Viscosity modification of different vegetable oils with EVA copolymer for lubricant applications

During these last years, special attention has been paid to the protection of the environment against pollution exerted by lubricants and hydraulic fluids based on mineral oils. Thus, vegetable oil-based lubricants are being actively demanded for many green industrial activities. Although vegetable oils have some excellent properties for their potential use as lubricants, some inconveniences should be technologically improved, i.e. limited range of viscosities available. Consequently, environmental friendly viscosity modifiers should be included in the lubricant formulation. In this paper, ethylene–vinyl acetate copolymer (EVA) has been successfully tested as viscosity modifier for several common vegetable oils, yielding potentially environmental friendly lubricants for some applications. EVA addition always yields an important increase in vegetable oil viscosity. The most important viscosity increments have been found for low-viscosity vegetable oils, i.e. sunflower oil (SO), high-oleic sunflower oil (HOSO) and soybean oil (SYO), at moderate temperatures. Viscosity increments up to 330–420% respecting the original oil have been obtained for these vegetable oil/EVA blends at 40 °C. On the contrary, the lowest increments correspond to castor oil/EVA blends, mainly at low temperature. Furthermore, ternary blends of high-oleic sunflower oil, castor oil (CO) and EVA may be used to design enhanced bio-lubricant formulations for some specific applications. In this sense, some CO/HOSO/EVA ternary blends (CO/HOSO weight ratios >1) show kinematic viscosities, at 40 °C, higher than 320 cSt, which may be considered a threshold viscosity value for gearboxes and four-strokes engine applications.

Research highlights▶ This work deals with the modification of vegetable oils viscosity for bio-lubricant applications. ▶ Use of EVA copolymer allows improving viscosity data for conventional vegetable oils studied. ▶ Viscosity increments up to 330–420% respecting the original oil have been obtained for these vegetable oils/EVA blends. ▶ Ternary blends of high-oleic sunflower oil, castor oil, and EVA may be used to design enhanced bio-lubricant formulations.