Facile preparation of flame-retardant phosphorylated chitin nanocrystals with reactive deep eutectic solvent based on...

Nanochitin, a biomass resource, is well-known for its abundance, renewability, environmental friendliness, and nanoscale dimensions, which have garnered significant interest from researchers. However, it is a highly flammable polysaccharide, which limits its applications, especially in areas requiring high thermal stability and low combustibility. In this study, urea phosphate/urea was used as a reactive deep eutectic solvent (DES) to prepare phosphorylated chitin. The impact of reaction temperature on the phosphorous content of the products was investigated. After subsequent ultrasonic treatment, phosphorylated chitin nanocrystal (PChNC) with an average length and width ranging from 166.2 to 185.6 nm and 6.0 to 13.4 nm, respectively, was obtained. Compared to unmodified chitin, PChNC exhibited a 73.2 % reduction in peak heat release rate (PHRR) and an 80.3 % reduction in total heat release (THR). Furthermore, the prepared PChNC-based films demonstrated excellent self-extinguishing behavior, high transparency (with visible light transmittance over 80 %), and robust mechanical properties. This research provides a new approach to the development of functionalized chitin and may promote broader interdisciplinary research into chitin in fields such as packaging, insulation, and flame-retardant materials.