The results of assessment of thermal characteristic (temp. up to 800 deg C in the air) of two grades of butadiene-acrylonitrile rubbers, differing in AN content (18% and 39%), were presented. Derivatogaphy and thermogravimetry coupled with infrared spectroscopy (TG-FT-IR) methods (Fig. 1 and 4) have been applied in the investigations. DTA curves have been interpreted on the basis of additional measurements such as determination of crosslinking density and value of limiting viscosity number, elemental analysis and FT-IR spectroscopy. Activation energy of destruction and indices of thermal stability of elastomers investigated (Table 1) have been determined. In the rubbers investigated, after heating to 160 deg C, thermooxidative processes occur leading to hydroperoxide groups formation, decomposition of which initiates degradation as well as crosslinking processes [equations (1)-(5)]. In these rubbers mainly the processes of thermal crosslinking, as a result of butadiene mers polymerization, occur. So the lower AN content in the copolymer the higher thermal crosslinking efficiency. It has been stated that acrylonitrile mers' content also influences significantly the rate of thermal decomposition of elastomers and their activation energy, while does not influence the initial decomposition temperature. Products of the thermal decomposition of the polymers mentioned are following: butadiene, methane carbon monoxide and carbon dioxide, other aliphatic hydrocarbons and also nitrogen compounds such as ammonia and hydrogen cyanide.
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