Lubrication performance of the cellulose nanocrystalline (CNC) aqueous suspensions as potential green lubricants

Industrial lubricants are widely introduced into mechanical systems to reduce wear and energy losses. With the increasing demand for environmental protection, developing eco-friendly lubricants becomes more crucial. Due to their abundance, biodegradability, non-toxicity, high thermal stability and low cost, cellulose nanocrystals (CNCs) may be an appropriate choice for formulating green lubricants. The wear and friction coefficient are the tribological properties that assess the effectiveness of a lubricant. Minimizing the friction coefficient and wear, using a proper lubricant, would improve lifespan of the mechanical systems in different lubrication applications. In this study, using different chemical, microstructural, rheological and tribological characterization methods, we systematically investigated the effect of particle concentration and ultrasonic treatment on the lubrication performance of CNC suspensions as potential green lubricants. It was found that the lubrication performance of liquid CNC suspensions is optimal within sonication energy of 4-50 kJ/gCNC, and the concentration regime of 1-2 wt%. The yield stress is an important rheological property for evaluating the lubrication performance of the lubricating greases. This property determines the pumpability and leakage of grease in bearing applications. In this study, we examined the effect of ultrasonic treatment and particle concentration on yield stress of highly concentrated CNC gels to evaluate their performance as potential green lubricating greases. It was found that yield stress scales linearly with CNC concentration, whereas it decreases with sonication energy through a four-step mechanism governed by microstructural transformation of the CNC agglomerates. The results confirmed that CNC aqueous suspensions may be potentially used as green lubricants. The results also suggested that by tuning ultrasonication processing and particle concentration, one may be able to optimize lubrication performance of CNC aqueous suspensions. Under the optimum CNC concentration regime (1-2 wt%), COF decreased by 50% compared to DI water. Whereas, under the optimum sonication energy regime (4-50 kJ/gCNC), COF and wear decreased by 25 and 30% compared to unsonicated CNC suspension.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat