A High‐Strength and Water‐Resistant Fully Biomass Adhesive Enabled by Schiff Base Cross‐Linking Between Chitosan and Oxidized Starch

ABSTRACT Formaldehyde‐based adhesives are widely utilized in the wood industry due to their high adhesion performance, cost‐effectiveness, and favorable processability. However, their reliance on fossil resources, formaldehyde emissions, and considerable carbon footprint raise substantial sustainability concerns. To address these issues, an all‐biomass, high‐strength, and water‐resistant adhesive based on chitosan and oxidized starch was developed. Specifically, a Schiff base reaction between the amino groups of chitosan and the aldehyde groups of oxidized starch establishes a robust covalent imine‐based framework. This network is further stabilized through hydrogen‐bonding interactions, resulting in a multi‐mechanism cross‐linking structure. The cross‐linking via dynamic imine bonds facilitates energy dissipation, while the dense hydrogen‐bonding function as stress‐concentrating sites that deflect crack propagation, thereby enhancing toughness. The adhesive exhibits dry and wet shear strengths of 2.68 MPa and 1.36 MPa, which are 2.19 and 1.86 times higher than those of pure chitosan adhesive, respectively. The toughness is significantly improved, with the debonding work reaching 826 mJ, representing a 9.3‐fold increase over the chitosan adhesive. Moreover, due to the antimicrobial activity of chitosan, oxidized starch, and the dense cross‐linked structure, the adhesive demonstrates excellent mold resistance over 20 days. This recyclable and biodegradable adhesive achieves an impressive combination of performance and sustainability, underscoring its potential as an eco‐friendly alternative to formaldehyde‐based petroleum adhesives in the wood industry.