Scallop-inspired of multi-bond network protein adhesive with excellent bonding strength, mildew resistance and flame retardancy

Designing sustainable natural biomass adhesives with high bonding performance (particularly cold-pressing bonding strength) while maintaining excellent coating, mildew resistance, and flame-retardant properties is important for developing formaldehyde-free wood adhesives. Inspired by the wet adhesion system of scallops, we developed a novel bionic soybean meal (SM) adhesive with excellent bonding strength. In this adhesive system, keratin (KT) acts as a source of disulfide bonds (S–S) contributing formation/exchange donor, while Fe³⁺ ions formed dynamic coordination bonds with carboxyl groups and tannic acid, resulting in strong adhesion. The multiple crosslinking network system synergistically enhanced the adhesion, resulting in a cold-pressing bonding strength of 582.4 kPa, which is an improvement of 171.3 %. The dry and wet bonding strength was 3.19 MPa and 1.34 MPa, which was increased to 73.4 % and 97.1 % compared to the SM adhesive, respectively. Additionally, the adhesive exhibited desirable mildew resistance (under storage for 15 days) and superior flame resistance, which was attributed to the synergistic inhibition by the metal cations and phenolic hydroxyl groups. The design of this bionic system offers a novel approach for developing environmentally friendly wood adhesives.