Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/23/2011
Publication Date: 3/23/2011
Citation: Harry O Kuru, R.E., Biresaw, G., Cermak, S.C., Gordon, S.H., Vermillion, K. 2011. Investigation of some characteristics of polyhydroxy milkweed triglycerides and their acylated derivatives in relation to lubricity. Journal of Agricultural and Food Chemistry. 59(9):4725-4735. Interpretive Summary: In the quest for expanding the use of vegetable oils in the area of bio-lubricants, we have explored the potential of modified milkweed seed oil to reduce friction in moving equipment parts. Modified oil’s suitability, that is, stability under working conditions, is determined by pour point and cloud point, which are measures of cold flow behavior of a lubricant, along with other very important characteristics of lubricant quality, such as viscosity and film thickness under a load as well as wear scar measurements. Tests show that the modified milkweed oil has very promising qualities. The data obtained from this study shows that appropriately modified milkweed seed oil would constitute a quality industrial bio-lubricant from a renewable domestic source. This information should encourage farmers with marginal or non-utilized acreage to invest in growing milkweed as a crop, and encourage the lubricant industry to consider development of milkweed oil as an environmentally-friendly source of bio-lubricant.
Technical Abstract: Most industrial lubricants are derived from non-renewable petroleum-based sources. As useful as these lubricants are, their unintended consequences are the pollution of our environment as a result of the very 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 could readily be overcome by appropriate derivatization and yet retain the inherent biodegradative property of the derived oil. Pursuant to the latter, we have investigated derivatized milkweed seed oil to assess its suitability as an industrial lubricant. The milkweed plant belongs to the family Asclepiadaceae L, a family with many genera which include the common milkweeds, Asclepias syriaca L, A. speciosa L and A. tuberosa L, etc. The seeds of these species contain mainly C-18 triglycerides that are highly unsaturated, ca. 92%. Chemical modification of the unique olefinic character of this seed oil generates polyhydroxy triglycerides (HMWO) that show high viscosity and excellent water retention characteristics. In this paper, we have studied the effects of branching on the viscosity of HMWO by esterifying its hydroxyl groups with acyl substituents of varying chain lengths - acetate, butyrate and valerate. Data obtained in studies on oxidative stability, elastohydrodynamic film thickness under load, as well as their coefficient of friction and wear scar test behavior on metal surfaces, show lower coefficient of friction as well as lower wear scar dimension on test surfaces for two of the three derivatives. The overall impact of modification of the parent HMWO are polyester materials with promising lubricity characteristics.