Phytic acid-derived 3D crosslinked bio-based hybrid adhesive integrating strong adhesion, phosphorus–nitrogen synergistic flame retardancy, and antifungal performance

To address the sustainability and multifunctionality limitations of conventional wood adhesives, a formaldehyde-free bio-based hybrid adhesive was developed. PAGMA, a reactive monomer derived from phytic acid, was combined with chitosan (CS) and polyvinyl alcohol (PVA) to construct a three-dimensional crosslinked network. The adhesive exhibits tunable viscosity and good processability, while providing strong bonding, water resistance, flame retardancy, and antifungal performance. Structural characterization and molecular dynamics simulations indicate that the system evolves from a network dominated by physical interactions into a thermally stabilized hybrid crosslinked structure during curing, characterized by P–N and C–O–P bonding features. This transformation promotes network densification and facilitates the formation of a compact char layer during combustion, thereby enhancing thermal stability and flame retardancy. The optimized adhesive achieved dry and wet lap-shear strengths of 11.78 and 6.49 MPa, respectively, and a char yield of 27.41% at 800 °C. In addition, the coated wood exhibited an LOI of 50.2% and achieved UL 94 V-0, while the peak heat release rate and total smoke release decreased by 29% and 18.1%, respectively. After 30 d, fungal coverage remained below 5%, demonstrating strong antifungal performance. This work provides a molecular design strategy for multifunctional bio-based hybrid wood adhesives with balanced bonding strength, water resistance, fire safety, and antifungal performance.