Phosphorus Flame Retardants: 8 Types, How They Work and Where Each Is Used

Phosphorus flame retardants are 8 types of phosphorus compounds, from red phosphorus and ammonium polyphosphate to phosphate esters and DOPO, that make plastics pass fire tests such as UL 94 V-0 by forming char in the solid and trapping radicals in the flame, at loadings from about 1 wt% phosphorus in epoxy to 22-30 wt% of an APP system in polypropylene. Phosphorus works in both phases, which no mineral filler does, so which of the 8 types suits which plastic, and how much of it does that plastic need?

Flame retardants make up 13 % of all plastic additives by weight, behind plasticizers at 34 % and fillers at 28 %, and phosphorus compounds are one of their 4 chemistry groups, next to bromine and chlorine, nitrogen and mineral fillers. The Cefic sector group pinfa files them with inorganic and nitrogen products as "PIN" flame retardants.

This page defines the class and its 5 halogen-containing exceptions, explains the 2-phase mechanism and the 8 types, sets phosphorus content and loadings by polymer, compares phosphorus with bromine and minerals, and covers processing limits, fire tests, dated regulatory status and producers. The hub on flame retardants for plastics compares phosphorus with the other 12 flame retardant types.

Four figures that define phosphorus flame retardants

• 8 types: from inorganic red phosphorus, APP and hypophosphites to organic phosphinates, esters, phosphonates, DOPO and phosphorus-nitrogen salts
• About 1-1.2 wt% phosphorus: UL 94 V-0 in DOPO-based epoxy research formulations
• About 15 wt%: the aluminium diethylphosphinate loading (23.3-24.0 wt% phosphorus) that gives PA 6T/66 V-0 at 0.8 mm
• 3 phosphate esters on the REACH Candidate List: TCEP (2010), trixylyl phosphate (2013) and triphenyl phosphate (2024)

What Is a Phosphorus Flame Retardant?#

A phosphorus flame retardant is an inorganic or organic phosphorus compound, added to or reacted into a polymer, that delays ignition and slows flame spread by turning the burning surface into char and by trapping flame radicals. The term, abbreviated PFRs, covers elemental red phosphorus, phosphate salts, phosphinates, phosphate esters, phosphonates and reactive phosphorus monomers. "Organophosphorus flame retardant" is the broader chemical term, while "organophosphate flame retardant" (OPFR) names only the phosphate esters. Like every flame retardant, a phosphorus compound does not make a plastic non-combustible; it moves the plastic up one or more classes of a fire test such as UL 94.

Additive, reactive and polymeric phosphorus flame retardants#

Phosphorus flame retardants enter a plastic in 3 ways: as additives blended into the melt, as reactive monomers built into the polymer chain, or as phosphorus-containing polymers that are too large to migrate. The 3 forms differ in how the phosphorus is held in the plastic.

• Additive: blended into the melt and free to move, as ammonium polyphosphate, aluminium diethylphosphinate, TPP and RDP are
• Reactive: bonded into the polymer chain, as DOPO is in epoxy laminates, CEPPA in PET fibre and phosphorus polyols in polyurethane foam
• Polymeric: a phosphorus-containing polymer blended into another plastic, as polyphosphonates are

Additive phosphorus can migrate, leach or bloom; reactive phosphorus stays in the network. The trade-offs of each route are defined under reactive vs additive flame retardants.

Are phosphorus flame retardants halogen-free?#

Most phosphorus flame retardants are halogen-free, but 5 commercial ones are not: the chlorinated phosphates TCPP, TCEP, TDCPP and V6 carry chlorine, and FR-370 carries 70 % bromine next to 3 % phosphorus. Red phosphorus, APP, the phosphinates, aryl and alkyl phosphates, phosphonates, DOPO and the phosphorus-nitrogen salts contain no intentionally added chlorine or bromine. TCPP, the workhorse of polyurethane insulation foam, contains 9.5 % phosphorus and 32.5 % chlorine and acts through chlorine and phosphorus radicals plus charring, so it releases hydrogen chloride in a fire like any chlorinated flame retardant.

These dual-class compounds sit between 2 families, and a halogen-free specification rules out all 5 even though they are phosphorus flame retardants. The 6 classes that meet a zero-halogen specification are compared under halogen-free flame retardants.

How Do Phosphorus Flame Retardants Work?#

Phosphorus flame retardants work in 2 phases: in the solid they decompose to phosphoric and polyphosphoric acids that turn the polymer into char and glassy phosphate, and in the flame they release PO· radicals that trap the H· and OH· radicals driving combustion. Phosphorus cuts the combustion cycle on both sides of the burning surface: in the solid, before volatiles form, and in the flame, where chain-branching reactions such as H· + O2 → OH· + O· sustain it. Which phase dominates depends on the polymer and on how the phosphorus is bound, so why does one compound char in one plastic and act in the flame in another?

Bernhard Schartel at the German Federal Institute for Materials Research and Testing (BAM) set out these modes in his 2010 review "Phosphorus-based flame retardancy mechanisms: old hat or a starting point for future development?" in Materials: charring, intumescence and inorganic glass in the condensed phase, and flame inhibition in the gas phase. Table T0 lists the 4 resulting modes with examples and one signature number each.

Most phosphorus flame retardants use 2 or more modes at once; each row shows the dominant one.

The same combustion cycle for bromine, minerals and nitrogen is explained under how flame retardants work.

Condensed phase: char, intumescence and phosphate glass#

In the condensed phase, phosphorus flame retardants decompose to phosphoric and polyphosphoric acids, which dehydrate and crosslink the polymer into a carbon-rich char that holds fuel back and shields the material underneath. Ammonium polyphosphate shows the sequence most clearly: it releases ammonia and phosphoric acid, and the acid esterifies and dehydrates the carbon source into char. Aryl phosphates char the polycarbonate in PC/ABS, and aluminium diethylphosphinate leaves a glassy phosphate residue on the surface.

Intumescence is the swollen form of the same char. The char swells into an insulating foam when an acid source such as ammonium polyphosphate meets a carbon source such as pentaerythritol and a blowing agent such as melamine. In a 2025 study in Polymers, 0.25 wt% zinc oxide or manganese oxide lifted an APP and pentaerythritol polypropylene to LOI 30 % and UL 94 V-0, and 1.5 wt% zinc oxide to LOI 43.7 %. Component ratios and expandable graphite are covered under intumescent flame retardants.

Gas phase: PO· radicals and flame inhibition#

In the gas phase, phosphorus flame retardants volatilise into PO· and HPO2· species that scavenge the H· and OH· radicals of the flame, so combustion runs less completely and releases less heat from the same fuel. The phosphorus species scavenge the same radicals as bromine does, and aluminium diethylphosphinate and DOPO combine this flame inhibition with char, while triphenyl phosphate acts mainly in the gas phase. Flame inhibition lowers the combustion efficiency without changing the effective heat of combustion of the volatiles. The price is incomplete combustion: Schartel showed that gas-phase flame inhibition is always accompanied by a higher carbon monoxide yield, which is why heat release and smoke are measured together in a cone calorimeter.

Why does the same phosphorus compound act differently in different polymers?#

The same phosphorus compound acts differently in different polymers because its acids need a polymer that can char: in polycarbonate alone the aryl phosphate BDP works mainly in the flame, while in a PC/ABS blend it also turns the polycarbonate into char. Four polymer cases show the shift.

• Polycarbonate: BDP acts mainly by gas-phase flame inhibition
• PC/ABS: the same BDP also chars the polycarbonate fraction
• Glass-filled PA66: red phosphorus reaches UL 94 V-0 by carbonaceous charring
• Polypropylene: with a limiting oxygen index of about 17.5 % O2 and no char of its own, PP needs phosphorus plus an added carbon source (APP with pentaerythritol) or a salt that brings one (PAPP)

What Are the 8 Types of Phosphorus Flame Retardants?#

The 8 types of phosphorus flame retardants are red phosphorus, ammonium polyphosphate, metal hypophosphites, metal phosphinates, phosphate esters, phosphonates, DOPO and other reactive building blocks, and phosphorus-nitrogen salts; the first 3 are inorganic and the other 5 are organic compounds or organic salts. Table T1 lists the 8 types with their main examples, CAS numbers, mode of action, polymers and typical loading.

Loadings are supplier, ECHA-mapping or study examples, not universal values. Red phosphorus is used encapsulated or as a masterbatch.

The flame retardant hub folds these 8 into 3 broader phosphorus types, and the halogen-free guide into 5 sub-groups; the finer split here follows the chemistry that decides processing temperature and polymer fit.

1. Red phosphorus#

Red phosphorus works by oxidising in a fire to phosphorus acids that char the polymer: it is the amorphous, elemental form of phosphorus (CAS 7723-14-0), and it reaches UL 94 V-0 in glass-filled PA66 by charring, as Schartel described in 2010. The allotrope (EC 231-768-7, density 2.34 g/cm3) carries 100 % phosphorus and shows some gas-phase activity next to its char, but a verified loading for glass-filled PA66 is not yet established in our sources.

Handling sets the limits of red phosphorus. Its harmonised EU classification (CLP index 015-002-00-7) is Flam. Sol. 1, H228 and Aquatic Chronic 3, H412, so compounders receive it encapsulated or as a masterbatch (Masteret from Italmatch, Exolit RP from Clariant), and handling carries a fire and phosphine risk. The colour limits it to dark parts, electronics manufacturers that have seen corrosion-related electrical failures avoid it, and it is not a REACH SVHC. Grades and encapsulation types are covered on red phosphorus flame retardant.

2. Ammonium polyphosphate (APP)#

Ammonium polyphosphate (APP) is an inorganic polyphosphate salt whose long-chain phase II form, with more than 1,000 repeat units, decomposes from about 240 °C into ammonia and polyphosphoric acid, the acid that chars an intumescent compound. In plastics APP (CAS 68333-79-9, [NH4PO3]n) serves as the acid source of intumescent polypropylene and polyethylene, where formulated APP systems such as Exolit AP 750 and AP 766 reach UL 94 V-0 at 22-30 wt% with processing up to about 220 °C, and it also goes into polyurethane foam, epoxy and unsaturated polyester.

Clariant sells phase II APP as Exolit AP 422 and a coated version as Exolit AP 462, since short-chain grades with fewer than 100 units are more water sensitive. APP is neither an SVHC nor on the Proposition 65 list (edition 31 July 2026). Phase I and phase II grades and coated types are compared on ammonium polyphosphate.

3. Metal hypophosphites: aluminium and calcium hypophosphite#

Metal hypophosphites are inorganic phosphinate salts with the highest phosphorus content of the additive phosphorus flame retardants after red phosphorus: about 42 wt% (calculated) in aluminium hypophosphite (aluminum hypophosphite, CAS 7784-22-7), which is used in PBT, polyamide and polystyrene. Aluminium hypophosphite, Al(H2PO2)3, carries the PubChem hazard notifications H228 and H412 and is not an SVHC, as covered on aluminum hypophosphite.

Calcium hypophosphite (CAS 7789-79-9), Ca(H2PO2)2 with a molar mass of 170.06 g/mol, carries about 36 wt% phosphorus by formula, and ECHA's plastic additives mapping lists it at 1 wt% in polyolefins. A 2024 study in Polymers examined phosphine emission from aluminium hypophosphite in PA6, a processing risk this class shares with red phosphorus.

4. Metal phosphinates: aluminium diethylphosphinate (DEPAL)#

Metal phosphinates are organic phosphorus salts led by aluminium diethylphosphinate (AlPi, DEPAL, CAS 225789-38-8), which carries 23.3-24.0 wt% phosphorus, survives processing above 300 °C and gives glass-filled polyamide UL 94 V-0 at 15-20 wt%. Aluminium diethylphosphinate (aluminum diethyl phosphinate) is a non-hygroscopic powder that releases PO· into the flame and chars the surface, usually with melamine polyphosphate as synergist.

Three Clariant loadings define the class: about 15 wt% of Exolit OP 1230 gives PA 6T/66 V-0 at 1.6 and 0.8 mm, 15-20 wt% of the OP 1312 blend gives glass-filled PA6 and PA66 V-0 from 0.4 to 3.2 mm with a GWIT of 775 °C and a CTI of 600 V, and 18 wt% of OP 1260 gives glass-filled PBT V-0. AlPi is not an SVHC, but the OP 1312 and 1314 blends have carried a Repr. 2 label since 1 June 2015 because they contain more than 3 % zinc borate. Every Exolit OP grade with its polymer and thickness is compared under phosphinate flame retardants (DEPAL).

5. Phosphate esters: aryl, alkyl and chlorinated (TPP, RDP, BDP, TEP, TCPP)#

Phosphate esters are organic esters of phosphoric acid that act mainly in the gas phase and also plasticise the polymer, and they come in 3 sub-groups: aryl phosphates such as TPP, RDP and BDP, alkyl phosphates such as triethyl phosphate (TEP), and chlorinated phosphates such as TCPP.

Aryl phosphates serve PC/ABS and PPE/HIPS housings: triphenyl phosphate doubles as flame retardant and plasticizer in these blends, PVC and cellulose acetate film, while RDP and BDP (ICL Fyrolflex) are liquid or low-melting aryl phosphates used with a PTFE anti-drip agent. Each ester, its grades and its regulatory file are compared under organophosphate flame retardants.

Triethyl phosphate is a liquid alkyl phosphate ester with about 17 wt% phosphorus, calculated from its formula, that serves as flame retardant and viscosity reducer in rigid PU/PIR foam and unsaturated polyester.

Four further aryl phosphates, tricresyl phosphate (TCP, CAS 1330-78-5), 2-ethylhexyl diphenyl phosphate (EHDPP, CAS 1241-94-7), tert-butylphenyl diphenyl phosphate (BPDP, EC 700-990-0) and PIP (3:1) (CAS 68937-41-7), work as flame-retardant plasticizers in flexible PVC and polyurethane; PIP (3:1) and trixylyl phosphate carry the strictest regulatory status of the group.

Chlorinated phosphates are the foam branch. TCPP (ICL Fyrol PCF, Lanxess Levagard PP) is the workhorse of rigid and flexible polyurethane foam, TDCPP (CAS 13674-87-8) serves flexible foam and V6 (CAS 38051-10-4) automotive flexible foam, and TCEP (CAS 115-96-8) is the legacy member, with no EU production since 2001. Their chlorine chemistry and regulatory history sit with the other chlorinated phosphates.

6. Phosphonates and polyphosphonates (DMMP, DMPP)#

Phosphonates are liquid phosphorus flame retardants with a direct phosphorus-carbon bond, led by dimethyl methylphosphonate (DMMP, about 25 wt% phosphorus by formula), which is dosed into rigid polyurethane foam and unsaturated polyester resins. DMMP (CAS 756-79-6) boils at 181 °C, is a Schedule 2 chemical under the Chemical Weapons Convention and is not an SVHC. Its export controls and hazard notifications are detailed on DMMP.

Dimethyl propylphosphonate (DMPP, CAS 18755-43-6) carries about 20 wt% phosphorus by formula and appears in ECHA's mapping at 15 wt% in polyurethane; its REACH registration covers intermediate use only, and it is not on the Candidate List (ECHA CHEM, checked 22 September 2026).

Polyphosphonates carry phosphorus-carbon bonds in their backbone, and our sources hold no verified loading or grade for them yet. These high-molecular-weight polyphosphonates, which cannot migrate, are grouped with brominated polystyrene under polymeric flame retardants.

7. DOPO and reactive phosphorus building blocks#

DOPO (CAS 35948-25-5) is a reactive phosphorus building block that is bonded chemically into epoxy resins, where about 1-1.2 wt% phosphorus gives UL 94 V-0 in research formulations, which makes it a basis of halogen-free FR-4 circuit-board laminates. The name stands for 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (also HCA), a cyclic H-phosphinate with about 14 wt% phosphorus by formula that releases PO· into the flame and chars the resin; derivatives reach V-0 at 0.25-1.2 wt% phosphorus (Polymers, 2024), and DOPO is not an SVHC. Derivatives and laminate data are collected on DOPO.

Other reactive building blocks follow the same principle: CEPPA (CAS 14657-64-8) is a reactive phosphorus comonomer for PET fibre and film, reactive phosphorus polyols serve polyurethane foam, and phosphazenes are a further route in epoxy laminates. The brominated incumbent of FR-4, reactive TBBPA, carries a harmonised Carc. 1B classification from 1 September 2025.

8. Phosphorus-nitrogen salts (MPP, melamine pyrophosphate, PAPP)#

Phosphorus-nitrogen salts such as melamine polyphosphate (MPP), melamine pyrophosphate and piperazine pyrophosphate (PAPP) combine a phosphorus acid that chars with a nitrogen base that releases inert gas, so one salt does the work of 2 additives. MPP (BASF Melapur 200) is the synergist of aluminium diethylphosphinate in glass-filled PA6 and PA66, with the blooming and hydrolysis caveats listed under processing limits below. PAPP (Adeka Stab FP-2100JC and FP-2500S blends) is a single-component intumescent, and a 2:1 PAPP and MPP blend at 21 wt% total gives UL 94 V-0 in virgin and recycled polypropylene (ACS Applied Polymer Materials). Melamine on its own is a nitrogen flame retardant; it becomes part of a phosphorus flame retardant only as a phosphate salt. None of the 3 salts is an SVHC.

The 3 commercial phosphorus-nitrogen salts differ in role.

Melamine cyanurate and the other nitrogen-only salts are covered under nitrogen-based flame retardants.

How Much Phosphorus Does a Plastic Need?#

Plastics need from about 1 wt% phosphorus, in epoxy resins with reactive DOPO, to about 3.5 wt% phosphorus delivered by 15 wt% aluminium diethylphosphinate in high-temperature polyamide, while non-charring polypropylene needs 21-30 wt% of a complete intumescent package. The 3.5 wt% figure is calculated from Clariant's loading and AlPi's phosphorus content. Four factors set the phosphorus demand.

• Char tendency: epoxy, polycarbonate and polyamide char; polypropylene and polyethylene do not
• Target rating and wall thickness: V-0 at 0.8 mm needs more than V-2 or a thicker wall
• Phosphorus binding: reactive DOPO, the salt AlPi and the ester TPP act in different phases
• Synergists: MPP, PAPP and zinc oxide lower the total loading

Phosphorus content of 18 phosphorus flame retardants#

Phosphorus content runs from 3 wt% in the brominated phosphate FR-370 to about 42 wt% in aluminium hypophosphite and 100 % in red phosphorus, and a higher content means less additive for the same amount of phosphorus in the plastic. Table T3 gives 18 values, calculated from the molecular formula, in the order of the 8 types.

Calculated from the molecular formula and molar mass (P = 30.97 g/mol). Oligomeric commercial grades of RDP and BDP and the polymeric APP and MPP differ from the monomer or repeat-unit value. Supplier values, where published, are given in the last column.

Phosphorus content is a starting point, not a ranking: aryl phosphates carry only about 9-11 wt% phosphorus yet work at 20 wt% in PC/ABS because they act in the gas phase and char the polycarbonate, while APP carries about 32 wt% but needs a carbon source to protect polypropylene. Where suppliers state a value, the calculation agrees: Clariant gives 23.3-24.0 wt% for aluminium diethylphosphinate, and ICL gives 9.5 % for TCPP and 3 % for FR-370.

Loadings for UL 94 V-0 by polymer#

Published phosphorus systems reach UL 94 V-0 at about 1-1.2 wt% phosphorus in epoxy, 15-20 wt% of a phosphinate in polyamide, 18 wt% in PBT, 20 wt% of an aryl phosphate in PC/ABS and 21-30 wt% of an intumescent package in polypropylene. Table T4 lists 13 published combinations with loading, result and source type.

Supplier and study examples; the final loading is set by trials against the part's rating and thickness.

ECHA mapping values, such as DMPP at 15 wt% in polyurethane and calcium hypophosphite at 1 wt% in polyolefins, are typical use concentrations with no fire rating attached.

Which Phosphorus Flame Retardant Suits Each Polymer?#

The right phosphorus flame retardant follows the polymer's processing temperature and its ability to char: phosphinates, stable above 300 °C, for polyamides and PBT, APP or PAPP intumescent packages for polypropylene, aryl phosphates for PC/ABS and PPE/HIPS, DOPO for epoxy, and phosphonates or phosphate esters for polyurethane foam. Flexible PVC adds a sixth case, where phosphate esters double as plasticizers.

Polyamides and PBT#

Polyamides and PBT use aluminium diethylphosphinate because it is stable above 300 °C: 15-20 wt% of a phosphinate blend gives glass-filled nylon (PA6 and PA66) UL 94 V-0 from 0.4 to 3.2 mm, and 18 wt% gives glass-filled PBT V-0. For rail vehicles, glass-filled PA66 with Exolit OP compounds reaches EN 45545-2 R22 HL3 and glass-filled PBT R22 HL2 (Clariant). Red phosphorus remains the charring option for dark glass-filled PA66, and aluminium hypophosphite is a further phosphorus source in PBT and polyamide. Unfilled and glass-filled grades, including melamine cyanurate, are compared under flame retardants for nylon.

Polypropylene and polyethylene#

Polypropylene reaches UL 94 V-0 with phosphorus only as an intumescent package, 22-30 wt% of a formulated APP system or 21 wt% of a 2:1 PAPP and MPP blend, because PP (LOI about 17.5 %) drips and forms no char of its own. APP systems process up to about 220 °C, below the 240 °C decomposition onset of phase II APP, and polyethylene compounds take the same APP route. Brominated, mineral and NOR HALS routes for PP are compared under flame retardants for polypropylene.

PC/ABS and PPE/HIPS blends#

PC/ABS and PPE/HIPS blends use liquid aryl phosphates such as RDP and BDP with a PTFE anti-drip agent: in a 2024 study, 20 wt% of an aryl bisphosphate with 0.4 wt% PTFE gave PC/ABS UL 94 V-0, with a heat deflection temperature of 72.6 °C. The polycarbonate fraction makes the blend work, while ABS alone stays the hard case. Ecodesign Regulation (EU) 2019/2021 has banned halogenated flame retardants in electronic display enclosures since 1 March 2021, and PTFE falls within the pending EU universal PFAS restriction proposal (Annex XV dossier of 7 February 2023). Sulfonate salts for transparent PC and the phosphate route for blends are compared under flame retardants for polycarbonate.

Epoxy laminates and other thermosets#

Halogen-free epoxy laminates replace reactive TBBPA with DOPO-type phosphorus compounds, which reach UL 94 V-0 at about 1-1.2 wt% phosphorus in research formulations, while unsaturated polyester resins take APP, DMMP or triethyl phosphate. DOPO bonds into the epoxy network and cannot migrate out of the laminate, while aluminium diethylphosphinate and red phosphorus serve thermosets as additives. Laminate and composite systems are compared under flame retardants for epoxy resins.

Polyurethane foam#

Rigid polyurethane and PIR foams take liquid phosphorus flame retardants dosed into the polyol, such as DMMP, DMPP (15 wt% in PUR in ECHA's mapping) and triethyl phosphate, next to the chlorinated phosphate TCPP. APP serves as a solid acid source in rigid and flexible polyurethane foam.

Flexible foam relies on the chlorinated phosphates TCPP, TDCPP and V6, on APP and on reactive phosphorus polyols. In California, AB 2998 has capped organophosphorus flame retardants at 1,000 ppm in juvenile products, mattresses and upholstered furniture since 1 January 2020. Rigid and flexible systems, expandable graphite included, are compared under flame retardants for polyurethane foam.

Flexible PVC#

Flexible PVC uses phosphate esters as flame-retardant plasticizers, such as tricresyl phosphate, 2-ethylhexyl diphenyl phosphate and tert-butylphenyl diphenyl phosphate, which offset the flammability that ordinary plasticizers add to PVC. The trade-off is smoke: aryl groups in phosphate plasticizers generate smoke while alkyl groups do not, and magnesium hydroxide turns black smoke white (Hallstar plasticizer guide). Antimony, zinc borate and molybdate options are compared under flame retardants and smoke suppressants for PVC.

Phosphorus vs Brominated and Mineral Flame Retardants: What Is the Difference?#

Phosphorus flame retardants sit between bromine and minerals: they need more loading than a brominated system, such as 15-20 wt% of a phosphinate against about 8-12 wt% DBDPE with 5 wt% antimony trioxide, but far less than the 160-180 phr of aluminium trihydrate in a cable compound, and most of them release no hydrogen halide. Bromine works only in the gas phase through hydrogen bromide and antimony synergy, as set out under brominated flame retardants, while phosphorus adds the condensed phase and minerals act by endothermic cooling. Table T5 compares the 3 chemistries on 8 criteria.

Supplier and study examples in different polymers; not a like-for-like efficiency ranking.

Regulation divides them too: DBDPE faces a planned EU restriction (draft Annex XV dossier planned for December 2026), while the phosphorus SVHCs are 3 phosphate esters and the mineral hydroxides carry none. Grades, coatings and loadings of the fillers are compared under mineral flame retardants (ATH and MDH).

What Limits Phosphorus Flame Retardants in Processing and Use?#

Phosphorus flame retardants are limited by 7 factors: thermal stability, hydrolysis, blooming, plasticisation, colour, phosphine and corrosion risk, and the extra smoke and carbon monoxide of gas-phase action. Table T6 lists the decomposition, boiling or weight-loss temperature that sets each substance's processing ceiling.

Seven limits decide where a phosphorus flame retardant can go.

• Thermal stability: APP processes only up to about 220 °C, while AlPi is stable above 300 °C
• Hydrolysis: short-chain APP and MPP in phosphinate systems are water sensitive; coated APP and non-hygroscopic AlPi avoid the problem
• Blooming: AlPi/MPP compounds frost white after 85 °C and 85 % RH ageing; causes and fixes are covered under blooming and exudation
• Plasticisation: liquid aryl phosphates lower the heat deflection temperature, to 72.6 °C at 20 wt% in one PC/ABS study
• Colour: red phosphorus is limited to dark parts
• Phosphine and corrosion: red phosphorus and hypophosphites carry a phosphine risk, while the CTI of 600 V reached with Exolit OP 1312 shows that phosphinates need not cost tracking resistance
• Smoke and carbon monoxide: gas-phase action raises the CO yield, and aryl phosphates in styrenics gave more smoke in the EU ENFIRO project

How Are Phosphorus Flame-Retardant Plastics Tested?#

Phosphorus flame-retardant plastics are tested by 5 methods: the UL 94 vertical burn, the limiting oxygen index, the cone calorimeter, the glow-wire test and, for electrical parts, the comparative tracking index. UL 94 V-0 requires each afterflame to stop within 10 s and no flaming drips that ignite cotton; the V-0, V-1 and V-2 criteria are set out under UL 94 flammability ratings. Table T7 lists each test with its standard and its relevance to phosphorus.

The cone calorimeter matters most for phosphorus because heat release alone hides the extra carbon monoxide of gas-phase action. For household appliances, IEC 60335-1 clause 30.2.3 requires a GWFI of at least 850 °C and a GWIT of at least 775 °C, which glass-filled polyamide with Exolit OP 1312 meets at 960 °C and 775 °C. Air contains 20.9 % oxygen, and why an LOI above 21 does not mean self-extinguishing is explained under limiting oxygen index (LOI).

What Is the Regulatory Status of Phosphorus Flame Retardants?#

Most phosphorus flame retardants, including APP, aluminium diethylphosphinate, red phosphorus, DMMP, DOPO, MPP and TCPP, are not on the REACH Candidate List, but 3 phosphate esters are: TCEP since 2010, trixylyl phosphate since 2013 and triphenyl phosphate since 2024. Every flame retardant ban and deadline is tracked under flame retardant regulations. Table T8 gives the EU and US status of 12 phosphorus flame retardants and the melamine partner.

n/a = no entry in our sources for that jurisdiction.

EU: SVHC entries, Annex XIV and the organophosphate review#

In the EU, triphenyl phosphate has been a substance of very high concern since 7 November 2024 for endocrine-disrupting properties in the environment, and ECHA's draft recommendation of 2 February 2026 proposes it for the REACH Authorisation List. The consultation on that draft 13th recommendation closed on 2 May 2026, and the final recommendation was not published as of 22 September 2026. The SVHC dossier and the Annex XIV process are detailed on triphenyl phosphate.

Two phosphate esters already sit in REACH Annex XIV: TCEP as entry 13 (sunset date 21 August 2015) and trixylyl phosphate as entry 47 (sunset date 27 May 2023, Regulation (EU) 2020/171).

ECHA's Regulatory strategy for flame retardants (March 2023) found that organophosphorus flame retardants need more data, and a dedicated OPFR investigation is reported to be planned. TCPP and TDCPP are not SVHCs and not restricted under Annex XVII, and Directive 2014/79/EU limits TCEP, TCPP and TDCP to 5 mg/kg in toys for children under 36 months.

The Candidate List held 253 entries at its 4 February 2026 update; every flame retardant entry with its date is on the SVHC Candidate List.

US: TSCA, Proposition 65 and state laws#

In the United States, the TSCA §6(h) rule for PIP (3:1) prohibits the distribution of most articles containing this isopropylated aryl phosphate after 31 October 2026, and EPA's final risk evaluation of TCEP in September 2024 found unreasonable risk. The TCEP evaluation found that risk for workers, consumers and aquatic species, and EPA designated triphenyl phosphate a high-priority substance in December 2019. PBT rules and risk evaluations are explained under TSCA and plastic additives.

California's Proposition 65 has listed TCEP for cancer since 1 April 1992 and TDCPP since 28 October 2011, while triphenyl phosphate, APP and melamine are not on the OEHHA list edition of 31 July 2026.

California AB 2998 has banned halogenated and organophosphorus flame retardants above 1,000 ppm in juvenile products, mattresses and upholstered furniture since 1 January 2020. Listing dates and warning rules are explained under California Proposition 65.

Food-contact status under EU 10/2011 and FDA rules#

Few phosphorus flame retardants are authorised for food-contact plastics: under Regulation (EU) No 10/2011, 2-ethylhexyl diphenyl phosphate is listed with a specific migration limit of 2.4 mg/kg, TCEP must not be detectable, and DMPP and CEPPA are not listed. Calcium hypophosphite is authorised only indirectly as the calcium salt of hypophosphorous acid (FCM No 494, Article 6(3)(a)), and melamine, the partner of the phosphorus-nitrogen salts, carries an SML of 2.5 mg/kg. In the US, triphenyl phosphate appears in 21 CFR 175.105 for adhesives only, and EHDPP holds a prior sanction under 21 CFR 181.27. FCM numbers and the overall migration limit of 10 mg/dm2 are explained under EU 10/2011.

Who Makes Phosphorus Flame Retardants?#

Phosphorus flame retardants come from Clariant (Exolit OP phosphinates, Exolit AP ammonium polyphosphate, Exolit RP red phosphorus), ICL (Fyrolflex RDP and BDP, Fyrol PCF), Lanxess (Levagard, Reofos, Disflamoll), BASF (Melapur MPP), Adeka (PAPP blends) and Italmatch (Masteret red phosphorus). Table T9 lists 7 producers in the order of their main phosphorus type.

Companies named in our sources with verified phosphorus brand lines; not a market ranking.

Buyers should compare phosphorus grades by CAS number, phosphorus content and the rating reached in their own polymer, not by brand. Exolit, Fyrolflex and Melapur grades resolve to CAS numbers in the plastic additive trade name lookup.

The global flame retardant market is worth USD 8.1-9.3 billion (2025, analyst estimates including MarketsandMarkets); our sources hold no verified phosphorus share of it.

Brand names hide the chemistry: Levagard PP is TCPP and Disflamoll DPO is 2-ethylhexyl diphenyl phosphate. Plants and brand lines by company are in the directory of flame retardant manufacturers and suppliers.

─── The sections below cover related but broader questions, including health, recycling and look-alike phosphorus additives, that sit outside the core definition, selection and regulatory guidance above. ───

Are Phosphorus Flame Retardants Safe for Health and the Environment?#

Phosphorus flame retardants differ widely in hazard: the EU ENFIRO project, concluded in 2012, found good environmental and health profiles for APP, aluminium diethylphosphinate, MPP and DOPO, while 3 phosphate esters, TCEP, trixylyl phosphate and triphenyl phosphate, are now substances of very high concern. Flame retardants exist because they buy escape time: in a 1988 test by the US National Bureau of Standards, flame-retarded products gave more than 15 times longer escape time and a quarter of the heat release. Exposure and house-dust studies are reviewed under flame retardants and human health.

Phosphorus flame retardants in recycled plastics#

Phosphorus systems avoid the legacy-bromine problem of recyclers: a 2:1 PAPP and MPP blend reached UL 94 V-0 at 21 wt% in recycled polypropylene, while recovered plastics with PBDEs must fall to 200 mg/kg from 30 December 2027. Delegated Regulation (EU) 2025/1482 sets that schedule, with 350 mg/kg for recovered material from 30 December 2025 and 10 mg/kg for other mixtures and articles. Sorting and legacy-additive limits are covered under how additives affect plastic recyclability.

Phosphorus flame retardants vs phosphite antioxidants#

Phosphite antioxidants are not flame retardants: they are trivalent phosphorus esters such as Irgafos 168 that destroy hydroperoxides during processing and turn into phosphates as they work, while phosphorus flame retardants act only once the plastic burns. The reaction is P(OR)3 + ROOH → O=P(OR)3 + ROH. The names are close: TPP means triphenyl phosphate, the flame retardant, and TPPi triphenyl phosphite, the PVC co-stabilizer. Hydrolysis and dosage of the stabilizers are covered under phosphite antioxidants.

Phosphate ester plasticizers#

Phosphate ester plasticizers such as tricresyl phosphate and 2-ethylhexyl diphenyl phosphate soften PVC and add flame retardance in one additive, at the cost of more smoke from their aryl groups. EHDPP is used in food-packaging PVC. Their PVC formulations are compared under phosphate ester plasticizers.

The neurotoxicity of tricresyl phosphate (OPIDN) is linked to its ortho-cresyl isomers, so commercial grades minimise ortho content, and TCP is not an SVHC, unlike trixylyl phosphate. The ortho-isomer issue is explained on tricresyl phosphate.

Is phosphorus itself flammable?#

Red phosphorus, the form used in plastics, is classified as a flammable solid (Flam. Sol. 1, H228) under the EU CLP Regulation, which is why compounders receive it encapsulated or as a masterbatch rather than as a powder.

Is melamine a flame retardant?#

Yes: melamine is a nitrogen flame retardant and the blowing agent of intumescent systems, and it has been on the REACH Candidate List since 17 January 2023. Its SVHC and food-contact status are covered on melamine as a flame retardant.

What is another name for organophosphate flame retardants?#

Organophosphate flame retardants are also called OPFRs or phosphate ester flame retardants; "organophosphorus flame retardants" is the wider term that adds phosphonates and phosphinates. In plastics the names cover triphenyl phosphate, RDP, BDP and TCPP, not the pesticides also called organophosphates.

Which plastics reach UL 94 V-0 with phosphorus flame retardants?#

Glass-filled PA6, PA66 and PBT, high-temperature polyamide, polypropylene, PC/ABS and epoxy laminates all reach UL 94 V-0 with published phosphorus systems, from about 1 wt% phosphorus in epoxy to 30 wt% of an APP package in polypropylene. Ratings by polymer for every FR chemistry are listed under flame-retardant plastics.

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Byline: PlasticAdditives.net Editorial Team

Every figure on this page is checked against primary sources; see our methodology and fact-checking process.

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