Ammonium polyphosphate (APP) is an inorganic polymer flame retardant with the chemical formula (NH4PO3)n and CAS number 68333-79-9. At room temperature, it appears as a white powder with a polymerization degree typically exceeding 1000. Its thermal decomposition temperature is ≥280°C, density is approximately 1.9 g/cm3, phosphorus content is 30%-32%, nitrogen content is 14%-16%, and pH ranges from 5.5 to 7.0. It features low water solubility, high thermal stability, and halogen-free environmental properties. During combustion, it dehydrates to form polyphosphoric acid, catalyzing the formation of an expanded carbon layer that isolates oxygen and the fire source, while releasing non-combustible gases to achieve flame retardancy. It produces low smoke and does not generate corrosive gases.

This flame retardant was developed by Monsanto in the United States in 1965 and gradually applied in fire-resistant coatings, polyolefin plastics, polyurethane foams, and other fields. Domestic large-scale production began in the early 21st century, and after 2010, microencapsulation technology improved its compatibility with polymer materials^[2]. The group standard issued in 2023 further standardized the physicochemical indicators of modified products (such as melamine-modified APP), promoting their adaptability in applications like fire-resistant coatings and cable materials.

Chemical Indicators

• Molecular Formula: (NH?PO?)?
• Phosphorus Pentoxide (P?O?) Content: ≥68% (first-grade) to >72% (some products) ?
• Nitrogen (N) Content: ≥13% (first-grade) to >18% ?
• Polymerization Degree: >1500 (high polymerization degree products) or ≥50 (some products) ?