The Study Of Molecular Simulation Method And Modification Technology For UHMWPE

Ultra high molecular weight polyethylene(UHMWPE) is a thermoplastic engineering plastic with many excellent properties, and it was often used as the materils in friction pair system. However, the relationship of variation of structure and properties is largely unknown when it used in some particular environment, for example, in severely oxidative medium.Furthermore, the wear resistance and strength properties remain to be improved when it used in friction system and heavy duty applications. These defects seriously hinder the application and development of UHMWPE. The rapid development of modern molecular simulation technology provides a new insight and a convient research method, respectively, for the investigation of relationship of change in structure and properties of such UHMWPE polymers. In this paper, the accurency of molecular model of polymers was discussed by molecular dynamics(MD) simulations, and then a series of perl script were designed and developed for quantifing the results of reactive molecular dynamics(RMD) simulations.Finally the oxidation behavior of UHMWPE and the tribological properties of UHMWPE composites were systematically and deeply studied by using combination of molecular simulation technologies and traditionally experienmental methods. All works were supported by National Natural Science Foundation of China and National Scientific and Technical Project of China, etc. The main results and conclusions are as follows:1. Some results of RMD simulation, including thermodynamics, products distribution and reaction mechanism, are slightly affected by the molecular weight of atomic model, but the molecular weight significantly effect the calculations of diffusion coefficient and the cross-linked reaction. Therefore, the selection of molecular weight for modeling of macromolecules depends on the investigative category in RMD simulations.2. A series of script programs were developed for batch-processing the 3D trajectory files of RMD results by using perl language based on Materials studio software. The availability quantitative data includes the number of hydrogenbonds, functional groups and molecular fragment products, etc. It provides a convenient and reliable method for quantizing and counting the RMD results.3. The oxidation behavior of UHMWPE and polyoxymethylene(POM) in severe oxidizing environment(hydrogen peroxide solution) was comparied by the calculations of RMD simulations. The oxidation mechanism was deeply analyzed from an atomic perspective.Results of the simulations demonstreated that UHMWPE is superior to POM with repect toapplicating in hydrogen peroxide medium, and the relative simulation results are generally consistent with the previous experimental available in literature.4. The results of MD simulations demonstrate that Mult-wall carbon nanotubes(MWNTs)are effective filler for preparation of UHMWPE/MWNTs composite. Then a seris of tribological experiments were carried out in order to evaluate the effect of the weight fraction of MWNTs on the properties of UHMWPE/MWNTs composites. The research results indicated that the 0.3wt% MWNTs UHMWPE composite shows the optimum wear resistance,the wear width and depth is, respectively, reduced 29.2% and 43.5%.5. The properties of SiC reinforcing UHMWPE was investigated by the tribological experienments. Results indicated that the 5.0wt% SiC UHMWPE composite shows the optimum wear resistance, the wear width and depth is, respectively, reduced 9% and 23%.Then a seris of MD simulations were carried out for deeply analyzing the intermolecular absorption mechanism and the influence factors.