Bio-based epoxy vitrimers from phenolic mixtures of lignin oxidative depolymerization

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. Thus, the direct preparation of epoxy resins from phenolic mixtures (aromatic aldehydes, ketones and acids) in lignin depolymerized oil is more appealing. In this work, epoxy vitrimers with self-healing and recyclable properties were fabricated from lignin-derived phenolic mixtures by introducing dynamic covalent imine bonds into the crosslinking network via Schiff base reaction during amine curing. Investigations on monomer composition effects revealed that G-type aromatic aldehydes and S-type aromatic ketones improve thermal stability, while aromatic acids enhance mechanical strength. The 3, 5-dimethoxy groups in S-type units enhance the rigidity and solvent resistance of the materials due to steric hindrance but compromise the recyclability. These results confirm that the properties of epoxy vitrimers rely on the combined effects of monomer's structural units and functional groups. This study demonstrates that bio-based epoxy vitrimers with controllable properties can be prepared without specific phenolic monomers, merely by regulating the composition of phenolic mixtures from lignin oxidative depolymerization products, providing a new insight into the green preparation of lignin-based epoxy vitrimers.