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Within the past ten years the general trends of theory and experimental evidence suggest that aging or degradation is quite like polymerization in nature. These reactions are chain mechanisms; the physical changes of which are the net sum of several simultaneous processes: (a) cross-linking, cyclization, and continued polymerization which harden and stiffen the rubbers, and (b) scission which produces tackiness in the rubbers and results in loss of tensile strength. The relative degree to which different rubbers are susceptible to these mechanisms is discussed.
Several physical methods are available for isolating and measuring the relative rate of one or both of the cross-linking and scission reactions. Among these the use of viscosity, sol-gel relationships, stress-relaxation, creep and permanent set methods for measuring the oxidation effects in various rubbers are described and interpreted.
Throdahl, M. C.
Rubber Laboratory, Monsanto Chemical Co., Organic Chemicals Division, Nitro, W. Va.