Double‐Network Soy Protein Adhesives with Enhanced Water Retention and Bonding Strength

Abstract Developing soy protein adhesives with high water retention and strong bonding strength is essential. Such materials can serve as a sustainable alternative to petroleum‐based formaldehyde adhesives in wood panel manufacturing. However, a trade‐off between precure water retention and postcure bonding strength remains a major challenge, and current strategies rarely achieve simultaneous enhancement of both properties. Inspired by the multi‐enhancement mechanisms of double‑network systems, we established a hierarchical dual‑network adhesive system. It involves the self‐assembly of chitosan into a compliant supramolecular framework via dynamic hydrogen bonding and electrostatic interactions, along with the additional formation of a stiff covalent crosslinked network during curing. This design achieves synergistic optimization of water retention and bonding strength. The “skeleton–tentacle” structure formed by functionalized chitosan significantly enhanced water retention by 430% and was crucial to forming the dual‐network structure, improving wet shear strength by 445% and work of adhesion by 2133%. Additionally, the adhesive exhibited excellent mildew resistance and flame retardancy. The global warming potential was only 1.4 kg CO 2 eq, significantly lower than urea–formaldehyde and phenol–formaldehyde resins. This design provides a novel approach for developing high‐performance bio‐based adhesives and is expected to advance its practical application.

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