Swelling Mechanism and its Effect on Abrasive Wear Behavior of Nitrile Rubber in Water Medium

In this study, time-based static swelling behavior was first investigated via immersion experiments of nitrile rubber with different acrylonitrile weight percentages (18%, 26% and 41%, i.e. N18, N26, and N41) respectively. Then the unidirectional sliding abrasive wear tests with different particle shapes of the NBR samples before and after swelling tests were further conducted. In order to reveal the swelling mechanisms and its effect on the abrasive wear, the weighting method, hardness tests, nuclear magnetic resonance and scanning electron microscopy were conducted and analyzed accordingly. The results showed that the swelling degree increased with the immersion time and the main influence on aging was crosslink chain destruction and substance dissolution, which led to the decrease of the nitrile rubber mass and the formation of the swelling layer. The nitrile rubber hardness decreased with the increasing swelling time. The friction coefficient and abrasion increased after swelling and the wear degree of the sharp type abrasive particle were higher than the smooth type under the same particle size. The sharp type abrasive wear can be more affected by swelling, and the maximum wear increase was 1.56 times of the smooth type after swelling. During the wear process under smooth type abrasive particle, the abrasive particles entered the friction pair mainly in rolling, which led to the pit-like press indentation. While under the sharp type abrasive wear process, the main entry form was sliding, which led to the sharp embedded indentation instead. Since the sharp type abrasive particle was not conducive to the formation of the lubricating film, a large amount of abrasive debris remained on the worn surface. The loosened and softened rubber tissue after swelling caused the deeper indentation and the ridge pattern formation. The acrylonitrile content effect degree of the swollen abrasive wear of the smooth type was larger than the sharp type, which had the greater wear variation multiples among the three different acrylonitrile content nitrile rubber. In general, the swelling degree and its effect on the abrasive wear behavior of the nitrile rubber under water conditions decreased with the increase of the acrylonitrile content.