A Review on Synthesis, Characterization, and Decomposition of Biodegradable Functional Fluids Called Estolides

Abstract

Estolides are fatty acid oligomers, formed either through addition or condensation reactions of multiple fatty acids. They offer much better cold-flow behavior, oxidation stability, and viscosity against their monomers, making them plant-based alternatives to petroleum fluids. They can form among hydroxy fatty acids and unsaturated fatty acids; once a saturated fatty acid is attached to the chain, the oligomer becomes a capped estolide. Most plant-based oils crystallize easily, making them unusable for modern applications; however, estolides have a much lower pour point due to their complex structure, leading to a slow crystallization. Another key issue associated with plant-based oils is their poor oxidative stability caused by the unsaturation in them. This problem is also efficiently addressed in the case of estolides, as the chain propagation of these oligomers happens through the unsaturation present in them. Improvements is viscosity, reduction of acidity are other advantages associated with estolide formation. With a century of research background, these biodegradable fluids have applications in lubrication, cosmetics, and the food industry and will hopefully continue to expand their reach across the span of petroleum. This review is an updated consolidation of the trends and challenges associated with estolides.