Ammonium polyphosphate

Ammonium polyphosphate (CAS 68333-79-9), commonly abbreviated as APP, is an inorganic salt used primarily as a flame retardant and intumescent agent. Also approved as E545 for certain applications.

Where is Ammonium polyphosphate used?

• Plastics and polymer compounding: incorporated into polyolefins, polyurethanes, and epoxy systems to meet UL 94 and other fire safety standards without halogenated additives
• Intumescent coatings and fireproofing paints for steel structures: acid source in the intumescent system, activating expansion under fire conditions
• Textile and paper: APP-based treatments to achieve flame-retardant certification for technical fabrics, upholstery, and packaging materials
• Agriculture: concentrated phosphorus and nitrogen fertilizer source, applied in liquid fertilizer blends and foliar formulations
• Under heat it releases ammonia and phosphoric acid, forming a protective char layer that limits flame spread and combustion.
• In polyolefin-based wire and cable insulation it provides the flame retardancy needed to prevent fire hazards in electrical installations.
• Used as a fire-retardant impregnation for wood used in construction.
• In the rubber industry it is used in hoses, belts and seals requiring enhanced flame retardancy, especially for industrial and automotive applications.
• Ammonium polyphosphate-based intumescent flame retardants are effective in polypropylene, polyethylene, and ethylene-vinyl acetate copolymer.

Good to know: Phase II is preferred for most flame retardant applications due to its thermal stability. Microencapsulated variants offer improved compatibility in polymer matrices.

Formulation notes

• APP products used in fertilizer formulations may differ in physical form, solubility and nutrient analysis from flame retardant powders; fertilizer quality specifications must be requested separately.

Typical specification

• Average particle size (D50) is approximately 15–20 μm.
• Phosphorus content is at least 31.0%.
• Nitrogen content is at least 14.0%.
• Water solubility is at most 0.5 g/100 ml of water at 25°C.

Regulatory status

• Registered under EU REACH in 2010.

Storage, packaging and handling

• Store in a cool, dry warehouse in sealed containers, protected from moisture, avoiding direct sunlight and keeping away from strong acids and alkalis.

Frequently asked questions about Ammonium polyphosphate

What are the differences between Type I and Type II ammonium polyphosphate?

Crystalline form I has a short linear chain (n<100), is more sensitive to water (hydrolysis) and starts to decompose above 150 °C. Crystalline form II has a high degree of polymerization (n>1000), a cross-linked (branched) structure and very low water solubility (<0.1 g/100 mL).

What is the decomposition temperature of ammonium polyphosphate?

Decomposition temperature is approximately 275°C or higher, depending on grade and test method.

How is ammonium polyphosphate used in intumescent systems?

Intumescent action is obtained when ammonium polyphosphate is combined with polyols such as pentaerythritol and melamine as blowing agents. Coupling agents such as silane, siloxane, and aluminate can be added to increase flame retardancy, improve hygroscopicity, and enhance toughness and heat resistance.

Technical content is compiled and updated by the SoleChem product team from public technical sources; the certificate of analysis (COA) governs product-specific specifications.