Fabrication And Tribological Properties Of High Temperature Resistant Double-wall Self-lubricating Microcapsules

The rapid development of science and technology requires higher performance of self-lubricating microcapsules.At present,the traditional self-lubricating microcapsules are mostly single-walled,the compactness and mechanical strength of the wall materials are poor,and it is difficult to to be processed and applied at high temperature.Therefore,the development of a double-wall or even multi-wall microcapsule with high temperature resistance,compactness and high mechanical strength has become a hotspot in research.Three kinds of self-lubricating microcapsules with double-wall structure were prepared in this paper.At the same time,polypropylene（PP）and epoxy resin（EP）were used as the matrix to investigate the effects of the addition of double-walled microcapsules on the tribological properties and mechanical properties of the composites and to reveal the related self-lubricating mechanism.The main content of the article can be summarized as the following aspects:（1）Lubricating oil@PSF/SiO₂ double-wall microcapsules were prepared by solvent evaporation method and sol-gel method.The microcapsule has a regular spherical structure with an average particle diameter and a wall thickness of about 90μm and 6μm,respectively,and an initial thermal decomposition temperature of 300℃.In addition,the self-lubricating PP composites with double-walled microcapsules were prepared on the basis of PP and the tribological properties of the composites under different loads and friction rates were studied.The results indicated that the friction coefficient and wear rate of PP composites incorporating10 wt.%double-walled microcapsules were 54.9%and 54.3%lower than that of pure PP under the conditions of medium load（1.0 MPa）and medium friction rate（0.5 m/s）,respectively.（2）Lubricating oil@PUF/CNTs-o-PDA double-wall microcapsules were prepared by in-situ polymerization and surface loading.The double-wall microcapsules have a regular spherical structure with an average diameter of about 110μm and the initial thermal decomposition temperature elevated by 75℃than those of the lubricanting oil@PUF single-wall microcapsules.EP self-lubricating composites with different mass fractions of single and double-walled microcapsules were prepared and tested for tribological properties.The experimental results show that the friction coefficient and wear rate of EP composites incorporating 20 wt.%double-wall microcapsules were 33.79%and 74.28%lower than that of composites embedding the same mass fraction of single-wall microcapsules,and which were64.07%and 99.54%lower than that of pure EP,respectively.In addition,the tensile test of the composite showed that CNTs-o-PDA grafted on the surface of single-wall microcapsules can effectively improve the interface bonding performance between EP and microcapsules.（3）[BMIm]PF₆@PU/PUF double-wall microcapsules were prepared by the combination of interfacial polymerization and in-situ polymerization.Firstly,[BMIm]PF₆ was used as the core material.The optimal synthesis conditions of[BMIm]PF₆@PU single-wall microcapsules were optimized by interfacial polymerization.There was adhesion between the single-wall microcapsules,the compactness needed to be improved,and the interface bonding performance between the smooth outer wall and the resin matrix was poor.On this basis,[BMIm]PF₆@PU/PUF double wall microcapsules were prepared by polycondensation of Pre-UF to form PUF adsorbed on the surface of single-wall microcapsules.The double-wall microcapsules had regular spherical structure and rough outer surface,the core fraction was≈71.29%,the average diameter and thickness of the resultant microcapsules were about 52±18μm and 3μm,respectively.Finally,tribological properties of EP composites with double-wall microcapsules was investigated.Compared with the pure EP,the friction coefficient and wear rate of the EP composites incorporating 20 wt.%double-wall microcapsules were reduced by about 83.6%and 218 times,respectively.