Nature-derived adhesives based on chitosan and rosin acid with high strength, flame retardancy, and environmental friendliness

Abstract

Chitosan exhibits exceptional renewability and environmental compatibility, demonstrating significant potential for developing sustainable adhesives. However, its inadequate mechanical strength and pronounced hydrophilicity significantly constrain practical applications. This work developed a green multifunctional chitosan adhesive (CS-BA-ERA) based on epoxidized rosin acid (ERA), chitosan (CS), and boric acid (BA). The CS-BA-ERA adhesive imparted plywood with favorable dry and wet shear strengths of 2.71 MPa and 1.92 MPa. The particleboard prepared with this adhesive exhibited a flexural strength of 21.00 MPa, an internal bond strength of 0.85 MPa, and a thickness swelling rate of only 11.06% after 24 h of water immersion. The molecular dynamics simulation results demonstrated that synergistic crosslinking formed a strengthened network, increasing interfacial adhesion energy. Furthermore, the CS-BA-ERA adhesive exhibited excellent flame retardancy, achieving a limiting oxygen index of 81.10% and a char residue of 43.84% at 599.60 °C. Additionally, this adhesive displayed competitive environmental compatibility, with a reduced environmental impact compared to conventional melamine-formaldehyde resins and phenol-formaldehyde resins, alongside near-complete biodegradation (>95.00%) within 15 days. This work provides a green approach for developing sustainable biomass adhesives, offering a renewable and biodegradable alternative to petroleum-based adhesives in wood panel manufacturing.