Exploring the mechanical and recyclable properties of graphene oxide-reinforced lignin-derived non-isocyanate polyurethanes: A sustainable approach to material design

In pursuit of sustainable and non-toxic alternatives to conventional polyurethanes, a range of lignin-derived cyclic carbonates (LCCs) were obtained by catalytically incorporating CO 2 into lignin-derived epoxy intermediates via a cycloaddition reaction. These LCCs were subsequently crosslinked with structurally diverse amine curing agents to produce non-isocyanate polyurethane (NIPU) films. To improve their mechanical and thermal properties, graphene oxide (GO) was incorporated into the NIPUs to fabricate NIPU/GO nanocomposite films. The effects of lignin depolymerization degree, oligomer composition, GO content and amine structure on the properties of NIPUs were systematically investigated. The resulting NIPUs exhibited excellent thermal stability and mechanical strength. Particularly, separation of monomer-enriched fractions from lignin oligomers significantly enhanced the performance of the cured materials. The incorporation of 1.0 wt% GO further improved reinforcement, achieving a maximum tensile strength of 63.8 MPa. Additionally, the films were given remarkable recyclability, resilient dual-shape memory capabilities and thermal reconfigurability by the dynamic covalent architecture. After undergoing two hot-pressing cycles, the reprocessed samples maintained over 76.2% of their initial tensile strength. These findings highlight the potential of lignin-derived NIPUs as renewable, high-performance alternatives to conventional polyurethanes, offering a scalable and sustainable pathway for advanced functional coatings.