Superior intrinsic flame-retardant phosphorylated chitosan aerogel as fully sustainable thermal insulation bio-based material

Owing to the arising environmental pollution and energy-related challenges, the utilization of renewable polysaccharides such as chitosan (CS) in the preparation of biodegradable aerogel heat-insulation materials represents a growing interest. In this study, a simple and low-cost route was proposed to synthesize a phosphorylated chitosan (PCS) with a high substitution degree of phosphate groups in a homogeneous H3PO4/acetic acid solution, and its chemical structure was confirmed using FT–IR spectroscopy, nuclear magnetic resonance, and X–ray photoelectron spectroscopy. An outstanding intrinsic flame-retardant PCS aerogel was directly fabricated via freeze-thawing and freeze-drying process. Remarkably, limited oxygen index values of the PCS aerogels increased to above 80%, and their UL–94 test results achieved V–0 rating. The peak heat release rate and total heat release rate values of PCS-4 aerogel significantly decreased by 91.2% and 73.0% compared with those of chitosan aerogel, respectively. The bio-based PCS aerogel with superior intrinsic flame retardancy, low thermal conductivity, and excellent hydrophobicity shows promise as new sustainable flame-retardant heat-insulation material.