Molwcular Dynamics Study On Swelling And Wear Of Crosslinked Hydrogenated Nirrile Rubber

Hydrogenated nitrile butadiene rubber can also be referred to as HNBR.It is prepared by hydrogenation of unsaturated carbon-carbon double bonds existing on nitrile butadiene rubber(NBR).HNBR polymer has excellent mechanical properties and wear-resistant properties and is widely used in the field of petroleum exploitation.The application of macroscopic experimental means to study the properties of HNBR polymers has been very perfect,but there is still room for progress in the study of molecular principles from the microscopic level.Therefore,based on the principle of molecular dynamics,this study aims to investigate the effects of vulcanization crosslinking on the properties of hydrogenated nitrile butadiene rubber and clarify the corresponding microscopic mechanism.The details are as follows:(1)The main structure of the cross-linking reaction was analyzed,and the hydrogenated nitrile butadiene rubber vulcanization model with 99% hydrogenation degree was established according to the physical and chemical characteristics,and five different cross-linking density models were set up.Then,the glass transition temperature and mechanical properties were calculated,and the mean azimuth movement was obtained by extracting particle trajectories.The results show that the glass transition temperature increases with the increase of crosslinking density and the heat resistance improves.MSD decreased with the increase of crosslinking density,and the trajectory trend of the two models with higher crosslinking density was the same,indicating that the crosslinking density had reached the optimal level,and the molecular mobility was limited.The mechanical properties first increase and then decrease with the cross-linking density.When the cross-linking density exceeds 30%,the stress concentration in the lattice will result in uneven deformation in the cell,and the properties will begin to decline.(2)For the purpose of verifying the accuracy of the model,the crosslinking density of HNBR compound was measured by instruments.The experimental results showed that DCP could increase the crosslinking density of hydrogenated nitrile butene rubber molecules,and the glass transition temperature measured was in good agreement with the simulated values,which were within the reasonable range of literature records.The macroscopic mechanical properties characterization parameters increased with the increase of crosslinking density.When the dosage of DCP reached 6phr,the mechanical properties began to decline,and the change trend of experimental values was consistent with the simulation results.Both thermal conductivity and thermal decomposition stability increase with the increase of crosslinking density,and the best performance is at 30%.(3)Considering the actual situation,hydrogenated nitrile butadiene rubber models with good simulation performance of 30% crosslinking density were selected,filled with cyclohexane(C6H12)molecules,HNBR polymer models with different swelling volumes were established,and the glass transition temperature and mechanical properties of each model were calculated.The influence mechanism of swelling behavior on HNBR polymer was analyzed from microscopic level.The results show that the larger the swelling volume,the smaller the glass transition temperature,the stronger the mobile activity of the molecular chain,the oily molecules can weaken the intermolecular force,the restriction is weakened,the rubber matrix plasticized,the mechanical properties deteriorate,the deformation resistance deteriorates,the friction coefficient and the wear amount increase with the swelling volume.(4)A rubber metal friction pair model was established to reveal the microscopic mechanism of friction and wear after swelling behavior from three different aspects:relative atomic concentration distribution,atomic temperature distribution and mean azimuthal shift.The results show that the increase of temperature makes the HNBR polymer soften,and the damage degree of colloidal microstructure becomes greater.The number of HNBR polymer atoms attached to the iron atomic layer increases,the interaction area increases,and the wear amount increases,which seriously affects the service life of HNBR colloidal.