Mixtures of vegetable oils and di-2-ethylhexyl-sebacate as lubricants

Abstract

Lubricants based on vegetable oils are growing in popularity in various applications. Environmentally friendly, vegetable oils and their derivatives constitute alternatives to mineral-based lubricants. Soybean oil, sunflower oil and rapeseed oil have better viscosity indices than mineral oils and even some synthetic oils, are biodegradable and have low production costs. However, vegetable oils have disadvantages, such as poor thermo-oxidative stability due to the carbon–carbon double bonds and poor low-temperature properties, which limit their use as lubricant base stocks. This study describes new base-stock oils obtained from mixture of vegetable oils and di-2-ethylhexyl-sebacate synthetic oil, which become lubricants when additives are introduced. These mixtures offer a large range of kinematic viscosities, while their pour points are under −33°C and their flash points over 240°C. The copper strip corrosion test result is 1a. The diameters of wear scars measured under four-ball testing (40dyn) are less than 1mm. A differential scanning calorimetry study and a thermo-gravimetric study under a nitrogen atmosphere for the mixed oils are reported. In the former study two-endothermic processes were observed between −15°C and −50°C. In the thermo-gravimetric analysis curve the weight loss is specific for each vegetable and synthetic oil component. From these studies a higher thermal stability was observed for vegetable oils than for ester oils, and it was concluded that the mixtures of vegetable and synthetic oils of diester type are physically homogeneous mixtures. The low production cost of lubricants based on vegetable oils makes them attractive alternatives for mineral oil based lubricants. Overall the mixtures of vegetable and ester oils can be competitive base oils for environmentally friendly lubricants. Copyright © 2006 John Wiley & Sons, Ltd.