Lube-Tech Introduction


When using ester base oils, the product developers focus initially on application parameters such as viscosity, viscosity index, oxidation stability and pour point. But other parameters are not less important. This also includes the seal compatibility.


In the past, sealing materials like elastomers were optimised for the contact with mineral oils. These days, synthetic esters gain importance and are more often used. As there are fundamental differences between mineral and synthetic based esters the used sealing materials are not always compatible with the new base oils. For example, elastomers – especially those with higher polarity – tend to swell more when exposed to a synthetic ester while mineral oils only lead to slight swelling or even shrinking.


But even if we just keep an eye on synthetic esters, the different ester types show considerable differences in elastomer compatibility. They are mainly caused by differences in structure and physical characteristics as well as chemical parameters of the esters.


Knowledge on how different types of synthetic esters can impact elastomers is crucial for lubricant developers. It makes it possible to assess the potential influence on sealing materials during the first selection of suitable products.


24 LUBE MAGAZINE NO.167 FEBRUARY 2022


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.138 page 1


Sealing compatibility of ester base oils


Dr. Hermann Josef Stolz, Dr. Wilhelm Huber, Dr. Martina Mennicken-Meuthen, Denise Weber, Peter Greven GmbH & Co.KG


Elastomers and their Characteristics At the beginning of the last century, leaks and high levels of wear and tear, for example on bearings, were common in machine and vehicle construction. Felt or leather were often used as sealing materials. The next milestone was the shaft seal developed by Prof. Simmer, which initially consisted of leather as a sealing material. A decisive step forward was achieved through the use of synthetic elastomers, Buna (SBR) and later Perbunan (NBR) instead of leather.


Elastomers are amorphous polymers whose glass transition temperature is below the application temperature. They are dimensionally stable but elastic and return to their original state after mechanical deformation. This characteristic is caused by a linear structure of the molecular chains with a wide mesh network of the main valences. They cannot be melted, are non-soluble and swell in solvents.


Additionally, elastomers are sensitive to light, ozone,


Figure 1: Simplified elastomer structure


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