Halogen-Free Flame Retardants: 6 Classes, How They Work and How to Choose One

Halogen-free flame retardants are mineral, phosphorus, nitrogen and intumescent additives that let plastics pass fire tests such as UL 94 V-0 without chlorine or bromine, at loadings from about 15 wt% for phosphinates in polyamide to more than 60 wt% for metal hydroxides in cable compounds. They replace brominated and chlorinated systems where smoke, corrosive gases or regulation rule halogens out, so which of the 6 classes suits which polymer? Each class breaks the combustion cycle by a different route, cooling the melt, building char, diluting the flame with inert gas or trapping radicals in the gas phase, and the right choice depends on the polymer, the target rating and the processing temperature the compound must survive.

Flame retardants account for 13 % of all plastic additives by weight, the third-largest additive group after plasticizers and fillers, and halogen-free chemistries now span 6 distinct mechanisms across cable jackets, electronics housings, vehicle parts and construction profiles.

This page defines the term, explains the 4 modes of action behind the 6 classes, compares halogen-free systems with brominated and chlorinated ones, sets loadings and processing limits by polymer, lists the tests and standards used to prove a rating, and names the manufacturers that supply each class. The hub on flame retardants for plastics compares all FR families, halogenated ones included, while every section below covers the halogen-free routes only.

In brief:

• 6 halogen-free classes: mineral, phosphorus, nitrogen and nitrogen-phosphorus, intumescent, boron and tin synergists, low-dose specialty systems
• Heat absorbed on decomposition: ATH 1051 J/g from about 200 °C; MDH 1316 J/g, stable to about 320 °C
• Cable loading: 160-180 phr ATH or MDH in halogen-free EVA/polyethylene compounds (about 61.5 wt% at 160 phr)
• Intumescent PP: 21 wt% PAPP:MPP at a 2:1 ratio reaches UL 94 V-0 in virgin and recycled polypropylene

What Is a Halogen-Free Flame Retardant?#

A halogen-free flame retardant is an additive or reactive component that delays ignition and slows flame spread in a plastic without any intentionally added chlorine or bromine, working instead through water release, char formation, intumescence or phosphorus radical chemistry. The industry uses several near-synonyms for the same idea: HFFR, NHFR and ZHFR in general compounding, LSZH or LS0H in cable jargon, and "PIN" flame retardants (phosphorus, inorganic and nitrogen) as the term used by the sector group pinfa. Flame retardants of any kind do not make a plastic non-combustible; they move a compound up one or more classes in a standardized fire test, and formulators choose between additive, reactive and polymeric flame retardants depending on how permanently the chemistry must stay bound to the polymer, with DOPO as the main example of a reactive phosphorus flame retardant that becomes part of the epoxy backbone itself.

What does "halogen-free" mean in plastics?#

In plastics, "halogen-free" means that no chlorine- or bromine-containing flame retardant has been added, so the compound releases no hydrogen chloride or hydrogen bromide when it burns. The halogens are fluorine, chlorine, bromine and iodine, the group 17 elements of the periodic table, but the flame-retardant label focuses only on chlorine and bromine because those two elements are the ones used deliberately as fire-retardant chemistry in brominated and chlorinated systems. "Halogen-free" is not the same claim as "zero halogen content": the label covers the flame retardant that was intentionally added, not every trace element in the resin, filler or colorant, and reference documents such as IEC 61249-2-21 exist specifically to define halogen-free limits for laminates rather than leaving the term to marketing use. Cable and compound datasheets use 5 labels for the same idea.

• HFFR: halogen-free flame retardant, the general compounding term
• NHFR: non-halogenated flame retardant, used interchangeably with HFFR
• ZHFR: zero-halogen flame retardant, a marketing variant of the same meaning
• LSZH / LS0H: low smoke zero halogen, the standard cable-industry term (also written LSOH or LSF)
• PIN: phosphorus, inorganic and nitrogen flame retardants, the term used by the pinfa sector group

Do fluorinated additives such as PTFE count as halogens?#

Yes, chemically: fluorine is a halogen, so the PTFE anti-drip agent used in some formulations and the potassium perfluorobutane sulfonate (PFBS-K) used in polycarbonate are fluorinated, even though compounds containing them are still sold as "halogen-free" because they contain no chlorine or bromine. PTFE (CAS 9002-84-0) works as an anti-drip agent in UL 94 V-0 formulations, for example at 0.4 wt% alongside 20 wt% of an aryl phosphate in a 2024 PC/ABS study, and both PTFE and PFBS-K fall under a broader chemical debate than flame retardancy alone: PTFE sits inside the EU's proposed universal PFAS restriction (Annex XV dossier published 7 February 2023, still pending), while PFBS-K has been a Substance of Very High Concern since 16 January 2020. Both fall under the EU PFAS restrictions debate, and KSS is the fluorine-free alternative sulfonate used for the same charring effect in polycarbonate.

Is halogen-free the same as antimony-free?#

Halogen-free systems are antimony-free in practice, because antimony trioxide has no flame-retardant effect on its own and works only by forming antimony halides with a bromine or chlorine donor. Antimony trioxide (Sb2O3) reacts with the hydrogen halides released by a brominated or chlorinated flame retardant to form antimony oxyhalides and then volatile antimony trihalide, and it is that vapor-phase chemistry, not the oxide itself, that interrupts combustion, so a formulation with no halogen donor gains nothing from adding it. The synergy chemistry and Carc. 2 status are detailed on antimony trioxide (CAS 1309-64-4), which carries a harmonised classification of Carc. 2, H351 and an IARC Group 2A listing (Volume 131, 2022) and has been on the Proposition 65 list since 10 October 1990, though it is not a REACH Substance of Very High Concern; zinc borate and the zinc stannates serve as partial antimony trioxide replacements inside halogenated systems, not as halogen-free substitutes themselves.

How Do Halogen-Free Flame Retardants Work?#

Halogen-free flame retardants break the combustion cycle mostly in the condensed phase: metal hydroxides absorb heat and release water, phosphorus compounds turn the polymer surface into char, and intumescent systems swell that char into an insulating foam. A burning plastic follows a cycle: external heat pyrolyzes the polymer into flammable volatiles, those volatiles oxidize in the gas phase, and the resulting flame feeds heat back into the polymer to sustain pyrolysis. Halogenated flame retardants interrupt that cycle only in the gas phase, where hydrogen bromide or hydrogen chloride traps the H· and OH· radicals that drive oxidation, often assisted by antimony trioxide; halogen-free chemistries instead act mainly before the volatiles ever reach the flame, cooling the polymer, diluting the fuel with inert gas, or fixing carbon into a protective char and glassy barrier layer.

Bernhard Schartel at the German Federal Institute for Materials Research and Testing (BAM) showed in a 2010 study in Materials ("Phosphorus-based flame retardancy mechanisms: old hat or a starting point?") that the same phosphorus flame retardant can act mostly in the gas phase in polycarbonate while adding condensed-phase char when the same polymer is blended into PC/ABS, and that gas-phase flame inhibition, whether from phosphorus or from halogens, always raises the carbon monoxide yield of the fire. Gas-phase and condensed-phase chemistry for every class is explained in full under how flame retardants work.

What Are the 6 Classes of Halogen-Free Flame Retardants?#

The 6 classes of halogen-free flame retardants are mineral flame retardants such as ATH and MDH, phosphorus compounds, nitrogen and nitrogen-phosphorus salts, intumescent systems, boron and tin synergists, and low-dose specialty systems such as sulfonate salts for polycarbonate. The order mineral, phosphorus, nitrogen, intumescent, synergists, specialty is used consistently through every list and table on this page.

1. Mineral flame retardants: metal hydroxides and carbonates (ATH, MDH, boehmite, huntite)#

Mineral flame retardants are metal hydroxides and carbonates, mainly aluminium trihydrate (aluminum trihydrate, ATH) and magnesium hydroxide (MDH), that absorb heat and release water when a fire heats the plastic: ATH absorbs 1051 J/g from about 200 °C, MDH 1316 J/g only above about 320 °C. ATH decomposes as 2Al(OH)3 to Al2O3 plus 3H2O, losing 34.6 % of its mass on ignition in theory, while MDH follows Mg(OH)2 to MgO plus H2O and processes roughly 110 °C higher than ATH, a gap that lets compounders choose the mineral that matches their extrusion or injection temperature. Grades and coatings for mineral flame retardants (ATH and MDH) vary by particle size and surface treatment, and the oxide residue that both minerals leave behind also adsorbs soot, which is why mineral-filled compounds suppress smoke as a secondary benefit.

Two rarer minerals fill gaps in the temperature range. Boehmite (CAS 1318-23-6) dehydrates at a higher temperature than ATH, though its exact onset is not yet verified for publication here, while huntite-hydromagnesite blends (sold as UltraCarb) release water from about 220 °C, carbon dioxide from about 330 °C and leave a cement-like char at about 560 °C, giving a 3-stage cooling and barrier effect in one filler. Surface treatments such as vinyl-silane, amino-silane and fatty-acid coatings restore the elongation that raw mineral filler removes, and synthetic and brucite grades of magnesium hydroxide (MDH) are compared by particle size and coating on that page.

2. Phosphorus flame retardants: red phosphorus, APP, phosphinates and phosphate esters#

Phosphorus flame retardants work in both phases: in the solid they turn the polymer into char and glassy phosphate layers, and in the flame their PO· radicals trap the H· and OH· radicals that keep combustion going. Phosphorus flame retardants fall into 5 sub-groups.

• Red phosphorus: an elemental form (CAS 7723-14-0), very efficient by charring in glass-fibre PA66, always sold encapsulated or as a masterbatch because it carries a harmonised Flam. Sol. 1, H228 classification and is limited to dark colours
• Ammonium polyphosphate (APP): an inorganic salt (CAS 68333-79-9) whose phase II form (chain length above 1,000 units) decomposes from about 240 °C into ammonia and polyphosphoric acid
• Metal phosphinates: aluminium diethylphosphinate (AlPi, DEPAL, CAS 225789-38-8), the workhorse of glass-filled polyamide and PBT
• Phosphate esters: triphenyl phosphate (TPP), resorcinol bis(diphenyl phosphate) (RDP) and bisphenol A bis(diphenyl phosphate) (BDP), liquid or low-melting aryl phosphates that act mostly in the gas phase
• DOPO and phosphonates: DOPO as a reactive epoxy building block, plus dimethyl methylphosphonate (DMMP) and triethyl phosphate (TEP) used in rigid polyurethane, PIR and unsaturated polyester

Each sub-group is covered in full under phosphorus flame retardants, including the chain-length and decomposition data behind APP's char-forming phase II form. Aluminium diethylphosphinate reaches ultraviolet-stable ratings without char discoloration: AlPi runs at about 15 wt% for UL 94 V-0 at 1.6 and 0.8 mm in high-temperature polyamide (Exolit OP 1230), decomposes above 300 °C and carries 23.3-24.0 wt% phosphorus, which is why it dominates glass-filled engineering plastics rather than commodity resins.

Exolit OP grades and the wider phosphinate family are compared on phosphinate flame retardants (DEPAL), the class page that details grade-by-grade loadings for polyamide and PBT. DOPO, by contrast, reacts permanently into an epoxy resin rather than blending in as an additive, and its use in halogen-free laminates is covered separately in the epoxy section below.

3. Nitrogen and nitrogen-phosphorus flame retardants (melamine cyanurate, MPP, PAPP)#

Nitrogen and nitrogen-phosphorus flame retardants such as melamine cyanurate, melamine polyphosphate (MPP) and piperazine pyrophosphate (PAPP) release inert gases and, with phosphorus, build char, which makes them the standard partners of phosphinates in polyamides and of intumescent packages in polypropylene. Melamine cyanurate (CAS 37640-57-6) decomposes endothermically above about 300 °C, releases inert gas and promotes melt dripping, so unfilled polyamide 6 and 66 compounds use it to reach a V-2 or, combined with other systems, a V-0 rating by carrying heat away with the drips. MPP (CAS 218768-84-4) instead forms polyphosphoric acid char in the condensed phase while releasing melamine gas, and it acts as a synergist with AlPi in glass-filled polyamide, although Clariant notes that MPP can lower the hydrolytic stability of some phosphinate blends and that MPP-containing compounds can bloom, showing a white frost, after ageing at 85 °C and 85 % relative humidity.

A PAPP:MPP blend at a 2:1 ratio and 21 wt% total loading reaches UL 94 V-0 in both virgin and recycled polypropylene, a result published in ACS Applied Polymer Materials (2026, doi 10.1021/acsapm.6c00885), which makes the nitrogen-phosphorus route one of the few halogen-free packages proven to hold its rating through mechanical recycling. Melamine cyanurate salts are covered in full under nitrogen-based flame retardants, alongside the plain melamine used as a blowing agent inside intumescent packages and as a flame retardant in flexible polyurethane foam.

4. Intumescent flame retardants and expandable graphite#

Intumescent flame retardants swell into an insulating carbon foam when heated: an acid source such as ammonium polyphosphate dehydrates a carbon source such as pentaerythritol, and a blowing agent such as melamine inflates the char. Chemical intumescence needs all 3 components together: APP releases ammonia and phosphoric acid as it decomposes, the acid dehydrates pentaerythritol into a carbon-rich residue, and the gases released by the melamine blowing agent expand that residue into a low-density insulating foam. Formulation ratios are detailed under intumescent flame retardants, but as a reference point, APP-based polypropylene systems (Clariant Exolit AP 750 and AP 766) reach UL 94 V-0 at 22-30 wt% and process up to about 220 °C, and adding 0.25 wt% zinc oxide or manganese oxide as a char catalyst can lift an APP and pentaerythritol system to a limiting oxygen index of 30 % with a V-0 rating; a 2025 study in Polymers found that raising the zinc oxide level to 1.5 wt% pushed the oxygen index further, to 43.7 %.

Expandable graphite (CAS 12777-87-6) works as a physical intumescent rather than a chemical one: intercalated graphite flakes expand from about 200 °C (with an onset range of 140-230 °C reported across grades) to between 30 and 400 cm3/g, and because the expanded char is black, expandable graphite rules out light-coloured parts and processes typically below 230 °C. It is mainly used in polyurethane foam, where a 2024 study in Polymers found that 15 parts per hundred of expandable graphite combined with 30 parts of filler cut the peak heat release rate of a viscoelastic polyurethane foam by 52 %. Expansion grades of expandable graphite are listed by onset temperature and expansion volume on its substance page.

5. Boron and tin synergists: zinc borate and zinc stannates#

Zinc borate, zinc stannate and zinc hydroxystannate are synergists rather than stand-alone flame retardants: they strengthen the char of mineral and phosphorus systems and cut smoke, typically at 3-6 phr next to ATH. Zinc borate (Firebrake ZB, 2ZnO·3B2O3·3.5H2O, CAS 138265-88-0) releases water above about 290 °C, forms a glassy borate layer over the char, suppresses afterglow and smoke and improves resistance to electrical arc tracking; that 3-6 phr figure comes from PVC formulations that pair zinc borate with ATH, and because PVC itself is a chlorinated polymer, zinc borate there is a smoke and dripping synergist inside a halogenated system, not a standalone halogen-free flame retardant. In a halogen-free context, 10 wt% zinc borate combined with 10 wt% MDH in a PP/calcium carbonate compound reached a limiting oxygen index of 29.4 %, and the material is not a REACH Substance of Very High Concern, although some suppliers self-classify certain grades as Repr. 2; Exolit OP 1312 and OP 1314, for example, have carried a Repr. 2 label since 1 June 2015 because they contain more than 3 % zinc borate.

Hydrate grades and CAS numbers for zinc borate, together with the related zinc stannate (Flamtard S) and zinc hydroxystannate (Flamtard H, used at 3-5 phr in research PVC formulations), which add char strengthening and smoke suppression by a similar mechanism, are listed on its substance page.

6. Low-dose specialty systems: sulfonate salts, NOR HALS and nanofillers#

Low-dose specialty systems reach a rating at a small fraction of mineral loadings: sulfonate salts such as KSS make polycarbonate char, NOR HALS generate radicals that help thin polyolefin films self-extinguish, and nanofillers such as organoclay build a surface barrier. Sulfonate salts migrate to the surface of polycarbonate during processing and catalyse charring there at a very low dosage; potassium diphenylsulfone sulfonate (KSS, CAS 63316-43-8, EC 264-097-3) is the fluorine-free workhorse of this group and is not a Substance of Very High Concern, while the fluorinated alternative, potassium perfluorobutane sulfonate (PFBS-K, also called Rimar salt or Bayowet C4), has been an SVHC since 16 January 2020. The fluorine-free salt is profiled on KSS (potassium diphenylsulfone sulfonate), which compares it against the PFAS-classed alternative.

NOR HALS such as Flamestab NOR 116 and AddWorks LXR 920 act as radical generators rather than classic char formers, and Clariant reports that they help transparent polyolefin films reach the DIN 4102 B2 building-material rating; because NOR HALS also function as UV stabilizers in the same films, their light-stabilizing role is covered under NOR HALS. Nanocomposites built from organoclay, layered double hydroxides, carbon nanotubes or POSS particles lower the peak heat release rate through a surface barrier effect but seldom pass a UL 94 rating on their own, so researchers including Jeffrey Gilman at NIST and Serge Bourbigot at the University of Lille generally study them as a companion to one of the other 5 classes rather than as a replacement for it.

Halogenated vs Halogen-Free Flame Retardants: What Is the Difference?#

Halogenated flame retardants stop the flame chemically in the gas phase at low loadings, such as 8-12 wt% decabromodiphenyl ethane (DBDPE) with 5 wt% antimony trioxide in HIPS, while halogen-free flame retardants act mostly in the solid, need higher loadings and release no corrosive hydrogen halides when they burn. That loading gap is the central trade-off of the whole category: a brominated HIPS compound with about 10.7 wt% bromine and 5 wt% antimony trioxide reaches UL 94 V-0 at 0.8 mm, while the halogen-free routes to the same rating in other polymers run from about 15 wt% aluminium diethylphosphinate in polyamide to 21-30 wt% intumescent packages in polypropylene and up to 60-65 wt% mineral hydroxide in cables.

Loadings are supplier or study examples, not universal values.

Brominated flame retardants such as DBDPE and TBBPA remain the incumbent chemistry in several of these same markets, and the polymeric and non-polymeric grades still in use are covered under brominated flame retardants. On the acid-gas side of the comparison, cable compounds are judged against EN 60754-2's acidity class a1, which requires a conductivity below 2.5 µS/mm and a pH above 4.3, a bar that halogenated cable jackets fail by design and halogen-free ones are formulated to meet; the chlorinated alternatives that still compete in some of the same cable and flooring markets, including Dechlorane Plus and the chlorinated paraffins, are covered under chlorinated flame retardants.

Why are compounders replacing halogenated flame retardants?#

Compounders replace halogenated flame retardants for 6 reasons: EU display rules, the coming REACH restriction of aromatic brominated flame retardants, Stockholm Convention POP listings, US state bans, cable smoke and acidity classes, and rising OEM halogen-free specifications.

• EU Ecodesign Regulation (EU) 2019/2021: bans halogenated flame retardants in the enclosures and stands of electronic displays from 1 March 2021, a rule the EU General Court has upheld
• REACH restriction in preparation: ECHA published its investigation report on aromatic brominated flame retardants on 18 December 2024, received the Commission's restriction mandate on 11 November 2025, ran a call for evidence from 21 January to 18 March 2026, and plans a draft Annex XV restriction dossier in December 2026, covering non-polymeric aromatic brominated flame retardants (polymeric grades stay out of scope)
• Stockholm Convention POP listings: PBDEs (2009), HBCD (2013), decaBDE and short-chain chlorinated paraffins (2017), Dechlorane Plus (2023) and medium-chain chlorinated paraffins (2025) have progressively removed halogenated options from the market
• US state bans: New York bans organohalogen flame retardants in display enclosures and stands from 1 January 2024, Washington's Safer Products Cycle 1 restricts organohalogen flame retardants in electric and electronic products from 1 January 2025, and California's AB 2998 restricts halogenated and organophosphorus flame retardants above 1,000 ppm in juvenile products, mattresses and upholstered furniture from 1 January 2020
• Cable smoke and acidity classes: EN 13501-6's B2ca-s1a,d0,a1 rating, built from EN 50399, EN 61034-2 smoke measurement and EN 60754-2 acidity testing, is difficult to reach with a halogenated jacket compound
• OEM halogen-free specifications: electronics and automotive OEM purchasing standards increasingly specify halogen-free compounds directly, ahead of what regulation alone requires

Every ban and deadline above is tracked in full under flame retardant regulations, which follows each instrument from proposal through to the compliance date.

Which Halogen-Free Flame Retardant Is Best for Each Polymer?#

The best halogen-free flame retardant depends first on the processing temperature and the target rating: aluminium trihydrate for PE, EVA and PVC processed below about 200 °C, magnesium hydroxide or intumescent APP/PAPP packages for PP, phosphinates for polyamides and PBT, and aryl phosphates for PC/ABS. Table 3 sets out 17 documented polymer and system combinations, each with the loading and rating a supplier or published study reached.

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

Request quotes for halogen-free flame retardants: substance or grade (ATH, MDH, APP, DEPAL, MPP), polymer, target rating, volume and country, through the plastic additive supplier finder. Compounders who want the full matrix as a working reference can download the Flame Retardant Selector Matrix (PDF), which lists halogen-free systems by polymer, rating and processing temperature; the same data also powers the flame retardant selector filter tool.

Polypropylene and polyethylene#

Halogen-free polypropylene reaches UL 94 V-0 with about 21-30 wt% of an intumescent package based on APP or piperazine pyrophosphate, whereas mineral routes need up to 65 wt% magnesium hydroxide, because PP (limiting oxygen index about 17.5 %) drips and forms no char on its own. The PAPP:MPP 2:1 blend at 21 wt% and the APP-based Exolit AP grades at 22-30 wt% both reach V-0 without halogens, and adding 0.25 wt% zinc oxide or manganese oxide as a char catalyst can push the oxygen index higher still. Where mineral loading is preferred instead, Huber's HFFR PP reference formulation uses 185.7 phr of coated MDH to reach a limiting oxygen index of 30.2, and unfilled PE and EVA profiles follow the same mineral or expandable-graphite routes. V-2 grades and the brominated alternatives that compete with these systems are compared on flame retardants for polypropylene.

Wire and cable compounds (LSZH)#

Low-smoke zero-halogen (LSZH) cable compounds are EVA or polyethylene filled with 160-180 phr aluminium trihydrate or magnesium hydroxide, about 60 wt% of the compound, which is the standard route to the acidity class a1 and smoke class s1a of EN 13501-6. Huber's reference formulation runs EVA 67, LLDPE 17, coupling agents 16, aluminum trihydrate (ATH) 160 and antioxidants 1.0 parts per hundred resin, and at a cone calorimeter heat flux of 35 kW/m2, the unfilled EVA/LLDPE base peaks above 550 kW/m2 while the same compound with ATH or MDH delays ignition by 120-160 seconds. That performance is what lets a cable meet EN 13501-6's B2ca-s1a,d0,a1 class, which combines a flame-spread limit (FS ≤ 1.5 m), heat and smoke release limits (THR1200 ≤ 15 MJ, pHRR ≤ 30 kW, FIGRA ≤ 150 W/s under EN 50399), a light-transmittance smoke test (EN 61034-2) and a conductivity and pH-based acidity test (EN 60754-2).

CPR classes and the PVC cable systems that compete with LSZH in lower fire-performance classes are covered on flame retardants for wire and cable, and silane-crosslinked XLPE cables use the same vinyl-silane-coated ATH at up to 180 phr with a processing ceiling of about 200 °C, the point at which ATH begins to release water.

Polyamides and polyesters (PA6, PA66, PBT)#

Glass-filled polyamides and PBT use aluminium diethylphosphinate systems at 15-20 wt%, which reach UL 94 V-0 from 0.4 to 3.2 mm with a glow-wire ignition temperature of 775 °C and a CTI of 600 V in PA6/PA66. Clariant's Exolit OP 1312 blend delivers those figures together with a glow-wire flammability index of 960 °C, and PBT reaches V-0 at 18 wt% with the related OP 1260 grade; under EN 45545-2, the rail hazard-level standard, glass-filled PA66 with these systems reaches requirement set R22 at hazard level HL3 and glass-filled PBT reaches R22 at HL2. Unfilled polyamide, by contrast, more often uses melamine cyanurate for a V-2 melt-dripping route, while glass-filled PA66 sometimes takes encapsulated red phosphorus instead of a phosphinate, trading the phosphinate's colour flexibility for red phosphorus's charring efficiency at the cost of a dark compound. MPP and AlPi blends can bloom, showing a white frost, after ageing at 85 °C and 85 % relative humidity, and Clariant notes that MPP can lower the hydrolytic stability of some phosphinate systems. Unfilled and glass-filled grades are compared in detail under flame retardants for nylon.

Polycarbonate and PC/ABS#

Polycarbonate needs only a trace of a sulfonate salt such as KSS plus a PTFE anti-drip agent to move from V-2 to V-0, while PC/ABS blends need about 20 wt% of an aryl phosphate such as BDP or RDP. Unmodified polycarbonate is intrinsically rated V-2, so the sulfonate route (KSS or the fluorinated PFBS-K) works at a fraction of the loading of any other class because it only has to catalyse surface charring, not fill the compound; PC/ABS blends need far more phosphorus because the ABS component burns and drips more readily, and in one 2024 study a formulation with 20 wt% of the aryl phosphate BAPDP plus 0.4 wt% PTFE reached UL 94 V-0. Bernhard Schartel's BAM research also showed that the same aryl phosphate, BDP, acts mainly in the gas phase in plain polycarbonate but adds condensed-phase char once the resin is blended into PC/ABS. Transparent PC options and the sulfonate-versus-phosphate trade-off are compared on flame retardants for polycarbonate.

ABS and HIPS#

ABS and HIPS are the hardest commodity plastics to flame-retard without halogens: halogen-free V-0 housings are usually made by switching to PC/ABS or PPE/HIPS blends with aryl phosphates, since RDP alone did not rate ABS or EVA at 20-30 wt% in one comparative study. That 2020 study, published in ACS Omega, found RDP unable to reach a rating in either resin at those loadings on its own, while a combined APP and AlPi package at 20 wt% did reach a passing formulation in ABS research reported in Polymers in 2024. The EU's Ecodesign display rule, which bans halogenated flame retardants in display enclosures and stands from 1 March 2021, is one of the reasons manufacturers now favour the PC/ABS or PPE/HIPS route over trying to flame-retard plain ABS or HIPS directly.

Epoxy 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, often combined with ATH or boehmite. DOPO derivatives can reach the same rating at a slightly lower phosphorus content, from 0.25 to 1.2 wt%, depending on the derivative and the resin system, and because DOPO reacts into the epoxy network it stays permanently bound rather than migrating out over the laminate's service life. TBBPA, the halogenated incumbent in standard FR-4 laminates, has carried a harmonised Carc. 1B classification since 1 September 2025, which adds regulatory pressure to the DOPO-based route; IEC 61249-2-21 remains the reference standard for what counts as a halogen-free laminate, though its specific ppm limits are not published on this page pending verification. DOPO is the reactive building block of halogen-free laminates, and its full property and regulatory profile is on its substance page.

Polyurethane foam#

Halogen-free PU foams rely on expandable graphite, melamine and liquid phosphonates such as DMMP and triethyl phosphate, replacing the chlorinated phosphate TCPP that is still widely used in rigid PU and PIR insulation. Expandable graphite is the main commercial halogen-free route in flexible and viscoelastic foam, where 15 parts per hundred combined with 30 parts of filler cut peak heat release rate by 52 % in the 2024 Polymers study cited above, while melamine serves the same role in flexible foam and DMMP or TEP are used as liquid phosphonates in rigid PU and PIR insulation and in unsaturated polyester. Flexible and rigid foam systems, including how they compare against TCPP, are covered under flame retardants for polyurethane foam.

How Much Halogen-Free Flame Retardant Does a Plastic Need?#

Halogen-free plastics need from about 1 wt% phosphorus in reactive epoxy systems to 15-30 wt% of phosphinate or intumescent packages and about 60 wt% of mineral filler, with the level set by the target rating, part thickness and the polymer's own tendency to char. Four factors drive that range.

• Target rating and part thickness: a thin-wall V-0 part needs a higher loading than the same formulation at 3.2 mm
• Polymer char tendency and limiting oxygen index: a naturally char-forming resin needs less flame retardant than a dripping, low-LOI resin such as PP
• Processing temperature: the flame retardant's decomposition or expansion onset must sit above the melt-processing temperature of the compound
• Mechanical and electrical property limits: elongation, heat deflection temperature and comparative tracking index all cap how much filler or plasticising phosphate a formulation can carry

Processing temperature limits by class#

The processing temperature decides the class: ATH starts to release water at about 200 °C and expandable graphite expands from about 200 °C, while MDH is stable to about 320 °C and aluminium diethylphosphinate to above 300 °C.

A compound formulated above its flame retardant's onset temperature loses the additive to premature decomposition, gassing and surface defects before the part is even molded, so the processing window is the first filter compounders apply, ahead of cost or rating.

Property trade-offs at high loadings#

High halogen-free loadings trade fire performance against 5 properties: elongation, heat deflection temperature, hydrolysis resistance, surface appearance and colour.

• Elongation falls as mineral loading rises; silane or fatty-acid coatings, and coupling agents such as those used in Huber's cable formulation (Fusabond 226D, Lotader 3210), restore much of the loss
• Heat deflection temperature falls with liquid aryl phosphates, since they act partly as plasticisers: a 20 wt% BDP-type system reached an LOI of 25.4 and a V-0 rating but dropped heat deflection temperature to 72.6 °C in one study
• Hydrolysis resistance can fall in phosphinate systems once MPP is added as a synergist, an effect Clariant has documented directly
• Surface appearance can bloom, showing a white frost on AlPi/MPP blends after ageing at 85 °C and 85 % relative humidity
• Colour is restricted to dark shades whenever red phosphorus or expandable graphite is used, since both are intrinsically coloured fillers

Silane and maleated coupling agents restore elongation in filled compounds, and choosing the right coupling chemistry is usually the fastest way to recover mechanical properties without cutting the flame-retardant loading itself.

How Are Halogen-Free Flame-Retardant Plastics Tested?#

Halogen-free flame-retardant plastics are tested with the same 5 tools as any FR compound, UL 94, oxygen index, cone calorimeter, glow wire and, for cables, EN 50399 with smoke and acidity measurements, but smoke and acid-gas results are where they gain most over halogenated grades.

V-0, V-1, V-2 and 5VA criteria are set out in full on UL 94 flammability ratings. Why an LOI above 21 does not automatically mean a compound is self-extinguishing outside a laboratory atmosphere is explained on limiting oxygen index (LOI), since real fires rarely burn in the 20.9 % oxygen atmosphere the standard test controls for.

What Is the Regulatory Status of Halogen-Free Flame Retardants?#

Most halogen-free flame retardants, including ATH, MDH, APP, aluminium diethylphosphinate, MPP and zinc borate, are not on the REACH Candidate List, but 3 flame-retardant substances used in halogen-free formulations are: triphenyl phosphate, melamine and PFBS-K. PFBS-K is fluorinated rather than chlorinated or brominated, so its Candidate List entry sits alongside the wider PFAS debate rather than the halogen-free-versus-halogenated question, and none of the 3 listed substances changes the general rule that the mainstream halogen-free classes, mineral, phosphinate and nitrogen-phosphorus, carry no SVHC status.

Halogen-free is not hazard-free: SVHC and CLP entries#

Halogen-free is not the same as hazard-free: triphenyl phosphate has been an SVHC since 7 November 2024, melamine since 17 January 2023, and the US restricts the aryl phosphate PIP (3:1) in articles from 31 October 2026.

The endocrine-disruptor listing behind triphenyl phosphate's SVHC status is detailed on triphenyl phosphate, one of the organophosphate flame retardants that ECHA's 2023 flame-retardant strategy flagged for closer data review even though it is not itself a brominated or chlorinated substance. All flame-retardant entries with dates are on the SVHC Candidate List, and California's AB 2998 restricts organophosphorus flame retardants above 1,000 ppm in the same product categories as halogenated ones, so a halogen-free reformulation does not automatically clear every state or EU hazard list.

Food-contact listings under EU 10/2011#

Several mineral flame retardants are authorised additives under Regulation (EU) No 10/2011 without a specific migration limit, while melamine is listed with an SML of 2.5 mg/kg. The mineral hydroxides and carbonates used as flame retardants fall under the regulation's overall migration limit rather than a substance-specific one, while melamine, used in some nitrogen-based systems, carries both the 2.5 mg/kg SML and the regulation's general 10 mg/dm2 overall migration limit. FCM numbers and the overall migration limit that applies to unlisted-SML substances are explained on EU 10/2011.

Who Makes Halogen-Free Flame Retardants?#

Halogen-free flame retardants come from Clariant (Exolit phosphinates and APP), Huber (Martinal ATH and Magnifin MDH), Nabaltec (Apyral), BASF (Melapur), ICL (Fyrolflex aryl phosphates), Adeka (PAPP blends) and U.S. Borax (Firebrake zinc borate).

Huber Advanced Materials acquired Martinswerk from Albemarle in a deal completed on 1 February 2016, folding the Martinal ATH line into its current mineral portfolio, and Clariant announced an expansion of Exolit OP capacity at Daya Bay on 5 June 2026, a sign of continued investment in the phosphinate class specifically. Buyers should compare grades by CAS number, particle size or coating, and the rating reached in their own polymer, not by brand name, since two suppliers' grades with the same nominal chemistry can differ in decomposition onset or particle-size distribution. Plants and certifications by company are in the directory of flame retardant manufacturers and suppliers.

Request quotes for halogen-free flame retardants directly: send one request to several HFFR producers with the plastic additive supplier finder.

─── The sections below cover related but broader questions, including health and recycling, that sit outside the core definition, mechanism and selection guidance above. ───

Are Halogen-Free Flame Retardants Safer for Health and Recycling?#

Halogen-free flame retardants are generally the lower-concern option: the EU ENFIRO project, concluded in 2012, found good environmental and health profiles for APP, aluminium diethylphosphinate, ATH, MDH, MPP, DOPO and the zinc stannates, although triphenyl phosphate and melamine are now SVHCs. The ENFIRO project (EU Seventh Framework Programme, grant 226563) also found that RDP and BDP produced more smoke than mineral systems when used in styrenic polymers, so "halogen-free" does not mean every class performs identically on every environmental metric. Exposure studies across the flame-retardant category, halogenated and halogen-free alike, are reviewed under flame retardants and human health.

Halogen-free flame retardants in recycled plastics#

Halogen-free systems avoid the legacy-bromine problem of recyclers: the EU limit for PBDEs in mixtures and articles is 10 mg/kg, and articles made from recovered material must fall to 200 mg/kg from 30 December 2027, while a PAPP/MPP package has already reached UL 94 V-0 in recycled polypropylene. That PBDE limit comes from Delegated Regulation (EU) 2025/1482 under the EU's POPs Regulation, which sets an interim limit of 350 mg/kg for articles made from recovered material starting 30 December 2025 before tightening to 200 mg/kg two years later, a schedule that pushes recyclers toward feedstock that was never brominated in the first place. Sorting rules and legacy-additive limits for the wider additive package are covered under how additives affect plastic recyclability.

Flame-retardant plastics by UL 94 rating#

Most commodity plastics burn without additives, so halogen-free UL 94 V-0 grades of PP, PA, PBT and PC/ABS exist only as compounds built with one of the 6 classes above. Polycarbonate is the one exception on this page that starts intrinsically at V-2 before any flame retardant is added, while PP, with a limiting oxygen index of about 17.5 %, needs a mineral or intumescent package before it reaches any UL 94 pass at all. Ratings by polymer, gathered across every class in one reference table, are listed under flame-retardant plastics.

Is ATH a halogen-free flame retardant?#

Yes: aluminium trihydrate, Al(OH)3, contains no halogen and is the standard mineral flame retardant of LSZH cables.

Is antimony trioxide a halogen-free flame retardant?#

No: antimony trioxide contains no halogen itself, but it works only as a synergist of brominated or chlorinated flame retardants, so it belongs to halogenated systems.

What does LSZH mean?#

LSZH means low smoke zero halogen: a cable compound, usually EVA or polyethylene filled with ATH or MDH, that burns with little smoke and releases no hydrogen halides.

Does "flame retardant free" mean the same as halogen-free?#

No: "flame retardant free" means no flame retardant was added at all, while "halogen-free" means a flame retardant is present but contains no chlorine or bromine.

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

Byline: PlasticAdditives.net Editorial Team

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