Bonding Properties and Antifungal and Flame-Retardant Performances of Soy Protein Adhesive Modified by Vanillin Grafting and Iron–Dopamine Synergy

Abstract Currently, environmentally benign biomass-based adhesives have become a research focus of the wood-based panel industry. As an eco-friendly alternative to formaldehyde-based resins, soy protein isolate (SPI) adhesives hold broad application prospects. However, their inadequate mechanical properties and poor water resistance hinder their industrial application. This study utilized the trifunctional aldehyde monomer constructed from vanillin and Fe@polydopamine (Fe@PDA), inspired by the mussel biomimetic modification mechanism, to reinforce the cross-linking structure of SPI. The results indicated that the dry and wet shear strengths of the SPI-10TAM-5Fe@PDA adhesive reached 2.45 and 1.28 MPa, which were 140.20% and 137.04% higher than those of the pure SPI adhesive, respectively. Various characterization techniques confirmed that the adhesive composite system formed a stable cross-linking network structure, exhibiting an excellent water resistance and solvent resistance. Furthermore, the adhesive exhibited significantly improved mold resistance, ideal flame-retardant performance, remarkably reduced graphitization, and an enhanced thermal stability. The construction of this mussel-inspired nanophase-reinforced structure provides research insight for the development of high-performance water-resistant biomass-based adhesives.