Study On Anti-aging And Tribological Properties Of Engineering Polymers

With the promoted application of polymer materials in tribological field,some more property indicators?e.g.,mechanical properties,thermal endurance properties and anti-aging properties?must be satisfied besides tribological properties to fit the application demand of the modern engineering equipments.This paper used polyoxymethylene?POM?and ultra-high molecular weight polyethylene?UHMWPE?as the research objects from the view of the anti-aging properties and tribological performance.The changes of surface properties and tribological performance of polymers at various aging environments were studied by designing accelerated aging tests and tribology tests.The tribological modification technology and fabrication process of polymer materials were explored by combining molecular simulation and hot-press molding.The improvement effects of the composite materials on tribological properties were evaluated under different simulated tribological conditions.This research work can provide theoretical guidance,technical means and the test data reference for engineer polymers which meet many performance indexes,and help to enlarge the tribological application of polymer composites in complex work conditions.The major research contents and results are as follows:?i?Effects of three accelerated aging tests on tribological properties of POM and UHMWPE.The aging process of POM and UHMWPE in 90%concentration H₂O₂solution,340 nm ultraviolet light condition and thermo-oxidative environment were simulated.The effects of aging process on surface properties and tribological performance of POM and UHMWPE were studied comparatively.The work can offer experimental basis and material selection gist for tribological modification.The results show that the anti-aging properties of POM are poorer than those of UHMWPE when they were immersed in 90%concentration H₂O₂ solution and exposed in 340 nm ultraviolet light.During these two aging process the micro-pores and micro-cracks appear on the surface of POM specimens,the crystallinity of surface materials of POM specimens increase,and the surface hardness of POM specimens decrease;whereas UHMWPE specimens have no obvious changes on surface micro-topography and thermodynamic properties.The anti-aging properties of POM are better than those of UHMWPE in thermal oxygen aging environment.The friction coefficients of the aged POM?or UHMWPE?sliding against GCr15 are lower than those of un-aged POM?or UHMWPE?.The wear resistance of un-aged POM are obviously superior to that of UHMWPE.With the increase of aging time in high concentration H₂O₂ solution,the abrasion loss of POM decrease,whereas that of UHMWPE increase.With the increase of aging time in ultraviolet light and thermo-oxidative environment,the abrasion loss of POM and UHMWPE increase,and the influence of the aging time on POM is bigger.?ii?Research on the design and preparation of PI/UHMWPE composites.UHMWPE has excellent anti-aging properties in the high concentration H₂O₂ solution and ultraviolet light environment,but possesses poor wear and heat resistance as well.Thus polyimide?PI?which has excellent mechanical properties and heat-resistant properties was selected to modify the heat resistant and tribological performance of UHMWPE.In order to improve the compatibility of PI/UHMWPE composite system,maleic anhydride grafted low density polyethylene?MAH-g-LDPE?was chosen as the compatibilizer.To evaluate the enhancement effects of compatibilizer on the compatibility,dispersion and mechanical properties of the composite system,the molecular dynamics simulation,dissipative particle dynamics simulation and molecular mechanics simulation were conducted with the molecular structure software at microscopic and mesoscopic scale.PI/UHMWPE composites with compatilizer and various composition proportion were fabricated by using a thermo-compression molding machine.The mechanical properties,thermal properties,dispersion properties,surface properties,aging resistance and molecular structure of those fabricated composites were tested.The results show that the mixing properties and interface adhesive strength of PI/UHMWPE composite system increase after added the compatilizer of MAH-g-LDPE.The Young's modulus and shear modulus increase after added the compatilizer of MAH-g-LDPE as well.The micro-topography of cross profiles of PI/UHMWPE composites are flat and dense when the PI content is less than 50%.The density,surface hardness,compression modulus of the composites increase with the increase in PI content.The anti-aging properties in thermo-oxidative environment of the composites increase with the increase in PI content.?iii?Study on tribological properties of PI/UHMWPE composites under various working conditions.The friction condition of seawater lubrication,dry friction in thermal environment and dry friction at high-speed were simulated.The tribological properties of PI/UHMWPE composites with different composition proportion were tested in these simulated tribological condition.The improvement effects of composition proportion on tribological properties were evaluated.The optimum composition proportion of PI/UHWMPE composites for different tribological conditions was explored.The results show that the friction coefficients of the friction pairs composed by PI/UHMWPE composite and tin bronze decrease with the increase in PI content when they worked in sea-water lubricated condition.The friction coefficients of the friction pairs composed by composite and GCr15 firstly decrease and then increase with the increase in PI content when they worked in hot and dry friction condition.The friction coefficients of the friction pairs composed by composite and tin bronze also firstly decrease and then increase with the increase in PI content when they worked in high speed and dry friction condition.The composition proportion of PI/UHMWPE composite with minimum abrasion loss in sea-water lubricated condition,hot and dry friction condition,high speed and dry friction condition is 50/50,50/50 and 70/30,respectively.