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

Recently, the investigation into sustainable adhesives for wood composites has garnered significant attention. However, a notable limitation of biobased adhesives lies in their susceptibility to mildew growth and degradation. Chitosan, being the second most abundant biopolymer on Earth, featuring a multitude of functional groups and inherently possessing antimicrobial properties, has emerged as a compelling candidate to address this challenge. In this study, we devised a novel biomass-derived polyester, which was subsequently cross-linked with chitosan and amino trimethylene phosphonic acid in a streamlined one-pot process. This innovative approach yielded a versatile adhesive that exhibits resistance to boiling water, flame retardancy, and mildew inhibition. The adhesive’s exceptional shear strength, when applied to materials such as wood, bamboo, and glass, stems from its robust cross-linking network comprising ester, carbon–nitrogen double bonds, amides, and hydrogen bonds. Notably, when subjected to a 3 h immersion in boiling water, the adhesive demonstrated a remarkable wet strength of 1.43 MPa on wood, vastly exceeding the minimum threshold of 0.7 MPa specified by the Chinese national standard (GB/T 9846-2015) for plywood. Additionally, this adhesive imparted flame-retardant properties to wood composites, thereby broadening the scope of multifunctional biobased adhesives applicable across industries encompassing manufacturing, construction, and furniture sectors.