D. Grecov, M.J. Shariatzadeh
University of British Columbia,
Keywords: tribology, rheology, wear, liquid crystals
Summary:Lubrication is an effective means of controlling wear and reducing friction. Friction and wear are the major cause of material wastage and loss of mechanical performance. To reduce the friction, most of the mechanical devices are lubricated by oils or in some cases with water. To enhance the properties of the lubricants, a chemical component or blend could be added to improve the fluid performance. Additives can be soluble in oil-based, water-based or both lubricants. Cellulose Nanocrystals as a sustainable and environmentally friendly cellulose derivatives exhibit remarkable improvement of the coefficient of friction and wear when added to different lubricants. In this research, we have used Cellulose Nanocrystals (CNC) as additives for lubricants. CNC was synthesized from native cellulose, which is one of the most abundant biopolymer resource available. It has many advantages such as renewable, biodegradable and non-toxic. Tribological tests were performed on a pin on cylinder tribometer to investigate the performance of lubricants with Cellulose Nanocrystals (CNC) as additives. The coefficient of friction and wear were measured in the presence of CNC based lubricant with different concentrations. The effect of the normal force, the rotational speed and the shaft diameter on the coefficient of friction and wear were studied as well. The optimal CNC concentrations for an improved lubrication have been found. The friction coefficient between stainless steel shaft and chrome steel ball in presence of 2 wt.% CNC in water was found to be as low as 0.09 which is approximately 1/4 of the friction coefficient of water. In addition to friction reduction, CNC reduced the wear depth and width by more than 50%. In all experiments, due to the high Hertzian pressure between surfaces, boundary lubrication occurred and the fluid viscosity had little or no effect on the friction and wear reduction. The beneficial properties of CNC suspensions are mainly caused by the orientation and alignment of the high strength nanoparticles. The nanoparticles orient along the shear direction in the contact region between the two sliding surfaces, hence decreasing the friction coefficient and the wear between the sliding surfaces.