Supramolecular self-assembly for synthesis of novel chitosan-based adhesive in wood composites so as to improve waterproofing and flame retardancy.

As awareness of building safety and fire prevention grows, the demand for fire-retardant materials is gradually increasing. The need for flame-retardant wood composites is particularly urgent in public, high-rise, and commercial buildings. However, most of the current research has focused on adding flame retardants, often at the expense of mechanical properties. This study prepared a fully bio-based flame retardant, high-strength, and boiling water resistant adhesive using supramolecular self-assembly strategy. In this work, chitosan, malic acid, and phytic acid were dissolved in water in one step, and the resulting adhesive is fully bio-based and environmentally friendly. Next, this adhesive had been applied to multi-layer wooden boards to prepare wood composites with excellent mechanical properties (the highest shear dry strength was 1.66 MPa). Furthermore, the crosslinked network created by the ester and amide bonds provides the wood composites with exceptional water resistance (the highest shear strength after boiling water treatment was 1.13 MPa). More importantly, the wood composites obtained have excellent flame retardancy (LOI = 30.2 %) compared to natural wood. Therefore, this work provides a reference for producing water-resistant and flame-retardant wood materials without compromising their mechanical properties.