High-Performance Wet Adhesion of Wood with Chitosan

Strong adhesion is desirable when using wood with a wide range of moisture contents, but most of the existing adhesives face challenges in bonding wood under high-humidity conditions. Here, we report a simple strategy that involves the one-step dissolution of chitosan powder in acetic acid at room temperature, followed by direct use of the resulting chitosan slurry as an adhesive on dry/wet wood veneers. Mechanical interlocks and hydrogen bonds at cell wall interfaces provided strong adhesion. Moreover, heat treatment induced recrystallization and cross-linking of chitosan chains, resulting in a high cohesion. Meanwhile, heat treatment caused the acetylation reaction between the protonated amino groups (NH3+) of chitosan and acetate groups (CH3COO-) to produce hydrophobic acetyl groups. In addition, we prepared wooden products such as plywood (dry veneers) and wooden straws (wet veneers) using wood veneers with different moisture contents. The tensile shear strengths under 63 degrees C water and under boiling water of plywood were 1.12 and 0.81 MPa, respectively. The compressive strength of wooden straws is up to 35.32 MPa, which was higher than that of existing commercial straws (such as paper straws, polypropylene straws, and plastic straws). The chitosan wet adhesive showed good water resistance, high bonding strength, environmental degradability, and nontoxicity, thus providing a highly promising alternative to traditional wood composite adhesives.