Engineering Diesters From Saturated Fatty Acids and C2–C4 Diols: How Branching Influence Rheological, Flow, and Crystallization Properties

In response to the increasing demand for sustainable materials, this study explores the structure–property relationships of 22 novel diesters synthesized from C2–C4 linear and branched diols and saturated fatty acids (SFAs), targeting the improvement of vegetable oil-based lubricants’ oxidative stability and low-temperature performance. Diesters based on pelargonic (C9), lauric (C12), myristic (C14), and palmitic (C16) acids were characterized for viscosity, crystallization temperature, and flow behavior. Branched diols significantly enhanced low-temperature properties, with 1,2-butanediol and 1,3-butanediol diesters always exhibiting the lowest crystallization temperatures. Viscosity increased with fatty acid chain length, whereas branching caused a slight reduction due to steric hindrance. Most diesters showed shear-thickening behavior, modeled by the Herschel–Bulkley equation. Additionally, all diesters demonstrated excellent oxidative stability, surpassing 300 min in accelerated aging tests. These findings suggest that the synthesized diesters, particularly those with branched diols, offer promise as sustainable, high-performance alternatives for industrial lubricant applications. Practical Application: The diesters synthesized from saturated fatty acids and C2–C4 diols offer strong potential as bases for bio-based lubricants, particularly in applications requiring high oxidative stability. The esters, particularly those derived from branched diols, exhibit improved cold flow properties, due to their lower crystallization temperatures, making them ideal candidates for use in industries requiring lubricants that perform well in low-temperatures conditions. Their shear-thickening behavior also makes them ideal for shock-absorbing uses. The comprehensive analysis and results presented in this study provide a valuable reference for selecting the optimal combination of fatty acids and alcohols to tailor synthetic esters with specific properties, addressing diverse needs in the lubricant industry. This work serves as a practical guide for developing high-performance, sustainable lubricant formulations.