Synthesis of Lubricant Esters From Annona squamosa Seeds: A Novel Use of Tropical Biomass for Industrial Applications

ABSTRACT

This research developed lubricant esters from Annona squamosa L. seed oil (ASSO), primarily composed of oleic (43%) and linoleic (24%) acids. The oil was hydrolyzed to obtain free fatty acids, which were then esterified by homogeneous acid catalysis using trimethylolpropane (TMP) and pentaerythritol (PE). This led to the synthesis of Annona trimethylolpropane esters (ATMPE) and Annona pentaerythritol esters (APEE). The products were characterized by ¹H NMR, FTIR, physicochemical analyses, thermal analyses (TGA and DSC), and rheological measurements. Structural analyses confirmed the chemical modification of ASSO. Both polyol esters showed high conversion rates (> 90%) and low acidity values (~0.5 mg of KOH g⁻¹), confirming efficient esterification. They also exhibited high viscosity indexes (> 180). ATMPE and APEE may be classified as ISO VG 46 and 68, and SAE 30 and 40, respectively, indicating their suitability for hydraulic and automotive lubricant applications. The polyol esters demonstrated improved thermal stability compared with the raw oil, particularly APEE, which showed a T_onset of 276.8°C and 50% mass loss at 440°C. DSC analysis revealed crystallization and melting events at positive temperatures, favoring their application in tropical climates. Rheological evaluation showed Newtonian behavior up to 40°C and pseudoplastic behavior above 60°C. The results indicate that the polyol esters obtained from Annona squamosa seed oil possess favorable physicochemical, thermal, and rheological properties, presenting themselves as promising alternatives for industrial and automotive lubricant applications.