N/P-containing COF effectively improves flame retardancy of aminated chitosan-oxidized sucrose based wood adhesives

Inspired by the hard shells of crustaceans, this study utilizes chitosan extracted from their bodies as the raw material, aiming to enhance the mechanical properties and water resistance of the adhesive. However, chitosan exhibits poor solubility under neutral and alkaline conditions, leading to insufficient reaction and unsatisfactory results during the preparation of adhesives. In this study, aminated chitosan was designed and synthesized, which not only increased the number of active amino groups but also enhanced its water solubility. Subsequently, oxidized sucrose was prepared through the catalytic of sucrose by sucrase combined with air oxidation and then reacted with aminated chitosan to construct a multi-crosslinked network OS-ACS adhesive. Moreover, to impart flame-retardant properties to the adhesive, an N/P covalent organic framework (COF) was synthesized, and the synergistic effect of COF with OS-ACS adhesive was investigated. The study found that when the addition level of COF was 4%, the dry shear strength of the composite adhesive increased by 0.1 MPa (an increase of 7.81%), and the wet shear strength increased by 0.09 MPa (an increase of 7.76%). Most importantly, the limiting oxygen index (LOI) increased from 21.9% to 40.3%, achieving excellent flame-retardant properties.