Facile Synthesis of Lignin-Castor Oil-Based Oleogels as Green Lubricating Greases with Excellent Lubricating and Antioxidation Properties

In this study, a facile synthesis method was employed to create lignin-castor oil-based oleogels by modifying organic lignin with two silane coupling agents. The resulting oleogels demonstrated outstanding lubricating and antioxidation properties, establishing them as promising green lubricating greases. Compared with the pure castor oil, the oxidation induction time (OIT) value of the synthesized oleogels was significantly increased from 20 s (pure castor oil) to 1959 s (oleogel with 20 wt % lignin), indicating an effective improvement of the oxidation resistance. The steel contacts lubricated by the synthesized oleogel also had lower wear than those lubricated by pure castor oil, signifying the better lubricating properties of oleogels. The oleogel with 20 wt % lignin showed the lowest wear, which was around 64% lower than that of pure castor oil. The exceptional performance and environmentally sustainable composition of these oleogels, with the biomass content exceeding 80%, allow them to be used as green lubricating greases for industrial applications. Overall, this study provides valuable insights into the development of high-performance, eco-friendly lubricants.