Low-Temperature Set as a Measure of State of Vulcanization

In his various patents on vulcanization, Charles Goodyear made several references to the change produced in the low-temperature behavior of rubber. In his earliest patent he stated that vulcanized rubber would not be “injuriously affected by exposure to cold”. The reissues of this patent stated the problem more clearly. “The leading object of my exertions was to render india-rubber capable of resisting the action of heat and cold within the range of atmospheric temperatures…. When compounded with sulfur, by the application of a high degree of artificial heat, I obtained good results, and when compounded with sulfur and the carbonate of lead I obtained the best results.”…. The new product “is water-proof, permanently and highly elastic under all conditions of its use”. Whether Goodyear was referring to the freezing of rubber under tension or under no tension we do not know, but it is probable that he had experienced both effects without distinguishing between them. It is interesting to find now that, one hundred years later, rubber chemists are still looking at this change in low-temperature behavior which he recognized as an effect of vulcanization, and are using the effect as a measure of degree of vulcanization. In recent years the T-50 test has gained considerable popularity as a quantitative measure of the tendency of rubber to freeze under tension. Its popularity is justified, since it can be applied over a broad range of cure and since it measures very precisely a seemingly fundamental property of rubber. It is, however, not the only means of expressing this effect quantitatively. The purpose of the present paper is to demonstrate a simpler method which yields surprisingly precise results, in spite of the fact that none of the usual scientific equipment is used and no measurements other than length measurements are required. Although other papers have approached this subject, none has as yet offered a simple substitute for T-50.