Design of tough, strong and recyclable plant protein-based adhesive via dynamic covalent crosslinking chemistry

Conventional covalent crosslinked protein adhesives are brittle and cannot be reprocessed effectively, which restricts their practical application and limits the recyclability of wood-based panels. Inspired by biological cartilage and mussels, a tough, strong, and recyclable soybean protein isolate (SPI)-based adhesive, SPI/[email protected], was designed in this study by co-assembly of mica and SPI via dynamic boron-nitrogen (B-N) coordinated catechol-derived boronic ester (B-O) interfacial bonding. The dynamic covalent B-O, imine, and hydrogen bonds significantly improve the cohesive strength and energy dissipation capacity of SPI/[email protected] adhesive for high mechanical strength and toughness. The maximum wet shear strength and adhesion of SPI/[email protected] adhesive bonded plywood reach 1.05 MPa and 518.8 MJ, respectively, at increases of 94.4 % and 601.2 % over the original SPI adhesive. More importantly, we achieved a breakthrough in the recyclability of protein-based wood adhesives. Due to the synergistic triple dynamic mechanism and B-N coordination depolymerization of B-O bonds, second-generation particleboard prepared by recycling via hot-pressing and solvent-assisted repolymerization showed a rupture modulus of 12.1 MPa; to this effect, we fabricated a next-generation sustainable, reusable adhesive. The SPI/[email protected] adhesive showed excellent mold resistance (50-day shelf life) and flame retardancy (LOI = 29.7 %). Further, the cost of SPI/[email protected] adhesive is equivalent to the price of the phenol formaldehyde resin adhesive commonly used for wood-based panel. The proposed design strategy may promote the functional modification of composites and provide workable guidance for constructing robust, recyclable protein-based materials.