In Situ Synthesis of Hydroxyapatite Nanowires on Para-Aramid Microgels for Fire-Resistant Insulating Films

Although poly(p-phenylene terephthalamide) (PPTA) is extensively employed in electrical insulating composites, developing materials that simultaneously deliver superior electrical insulation and flame-retardant performance remains a significant challenge. In this study, a polymerization-induced self-assembly (PISA) strategy was implemented to achieve the in situ self-assembly of para-aramid nanofibers (PANFs) under mild conditions. This approach enabled the direct formation of PANFs during polymerization, eliminating the need for postpolymerization fiber processing. Furthermore, an in situ compositing strategy was proposed, wherein hydroxyapatite (HAP) nanowires, prepared via hydrothermal synthesis, were grown within the three-dimensional network of PANFs, followed by fabrication of hydroxyapatite/para-aramid (HAP/PANF) composite films via vacuum-assisted filtration. Notably, the composite films exhibited exceptional flame-retardant characteristics, achieving self-extinguishment within 5 s and a high electrical breakdown strength of 43.9 kV/mm─superior to conventional polymer-based insulators. The films also demonstrate remarkable mechanical flexibility with a tensile strength 34 times higher than that of pure HAP paper (54.31 vs 1.57 MPa), effectively overcoming the inherent brittleness of HAP-based materials. This work provides a scalable route for developing flexible, flame-retardant insulating materials with potential applications in wearable electronics and high-voltage equipment.