Development of a strong and multifunctional soy protein-based adhesive with excellent coating and prepressing in wet state by constructing a radical polymerization and organic-inorganic mineralization bionic structure

It is very important for industrial production to develop a strong bonding and multifunctional soy protein (SP)-based adhesive with excellent coating property and high prepressing strength especially for wet veneer. Inspired by mussels, catechol structure was grafted to soybean protein molecules (SPU) by ring opening reaction and free radical polymerization, which endowed the adhesive excellent coating performance on wet veneer. Inspired by oysters, magnesium hydroxide with unsaturated bond (MH@A172) was synthesized, and then mixed with SPU to obtain an organic-inorganic hybrid adhesive (SPU/MH@A172). During the curing process, the synergistic enhancement of the formed cross-linking structure and inorganic mineralization strategy improved the cohesion of SPU/MH@A172 adhesive and endowed strong bonding strength of prepared plywood. That is, when the SPU/MH@A172 adhesive was applied to wood veneer of 100% moisture content, it can be evenly coated and the prepressing bonding strength at 20 °C with 3 h reached 0.53 MPa, which meets the bonding strength requirement of plate forming (≥0.4 MPa). After hot-curing process, the wet and dry shear strength of the prepared plywood reached 1.07 MPa and 2.03 MPa, respectively. In addition, the adhesive had excellent stiffness (45.21 GPa) and micro adhesion (4.62 nN). Importantly, adhesives exhibited excellent mildew resistance (14 days, grade 2), flame retardancy (HRC = 114 kJ/g), low smoke suppression (Ds_max = 95.09) and volatile organic compound release (6.43*106 mg/m2⋅h). Therefore, this collaborative bionic strategy provides a possibility for the development and functional modification of underwater adhesive, film, hydrogels and composite materials.