Cooperative Gas‐Condensed Phase Flame Retardancy and High‐Performance Enhancement of Rigid Polyurethane Foam via <scp>DOPO</scp> / <scp>MMT</scp> Hybrid Modification

ABSTRACT Rigid polyurethane foam (RPUF) was widely used but suffered from high flammability and toxic smoke release, while traditional halogen‐based flame retardants posed environmental hazards. To address this, a gas‐condensed phase cooperative flame‐retardant system was constructed by compounding DOPO with montmorillonite (MMT) via an optimized one‐step all‐aqueous foaming process, a novel approach that balanced environmental friendliness and performance. Modified RPUF with 3 wt% MMT and varied DOPO contents were prepared. The sample with 8 wt% DOPO (DOPO8) showed optimal performance: it achieved a limiting oxygen index (LOI) of 22.8% with a UL‐94 V‐0 rating, a 66.40% lower peak heat release rate, and a 75.13% reduced total smoke production compared to DOPO0 at 25 kW/m 2 . It also had a 45.04% char residue at 800°C and a pyrolysis activation energy of 207.45 kJ/mol, along with the best compressive property and a peak energy absorption efficiency of 48.20. The enhancement originated from the cooperative effect between DOPO's gas‐phase radical quenching and MMT's condensed‐phase barrier. This study provided a feasible strategy for high‐performance, eco‐friendly flame‐retardant RPUF.