The Analysis of Antioxidants and Accelerators in Rubber Compounds and Vulcanizates

In the rubber industry the number of accelerators and antioxidants has increased greatly in the last few years. Van Alphen even in 1956 described 154 accelerators and 87 antioxidants of different chemical structure. The detection of such a large number of materials, depending on their combination in stocks, is more or less difficult, although the detection of the presence of one or another compound often makes possible a prejudgment as to which other substances can be counted on and which cannot. Besides the chemically homogeneous accelerators and antioxidants, use is also made of mixtures as combination products. The individual components are qualitatively detectable in mixtures. Information on the type of these products is given by quantitative determination methods such as described by Zijp, Kortum, Szalai and Szöke, among others. The original substances are often chemically altered during vulcanization or later in the preparation of samples for testing; e.g., symmetrically constituted disubstitution products may split into monomers, substituents split off from the basic molecule, or reactions of various types take place which render the investigation difficult. The identification of antioxidants and accelerators received a great impetus from the application of chromatography which is of importance today as a method of separating the individual materials for subsequent physical determination methods. After Tswett has recognized decades ago the separating effect of absorption columns in the analysis of compounds of chemically similar structure, this method was used only much later for the Chromatographic investigation of rubber compounds. The earlier analytical methods in this field depend on the use of conventional methods, e.g., selective extractions and precipitation of the substances to be isolated, which are then identified in pure form by melting point determination.