Ammonium Polyphosphate

Brief Overview
Ammonium Polyphosphate (APP) is a fully water-soluble phosphate widely employed in plant applications. It is an ammonia and polyphosphoric acid-derived inorganic salt with a variable and branched chain length. Short-chain APP is more water-sensitive and less stable than longer-chain varieties. Two primary types exist: Crystal Phase 1 APP with a linear structure and Crystal Phase 11 APP with a branched structure. APP is environmentally safe and non-toxic, finding use as a flame retardant that, due to its distinctive intumescence mechanism, does not produce smoke.
Manufacturing Process
APP is produced through the reaction of concentrated phosphoric acid with ammonia. However, impurities containing iron and aluminum dissolve in concentrated phosphoric acid, leading to the formation of gelatinous precipitates in APP. In industrial settings, APP is synthesized through polycondensation involving monoammonium phosphate and urea.