Ammonium Polyphosphate: Properties, Uses in Plastics and Regulatory Status

Ammonium polyphosphate (APP, CAS 68333-79-9) is an inorganic polyphosphate used as the acid source of intumescent, halogen-free flame retardant systems in polypropylene, polyurethane foam and thermosets. Because APP works by building a swollen char rather than by quenching the flame, its loading and its chain length matter more than its phosphorus content alone, which raises the question of which grade a compound actually needs.

Ammonium polyphosphate is registered under REACH with EC number 269-789-9, it has never been placed on the REACH Candidate List of Substances of Very High Concern (status 23 September 2026), and formulated APP systems sit in polypropylene at 22 to 30 wt% to reach UL 94 V-0. APP is one of 87 flame retardant pages in our directory of plastic additives, each with the same identity, dosage and regulatory fields.

This page carries the identity of the chain polymer [NH4PO3]n, the split between phase I and phase II, the 4-step intumescent mechanism, the dosage recorded per polymer, the published LOI and UL 94 data, a regulatory matrix dated 23 September 2026 with every unresolved cell marked, the comparison with melamine polyphosphate, piperazine pyrophosphate, expandable graphite, aluminium trihydrate and magnesium hydroxide, and the grades a buyer can source. Ammonium polyphosphate is also a liquid fertilizer and the food additive E452(v), and those markets stay in one supplementary section below.

Table T1. Ammonium polyphosphate identity card.

Footnote: identity data from the ECHA CHEM infocard 100.063.425 and the Clariant Exolit AP 422 product literature. Regulatory status as of 23 September 2026. Cells marked "being verified" carry no value in our dataset and are not filled by estimate.

What Is Ammonium Polyphosphate (APP)?#

Ammonium polyphosphate is the ammonium salt of polyphosphoric acid, a linear chain of PO3 units written [NH4PO3]n, and it acts in the condensed phase as the acid source that turns a polymer surface into char. Each repeat unit carries one ammonium cation, and the chain terminates in hydroxyl groups, which is why the formula is also written H(NH4PO3)nOH. What exactly does the name cover, given that the chain length is not fixed?

The name covers every degree of polymerisation, from short chains below 100 repeat units to crystalline long chains above 1,000, and the grades differ in decomposition onset and water sensitivity rather than in chemistry. Chemically the class is an inorganic polyphosphate; functionally it is an acid source, because on heating it releases polyphosphoric acid, which dehydrates a second additive into carbon instead of letting the polymer volatilise into fuel. As a condensed-phase char former, APP belongs to the phosphorus branch of flame retardants for plastics, where the hub compares every mechanism class.

What is another name for ammonium polyphosphate?#

Ammonium polyphosphate is also written APP, APP-II or APP phase II, and it is registered under the name "polyphosphoric acids, ammonium salts", which also appears in the singular form polyphosphoric acid ammonium salt. In commerce it carries trade names instead: Clariant sells Exolit AP 422 and AP 423 as pure grades, AP 462 as a coated grade, and AP 750 and AP 766 as formulated one-pack systems.

What is the formula of ammonium polyphosphate?#

The formula of ammonium polyphosphate is [NH4PO3]n, also written H(NH4PO3)nOH when the hydroxyl end groups are shown, and the repeat unit NH4PO3 has a molar mass of 97.01 g/mol. No single molecular weight exists, because APP is a chain polymer whose mass follows the degree of polymerisation n, which runs from below 100 in short-chain grades to above 1,000 in the long-chain crystalline form. A data sheet printing one molecular weight is describing a short-chain molecule, not the polymeric flame retardant. The 3 identity values a compounder needs are set out below.

APP phase I and phase II: which one goes into plastics?#

Plastics compounds use phase II APP, the long-chain crystalline form with n above 1,000, because short-chain phase I grades with n below 100 are more water sensitive and would migrate or bloom out of the part. Phase II also carries the higher decomposition onset: the long chain starts to decompose at about 240 °C (464 °F), which puts the intumescent reaction in the fire and not in the extruder. Clariant states that Exolit AP 422 is a phase II grade with less than 0.1 % melamine and low water solubility, and that combination is what a compounder buys when a data sheet says phase II. The 3 properties that separate the phases are compared below.

Chain length is the variable that separates the grades of APP from the other phosphorus flame retardants, which are mostly discrete molecules with one fixed molar mass, such as aluminium diethylphosphinate and the phosphate esters. Two APP powders sharing one CAS number therefore behave differently in a humid compound, and the phase is what tells them apart.

How Does Ammonium Polyphosphate Work as a Flame Retardant?#

Ammonium polyphosphate works in the condensed phase: from about 240 °C (464 °F) it decomposes to ammonia and polyphosphoric acid, the acid dehydrates the carbon source in the formulation to carbon char, and the released gases blow that char into an insulating foam. The foam is the flame retardant, not the powder that made it: a swollen char layer cuts the heat reaching the polymer and starves the flame of volatile fuel, and that behaviour is called intumescence.

Phosphorus flame retardants are not limited to that route. Bernhard Schartel at BAM Berlin, in his 2010 review of phosphorus flame retardancy mechanisms in Materials, separates the condensed-phase action (charring, intumescence, inorganic glass) from the gas-phase action (flame inhibition, lower combustion efficiency, higher CO yield). Ammonium polyphosphate sits at the condensed-phase end, which is why it needs a partner additive and is dosed in tens of percent. The intumescent sequence runs in 4 steps.

1. Decomposition of APP from about 240 °C (464 °F) into ammonia and polyphosphoric acid.
2. Esterification and dehydration of the carbon source by that acid.
3. Crosslinking of the carbon residue into a continuous char layer.
4. Expansion of the char by ammonia and water vapour into a closed insulating foam.

The condensed-phase and gas-phase routes are set out side by side on how flame retardants work. The residue that protects the polymer beneath is char, a carbon-rich layer that forms instead of volatile fuel, and its continuity, thickness and adhesion decide the rating a compound reaches.

The intumescent triangle: acid source, carbon source and blowing agent#

A chemical intumescent system needs 3 components working together: ammonium polyphosphate as the acid source, pentaerythritol or dipentaerythritol as the carbon source, and melamine as the blowing agent. The carbon source is usually pentaerythritol, the polyol that the phosphoric acid dehydrates into char, and each of its hydroxyl groups is an esterification site for that acid. The 3 roles are set out below.

The blowing-agent position carries a regulatory consequence that supplier data sheets do not state. Melamine as a flame retardant is the gas source of the classic triangle, and it has been on the REACH Candidate List since 17 January 2023 under Article 57(f), with a harmonised classification of Carc. 2 H351 and STOT RE 2 H373. An APP, pentaerythritol and melamine pack therefore contains an SVHC even though ammonium polyphosphate itself is not one, so a compounder answering an Article 33 request has to check all 3 components. Every architecture that builds a swollen char is compared on intumescent flame retardants.

Is ammonium polyphosphate a flame retardant?#

Yes: ammonium polyphosphate is a halogen-free flame retardant, and more precisely it is the acid source of an intumescent system rather than a stand-alone flame retardant, because it needs a carbon source to build char. APP sits in the phosphorus group of halogen-free flame retardants, which carry no bromine and no chlorine and therefore release no hydrogen halide when they decompose.

What Are the Physical and Chemical Properties of APP?#

Ammonium polyphosphate is a white powder with a density of 1.9 g/cm3, a bulk density of about 0.7 g/cm3 and a decomposition onset near 240 °C (464 °F) in the long-chain phase II form. The recorded values follow.

Table T2. Physical and chemical properties of ammonium polyphosphate.

Bulk density and true density are two different numbers, and the gap is felt at the feeder, because a 22 to 30 wt% loading of a powder that packs at 0.7 g/cm3 occupies a large volume in a dosing system. The decomposition onset is the second constraint, since it sits only about 20 °C above the 220 °C (428 °F) ceiling Clariant gives for processing its formulated grades in polypropylene. Four properties that appear on competitor pages are deliberately absent here: our source library holds no melting point, no particle-size distribution, no pH value and no phosphorus content in wt% for ammonium polyphosphate.

How soluble is ammonium polyphosphate in water?#

The water solubility of ammonium polyphosphate falls as the chain gets longer: short-chain phase I grades with n below 100 are the more water sensitive, while long-chain phase II grades such as Exolit AP 422 are described by Clariant as having low water solubility. No numeric solubility value for either phase sits in our source library, so this page gives the comparison and not a figure in g/100 mL. Water sensitivity decides service life rather than fire performance: a soluble grade migrates to the surface of a part in humid conditions and blooms there, which is why coated and microencapsulated grades exist.

Which Polymers Use Ammonium Polyphosphate, and at What Dosage?#

Ammonium polyphosphate goes into flexible, low-temperature polymers, above all polypropylene, where formulated APP systems such as Exolit AP 750 and AP 766 reach UL 94 V-0 at 22 to 30 wt%. Polyurethane foam, epoxy and unsaturated polyester thermosets follow, in each case in a blend with synergists. Why does APP need so much more loading than a brominated flame retardant? The char has to be built out of the formulation itself, so acid source, carbon source and blowing agent together make up roughly a quarter of the compound, while a bromine donor only delivers radicals.

Intumescent recipes are therefore quoted in wt% rather than in PHR (parts per hundred resin), because the flame retardant is a large fraction of the compound and not a small addition to 100 parts of resin. The recorded levels, with the source behind each, are listed below.

Table T3. Ammonium polyphosphate levels by polymer.

Footnote: where the cell says the loading is not specified, no sourced value exists in our source library. We do not estimate loadings.

APP in intumescent polypropylene#

Polypropylene is the main plastics market for ammonium polyphosphate: formulated APP systems reach UL 94 V-0 at 22 to 30 wt%, and the compound has to be processed at or below about 220 °C (428 °F) so the APP does not decompose in the extruder. That ceiling is the hardest constraint on the compound, because it removes the headroom a compounder uses to disperse a load of nearly a third by weight. Intumescent systems compete with brominated and mineral options across flame retardants for polypropylene, and the processing window is the first filter between them.

The starting point explains the loading. Unmodified polypropylene has a limiting oxygen index of about 17.5 % oxygen, below the 21 % of air, so it burns freely in ambient conditions. Lifting that index to 30 % takes a complete intumescent pack, not a single additive. A flame-retardant PP compound still needs the rest of the package, from antioxidants to nucleating agents, listed under additives for polypropylene.

APP in polyurethane foam#

Ammonium polyphosphate is used in both rigid and flexible polyurethane foam, usually in combination rather than alone: in one 2026 study published in Polymers, a system of expandable graphite, APP and a phosphorus-containing polyol reached UL 94 V-0 with a limiting oxygen index of 28 to 31 % and a peak heat release rate 92 % below the unmodified foam. The phosphorus polyol belongs to that published formulation and is not a recommendation. No commercial APP loading for polyurethane foam sits in our source library, so the study is reported as a result, not a dosage.

Foam systems combine 3 flame retardant families at once, expandable graphite, ammonium polyphosphate and phosphorus bound into the polyol, and they are compared on flame retardants for polyurethane foam. The wider package sits under additives for polyurethane and TPU.

APP in epoxy and unsaturated polyester thermosets#

In epoxy and unsaturated polyester thermosets, ammonium polyphosphate is used in blends with synergists rather than on its own, and glass-reinforced unsaturated polyester laminates combine it with aluminium trihydrate, zinc borate and zinc stannates. A review of flame-retarded thermosets in Polymers records that combination, listing aluminium trihydrate, ammonium polyphosphate, zinc borate and zinc stannate or zinc hydroxystannate as the options used together. No loading exists in our source library for either resin. Reactive and additive options for these resins are set out on flame retardants for epoxy resins.

Which polymers APP cannot be used in#

Ammonium polyphosphate is ruled out of engineering thermoplastics such as polyamide and PBT, which are processed at 240 to 320 °C (464 to 608 °F), because APP begins to decompose at about 240 °C (464 °F) and its compounds are held to about 220 °C (428 °F). The exclusion is a processing-window rule, since the additive would release ammonia before the melt reached the die. Above that ceiling, aluminum diethylphosphinate takes over, because it decomposes only above 300 °C (572 °F) and reaches UL 94 V-0 at 15 to 20 wt% in glass-filled PA6 and PA66.

What Is Ammonium Polyphosphate Used For? 4 Application Areas in Plastics#

Ammonium polyphosphate is used in 4 areas of plastics: intumescent polypropylene and polyethylene compounds, rigid and flexible polyurethane foam, epoxy and unsaturated polyester thermosets, and the glass-reinforced composites built from those resins. A fifth large market, intumescent coatings, is not a plastics use and is named only to close the list. The 4 plastics areas are listed below.

• Intumescent polypropylene and polyethylene compounds, the largest plastics use, at 22 to 30 wt% in the formulated Clariant systems.
• Rigid and flexible polyurethane foam, where APP is combined with expandable graphite and phosphorus-containing polyols.
• Epoxy and unsaturated polyester thermosets, where APP is used in blends with synergists rather than alone.
• Glass-reinforced composites built from those thermosets, including rail and transport interior parts.

Construction plastics are the largest of these markets and are covered under additives for building and construction.

Rail and transport composites#

Unsaturated polyester composites for rail interiors are specified against EN 45545-2 hazard levels HL2 and HL3, and the flame retardant options used in them include aluminium trihydrate at high loadings, ammonium polyphosphate and phosphate esters such as triethyl phosphate. Our dossier records those options as a mapping between specification and flame retardant family, with no loading and no per-substance test result, so no HL2 or HL3 result is attributed to ammonium polyphosphate alone. Reaction-to-fire classes and the systems that meet them are tabulated on flame retardants for building and construction plastics.

How Does APP Perform? LOI, UL 94 and Heat Release#

An intumescent ammonium polyphosphate system changes polypropylene from a material that burns freely to one that self-extinguishes: unmodified PP has a limiting oxygen index of about 17.5 % oxygen, and published APP formulations with a metal oxide synergist reach 30 % and UL 94 V-0. How far can the limiting oxygen index be pushed? In the 2026 Polymers study of metal oxide synergists, raising zinc oxide to 1.5 wt% in an APP and pentaerythritol compound lifted the index to 43.7 % oxygen, more than twice the fraction in air. The indicators, reference states and test methods are set out below.

Table T4. Fire performance indicators for ammonium polyphosphate systems.

The V-0, V-1 and V-2 criteria and the specimen thicknesses are explained on UL 94 flammability ratings, and every fire figure above comes from a published formulation, not a supplier specification.

Heat release is the third indicator and the one fire engineers read. In the 2026 Polymers study of rigid polyurethane foam, the expandable graphite, APP and phosphorus-polyol system cut peak heat release rate by 92 %, measured by cone calorimeter testing. Four further indicators stay empty here, because no values for smoke production, acid-gas evolution, heat of decomposition or mechanical properties exist in our source library for APP.

What LOI and UL 94 rating does intumescent PP reach?#

Intumescent polypropylene built on ammonium polyphosphate reaches UL 94 V-0, the highest vertical-burn class short of the 5V series, at a loading of 22 to 30 wt% in the formulated Clariant systems. The limiting oxygen index (LOI) measures the minimum oxygen fraction that sustains burning, under ISO 4589-2 and ASTM D2863, and published APP formulations reach 30 % with 0.25 wt% zinc oxide or manganese oxide. The 4 criteria a V-0 specimen meets are listed below.

• Afterflame time of 10 s or less after each single flame application.
• Total afterflame time of 50 s or less over 10 applications.
• Afterglow time of 30 s or less after the second application.
• No flaming drips that ignite the cotton indicator beneath the specimen.

How Does APP Interact with Synergists and Other Additives?#

Ammonium polyphosphate is never used alone: it needs a carbon source to build char, it responds strongly to metal oxide synergists, and it competes with pre-blended one-pack systems that bring their own acid and nitrogen sources. The 3 groups of additives an APP system depends on are listed below.

• Carbon sources: pentaerythritol and dipentaerythritol, the polyols that polyphosphoric acid dehydrates into char.
• Nitrogen sources and blowing agents: melamine and melamine polyphosphate, which release gas and dilute the flame.
• Metal oxide synergists: zinc oxide and manganese oxide, effective at fractions of a percent.

How much a small addition can change a system is the subject of flame retardant synergists, which covers antimony trioxide, zinc borate, the stannates and the anti-drip agents. The competing architecture is the one-pack: a piperazine pyrophosphate and melamine polyphosphate blend at 2:1 reaches UL 94 V-0 in polypropylene at 21 wt% total, carrying acid source and nitrogen source in one powder rather than 3 dosed streams.

Metal oxide synergists: ZnO and MnO#

A fraction of a percent of metal oxide changes what an intumescent system can do: in a 2026 study in Polymers, adding 0.25 wt% zinc oxide or manganese oxide to an APP and pentaerythritol polypropylene compound lifted the limiting oxygen index to 30 % and delivered UL 94 V-0. The same work records the dose response, with 1.5 wt% zinc oxide reaching 43.7 % oxygen. Some systems use dipentaerythritol as the carbon source instead, which carries more hydroxyl groups per molecule and offers the acid more esterification sites.

Coated and formulated APP grades: water sensitivity and migration#

Suppliers sell ammonium polyphosphate in 3 forms that solve different problems: pure phase II powder (Exolit AP 422 and AP 423), a coated grade for humid service (Exolit AP 462), and formulated one-pack systems that already contain the carbon source and the synergists (Exolit AP 750 and AP 766). The coating chemistry on AP 462 is not recorded in our source library, and neither is a water-uptake figure, so this page names the grade type only. Surface bloom and water uptake are two of the defects covered in troubleshooting additive-related defects, and both explain why the coated grade exists: a part in humid service is a harder test than a data sheet.

What Is the Regulatory Status of Ammonium Polyphosphate?#

Ammonium polyphosphate is registered under REACH, is not on the REACH Candidate List of Substances of Very High Concern, and is not among the flame retardants listed under the Stockholm Convention or restricted by RoHS (status 23 September 2026). Six cells below read "being verified" rather than carrying a value: the EU 10/2011 food-contact entry, the REACH Annex XVII entry, the CLP and GHS classification, the US FDA status, the TSCA status and California Proposition 65. Our methodology forbids writing an absence of data as an absence of restriction.

Table T5. Regulatory matrix for ammonium polyphosphate, as of 23 September 2026.

What registration, authorisation and restriction each mean for a compounder is explained on REACH and plastic additives. The distinction matters here, because a registered substance with no Annex XIV and no POPs entry still has to be rechecked against the Candidate List at every update.

Is APP REACH registered, and is it an SVHC?#

Yes, ammonium polyphosphate is registered under REACH (Regulation (EC) No 1907/2006) under EC number 269-789-9, and no, it is not a Substance of Very High Concern: it is absent from the Candidate List as of 23 September 2026. The registration tonnage band and the registration year are not in our dataset. The SVHC question is answered differently at pack level: melamine joined the SVHC Candidate List on 17 January 2023, and ammonium polyphosphate has never been added, so an intumescent pack built on APP and melamine still contains an SVHC and still triggers the Article 33 duty to communicate.

Is APP allowed in food-contact plastics?#

The food-contact status of ammonium polyphosphate under Regulation (EU) No 10/2011 is being verified and is not stated on this page; 7 other flame retardants in our dataset do carry Annex I entries, among them aluminium trihydrate as FCM 629 and melamine as FCM 239 with a specific migration limit of 2.5 mg/kg. The full set is antimony trioxide (FCM 398, SML 0.04 mg/kg as antimony), melamine (FCM 239), TCEP (FCM 280), aluminium trihydrate (FCM 629), magnesium hydroxide (FCM 396), huntite (FCM 627) and hydromagnesite (FCM 600). The US position stands the same way: the FDA food-contact status of APP is being verified.

One conflation has to be avoided in both jurisdictions. The food-additive number E452(v) belongs to a different legal regime and says nothing about whether an APP-filled compound may touch food. Which flame retardants carry an Annex I entry, and with what limit, is listed on EU 10/2011.

Is APP restricted under RoHS, the POPs Regulation or US rules?#

No: every flame retardant restricted under the EU POPs Regulation, the Stockholm Convention and RoHS is halogenated, and ammonium polyphosphate is a phosphorus-nitrogen compound with no halogen in it. The listed substances are PBDEs, hexabromobiphenyl, HBCD, decaBDE, short-chain chlorinated paraffins, Dechlorane Plus and medium-chain chlorinated paraffins under Regulation (EU) 2019/1021, and PBB and PBDE at 0.1 % in homogeneous materials under RoHS.

The restriction work in preparation points the same way. The Commission mandate of 11 November 2025 covers non-polymeric aromatic brominated flame retardants, ECHA ran the call for evidence from 21 January to 18 March 2026, and the draft Annex XV dossier is planned for December 2026, with phosphorus compounds outside its scope. The US cells stay open: the TSCA and Proposition 65 status of APP are being verified. The flame retardants RoHS does restrict, PBB and PBDE, are covered on RoHS and plastic additives.

Is Ammonium Polyphosphate Hazardous? Health and Environmental Profile#

Ammonium polyphosphate is not a Substance of Very High Concern and is not restricted under any of the flame retardant rules covered on this page; its GHS classification is being verified against the ECHA classification and labelling inventory before it is stated here (status 23 September 2026). The honest answer to the hazard question has 3 parts, listed below.

• Regulatory classification: no Candidate List entry, no Annex XIV entry, no POPs or RoHS listing; the CLP and GHS classification is being verified.
• Decomposition products: ammonia and polyphosphoric acid, released from about 240 °C (464 °F).
• Independent assessment: the EU ENFIRO project, concluded in 2012, placed APP among the halogen-free flame retardants with good environmental and health profiles.

Two limits follow. This page does not call ammonium polyphosphate safe or non-toxic, because no GHS classification, no LD50 and no aquatic toxicity value sits in our source library, and a gap in the data is not a clean bill of health. It also does not use E452(v) as evidence of safety in a plastic part. Public concern about flame retardants is driven by the halogenated legacy substances discussed on flame retardants and human health, not by inorganic phosphates.

What did the EU ENFIRO project find about APP?#

The EU ENFIRO project (FP7 grant 226563, concluded 2012) assessed halogen-free flame retardants and reported that ammonium polyphosphate, aluminium diethylphosphinate, aluminium trihydrate, magnesium hydroxide, melamine polyphosphate, DOPO, zinc stannate and zinc hydroxystannate showed good environmental and health profiles. The same project reported that resorcinol bis(diphenyl phosphate) and bisphenol A bis(diphenyl phosphate) produced more smoke in styrenics. The finding carries its date: ENFIRO concluded in 2012, eleven years before melamine, the blowing agent of the classic APP pack, joined the REACH Candidate List on 17 January 2023.

What Are the Alternatives to Ammonium Polyphosphate?#

The 4 main alternatives to ammonium polyphosphate are melamine polyphosphate, piperazine pyrophosphate, expandable graphite and the mineral flame retardants aluminium trihydrate and magnesium hydroxide, and the choice turns on processing temperature, colour and whether the system has to be a one-pack. The 6 substances compared below are set against APP on class, role, activation temperature and the limit that decides each case.

Table T6. Ammonium polyphosphate against 5 halogen-free alternatives.

Footnote: cells marked "not recorded in our dataset" mark values that are not in our source library. We do not estimate them.

All 5 alternatives belong to the halogen-free flame retardant systems group, which is why they appear together in one selection table rather than in separate chapters.

APP vs melamine polyphosphate (MPP)#

Melamine polyphosphate is a flame retardant in its own right, but it is not a substitute for ammonium polyphosphate in the same slot: MPP brings both phosphorus and nitrogen and is used mainly as a synergist, with aluminium diethylphosphinate in glass-filled polyamide and with piperazine pyrophosphate in polypropylene. Melamine polyphosphate carries both elements in one salt, under CAS 218768-84-4 (also 56386-64-2) and EC 606-855-1, sold by BASF as Melapur 200, and it is not an SVHC.

Its mechanism pairs condensed-phase polyphosphoric acid char with melamine-derived gas dilution, the nitrogen half of what a classic APP pack takes from free melamine. One caution follows that no competitor page publishes: Clariant does not recommend MPP as a synergist in some phosphinate systems, because it lowers hydrolytic stability.

APP vs piperazine pyrophosphate (PAPP)#

Piperazine pyrophosphate is the main one-pack competitor to ammonium polyphosphate in polypropylene: a PAPP to melamine polyphosphate blend at a 2:1 ratio reaches UL 94 V-0 at 21 wt% total, against 22 to 30 wt% for the formulated APP systems, and the same blend works in recycled polypropylene. The two loadings come from different sources, the 21 wt% from a 2026 study in ACS Applied Polymer Materials and the 22 to 30 wt% from the Clariant Exolit Thermoplastics brochure, so the gap is not a measured head-to-head result.

Piperazine pyrophosphate is the basis of the Adeka one-pack intumescents for polypropylene, Adeka Stab FP-2100JC and FP-2500S, under CAS 66034-17-1 and EC 457-330-7, formula C4H14N2O7P2, molecular weight 264.11 g/mol, and it is not a Substance of Very High Concern.

APP vs expandable graphite#

Expandable graphite is a physical intumescent rather than a chemical one: its intercalant decomposes from about 200 °C (392 °F) and exfoliates the graphite into insulating carbon worms, so it needs no separate carbon source, while ammonium polyphosphate has to be paired with pentaerythritol. Expandable graphite is the physical intumescent: it needs no carbon source at all, it expands by 30 to 400 cm3/g with an onset between 140 and 230 °C, and it carries CAS 12777-87-6 and EC 235-819-4.

Two practical limits follow. It is black, which rules it out of light-coloured parts, and its maximum processing temperature is typically below 230 °C (446 °F), close to the APP ceiling. In polyurethane foam the two work together more often than they substitute for each other, as the 2026 Polymers study of an expandable graphite, APP and phosphorus-polyol system shows.

APP vs mineral flame retardants (ATH and MDH)#

Aluminium trihydrate and magnesium hydroxide work by a completely different mechanism from ammonium polyphosphate: they release water endothermically, absorbing 1,051 J/g and 1,316 J/g respectively, instead of building a char. Aluminum trihydrate (ATH) absorbs 1,051 J/g as it releases water from about 200 °C (392 °F), with a theoretical loss on ignition of 34.6 %, under CAS 21645-51-2.

The temperature ceiling separates the two minerals. Magnesium hydroxide (MDH) holds to about 320 °C (608 °F), roughly 110 °C above ATH, which is what lets it into polyolefin cable compounds, and it releases 1,316 J/g with a loss on ignition of 31.0 % under CAS 1309-42-8 (natural brucite 1317-43-7). The cost of that mechanism is loading: halogen-free cable compounds run 160 to 180 phr of mineral flame retardant, about 61.5 wt% at 160 phr, against 22 to 30 wt% for a formulated APP system.

Who Manufactures Ammonium Polyphosphate? Grades and Suppliers#

Ammonium polyphosphate for plastics is made by a small number of specialist phosphate producers, of which Clariant, with the Exolit AP line, and Budenheim are the two named in our supplier dataset. Clariant's line splits into 3 grade types, and that split is where a price comparison starts: pure phase II powder, a coated grade and a formulated one-pack. Buyers should ask for the phase, the chain length, the coating status and a current SDS before comparing prices, because a pure powder and a one-pack do not carry the same active chemistry per kilogram.

Table T7. Recorded ammonium polyphosphate producers and grades.

More producers and their product lines are in the directory of flame retardant manufacturers and suppliers. To narrow the options before sending an enquiry, use the flame retardant selector by polymer and UL 94 rating.

Where Does APP Sit in the Wider Flame Retardant Family?#

Ammonium polyphosphate is the workhorse acid source of the phosphorus flame retardant class, the halogen-free group that sits beside brominated, chlorinated, mineral and nitrogen-based flame retardants in a global market worth USD 8.1 to 9.3 billion in 2025 according to analyst estimates, which differ across that range. The class is defined by mechanism rather than by a single chemistry: its members act in the condensed phase by charring, intumescence or the formation of an inorganic glass, and in the gas phase by flame inhibition. Regulation sets the direction of travel, because Regulation (EU) 2019/2021 has banned halogenated flame retardants in the enclosures and stands of electronic displays since 1 March 2021. The blowing agents and gas sources of intumescent packs belong to nitrogen-based flame retardants, the neighbouring class that supplies melamine.

Non-plastics uses: fertilizer and food additive E452(v)#

Ammonium polyphosphate has two large markets outside plastics: liquid fertiliser, where it is sold under grades such as 10-34-0, and the food-additive number E452(v), and neither status says anything about its use in a plastic part. The 3 uses share a CAS number and little else. A fertilizer grade is chosen for its nutrient content, a food-additive grade for its function in food, and a flame retardant grade for its chain length, decomposition onset and water sensitivity.

Readers arriving from a fertilizer query find no application rates and no agronomy here, because this site covers additives used in plastics only. The reverse point matters for compliance: an E number is not a food-contact clearance for a plastic.

Ammonium polyphosphate price and sourcing#

We do not publish an ammonium polyphosphate price, because no sourced figure sits in our source library; what buyers can compare is the grade type, since a formulated one-pack such as Exolit AP 750 already contains the carbon source and the synergists that a pure phase II powder does not. The additives for which we do publish sourced figures are listed under plastic additive prices.

Grade type is the first comparison, origin the second. Buyers searching for regional supply can start from plastic additive manufacturers and suppliers in India, which answers the sourcing question this page cannot answer with a figure. Raw-material and supply-risk drivers are tracked on flame retardants market.

Is ammonium polyphosphate safe?#

Ammonium polyphosphate is not a Substance of Very High Concern and is not restricted under the EU POPs, Stockholm Convention, RoHS or Ecodesign rules covered on this page (status 23 September 2026); its GHS hazard classification is being verified before we state it. The grade-specific classification sits in the supplier's safety data sheet.

Can ammonium polyphosphate replace halogenated flame retardants?#

In polypropylene, polyurethane foam and thermosets, yes: intumescent ammonium polyphosphate systems reach UL 94 V-0 without halogen, which is what the Ecodesign ban on halogenated flame retardants in electronic display enclosures, in force since 1 March 2021, pushes formulators toward. The replacement stops at the processing window: APP cannot follow into engineering thermoplastics processed at 240 to 320 °C (464 to 608 °F), where metal phosphinates take over at 15 to 20 wt%.

Does ammonium polyphosphate need an SDS?#

Yes: suppliers provide a safety data sheet for ammonium polyphosphate as for any traded chemical, and the SDS is the document that carries the grade-specific GHS classification. A coated grade, a pure phase II powder and a formulated one-pack are 3 different products, so the SDS is requested per grade, not per substance.

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