A multiscale structure enabled strong, ultra-tough and sustainable polyurethane adhesives

Developing sustainable adhesives with simultaneous high adhesive strength and excellent work of debonding remains challenging. Here, strong, ultra-tough, environmentally reliable, and recyclable polyurethane adhesives are reported, utilizing a multiscale engineering approach. The multiscale structure employs a top-down design philosophy to merge the advantages of both thermoplastic and thermosetting systems, integrating multi-level organizations including macroscale dual-length dynamic crosslinked networks, mesoscale initial and fibrillar crystals, nanoscale hard phase domains, and molecular scale weak hydrogen bonds. The multiscale structure exhibits the following features: multi-level organizations and surface-anchored high energy phases significantly enhance the bulk cohesion and interfacial adhesion, respectively. And hydrophobic organizations provide barrier mechanisms, while dynamic crosslinking enables network reconfiguration. As a result, the developed adhesive exhibits both high adhesive strength (21.24 MPa) and ultrahigh work of debonding (35,731 N m^-1), coupled with excellent physical and chemical recyclability and environmental reliability (high humidity, water, organic solvents, acids and alkalis, high and ultralow temperatures, aging). This work highlights how multiscale structure enabled by dual-length crosslinked networks simultaneously optimizes bulk cohesion and interfacial adhesion, offering a perspective for designing strong and tough adhesives.