SYNTHESIS AND PHYSICOCHEMICAL PROPERTIES OF ESTOLIDE ESTER AND AMIDE MADE FROM USED COOKING OIL AS BIO-LUBRICANT

Palm-based used cooking oil (UCO) is an inexpensive material that could be used as a bio-lubricant. However, its use as a bio-lubricant is limited by its inferior cold flow and oxidation stability properties. This study shows an approach to make bio-lubricant base oil from UCO that displayed good cold flow and oxidation stability. UCO was saponified and hydrolysed to yield a mixture of fatty acids, which was subsequently reacted with hydrogen peroxide and acetic acid to generate an estolide mixture with hydroxyl and carboxylic acid groups. The hydroxyl groups of the estolide mixture were end-capped with lauric acid, while its carboxylic acid groups were converted to either ester or amide functionality with 2-ethylhexanol and dibutylamine, respectively. Physicochemical properties evaluation revealed that the saturated branched structure of estolide ester and amide contributed to improved pour point (-12 o C) and better oxidation stability up to 200 o C as compared to UCO. Additionally, the estolide ester and amide exhibited a better viscosity index and pour point than a commercial mineral oil lubricant. The estolide ester can be classified as ISO VG 68 base oil, while the estolide amide displayed a higher viscosity grade (ISO VG 150) due to the presence of dibutylamide moiety.