Development of flame‐retardant and heat‐resistant aramid nanofiber reinforced rigid polyurethane foam aerogel

Abstract This study addresses the growing demand for advanced flame‐retardant materials by developing an aramid nanofiber–reinforced rigid polyurethane foam (ANF–RPUF) composite through freeze‐drying. Four composite formulations, incorporating different ANF architectures, were designed to establish a hydrogen‐bonded semi‐interpenetrating network. The materials' flame resistance and thermal stability were thoroughly evaluated. Thermal performance was assessed through limiting oxygen index ( LOI ) tests, thermogravimetric analysis, and controlled combustion experiments, while morphological features were analyzed using scanning electron microscopy. The optimized ANF 2 –RPUF composite exhibited superior flame retardancy, achieving a 16.7% increase in LOI (reaching 25.8%) and a 13.6%–25.2% reduction in residue mass below 420°C compared to RPUF. Its unique aerogel structure effectively suppressed flame propagation and heat transfer, enabling rapid self‐extinguishing (<10 s) and a ninefold improvement in long‐term thermal resistance (180 s). A parallel development of a tetra‐copolymer‐modified system (T–ANF) further enhanced thermal stability, demonstrating a 13.6% increase in residue retention. This fireproof, heat‐preserving, and lightweight composite is an ideal candidate for next‐generation biological protective materials, offering robust defense against heat damage in applications across transportation, military, and aerospace sectors. Highlights Development of ANF–RPUF aerogels via freeze‐drying. Exhibit self‐extinguishing behavior and biological protection properties. Superior dimensional stability under ethanol flame exposure. Formation of semi‐interpenetrating networks and hydrogen bonds. Enhanced LOI values and thermal resistance with novel tetra‐copolymer.