Handling-friendly, waterproof, and mildew-resistant all-bio-based soybean protein adhesives with high-bonding performance via bio-inspired hydrophobic-enhanced crosslinking network

Eco-friendly and formaldehyde-free soybean protein adhesives are highly attractive to the wood-based panel industry but typically suffer from low water-resistant bonding strength, high viscosity, and susceptibility to mildew. Inspired by adaptive hydrophobic and hydrophilic interactions of mussel foot proteins, herein, a high-performance and versatile all-bio-based adhesive (STF) was synthesized through employing bio-derived furfural and natural tannic acid to assist soybean protein in developing a biomimetic physical/chemical cross-linking network. The collaboration of the hydrophobic furan ring and the hydrophilic catecholic moiety endowed the as-prepared STF adhesives with exceptional water-resistant bonding strength, easy-coating performance, and mildew resistance. Compared to the original soybean protein, the optimal STF demonstrated dry and wet shear strengths of up to 2.52 MPa and 1.71 MPa, respectively, representing an increase of 65.8 % and 263.8 %. Notably, the aged bonding strength of STF surpassed that of previously reported soybean protein-based adhesives with a value as high as 1.19 MPa. The viscosity of the STF decreased by ≈ 98.1 % compared to the unmodified adhesive. Additionally, the STF exhibited excellent mildew resistance (no mildew for 7 days) and storage stability (> 72 h). Combined with life cycle assessment, the biomimetic STF adhesive holds great potential for large-scale production of environment-friendly wood panels.