|Chemical name||Ammonium polyphosphate|
|H phrases according to GHS Labelling||none|
Suppliers / trade names (pinfa member companies)
|Thor||Aflammit® PCI 202|
|Clariant||Exolit® AP 42x|
|Solid Thermoplastics||Polypropylene (PP)||Applicable|
|Themoplastic elastomers||Could be applied|
|Foams||Rubbers/Elastomers||Could be applied|
|PUR flexible foam||Applicable|
|PUR Rigid foam||Applicable|
|Textiles/Paints/Adhesives||Other textile fibers||Applicable|
|Latex/adhesives||Could be applied|
|Textile backcoating||Could be applied|
|Vinyl esters||Could be applied|
|Others||Paper/Wood||Could be applied|
Ammonium polyphosphate is an inorganic salt of polyphosphoric acid and ammonia containing both chains and possibly branching. The properties of ammonium polyphosphate depend on the number of monomers in each molecule and to a degree on how often it branches. Shorter chains (n < 100) are more water sensitive and less thermally stable than longer chains (n > 1000). Consequently, short polymer chains and oligomers (e.g. pyro-, tripoly-, and tetrapoly-) are more soluble and show decreasing solubility with increasing chain length.
Ammonium polyphosphate (APP) is used as a flame retardant in many applications such as paints and coatings, and in a variety of polymers: the most important ones are polyolefins, and particularly polypropylene, where APP is part of intumescent systems. Compounding with APP-based flame retardants in polypropylene is described in. Further applications are thermosets, where APP is used in unsaturated polyesters and gel coats (APP blends with synergists), epoxies and polyurethane castings (intumescent systems).
Ammonium polyphosphates as used as flame retardants in polymers have long chains and a specific crystallinity (Form II). They start to decompose at 240 °C to form ammonia and polyphosphoric acid. The phosphoric acid acts as a catalyst in the dehydration of carbon-based poly-alcohols, such as cellulose in wood. The phosphoric acid reacts with alcohol groups to form heat-unstable phosphate esters. The esters decompose to release carbon dioxide and regenerate the phosphoric acid catalyst. In the gas phase, the release of non-flammable carbon dioxide helps to dilute the oxygen of the air and flammable decomposition products of the material that is burning. In the condensed phase, the resultant carbonaceous char helps to shield the underlying polymer from attack by oxygen and radiant heat therefore preventing the pyrolysis of the substrate. Use as an intumescent is achieved when combined with polyalcohols such as pentaerythritol and melamine as expanding agent. The mechanisms of intumescence and the mode of action of APP are described in a series of publications. Due to its uncritical toxicological and environmental profile, ammonium polyphosphate has the potential to widely substitute halogen-containing flame retardants in a series of applications like flexible and rigid PUR-foam and thermoplastics.
1. Wikipedia entry https://en.wikipedia.org/wiki/Ammonium_polyphosphate
2. GreenScreen Assessment on GreenScreen® Store
5. US Environment Protection Agency Design for Environment projects on Alternatives to brominated Flame Retardants
6. US-EPA Provisional Peer-Reviewed Toxicity Values for Ammonium polyphosphate
7. US National Research Council (2000) Toxicological Risks of Selected Flame-Retardant Chemicals
8. Umweltbundesamt (2000): Erarbeitung von Bewertungsgrundlagen zur Substitution umweltrelevanter Flammschutzmittel (in German)