Insights into the rheological behaviors and tribological performances of lubricating grease: entangled structure of a fiber thickener and functional groups of a base oil

Abstract

Herein, a series of lithium greases, with different thickener concentrations, fibers morphologies, and types of base oil, was synthesized via the saponification reaction. The corresponding rheological behaviors, such as structural strength, structural rearrangement speed, and recoverability, were investigated carefully. Results indicate that greases with higher entanglement levels of thickener fibers display higher structure strength, lower structural rearrangement speed, and lower recoverability. On the other hand, greases with a lower level of entanglement show counter trends. In addition, the structure strength dramatically decreases with a decrease in thickener concentration; this is accompanied by a significant increase in structural rearrangement speed and recoverability. Furthermore, the difference in these rheological behaviors between greases becomes narrow with a decrease in the fiber entanglement level. In addition, the influence of functional groups of base oil on the rheological behaviors was investigated. By introducing base oils with rigid molecular chains (containing ester bond and aromatic ring), the structure strength of lithium greases improved remarkably, especially for greases with a lower entanglement level. Moreover, the results of tribological tests indicate that the lithium greases with a fast structural rearrangement speed display better friction-reducing property in the frequency ramp tests. On the other hand, greases with a higher structure strength display good load-bearing property.