A strong soybean meal adhesive enhanced by aluminum hydroxide nanoparticles via a low-cost and simple organic-inorganic hybrid strategy

Soybean meal (SM), as a byproduct of bean oil production, used to develop formaldehyde-free bio-adhesives to solve the formaldehyde release problem in the wood industry is very meaningful. However, the low water resistance and weak adhesion stability of SM-based adhesives limited their application and development. In this study, inspired by nacre and mussel byssus, a novel organic-inorganic hybrid system was formed by introducing Al(OH)3 nanoparticles into SM adhesive. Al(OH)3 nanoparticles interacted with SM to form dense noncovalent crosslinking network based on hydrogen and coordination bonds, enhancing the adhesion performance and water resistance of SM adhesive. The dry and wet shear strength of the SM/Al adhesive were improved to 1.75 MPa and 1.25 MPa, respectively. Meanwhile, the hydrogen and coordination bonds served as sacrificial bonds, which promoted dissipating energy and caused the toughness of SM/Al adhesive to improve by 133.3% to 11.2 MJ/m3. In addition, the dehydration process of Al(OH)3 nanoparticles reduced the heat release of the adhesive combustion and improved adhesive flame retardancy. Therefore, the SM/Al adhesive showed a comprehensive improvement in adhesion strength, toughness, water resistance, and flame retardancy performances. This work provides a novel strategy for preparing strong, eco-friendly, multiple performances and low cost SM adhesives.