Application Inventory of Ammonium Polyphosphate Flame Retardants in Thermoplastic Polymers

Application Inventory of Ammonium Polyphosphate Flame Retardants in Thermoplastic Polymers

Ammonium polyphosphate (APP) flame retardants have gained significant attention due to their excellent thermal stability, low toxicity, and compatibility with thermoplastics. APP flame retardants find extensive utilization in various thermoplastic polymers, such as polyethylene, polypropylene, acrylonitrile-butadiene-styrene, and polystyrene, etc. Herein, Alfa Chemistry takes stock of the applications of APP flame retardants in various thermoplastic polymers.

APP Flame Retardant for Polyethylene

Polyethylene materials treated with APP flame retardants are commonly used in various industries, including construction, automotive, electrical, and packaging. Some typical applications include cable insulation, wire coatings, pipes, films, and sheets. Among wood flourpolyethylene composites, the composite with 10 wt% APP as a flame retardant showed the best flame retardant performance, with the highest increase in limiting oxygen index (LOI) of about 29%.

LOI for wood flour-polyethylene composites with flame retardantLOI for wood flour-polyethylene composites with flame retardant. [1]

APP Flame Retardant for Polypropylene

APP is typically added to polypropylene through compounding or directly during the polymerization process. It enhances the fire resistance of PP by reducing flammability, lowering the heat release rate, and inhibiting the formation of toxic smoke and gases during combustion.

APP Flame Retardant for Polystyrene

APP is a commonly used flame retardant for polystyrene (PS). The chemical interaction between APP and MgAl layered double hydroxide (LDH) on PS composites was explored. The results show that the introduction of APP/MgAl LDH improves the dispersion, flammability and thermal stability of PS composites, but also adversely affects its mechanical properties.

TEM micrograph of PS added with MgAl LDH/APP.TEM micrograph of PS added with MgAl LDH/APP. [1]

APP Flame Retardant for Poly(methyl methacrylate)

When APP is incorporated into poly(methyl methacrylate) (PMMA), it acts as a flame retardant by releasing water when exposed to heat or flame. The released water vaporizes, diluting the concentration of flammable gases and reducing their ability to support combustion. Additionally, the APP decomposes to form phosphoric acid, which reacts with the polymer to produce a char layer.

APP Flame Retardant for Poly(ethylene terephthalate)

In poly(ethylene terephthalate) (PET) composite materials, as the APP content in the composite material increases, the LOI value gradually increases. The mode of action of APP as a flame retardant for PET involves multiple mechanisms.

  • The phosphorus present in APP reacts with PET during the thermal degradation process to form stable phosphorus-containing compounds. The compound helps inhibit the release of flammable gases and the formation of flammable atmospheres.
  • The polymeric nature of APP enables it to form a protective carbon layer when heated. This charcoal layer acts as an insulator, maintaining the material's structural integrity and preventing the spread of flames.
  • APP will also release ammonia when heated, diluting the oxygen concentration near the flame and further inhibiting combustion.

LOI of PET composites added with APP and coal.LOI of PET composites added with APP and coal. [1]

APP Flame Retardant for Engineering Thermoplastics

APP is a commonly used flame retardant additive for engineering thermoplastics, such as acrylonitrile-butadiene-styrene (ABS), polyamide, poly(vinyl alcohol) , etc.


  1. Lim, Kien-Sin, et al. et al. Composites Part B: Engineering, 2016, 84, 155-174.
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