A forest industry by-product could become the lubricant grease of the future

A new lubricating grease based on lignin shows that renewable materials can compete with today’s fossil-based industrial products. In tests, the material demonstrated low friction, good wear resistance and high resistance to oxidation without the use of conventional additives.

Lubricating grease plays a crucial role in reducing friction and wear in machines and industrial systems. Most commercial greases are currently based on petroleum oils combined with thickeners, typically metallic soaps. These thickeners mainly increase viscosity to prevent oil leakage, but such systems have several limitations, including poor biodegradability, risk of oil separation, and sensitivity to high temperatures and mechanical loads.

Traps the oil inside a solid-like structure

In his doctoral thesis, Zhipeng Wu, Doctoral Student in Machine Elements at Luleå University of Technology, has investigated how these challenges can be addressed by replacing conventional thickening concepts with lignin-based gelation. Lignin is a by-product of the forest industry and a renewable material with inherent antioxidant properties.

Unlike traditional thickeners that simply make the oil more viscous, lignin acts as a gelator, forming a continuous three-dimensional network that physically traps the oil inside a solid-like structure, similar to a sponge.

“Lignin has a chemical structure that makes it possible to build stable gel networks that both retain the based fluids and actively contribute to lubrication performance,” says Zhipeng Wu.

By applying different gelation strategies, the research has developed lignin-based lubricating gels tailored for a wide range of environments, from vegetable oils to water-based and ionic systems. This has made it possible to study both hydrophobic and hydrophilic applications within the same material platform.

Outperforming commercial greases

In tribological tests conducted at high temperature and high contact pressure, a lignin-based gel formulated with castor oil showed a lower coefficient of friction than several established industrial greases. At the same time, the wear level was comparable to that of commercial reference products, despite the lignin gel lacking the additives normally required to reduce wear.

The results indicate that the continuous lignin gel network not only immobilizes the base oil but also helps form a stable protective film between sliding surfaces under load.

“This shows that good wear resistance can be achieved through material and structural design, not only through chemical additives,” says Zhipeng Wu.

Zhipeng Wu, doctoral student in machine elements at Luleå University of Technology.

High resistance to oxidation

In addition to their mechanical performance, the lignin-based gels also exhibited strong resistance to oxidation. In several cases, the oxidation stability was higher than that of commercial greases, which could lead to longer service life and reduced reliance on synthetic antioxidants.

Overall, the thesis demonstrates that lignin-based gel systems, rather than simple thickened oils, can address many of the limitations associated with conventional lubricating greases, such as temperature sensitivity, oil separation, and dependence on additives. This opens the door to more sustainable lubricants for demanding industrial applications.

“The long-term goal is for these materials to contribute to both reduced environmental impact and more robust industrial operation,” says Zhipeng Wu.

• Machine elements