An easy-coating, versatile, and strong soy flour adhesive via a biomineralized structure combined with a biomimetic brush-like polymer

The development of a formaldehyde-free soy flour adhesive with good coating ability, mildew resistance, and flame retardancy while maintaining high bond strength, is urgent but presents a challenge. Inspired by the strong adhesive performance derived from the brush-like structure of gecko toes, a brush-like polymer with a catechol group was synthesized to improve the adhesive behavior of soy flour adhesives. Prompted by the high strength derived from the biomineralized structure of oysters, Ca3(PO4)2 was sedimented on soy protein and combined with the brush-like polymer to construct a biomineralized structure, which endowed the resultant adhesive with mildew resistance and flame retardancy while maintaining high bond strength. The dry and wet shear strengths of the bonded plywood by the resultant adhesive increased by 118.8 % and 750 % relative to those of the unmodified adhesive. Moreover, the resultant adhesive possessed outstanding coating performance, superior mildew resistance (no mildew for 7 d), and high toughness (4.05 J of the work of adhesion). The limiting oxygen index of the resultant adhesive was increased from 26.4 % to 30.1 %. Thus, developing a system combined with a bioinspired biomineralized strategy and a brush-like polymer can potentially offer a template for the fabrication of hydrogels, functionalized surfaces, and composite materials.