Solvent-free all-bio-based underwater adhesives featuring degradability and closed-loop recycling

Abstract

Bio-based adhesives show significant promise for biomedical, tissue-engineering, and electronic-packaging applications, yet developing a solvent-free, degradable, and closed-loop recyclable all-bio-based underwater adhesive remains a formidable challenge. In this study, an all-bio-based solvent-free, degradable and closed-loop recyclable underwater adhesive was designed via a dynamic covalent polymer-empowered plant protein adhesive strategy. The PTA-Zein adhesive was successfully synthesized through ethanol evaporation-induced ring-opening polymerization of thioctic acid (TA) in the presence of zein. The underwater adhesive demonstrated outstanding adhesion performance, reusability, long-term stability, solvent resistance, and low-temperature resistance. Molecular dynamics simulations confirmed that zein enhanced cohesive energy and interfacial adhesion energy. Furthermore, life cycle assessment showed that this adhesive emitted merely 0.84 kg CO₂-eq. per kg, significantly lower than conventional urea–formaldehyde and phenolic resins, with complete soil degradation within 27 days. Notably, the adhesive can be applied to fabricate green wooden building materials, which showed a flexural strength of 3.52 MPa and an impact resistance of 510.89 N. This work provides valuable insights into the development of sustainable bio-based solvent-free adhesive materials for advancing next-generation eco-friendly bonding materials.