The Minimum of Sulfur Required for Vulcanization. A Résumé
Abstract The problem of the minimum proportion of sulfur necessary to effect vulcanization is fundamental to an interpretation of the very nature of vulcanization itself. Since the introduction of ultra-accelerators, it has been recognized that very small quantities of sulfur are sufficient to bring about vulcanization. In experiments carried out in 1918 in collaboration with G. Menghi in the Laboratory of Chemical and Physical-Chemical Research of the Pirelli Company of Milan, the author found that by the aid of zinc dimethyldithiocarbamate or of similar substances there is an appreciable vulcanization with 0.2 per cent of sulfur. This fact was made public in patents applied for by the author the next year. On the other hand, it is generally recognized today that all vulcanization originates in a chemical reaction, though a fundamental difficulty lies in the fact that it has never been possible to give an exact definition of what is meant by vulcanization. When is a rubber considered vulcanized? From a technical point of view this question may be answered, but there has not been a satisfactory explanation up to this time.