Bioinspired dual-crosslinking strategy for fabricating soy protein-based adhesives with excellent mechanical strength and antibacterial activity

Plant-derived biomass adhesives are increasingly in demand to replace traditional non-biodegradable petrochemical materials. However, the insufficient mechanical strengths and poor antibacterial activities of biomaterials severely limit their applicability. Inspired by the amphiphilic characteristics of mussel protein, a dual-crosslinking strategy is reported here for preparing soy meal (SM)-based adhesives with excellent adhesion and antibacterial properties. Specifically, castor oil containing abundant hydroxyl groups was used to prepare the cationic waterborne polyurethane (WPU) dispersion. Subsequently, the dynamic glue bridges were synthesized from the tannic acid-functionalized borax (TA@BA) complexes via multiple coordination bonds. Finally, the enhanced cross-linking network system was then constructed in the protein matrix based on the synergy of dynamic covalent bonds, electrostatic interactions, and hydrogen bonds. As a result, the wet strength of the resultant adhesive significantly increased by 154.77% compared to the SM adhesive. Additionally, the resultant adhesive exhibited remarkably enhanced thermal stability, flame retardancy, and water resistance. Based on the synergistic effect of the cationic WPU, polyphenol components, and borate groups, the SM/WPU/TA@BA adhesive exhibited desirable anti-mildew and antibacterial properties. This biomimetic dual-crosslinking design therefore provides a novel and facile strategy for the preparation of high-performance biopolymer adhesives used in the fields of biology and engineering.