Tribological properties of oil-impregnated porous polyimide modified by rare-earth compounds

Porous polyimide (PPI) exhibits good tribological performances due to excellent oil-storage properties. Porous structure could store lubricant but also make PPI materials difficult to be strengthened by most fillers, because fillers will destroy the pore structure and reduce the strength significantly. Rare-earth compounds (RECs) have high surface activity, which allow them to bond well with polymer. In this study, the tribological properties of REC modified PPIs were investigated using a ball-on-disc tribometer, along with an analysis of oil-impregnated properties, including oil content, oil retention, oil contact angle and oil absorption speed. The mechanical properties, including hardness (Shore D), impact strength and tensile strength, were tested to evaluate the effect of RECs. The results show that CeF3 and LaF3 fillers can lead to an increase of about 40% in oil content of PPI. PrF3 modified PPI were found to have better oleophilic properties, as the oil contact angle reduced 33% compared with pure PPI and oil retention could reach 88% after 120 min centrifugation. Moreover, PrF3 can enhance the surface hardness, impact strength and wear resistance performance of PPI despite a slight decrease in tensile strength. Better oil-impregnation and mechanical properties of PPI modified by PrF3 effectively reduce the friction and wear.