Improving the Oil Separation of Composite Lubricating Polyurea Grease via Regulating the Thickener Network Structure

Lubricating grease comprises a thickener network filled with base oil. It mainly exerts a lubricating effect by secreting oil inside its network to protect the friction surface. The increase in lithium prices and its physiological toxicity have positioned polyurea grease as one of the most promising lubricants. Presynthetic thickener-based fabrication strategy, which avoids using toxic raw materials, represents a green production route for grease. However, the correlation among thickener structure, oil separation, and tribological performance remains unclear. Herein, three polyurea greases with different thickener structures were synthesized by adjusting the polymerization degree of the polyether oil via the presynthetic thickener strategy. The real-time observation of the thickener structure evolution revealed that increasing the oil polymerization degree would help form longer thickener fibers. A high-strength network structure composed of long fibers was observed in a higher polymerization degree oil (HG). The combined results of low field nuclear magnetic resonance characterization and molecular simulations reveal that a higher polymerization degree oil will induce more hydrogen bonds between base oil and thickener, thereby providing a strong binding ability to the base oil molecules and stable oil separation at the interface during the shearing process. As a result, HG grease could maintain effective protection even under strict test conditions. These results can provide new insights into the structure–property relationship of composite grease and help to develop high-performance lubricants.