Facile fabrication of a starch-based wood adhesive showcasing water resistance, flame retardancy, and antibacterial properties via a dual crosslinking strategy

The demand for non-toxic, environmentally friendly, easily processable, water-resistant, flame-retardant and antimicrobial adhesives in the wood processing industry is becoming increasingly urgent. Few adhesives can possess these functions altogether while being synthesized easily. This paper presents a one-pot process utilizing corn starch, sodium hypochlorite, itaconic acid, and borax to synthesize a starch-based adhesive with dual crosslinking. Initial crosslinking takes place between the carboxyl groups of itaconic acid and hydroxyl groups on oxidized starch due to the formation of ester bonds. Secondary crosslinking by borate ester bonds occurs between starch hydroxyl groups and boric acid. The entire reaction process is environmentally benign, generating no waste, with all reactants converted into final products, aligning with "green" chemistry principles. When used to bond wooden boards, this adhesive achieved a dry shear strength of 5.34 +/- 0.24 MPa, and a wet shear strength of 1.22 +/- 0.06 MPa after soaking in water. Additionally, this starch-based adhesive exhibited antibacterial properties against Escherichia coli (ATCC 8739) and Staphylococcus aureus. Moreover, with borax incorporated, the adhesive demonstrated flame-retardancy. The limiting oxygen index for bonded wooden boards was 30.9 %, qualifying it as a flame-retardant material. These multiple functions render it promising for applications in the wood processing industry.