Molecular Modeling and Engineering of Vegetable-Oil Based Lubricants

Mary Biddy, University of Wisconsin - Madison

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Concerns over the availability and the rising cost of petroleum-based products have generated considerable interest in developing alternative renewable sources. Industrial lubricants derived from vegetable oils provide a promising alternative to petroleum-based products. Unlike petroleum oils they are a naturally occurring, renewable, nontoxic, and biodegradable resource. Vegetable oils in the natural form, however, have had limited use as industrial fluids because of their poor oxidative stability, unsuitable low temperature properties, and rapid degradation under severe conditions of temperature, pressure, and shear stress.

In order to formulate vegetable oils with optimal lubrication characteristics, the influence of the individual molecular components on the overall oil properties must be understood. Vegetable oils are essentially mixtures of triglycerides. Although triglycerides are naturally abundant, little is understood about the effect of molecular structure on their physical properties. Computer simulations can directly relate molecular composition to physical properties and offer a valuable tool for improving our knowledge of this important class of materials.

Here we present our findings on the computational prediction of the transport coefficients, including viscosity, of triglycerides and vegetable oil mixtures. By employing molecular dynamics simulations, we obtain viscosities and densities that agree well with experimentally observed values. The influence of molecular structure on physical properties is explored for triglycerides that are 1) difficult to isolate in vegetable oils and 2) chemically modified. We also explore the low temperature properties of vegetable oils, which pose one of the major limitations in their application as lubricants. The gel transitions predicted by our simulations are shown to be in remarkable agreement with experimental pour point data.

Abstract Author(s): Mary Jo Biddy<br />Juan J. de Pablo