Evaluation of the oxidative properties of vegetable oils as base stocks for industrial lubricants using spectroscopic and thermogravimetric analyses

Abstract

AbstractThis paper presents the study of the oxidative behaviour of vegetable oils using Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) spectroscopic methods and thermogravimetric analysis/differential thermal analysis (TGA/DTA) techniques. The properties of vegetable oils were determined by their fatty acid (FA) composition. A high content of polyunsaturated FAs, like linoleic and linolenic acids, decreases thermal‐oxidative stability. FTIR spectroscopy can be used as a quick method to measure the degree of unsaturation in vegetable oils in a qualitative manner. NMR spectroscopy can be used to quantitatively evaluate the degree of unsaturation in vegetable oils. TGA/DTA techniques were used to evaluate the oxidative properties of vegetable oils. In the present study, TGA/DTA analyses was performed on different vegetable oils under isothermal conditions at 150 °C for 3 hours. TGA/DTA thermograms showed weight changes and thermal activities in terms of exothermic or endothermic heat flows during the oxidative reactions. The oxidative degradation was evaluated in terms of the weight gain by the respective vegetable oils under the test conditions, due to the formation of oxidative polymerization products and the value of exothermic peaks as obtained from the DTA. The comparative study of the oxidative performance of different vegetable oils showed that the higher the degrees of unsaturation, the higher are the weight gains and the exothermic peaks. The evaluation of the effect of a chosen antioxidant showed marked improvement on the oxidative stability of vegetable oils. Copyright © 2008 John Wiley & Sons, Ltd.