Tribological properties of oxidized wood-derived nanocarbons with same surface chemical composition as graphene oxide for additives in water-based lubricants

The tribological properties of oxidized wood-derived nanocarbons (oWNCs), which have the same surface chemical composition as graphene oxide (GO), were investigated as additives in water-based lubricants using a sintered tungsten carbide ball and a stainless steel flat plate with a reciprocating sliding configuration. WNCs were synthesized from four kinds of Japanese wood powder by metal-catalyzed carbonization, and were strongly oxidized by a modified Hummer's method. The four oWNCs have aggregated chain-like nanostructures and maintain graphitic layers. In addition, the four oWNCs were well-dispersed in water due to their high level of oxidation. The four oWNC aqueous dispersions improved lubrication. In particular, the aqueous dispersion of the oWNC derived from Japanese cedar (J. Cedar) wood powder showed a very low friction coefficient and formed a thick tribofilm on the plate surface. The most distinctive properties of the J. Cedar oWNC, compared to the other oWNCs, were the small primary and secondary particle sizes, which were much smaller than those of the other oWNCs. The small-sized J. Cedar oWNC may possibly enter the frictional interface, preventing direct contact between the ball and plate surfaces and forming a tribofilm.