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 Tg (> 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 CN 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.