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 Al 2 O 3 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 Al 2 O 3 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.