Biobased epoxy covalent adaptable networks for high-performance recoverable adhesives

Biobased epoxy covalent adaptable networks (ECANs) with renewability, recyclability, and reprocessability are thought as ideal alternatives to petroleum-based epoxy thermosets with respect to sustainable development. In this study, biobased ECANs based on dynamic imine bonds were prepared from glycerol triglycidyl ether (GTE), vanillin (VA), and diamines via a facile two-step solvent-free procedure. In detail, a trialdehyde monomer was first synthesized via ring-opening reaction of GTE with VA and then cured with diamines to obtain imine-based ECANs with a carbon biobased content of > 50.0%. The biobased ECANs had an excellent tensile strength (> 70 MPa), Young’s modulus (> 2500 MPa), and T g (> 90 °C) due to the introduction of rigid imine bonds, several aromatic groups, and the conjugated systems formed between imine bonds and benzene rings. Meanwhile, the incorporation of C N structure endowed ECANs with UV shielding properties. Based on the topology rearrangement induced by exchange reaction of imine bonds, ECANs exhibited excellent malleability with a stress relaxation time < 30 s at 120 °C. Thus, they showed reprocessability without sacrificing the mechanical and thermal performance. Moreover, biobased ECANs could be used as high-performance recoverable adhesives for aluminum with an original and recovered lap shear strength of > 53.9 MPa and > 40.0 MPa, respectively.