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Investigation of Some Characteristics of Polyhydroxy Milkweed Triglycerides and Their Acylated Derivatives in Relation to Lubricity

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Rogers E. Harry-O’kuru*†, Girma Biresaw†, Steven C. Cermak†, Sherald H. Gordon‡, and Karl Vermillion#

^†Bio-Oils Research Unit, ^‡Plant Polymer Research Unit, and ^#Functional Foods Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, 1815 North University Street, Peoria, Illinois 61604, United States

J. Agric. Food Chem., 2011, 59 (9), pp 4725–4735

DOI: 10.1021/jf104746v

Publication Date (Web): March 23, 2011

*Phone: (309) 681-6341. Fax: (309) 681-6524. E-mail: Rogers.HarryOkuru@ars.usda.gov.

Abstract

Most industrial lubricants are derived from nonrenewable petroleum-based sources. As useful as these lubricants are, their unintended consequences are the pollution of the Earth's environment as a result of the slow degradation of the spent materials. Native seed oils, on the other hand, are renewable and are also biodegradable in the environment, but these oils often suffer a drawback in having lower thermal stability and a shorter shelf life because of the intrinsic −C═C− unsaturation in their structures. This drawback can be overcome, yet the inherent biodegradative property retained, by appropriate derivatization of the oil. Pursuant to this, this study investigated derivatized polyhydroxy milkweed oil to assess its suitability as lubricant. The milkweed plant is a member of the Asclepiadaceae, a family with many genera including the common milkweeds, Asclepias syriaca L., Asclepias speciosa L., Asclepias tuberosa L., etc. The seeds of these species contain mainly C-18 triglycerides that are highly unsaturated, 92%. The olefinic character of this oil has been chemically modified by generating polyhydroxy triglycerides (HMWO) that show high viscosity and excellent moisturizing characteristics. In this work, HMWO have been chemically modified by esterifying their hydroxyl groups with acyl groups of various chain lengths (C2−C5). The results of investigation into the effect of the acyl derivatives' chemical structure on kinematic and dynamic viscosity, oxidation stability, cold-flow (pour point, cloud point) properties, coefficient of friction, wear, and elastohydrodynamic film thickness are discussed.

Keywords:

Asclepiadaceae oil; polyhydroxy triglycerides; polyacyl triglycerides; rheology; cold-flow properties; film thickness; coefficient of friction; wear scar dimensions; lubricity

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