Alkoxide-Catalyzed Synthesis and Characterization of Acylglycerol-Estolide Biolubricants From Neat Castor Oil

Estolides are fatty acid oligomers that can be employed in the formulation of lubricants as an environmentally friendly alternative to mineral and synthetic oils. These bio-based esters often exhibit improvements in essential lubricant properties (oxidative stability, cold flow properties, viscosity index [VI], etc.) with respect to unmodified vegetable oils. In this study, we evaluate a potential new series of renewable high viscosity lubricants on the basis of mixtures of acylglycerol-estolides obtained from simultaneous potassium methoxide-catalyzed transesterification and interesterification of neat castor oil. The physicochemical and lubricant properties of the products were evaluated and compared to similar commercial products and estolides described in the literature. The estolide sample obtained with the highest viscosity (635 mm² s⁻¹) displayed equivalent lubricant properties with other commercial lubricants ‒ pour point (−30°C) and VI (173). This investigation attested to the potential application of acylglycerol-estolides derived from neat castor oil as high viscosity biolubricants for industrial equipment.

Practical Applications: When compared with estolides reported in the literature, the mixtures of acylglycerol-estolides described in the present work were obtained through a less costly production process (in terms of number of reagents and reaction time). Furthermore, without carrying out further modifications of the products or incorporation of additives, in general, similar, or even superior, physical properties were observed for these materials compared to mineral-based commercial lubricants, attesting to the potential application of these value-added materials as high viscosity base oils or additives used in the formulation of green industrial lubricants.