Oxidative stabilization of high-PUFA biodiesel feedstocks using squalene: A multi-scale chemical and thermal analysis

Oxidative instability of highly unsaturated plant oils limits their application as biodiesel feedstocks, as oxidation products negatively affect fuel properties, storage stability, and emissions. While squalene is recognized as a natural antioxidant in low-unsaturation systems, its effectiveness in highly polyunsaturated oils relevant to fuel applications remains insufficiently understood. This study evaluates the antioxidant performance of squalene in cottonseed oil (rich in linoleic acid, C18:2) and linseed oil (rich in linolenic acid, C18:3), representing di- and tri-unsaturated systems. Oxidation was monitored over time at 25 °C and 80 °C using peroxide value (PV), p-anisidine value (p-AV), and total oxidation (TOTOX), supported by FTIR, 1H NMR, DSC, and TGA analyses to provide a multi-scale assessment of degradation. The addition of 0.1 wt% squalene significantly reduced oxidation in both oils. In cottonseed oil, PV and TOTOX decreased by up to ∼32% and ∼ 34.78% at 80 °C, with smaller reductions (6–11%) at 25 °C. In linseed oil, stronger effects were observed, with PV reductions of up to ∼80% and TOTOX reductions of ∼51% at 80 °C, and 20–48% at ambient conditions. FTIR confirmed delayed hydroperoxide formation (∼28% reduction), while 1H NMR showed preservation of bis-allylic protons. Thermal analysis further indicated improved oxidative stability through delayed oxidation onset and increased degradation temperatures. These findings demonstrate temperature-dependent antioxidant behavior, with enhanced effectiveness in highly unsaturated systems. Squalene acts as a sacrificial antioxidant, delaying both primary and secondary oxidation, highlighting its potential as a sustainable additive for improving biodiesel feedstock stability.