Chromatographic Analysis of Rubber Compounding Ingredients and Their Identification in Vulcanizates

The work is still in a preliminary stage, but sufficient has now been done to demonstrate the applicability of chromatographic methods to rubber analysis. The acetone extracts of vulcanizates are complex mixtures not readily amenable to analysis by normal chemical methods. By the use of this elegant technique, however, it has been possible to effect the efficient separation of wax, fat acids, accelerators, and antioxidants, not only from each other but also from naturally occurring coloring matter and from degradation products. The subsequent identification of the main fractions is then a relatively simple matter, as tests such as the cobalt oleate reaction for accelerators and the spot reactions for antioxidants can be applied without interference from any other components. The elegance of the method is further demonstrated by the fact that it can be used in the identification of components present in much smaller quantities than are detectable by other chemical methods. The accelerators and antioxidants studied so far are rather limited in number, but cover the main classes of these materials, and the method should, therefore, be applicable to the analysis of a number of technical vulcanizates, and the authors have, in fact, already made use of it with some success for this purpose. It is noteworthy that the adsorption and elution processes are quantitative, and that the whole of the material put on to a column can, therefore, be recovered from the various fractions. This, therefore, offers the possibility of quantitative work on such problems as the rate of consumption of accelerators during cure or the relationship of antioxidant content to behavior on aging. Such work would necessarily be restricted to experiments using pure accelerators and pure antioxidants which are single chemical entities. In this connection the degradation products obtained from mixes accelerated with T.M.T. or M.B.T.S. or D.P.G. are of interest both in the actual isolation of the components in question and in partial confirmation of the work of others in this field. A much more intensive study of the degradation products of each accelerator in mixes cured to varying degrees may well throw more light on the complex subject of accelerators. Although, therefore, the authors have been able to show the utility of chromatography for their own particular analytical problems, it is likely, ultimately, to be of great value in the exploration of some of the fundamental problems of rubber chemistry.