Improving Tribological Performance of Porous Polyimide by Surface Polishing

Because of its self-lubricating qualities, porous polyimide (PPI) has been used as a crucial cage material for space bearings; however, overcoming the failure followed by blackening of PPI remains a challenge. Herein, we developed a surface smoothening approach to optimize the tribological performance of PPI in an oil-impregnated state. Pre-polishing using sandpaper and then with Al2O3 paste enables the fabrication of nanoscale rough PPI surfaces with significantly reduced friction and surface wear and complete suppression of the blackening phenomenon. Compared with polishing using sandpaper or Al2O3 paste, the compound polishing method created a substantially smoother surface. It exposed more polytetrafluoroethylene at the outermost surface, improving the liquid and solid lubrication properties of the contact interface under a mixed lubrication state. The further analysis indicated that decreasing the size of PPI surface pores during pre-polishing using sandpaper was crucial in resisting the adsorption of residual polishing particles.