Facile construction strategy for intrinsically fire-safe and thermal-insulating bio-based chitosan aerogel

Bio-based aerogels have become a research hotspot in the emerging fields because of their remarkable biocompatibility, degradability and light weight, but their low strength and flammability limits their further application. In this study, chitosan (CS) containing flame retardant element was selected as the matrix, and a lightweight, flame retardant and thermal insulating CS aerogel was successfully prepared by the ion exchange between methylphosphonic acid (MPA) and acetic acid (HAc), and directional freeze-drying technology. The compressive strength and elastic modulus of CS@MPA aerogel were 15.2% and 8.5% higher than that of CS@HAc aerogel due to the 3D cross-linking structure between MPA and CS. Compared with CS@HAc aerogel, CA@MPA1.1 aerogel demonstrated excellent thermal insulating properties, and its thermal conductivity (25.46 mW/mK) was significantly lower than that of air (26.7 mW/mK). The introduction of MPA promoted the degradation and charring of CA@MPA aerogel, and the formation of high quality char layer efficiently exerted the barrier effect. Meanwhile, the phosphorus oxygen radicals and inert gases from the decomposition of CS@MPA aerogels effectively decreased the combustion intensity in gas phase. Therefore, the PHRR and THR of CS@MPA1.1 aerogels were decreased by 91.7% and 69.5% compared to CS@HAc aerogels. In summary, CS@MPA aerogel not only conforms to the current concept of sustainable development, but also possessed excellent thermal insulation, mechanical, and fire safety properties. It is expected to replace the traditional petrochemical-based materials, and shows broad application prospects in the fields of building insulation and energy storage.