Work

Carboxylic Acid-Cured Epoxidised Soybean Oil under Catalyst-Free Conditions: Kinetics and Sustainable Packaging Potential

Year: 2026

Type: article

Abstract: This work investigates the curing behavior of epoxidised soybean oil (ESO) with citric (CA), maleic (MA), and salicylic (SA) acids. The curing process was monitored by Fourier-transform infrared (FTIR) and dynamic differential scanning calorimetry (DSC) at heating rates of 5–20 °C min–1. FTIR analysis showed a progressive decrease of the epoxide band (∼950 cm–1) for ESO/CA and ESO/SA systems, while ESO/MA retained oxirane signals after thermal treatment, indicating incomplete curing. ESO/CA and ESO/SA exhibited gel contents above 80% and low swelling, with cross-link densities of ∼1.7–2.1 mmol cm–3, whereas ESO/MA presented a much lower value (∼0.3 mmol cm–3). DSC analysis revealed two exothermic curing stages for ESO/CA and ESO/SA that shifted to higher temperatures, consistent with primary cross-linking followed by secondary reactions. Cure kinetics were evaluated using the Friedman, Vyazovkin, Ozawa–Flynn–Wall (OFW), and Kissinger–Akahira–Sunose (KAS) models. Model-free Friedman and Vyazovkin approaches provided the best description of the experimental data (R2 > 0.99), revealing conversion-dependent activation energies that increased with the degree of conversion, reaching ∼85 kJ mol–1 for CA and ∼87 kJ mol–1 for SA systems. In contrast, OFW and KAS models showed lower fitting quality (R2 < 0.88), indicating that single-activation-energy approaches are insufficient to describe the curing process. Tensile tests confirmed structure–property differences between the networks: ESO/CA exhibited higher modulus and strength (∼0.85 and ∼0.55 MPa), while ESO/SA showed greater elongation (∼147%). Overall, catalyst-free ESO/CA and ESO/SA systems form cross-linked biobased thermosets with tunable mechanical behavior and well-defined curing kinetics, demonstrating their potential for the development of sustainable epoxy materials.

Source: ACS Omega

DOI: 10.1021/acsomega.5c11969