Dynamic Schiff Base Bonds Enable Recyclable, High-Toughness Vanillin Epoxy Resins via Micro–Nano-Phase Engineering

Epoxy resins are widely used in composite materials due to their excellent thermal stability and mechanical properties. However, their covalent cross-linked networks prevent their recyclability, and the reliance on petroleum-based raw materials hinders sustainable development. Although the reversible cross-linking of biobased dynamic epoxy resins such as vanillin-Schiff base systems enables their recycling, the synergistic effect of high cross-linking density and rigid dynamic bonds leads to significant brittleness. To overcome these problems, this work proposes a strategy to achieve microphase separation via polarity modulation. Specifically, a m-xylylenediamine derivative that incorporates long alkyl chains was designed to react with a vanillin-based epoxy resin containing dynamic Schiff base bonds, resulting in the formation of chemically bonded micro/nanophase domains during curing. Results revealed that this strategy regulated the cross-linking density and improved the compatibility between the alkyl chains and epoxy cross-linked networks, endowing the biobased epoxy resin with 80% elongation at break and a remarkable tensile toughness of 12.8 MJ·m–3, which represents a 6.1-fold enhancement over conventional systems. The designed low-density cross-linked networks show dual advantages: facile acid-catalyzed degradation with full depolymerization in 5 h and supporting low-temperature reprocessing. Besides, the solvent resistance remains largely unaffected. In addition, glass fiber-reinforced composites prepared using the biobased epoxy resin exhibited outstanding interfacial bonding and degradation performance, with a fiber recycling rate exceeding 95%, demonstrating high strength, high toughness, and recyclability. This study offers a previously unexplored route toward achieving both high tensile toughness and recyclability in biobased epoxy resins used for glass fiber-reinforced composites.