Keywords: Esterification; sunflower oil unsaturated fatty acids; pentaerythritol; pentaerythritol ester; polyol ester

Abstract

Sunflower oil (SFO) presents itself as a promising renewable resource for biolubricants production, offering a sustainable alternative to traditional lubricants. However, a drawback of SFO is its low oxidative and thermal stability, primarily due to the presence of beta hydrogen on the glycerol backbone. This issue can be effectively addressed through a chemical modification process involving esterification with polyhydric alcohol. In the esterification process, unsaturated fatty acids derived from sunflower oil (SFOUFA) were reacted with pentaerythritol (PE) to produce sunflower oil unsaturated fatty acids pentaerythritol ester (SFOUFAPEE). This reaction was carried out with a mole ratio of 5:1 by employing 1.5% sulfuric acid as the catalyst at a temperature of 160 °C for 6.0 hours. The confirmation of the functional group and chemical structure of SFOUFAPEE was achieved through Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) techniques. Notably, the results indicate the successful synthesis of SFOUFAPEE with a remarkable 60% yield. SFOUFAPEE remains in liquid form at room temperature. Key indicators of its structure include the presence of the C=O (ester) group at 1742.32 cm-1 and the absence of the C=O (carboxylic acid) group at 1710.60 cm-1, with OH stretching observed within the range of 2400-3400 cm-1 in FTIR spectrum. For NMR, the existence of the ester group was at a chemical shift of 1H NMR at 4.10 to 4.15 ppm (from PE) and 13C NMR at 173.21 ppm for ester. Analysis of the physicochemical properties revealed the thermal stability of SFOUFAPEE was at 354.95 °C, a pour point of -21 °C, a flash point of 302 °C, and a viscosity index of 145. These characteristics render SFOUFAPEE a promising alternative for use as a lubricant base stock.