Biobased industrial lubricants

Vegetable oils as lubricants are preferred over mineral-based oils because they are biodegradable and non-toxic. They have very low volatility due to the high molecular weight of the triglyceride molecule and have a narrow range of viscosity changes with temperature. Their polar ester groups are able to adhere to metal surfaces producing good boundary-lubrication properties. Vegetable oils also have high solubilizing power for polar contaminants and additive molecules. On the other hand, vegetable oils have poor oxidative stability due primarily to the presence of bis-allylic protons; thus, vegetable oils are highly susceptible to radical attack and subsequently undergo oxidative degradation to form polar oxy-compounds. This phenomenon results in the formation of insoluble deposits and increases in oil acidity and viscosity. In addition, the presence of the ester functionality renders these oils susceptible to hydrolytic breakdown. Low temperature studies have also shown that, in contrast to mineral oil based fluids, most vegetable oils undergo cloudiness, precipitation, poor flow, and solidification at -10° C upon prolonged exposure to cold temperatures. Contamination with water in the form of emulsions must be prevented at every stage of production. Here we present a series of structural modifications of vegetable oils using anhydrides of different chain lengths. The chemically-modified base oils exhibit superior oxidation stability in comparison with unmodified vegetable oils. A systematic approach of antioxidant/antiwear additive synergism to improve the oxidation and cold flow behavior of vegetable oils using pressure differential scanning calorimetry and rotary bomb oxidation tests will also be presented.