Pequi Oil Esters as an Alternative to Environmentally Friendly Lubricant for Industrial Purposes

This study reports the synthesis of bio-based lubricants using pequi oil (PO) as a raw material, along with its chemical, thermal, and rheological characterization, as well as its cytotoxic behavior and the kinetic study of the reaction involved in the production of biolubricants. Free fatty acid pequi oil (PFFA) was esterified using 2-ethyl-1-hexanol (P2EHE), pentaerythritol (PPEE), and p-TSA as catalysts. The ¹H NMR spectra confirmed the replacement of hydroxyl groups of both alcohols by PFFA. PPEE showed better thermal stability (T_onset 274.50 °C). Besides, at 50% of thermal weight loss, the PPEE showed a higher decomposition temperature (437.9 °C) than PO (366.6 °C). The melting points determined by DSC indicate that P2EHE exhibits better performance at low temperatures (p.p. −22.86 °C) than PPEE (p.p. −33.28 and 8.02 °C) due to the presence of some crystals of saturated fatty acids in the pentaerythritol ester. The esters showed Newtonian behavior in a wide range of shears; however, they showed pseudoplastic behavior at temperatures above 60 °C. The viscous nature of bio-based lubricants was confirmed (G″ > G′) even with increasing temperature. The kinetic study provided the value of the activation energy to P2EHE and PPEE, similar to that reported in the literature for other types of biolubricants. The toxicity analysis of bio-based lubricants on adult zebrafish showed no lethality after 96 h. These results suggest that pequi oil is a potential raw material to produce lubricants that are less harmful to the environment.