Aging and Stabilization of Raw and Cured Rubbers

Abstract

Abstract In recent years a number of monographs and survey articles have been published on individual problems of aging, from which we can compile an idea of the modern state of the problem. In this article we shall attempt to generalize certain new results, analysis of which may be of interest for further development of work on aging and stabilization of raw and cured rubbers. The substantial differences in the mechanisms and rates of aging of purified and technical raw and cured rubbers prepared from them have many times been noted in the literature The presence in technical raw rubbers of contaminants, introduced with the monomers, as well as residues of the catalysts, initiators, and regulators of polymerization exert a vital influence on the aging of rubbers and the behavior of inhibitors. It is also known that introduction of a large number of ingredients into raw rubbers (sulfur, vulcanization accelerators, carbon blacks, plasticizers) radically changes the character of the processes of aging of rubber mixtures. Free impurities and ingredients in most cases weaken, and sometimes suppress the action of antioxidants. For example, sulfur substantially reduces the effectiveness of secondary aromatic amine antioxidants. Other cases are also known when the action of antioxidants is intensified by certain ingredients. Thus, both negative and positive synergic effects may appear in rubber mixtures. Impurities contained in the monomers enter the structure of the polymer chains during polymerization, disturb their regularity, and frequently are the weak sites with which their thermal and thermooxidative decomposition begins. Hence the tendency to produce purer polymers from purified monomers, which will promote a substantial increase in their stability to aging, has now been outlined.