Synergistic effect of expandable graphite and melamine phosphate on flame‐retardant polystyrene

The halogen‐free flame‐retardant polystyrene (PS) composites containing expandable graphite (EG) and melamine phosphate (MP) were prepared successfully, and the thermal degradation behavior and fire performance were investigated by various measurements. The experimental results show that EG and MP have a synergistic effect on flame‐retardant PS, which can catalyze the char formation from PS. PS/MP/EG (1:2) composite achieves limited oxygen index value of 28.0% and UL‐94V‐0 (1.6 mm) rate. The mass retention at high temperature (800 °C) under air atmosphere of PS composites have a large increase by the introduction of EG and MP. Microscale combustion calorimeter (MCC) and cone calorimetric analysis indicate that the heat release rate and total heat release of PS/MP/EG (1:2) composite are reduced significantly, because the formed thick char layer has a notable barrier property. The study on the char residue of PS/MP/EG (1:2) composite by X‐ray photoelectron spectroscopy (XPS) analysis confirms the formation of the stable structures containing POC. Furthermore, the mechanical properties of PS composites were also investigated; compared with neat PS, the addition of flame retardants leads to the decrease of tensile strength and flexural strength, but the impact strength of PS/MP/EG (1:2) has increased by 44.2%.