Haitao Duan

Comparison of oxidation resistance of UHMWPE and POM in H2O2 solution from ReaxFF reactive molecular dynamics simulations.

The oxidation mechanism of ultra-high-molecular-weight polyethylene (UHMWPE) and polyoxymethylene (POM) in hydrogen peroxide solution was investigated by molecular dynamics (MD) simulations via reactive force field (ReaxFF) method. MD results from ReaxFF suggested that UHMWPE provided better antioxidation activity at high temperature (>373 K) than its POM counterpart in the same concentration of hydrogen peroxide solution. Furthermore, POM was relatively more susceptible to erosion and swelling because of the infiltration of H2O2 solution. Calculations of the diffusion coefficient at different temperatures permit further understanding of the chemical phenomena involved in the level of oxidation in the course of MD simulations. Results of the simulations are generally consistent with the previous experimental available in literature. The simulations also provide new insights into understanding the mechanism resulting oxidation products among the interested polymers.

Fabrication of Polyimide-Modified UHMWPE Composites and Enhancement Effect on Tribological Properties

ABSTRACT Polyimide-modified ultrahigh molecular weight polyethylene (UHMWPE) composites were fabricated by hot-press molding process. Mesoscopic morphologies of polyimide/UHMWPE blending systems show high compatibility between the phases of polyimide and UHMWPE when the weight ratio of polyimide is no more than 50 wt%. Investigation of the tribological properties with a reciprocating ball-on-flat contact tribometer shows that the polyimide filler has important effects on the friction and wear behavior of UHMWPE composites. Compared to pure UHMWPE, the composite with 50 wt% polyimide improved tribological properties best and exhibited 43.1% reduction in friction coefficient and 66.7% reduction in wear volume loss. GRAPHICAL ABSTRACT

Discussion on the influence of driving parameters of civilian cars on motor oil degradation

Although the reason is not clear, mileage is commonly recommended as an indicator to evaluate the oil drain interval of a car. This paper tries to investigate whether the mileage is the most suitable indicator to evaluate the oil drain interval based on scientific experiments and data analysis method. Three civilian cars and motor oils (contained mineral oil, semisynthetic oil, and synthetic oil) were subjected to road tests under urban traffic condition. The real-time driving parameters comprising speed, mileage, idle time, engine operation time, and number of starts were obtained by on-board diagnostic system. Synchronous oil samples were collected about every 30 days. The physicochemical properties and component changes of experimental oils were analyzed in laboratory. The effects of driving parameters on oil properties were studied with the improved grey relational analysis method. The results show that the influencing factors of driving parameters on motor oil degradation were different in different experimental cars. The influence of mileage on oil degradation was not obvious. The idle time of engine, engine operation time, and number of starts were the three most significantly influential factors on oil deterioration after comprehensive analysis of the three experimental cars.

A molecular modeling study for miscibility of polyimide/polythene mixing systems with/without compatibilizer

Abstract Molecular models were established to predict the miscibility of polyimide/polythene mixing systems and the enhancing effects of compatibilizer addition of maleic anhydride grafted polythene (MAH-g-PE). Molecular dynamics simulations were applied to investigate radial distribution functions and Flory-Huggins parameters of the mixing systems. Results show that polyimide/polythene is miscible to a certain degree, and the miscibility gets better after adding MAH-g-PE. Dissipative particle dynamics (DPD) simulations display that micro-phase separation occurs in the polyimide/polythene mixing systems, however, effective interfaces appear between polyimide and polythene phases after adding MAH-g-PE. The results of molecular mechanics simulations indicate that the ability of mixing systems to resist stretch, compression and shear deformation increases after adding MAH-g-PE. This work offers a promising technique to predict miscibility properties for polyimide/polythene system prior to actual production and attempt to find a suitable compatibilizer for that system.