Ammonium Polyphosphate is an inorganic polymeric salt composed of repeating ammonium phosphate units. Unlike simple orthophosphates, APP chains can number in the hundreds to thousands of repeat units, giving rise to significantly different physical and chemical behavior depending on chain length and branching. It is non-toxic, environmentally friendly, low-smoke, and halogen-free.
Contact The Chemical Company to learn more about our chemical supply and distribution solutions for Ammonium Polyphosphate (APP). We supply Phase I, Phase II, and surface-treated grades for flame retardant, agricultural, and specialty applications.
The Chemical Company’s Ammonium Polyphosphate (APP) is a white, fine crystalline powder and one of the most effective non-halogenated, inorganic flame retardants available today. Chemically, APP is an inorganic salt of polyphosphoric acid and ammonia, represented by the repeating formula (NH4PO3)n, where each monomer unit consists of a phosphorus atom bonded to three oxygens and one ammonium cation, with two free bonds enabling polymerization into linear or branched chains. Its degree of polymerization (n) can range from fewer than 20 to greater than 1,000, and this variable chain length is the primary factor governing its water solubility, thermal stability, and suitability for different end-use applications.
APP is valued across a wide range of industries — from construction and transportation to agriculture and textiles — for its combination of high phosphorus and nitrogen content, low toxicity, low smoke generation, and halogen-free profile. It is the principal acid source in intumescent flame retardant systems, where it works synergistically with a carbon source (char-forming agent) and a blowing agent to generate an expanding, insulating char layer when exposed to fire. TCC supplies APP in both Phase I (water-soluble, short-chain) and Phase II (water-insoluble, long-chain, cross-linked) grades, as well as surface-treated variants for improved compatibility with polymers.
The intumescent flame retardant mechanism of APP Phase II involves a two-stage thermal response: above approximately 300°C, APP decomposes to release ammonia gas (acting as a blowing agent) and polyphosphoric acid, which catalyzes the dehydration and char formation of co-present polyols or carbon-rich compounds. The resulting multicellular carbonaceous foam char acts as a physical barrier that insulates the substrate from heat and oxygen, substantially slowing flame spread without generating toxic halogenated combustion gases.
In agriculture, short-chain APP (n ≤ 20) is used as a high-efficiency liquid nitrogen-phosphorus fertilizer, typically formulated as a 10-34-0 or 11-37-0 N-P2O5-K2O blend. Unlike orthophosphate fertilizers, polyphosphate fertilizers remain crystal-free over a wide temperature range, store well for extended periods, and are highly effective carriers for micronutrient blending. They also provide enhanced phosphorus availability in high calcium carbonate soils due to the sequestering action of the polyphosphate chain.
| Property | Value |
| Molecular Formula | (NH4PO3)n |
| Repeating Unit Mol. Weight | 97.03 g/mol per monomer unit |
| Appearance | White fine crystalline powder |
| Odor | Odorless |
| Density | ~1.9 g/cm³ (Phase II) |
| Phase I (n < 100) | Short-chain, linear; water-soluble; decomposes >150°C |
| Phase II (n > 1000) | Long-chain, cross-linked; water-insoluble; decomposes >300°C |
| Thermal Decomposition | Phase I: >150°C; Phase II: >300°C (releases NH3 + polyphosphoric acid) |
| Solubility (Phase I) | >150 g/100 mL at 25°C |
| Solubility (Phase II) | <0.1 g/100 mL at 25°C |
| Solubility (Industrial APP) | ~3.0 g/100 mL at 25°C |
| Phosphorus Content (P2O5) | ~72.5% (as P2O5) for Phase II |
| Nitrogen Content | ~14–15% by weight |
| pH (10% aqueous slurry) | ~5–7 (near neutral) |
| Average Particle Size | Typically 10–25 μm (standard); finer grades available |
| Available Grades | Phase I, Phase II, melamine-coated, silicone-coated, microencapsulated |
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