Synthesis of Biophenol‐Derived Biolubricants With Enhanced Antioxidant Properties

ABSTRACT The main challenge to the use of vegetable oils as green lubricants is their oxidative stability. In this work, biolubricants with efficient antioxidant properties have been specifically designed and synthesized with the aim of maximizing the oxidative stability of vegetable oils by combining biophenols (p‐coumaric, ferulic, and sinapic acids) with epoxidized ring‐opened soybean oil in a single molecule. The synthetic products were named OIS‐ESO‐PCA (epoxidized ring‐opened soybean oil grafted with p‐coumaric acid), OIS‐ESO‐FA (epoxidized ring‐opened soybean oil grafted with ferulic acid), and OIS‐ESO‐SA (epoxidized ring‐opened soybean oil grafted with sinapic acid), respectively. Biophenols improve biolubricant antioxidant properties, addressing energy, and environmental challenges. The modified samples were characterized by Fourier transform infrared spectroscopy (FT‐IR) and nuclear magnetic resonance (NMR). The free radical scavenging activity of the oil samples was evaluated using the DPPH (1,1‐diphenyl‐2‐trinitrophenylhydrazine) method and was found to be much higher than that of the soybean oil (SBO). The oxidation resistance and thermo‐oxidative stability of the oil samples were evaluated based on pressure differential scanning calorimetry (PDSC), rotary bomb oxidation test (RBOT), and thermogravimetry (TGA). Compared with SBO, the oxidative induction time of OIS‐ESO‐PCA, OIS‐ESO‐FA, and OIS‐ESO‐SA increased by 118%, 296%, and 384%. The modified oils showed excellent antioxidant properties compared to the SBO. Therefore, biophenolic acid can be effectively used to improve the antioxidant properties of vegetable oils.