Predicting the Viscosity of Ester Biolubricants by the Functional Groups of Their Compounds Using a Sensitivity Parameter Model

Oleic-based trimethylolpropane (TMP) ester mixtures can be produced via esterification reaction between oleic acid (OA) and TMP, presenting important application as biobased lubricants. In this study, a new mathematical model that allows us to predict kinematic viscosities of such mixtures based on kinematic viscosity sensitivity parameters from product functional groups was developed, and it was also checked by fitting the experimental kinematic viscosities of the biolubricant products at 40 and 100 °C. This way, it is possible to predict kinematic viscosities and the viscosity index of these biolubricant mixtures and even pure TMP-esters without the availability to measure purified compounds. Moreover, the influence on the viscosity properties of the different chemical functional groups can be assessed with this physical model. So, the deleterious or beneficial effects of intermediate products and unreacted OA on the biolubricant viscosity index (VI) were quantified, showing that Trioletate and also Dioleate TMP-ester and their mixtures meet very interesting lubricant properties (VI up to 218), whereas the Monooleate TMP-ester and the unreacted OA decrease dramatically the viscosity properties. We believe that these findings can pave the way for the improvement and development of bio-based lubricant formulations towards effective industrial development.