Polyphenols induced in situ organic-inorganic crosslinking/mineralization strategy for constructing eco-friendly soy adhesive with high waterproof bonding strength

The utility of inorganic filler hybrid soy protein (SP) adhesives is restricted by the difficulty in the control of dispersion and mineralization during the production and usage. Herein, inspired by the biomineralization from marine mollusks, a novel SP adhesive containing a macrocrosslinker system was developed, which showed high water-resistant bonding strength. This mineralization system was constructed by the in-situ crystallization of tannin acid (TA) regulated calcium carbonate (CaCO3), providing a reasonable pathway for controlling mineralization to fit different demands. Carboxyl-containing waterborne epoxy resin emulsion (WEU), a multifunctional crosslinking agent, was introduced into the adhesion system, which improved the crosslinking density and served as in situ mineralized sites for CaCO3 crystallization via –COOH groups as the mineral foothold. Benefiting from carboxyl catching, TA-regulation and epoxy ring-opening reaction, the mineralization of CaCO3 was controllable and uniformly dispersed, meanwhile, the obtained SP adhesive exhibited a great water-resistant bonding adhesion, reaching its maximum wet and boiling shear strength at 1.73 and 1.51 MPa, far higher than the standard of 0.7 MPa for type II plywood (GB/T 9846-2015) in Chinese standard. The strategy of constructing biomineralization system in SP adhesive mimics the feasible crystallization regulation, as well as represents a novel route to design high-performance plant protein adhesives for wood-based panel industries.