| In order to solve the shortcomings of ultra-high molecular weight polyethylene(UHMWPE) in the application domain of tribology, two functional fillers possessing thermal storage capacity were designed in this project. The two fillers were added into the UHMWPE matrix to obtain a series of functional UHMWPE-matrix composites. Afterwards, tribological properties of different composites under various test conditions were carefully measured, and the corresponding abrasion mechanisms were thoroughly analyzed. At last, temperature field distribution in the friction test process was explored. Following are the main points:(1) Two kinds of microcapsules containing phase change material of paraffin wax were successfully prepared by the process of in-situ polymerization. The parameters in the synthetic process were optimized by orthogonal experiments, and the best synthetic condition was as follows: the emulsification speed was 1000 rpm, and sodium dodecyl benzene sulfonate(SDBS) was selected as the emulsifier, the core-and-wall ratio was 1:1.5, and the dropping speed of prepolymer was maintained 2ml/min. The morphology and structure of microcapsules were determined. And results indicated that the prepared microcapsules presented as uniform sphere and had a average grain diameter of 1~2μm.By mixing expanded graphite with paraffin material, two kinds of functional fillers consist of expanded graphite/paraffin were prepared. By means of SEM, its microstructure was studied and the adsorption mechanism that porous structure absorbs paraffin was revealed. At last, its thermal storage-and-release property was tested by self designed experiments, and the results showed that the prepared expanded graphite / paraffin fillers had a high thermal conductivity and stability.(2) The mould pressing machine applicable to UHMWPE was designed and assembled.The molding process of UHMWPE-matrix material was explored in detail, and the corresponding technological parameter was determined. On this basis, MF/UHMWPE composites and EG/P/UHMWPE composites were prepared with paraffin microcapsules(MF) and expanded graphite/paraffin(EG/P) as the fillers, and UHMWPE as matrix.(3) An MM-200 friction-abrasion tester was used to determine the tribological performance under the condition of dry friction. Results showed as follows.On the low-speed condition, the addition of proper percentage of paraffin microcapsules can improve both abrasive resistance and friction coefficient of UHMWPE. The optimized percentage was 20%, and unfer this condition, the friction coefficient of composites decreased more than 60% while the abrasive resistance could be improved by 17%. After different percentages of expanded graphite/paraffin were filled, the friction coefficients of the composites decreased significantly and the minimum could reach about 0.1, while there was no obvious enhancement of its abrasive resistance.When it come to the high speed, after proper percentage of paraffin microcapsules or expanded graphite/paraffin were filled, both abrasive resistance and friction coefficient of UHMWPE would be improved. The optimized percentage of paraffin microcapsules was 20%, and unfer this condition, the abrasive resistance of composites improved more than 40%. While for the expanded graphite/paraffin, the modified effect varied from the type of paraffin and its adding proportion.(4) Friction stability in the sliding process was explored, and the results showed that the stability of the modified composites apparently enhanced, and theirs fluctuation of friction coefficients decreased sharply. Temperature distribution on the UHMWPE friction interface was explored in different ways during friction test, and the results of actual measured temperature, analyzed temperature, and computersimulated temperature were compared. The significant influence of flashing temperature on the tribological performance of UHMWPE composites was revealed in this thesis. |
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