Multi-Layer Biocarbon Carbonized from Cellulose Nanocrystals as a Novel Lubricant Nanoadditive in Rapeseed Oil

It is limited to use cellulose nanocrystals (CNCs) as green lubricant nanoadditives due to their high biodegradability. A promising solution is to convert CNCs into biocarbon. Herein, a multi-layer biocarbon (MLC) was prepared by carbonizing CNCs with an ionic liquids–thermal method. MLC was characterized comprehensively and then dispersed into rapeseed oil for use as a nanoadditive. The tribological performance of the MLC nanoadditive was evaluated using a ball-on-disc tribometer. The lubrication mechanism of the MLC nanoadditive was elucidated according to wear analysis of the worn surfaces and wear residues. It was found that MLC had a high carbon content of 77 at% and showed a two-dimensional multi-layered morphology. Each layer was composed of amorphous carbon nanosheets embedded with many crystalline carbon dots. The MLC nanoadditive was of excellent dispersibility and stability in rapeseed oil. Tribological experiments showed that the MLC nanoadditive, with a concentration of merely 0.04 wt%, led to a decrease in the frictional coefficient by 12.4% and the wear volume by 50.7%, having higher efficacy than the CNC nanoadditive. The exceptional lubrication effect of the MLC nanoadditive was mainly attributable to its interfacial deposition behavior and its subsequent fragmenting behavior. This work develops a novel method for biocarbon preparation and showcases its significant potential in lubrication applications.