Tribological and Rheological Characterization of New Completely Biogenic Lubricating Greases: A Comparative Experimental Investigation

Abstract

Against the background of raw material shortage and the ever-expanding environmental consciousness, the use of biodegradable greases becomes more and more important. The aim of this experimental work is to investigate the tribological response of completely biodegradable greases. Complete biodegradable lubricating greases were formulated with high-oleic sunflower oil (HOSO) and/or castor oil, and different biodegradable thickener agents such as natural cellulose fibers of different lengths and some derivatives, as well as glyceryl and sorbitan stearates. To investigate the friction process, the model greases were tribologically examined with a nanotribometer at a normal force of 200 mN using a material combination of a steel ball on a steel disc. All frictional results, along with the volumes of wear tracks and micrographs of the main contacting area on the steel plate, are presented and discussed. In addition to this, rotational transient flow measurements were carried out on a rheometer at different temperatures to monitor the evolution of the shear stress with time at a constant shear rate, and to characterize the internal friction behavior by quantifying the energy density. All results were also analyzed from an energetic point of view.

Lignin-Based Additives for Improved Thermo-Oxidative Stability of Biolubricants

“…It has been reported that lignin can be incorporated into various biolubricant formulations. Gallego et al, Acar et al, and Borrero-López et al demonstrated that lignin derivatives (hexamethylene diisocyanate cross-linked, epoxide, or isocyanate functionalized lignin) act as thickening agents in castor and sunflower oils. − Delgado et al. showed that epoxidized lignin can be used as a thickener in castor oil biogreases exhibiting improved tribological and antiwear performance .…”

Influence of Rheological Properties of Lithium Greases on Operating Behavior in Oscillating Rolling Bearings at a Small Swivel Angle

“…In order to take a closer look at fluid friction, which occurs inside the lubricant, rheological energy densities were investigated. It represents the energy expenditure required to deform a certain lubricant volume [24]. The rotational transient flow measurements of the model greases were carried out on an MCR-102 rheometer (Anton Paar Germany GmbH, Ostfildern, Germany) by using a PP25 plate-plate system (Anton Paar Germany GmbH, Ostfildern, Germany).…”

Investigation of Tribological Behavior of Lubricating Greases Composed of Different Bio-Based Polymer Thickeners

“…The flow limit was determined by the intersection of the logarithmically plotted curves from the storage and loss modulus. It was shown that castor oil is a suitable candidate regarding stability of produced grease and tribological characteristics such as friction coefficient [13,14,24]. Thus, castor oil was chosen as the base oil to produce the bio-based greases.…”

“…The cellulose pulp was also optimized in another study as a suggestion for bio-based thickener production [12]. Moreover, in [13] it was shown that bio-based greases were developed based on castor oil and high-oleic sunflower oil with cellulose fibers as thickener. In other studies, friction coefficients of developed bio-based greases were comparable to the petrochemical greases [14][15][16].…”