Investigating the impact of a newly developed chemical modification technique on improving the tribological properties of high oleic soybean oil

Abstract

Soybean oil is currently being studied as lubricating oils in various industries, including automotive, aerospace, and UAV, due to its renewability, biodegradability, and non-toxicity. In vegetable oils, the vast majority of fatty acids are unsaturated. This research demonstrates that the tribological properties of high oleic soybean oil (HOSO) can be improved by the conversion of the unsaturated fatty acids to saturated fatty acids via a novel chemical modification process. Ethylaluminum sesquichloride (Et₃Al₂Cl₃) and isopropyl bromide were added to a HOSO solution in methylene chloride for chemical modification of the base oil. After stirring and characterization via thin layer chromatography (TLC), the organic phase was washed with hydrochloric acid, water, and brine solution. Gas chromatography-mass spectrometry (GCMS), 1D nuclear magnetic resonance (NMR) spectrometry, and 2D heteronuclear single quantum coherence (HSQC) NMR were leveraged to characterize raw and chemically modified soybean oils. The physicochemical properties of high oleic soybean oil (HOSO), chemically modified branched high oleic soybean oil (BHOSO), and high oleic sunflower oil (HOSuO) were determined and correlated with their tribological behavior. The reciprocating friction and wear performance of select lubricants were tested using a ball-on-flat type reciprocating tribometer at room temperature and 100 °C. It was found that the chemical modification process increased wear resistance by around 10% at room temperature and 100 °C. Major differences in wear mechanisms were further analyzed using white light interferometry, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques.