Ultralow friction of glycerol and its emulsion with oleic acid in a steel elastohydrodynamic contact at 40 °C and 100 °C

Abstract

Glycerol is an abundant, inexpensive, biodegradable substance that is environmentally safe and has low potential for bioaccumulation. We evaluated its tribological performance, neat and emulsified with 4 %wt of oleic acid, using friction maps encompassing surface kinematics typical of mechanical devices such as roller bearings, camshafts, and gears. We set the maximum Hertz contact pressure around 1.0 GPa to achieve the elastohydrodynamic lubrication regime in a ball-on-disk apparatus. The entrainment speed ranged from 0.1 to 2.0 m/s, and the slide-to-roll ratio between 10 % and 30 %. The measurements were made at 40 °C and 100 °C. Under these conditions, extensive portions of the friction maps showed ultralow friction (≤ 0.01). The regression models developed are consistent with lubrication mechanisms accepted for similar tribosystems and exhibit a coefficient of determination R² better than 90 %.