Low-temperature flow behaviour of vegetable oil-based lubricants

Low temperature performance is one of the main constraints concerning the use of vegetable oils as lubricants, more than mineral or synthetic oil-based lubricants. In this work, the low-temperature behaviour of a variety of vegetable oil basestocks for lubricating applications, as well as their blends with some viscosity improvers and pour point additives, was studied through pour point determinations, thermal analysis (DSC) and viscosity measurements at low temperature. The concentration of polyunsaturated fatty acids (PUFAs) was found a predominant parameter influencing the low-temperature properties of vegetable oil-based lubricants. The pour point depressant (PPD) additives used had a positive influence by lowering the pour point and increasing the low-temperature performance of the vegetable oils studied, which was found dependent on vegetable oil fatty acid composition. In this sense, the most striking result was shown by the sunflower (SO)/PPD blend, whose pour point temperature reached −36 °C in comparison to −18 °C for the neat oil. By contrast, the worst result was obtained for the high oleic sunflower oil (HOSO)/PPD blend (−21 °C) in comparison with HOSO (−18 °C). On the other hand, it was found that the ethyl cellulose (EC), used as viscosity modifier, induces a delay in HOSO crystallization, producing a similar effect than PPD tested, besides increasing the viscosity. However, the ethylene–vinyl acetate copolymer (EVA) induces an undesirable increase in HOSO viscosity at around 13 °C.