Preparation and Characterization of Flame‐Retardant Cellulose Aerogels Modified With In Situ Synthesized Borax and Zinc Borate

ABSTRACT As a natural polymer, cellulose offers advantages such as abundant raw material availability, natural degradability, and good biocompatibility. Cellulose‐based aerogel has outstanding thermal insulation properties, but the flammability of cellulose limits its application. Therefore, it is of great significance to give cellulose aerogel flame retardancy. This study presents a simplified and efficient method for preparing flame‐retardant cellulose aerogels through the dissolution of cellulose in a NaOH, ZnO, and urea solution, followed by freeze‐drying and in situ modification with boric acid. The resulting aerogels were extensively characterized to evaluate their morphology, mechanical performance, and flame‐retardant properties. The incorporation of urea and boric acid significantly enhanced flame retardancy, achieving Limiting Oxygen Index (LOI) values exceeding 80% and V‐0 ratings in the UL‐94 vertical burning test. Additionally, the modified aerogels demonstrated superior self‐extinguishing capabilities and improved mechanical strength. Thermal degradation analysis using TG‐FTIR revealed that the formation of a protective glassy layer of borax, along with the release of CO 2 and NH 3 gases, effectively suppressed combustion and delayed cellulose pyrolysis. Overall, this study demonstrates that the in situ formation of flame retardants in cellulose aerogels can markedly enhance fire resistance while preserving structural integrity, offering a promising approach for developing high‐performance materials.