Ecolubricants based on vegetable oils with ionic liquid

Abstract

There is increasing interest in vegetable oils for applications in industrial lubrication rather than mineral oils. Vegetable oils are biodegradable and come from natural resources; with null toxicity in comparison with mineral oils derived mainly from petroleum. Nevertheless, the properties of these natural oils must be modified to improve their thermal stability and resistance to oxidation, in order to extend the service life. The tribological properties of vegetable oils, such as the friction coefficient, wear resistance, or load-carrying ability, need to be improved to make them suitable for high-performance applications. To achieve this requires the development of new lubricant formulations that include chemical modification as well as the use of additives. The ecolubricants obtained will have a minimal environmental impact and better tribological performance, thereby making them a more attractive alternative to mineral oils. Ionic liquids (IL), a new class of compounds, have demonstrated their potential as neat lubricants or as additives for lubricants in a variety of types of contacts and configurations, due mainly to the polar nature of IL molecules. This ability makes it possible to develop tribolayers on metal surfaces and diminish the friction and surface damage [1-2]. Furthermore, other properties such as non-flammability, nonvolatility, high thermal-oxidative stability, and high thermal conductivity support IL use in tribology as eco-friendly lubricants. Although the addition of IL to vegetable oils has scarcely been studied, the conjunction of the triglycerides and fatty acids contained in vegetable oils and the IL, enables the formation of tribofilms on metallic surfaces. This protects the surface from damage and reduces friction, and it is the key for the formulation of potential new biolubricants [3-4]. The present communication shows the tribological properties of neat and epoxidized avocado oils in comparison to those with the addition of IL diethylmethylammonium methanesulfonate. Friction coefficients and wear rates were studied with a pin-on-disc tribometer using a tribopair of sapphire/stainless steel at 1.4 GPa of Hertz contact pressure. The friction coefficient and wear rate in the case of epoxidized avocado oil (EAv) with 1 wt.% of IL showed an important reduction (Figure 1). Optical and Electronic microscopy, and different spectrocospic techniques were used to establish wear mechanisms and the stability of the oils in tribological conditions.