A chitosan-based adhesive with high flame retardancy and superior bonding strength fabricated by interface...

With an emphasis on sustainable development, the wood industry faces great challenges, including studies on bio-based, aldehyde-free, high-strength and water-resistant adhesives. Here, a high-strength water-resistant chitosan-based adhesive was prepared by mixing of polyacrylic acid (PAA) and chitosan (CS) with assist of a little Ca²⁺. Meanwhile, bonding strength was enhanced through wood surface activation caused by wood: adhesive interfacial interaction. The dry and wet bonding strengths of the three-layer plywood were 3.28 MPa and 2.16 MPa, respectively. Bonding strength of the plywood remained 1.38 MPa after a "4 + 4 + 1" harsh test. The main reasons for the excellent performance were: 1) Covalent crosslinking and entanglement between PAA and CS significantly improved the cohesiveness of adhesive. 2) The introduction of Ca²⁺ formed organic-inorganic hybrid structure, which enhanced the cohesion and interfacial force of adhesive. 3) The active functional groups on wood surface were further cross-linked with adhesive, which greatly enhanced the interfacial bonding. After the adhesive was compounded with ammonium polyphosphate, the plywood exhibited excellent flame retardancy. These strategies have provided valuable ideas for studying high-performance wood adhesives and expanding the functionality of adhesives.