Application of ATR-FTIR spectroscopy to characterize the acrylonitrile content of degraded filled nitrile rubber compounds

In this study, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) with germanium crystals was used to characterize the acrylonitrile content (ACN) of nitrile rubber (NBR) filled with carbon black after undergoing thermal and chemical degradations. Five NBR/carbon black formulations with ACN contents ranging from 29.7 to 45.4% were prepared. The mechanical and chemical properties of the NBR compounds were determined before and after exposure at 120 degrees C for 7, 15, 30, 60, and 90 days in the following environments: thermo-oxidative and simulated production fluid Type A.1.ii specified in ISO 23936-2:2011. A linear model with an R-squared statistic of 99.6% and a correlation coefficient of 0.998 was generated using the ATR-FTIR data of the A2237/A967 ratio of unaged NBR compounds and the actual value of the acrylonitrile content of neat NBR elastomers determined by 13-carbon nuclear magnetic resonance spectroscopy. This model was used to estimate the acrylonitrile content of degraded NBR compounds. The times that caused severe degradation of NBR compounds in thermo-oxidative and simulated production fluid environments were 15-30 days and 30-90 days, respectively. The ACN contents of those aged NBR compounds were successfully estimated using ATR-FTIR experimental values applied to the linear fit model of unaged NBR/carbon black compounds. This made it possible to differentiate between compounds with high and low ACN content, despite the high level of degradation. Thus, the ATR-FTIR technique combined with statistical tools can be a useful tool to predict the service life of rubber products and other composite materials.