Synthesis of 12-hydroxystearic estolide and its esters to study the effect of molecular structure on physicochemical properties

The global point of view associated with bio-lubricants has dramatically changed due to depleting petroleum supplies, volatile prices, growing environmental concerns, and strict government regulations. Vegetable oils are considered a potential replacement for petroleum-based lubricants; however, they are constrained by poor cold-flow characteristics, low hydrolytic stability, and low resistance to oxidative deterioration. Increased oxidative and hydrolytic stability and enhanced cold flow properties result from a chemical alteration of vegetable oil by esterification or estolide formation. This work prepares a 12-hydroxystearic acid estolide (HSAE) series, followed by esterification with alcohols (i.e., 2-ethyl hexanol, trimethylolpropane, and pentaerythritol) to obtain estolide esters. The effect of reaction time on the degree of oligomerization of 12-hydroxystearic acid estolide has been studied. Further, the comparative analysis of the physicochemical properties (i.e., kinematic viscosity at 40 °C & 100 °C, viscosity index, and pour point) of estolide esters was also evaluated to study the effect of oligomerization and molecular structure of alcohol on kinematic viscosity, viscosity index, and pour point. [Display omitted] •Estolides with varying estolide number were synthesized from 12-hydroxystearic acid.•Linear and polyol esters of estolide were synthesized with > 85% conversion.•The influence of the structure of ester on viscosity & viscosity index was studied.•The role of branching and molecular asymmetry on the pour point was analyzed.