Ester Oils Prepared from Fully Renewable Resources and Their Lubricant Base Oil Properties

The work reports on the physicochemical and tribological properties of gallate ester oils prepared from fully renewable resources, such as gallic acid and fatty acids. The ester structures were identified by proton nuclear magnetic resonance spectroscopy (¹H NMR), carbon nuclear magnetic resonance spectroscopy (¹³C NMR) and high-resolution mass spectra (HRMS) data. The density at 20 °C (d ₂₀), kinematic viscosity (KV), viscosity index (VI), pour point (PP), flash point (FP), thermal and oxidative stabilities, friction-reducing and antiwear properties of gallate ester oils were evaluated. The tribological properties of gallate ester oils as lubricants for steel, copper, and aluminum tribo-pairs can be compared with those of the commercially available lubricating oil tris(2-ethylhexyl) trimellitate (Phe-3C_i8), but their viscosity-temperature characteristics, thermal and oxidative stabilities are better than those of Phe-3C_i8. More importantly, they have much higher biodegradabilities than Phe-3C_i8. The study of the lubrication mechanism shows that the physical and/or chemical adsorption film formed by gallate ester molecules between friction pairs is the key factor for them to obtain friction-reducing and antiwear properties.