Simulated phenolic mixtures from lignin oxidative depolymerization toward bio-based epoxy vitrimers

Bio-based bisphenol compounds from lignin oxidative depolymerization-derived phenolic monomers exhibit great potential in epoxy resins, yet the existing technologies for the separation and purification of specific phenolic monomers are cumbersome and costly. The direct use of unpurified phenolic mixtures (aromatic aldehydes, ketones and acids) would therefore be far more practical, provided that the influence of monomer composition on the crosslinking network can be rationalized. Here, bio-based epoxy vitrimers with self-healing and recyclable properties were fabricated from lignin-derived phenolic model mixtures by introducing dynamic covalent imine bonds into the crosslinking network via Schiff base reaction during amine curing. Systematic variation in the contents of H-, G-, and S-type aromatic aldehydes, ketones, and acids revealed that G-type aromatic aldehydes and S-type aromatic ketones improve thermal stability, aromatic acids increase mechanical strength, and the 3, 5-dimethoxy groups in S-type units increase rigidity and solvent resistance through steric hindrance but slow imine exchange and reduce recyclability. Aldimine bonds proved more solvent-resistant than ketimine bonds, and G-type-dominated systems were more efficiently reprocessed than S-type-dominated systems. This work establishes composition-structure–property relationships for lignin-derived phenolic model mixtures in dynamic epoxy networks, providing a new insight for the high-value valorization of lignin oxidative depolymerization products.