Tribological properties of 100% cellulose nanofiber (CNF) molding under dry- and boundary lubrication-conditions at CNF/steel contacts

Cellulose nanofibers (CNFs), which are plant-derived materials, have recently garnered considerable attention owing to their excellent mechanical properties, such as their low weight and high Young's modulus. Novel methods for producing 100% CNF bulk structural materials have been developed. However, the tribological properties of CNFs have not been investigated thus far although their mechanical properties are known and are comparable to those of some conventional structural materials. In this study, the tribological properties of a novel biomass material, 100% CNF molding, were investigated based on CNF/steel contacts under dry and boundary lubrication conditions at various temperatures. The friction test results showed that the friction coefficient and wear volume of the CNF molding increased with the test temperature of the CNF/steel tribopair under dry-sliding conditions. Conversely, no significant temperature dependence of the friction and wear properties was observed upon lubrication with a pure polyalfaolefin. The surface analytical results revealed that the amorphization of the CNF molding progressed on the worn surface, especially under dry-sliding conditions at a high temperature. All the results suggested that the friction and wear performance of the 100% CNF moldings strongly depends on the sliding test conditions, and the amorphization process of the CNF molding can affect its friction and wear performance.