Base oil solvency and viscosity: Impact on Polyurea Grease
Joining forces to find what impact the base oil solvency and viscosity has on the performance of polyurea greases, researchers from Nynas and the Spanish industrial lubrication specialist Brugarolas made some unexpected but useful discoveries.
Mehdi Fathi-Najafi
Chief Specialist, Technical Development and Support, Nynas AB
“Polyurea greases are of growing interest, especially for high performance applications, which is why we wanted to investigate how some characteristics of the base oil might influence the performance of such greases,” explains Mehdi Fathi-Najafi, Chief Specialist at Nynas.
However, polyurea greases are formed in a controlled reaction between amines and isocyanates, and the use of these toxic ingredients is strictly limited. Handling them in Nynas’ own experimental grease lab is not allowed.
Instead, Mehdi Fathi-Najafi approached Leandre Muntada, R&D Manager at Brugarolas, the Spanish industrial lubrication specialist and producer of polyurea greases.
“I immediately thought it sounded like an interesting project, as not much research has been conducted in this area. And, because I know that Nynas and Mehdi Fathi-Najafi are very capable and produce high-class research,” says Leandre Muntada.
“Polyurea greases have been produced by Brugarolas since 1995, and they are of strategic importance, enabling us to reach niche markets,” he explains.
Leandre Muntada
R&D Manager, Brugarolas
Uunique properties, such as a high degree of water resistance, high temperature, long life, and low noise, make polyurea greases useful for several advanced and challenging applications. In 2023, such greases represented only about seven percent of the global grease production. However, production volumes are growing, particularly for very fast-growing applications such as electric vehicles and electric motors.
The Nynas-Brugarolas research partnership resulted in an extensive study presented at the 2024 ELGI annual general meeting in Madrid.
“The study generated a lot of interest at the conference, and our findings will prove useful not only for us, but for the industry in general. We are also looking forward to continuing our research cooperation with Nynas,” says Leandre Muntada.
Teaming up in two-part study
- In order to investigate the impact of two base oil characteristics – solvency and viscosity – the study was divided into two parts. In the first, the researchers focused on the solvency of four base oils and their potential impact on the performance of polyurea greases.
- Tribological testing showed that the base oil with the highest degree of solvency resulted in the lowest friction coefficient measured by SRV. This supports findings from an earlier study, suggesting that naphthenic oil compresses faster under applied pressure, resulting in a higher pressure viscosity coefficient.
- Furthermore, it was found that by using naphthenic oils in the preparation of polyurea greases, the thickener content can be reduced to almost one third when compared to, for instance, synthetic- based oil. V In the second part, the team examined the role of the viscosity of base oils with the same degree of solvency. Three naphthenic base oils with different ISO VG grade (100, 220, and 320) were used.
- The neat greases with the higher base oil viscosity seemed to create a tackier grease, which in turn may have some effect on the tribological behaviour, measured by SRV, according to ASTM D 5707. In short, the higher the viscosity, the more the fluctuation (friction curve instability, with peaks); see Figure 1. However, this behaviour disappeared when anti-wear additive was used; see Figure 2.
