Environmentally friendly vegetable oils and their derivatives represent alternatives to mineral-based lubricants. Vegetable oils have high biodegradability and low production costs. Their poor thermo-oxidative stability and poor low temperature properties are disadvantages in their use as lubricant basestocks. In our study we used corn oil and diester mixtures, which become lubricants when additives are introduced. These mixtures of corn oil and di-2-ethylhexyl-adipate (DOA) and di-2-ethylhexyl-sebacate (DOS) offer a wide range of kinematic viscosities, pour points lower than -39°C and flash points over 218°C. The diameters of wear scars measured under four-ball testing (40 daN) are less than 0.90 mm and the copper strip corrosion test result is 1a. The differential scanning calorimetry study and thermogravimetric study under nitrogen atmosphere and in synthetic air are reported. From these studies a higher thermal stability was observed for corn oil than for diester oils. The thermo-oxidative instability occurred at temperatures higher than 350°C. The low production cost of corn oil and its mixtures with diesters makes them an attractive alternative to mineral oil lubricants.

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 (40 dyn) are less than 1 mm. 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.

New lubricating oils obtained from mixtures of synthetic diesters (di-2-ethylhexyl-adipate (DOA) and di-2-ethylhexyl-sebacate (DOS)) and vegetable oils (sunflower, SFO, soybean, SO and rapeseed oil, RO) are studied. The characteristics of all these mixtures are given together with differential scanning calorimetry (DSC) and thermal gravimetric (TG) analyses.