Vanillin-derived bio-based epoxy resins containing dual dynamic Schiff base and disulfide bonds with reprocessability and degradability

Incorporating reversible covalent bonds into the crosslinked matrix of bio-based epoxy resins can address the challenges of difficult degradation and sustainable development associated with petroleum-based epoxy resins. However, the dynamic capability conferred by a single dynamic chemical bond proves relatively insufficient in thermosetting polymers. Therefore, we propose a strategy to introduce proportionally adjustable dual dynamic covalent bonds in the bio-based epoxy resin system to leverage the advantages of different dynamic bonds and improve the dynamic properties of the resulting epoxy vitrimers in this study. First, a bio-based epoxy monomer (BVF-EP) derived from vanillin was prepared and cured with a diamine hardener (AFD). Subsequently, vanillin- derived epoxy vitrimers were prepared by varying the stoichiometric ratio of AFD to BVF-EP (R = 0.5, 1.0, and 1.5) without catalysts. Some of the vitrimers showed good thermal stability and excellent reprocessability and degradability. Notably, BVF-EP/AFD (R = 1.5) containing both dynamic reversible covalent bonds of S-S and C=N with the highest crosslink density, exhibited the highest thermal decomposition temperature, highest tensile modulus (7175 MPa), and the shortest stress relaxation time (6 s at 200 degrees C). Simultaneously, BVF-EP/AFD (R = 1.5) demonstrated good multiple reprocessing capacity under a pressure of 5 MPa at 140 degrees C. It can be completely degraded in two distinct mixed solutions (50 % DMF/50 % beta-ME and 50 % 1 M HCl/50 % DMF), offering great potential in recovering high-value carbon fibers from its carbon fiber-reinforced composites. This work advances the development of bio-based epoxy resins with dual dynamic crosslinked networks, providing new insights for the degradation and reprocessing of thermoset polymers.