High‐efficiencyammonium polyphosphate intumescent encapsulated polypropylene flame retardant

Abstract The flame retardant polypropylene containing the micro‐envelope core‐shell structure flame retardant, which encapsulated ammonium polyphosphate into melamine‐formaldehyde resin and sodium silicate through in situ polymerization was prepared with polyamide 6, added as a carbon‐forming agent. The composition of ammonium polyphosphate, encapsulated ammonium polyphosphate with melamine‐formaldehyde resin and the micro‐envelope core‐shell structure flame retardant were characterized. The fire safety and thermal stability were investigated and showed an improvement including limiting oxygen index, thermogravimetric analysis, vertical burning tests, and microscale combustion calorimeter. The burned compounds were also studied to confirm the burning mechanism. The results showed the flame retardant performance had been greatly improved, while polyamide 6 had better char‐forming effect. Besides, the water solubility of flame retardants and their influence on the mechanical properties of polypropylene were also investigated. The results on the effects of additives demonstrated a high efficiency flame retardant to polypropylene. A core‐shell flame retardant that sodium silicate and melamine‐formaldehyde resin‐coated ammonium polyphosphate had been constructed. The effect of the built flame retardant system on the combustion performance of polypropylene was studied from the mechanism and performance. The LOI of the most flame retardant polypropylene reached 28.6%, and UL‐94 reached the V‐0 level.