May / June 2015 NLGI Spokesman

Blends:

Friend or Foe?

Base oil Blends for Grease Formulations Mehdi Fathi-Najafi* Linda Malm, René Abrahams Luis Bastardo-Zambrano *Corresponding author

Nynas AB Sweden

Abstract

ἀ e introduction of Group II and III base stocks, with better oxidation stability and higher viscosity index than Group I base stocks, will create two main drawbacks; lack of solvency (solvent power) and lack of high viscosity.

Highly naphthenic oils have been regarded as an excellent solution to these drawbacks. Put simply, it is possible to “kill two birds with one stone”. Nynas has, during the last years, in a number of publications offered some practical solutions to these forthcoming obstacles.

ἀ e purpose of this work is to compare “side by side” three base oil blends where GrI, GrII and GrIII, in combination with naphthenic, were used for preparation of lubricating greases. Since the target viscosity was 150 mm2/s at 40 ºC, a naphthenic oil was used in order to reach this viscosity. Key parameters in this study were frictional and thermal stability of the base oil blends, as well as low temperature flowability, elastomer compatibility and rheological properties of the corresponding greases. Last but not least, an attempt was made to minimize the thickener content level. ἀ e prepared base oil blends have been thoroughly characterized. ἀ e overall results obtained, reveal some interesting aspects of the use of Gr II as a substitute to Gr I for preparation of greases. ἀ e outcome of this work emphasizes that blends should be regarded as a great opportunity for grease formulators who are looking for some further development of their current formulations and furthermore, the lubricating grease based on the blend of paraffinic Gr II and naphthenic oil performs better than others.

1. Introduction

ἀ e base oil industry has been going through fundamental changes in the last decade. ἀ ese changes have been marked by the rapid growth in production capacity for Group II and Group III base oils. ἀ e total production of Gr I is estimated to fall to about 40% of the total base oil production by the year 2020. ἀi s global rationalization of Group I production, and its potential impact on the future availability of paraffinic bright stock, has led several lubricant formulators to start evaluating alternative products. Lubricating greases are, by far, one of the product types that strongly depend on highly viscous oils, especially for industrial and automobile applications. ἀ ere are of course a few alternatives to bright stocks, such as synthetic oils. But they are expensive, and furthermore, in some applications such as in the case of elastomer compatibility, PAO would probably cause some problems.

Mineral oils used by grease manufacturers can be divided into two major groups, naphthenic oils and paraffinic oils. Of course both categories of base oils have their own advantages and disadvantages. ἀ e most important advantages of the naphthenic oils over the paraffinic oils, with the same viscosity and similar aromatic content, are better low-temperature flowability and better solvency. ἀ e contribution of having base oils with good solvency towards the thickener is that less thickener is needed to obtain a certain consistency of the finished product.

It is notable that the higher soap content in greases

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