Polysilazane-impregnated high-entropy LDH-grown cellulose nanofiber aerogels for flame-resistant thermal insulation

Lightweight flame-resistant thermal barriers are required for systems exposed to localized heat or flame, where low heat transfer and structural stability must be maintained simultaneously. However, conventional organic porous materials often suffer from flammability, limited thermal stability, and collapse of their pore structures under severe thermal exposure. In this study, a polysilazane-based porous composite was fabricated through the in situ growth of a high-entropy layered double hydroxide (HE-LDH) on a cellulose nanofiber aerogel (CNFA), followed by polysilazane (PSZ) impregnation and thermal curing. The interconnected CNFA framework provided a lightweight air-filled scaffold, while HE-LDH contributed endothermic heat absorption and the formation of inorganic residues during thermal decomposition. PSZ further reinforced the porous framework and generated a protective ceramic-containing residue upon heating. Structural and compositional analyses confirmed the incorporation of multimetal HE-LDH along the CNF network and the retention of the porous aerogel-derived structure after PSZ impregnation. The resulting PSZ/HE-LDH@CNFA composite exhibited a low thermal conductivity of 0.0761 W m^-1 K^-1 and a high residue yield of 83.98 wt% at 800 °C. It also showed reduced afterflame time and improved structural retention compared with the corresponding PSZ/CNFA samples under repeated flame exposure. In addition, the composite exhibited an electromagnetic shielding effectiveness of approximately 21.3 dB and maintained improved tensile properties relative to pure PSZ and PSZ/HE-LDH. These results demonstrate that integrating a porous CNFA scaffold, HE-LDH-derived inorganic protection, and ceramic-forming PSZ is an effective strategy for developing lightweight multifunctional thermal barrier composites with enhanced heat and flame resistance.