Fabrication of strong and tough multifunctional soy protein adhesives via constructing catechol-iron ion fiber-reinforced hierarchical structure inspired by mussel byssus

It is challenging to prepare strong and tough soy protein (SP) adhesives with multifunction to replace formaldehyde-based adhesives. Herein, inspired by the catechol-iron ion (Fe3+) fiber-reinforced hierarchical structure of the mussel byssus, the tannic acid-functionalized cellulose nanofiber (CNF-TA) was used to mimic the fibrous core and catechol derivative, ferric chloride mimicked the Fe3+, and the SP mimicked the protein matrix in the mussel byssus to fabricate a multifunctional SP adhesive with high strength and toughness. Due to the construction of a stable fiber-reinforced covalent crosslinked network, along with the energy dissipation of sacrificial coordination and hydrogen bonds, the dry shear strength and fracture toughness increased by 130.6% and 247.1% to 2.49 MPa and 1.18 MJ m−2, respectively. Furthermore, the water-resistant wet shear strength rose by 264.1% to 1.42 MPa benefiting from the stable crosslinked structure. The Fe3+-induced organic-inorganic hybrid structure imparted the adhesive with outstanding flame retardance. Moreover, the adhesive also exhibited excellent antibacterial properties, mildew resistance, and oxidation resistance. This research offers a viable biomimetic method for fabricating multifunctional high-performance bio-based adhesives, hydrogels, and composites.