Temperature-dependent changes of physicochemical and tribological properties of acrylonitrile-butadiene rubber elastomer upon ageing in hexadecane and diethylene glycol dibutyl ether

Abstract

Acrylonitrile-butadiene rubber elastomers are widely used in seal and tire industries. Physiochemical, surface and tribological properties of acrylonitrile-butadiene rubber exposed to a lubricant in a sealed mechanical contact may gradually change, in particular, at elevated temperatures. In this study, industrial-grade acrylonitrile-butadiene rubber elastomers were aged in two model non-additivated base oils, namely non-polar hexadecane and polar diethylene glycol dibutyl ether at both ambient (298 K) and elevated (398 K) temperatures from 1 to 168 h. Mass changes of acrylonitrile-butadiene rubber before and after ageing indicated that acrylonitrile-butadiene rubber had distinct ageing dynamics in different model base oils and at different temperatures. For acrylonitrile-butadiene rubber aged in nonpolar hexadecane, the rate of weight loss of the rubber was larger at 398 K compared to that at 298 K. On the contrary, distinct weight-gaining (swelling) dynamics were observed for acrylonitrile-butadiene rubber aged in polar diethylene glycol dibutyl ether at 298 and 398 K. Based on Fourier transform infrared spectroscopy, liquid and solid-state nuclear magnetic resonance spectroscopy and energy dispersive spectroscopy analyses, it was found that aldehydes and sulfur- and zinc-containing compounds were leached out from acrylonitrile-butadiene rubber aged in both hexadecane and diethylene glycol dibutyl ether. The results of tribological studies showed that the non-aged acrylonitrile-butadiene rubber has a good wear-resistance. Acrylonitrile-butadiene rubber samples had a very similar surface topography before and after tribo-tests. However, the worn surfaces of acrylonitrile-butadiene rubber samples were characterized by fine scoring (abrasion) marks after ageing in both model base oils. This has been attributed to changes in the steel–rubber contact environment during the sliding process and degradation of mechanical properties of acrylonitrile-butadiene rubber after ageing. For one acrylonitrile-butadiene rubber sample (after ageing in hexadecane at 398 K), very stable friction in the steel–rubber contact was observed.