Intercalated Organically Modified Montmorillonite for Flame Retardancy of Aramid Reinforced Epoxy Resin Composites

ABSTRACT The flammability of the epoxy matrix limits the widespread application of aramid fiber‐reinforced epoxy resin (AF/EP) composites, while adding traditional flame retardants compromises their mechanical properties. To address this challenge, a novel silicon‐phosphorus hybrid nano‐flame retardant (ODOPB‐@MMT) was successfully constructed by intercalating 10‐(2,5‐Dihydroxyphenyl)‐10‐hydrogen‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (ODOPB) into organically modified montmorillonite (@MMT). This design leverages the synergistic effect between the phosphorus and silicon components to enhance flame retardancy while preserving the material's mechanical integrity. The results indicated that the obtained AF/EP composites achieved a UL‐94 V‐0 rating and a high Limiting Oxygen Index (LOI) of 33.5% with only a 4 wt% ODOPB‐@MMT loading. Remarkably, the composites retained 98.3% of their original tensile strength, demonstrating minimal compromise on mechanical properties. During the combustion process, the peak heat release rate (p‐HRR) and total heat release (THR) decreased by 48.4% and 27.5%, indicating a significant reduction in fire hazards. The flame‐retardant mechanism analysis revealed the formation of a more stable and graphitized char layer in the condensed phase, alongside gas‐phase radical quenching. This work provides an effective strategy for developing high‐performance AF/EP composites with superior and balanced fire safety and mechanical properties.