High performance, water resistant and antimicrobial bioadhesives by epoxidized lignin-polylysine networks

Bio-derived adhesives have attracted increasing interest as sustainable alternatives to petroleum-based adhesives. However, their practical applications are often limited by poor water resistance arising from the hydrophilic nature of biomass macromolecules and insufficient cross-linking density. Meanwhile, integrating durable antibacterial functionality into bio-based adhesive systems remains a significant challenge. In this study, a bio-based thermosetting adhesive was developed by constructing a dense three-dimensional covalent cross-linked network through epoxy–amine ring-opening reactions between epoxidized lignin (GL) and polylysine (PPL). Plywood bonded with the optimized adhesive met the requirements for Class II plywood specified in GB/T 17657–2022, exhibiting a wet bond strength of 1.10 MPa after immersion in hot water at 63 °C for 3 h. In addition, the adhesive exhibited good bonding performance on both bamboo and metal substrates. Owing to the incorporation of cationic PPL chains, the adhesive exhibited excellent antibacterial activity against Escherichia coli and S. aureus , with an antibacterial rate of up to 99.9 %. These findings establish a scalable route for transforming lignin into multifunctional structural adhesives and highlight the potential of renewable polymers for replacing fossil-derived adhesive systems.