Fully biobased flame-retardant lignin-incorporated chitosan-derived aerogel

• Fully biobased waterborne lignin-chitosan incorporated aerogel was fabricated. • The generated materials showed excellent performance as a flame retardant and thermal insulator. • The generated materials were biodegradable and sensitive to UV exposure. • The generated aerogel can be used as insulator for the construction industry. Biobased aerogels aim to address environmental and safety challenges, but their low strength and flammability still hinder their practical uses in the construction industry as thermal insulators. This study presents a high-performance aerogel (APK) synthesized from chitosan (CH) and phosphorylated kraft lignin (PK), designed to be strong, lightweight, thermally insulating, and flame-retardant. Using Taguchi optimization, the ideal fabrication conditions were identified, resulting in an aerogel with a porosity of 0.947 cm 3 /g, thermal conductivity of 0.35 W/mK, compression strength of 0.83 MPa, and Young’s modulus of 6.21 MPa. Structural and chemical analyses (FTIR, NMR, XPS, XRD) confirmed successful cross-linking and hybrid structures. APK aerogel was sensitive to UV exposure. The flame retardancy of APK was validated via LOI, UL-94, and smoke density tests. When APK was ignited, it degraded more intensely due to the presence of phosphorus elements, leading to a high-quality char layer that served as an effective barrier for flame progress. The APK aerogel combines excellent thermomechanical properties with biodegradability, making it a promising candidate for sustainable thermal insulation in the construction industry.