Antioxidants for Plastics: 7 Types, Mechanisms, Dosage and Selection

Antioxidants for plastics are additives that slow the thermo-oxidative degradation of a polymer by trapping free radicals or destroying hydroperoxides, and this reference sorts them into 7 types in 3 mechanism groups. They make up 6 % of all plastic additives by weight and sit in the finished product at only 0.05-3 wt% (Chea et al. 2025, adapted from Hahladakis et al. 2018), so why does almost every polyolefin, polyamide and styrenic compound contain them? Melt processing at 150-320 °C tears hydrogen atoms and bonds out of the chain, and the radical chain that follows keeps running in the finished part for as long as heat and oxygen reach it.

The 7 types of antioxidants for plastics are hindered phenols, phosphites and phosphonites, thioesters, aminic antioxidants, hydroxylamines, benzofuranone lactones and vitamin E. Three mechanism groups hold them: primary antioxidants (hindered phenols, aminic antioxidants, vitamin E) trap peroxyl radicals, secondary antioxidants (phosphites and phosphonites, thioesters) destroy hydroperoxides before they split, and carbon-radical scavengers (hydroxylamines, benzofuranone lactones) catch alkyl radicals inside the melt.

Antioxidants belong to the stabilizer group of plastic additives, next to UV stabilizers and PVC heat stabilizers. This page covers the autoxidation cycle every type interrupts, why phenols and phosphites are blended rather than used alone, how much each system needs in wt% and ppm, which package matches polypropylene, polyethylene, polyamide, polyurethane, ABS, POM, polycarbonate and recyclate, how performance is measured by oxidation induction time, melt flow rate, oven ageing and yellowness index, which EU and US food-contact limits apply, who makes the grades, and it lists all 43 antioxidant substances in the directory with CAS number, type and regulatory status.

The table compares the 7 types of antioxidants for plastics by mechanism, example grades and typical level.

Levels are typical use levels from supplier data and studies; FDA figures are legal maxima.

What Are Antioxidants for Plastics?#

An antioxidant for plastics is an additive that slows thermo-oxidative degradation by interrupting the free-radical autoxidation chain, and it protects the polymer during processing, storage and service life. The same substance class carries four names in industry: polymer antioxidant, plastic antioxidant, thermal stabilizer and process stabilizer all describe it, and compounders abbreviate individual grades as "AO", as in AO-1010 for Irganox 1010. In the additive taxonomy, antioxidants are one branch of the polymer stabilizers, also written stabilisers in British usage, which sit one level below plastic additives as a whole.

Is every antioxidant a polymer additive? No. This page covers additives that protect polymers, not "antioxidant polymers" built from vitamins or polyphenols for food and medical use, and not food or cosmetic antioxidants, which belong to different regulatory systems entirely. The sibling stabilizer families are UV stabilizers, PVC heat stabilizers, acid scavengers, metal deactivators and hydrolysis stabilizers, and each of them answers a different degradation agent: sunlight, hydrogen chloride, acidic catalyst residues, metal ions and water.

Why do plastics need antioxidants?#

Plastics need antioxidants because heat, shear and oxygen during melt processing at 150-320 °C start a self-accelerating radical chain that breaks or crosslinks polymer chains. Oxidation attacks a polymer at three distinct stages, listed below.

• Processing: extrusion, compounding, injection moulding and every regrind pass generate alkyl radicals by thermal and mechanical chain scission.
• Storage: hydroperoxides formed in the melt survive in the pellet and decompose slowly, and nitrogen oxides in warehouse air attack phenolic antioxidants directly.
• Service life: heat, oxygen and metal contact consume the remaining antioxidant until the part embrittles, cracks or discolours.

The consequence differs by polymer. Polypropylene carries a tertiary carbon-hydrogen bond on every repeat unit, oxidises by chain scission, loses molecular weight, shows a rising melt flow rate and finally embrittles. Polyethylene reacts the opposite way and crosslinks, which shows up as gels in film and as a falling melt flow rate. Unsaturated rubbers and the polybutadiene phase of ABS lose allylic hydrogen first, so they harden and yellow. Metal ions accelerate all of this: copper, iron, manganese and cobalt residues catalyse hydroperoxide decomposition, which is why copper wire in contact with polyethylene insulation needs a metal deactivator beside the antioxidant.

Processing stabilizers vs long-term thermal stabilizers#

A processing stabilizer protects melt flow and colour during compounding and moulding, while a long-term thermal stabilizer keeps the finished part from oxidising for years in service. Phosphites, benzofuranone lactones and hydroxylamines act in the melt, where they suppress the viscosity shift and the yellowing that repeated passes produce. High-molecular-weight hindered phenols and thioesters act in the solid part over months and years, and thioesters in particular work mainly in long-term heat ageing at about 100-150 °C rather than at melt temperature.

One grade often carries both jobs. Irganox 1010 is sold as a primary antioxidant, as a long-term thermal stabilizer and as a processing co-stabilizer, because its molecular weight of 1,177.6 g/mol keeps it in the part while its four hindered phenol groups keep trapping radicals. The practical split is therefore not between products but between functions: the phosphite covers the extruder, the high-molecular-weight phenol covers the decade that follows.

Is a PVC heat stabilizer an antioxidant?#

No: a PVC heat stabilizer neutralises the hydrogen chloride that PVC releases, while an antioxidant stops radical oxidation, and PVC uses antioxidants only as co-stabilizers. The naming collision is a trap in formulation datasheets, because "heat stabilizer" in PVC means a calcium-zinc, organotin or lead system whose first job is HCl scavenging. In the US food-contact rules, BHT appears in 21 CFR 178.2010 only as an optional component at up to 5 % of one methyltin stabilizer formulation, which shows the co-stabilizer role exactly. Calcium-zinc, tin and organic systems are compared on PVC heat stabilizers.

How Do Antioxidants Work in Plastics?#

Antioxidants work in plastics in 3 ways: primary antioxidants trap peroxyl radicals, secondary antioxidants destroy hydroperoxides before they split into new radicals, and carbon-radical scavengers catch alkyl radicals in the melt. Each group enters the same cycle at a different point, which is why a real formulation almost never uses one alone. The diagram below marks where all 7 types intervene in the oxidation of a polyolefin.

The autoxidation cycle: how polymers oxidise#

Polymers oxidise through the autoxidation cycle described by J. L. Bolland and G. Gee at the British Rubber Producers' Research Association in the 1940s: an alkyl radical adds oxygen, the peroxyl radical abstracts hydrogen from the next chain, and the hydroperoxide formed splits into two new radicals. The basic autoxidation scheme runs in four steps, listed in order.

1. Initiation: heat and shear split a bond, R-R becomes 2 R•, and each alkyl radical adds oxygen (R• + O2 → ROO•) at a diffusion-controlled rate of 10^7 to 10^9 L mol-1 s-1.
2. Propagation: the peroxyl radical abstracts a hydrogen atom from a neighbouring chain (ROO• + RH → ROOH + R•), which regenerates an alkyl radical and closes the loop.
3. Chain branching: the hydroperoxide decomposes (ROOH → RO• + •OH, or ROOH + RH → RO• + R• + H2O), so one hydroperoxide produces two radicals and the reaction becomes autocatalytic.
4. Termination: radicals combine to non-radical products, which is slow while oxygen is present.

Chain branching explains the shape of the damage. Oxygen uptake is sigmoidal: nothing measurable happens during an induction period, then the rate climbs steeply once the hydroperoxide pool starts splitting. Modern kinetics has revised the propagation step rather than the picture as a whole. Gregory Smith, Heather Aitken and Michelle Coote at the Australian National University showed in Accounts of Chemical Research 51 (2018) 2006 that hydrogen transfer from a saturated polymer chain to a peroxyl radical is strongly disfavoured, and that it becomes favourable only at allylic or unsaturated defect sites. Each step, its rate constants and the branching kinetics are set out on the autoxidation (Bolland-Gee) cycle page.

Primary antioxidants: chain-breaking radical scavengers#

Primary antioxidants, mainly hindered phenols and aromatic amines, donate a hydrogen atom to a peroxyl radical, and each phenol group stops about 2 radical chains before it is used up. The reaction is ROO• + ArOH → ROOH + ArO•, and the phenoxyl radical left behind is too stabilized to continue the chain. It ends as non-radical products, typically quinone methides, which are colour bodies and the reason phenolic stabilization and yellowing are linked. The stoichiometric factor of about 2 peroxyl radicals per phenol group has been measured for alpha-tocopherol, BHT, BHA and PMHC.

Molecular weight is the second design variable after the phenol itself. Primary antioxidants carry molecular weights of 300 to 1,000 g/mol, because a small molecule evaporates out of the melt and migrates out of the part. The three volume grades show the range directly: BHT at 220.35 g/mol is volatile enough to be displaced from most plastics, Irganox 1076 at 530.9 g/mol stays in polyolefin film, and Irganox 1010 at 1,177.6 g/mol stays in thick sections for years. Aromatic amines belong to the same chain-breaking group and trap peroxyl radicals by the same hydrogen-donation step.

Secondary antioxidants: hydroperoxide decomposers#

Secondary antioxidants, mainly phosphites, phosphonites and thioesters, reduce hydroperoxides to stable alcohols before they split into new radicals. The phosphite reaction is P(OR)3 + ROOH → O=P(OR)3 + ROH, in which the trivalent phosphorus is oxidised to a phosphate and the hydroperoxide becomes an alcohol that cannot branch the chain. Reactivity in that reduction falls in a clear order: phosphonites react faster than alkyl phosphites, alkyl phosphites faster than aryl phosphites, and hindered aryl phosphites slowest of all, which is also the order of increasing hydrolytic stability.

Thioesters reach the same hydroperoxides through sulfur chemistry and on a different timescale. The thioether is oxidised to a sulfoxide and then to a sulfone, and both oxidation products are themselves active against hydroperoxides, which is why one thioester molecule destroys more than one hydroperoxide. That cascade is slow, so thioesters are effective mainly for long-term heat ageing at about 100-150 °C and contribute little inside the extruder. Primary antioxidants stop radicals that already exist; secondary antioxidants stop new radicals from forming.

Carbon-radical scavengers#

Carbon-radical scavengers are lactones, hydroxylamines and acrylated phenols that trap alkyl radicals before oxygen reaches them, which makes them processing stabilizers rather than long-term stabilizers. Catching an alkyl radical is hard, because R• + O2 runs at 10^7 to 10^9 L mol-1 s-1, close to the diffusion limit, so the scavenger has to compete with dissolved oxygen for the same radical. That competition is winnable only where oxygen is scarce, which is exactly the situation inside an extruder barrel.

Three chemistries take that position. Benzofuranone lactones such as Irganox HP-136 give up the weak carbon-hydrogen bond at the ring 3-position, hydroxylamines such as Irgastab FS 042 donate their N-H hydrogen, and acrylated phenols such as Sumilizer GM add alkyl radicals across the double bond, the last of these specifically in oxygen-poor melts. Because they act before oxygen is consumed, all three lower the load on the phenol and the phosphite that follow them in the cycle.

7 Types of Antioxidants for Plastics#

The 7 types of antioxidants for plastics are hindered phenols, phosphites and phosphonites, thioesters, aminic antioxidants, hydroxylamines, benzofuranone lactones and vitamin E. The order follows commercial prominence: phenolics hold 39.72 % of plastic antioxidant revenue in 2025 and phosphites and phosphonites are the fastest-growing type at 6.18 % CAGR, both according to Mordor Intelligence, after which come the long-term heat-ageing synergists, the aminics and the three niche carbon-radical and bio-based chemistries. Every table, list and diagram on this page keeps that same order.

1. Hindered phenols (phenolic antioxidants)#

Hindered phenols are phenols shielded by tert-butyl groups that trap peroxyl radicals, and Irganox 1010, the volume leader since its 1962 invention at Geigy, is used at 0.05-0.4 wt% in polyolefins. Steric hindrance is what makes the chemistry work: the bulky groups next to the hydroxyl weaken the O-H bond enough for fast hydrogen donation and then stabilize the phenoxyl radical so it cannot restart the chain. Most commercial grades attach that phenol to a propionate ester backbone, which sets molecular weight, melting point and compatibility independently of the active group.

Three grades carry the volume. Irganox 1010 (Antioxidant 1010) is tetrafunctional, with four hindered phenol groups on a pentaerythritol core, and the US Chemical Data Reporting cycle of 2023 puts its national volume at 40 to below 55 million lb. Irganox 1076 (Antioxidant 1076) is the monofunctional octadecyl ester, dosed at 0.1-0.4 wt% in polyolefins under supplier guidance, and BHT is the small, volatile classic that higher-molecular-weight phenols have displaced in most plastics. Commodity polypropylene grades carry less than 400 ppm phenolic antioxidant as base stabilization. Beyond the plain phenols sit the multifunctional hybrids: phenol plus thioether in Irganox 1035, 1520, 1726 and 565, phenol plus copper deactivator in Irganox MD 1024, and the acrylated bisphenol Sumilizer GM, also sold as Irganox 3052. Trade-name equivalents matter in sourcing, since Irganox 1010, ADK STAB AO-60 and SONGNOX 1010 are the same substance, and every grade from BHT to Irganox 1010 is compared under phenolic antioxidants (hindered phenols).

The drawback is colour. Phenolic antioxidants react with nitrogen oxides to give quinone methides, so parts stored near gas-fired heaters or forklifts yellow or pink, and phenolics are not suitable for polymers dried or cured in direct gas-fired ovens.

2. Phosphites and phosphonites#

Phosphites and phosphonites are phosphorus(III) esters that reduce hydroperoxides to alcohols during melt processing, and Irgafos 168 is used at 0.05-0.2 wt% in polyolefins, almost always with a phenol. The aryl phosphite structure of Irgafos 168 (Antioxidant 168) buys hydrolytic stability at the cost of reaction speed, while the spiro diphosphite structure of Ultranox 626 buys speed at the cost of storage stability. Aryl phosphites hydrolyse at 150-180 °C to phenols and hydrogen phosphites, and the released phenols themselves act synergistically.

Grade choice is therefore a hydrolysis decision as much as an activity decision. Ultranox 626 has higher activity but lower hydrolytic stability than Irgafos 168, so it is supplied with a trace amine for storage life and blended with magnesium-aluminium hydrotalcite in products such as SONGNOX 6280, a 93:7 mixture. Doverphos S-9228 was developed as a second-generation spiro diphosphite with better hydrolysis resistance. The phosphonite P-EPQ is dosed at 0.05-0.1 wt% in recycled LLDPE, where processing stability and gel reduction matter most. Irgafos 168 degrades in use to tris(2,4-di-tert-butylphenyl) phosphate and 2,4-di-tert-butylphenol, its US volume in the 2023 Chemical Data Reporting cycle is 40 to below 55 million lb, and hydrolysis data by grade are on phosphite and phosphonite antioxidants.

One practical advantage sets phosphites apart from phenols: Irgafos 168 is usable in direct gas-fired ovens, where phenolics discolour.

3. Thioesters (thiosynergists)#

Thioesters are sulfur-based secondary antioxidants, such as DLTDP and DSTDP, that decompose hydroperoxides during long-term heat ageing at about 100-150 °C rather than in the melt. The two volume grades are dilauryl thiodipropionate, sold as Irganox PS 800, and distearyl thiodipropionate, sold as Irganox PS 802, with distearyl disulfide as a related organosulfur option. Their contribution is measured in oven ageing rather than in multipass extrusion.

Ratio decides the outcome. In polypropylene, an AO-1010 to DSTDP ratio of 20:80 gives the best long-term thermal stability at 150 °C, while 80:20 gives the best processing stabilization, so the same two ingredients serve opposite purposes depending on the split. In EU food contact, DLTDP and DSTDP share group restriction 14 under Regulation (EU) No 10/2011, with a total specific migration limit of 5 mg/kg for the substances and their oxidation products. Their one hard incompatibility is with hindered amine light stabilizers, and the full picture is set out under thioester antioxidants.

4. Aminic antioxidants#

Aminic antioxidants are aromatic amines, mainly alkylated diphenylamines such as Irganox 5057 and Naugard 445, that trap peroxyl radicals more efficiently than phenols but discolour the polymer. Pronounced discolouration and staining keep them out of white and pastel goods, so their home is in dark, high-temperature and chemically demanding parts where colour is not sold.

Polyurethane is the clearest plastics use. Irganox 5057 combined with the liquid phenol Irganox 1135 is used at 0.1-0.4 % against scorch in flexible foam and in stored polyols, where oxidation shows up as a browned foam core. In US food contact, 21 CFR 178.2010 allows up to 0.3 % Naugard 445 in polypropylene for non-fatty foods, which is a legal maximum and not a recommended dosage. Diphenylamines and the dihydroquinoline TMQ are covered under aminic antioxidants.

5. Hydroxylamines#

Hydroxylamines are nitrogen-based radical scavengers, such as Irgastab FS 042, that replace phenols in phenol-free stabilizer systems at 0.05-0.15 %, so white polypropylene fibre does not yellow from gas fading. Paired with a phosphite, they cover both the alkyl radical and the hydroperoxide without putting a phenol into the compound at all, which removes the substrate that nitrogen oxides convert into colour bodies. N,N-dibenzylhydroxylamine was patented for exactly that purpose, to prevent gas fading of polypropylene stabilized with phenolic antioxidants (US 4,590,231).

Irgastab FS 042 is used with a phosphite in polypropylene fibre and thermoplastic polyolefins. Under Regulation (EU) No 10/2011 it is FCM substance 768, with no numeric specific migration limit but with use limited to 0.1 % in polyolefins and 0.25 % in PET, and it is not authorised for fatty foods. Hydroxylamine and lactone systems are compared on phenol-free stabilization.

6. Benzofuranone lactones#

Benzofuranone lactones, such as Irganox HP-136, trap carbon-centred radicals at their weak ring C-H bond and are used as processing stabilizers at low levels. The lactone donates the hydrogen at the 3-position of the benzofuran-2(3H)-one ring, which intercepts the alkyl radical before oxygen converts it into a peroxyl radical, so the lactone works one step upstream of every phenol and phosphite in the same formulation.

Irganox HP-136 carries CAS 181314-48-7 and is authorised in the EU as FCM substance 26 under Regulation (EU) No 10/2011, with a specific migration limit of 5 mg/kg. In the United States, 21 CFR 178.2010 allows up to 0.1 % in olefin polymers for the listed food types and up to 0.02 % in polypropylene for the others, and those percentages are legal maxima rather than use levels. Our source library holds no sourced typical dosage for this type.

7. Vitamin E and other natural antioxidants#

Vitamin E (alpha-tocopherol) is a natural phenolic antioxidant that stabilizes polyethylene and polypropylene melts at only 100-300 ppm. Sahar Al-Malaika at Aston University established that melt-stabilization range, and in high-density polyethylene 200 ppm of vitamin E retained the melt flow index over three extrusion passes where 200 ppm of Irganox 1010 did not. Under Regulation (EU) No 10/2011 alpha-tocopherol is FCM substance 110 with no specific migration limit.

Medical implants are its second stronghold, because vitamin E in irradiated UHMWPE improves oxidation resistance while keeping wear and fatigue properties, a route standardised as ASTM F2695. Other bio-based phenols are moving out of the laboratory: sinapic acid stearyl ester gave processing stability in polypropylene comparable or superior to Irganox 1076 in work published by Fraunhofer LBF in 2023. Both routes are followed on natural and bio-based antioxidants for plastics.

Why Do Phenols and Phosphites Work Better Together? Synergy, Blends and Antagonism#

Phenols and phosphites work better together because the phenol turns peroxyl radicals into hydroperoxides and the phosphite then reduces those hydroperoxides to harmless alcohols. The phenol alone would leave behind the very species that branches the chain, and the phosphite alone would never touch the peroxyl radicals, so the pair closes the cycle at two points instead of one. The usual polyolefin working range is a phosphite:phenol ratio of 1:1 to 4:1.

Patent literature spans a far wider window, roughly 20:1 to 1:10 phenol:phosphite, which reflects how differently the pair is weighted for melt stability and for service life. Synergy is not automatic between families, because additive pairs such as thioesters and hindered amine light stabilizers cancel each other, and the full matrix across all families is on additive interactions: synergy and antagonism.

Antioxidant blends and ratios#

Antioxidant blends are pre-mixed phenol and phosphite powders, such as Irganox B 215 (2 parts Irgafos 168 to 1 part Irganox 1010), that save weighing steps and fix the ratio. Four combinations cover most polyolefin and foam formulations.

• Irganox B 215: Irgafos 168 to Irganox 1010 at 2:1 (67/33), the general-purpose polyolefin blend.
• Irganox B 225: Irgafos 168 to Irganox 1010 at 1:1, for higher processing severity.
• Irganox B 900: Irgafos 168 to Irganox 1076 at 4:1 (80/20), phosphite-heavy for film extrusion.
• Phenol plus aminic: Irganox 1135 with Irganox 5057 at 0.1-0.4 % against scorch in polyurethane foam.

Thioester blends follow a different arithmetic, because a phenol:thioester ratio of 20:80 favours long-term heat ageing in polypropylene while 80:20 favours processing. Cross-supplier equivalents are listed on antioxidant blends.

Antagonism: thioesters, HALS and moisture#

Thioester antioxidants weaken hindered amine light stabilizers because their acidic sulfur oxidation products deactivate the basic HALS, so outdoor compounds avoid the pair. Three antagonistic combinations recur in polyolefin formulation.

• Thioester plus HALS: sulfoxides and sulfones acidify the compound and neutralise the hindered amine.
• Phosphite plus moisture: Ultranox 626 needs hydrotalcite or amine buffering against hydrolysis, and Doverphos S-9228 was designed to be more resistant.
• Phenol plus nitrogen oxides: gas fading converts the phenol into quinone methides and costs colour rather than stability.

Outdoor and roofing compounds therefore pair light stabilization with phenol-phosphite systems instead of thioesters, and the compatible packages are listed under hindered amine light stabilizers (HALS).

How Much Antioxidant Does a Plastic Need? Dosage by Type and Polymer#

Most plastics need 0.05-0.4 wt% of a phenolic antioxidant plus 0.05-0.2 wt% of a phosphite, while vitamin E works at 100-300 ppm and recycled polyolefins take 0.1-0.3 wt% of a restabilizing blend. Across all plastic products, antioxidants make up 0.05-3 wt% of the article. The table lists the sourced dosage anchors by system and polymer.

FDA 21 CFR 178.2010 percentages are legal maxima, not recommended dosages.

Every level needs its unit and its base stated, because the same number means different things in different systems: wt% and ppm refer to the compound, a phosphite:phenol ratio refers to the two additives only, and phr appears in PVC and rubber recipes rather than in polyolefin stabilization. Regulatory percentages are a separate category again, since 21 CFR 178.2010 states the maximum a food-contact polymer may contain, not the amount a formulator should add. Levels for every additive family are on additive dosage levels in plastics.

Which Antioxidant for Which Polymer?#

Each polymer needs an antioxidant package matched to how it oxidises: polypropylene breaks down by chain scission and takes a phenol-phosphite blend, polyethylene film forms gels, and polyamides need copper-halide or amide-phenol heat stabilizers. Polypropylene alone takes 34.68 % of plastic antioxidant revenue in 2025 according to Mordor Intelligence, which follows directly from its tertiary carbon-hydrogen bonds. The matrix below pairs each polymer with its standard package.

Antioxidants for polypropylene#

Polypropylene needs a phenol-phosphite blend because its tertiary carbon atoms make it the most oxidation-sensitive commodity polymer, and it takes 34.68 % of plastic antioxidant revenue. Every third carbon in the chain carries a hydrogen that a peroxyl radical can abstract, the resulting alkoxy radical cleaves the backbone, and the melt flow rate climbs pass by pass. The standard answer is a hindered phenol with an aryl phosphite plus an acid scavenger, calcium stearate or hydrotalcite, to neutralise the chloride residues of the Ziegler-Natta catalyst. Commodity grades leave the reactor with less than 400 ppm of phenolic antioxidant as base stabilization, which covers pelletising but not a demanding second life.

Three cases need more. Parts that run hot for years, such as pipes and under-bonnet components, add a thioester, and distearyl thiodipropionate at a phenol:thioester ratio of 20:80 gives the best long-term thermal stability at 150 °C. Filled grades with talc or calcium carbonate need a higher antioxidant load, because the filler surface adsorbs antioxidant and the filler carries metal impurities that catalyse hydroperoxide decomposition. White fibre uses phenol-free systems instead, since gas fading would yellow it. The full polypropylene package beyond antioxidants, including nucleating agents, acid scavengers and light stabilizers, is on additives for polypropylene.

Antioxidants for polyethylene film, pipe and cable#

Polyethylene film, pipe and cable each need a different antioxidant package: film needs gel control, pipe needs a long oxidation induction time and chlorine resistance, and cable needs a copper deactivator. Film is the gel case, because polyethylene crosslinks rather than scissions when it oxidises, and chromium-catalysed high-density grades are especially prone to it. Irganox 1076 or Irganox 1010 with Irgafos 168 is the working combination, with the phosphite carrying the extrusion and the phenol carrying the reel.

Pipe is the durability case. A pressure pipe compound is qualified on oxidation induction time, with a minimum of at least 20 minutes at 210 °C under EN 12201-1 and ISO 4427-1, and the antioxidant package has to survive the water inside as well as the air outside. Disinfectant chemistry decides how fast it is consumed: antioxidant depletion in water containing 4 ppm chlorine dioxide at 90 °C runs about 4 times faster than in chlorinated water.

Cable is the metal case. Copper conductors catalyse hydroperoxide decomposition directly at the insulation interface, so crosslinked polyethylene cable compounds pair the thioether-bridged phenol Irganox 1035 with the metal deactivator Irganox MD 1024, which is a hindered phenol and a chelating hydrazide in one molecule. The wider formulation picture for film, pipe and cable grades is on additives for polyethylene.

Antioxidants for polyamide, POM and polycarbonate#

Polyamides need heat stabilizers for service at up to 180 °C and beyond, which is why copper-halide systems and the amide phenol Irganox 1098 dominate nylon stabilization. Irganox 1098 is used at 0.05-1.0 % in polyamide, with 0.05-0.2 % typical, and copper systems combine 0.001-0.03 wt% copper with 0.1-5 wt% of a halide such as potassium iodide. Brüggemann states service up to 180 °C for its copper systems, and its H1805 grade retains more than 50 % of tensile strength after 3,000 h at 200 °C. Antioxidants slow but do not redirect the ageing chemistry: in glass-fibre-reinforced PA56T aged at 150 °C, stabilizers extended the life without changing the ageing pathway.

Polyoxymethylene is a different problem, because its degradation releases formaldehyde, so the package pairs the phenol Irganox 245 with formaldehyde scavengers. Under 21 CFR 178.2010 the legal maximum for Irganox 245 is 0.75 % in POM copolymer and 0.25 % in the homopolymer.

Polycarbonate is stabilized mainly for colour rather than for molecular weight, and phosphites do that job during the high processing temperatures the polymer demands. The US food-contact maxima for polycarbonate are 0.2 % for Doverphos S-9228, 0.1 % for P-EPQ and 0.3 % for Irgafos 168.

Antioxidants for recycled plastics (restabilization)#

Recycled polyolefins need restabilization because every processing pass consumes antioxidant, and adding 0.1-0.3 wt% of a phenol-phosphite blend restores processing stability for the next life. Rudolf Pfaendner at Fraunhofer LBF defined restabilization as adding phenol and phosphite packages, with hindered amine light stabilizers and UV absorbers where needed, to compensate for depleted antioxidant and for the oxidised groups the recyclate already carries (Polymer Degradation and Stability 203 (2022) 110082).

Residual antioxidant is not always zero. Polypropylene regranulate processed without any new antioxidant still held more than 150 ppm of intact Irgafos 168, enough for one or two further processing steps, and a study dose of 500 ppm Irganox 1010 with 1,000 ppm Irgafos 168 has been used to restabilize polypropylene recyclate. Knoben and colleagues showed in 2025 that closed-loop recycling with antioxidant added in every cycle builds the antioxidant level up rather than down, measured as the DSC oxidation induction temperature. Study data per recyclate type are on restabilization of recycled plastics.

Regulation is now pushing the volumes. Regulation (EU) 2025/40 (PPWR) Article 7 sets minimum recycled content from 2030 of 30 % for contact-sensitive PET packaging, 10 % for other contact-sensitive packaging, 30 % for single-use plastic beverage bottles and 35 % for other plastic packaging, which puts restabilized material into applications that previously took virgin resin only.

How Do You Select an Antioxidant for a Plastic? 6 Criteria#

Select an antioxidant for a plastic in 6 steps: identify the polymer, check the processing temperature, define the service temperature, check colour risk, screen the regulations, then set the ratio and test. The order matters, because each step narrows the candidate list before the next one adds cost.

1. Identify the polymer and how it degrades. Polypropylene scissions, polyethylene crosslinks, polyamide ages thermally and ABS yellows through its polybutadiene phase, and each failure mode points to a different primary antioxidant.
2. Check the processing temperature and the number of passes. Melt processing runs at 150-320 °C, and more passes or higher barrel temperatures should raise the phosphite share of the package.
3. Define the service temperature and the service life. Long-term heat at about 100-150 °C should bring in a thioester or a high-molecular-weight phenol, since a phosphite contributes almost nothing once the part has cooled.
4. Check the colour and gas-fading risk. White fibre, pastel packaging and warehouse storage near gas-fired equipment should move the formulation to a phenol-free hydroxylamine and phosphite system.
5. Screen food-contact and SVHC status in every market sold into. Regulation (EU) No 10/2011 and 21 CFR 178.2010 decide which grades are usable at all, and the REACH Candidate List decides which ones carry communication duties.
6. Set the ratio and dosage, then confirm by testing. Oxidation induction time, multipass melt flow rate and oven ageing turn a paper package into a qualified one.

Selection should always be closed by measurement rather than by datasheet comparison, because antioxidant performance depends on the polymer, the filler surface and the process as much as on the molecule. The general framework that applies to every additive family is on how to select plastic additives.

Why do antioxidants turn plastics yellow or pink?#

Antioxidants turn plastics yellow or pink when phenolic antioxidants oxidise to coloured quinone methides, most often through nitrogen oxides from gas-fired heaters and forklifts, an effect called gas fading. The colour body is a reaction product of the stabilizer itself, not of the polymer, which is why a better-stabilized compound can look worse than an unstabilized one after storage. BHT forms stilbenequinone by this route.

Three remedies follow from the mechanism. Phenol-free systems built from a hydroxylamine and a phosphite remove the substrate that nitrogen oxides attack, phenolics are kept out of processes that use direct gas-fired ovens while Irgafos 168 remains usable there, and aminic antioxidants are reserved for parts where their inherent discolouration is acceptable. Vitamin E needs a phosphite co-additive to avoid yellowing in the same way. Fixes sorted by cause, including pinking and process-related discolouration, are on why plastics turn yellow or pink.

How Is Antioxidant Performance Tested?#

Antioxidant performance is tested in 4 ways: oxidation induction time by DSC, melt flow rate retention over repeated extrusion passes, oven ageing to embrittlement and yellowness index. Each method answers a different question, so a package qualified on one alone is not qualified at all. The table gives the method, the standard and the conditions used in polyolefin work.

Oxidation induction time is the closest thing the industry has to a direct antioxidant assay, because the time to the exotherm onset scales with the amount of active stabilizer still present. Two limits keep it from being a universal answer. Volatile antioxidants can evaporate during the isothermal hold and give a low OIT while performing well in the application, a caveat written into ASTM D3895 itself, and phosphites and thioesters contribute little at 200 °C, so a phenol-free or thioester-heavy package tests worse than it behaves. High-pressure OIT under ASTM D5885, at 3.4 MPa oxygen and 150 °C, lowers the temperature enough to see stabilizers the standard test misses. All methods used across additive families are indexed under testing plastic additives.

How Are Antioxidants for Plastics Regulated?#

Antioxidants for plastics are regulated in 4 layers: EU food-contact limits under Regulation (EU) No 10/2011, US food-contact limits under 21 CFR 178.2010, the EU REACH Candidate List and US TSCA reporting. The first two decide whether a grade may touch food and at what level, the third attaches communication and authorisation duties, and the fourth records volumes placed on the US market.

Food contact is where the numbers are hardest, because every grade carries its own FCM number and specific migration limit, and group restrictions cap chemically related grades together. Every grade's specific migration limit and US maximum is on food contact antioxidants. The matrix below gives the 13 grades that carry the volume.

EU values as verified against the consolidated Annex I (see methodology); "no" means not on the Candidate List as of September 2026.

Food contact: EU 10/2011 SMLs and FDA 21 CFR 178.2010#

Food-contact plastics in the EU may contain only antioxidants on the Union list of Regulation (EU) No 10/2011, and Irganox 1076, for example, may migrate into food at no more than 6 mg/kg. Grades listed without a specific migration limit are not unrestricted, because the overall migration limit of 10 mg/dm2 still applies, which is the case for Irganox 1010, Irganox 1330 and Irgafos 168. Three group restrictions bundle chemically related grades under one total limit: group 13 caps Antioxidant 2246 with FCM 163 at 1.5 mg/kg, group 14 caps DLTDP, DSTDP and ditetradecyl thiodipropionate at 5 mg/kg including their oxidation products, and group 24 caps Irganox 1520 with Irganox 1726 at 5 mg/kg. Migration testing rules and simulants are set out on EU 10/2011.

The US system works from the polymer down rather than from the substance out. 21 CFR 178.2010 paragraph (a) limits use to the amount reasonably required to accomplish the technical effect, and paragraph (b) lists each substance with polymer-specific maxima, so a grade can be legal in polypropylene and absent for polycarbonate. A second route exists for older substances: 21 CFR 181.24 covers prior-sanctioned antioxidants including BHA, BHT, DLTDP, DSTDP and propyl gallate, with a limit of 0.005 % addition to food. No grade is ever "FDA approved"; a substance is listed in 21 CFR 178.2010 for defined uses, and the full table is explained on 21 CFR 178.2010.

Safety assessments underpin both systems. Neal-Kluever and colleagues at the FDA published a re-evaluation of Irganox 1076 in 2015 with a NOAEL of 64 mg/kg body weight per day, a cumulative estimated daily intake of 4.5 mg per person per day and a margin of exposure of about 850. Markley and colleagues at the FDA assessed Irgafos 168 in 2023 and set an acceptable daily intake of 1 mg/kg body weight per day against a cumulative estimated daily intake of 0.09 mg/kg body weight per day for the phosphite together with its phosphate.

Restricted antioxidants: TNPP, Antioxidant 2246, 2,4,6-TTBP and BHT#

Three antioxidant-related substances are on the REACH Candidate List: TNPP since 16 July 2019, Antioxidant 2246 since 17 January 2022 and 2,4,6-tri-tert-butylphenol since 23 January 2024, while BHT is under review but not restricted. Candidate List entry does not remove a substance from the market, and two of the three remain authorised for EU food contact. The four substances that dominate the restriction discussion are listed below.

• TNPP (tris(nonylphenyl) phosphite, CAS 26523-78-4): Candidate List since 16 July 2019 as endocrine disrupting for the environment under Article 57(f), with the entry updated on 21 January 2025 to cover its intrinsic endocrine-disrupting properties, and still FCM substance 69 with a specific migration limit of 30 mg/kg.
• Antioxidant 2246 (DBMC, CAS 119-47-1): Candidate List since 17 January 2022 as toxic for reproduction under Article 57(c), with a harmonised CLP classification of Repr. 1B, H360F introduced by ATP17, and still FCM substance 285 under group restriction 13.
• 2,4,6-tri-tert-butylphenol (CAS 732-26-3), an antioxidant intermediate and impurity: Candidate List since 23 January 2024 for reproductive toxicity and PBT properties.
• BHT (CAS 128-37-0): not on the Candidate List as of September 2026, under REACH substance evaluation on CoRAP for suspected endocrine disruption, and the subject of an FDA Request for Information published on 13 May 2026 (docket FDA-2026-N-2526) whose comment period reopened to 31 August 2026. BHT is not on the Proposition 65 list; BHA is.

Candidate List status triggers duties rather than bans: notification to ECHA, supply-chain communication above 0.1 % by weight in articles, and safety data sheet updates. Every listed plastic additive is tracked on the SVHC Candidate List page.

Who Makes Antioxidants for Plastics? Market Size and Suppliers#

The plastic antioxidant market is worth USD 5.41 billion in 2025 according to Mordor Intelligence (other analysts give USD 5.86-5.9 billion), and BASF, Songwon, SI Group and Adeka are among the largest producers. Mordor Intelligence puts the same market at USD 5.69 billion in 2026 and forecasts USD 7.33 billion by 2031, a compound annual growth rate of 5.18 %. Within that total, phenolics hold 39.72 % of revenue, phosphites and phosphonites grow fastest at 6.18 % CAGR, packaging takes 39.22 % of demand, polypropylene takes 34.68 %, and Asia-Pacific accounts for 36.40 %.

Volumes confirm which molecules carry the market. The US Chemical Data Reporting cycle of 2023 records 40 to below 55 million lb each for Irganox 1010 and Irgafos 168, and 25 to below 40 million lb for Irganox 1076. The table lists the producers and their antioxidant brand lines.

Grades, production sites and certifications are compared in polymer antioxidant manufacturers and suppliers.

Complete List of Antioxidants for Plastics: 43 Substances#

The complete list below gives all 43 antioxidants for plastics in the directory with CAS number, type and EU food-contact status, grouped in the order of the 7 types. Within that grouping, the four volume grades are compared head to head in the antioxidant grade comparison.

SML values are in mg/kg. "n/a" means our source library holds no verified EU 10/2011 entry for that grade.

Every other additive family, from plasticizers to flame retardants, is indexed with the same fields in the plastic additives database.

How Do Antioxidants Differ from UV Stabilizers and Other Stabilizers?#

Antioxidants protect a plastic against heat and oxygen, while UV stabilizers protect it against sunlight, acid scavengers neutralise catalyst residues, metal deactivators bind copper and hydrolysis stabilizers stop water attack. All five families belong to the stabilizer group of plastic additives, and they are dosed together rather than chosen against each other: a polypropylene garden chair carries a phenol, a phosphite, an acid scavenger and a hindered amine light stabilizer at the same time. Scale separates them, since antioxidants account for 6 % of global additive consumption by weight against 1 % for light stabilizers. The table shows how each sibling family connects to antioxidant chemistry.

Are antioxidants in plastics safe? NIAS and BHT#

Most antioxidants for plastics carry no harmonised hazard classification, but their breakdown products, such as 2,4-di-tert-butylphenol from Irgafos 168, are non-intentionally added substances (NIAS) that food-contact risk assessments must cover. Measured levels put numbers on that: 2,4-di-tert-butylphenol reached 45.568 ± 31.513 mg/kg in BOPP and LDPE food-contact products, and it is not on the Union list of Regulation (EU) No 10/2011. Oxidized Irgafos 168 has also been found outside packaging, at up to 851 ng/m3 in urban PM2.5 in China.

The regulatory system already accounts for part of this, because the specific migration limits for ADK STAB PEP-36, Doverphos S-9228 and ADK STAB AO-80 are expressed as the sum of the substance with its oxidation or hydrolysis products. Commercial PE, PP and PVC packaging typically contains Irganox 1010, Irganox 1076 and Irgafos 168 together with the phosphate of the last. BHT is not on the REACH Candidate List as of September 2026, and the FDA opened a Request for Information on it on 13 May 2026. Analysis methods and risk assessment routes are on NIAS: non-intentionally added substances.

Antioxidants for radiation-sterilized medical plastics#

Radiation sterilization creates radicals that keep oxidising a plastic after treatment, which is why irradiated UHMWPE hip and knee implants are stabilized with vitamin E (ASTM F2695). Alpha-tocopherol blended into the polyethylene improves oxidation resistance while keeping wear and fatigue properties, which makes it an alternative to post-irradiation melting, the older route that costs crystallinity and mechanical strength. No sterilization dose or polypropylene-specific antioxidant level is established in our source library. Gamma, e-beam and ethylene oxide routes are compared on radiation and sterilization stabilizers for medical plastics.

Antioxidants in rubber and elastomers#

Rubber uses the same phenolic antioxidants as plastics plus rubber-only antiozonants such as 6PPD, whose transformation product 6PPD-quinone was identified in December 2020 as toxic to coho salmon. Paraphenylenediamines including 6PPD and IPPD, and the dihydroquinoline TMQ, are rubber antidegradants and stay outside the plastics scope of this reference. Phenolics cross the border in the other direction: Antioxidant 2246 and Wingstay L serve light-coloured rubber goods and emulsion ABS, where staining amine chemistry cannot be used. California's Department of Toxic Substances Control listed tires containing 6PPD as a Priority Product in October 2023, and the 6PPD question is tracked on antioxidants and antiozonants for rubber.

A short history of antioxidants for plastics#

The modern antioxidant toolbox dates from the 1940s autoxidation work of Bolland and Gee and from Irganox 1010, patented by M. Dexter and colleagues at Geigy with a priority date of 5 January 1962. That single molecule is still the volume number one today, as Rudolf Pfaendner records in "A Brief History of Plastic Additives. Part 1: Antioxidants" (Macromolecular Materials and Engineering, 2025). Ownership of the brand moved with the industry: BASF completed its acquisition of Ciba on 9 April 2009, which brought the Irganox and Irgafos lines under one roof, and Songwon doubled its one-pack stabilizer capacity to 14,000 t/a in 2012 on its way to second place in polymer stabilizers. The longer arc from camphor in celluloid onwards is on history of plastic additives.

Frequently asked questions about antioxidants for plastics#

The 4 questions below are the ones formulators and buyers ask most often about antioxidants for plastics: the classic type count, the legal status of BHT, the US listing of Irganox 1010 and the compatibility of thioesters with light stabilizers.

What are the four main types of antioxidants?#

In plastics, the four classic antioxidant types are hindered phenols and aromatic amines (primary antioxidants) and phosphites and thioesters (secondary antioxidants); this reference adds hydroxylamines, lactones and vitamin E for 7 types. Primary types donate hydrogen to peroxyl radicals, secondary types reduce hydroperoxides to alcohols, and the three additional types scavenge carbon-centred radicals or replace synthetic phenols with a bio-based one.

Is BHT banned in plastics?#

No: BHT is authorised in EU food-contact plastics with a specific migration limit of 3 mg/kg and is not on the REACH Candidate List, although it is under evaluation for endocrine disruption and the FDA opened a Request for Information on 13 May 2026. Its practical limit is technical rather than legal, because a molecular weight of 220.35 g/mol makes it volatile enough to be displaced by higher-molecular-weight phenols such as Irganox 1076 in most plastics.

Is Irganox 1010 FDA approved?#

Irganox 1010 is listed in 21 CFR 178.2010 for food-contact polymers at up to 0.5 % unless otherwise specified; the FDA lists substances for uses, it does not approve products. That 0.5 % is a legal maximum, while the typical use level in polyolefins is 0.05-0.4 wt%. In the EU, the same substance is FCM 496 with no specific migration limit, so the overall migration limit of 10 mg/dm2 applies.

Can HALS and thioester antioxidants be used together?#

No, not without a performance loss: the acidic sulfur products of thioesters deactivate HALS, so outdoor compounds pair HALS with phenol-phosphite blends instead. Thioesters keep their place in non-weathered parts that need long-term heat ageing at about 100-150 °C, such as under-bonnet polypropylene, where no hindered amine light stabilizer is present to be neutralised.