Preparation of microencapsulated nitrogen‑phosphorus‑silicon flame retardant and its effect on high impact polystyrene flame retardancy

High-impact polystyrene is a widely-used construction material due to its superior comprehensive performance, but its susceptibility to fire can lead to the production of toxic and harmful gases. To address this issue, a novel, environmentally-friendly microencapsulated nitrogen‑phosphorus‑silicon flame retardant for high-impact polystyrene was prepared in this study. SiO₂, produced by the hydrolysis condensation of tetraethyl orthosilicate, was used as the wall material, while melamine cyanurate was used as the core material. The microencapsulated nitrogen‑phosphorus‑silicon flame retardant was compounded with high-impact polystyrene and aluminum hypophosphite, and the composites were evaluated for their performance in terms of fire behavior, thermal stability, and morphology of the resulting carbon residues. When melamine cyanurate@SiO₂ and aluminum hypophosphite were added in a 1:4 ratio, the UL-94 rating of L5 reached V-0, and the LOI value increased to 27.0%. The conical calorimeter test results showed that the peak heat release rate of the L5 composite decreased by 78.7% compared to pure HIPS, and the corresponding total heat release rate decreased by 45.7%. Thermogravimetric analysis results illustrated that the amount of carbon residue increased significantly, from 2.46% to 22.26% of pure high-impact polystyrene. These findings indicate that the prepared microencapsulated nitrogen‑phosphorus‑silicon flame retardant is multifunctional, highly efficient, and can be applied to high-impact polystyrene.