Abstract
The next generation of adhesives requires effective debonding capabilities that can be triggered on demand to enable advanced circular repair and recycling strategies. A new class of lignin-inspired, two-component (2K) structural adhesives offers bonding strengths of up to 20 MPa and clean, on-command electrochemical debonding within 5-30 min. The debonding is induced by a distinct electrochemical oxidation of thiol-catechol connectivities (TCCs) within the entire adhesive network, enforcing rapid and clean adhesive failure on the cathodic substrate side. The TCC-functionalities are formed during curing by a thiol-quinone Michael-type polyaddition, reacting polyester-based trithiols with tris-quinones as lignin-inspired minimal building blocks. The structural adhesive can be fine-tuned by adjusting the formulation. The addition of carbon black and ionic liquids facilitates the desired electrochemical transformation of TCC-catechols to TCC-quinones. Applying only 9 V for 5-30 min, leads to clean debonding with 72-86% loss of shear strength. A comprehensive study of curing, bonding, and debonding behavior by rheological, spectroscopic, and electrochemical investigations reveals the debonding mechanism by correlating catechol oxidation to adhesive performance. The electrochemical debonding capability of TCC-structural adhesives is demonstrated in a functional prototype, where on-command detachment of a cover glass from a display device is achieved within 6.5 min.