Study On Swelling And Tribological Behavior Of The Nitrile Rubber In Water

Nitrile rubber(NBR)is an indispensable and important material in the national economy,national defense industry and people’s lives.Due to its outstanding properties of solvent resistance and abrasion resistance,it is widely used as seal or wear-resistant material in marine,automotive,petroleum,mining and some other fields,in which the failure of nitrile rubber parts under water conditions has always been the focus of researchers.Swelling and abrasion are the primary reasons leading to the problems above.As they both have the time-varying characteristics and influence each other,the interaction between the water medium and the nitrile rubber and its influence mechanism on the wear behavior of the nitrile rubber are the difficulties in the study of tribological behavior of nitrile rubber under water conditions.Therefore,aiming at the problems of swelling aging,insufficient lubrication,interference fit and abrasive intervention,the swelling behavior of nitrile rubber in water and its influence on the tribological behavior of nitrile rubber are studied.In this paper,it is aimed to reveal the water swelling mechanism of nitrile rubber and the effect of swelling on the mechanical properties,and explore the interaction relationship between the water swelling behavior and the wear behavior to further determine the wear mechanism of nitrile rubber under the influence of water swelling.This research provide a theoretical basis for the selection and life prediction of nitrile rubber wear-resistant materials under water medium conditions,and have far-reaching significance for solving the tribological problems of nitrile rubber under the coupling conditions of medium factors and multiple operating conditions.In this study,nitrile rubber is selected as the research object.Swelling is introduced as the main influencing factor of the tribological behavior of rubber materials from the perspective of the influence of medium solution.Using experimental methods,the swelling behavior of nitrile rubber and the tribological behavior under the influence of swelling are studied.In the choice of tribological system,by simulating the three basic forms of sliding wear of the two-body dry sliding wear,two-body wet sliding wear and three-body abrasive wear under the influence of the water medium environment,the interaction relationship between the swelling behavior and the wear behavior of rubber materials is discussed.In the selection of materials,three acrylonitrile rubbers with different acrylonitrile content are selected as the research object.By studying the corresponding relationship between the formula ratio and the swelling and tribological behavior of nitrile rubber materials,the rule of selecting materials for rubber solvent-resistant and wear-resistant parts under different working conditions is explored.Three different kinds of nitrile rubber samples with different acrylonitrile weight percentages of 18%,26%and 41%(i.e.N18,N26,and N41)were manufactured according to the basic formulation of nitrile rubber.The deionized water was chosen as the solvent and different swelling time was set for the swelling tests.The swelling behavior and mechanism of the NBR under water were first discussed to evaluate the swelling effects on the rubber physical and structural properties based on the weighting method,nuclear magnetic resonance(NMR)analysis,Fourier transform infrared spectroscopy(FT-IR)analysis and scanning electron microscopy(SEM)analysis.This is followed by the research on the mechanical properties of the NBRs with different acrylonitrile contents represented in hardness and tensile properties to explore the swelling effects systematically.Finally,the friction coefficient,wear variation and SEM morphologies of the NBR samples were presented to compare the wear mechanism and resistance of the un-swollen and swollen rubbers after unidirectional sliding wear tests under dry friction,water lubrication and abrasive wear with different particle shapes conditions.Meanwhile,the interaction between swelling and wear behavior was discussed in depth.The results indicated that,water molecules penetrated into the nitrile rubber structure under water condition,causing the swelling behavior,which further stretched the rubber molecular chain and reduced the intermolecular force.The reduction in the flexibility of the molecular chain led to the damage of the crosslinking structure of the NBR molecular network,the substance dissolution and the decrease of the mechanical properties of hardness and stretching.Under friction,the overflow of the dissolved water medium causes a change in the lubrication state,which in turn affects the wear behavior of the nitrile rubber.The increase in the contact area between the water solvent and the rubber tissue caused by abrasion made water molecules more easily immersed into the rubber tissue,which further exacerbated the occurrence of swelling and wear behavior.With the increase of the acrylonitrile content,the increased cross-link density and hardness reduced the deformation of the rubber structure under the same load and prevented the swelling microcirculation to a certain extent,resulting in the reduction in wear loss.As swelling behavior was still occurring during the wear process under water conditions,the tribological behavior was carried out under the interaction of the pre-wear state and the swelling behavior.The swelling influences on the tribological behavior of nitrile rubber affected and acted on the entire wear process.The purpose of this paper is to establish the relationship between the swelling time and the swelling rate,crosslink density and composition changes of nitrile rubber by studing the swelling behavior of nitrile rubber,and reveal the swelling mechanism of nitrile rubber and determine the influence of swelling behavior on the mechanical properties of nitrile rubber combined with surface analysis and cross-sectional analysis.By analyzing and summarizing the sliding wear mechanism of nitrile rubber before and after swelling on the basis of experimental research and theoretical analysis,enrich the theoretical system of rubber material tribology and improve the overall service life of rubber materials and the application equipment.The results of this study can provide research methods and theoretical basis for the study of the tribological properties of rubber and other polymer materials under the influence of swelling,and provide theoretical basis and ideas for reference for the selection and design of nitrile rubber parts under different abrasion conditions in the water environment and the swelling resistance of nitrile rubber and the formulation improvement of wear resistance.