Location: Bio-oils Research Unit
Title: Synthesis and tribological investigation of lipoyl glycerides Authors
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 18, 2014
Publication Date: March 12, 2014
Citation: Biresaw, G., Laszlo, J.A., Evans, K.O., Compton, D.L., Bantchev, G.B. 2014. Synthesis and tribological investigation of lipoyl glycerides. Journal of Agricultural and Food Chemistry. 62(10):2233-2243. Interpretive Summary: Vegetable oils have a number of properties that make them more desirable than petroleum based products for use in biobased lubricant formulations. Vegetable oils also display a number of less desirable tribological properties. The ability to formulate new lubricants with vegetable oils that take advantage of their desirable properties while improving their less desirable properties is of high interest. One of the approaches to achieving this goal involves modifying the chemical structure of the vegetable oils. This can be achieved by subjecting the vegetable oils to chemical or enzymatic synthetic modifications. In the work described here, enzymatically modified high oleic sunflower oil (HOSuO) displayed significantly superior oxidation stability, cold flow, and EP properties over the unmodified parent HOSuO. The results demonstrate that through enzymatic modification, biobased lubricant ingredients with considerably improved tribological properties can be developed from vegetable oils and their derivatives. The results of this work will be of great interest to scientists and engineers who are engaged in the development of biobased lubricant formulations for a variety of applications. The enzymatically modified HOSuO products from this work have potential for use as ingredients of biobased hydraulic, engine, metalworking, and grease lubricants.
Technical Abstract: Lipoyl glycerides (LG) were synthesized by enzymatic transesterification of lipoic acid (LA) with high oleic sunflower oil (HOSuO) in 2-methyl-2-butanol solvent. The synthesis gave a crude product mixture (LGc) comprising unreacted LA, free fatty acids (FFA), and various LG structures with varying degrees of LA substitution on the HOSuO triglyceride. A more purified product mixture (LGp) devoid of unreacted LA and FFA was obtained in 61% yield. The product mixtures LGc and LGp were thoroughly characterized and their components positively identified using a combination of HPLC and LC high resolution mass spectroscopy methods. The tribological properties of LGc and LGp were further investigated using a variety of methods including: solubility, density, viscosity, viscosity index, surface and interfacial tension, pressurized differential scanning calorimetry, 4-ball anti-wear, and 4-ball extreme pressure (EP). LGc and LGp displayed significantly improved oxidation stability, cold flow, and EP properties over the parent HOSuO. The EP results showed a higher weld point for neat LGc than for neat LGp. Analysis of the EP results indicates that this difference can be attributed to the differences in the chemical properties of the components in the product mixtures.