Extrudable, robust and recyclable bio-based epoxy vitrimer via tailoring the topology of a dual dynamic-covalent-bond network

Abstract

Vitrimers offer possibilities for sustainable materials due to their reprocessability and recyclability. However, enhancing both their mechanical strength and network dynamics simultaneously remains a challenge. Previous attempts to address this issue have not achieved the desired mechanical strength comparable to traditional cured resins and have also fallen short in dynamic performance during compression molding and extrusion processing. In our study, we have successfully created an epoxy vitrimer, EOCY, by a rational design of the topology of a dual dynamic-covalent-bond (D-DCBs) network based on disulfide and imine bonds. The network of this design incorporates a high density of DCBs through the combined utilization of a rigid monomer containing imine bonds and a flexible crosslinker that carries disulfide bonds. The rigid epoxy monomers in EOCY result in superior tensile strength (85.35 MPa), high Tg (112.01 °C), high Young's modulus (2.01 GPa) and improved solvent resistance. Moreover, the flexibility of the curing agent and plentiful D-DCBs lead to reduced activation energy (Ea = 42.23 kJ/mol) and short relaxation time (τ = 4.84 s at 140 °C), enabling EOCY to withstand multiple cycles of compression molding and continuous extrusion processing. Our vitrimer also demonstrates recyclability through various chemical methods, leveraging the unique properties of disulfide and imine bonds. In summary, this study presents a rational approach to network structure design for vitrimers with exceptional mechanical and dynamic properties.