Effect of the natural antioxidant ferulic acid and its ester derivatives on the oxidative stability of ester-based lubricants: Experimental and molecular simulation investigations

•Isooctyl ferulate has been expected the optimal performance in PETO matrix from simulation.•Physical factors play the key role in the antioxidant capacity of isooctyl ferulate.•A molecular simulation method for assess the antioxidant activity of antioxidants in lubricants was developed. Pentaerythritol oleate, as one of the ester-based lubricants, has excellent lubricity and low temperature properties, but is susceptible to oxidation due to the susceptible α-H of isolated double bonds in the molecular structure. Ferulate natural antioxidants, including the ferulic acid and its two ester derivatives were selected, focusing on exploring mechanisms, especially the effect of physical factors on the antioxidant properties. The chemical activity, dispersion, mobility and oxygen resistance of antioxidants were studied by molecular simulation. These combined results of the simulations show that the sequence of the antioxidation were isooctyl ferulate > ethyl ferulate > ferulic acid. Then the rotational oxygen bomb test and the pressure differential scanning calorimetry results confirmed the antioxidant activities of the three species. According to the Rancimat test, the oxidation induction time of the isooctyl ferulate/PETO was increased by 300% compared to the control.