LAUSR

Abstract Hydrogenated acrylonitrile-co-butadiene (HNBR) elastomers containing three concentrations of acrylonitrile (34, 39 and 50 wt%) and less than 1% residual double bond content were heat aged up to 150°C. Fourier transform Infrared (FTIR) spectroscopy, elemental analysis and liquid proton Nuclear Magnetic Resonance (NMR) were used to analyze the thermo-oxidized samples. FTIR clearly shows the development of esters, ketones, carboxylic acids and secondary alcohols upon heat aging which were confirmed by NMR. The acrylonitrile content was not affected by the employed heat aging conditions. Using the carbonyl growth index and time-temperature superposition (T-TS), the long term thermo-oxidative kinetics possessed three distinct regions: 23-85°C, 85-100°C and 100-150°C. The slower oxidation kinetics in the 85 - 100°C in combination with an induction period shown by T-TS region likely contributes to the enhanced oxidative heat aging resistance of HNBR. In addition, an induction period was observed by T-TS between 85 and 115°C. Activation energies increased with temperature and lower acrylonitrile levels. A series of reaction mechanisms has been put forth to explain functional group development or loss during oxidative heat aging.