Some Infrared Studies on the Vulcanization of Rubber
Abstract The two most effective ways of altering the physical and mechanical properties of natural rubber are vulcanization and the addition of carbon black. There is, however, little understanding of the structural changes brought about by these processes, in spite of extensive research by chemical and physical methods. For instance, in vulcanization it is not yet decided how the sulfur atoms are incorporated in the rubber polymer, what proportion are in bridges formed between the isoprene chains, whether such bridges are formed by —C—S—S—C— or —C—S—C— links, whether one double bond is broken for each sulfur atom incorporated, and so on. An ancillary problem is the effect of certain “accelerators” on the speed of vulcanization, about which even less is known. Again in the case of reinforcement of rubber by materials such as carbon black, there is controversy on the structural relationship of the carbon black and the rubber. Until such structural problems have been solved on the molecular scale there is little hope of controlling the macroscopic properties of rubber compounds in a truly scientific manner. This paper gives a preliminary account of the application of infrared spectroscopy to some of these problems.