Vanillin-derived multifunctional reinforcing agent enabling recyclable epoxy vitrimer composites via hydrogen/dynamic covalent collaborative networks

Epoxy vitrimers impart dynamic functionality to thermoset polymers and carbon fiber-reinforced composites (CFRC) through reversible crosslinking networks. However, this often results in reduced stability and a trade-off between dynamic performance and mechanical strength. Herein, a novel reinforcing agent (Bio-based Vanillin-Tyramine, BVT) containing Schiff base and tetraphenol hydroxyl groups was synthesized to address this challenge. The incorporation of BVT constructs the hierarchical crosslinking networks that simultaneously enhance the strength and toughness of bio-based vitrimers (Tensile strength and impact strength were increased by 44 % and 225 %, respectively.). The synergistic effect of dual dynamic imine and siloxane bonds further optimizes dynamic behaviors, resulting in a 51 s stress relaxation time and a 14 % decrease in activation energy for the dynamic bond exchange reaction. In addition, CFRC containing dynamic crosslinked networks demonstrate closed-loop recyclability under mild conditions, preserving the surface morphology and chemical structure of recovered carbon fibers, while maintaining the crosslinking architecture of the recycled vitrimer for reshaping. This work presents a simple and efficient strategy for constructing hybrid hydrogen-bonding/covalent adaptable networks, providing valuable insights into the development of high-performance, multifunctional, and recyclable bio-based epoxy vitrimers and CFRC.