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

Polyurethane foam is regarded as a versatile polymeric material for its comparatively excellent properties such as low density, high specific strength, great insulation, large specific surface area, and good sound-absorbing performance. 

Polyurethane foam is more easily burned compared to other foams since there are many easily decomposing urea bonds in it. 

Thus, it is necessary to improve the flame retardant property of polyurethane foam

Ammonium polyphosphate (APP), as inorganic phosphorus flame retardant with nitrogen-phosphorus synergistic intumescent effect, has the advantages of thermal stability and lasting effect. 

APP can also improve the mechanical properties of the material, so it is often used with other flame retardants, and the most common APP flame retardant studied by researchers is form II, of which the polymerization degree is greater than 1000. 

In this paper, the water blown SPUF is synthesized only with soluble ammonium polyphosphate (SAPP) with a low polymerization degree. 

Our aim is to study the effect of SAPP on the thermal degradation, the flame-resistant, and the mechanical properties of the SPUF.

Ammonium Polyphosphate (APP), Cas No 68333-79-9, is an environment-friendly and halogen-free flame retardant. APP is the main constituent of many intumescent flame retardant systems: coatings, paints and engineering plastics.

For the chemical point of view, Ammonium Polyphosphate is an inorganic salt of polyphosphoric acid and ammonia. Depending on the polymerization degree, there are two main families of ammonium polyphosphate: Crystal phase I APP (or APP I), and Crystal phase II APP (or APP II).

- APP phase I has a short and linear chain (n < 100), it is more water sensitive (hydrolysis) and less thermally stable; actually it begins to decompose at temperatures above 150 °C.

- The second family of Ammonium polyphosphate is the APP Phase II; which has an high polymerization degree, with n>1000, its structure is cross linked (branched), and it is an high-quality non-halogenated flame retardant. 

APP phase II, Ammonium polyphosphate, has an higher thermal stability (the decomposition starts at approximately 300°C) and lower water solubility than APP I.

Tecnosintesi APP phase II is a fine-particle ammonium polyphosphate which has been developed in accordance with requirements of all main European end-users. 

The product is suitable for water and solvent based intumescent coatings. 

It has low water solubility which makes it useful in application where the product is exposed to high humidity conditions or water. 

Our Ammonium Polyphosphate contains 72.5% of phosphorus (as P2O5) which makes it a very effective fire retardant. 

APP phase II is probably one of the most effective non-halogen fire retardants in the market.

Main Applications:

Solvent based and Water based intumescent coatings.

Flame retardant for polyurethanes.

Flame retardant for unsaturated polyesters.

Flame retardant for epoxies.

Flame retardant for acrylics.

Ammonium polyphosphate (APP) is an organic salt of polyphosphoric acid and ammonia. 

As a chemical, it is non-toxic, environmentally friendly and halogen-free. 

It is most commonly used as a flame retardant, selection of the specific grade of ammonium polyphosphate can be  determined by the solubility, Phosphorus content, chain length and polymerization degree. 

The chain length (n) of this polymeric compound can be linear or branched. Depending on the polymerization degree, there are two main families of ammonium polyphosphate: Crystal phase I APP (or APP I), and Crystal phase II APP (or APP II).

APP phase I has a short and linear chain (n < 100), it is more water sensitive (hydrolysis) and less thermally stable; actually it begins to decompose at temperatures above 150 °C.

The second family of Ammonium polyphosphate is the APP Phase II; which has an high polymerization degree, with n>1000, its structure is cross linked (branched), and it is an high-quality non-halogenated flame retardant. 

APP phase II, Ammonium polyphosphate, has an higher thermal stability (the decomposition starts at approximately 300°C) and lower water solubility than APP I.

Ammonium polyphosphate is a specialty chemical that finds many different uses in key industries.  

Ammonium Polyphosphate, is an environment-friendly and halogen-free flame retardant. It is the main constituent of many intumescent flame retardant systems: coatings, paints and engineering plastics. It is used to prepare 20% Phosphorous/Nitrogen containing flame retardants, it can be used solely or in conjunction with other materials in the flameproof treatment for textiles, papers, fibers and woods. Special treatment can be used to prepare 50% high concentration flameproof formulations required for special applications.

The most common ammonium polyphosphate fertilizers have a N-P2O5-K2O (nitrogen, phosphorus and potassium) composition of 10-34-0 or 11-37-0. Polyphosphate fertilizers offer the advantage of a high nutrient content in a clear, crystal-free fluid that remains stable within a wide temperature range and stores well for long periods. A variety of other nutrients mix well with polyphosphate fertilizers, making them excellent carriers of micronutrients typically needed by plants.

Description

Ammonium polyphosphates are liquid fertilizers with compositions up to 11-37-0, manufactured by the reaction of anhydrous ammonia with superphosphoric acid. Superphosphoric acid is made by the concentration of regular wet-process acid up to P2O5 concentrations of 78%. Granular polyphosphates suitable for bulk blending are made by reacting ammonia with regular wet process acid of 52% P2O5 content and using the heat of reaction to drive off water to produce a phosphate melt of 10-43-0, with about 40% of the phosphorus in the polyphosphate form.

Exolit®  AP 435 is a fine-particle ammonium polyphosphate (phase II) optimized for low viscosity in aqueous suspension and intumescent coatings. 

The product is largely insoluble in water and completely insoluble in organic solvents. It is colourless, non-hygroscopic and non-flammable.

Benefits

Optimized for low viscosity in aqueous suspension, low water solubility and low acid number

Non-halogenated flame retardant with favorable environmental and health profile

Particularly suitable as an ”acid donor” for intumescent coatings thanks to its low water solubility. Steel structures coated with intumescent paints can meet the requirements of fire resistance classes specified in EN, DIN, BS, ASTM and others. 

Their application on wood or plastics enables these materials to qualify for Building Material Class B (DIN EN 13501-1)

Imparts a good flame-retardant effect to adhesives and sealants when it is incorporated into the base formulation at the rate of 10 - 20%

Suitable non-halogenated flame retardant for polyurethane foams. 

PUR Foams with Exolit® AP 435 can be recycled

Excellent flame-retardant effect in cellulose-containing materials such as paper and wood products. 

With chipboard products, the DIN EN 13501-1 classification can be achieved by adding 15 - 20 % Exolit® AP 435

An essential component in intumescent formulations for thermoplastics, particularly polypropylene, for which the classification UL 94-V0 is specified for applications in the electrical sector

In the case of thermosets like epoxy resins and unsaturated polyester resins, it paves the way for the production of lightweight components with low solids content

(Bio-)degradable by breaking down to naturally occurring phosphate and ammonia

Flame retardants help to save lives by slowing down or stopping the spread of fire or reducing its intensity. 

Also called fire retardants, they are used in anything from phones and curtains to car seats and buildings. 

If a fire starts, they may be able to stop it completely – or slow it down and so provide precious extra time for escape.

Clariant’s flame retardants are produced to modern standards in Germany, Switzerland and China. 

Their brand name Exolit® has become a byword for sustainable fire safety.

Intumescent flame retardant systems

Mode of action: formation of a voluminous, insulating protective layer through carbonization and simultaneous foaming

Intumescent systems puff up to produce foams. They are used to protect combustible materials such as plastics or wood, and those like steel, which lose their strength when exposed to high temperatures, against the attack of heat and fire.

Basically, intumescent flame retardant systems consist of the following:

1. "Carbon" donors (e.g. polyalcohols such as starch, pentaerythritol)

2. Acid donors (e.g. ammonium polyphosphate)

3. Spumific compounds (e.g. melamine)

Process of intumescent mechanism

1. Softening of the binder/polymer (e.g. polypropylene)

2. Release of an inorganic acid (e.g. ammonium polyphosphate)

3. Carbonization (e.g. of polyalcohols)

4. Gas formation by the spumific compound (e.g. melamine)

5. Foaming of the mixture

6. Solidification through cross-linking reactions