Simultaneously Improving the Eco-friendliness and Tribological Performance of Lithium Grease by Cellulose Nanocrystal Additive

The development of eco-friendly lubricating additives attracts more and more research attention. However, their tribological performance remains a challenge compared to conventional metal thiophosphate additives in the industry. This study investigated the use of cellulose nanocrystals (CNCs) as an eco-friendly additive to partially replace conventional metal thiophosphate additives in a commercial lithium grease. The friction tests showed that compared to the Full grease containing the standard content of molybdenum dialkyl dithiophosphate (MoDTP) and zinc dialkyl dithiophosphate (ZDDP), the Half grease (i.e., the content of MoDTP and ZDDP was halved based on the Full grease) performed superior anti-friction and anti-wear ability by incorporating 0.5 wt% CNC nanoparticles. Surface analysis of the friction pairs revealed that CNC nanoparticles facilitated lubrication through a mending effect on the worn surfaces. Moreover, the function of CNCs became even more effective under high loads, resulting in an excellent extreme-pressure capacity. This study suggests that CNCs are a promising bio-based additive that can simultaneously improve the eco-friendliness and tribological performance of lubricating greases.