Influence of degradation on the film-forming properties of polyolester oils

Abstract

The film thicknesses of two polyolester degraded oils were measured over a wide range of temperatures to investigate the influence of degradation on film-forming properties. The results have been interpreted in the light of the idea that degradation of an ester lubricant can produce two different types of product which have opposing influences on film-forming properties. One is the formation of smaller, polar molecules, such as acids, which may result in a decrease in effective pressure—viscosity coefficient. The other is the formation of larger, bulky molecules such as sludge, which result in increased pressure—viscosity coefficient. The effective pressure—viscosity coefficient decrease with degradation of the oil thus is made up of an earlier stage involving a series of reactions, followed in a later stage by an increase.