Abstract:
Lubrication is an important measure for reducing friction and wear of mechanical equipment and prolonging the service life of the metal parts, thus being of great significance in saving raw materials and energy. Note that to achieve good lubrication, the assurance and support from advanced lubricating materials are urgent and essential. Over past decades, with the continual progress in nano science and technology, new hope and opportunities have been brought for developing novel lubricating materials, resulting in the fact that a variety of neotype nanosized lubricating materials continuously spring up. Among them, nanocellulose, in particular, is considered as a promising candidate for nanosized lubricating material with high-performance and greenness, owing to its outstanding tribological properties, mature preparation methods, and biodegradability as well as renewability which are exactly the unique advantages of nanocellulose. In recent years, the tribological application of nanocellulose has gradually attracted the extensive attention of scientists. Accordingly, this review summarizes the research status of nanocellulose in the field of tribology. This article mainly included three parts: construction and prominent properties of nanocellulose; application status of nanocellulose in tribology; and outlook on using nanocellulose in the field of tribology. Firstly, the chemical constitution and the resultant surface chemical property of nanocellulose were briefly introduced, followed by the typical physical and mechanical properties. Nanocellulose has the relatively high chemical reactivity, which facilitate surface modification for nanocellulose, and the ultrastrong mechanical properties and many excellent physical properties such as low density, high crystallinity, large specific area and length-diameter ratio, and ultralow thermal expansion, which together endow nanocellulose with immense application potentials in tribology field. Secondly, the research status on applying nanocellulose in tribology were detailed, specifically involving five tribology branches including polymer reinforcing filler, water-based lubricant additive, lube oil additive, grease additive, and electroactive regulation for lubrication. Moreover, for each branch above, the corresponding antifriction and antiwear mechanisms of nanocellulose were discussed, and the major problems facing the current studies about nanocellulose lubricating material were summarized, mainly including the weak interface between nanocellulose and polymer, the adverse effect of nanocellulose aqueous dispersion with high viscosity to tribological performances, the ultralow susceptibility to friction heat of nanocellulose, and the dramatic change in physical properties of grease caused by nanocellulose. Finally, the future development of studies on tribological applications of nanocellulose, which were still in their infancy nowadays, were also prospected. Aiming at the current problems proposed by this review, in-depth studies need to be carried out in the following aspects: (1) explore low-cost, high-efficient and environment-friendly modification methods to realize higher hydrophilicity and lipophilicity for nanocellulose; (2) improve the susceptibility to friction heat of nanocellulose to enrich the lubrication mechanism content; (3) enhance the accuracy and sensitivity of electroactive regulation for lubrication with nanocellulose and make it move forward to engineering application.