The thermal stability of rapeseed oil as a base stock for environmentally friendly lubricants

It is well known that the good tribological and environmental properties of vegetable oils contrast with their lack of complete thermal and hydrolytic stability. The purpose of the current study is to determine the influence of thermal oxidation on the lubrication and physicochemical properties of rapeseed oil. The oxidation procedure was performed using a Rancimat 743 apparatus. Standard methods were used to determine viscosity parameters, acidity and peroxide values. A visible light spectroscopy method was introduced to estimate the oxidation rate of rapeseed oil. The transmission spectra of rapeseed oil undergoing oxidation show a precise correlation between transmission and degree of oxidation. Using this method, the end of the induction period can be easily observed. The observed results show clear influence of oxidation in the change of physicochemical properties and the lubricating ability of rapeseed oil. Increasing the amount of primary oxidation products decreases the lubrication properties, while the secondary oxidation products that are formed improve the friction reduction properties of rapeseed oil.