Thermal insulation, thermal degradation and fire resistance of enhanced poly(p-phenylene benzobisoxazole) nanofiber aerogels

Rapid industrialization has intensified global energy demand, highlighting the need for efficient thermal insulation in building heating and cooling systems. Although conventional polymer aerogels are effective thermal insulators, their inherent flammability and toxic smoke release severely limit their safe applications. In this work, we report a protonation-enabled, hydrogen-bond-assisted sol-gel strategy to fabricate intrinsically flame-retardant and thermally insulating poly(p-phenylene benzobisoxazole) (PBO) aerogels. Protonation converts micron-scale PBO fibers into well-dispersed PBO nanofibers (PNFs) that co-assemble with cellulose acetate via hydrogen bonding, enabling robust cellulose/PNF aerogels. This strategy effectively overcomes the gelation instability and structural fragility of pure PBO aerogels, resulting in improved dimensional stability and thermal insulation performance. The resulting aerogels exhibit low density (55 mg·cm −3 ), improved compressive strength (0.64 MPa), and excellent thermal insulation performance. Remarkably, despite the incorporation of flammable cellulose, the aerogels achieve a high limiting oxygen index (LOI, 45–52), demonstrating outstanding flame retardancy (UL 94 V-0) and structural stability. Cone calorimetry tests show that the Cellulose/PNF aerogel has a very low peak heat release rate (pHRR, 23.8 kW/m 2 ), total heat release (THR, 2.3 MJ/m 2 ), and total smoke release (TSR, 3.3 m 2 /m 2 ), indicating a low fire hazard. This work provides an effective approach for converting PBO fibers into flame-retardant PBO aerogels for advanced thermal insulation applications.