Fabrication of a chitosan-based adhesive with high bonding performance and superior flame retardancy via embedding carbon dots to enhance its cohesion.

Traditional adhesives often contain petroleum-based compounds, which release harmful substances such as formaldehyde in the curing process, while traditional flame retardants release harmful substances are also characterized by toxic substance emission such as halogens or heavy metals in the combustion process, potentially threatening human health and the living environment. Therefore, in order to promote wood composites towards high performance, high safety and sustainability, it is of vital importance to derive biomass-based adhesives from renewable resources and develop environmentally friendly and highly efficient flame retardants. In this work, a novel carbon dots (CDs) synergistic biomass-based flame retardant adhesive was developed. Pyrogallol (PG) derived from gallnut and ammonium polyphosphate (APP) were carbonized into PG&APP-CDs, which then reacted with epichlorohydrin to obtain PG&APP-CDs-ECH. The as-prepared PG&APP-CDs-ECH further reacted with chitosan to ultimately form covalent crosslinked networks (PG&APP-CDs-CS adhesive). The PG&APP-CDs-CS plywood possessed a dry bonding strength of approximately 3.19 ± 0.12 MPa at a hot-pressing temperature of 140 °C, meeting the GB/T 17657-2022 standard. The dual flame-retardant effect of PG&APP-CDs-CS adhesive and flame-retardant wood resulted in a limiting oxygen index (LOI) of 37.9 % for the flame-retardant plywood. The total heat release rate was reduced by 40.45 % compared to pure chitosan plywood. This work introduced a simple and environmentally friendly method for fabricating flame-retardant wood composites applicable in furniture manufacturing.