Preparation of Flame Retardant PPO / PS Foams via Supercritical CO 2 Confinement Foaming and Synchronous Bonding Technology

ABSTRACT Polyphenylene oxide (PPO) foams possess outstanding flame retardancy and high thermal stability characteristics, which have emerged as a promising material for lightweight and complex structural components. However, the preparation of high accuracy PPO foams with profile geometries remains a significant challenge. In this work, an integrated strategy combining supercritical CO 2 confinement foaming with inter‐bead bonding is proposed to fabricate precise and complex irregular PPO cellular structures without further adhesive processes. Polystyrene (PS) was applied to improve processing fluidity and foaming behavior, while triphenyl phosphate (TPP) enhanced flame retardancy. A series of composite foams with PPO contents of 10–50 wt% were successfully prepared, and their density ranges from 0.06–0.12 g/cm 3 . Uniform cellular structures and dense interfacial bonding layers were found, indicating excellent stability and strong inter‐bead adhesion. Besides, mechanical and flame‐retardant performances were evaluated through impact, compression, and cone calorimetry tests. The PPO/PS composite foams exhibited self‐extinguishing behavior, low smoke emission, and reduced heat release, demonstrating effective suppression of thermal runaway hazards. This research has provided a feasible approach for high‐precision foaming and molding of engineering plastic foams for advanced safety applications.