A kinetic model has been proposed for high-temperature oxidative degradation of lubricants under boundary lubrication conditions. This model incorporates primary oxidation reactions as well as subsequent condensation polymerization reactions that result in viscosity increase and sludge formation. Evaporation of the oil and its volatile primary oxidation products has also been considered. The model has been examined by conducting oxidation and evaporation studies on a commonly used neopentyl polyol ester, trimethylolpropane trlheptanoate, in the Penn State microoxidation test. This thin-film laboratory test simulates lubricant behavior in bearings under elastohydrodynamic and boundary lubrication conditions. The kinetic rate constants for the primary oxidation and the subsequent polymerization reactions have been determined. The rates of reaction appear to be first order. This information coupled with evaporation rates has been used to examine the ability of the model to correctly predict the oxidative behavior of the lubricant. Klaus, , 1983 suggests that the primary reaction is associated with the C-C chain and not the heteroatoms in these molecules.This study treats the oxidation of a polyolester, trimethylolpropane triheptanoate (TMPTH), as a simple reaction with no oxygen diffusion limitations. The basic data are used to model the primary oxidation reaction and subsequent reactions, thereby providing a relationship that can be used to predict the behavior of lubricants given the 0196-4321/86/1225-0596S01.50/0 environments in which they function.
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