Linking molecular antioxidant activity to polyurethane foam stability - the case of Abies marocana essential oil

Abstract In this work, compounds from Abies marocana essential oil (AMEO) were studied for their antioxidant potential using density functional theory (DFT) calculations at the M06-2X/6-311 + G(d,p) level of theory. The antioxidant activity was evaluated through three mechanistic pathways: hydrogen atom transfer (HAT), single electron transfer–proton transfer (SET-PT), and sequential proton loss–electron transfer (SPLET). The corresponding thermodynamic descriptors, including bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA), and electron transfer enthalpy (ETE), were calculated in the gas phase, while the HAT mechanism was additionally investigated in water and ethylene glycol to assess solvent effects. Additionally, frontier molecular orbital (FMO) analysis revealed that α- pinene possesses the smallest HOMO-LUMO energy gap (E g ), followed by limonene, further supporting the higher chemical reactivity and radical scavenging potential of these compounds. The influence of the studied essential oil as a natural antioxidant additive at varying concentrations on the thermal degradation (ageing) of flexible polyurethane foams was also assessed. Compression tests before and after dry heat ageing indicated that AMEO-modified foams showed improved compression-force retention compared with the reference sample. Higher AMEO concentrations increased the absolute compression force before and after ageing, while the calculated percentage compression-force loss was generally lower than that of the reference sample, indicating improved ageing resistance. Fourier transform infrared spectroscopy (FTIR) analysis suggested that AMEO does not form strong chemical interactions with the polyurethane matrix, supporting a physical radical scavenging mechanism. These results suggest that AMEO can serve as a multifunctional additive in polyurethane foams, providing both antioxidant activity and mechanical property tuning.