Enhanced water resistance and toughness of soy protein adhesive via SADP multiple cross-linking network

Objective Soy protein adhesives suffer from poor water resistance, brittleness, and low bonding strength. This study constructs a strong-weak multiple cross-linking network within the adhesive system using sucrose/ammonium dihydrogen phosphate (SADP). The synergistic effect of covalent and hydrogen bonds increases cross-linking density, thereby improving cohesive strength, toughness, and water-resistant bonding performance.

Method Low-temperature defatted soybean meal served as the matrix. Modified adhesive was prepared using SADP as the modifier and triglycidylamine (TGA) as the cross-linking agent via a synergistic cross-linking reaction. The structure, morphology, thermal stability, and mechanical properties were systematically characterized to elucidate the underlying mechanism.

Result The N–H group content decreased after modification, confirming that SADP reacted with amino acids to form a strong-weak multiple cross-linking network with synergistic covalent and hydrogen bonds. This network significantly improved water-resistant bonding strength, thermal stability, and toughness. At an SADP dosage of 2%, water-resistant bonding strength reached 1.44 MPa, representing a 77.78% increase over the unmodified adhesive. This demonstrates that the strong-weak multiple cross-linking network effectively optimizes adhesive performance.

Conclusion This strong-weak multiple cross-linking network significantly enhances the bonding strength, water resistance, toughness, and thermal stability of soybean protein adhesives. This approach provides a new strategy for developing high-performance bio-based adhesives. Future research should optimize cross-linking agent ratios and reaction conditions, and extend this multiple network system to other bio-based adhesives.