Effect of Thickeners on the Low-Temperature Rheological and Tribological Properties of Lubricating Grease

SEM results revealed significant differences in the microstructures formed by the different thickeners. Both LG and LCG exhibited intertwined fiber networks. However, the fibers in LG were more loosely arranged, resulting in larger pore sizes.

PG microstructure consisted of highly dense, cross-linked fibers with the smallest dimensions, while BTG formed stacked lamellar structures. These microstructural distinctions strongly influenced the rheological properties and flow behavior of the greases at low temperatures. Rheological tests indicated that LG and LCG exhibited favorable viscosity–temperature behavior at low temperatures, contributing to improved flowability.

In contrast, PG and BTG exhibited higher structural strength and viscosity at low temperatures, leading to poorer flow performance. Low-temperature flow-pressure and bearing-torque tests further supported these findings. At −30 ℃, LG and LCG showed significantly lower flow pressure, starting torque, and running torque compared with PG and BTG.

Tribological performance tests revealed a significant influence of thickener type on lubrication properties. Within 0~30 ℃, both LG and LCG exhibited excellent friction reducing and antiwear properties. Additional tests under varying loads revealed that LCG offered superior friction reducing and antiwear performance at low loads (25, 50 N), whereas PG exhibited lower friction coefficients and minimal wear volume at higher loads (100, 200 N).

XPS analysis of worn surfaces indicated that, at low temperatures, the lubricating film was mainly formed through the combined contribution of the base oil and thickener, providing both friction reducing and antiwear functions. Overall, the results confirm the decisive role of grease microstructure in governing rheological behavior, low-temperature flowability, and tribological performance. These findings clarify the intrinsic relationships and underlying mechanisms linking grease microstructure, rheological characteristics, and lubrication behavior, thus offering valuable theoretical guidance for the design and optimization of high-performance greases for low-temperature applications.