APP
Ammonium polyphosphate commercially produced by Clariant, (former business area of Hoechst AG), Budenheim and other sources is an inorganic salt of polyphosphoric acid and ammonia
containing both chains and possibly branching. Its chemical formula is [NH4 PO3]n(OH)2 showing that each monomer consists of an orthophosphate radical of a phosphorus atom with three
oxygens and one negative charge neutralized by an ammonium cation leaving two bonds free to polymerize. In the branched cases some monomers are missing the ammonium anion and instead
link to three other monomers.
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),[1] but short polymer chains (e.g. pyro-, tripoly-, and tetrapoly-) are more soluble and show increasing solubility with increasing chain length.
Ammonium polyphosphate can be prepared by reacting concentrated phosphoric acid with ammonia.
However, iron and aluminum impurities, soluble in concentrated phosphoric acid, form gelatinous precipitates or “sludges” in ammonium polyphosphate at pH between 5 and 7.
Other metal impurities such as copper, chromium, magnesium, and zinc form granular precipitates.
However, depending on the degree of polymerization, ammonium polyphosphate can act as a chelating agent to keep certain metal ions dissolved in solution.
Ammonium polyphosphate is used as a food additive, emulsifier, (E number: E545) and as a fertilizer.
Ammonium polyphosphate (APP) is also 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.[6] 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).
APP is also applied to flame retard polyurethane foams.
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 phosphoric
acid. The phosphoric acid acts as an acid 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.
Use as an intumescent is achieved when combined with starch-based materials such as pentaerythritol and melamine as expanding agents.
The mechanisms of intumescence and the mode of action of APP are described in a series of publications.
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.
Soluble ammonium polyphosphate (SAPP) is employed to prepare flame retardant semirigid polyurethane foam (SPUF) using water as blowing agent.
The flame retardant property of SPUF is evaluated by limiting oxygen index (LOI) and horizontal burning test