Dual-interlocking inspired multiple crosslinked chitosan-based composites with synergistic water resistance and flame retardancy for sustainable wood adhesives

Developing sustainable and high performance wood adhesives to replace traditional formaldehyde-based resins remains a key challenge for the wood industry. In this study, a novel double crosslinked chitosan-based adhesive, AMS-AHC-CS@IRMOF-3@P, was designed and synthesized inspired by zippers. Utilizing modified chitosan (AMS) and modified polyamine citrate (AHC) containing bifunctional groups as “zipper teeth” and “zipper head”, respectively, and chitosan @ phosphorus-containing metal organic skeleton complex (CS@IRMOF-3@PCT) as a reinforcement and flame retardant, all of which were fused together by a “zipper” cross-linking strategy. Comprehensive characterization (FTIR, XPS, SEM, XRD) confirmed successful chemical interactions and structural integration between the components. The resulting adhesive has excellent mechanical strength (shear strength under boiling water: 1.05 MPa, exceeding the GB/T 9846–2015 standard), and excellent flame retardancy (LOI: 49.7 %, reaching the UL-94 rating of V-0). In the complex CS@IRMOF-3@PCT, chitosan acts as a carbon source and IRMOF-3@P acts as a phosphorus and gas source, which synergistically and significantly improve the thermal stability and fire resistance of the adhesive. In addition, the adhesive AMS-AHC can be prepared by freeze-drying into an aerogel exhibiting excellent compressibility (modulus of elasticity of 117.82 MPa). This work presents an environmentally friendly multifunctional adhesive that addresses the limitations of conventional bio-based adhesives. It provides a sustainable alternative with industrial potential for wood composites and fire-retardant coatings. • A novel double crosslinked chitosan-based adhesive was designed and synthesized inspired by zippers. • Acidification and alkenylation of chitosan as “zipper teeth” enhances its water solubility and reactivity. • A new biomass polyamine citrate is developed with bifunctional groups as “zipper head”. • Chitosan @ phosphorus-containing metal organic skeleton complex as a reinforcement and flame retardant.