Tribological characterization of green lubricating greases formulated with castor oil and different biogenic thickener agents: a comparative experimental study

Purpose – The aim of this paper is to characterize some selected formulations based on castor oil and a variety of biogenic thickeners from a tribological point of view and compare them with some traditional lithium greases.Design/methodology/approach – The evolution of the friction coefficient in several tribological tests performed using several ball‐on‐disc configurations and coupling materials was monitored for the different oleogels proposed as biodegradable lubricating greases. Both a rotational ball‐on‐disc classical tribometer designed at MuT laboratory and a nanotribometer were used in rotational and oscillatory modes.Findings – Generally, the use of castor oil‐based formulations potentially applicable as biodegradable lubricating greases provides similar or lower values of the friction coefficient than traditional lithium greases, depending on the nature of thickener agent employed and tribological contact. In all cases, biodegradable formulations provide significantly lower values of the fricti...