co. of Silvertown, near London, as a result of an effort to improve the properties of rubber even more than was possible by zinc oxide. The (American) Goodrich Company purchased certain manufacturing rights from the Silvertown company in 1912, and by 1915, the inclusion of carbon black in rubber compounds of high quality had become general. The most important effect observed upon introduction of carbon black into rubber was the vast improvement in abrasion resistance. As long as natural rubber was the unique elastomer in general use, other effects of carbon black, although by no means insignificant, were not of the same great importance, with the possible exception of tear resistance. With the outbreak of war in 1939 and the consequent shortage of natural rubber in the industrial West, the introduction of the copolymer of butadiene and styrene, then known as Buna or GR-S, as an almost total replacement for natural rubber, would not have been possible without carbon black. It may be stated, with little likelihood of contradiction, that no other product exists which contributes as much strength and abrasion resistance to noncrystallizing rubbers, while maintaining to a large extent their desirable elastic properties, as does carbon black. In spite of the tremendous consumption of carbon black, mainly in tires, and the steady progress made in improving its quality, the reasons for its unique behavior are still largely a matter of speculation and debate. The subject is enormously complex, as may be gathered from a survey of the literature. Many studies have been published describing one aspect or another of the behavior of carbon black (or carbon blacks, since there are many grades available) and these are still appearing. Some excellent papers and books survey and analyze the available information, such as those by Studebaker, Kraus, Donnet and Voet, and Medalia.