DOPO-modified HNTs reinforced silica aerogel composites: enhanced flame retardancy, thermal insulation, and environmental stability for silicone resins

A novel silica-based composite aerogel SA-DKH was synthesized via functionalization of alkali-treated halloysite nanotubes (HNTs-OH) with a DOPO (10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide)-derived silane coupling agent. SA-DKH exhibited exceptional thermal stability and high specific surface area (748.53–779.62 m 2 /g). In air atmosphere, SA-DKH3 demonstrated a 219.0 °C increase in initial decomposition temperature compared to SA-HNTs3 (composite aerogel synesis using 6 g 4.5 % HNTs-EtOH suspension). SA-DKH significantly enhanced thermal insulation, smoke suppression, and flame retardancy when incorporated into silicone resin composites. Notably, the total smoke production (TSP) of SSDKH4 (composite resin with 8 % SA-DKH) was reduced by 12.2 % (3.90 m 2 ) relative to SSHNTs4 (composite resin with 8 % SA-HNTs). Furthermore, SSDKH4 displayed ultralow thermal conductivity (0.10 W/m·K) and minimal water absorption (0.32 %), while maintaining robust resistance to acids, alkalis, and stains after 12 months of aging. The synergistic flame retardant mechanism involving gas-phase radical quenching by PO·/PO 2 · and condensed-phase char reinforcement via DOPO-HNTs interactions was systematically elucidated. This work provides a novel strategy for designing flame retardant and thermal insulation silicone resin composites.