Unlocking the potential of lignin-based polyhydroxyurethanes: Insights into kinetics, physical behavior, and recyclability

Safe, sustainable and recyclable lignin-based polyhydroxyurethanes (PHUs) were synthesized through a simple methodology. Aminated lignins (L-NH 2 ) were produced without formaldehyde and used as precursors for the aminolysis of cyclocarbonates (CCs). The impact of lignin up to 50 wt% on reaction kinetics, gelation, material properties and behaviors was evaluated. While lignin had minimal influence on the aminolysis kinetics and CC conversion, it accelerated considerably the gelation (from 11 h to less than 1 min) and enhanced the thermal and mechanical properties of the PHUs. For instance, Young's modulus and tensile strength of the PHUs increased with lignin content from 1.2 to 35 MPa and 0.24–4.3 MPa, respectively. Leveraging on the dynamicity of urethane bonds, PHUs could then be recycled, maintaining material integrity across multiple cycles. However, a gradual decline in mechanical properties was observed, attributable to side reactions such as urethane-to-urea condensation. This study establishes a proof-of-concept for the production of biobased PHUs with tunable properties from aminated lignins, and also provides a deeper understanding of the influence of lignin on the behavior of these materials. The rapid gelation step induced by lignin opens several opportunities. These findings pave the way for sustainable development of renewable, high-performance polymeric materials, offering a large range of potential applications in e.g., coatings, adhesives, and foams. This study reports the synthesis of reprocessable lignin-based polyhydroxyurethanes. The role of lignin on the kinetics, gelation, and materials properties is particularly analyzed. The end of life of these materials was also considered.