hosphorus based flame retardants have the characteristics of non toxicity, halogen-free, smoke suppression, good flame retardant effect, and environmental friendliness. Ammonium polyphosphate APP, as a common phosphorus based flame retardant, has received widespread attention from researchers. At present, ammonium polyphosphate has been widely used in polymer materials such as polypropylene (PP), epoxy resin (EP), and polyurethane (PU).
Introduction to Ammonium Polyphosphate
Ammonium polyphosphate, abbreviated as APP, is also known as condensed ammonium phosphate or polyphosphate. It was first synthesized in 1857 from P2O5 and NH3. Its molecular formula is (NH4)n+2PnO3n+1, where n represents the degree of polymerization. When n is sufficiently large, its chemical formula can be written as (NH4PO3)n.
Generally, APP with different degrees of polymerization has different physicochemical properties. The larger the degree of polymerization (n), the lower the water solubility of APP. If n > 20, it is sparingly soluble in water; if n < 20, it is readily soluble in water.
APP has a high nitrogen and phosphorus content, making it suitable for applications in fertilizers and flame retardants. The degree of polymerization determines the application of APP. Oligomeric water-soluble APP is often used as a high-efficiency fertilizer, while high-polymer APP is a commonly used halogen-free environmentally friendly flame retardant.
APP exists in two solid forms: crystalline and amorphous (glassy). Crystalline APP is a white powder, relatively stable at room temperature, and odorless. Currently, there are six known crystalline forms of APP (Types I, II, III, IV, V, and VI). Types I and II are the most widely used. Type I has a lower degree of polymerization, smaller molecular weight, and higher solubility, and is often used in the preparation of fire-retardant coatings and fertilizers. Type II has a high degree of polymerization, low water solubility, stable structure, and high decomposition temperature, and is often used in flame retardant applications.
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Post time: Aug-14-2026
