Synthesis and application of highly efficient multifunctional vegetable oil additives derived from biophenols

3 The greatest challenge of vegetable oils (VOs) used as green lubricants is their oxidation stability. The potential of incorporating sustainable components to VOs as high efficient antioxidant additives can be beneficial to both energy conservation and environment protection. In this paper, bio-based multifunctional additives (BMAs) were specially designed and synthesized with the aim of maximizing VOs’ oxidation stability by combining biophenols (gallic acid, caffeic acid and p-hydroxycinnamic acid) with 4-aminodiphenylamine in one molecular. The BMAs were found to have extraordinary higher thermal stability and free radical scavenging activity than that of commercial antioxidants. BMAs were evaluated as multifunctional additives in VOs. Pressure differential scanning calorimetry (PDSC) indicated that the oxidation induction time (OIT) of rapeseed oil (RO), coconut oil (CO) and epoxy soybean oil (ESO) can be increased correspondingly by about 2.2, 14.0 and 32.0 times with the addition of BMAs. Four ball test showed that bio-based multifunctional additives 3 (BMA3) had the best antiwear activities among three BMAs (18% decrease in RO), better than traditional zinc dialkyl dithiophosphate (ZDDP) in CO and ESO. In a comparison to commercial phenol, arylamine antioxidants and their physical mixtures, BMAs demonstrated superior antioxidant properties with the increase of phenol hydroxyl group, which mostly benefit from the polyphenolic and aryl amine intramolecular synergism.