Abstract: In this study, castor oil and mineral oil were employed as base oils, while chitin, calcium stearate, and lithium stearate served as thickeners, respectively. The optimal grease formation conditions were determined through orthogonal experimental design to prepare base greases. The physicochemical properties of the castor oil-chitin system were systematically compared with those of metal soap-based (calcium/lithium stearate) greases. Microstructural characteristics, thermal stability, rheological properties, and tribological behavior were analyzed using scanning electron microscopy (SEM), thermogravimetric-differential scanning calorimetry (TGA-DSC), rheometer, and a four-ball tribometer. Results demonstrated that the castor oil-chitin grease exhibited superior performance: a dropping point exceeding 330 ℃, steel mesh oil separation rate of 3.71%, and enhanced mechanical stability, colloidal stability, and high-temperature stability compared to metal soap-based greases. TGA revealed higher initial decomposition temperatures, indicating superior thermal stability. Rheological analysis highlighted exceptional viscosity retention and shear recovery capabilities at elevated temperatures. The four-ball test showed a weld load of 2452 N (exceeding metal soap-based greases) and comparable friction coefficient (0.0765). The castor oil-chitin grease exhibits excellent overall performance and environmental friendliness, offering a novel approach for the development of bio-based lubricants and contributing to low-carbon and sustainable development strategies.

Key words: bio-based grease, castor oil, chitin, rheological properties, tribological performance