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

Abstract

Recently, the cellulose nanofiber (CNF), which is a pure, plant-derived material, has attracted considerable attention owing to its excellent mechanical properties such as low weight (one-fifth that of steel) and high Young’s modulus (five times that of steel) as a fiber. Novel methods for producing 100% CNF bulk structural materials have been developed. However, the tribological properties of CNFs have never been investigated although their mechanical properties are well-known, which are comparable to those of some of the conventional structural materials. Herein, the tribological properties of a novel biomass material, 100% CNF molding, were investigated under dry- and boundary-lubrication conditions at various temperatures for CNF/steel contacts. The friction test results showed that the friction coefficient and wear volume of the CNF molding increased with the test temperature for the CNF/steel tribopair under the dry-sliding conditions. Conversely, upon the lubrication with pure-poly-alfa-olefin, no significant temperature dependence of the friction and wear properties was observed. The surface analytical results revealed that the amorphization of the CNF molding progressed on the worn surface, especially under the dry-sliding conditions at a relatively high temperature. All the results suggested that the friction and wear performance of the 100% CNF moldings strongly depend on the sliding test conditions, and the amorphization process of the CNF molding can affect its friction and wear performance.