Dual dynamic bonds toughened flame-retardant epoxy resin and its application in wood modification

Resin impregnation is an important wood modification technique. However, conventional thermosetting resins are inherently insoluble and infusible, posing significant challenges to their recycling and reuse-a fundamental contradiction with wood's eco-friendly and renewable nature. This study introduced Schiff base and boronate ester bonds into a water-based epoxy (EP) resin system. The reversible cleavage and rearrangement of these dynamic bonds endowed the EP resin with plasticity, enabling reprocessing and reforming, while enhancing its toughness to overcome the high brittleness of common epoxy resins. The resin formed a stable network within the wood, reducing leaching and improving wood water resistance and dimensional stability. Additionally, silicon in Schiff base moieties and boron in boronate ester groups conferred good flame retardancy to the water-based epoxy resin. For the modified wood: limiting oxygen index (LOI) increased by 28.3%; vertical burning rating reached V-0; infrared thermal imaging central temperature decreased by 61.2%; thickness swelling rate reduced to 2.3%; and elastic modulus significantly increased by 73.33%. Life cycle assessment showed that compared with the PMMA impregnation process, the epoxy resin impregnation process reduced global warming and marine eutrophication impacts by 21.7% and 87.6%, respectively. Accelerated aging tests confirmed that dynamic bonds did not undergo irreversible fracture, and the mechanical properties and water resistance of modified epoxy resin and resin-impregnated wood remained stable. This research provides a novel strategy for strengthening, toughening, flame-retarding, and enabling recyclability of fast-growing wood via dual dynamic bonds in water-based epoxy resin. It addresses thermosetting resin recycling, allows wood reprocessing, extends service life, and expands the application fields of wood-based materials.