Closed-Loop Recyclable Fully Bio-Based Epoxy Vitrimers from Ferulic Acid-Derived Hyperbranched Epoxy Resin

Epoxy vitrimers with dynamic covalent networks enable reprocessing and recycling of epoxy thermosets. However, achieving high mechanical performance remains a challenge. In this work, ferulic acid-based hyperbranched epoxy resin (FEHBP) was synthesized to produce closed-loop recyclable and catalyst-free epoxy vitrimers without compromising its thermal and mechanical properties. The incorporation of FEHBP with a hyperbranched topological structure improved the tensile strength, modulus, and toughness of epoxy vitrimers through an in situ reinforcing and toughening mechanism. The hydroxyls of FEHBP catalyzed the dynamic transesterification and accelerated the reprocessing of epoxy vitrimers. Thus, the obtained epoxy vitrimers demonstrated excellent weldability, malleability, and programmability. Epoxy vitrimers with 10 phr FEHBP exhibited high tensile strength (126.4 MPa), usable Tg (94 °C), fast stress relaxation (a relaxation time of 45 s at 140 °C) and a retention of tensile strength (above 88.3%) upon recycling. The degradation products were reused to produce new epoxy vitrimers under mild conditions with similar mechanical properties and thermal stability as the original epoxy vitrimers, leading to closed-loop recyclable, fully bio-based epoxy vitrimers with potential for industrial applications.