Development of a Boiling Water Resistant, Flame Retardant,\nand Mildew Resistant Multifunctional Adhesive Cross-Linked with Chitosan\nand Biomass Polyester

Recently,\nthe investigation into sustainable adhesives for wood\ncomposites has garnered significant attention. However, a notable\nlimitation of biobased adhesives lies in their susceptibility to mildew\ngrowth and degradation. Chitosan, being the second most abundant biopolymer\non Earth, featuring a multitude of functional groups and inherently\npossessing antimicrobial properties, has emerged as a compelling candidate\nto address this challenge. In this study, we devised a novel biomass-derived\npolyester, which was subsequently cross-linked with chitosan and amino\ntrimethylene phosphonic acid in a streamlined one-pot process. This\ninnovative approach yielded a versatile adhesive that exhibits resistance\nto boiling water, flame retardancy, and mildew inhibition. The adhesive’s\nexceptional shear strength, when applied to materials such as wood,\nbamboo, and glass, stems from its robust cross-linking network comprising\nester, carbon–nitrogen double bonds, amides, and hydrogen bonds.\nNotably, when subjected to a 3 h immersion in boiling water, the adhesive\ndemonstrated a remarkable wet strength of 1.43 MPa on wood, vastly\nexceeding the minimum threshold of 0.7 MPa specified by the Chinese\nnational standard (GB/T 9846-2015) for plywood. Additionally, this\nadhesive imparted flame-retardant properties to wood composites, thereby\nbroadening the scope of multifunctional biobased adhesives applicable\nacross industries encompassing manufacturing, construction, and furniture\nsectors.