Molecularly engineered cardanol derived epoxy vitrimers based on dynamic disulfide and dynamic ester exchanges with desirable dynamic response, degradability, and recyclability

Abstract

Dynamic covalent chemistry provides a solution to the recycling problem of epoxy resins, and the graphene functional composites. Nevertheless, the study on chemical structures of the curing agent, and the type of dynamic covalent bonds associated with the nature of the epoxy resins still face challenge due to unclear mechanism and improper design strategy. Herein, a bio-based epoxy monomer was designed from cardanol, and used to fabricate a double dynamically crosslinked epoxy vitrimer. The mechanical properties, dynamic mechanical properties, thermal stability, relaxation behavior, self-healing efficiency, recovery, and reprocessing efficiency of the resulting resins were investigated, focusing on the effects of the soft and hard structure of the curing agent, and the types of dynamic covalent bonds. Bio-based epoxy vitrimers demonstrated several advantages, including multi-stimulus responsiveness, multi-channel self-healing ability, mechanical and chemical recovery, and biodegradability. Specifically, the epoxy vitrimers containing rigid furan rings exhibited better mechanical properties (6.85 MPa) and stability (Tg = 40.81 °C) compared to those with flexible fatty chains. Additionally, the double dynamically crosslinked vitrimer showed faster stress relaxation time (5.6 min) and lower activation energy (36.58 kJ/mol) compared to systems with a single dynamic bond. Finally, the addition of graphene enabled the production of cardanol-based composites with conductivity. Overall, the ease with bio-based epoxy vitrimer and its composites with excellent degradability can be fabricated, utilized, recycled and re-used, which is a novel direction for sustainable composites.