Phenolic Antioxidants (Hindered Phenols): 8 Types, 26 Grades and Dosage

Phenolic antioxidants are sterically hindered phenols, such as Irganox 1010, Irganox 1076 and BHT, that protect plastics from thermo-oxidation by donating a hydrogen atom to peroxyl radicals, typically at 0.05-0.4 wt% in polyolefins. They are the most widely used primary antioxidants in polymers, so which of the 26 commercial grades fits which polymer, and why are they almost always paired with a phosphite?

Hindered phenols account for 39.72 % of plastic antioxidant revenue (2025, Mordor Intelligence), the largest share of any antioxidant class and one of the core stabilizer groups among plastic additives.

This page defines phenolic antioxidants and hindered phenols, explains the hydrogen-donation mechanism that protects a polymer from processing through service life, sets out the 8 structural types and the 26 commercial grades with CAS numbers, molecular weights and EU and US regulatory status, gives dosage ranges by polymer, shows why phenols are blended with phosphites and thioesters, explains the yellowing, pinking and gas fading that hindered phenols can cause, describes the tests used to measure their performance, and lists the manufacturers and trade names behind each grade.

Key figures

• 8 structural types of phenolic antioxidant and 26 commercial grades tracked in Table T2, with CAS number, molecular weight and EU/US regulatory status
• 0.05-0.4 wt% is the typical Irganox 1010 dosage in polyolefins (BASF technical data sheet)
• Each phenol group deactivates about 2 peroxyl radicals before it is used up
• 39.72 % of 2025 plastic antioxidant revenue went to phenolics, the largest single class (Mordor Intelligence)

What Are Phenolic Antioxidants?#

Phenolic antioxidants for polymers are organic compounds with a hydroxyl group on an aromatic ring, shielded by bulky alkyl groups, that stop the oxidation chain reaction in a plastic by giving up a hydrogen atom to peroxyl radicals. Primary antioxidants of this kind have a molecular weight of 300-1000 g/mol in most commercial grades and protect a polymer at three separate stages: melt processing, storage and in-service use. The abbreviation "AO" and the Asian generic numbering system, such as "antioxidant 1010" for Irganox 1010 and "antioxidant 264" for BHT, both refer to the same hindered phenolic antioxidant chemistry.

In the classification of antioxidants for plastics, hindered phenols form the primary (chain-breaking) group, next to aminic antioxidants, while phosphites and thioesters form the secondary group. Phenolic antioxidants for polymers remain the default primary choice across polyolefins, styrenics and engineering plastics.

What are hindered phenols?#

Hindered phenols are phenols whose hydroxyl group sits between two bulky tert-butyl groups in the 2- and 6-positions; this steric hindrance protects the phenoxyl radical formed after hydrogen donation, so it does not start new oxidation chains. The two ortho tert-butyl groups shield the oxygen-centred radical both sterically and by resonance, which is the structural reason a hindered phenolic antioxidant survives long enough to be useful rather than immediately triggering more oxidation. Most commercial grades build on the same reactive head, a 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate group, attached to anchors of very different size and function.

Fully hindered vs semi-hindered phenols#

Fully hindered phenols such as Irganox 1010 carry two ortho tert-butyl groups, while semi-hindered phenols such as Irganox 245 and ADK STAB AO-80 replace one of them with a methyl group. The degree of hindrance changes the steric shield around the phenoxyl radical without changing the basic hydrogen-donation chemistry. Cyanox 1790, an isocyanurate-type grade, is described in supplier literature as "partially hindered" and is used specifically where low gas-fade discolouration matters.

Our source library does not give a quantitative reactivity or colour ranking between these three categories, so this page does not claim that semi-hindered phenols are more reactive or less discolouring than fully hindered ones beyond the documented statement that Cyanox 1790 is a low gas-fade grade.

Are phenolic antioxidants primary or secondary antioxidants?#

Phenolic antioxidants are primary antioxidants: they trap radicals, whereas secondary antioxidants such as Irgafos 168 (a phosphite) and DSTDP (a thioester) destroy the hydroperoxides that the radical trapping leaves behind. A phenolic antioxidant alone cannot decompose a hydroperoxide, which is why formulations combine it with a phosphite or a thioester rather than raising the phenol dose alone.

How Do Phenolic Antioxidants Protect Polymers?#

Phenolic antioxidants protect polymers by breaking the autoxidation chain at its propagation step: they reduce peroxyl radicals to hydroperoxides before those radicals can abstract hydrogen from the polymer backbone. The underlying process is the autoxidation cycle described by Bolland and Gee at the British Rubber Producers' Research Association in the 1940s: initiation, propagation (ROO• + RH → ROOH + R•), branching and termination, a cycle that is autocatalytic and runs after an induction period once the polymer's own stabilizer reserve is consumed.

The full cycle, from initiation by heat and shear to chain branching, is described under polymer oxidation and antioxidant mechanisms.

Hydrogen donation to peroxyl radicals#

A hindered phenol donates the hydrogen of its hydroxyl group to a peroxyl radical (ROO• + ArOH → ROOH + ArO•), and each phenol group can deactivate about two peroxyl radicals before it is used up. This stoichiometric factor of about 2, measured for alpha-tocopherol, PMHC, BHA and BHT, is why phenolic antioxidant dosage is calculated in parts per million or weight percent rather than as a 1:1 radical scavenger. The reaction targets peroxyl radicals specifically because the competing step, R• + O2, is diffusion-controlled at 10^7 to 10^9 L mol-1 s-1, so carbon radicals are converted to peroxyl radicals almost as fast as they form.

In a 2018 study titled "The Fate of the Cyclohexadienyl Radical in Autoxidation" in Accounts of Chemical Research (volume 51, page 2006), Smith, Aitken and Coote at the Australian National University showed that hydrogen transfer from ROO• to a saturated polymer chain (RH) is strongly disfavoured thermodynamically, which is why propagation in a saturated polymer runs mainly at weak points such as tertiary carbons and processing-induced defect sites rather than uniformly along the backbone.

What happens to a phenolic antioxidant after it reacts?#

After donating its hydrogen, a phenolic antioxidant becomes a stabilized phenoxyl radical, which traps a second radical and ends as non-radical products, mostly quinone methides, the yellow compounds behind antioxidant discoloration. A phenolic antioxidant passes through 3 stages as it is consumed.

1. Phenol. The intact hindered phenol donates a hydrogen atom to a peroxyl radical and becomes a phenoxyl radical.
2. Phenoxyl radical. The steric shield around the oxygen keeps this radical stable enough to survive long enough to trap a second radical rather than propagating further oxidation.
3. Quinone methide (or other non-radical product). The phenoxyl radical ends as a non-radical species, typically a coloured quinone methide; according to the antioxidant literature, propionate-type quinone methides can partly rearrange to a hydroxycinnamate and regenerate a phenol, though this pathway is not fully quantified.

A phenolic antioxidant is sacrificial: once the dose in a compound is consumed by this three-step process, the polymer itself begins to oxidize.

Processing stability vs long-term thermal stability#

Phenolic antioxidants protect a polymer twice: during melt processing at 150-320 °C, together with a phosphite, and during service at typically 60-150 °C, where high-molecular-weight phenols such as Irganox 1010 carry long-term thermal stability. Thioesters, by contrast, work mainly at about 100-150 °C and contribute little during the melt itself. Engineering polymers that process at 240-320 °C exclude low-molecular-weight phenolics such as BHT, which volatilize before they can do their job.

What Are the 8 Types of Phenolic Antioxidants?#

The 8 types of phenolic antioxidants are propionate esters, thiosynergistic phenols, benzyl and isocyanurate phenols, amide phenols, bisphenols, phosphonate salts, low-molecular-weight phenols such as BHT and natural phenols such as vitamin E; propionate esters such as Irganox 1010 and 1076 dominate by volume. Most grades share the same reactive head, a 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate group, attached to anchors of different size, from BHT's simple aromatic ring (220 g/mol) up to the tetrafunctional Irganox 1010 (1,178 g/mol); a higher-molecular-weight anchor lowers volatility, which is why films, fibres and hot-water pipe applications favour the heavier grades. Under the US Chemical Data Reporting rule for 2023, Irganox 1010 was produced or imported at 40 to under 55 million lb, Irganox 1076 at 25 to under 40 million lb and BHT at 2.5 to under 4 million lb, a volume order that tracks the list below.

1. Propionate esters: Irganox 1010, Irganox 1076, Irganox 1135, Irganox 245 and AO-80#

Propionate esters are the largest phenolic group: Irganox 1010 (1,178 g/mol) and Irganox 1076 (531 g/mol) are the two highest-volume phenolic antioxidants in plastics, used at 0.05-0.4 wt% and 0.1-0.4 wt% in polyolefins. Irganox 1010 is the tetrafunctional volume leader, built on four propionate arms around a pentaerythritol core, which gives it very low volatility and makes it the standard long-term thermal stabilizer for polyolefins.

Irganox 1076 is the octadecyl ester used in PE and PP film; its single long alkyl chain gives it much higher volatility than Irganox 1010, 2.5 x 10^-7 Pa against 7 x 10^-10 Pa at 20 °C, which is why fibre and hot-water pipe formulations favour the heavier grade. Irganox 1135, Irganox 245 and ADK STAB AO-80 fill specialised niches, from liquid dosing in polyurethane to low-discolouration polypropylene.

2. Thioether and thiosynergistic phenols: Irganox 1035, Irganox 1520, Irganox 1726 and Irganox 565#

Thiosynergistic phenols carry sulfur in the same molecule as the hindered phenol, so one additive combines radical trapping with the hydroperoxide decomposition of a thioester; Irganox 1520 and Irganox 1726 are the liquid examples for elastomers. Our source library supports only this multifunctional description, not an efficiency comparison against a separate phenol-plus-thioester blend.

• Irganox 1035: a thiodiethylene-bridged bis-propionate (642.9 g/mol) for wire and cable compounds (XLPE) and rubber.
• Irganox 1520: a liquid 4,6-bis(octylthiomethyl)-o-cresol (424.8 g/mol), FDA-capped at 1.7 % in rubber articles; also one of seven candidates in California's 6PPD alternatives analysis for tyre rubber, outside this page's plastics scope.
• Irganox 1726: the dodecyl homologue of Irganox 1520, with lower volatility, for adhesives and elastomers.
• Irganox 565: a triazine-thioether hybrid (589.0 g/mol) for styrene block copolymers and hot-melt adhesives.

3. Benzyl, isocyanurate and trisphenol types: Irganox 1330, Irganox 3114, Cyanox 1790 and Topanol CA#

Benzyl and isocyanurate phenols, such as Irganox 1330 and Irganox 3114, have no hydrolysable ester group and melt above 215 °C, which suits them to long-term heat ageing and hot-water applications such as polyolefin pipes. Irganox 1330 melts at 241-247 °C and carries no ester group, a benzylic trisphenol structure (775.2 g/mol) used in PE pipe, PP and polyamide compounds where a hydrolysable ester would be a liability in hot or humid service.

Irganox 3114 is the isocyanurate used for long-term heat ageing; at 784.1 g/mol with a melting range of 218-223 °C, it suits polypropylene and polyethylene where both heat resistance and low gas-fade discolouration matter. The very high melting points of this type need good dispersion during compounding. Cyanox 1790 and Topanol CA, a 544.8 g/mol trisphenol used in polyolefins and cable compounds, round out this group.

4. Amide and hydrazide phenols: Irganox 1098, Irganox MD 1024 and Naugard XL-1#

Amide and hydrazide phenols add a nitrogen function to the hindered phenol: Irganox 1098 is the standard phenolic antioxidant for polyamides, and Irganox MD 1024 also deactivates copper ions in wire and cable insulation. Irganox 1098 is the amide phenol for polyamides, a propionamide (636.9 g/mol, melting range 156-162 °C) used at 0.05-1.0 wt% in PA6 and PA66 according to BASF guidance via SpecialChem, with 0.05-0.2 wt% the typical working range.

Irganox MD 1024 combines the hindered phenol function with a hydrazide copper deactivator (552.8 g/mol); PP and recycled XLPE blends made from end-of-life cable insulation retained their mechanical properties over 6,000 hours of ageing at 105 °C when stabilized with it. Naugard XL-1, an oxamide-type phenol plus metal deactivator, is chemically a hindered-phenol oxamide and is counted among the 26 grades on this page, though it is filed under metal deactivators in the site's substance index.

5. Bisphenols: Antioxidant 2246, Antioxidant 4425, Santonox R and related grades#

Bisphenols join two hindered phenol rings through a methylene, butylidene or sulfur bridge; Antioxidant 2246, Antioxidant 4425 and Santonox R are the main examples, used mostly in rubber, latex, ABS and polyethylene. Antioxidant 2246 has been an SVHC since 17 January 2022, classified as toxic for reproduction (Repr. 1B, H360F under CLP ATP17), yet it remains authorised in EU food-contact plastics under FCM 285 with a group SML(T) of 1.5 mg/kg. The bisphenol grades in commercial use are:

• Antioxidant 2246 (DBMC): methylene-bridged bisphenol, used in rubber, latex and ABS; SVHC status as above.
• Antioxidant 4425: butylidene bisphenol (382.6 g/mol), melting range 208-214 °C.
• Santonox R: a thiobisphenol (358.5 g/mol), melting range 150-161 °C.
• Ethanox 702: 4,4'-methylenebis(2,6-di-tert-butylphenol) (CAS 118-82-1, 424.7 g/mol).
• Hostanox O3: a bisphenolic butyrate ester (795.1 g/mol).
• Wingstay L: a polymeric UVCB phenol used in emulsion ABS and elastomer latex.
• Sumilizer GM (the same substance as Irganox 3052): an acrylated bisphenol that traps alkyl (carbon-centred) radicals in oxygen-poor melts, unlike the other grades on this page.

Antioxidant 2246 is the only phenolic antioxidant grade in this list on the REACH Candidate List; none of the other bisphenols carries a harmonised hazard classification in our source library.

6. Phosphonate-salt phenols: Irganox 1425#

Irganox 1425 is a calcium phosphonate salt of a hindered phenol, designed for low gas-fade discoloration in polyolefin fibres. Chemically it is calcium bis[monoethyl(3,5-di-tert-butyl-4-hydroxybenzyl)phosphonate] (694.8 g/mol), and it carries an FDA cap of 0.25 % in polypropylene. Irganox 1425 is designed for low gas fade in fibres, which places it alongside Cyanox 1790 and the isocyanurate grades as a low-discolouration option for white polypropylene fibre.

7. Low-molecular-weight phenols: BHT#

BHT (butylated hydroxytoluene, 220 g/mol) is the simplest commercial hindered phenol, but its volatility has made higher-molecular-weight phenols such as Irganox 1076 the standard in most plastics. BHT is the simplest commercial hindered phenol (CAS 128-37-0, melting point 70-71 °C), and its high vapour pressure limits its use in high-temperature processing; it also raises VOC emissions and fogging in vehicle interiors under DIN 75201 testing, according to secondary sources. BHT is still sold under the generic name "antioxidant 264" and remains common in lower-temperature polymer production, rubber and adhesives.

8. Natural phenols: vitamin E (alpha-tocopherol)#

Vitamin E (alpha-tocopherol) is a natural hindered phenol that stabilizes polyethylene and polypropylene melts at only 100-300 ppm, according to work by Sabah Al-Malaika at Aston University. In one HDPE trial, 200 ppm of vitamin E (alpha-tocopherol) retained melt flow index over 3 extrusion passes where 200 ppm of Irganox 1010 did not. Vitamin E causes more yellowing than the synthetic phenols, so a phosphite is normally added for colour control, and it is also used in irradiated UHMWPE for orthopaedic implants under ASTM F2695.

Bio-based alternatives are covered under natural antioxidants for plastics. A related development is a bio-based sinapic acid stearyl ester that gave processing stability in polypropylene comparable to or better than Irganox 1076, reported by Fraunhofer LBF in 2023.

Phenolic Antioxidant Grades Compared: CAS, Molecular Weight and Regulatory Status#

Table T2 lists the 26 phenolic antioxidant grades by type, identity and EU and US food-contact status. The 26 phenolic antioxidant grades used in plastics differ by a factor of five in molecular weight, from BHT at 220 g/mol to Irganox 1010 at 1,178 g/mol, and range from unrestricted food-contact use to SVHC status.

SML in mg/kg food. "No SML" means the overall migration limit of 10 mg/dm² applies. EU values checked against the consolidated text of Regulation (EU) No 10/2011 of 16 March 2025. FDA values are maximum use levels under 21 CFR 178.2010 for the named polymer; check food type and condition of use. "Not in our sources" means the value has not been verified, not that the grade is unlisted.

Request quotes for phenolic antioxidants: grade or CAS number, volume, polymer, country. Use the plastic additive supplier finder to send one request to several producers at once.

How Much Phenolic Antioxidant Does a Polymer Need?#

Polymers need 100 ppm to 0.4 wt% of a phenolic antioxidant in most cases: commodity polypropylene is base-stabilized with less than 400 ppm, while Irganox 1010 is used at 0.05-0.4 wt% in polyolefins that need long-term heat resistance. Commodity PP grades that carry no long-term heat-ageing requirement are often built with less than 400 ppm of phenolic antioxidant as base stabilization, according to Mayer et al. (2023); 400 ppm equals 0.04 wt%.

Supplier and study ranges; trials decide the final level.

Typical dosage vs FDA maximum limits#

FDA percentages for phenolic antioxidants are legal ceilings, not recommended dosages: 21 CFR 178.2010 limits use to the amount reasonably required for the technical effect and then caps each grade per polymer, for example Irganox 1076 at 0.25 % in listed olefin polymers. A supplier's technical-data-sheet range can exceed an FDA cap for a specific polymer: Irganox 1076 is offered at a typical 0.1-0.4 wt% in polyolefin technical literature, but a food-contact article made from a listed olefin polymer must stay at or below the 0.25 % legal cap regardless of the supplier range.

Which Phenolic Antioxidant Is Best for Each Polymer?#

The best phenolic antioxidant for a polymer depends on processing temperature, service temperature, contact with copper or food, and colour demands: Irganox 1010 or 1076 with a phosphite for polyolefins, Irganox 1098 for polyamides, and Irganox 245 or 1076 for styrenics. A grade-by-grade comparison of Irganox 1010, 1076, Irgafos 168 and BHT is covered separately; this section compares grades across 7 polymer families.

Phenolic antioxidants for polypropylene#

Polypropylene uses a high-molecular-weight phenol such as Irganox 1010 together with a phosphite, because its tertiary carbon atoms make it the most oxidation-sensitive commodity polymer. Chain scission at these tertiary sites raises melt flow rate as PP degrades, and PP alone accounts for 34.68 % of plastic antioxidant revenue (2025, Mordor Intelligence). Commodity grades run below 400 ppm; fibre applications favour gas-fade-resistant grades such as Irganox 1425 or Cyanox 1790; pipe and under-hood compounds add a thioester; and talc-filled grades need a stronger package since talc adsorbs part of the dose. The complete PP package is on antioxidants for polypropylene.

Phenolic antioxidants for polyethylene#

Polyethylene film is stabilized with Irganox 1076 or Irganox 1010 plus a phosphite, while HDPE pipe compounds rely on high-molecular-weight phenols such as Irganox 1330 and Irganox 1010 for long-term oxidation resistance. Unlike PP, polyethylene tends to crosslink and form gels, particularly in LLDPE and HDPE film, rather than only chain-scissioning. Santonox R carries an FDA cap of 0.25 % in PE with density 0.926 or above. Film and pipe packages are on antioxidants for polyethylene.

Phenolic antioxidants for nylon (polyamide)#

Nylon is stabilized with the amide phenol Irganox 1098 at 0.05-1.0 wt%, and with copper-halide systems when the part must survive long-term heat above about 180 °C. The FDA cap for Irganox 1098 is 1 % in nylon resins and 0.75 % in nylon 12. Brueggemann's copper-halide systems, for example its H1805 grade, retain more than 50 % tensile strength after 3,000 hours at 200 °C, well above what a phenol alone can hold. In one PA56T/GF study, Irganox 1098 slowed ageing at 150 °C without changing its underlying pathway. Copper-halide systems are covered with the other additives for nylon (polyamide).

Phenolic antioxidants for ABS and styrenics#

ABS and other styrenics use Irganox 1076 and the semi-hindered Irganox 245, because the polybutadiene rubber phase oxidizes first and yellows; 0.2 wt% Irganox 1076 is an industrially attractive level in ABS. In a 2019 statistical study of commercial mass- and emulsion-polymerized ABS grades published in Polymers (volume 11, article 25), mass ABS proved more stable than emulsion ABS, and combining Irganox 1076 with Irganox 245 gave a higher oxidation onset and peak temperature than either grade alone. Emulsion ABS is often stabilized by dosing Wingstay L with DLTDP directly into the latex. FDA caps include 0.5 % for Irganox 1076 and 0.3 % for Irganox 245 in ABS. Emulsion and mass ABS packages are on antioxidants for ABS and styrenics.

Phenolic antioxidants for polyurethane foam and polyols#

Polyurethane foam and polyols use the liquid phenol Irganox 1135 at 0.15-0.5 wt%, usually together with the aminic antioxidant Irganox 5057, to prevent scorch in the foam core. Scorch, the internal discolouration of flexible slabstock foam during the exothermic reaction, is the main failure mode this combination addresses, and BHT-free systems are generally preferred because BHT's volatility raises fogging and VOC concerns in enclosed spaces. Scorch prevention is covered under antioxidants for polyurethane.

Phenolic antioxidants for wire and cable compounds#

Wire and cable compounds use phenolic antioxidants with a second function: Irganox MD 1024 deactivates copper from the conductor, and the thioether-bridged Irganox 1035 is used in crosslinked polyethylene (XLPE) insulation. Copper in direct contact with a polyolefin insulation compound catalyses oxidation unless a copper-deactivating additive is present. Santonox R and DSTDP appear as thiosynergist partners, and peroxide-crosslinked compounds need antioxidants chosen so they do not interfere with the peroxide cure. The full insulation package is on additives for wire and cable compounds.

Phenolic antioxidants for recycled plastics#

Recycled polyolefins are restabilized with a phenol and phosphite blend, typically 0.1-0.3 wt% of an Irganox 1010 and Irgafos 168 mixture, to replace the antioxidant consumed in the first life of the plastic. Rudolf Pfaendner at Fraunhofer LBF, in a 2022 restabilization study published in Polymer Degradation and Stability (volume 203, article 110082), showed that 500 ppm Irganox 1010 plus 1,000 ppm Irgafos 168 restored oxidative stability to PP recyclate, while unstabilized PP regranulate retained more than 150 ppm of intact Irgafos 168 from its first life. Closed-loop recycling that adds fresh antioxidant every cycle can build up antioxidant concentration over successive loops, according to Knoben et al. (2025), published in Materials (volume 18, article 1640). Study doses and OIT data are on restabilization of recycled plastics.

Phenolic Antioxidant Synergy: Why Hindered Phenols Are Blended with Phosphites and Thioesters#

Hindered phenols are blended with phosphites and thioesters because every peroxyl radical a phenol traps becomes a hydroperoxide, and only a secondary antioxidant can decompose that hydroperoxide before it splits into two new radicals. Ready-made one-pack products such as Irganox B 215 are covered under antioxidant blends and synergy.

Phenol + phosphite antioxidants for processing stability#

Phenol and phosphite antioxidants are the standard processing package for polyolefins, at a phosphite-to-phenol ratio of 1:1 to 4:1, as in BASF's Irganox B 225 (1:1) and Irganox B 215 (2:1). A phosphite reduces a hydroperoxide to an alcohol, and the transesterification that occurs during this reaction can release a free phenol back into the system; phosphites also help reduce the coloured quinoid species that build up during processing. Blend ratios are written here as phosphite:phenol exactly as documented; some third-party sources reverse the B 215 ratio, and that error is not repeated on this page.

Hydrolysis resistance is compared on phosphite antioxidants.

Phenol + thioester antioxidants for long-term heat ageing#

Phenol and thioester antioxidants work together in long-term heat ageing at about 100-150 °C: in polypropylene aged at 150 °C, a 20:80 blend of Irganox 1010 and DSTDP gave the best long-term thermal stability. In a 2021 study by Allen et al., published in the Journal of Vinyl and Additive Technology, an 80:20 ratio of the same two additives performed best for processing stability, showing that the optimum phenol-to-thioester ratio depends on whether the goal is melt processing or long-term heat ageing. DLTDP, DSTDP and ditetradecyl thiodipropionate share an EU group restriction with an SML(T) of 5 mg/kg. DLTDP and DSTDP are covered under thioester antioxidants.

Phenolic antioxidants with HALS, pigments and fillers#

Phenolic antioxidants and HALS are complementary in outdoor polyolefins, but a thioester added for heat ageing weakens the HALS, and low-treated titanium dioxide can turn a phenolic antioxidant pink. HALS protect a polymer well during outdoor service but are weaker than phenolic antioxidants during melt processing, which is why outdoor parts typically carry both classes together.

• Thioesters: their acidic sulfur oxidation products antagonise HALS, so a phenol-plus-thioester package conflicts with a HALS-based light-stabilization system.
• Low-treated titanium dioxide: forms Ti-quinone complexes with a phenolic antioxidant, producing a pink discolouration; adding zinc stearate helps counter this effect.
• Talc: adsorbs part of the antioxidant dose, so talc-filled compounds need a stronger phenolic package to reach the same protection level.
• HALS: basicity and thioester antagonism are explained under hindered amine light stabilizers (HALS).

Download the AO + HALS Pairing Chart (PDF): which phenol, phosphite, thioester and HALS combinations work, and which conflict.

Why Do Phenolic Antioxidants Cause Yellowing, Pinking and Gas Fading?#

Phenolic antioxidants cause yellowing because their oxidation products, the quinone methides, are coloured: over-oxidation in processing, nitrogen oxides from gas-fired equipment and interaction with titanium dioxide all convert the phenol into these yellow to pink compounds. Phenolic antioxidants discolour through 4 routes.

• Over-oxidation. Excess processing heat or shear drives more phenol through the quinone methide pathway than the formulation was designed for.
• NOx gas fading. Nitrogen oxides, typically from gas-fired forklifts or warehouse heaters, convert phenolic antioxidants into quinone methides, such as stilbenequinone from BHT; this is a recognised problem for white PP fibre, film and TPO stored in warehouses.
• Pigment interaction (TiO2 pinking). Low-treated titanium dioxide forms Ti-quinone complexes with a phenolic antioxidant, producing a pink cast.
• Cardboard yellowing. Migration of phenolic antioxidant vapour into packaging cardboard can leave a yellow stain, a formulation-level side effect rather than a colour change in the plastic itself.

Remedies include phenol-free systems built from a hydroxylamine and a phosphite, phosphite-rich blends, and low-gas-fade phenol grades such as Irganox 1425 and Cyanox 1790. N,N-dibenzylhydroxylamine, protected under US patent 4,590,231, prevents gas fading of phenolic antioxidant systems in polypropylene. Phenolic antioxidants are not recommended for direct gas-fired ovens; Irgafos 168 is rated for that use according to its BASF technical data sheet. Quinone methides can also photo-bleach under light exposure, which partly reverses the discolouration outdoors. Every cause and fix of yellowing, pinking and gas fading is covered in the troubleshooting guide.

How Is the Performance of Phenolic Antioxidants Tested?#

Phenolic antioxidant performance is tested in 3 ways: oxidation induction time by DSC, multiple-pass extrusion with melt flow rate and yellowness measurements, and long-term oven ageing to embrittlement.

Oxidation induction time (OIT)#

Oxidation induction time measures how long a phenolic-stabilized sample resists oxygen at a fixed 190-220 °C in a DSC, following ISO 11357-6 or ASTM D3895, and it mainly reflects how much active phenolic antioxidant remains. The test heats the sample under nitrogen, then switches to oxygen at the fixed temperature and records the time to the onset of an exothermic oxidation peak. ISO 11357-6:2018 and ASTM D3895-19 are not technically equivalent methods, so results from the two standards should not be compared directly. A volatile antioxidant can give a low OIT result while still performing adequately in use, a limitation ASTM D3895 itself notes; OIT tracks residual active phenolic antioxidant, not service life at the 60-110 °C range typical of many applications. Method variants and limitations are on the oxidation induction time (OIT) page.

Multiple-pass extrusion: melt flow rate and yellowness#

Multiple-pass extrusion tests processing stability by re-extruding a compound several times and measuring melt flow rate (230 °C / 2.16 kg for PP) and yellowness index (ASTM E313) after each pass. Melt flow rate follows ISO 1133-1 or ASTM D1238-26, using 230 °C and 2.16 kg for PP and 190 °C and 2.16 kg for PE. Yellowness index follows ASTM E313-20 (reapproved 2025), never the withdrawn ASTM D1925 standard. Songwon has generated multipass data at 250 °C for PP and 220 °C for HDPE recyclate blends using this method.

Oven ageing#

Oven ageing tests long-term thermal stability by holding plaques at an elevated temperature, for example 150 °C for polypropylene under ASTM D3012, until they embrittle. Related standards include UL 746B, which produces a relative thermal index, and ISO 188 for rubber. In one example using a commercial stabilizer blend, recycled PP embrittled after about 25 days unstabilized at 150 °C, compared with 37 to 42 days when stabilized at 0.2-0.4 % of the blend.

How Are Phenolic Antioxidants Regulated?#

Most phenolic antioxidants are authorised for food-contact plastics in both the EU and the US, but Antioxidant 2246 is a REACH SVHC, BHT is under EU and US reassessment, and several grades such as Irganox 1135 are not on the EU Union list.

EU 10/2011: FCM numbers and SMLs for phenolic antioxidants#

Under Regulation (EU) No 10/2011, phenolic antioxidants fall into 3 groups: grades with no specific migration limit such as Irganox 1010 (FCM 496), grades with an SML from 45 mg/kg (Irganox 1098) down to 0.05 mg/kg (ADK STAB AO-80), and grades not on the Union list at all, such as Irganox 1135. Where no SML applies, the overall migration limit of 10 mg/dm² governs instead. OML and SML rules are explained on EU 10/2011; values on this page are checked against the consolidated text of 16 March 2025.

Group restrictions apply where several substances share a limit: group 13 (FCM 163 plus FCM 285) shares an SML(T) of 1.5 mg/kg, and group 24 (Irganox 1520 plus Irganox 1726) shares an SML(T) of 5 mg/kg. Grades not listed in EU 10/2011 at all include Irganox 1135, Antioxidant 4425 and Ethanox 702.

Phosphites and thioesters are added in the full matrix of food contact antioxidants.

US FDA: 21 CFR 178.2010 limits and 21 CFR 181.24#

In the US, phenolic antioxidants for food-contact plastics are listed in 21 CFR 178.2010 with a maximum per polymer, such as 0.5 % for Irganox 1010 and 0.25 % for Irganox 1076 in listed olefin polymers, while BHT is covered as a prior-sanctioned packaging antioxidant under 21 CFR 181.24. The prior-sanctioned category under 21 CFR 181.24 covers BHA, BHT, DLTDP, DSTDP, propyl gallate and several others, with a limit in food of 0.005 %. Vitamin E is separately GRAS under 21 CFR 182.3890. In a 2015 FDA re-evaluation of Irganox 1076 by Neal-Kluever, Bailey and Hatwell, published in Food and Chemical Toxicology (volume 86, page 176), the additive's NOAEL was set at 64 mg/kg body weight per day, giving a cumulative estimated daily intake of 4.5 mg per person per day and a margin of exposure of about 850. Food types and conditions of use are decoded on the 21 CFR 178.2010 page.

REACH: SVHC listings and substance evaluation#

Antioxidant 2246 is the only phenolic antioxidant grade on the REACH Candidate List: it was added on 17 January 2022 as toxic for reproduction, yet it remains authorised in EU food-contact plastics under FCM 285. This holds for the 26 grades in Table T2; 2,4,6-tri-tert-butylphenol, an intermediate and impurity rather than a commercial grade, was separately added to the Candidate List on 23 January 2024 for reproductive toxicity and PBT properties.

BHT is not on the REACH Candidate List and is never described as "banned" or as an "endocrine disruptor" on this page; it is under evaluation for suspected endocrine disruption. Every listed additive is tracked on the SVHC Candidate List page.

NIAS: degradation products of phenolic antioxidants#

Phenolic antioxidants leave degradation products in food-contact plastics, such as BHT-quinone and 2,6-di-tert-butylphenol, which count as non-intentionally added substances (NIAS) and must be covered by the risk assessment under Article 19 of Regulation (EU) No 10/2011. Han et al. (2024), in the Journal of Hazardous Materials (volume 470), measured synthetic phenolic antioxidants in Chinese take-away food-contact materials at 44.18 to 69,485.12 µg/kg (median 2,615.63 µg/kg), dominated by 2,4-di-tert-butylphenol, 2,6-di-tert-butylphenol and BHT-quinone, with Antioxidant 2246 found mainly in PE and PET. Dopico-Garcia et al. (2007), in the Journal of Agricultural and Food Chemistry (volume 55, page 3225), found that commercial PE, PP and PVC packaging typically contains Irganox 1010 and 1076 together with Irgafos 168 and its phosphate. Most 2,4-di-tert-butylphenol in food-contact plastics comes from phosphite degradation rather than from phenolics directly; Qian et al. (2018), in PLoS One, measured up to 45.568 mg/kg of it in BOPP and LDPE, and the substance is not on the EU Union list. Risk-assessment rules for NIAS are explained separately.

Who Manufactures Phenolic Antioxidants?#

Phenolic antioxidants are made by BASF (Irganox), Songwon (SONGNOX), SI Group (Anox, Lowinox, Naugard), Adeka (ADK STAB), Sumitomo Chemical (Sumilizer), Clariant (Hostanox) and Syensqo (Cyanox), and Irganox 1010 alone is sold under at least 10 trade names. Other producers include Dover Chemical (Dovernox), Everspring (Evernox), Lanxess (Vulkanox BKF) and Rianlon. Plants, grades and certifications are in the directory of polymer antioxidant manufacturers. SI Group acquired Albemarle's antioxidants business in 2014, and Songwon, which describes itself as the world's second-largest polymer stabilizer producer (a company claim), launched SONGNOX 1076 as its first RSPO-certified product on 14 July 2026. Irganox 1010 was invented by M. Dexter and co-workers at Geigy, with a patent priority date of 5 January 1962, and remains the volume leader today, according to Rudolf Pfaendner's 2025 history of plastic antioxidants in Macromolecular Materials and Engineering. Buyers should compare phenolic antioxidants by CAS number and food-contact status, not by trade name.

Same CAS number, different trade names (not a claim of performance equivalence):

• Irganox 1010 (6683-19-8) = Songnox 1010 = ADK STAB AO-60 = Anox 20 = Dovernox 10 = Naugard 10 = Sumilizer BP-101 = Ralox 630 = Lowinox PP35 = Evernox 10 (generic "antioxidant 1010")
• Irganox 1076 (2082-79-3) = Songnox 1076 = ADK STAB AO-50 = Anox PP18 = Naugard 76 = Ralox 530 = Sumilizer BP-76 = Ultranox 276 = Lowinox PO35
• Irganox 1330 (1709-70-2) = Ethanox 330 = Ionox 330 = Songnox 1330
• Irganox 245 (36443-68-2) = Songnox 2450 = Tominox 917
• Irganox 1035 (41484-35-9) = Songnox 1035 = Anox 70 = Naugard EL-50
• Irganox MD 1024 (32687-78-8) = SONGNOX 1024 = Lowinox MD24 = ADK STAB CDA-10
• Irganox 1135 (125643-61-0) = Songnox 1135 = Vanlube BHC
• Cyanox 1790 (40601-76-1) = Lowinox 1790 = ADK ARKLS DH-48
• ADK STAB AO-80 (90498-90-1) = Sumilizer GA-80
• Antioxidant 2246 (119-47-1) = Cyanox 2246 = Vulkanox BKF = Lowinox 22M46 = Sumilizer MDP = Plastanox 2246
• Santonox R (96-69-5) = Sumilizer WX-R = Lowinox 44S36 = Nocrac 300 = Ultranox 236
• Sumilizer GM (61167-58-6) = Irganox 3052
• Topanol CA (1843-03-4) = Lowinox CA22 = Mark AO-30
• BHT (128-37-0) = Ionol = Topanol O = Tenox BHT = Vulkanox KB = Sumilizer BHT (generic "antioxidant 264")

Trade-name mappings from PubChem synonyms and supplier sheets. Grades with the same CAS number can differ in purity, physical form and certification.

Request quotes for phenolic antioxidants: grade or CAS number, volume, polymer, country. Send one request to several phenolic antioxidant producers with the plastic additive supplier finder.

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Which Other Antioxidants Work Alongside Hindered Phenols?#

Hindered phenols are the main primary antioxidants in plastics, but aminic antioxidants, hydroxylamines, lactones and metal deactivators take over where a phenol discolours, reacts too slowly or cannot stop metal-catalysed oxidation.

Aminic antioxidants#

Aminic antioxidants such as Naugard 445 and Irganox 5057 are more effective than hindered phenols at high temperature but discolour strongly, so they are kept to dark parts, polyols and polyamides. Diphenylamines are covered under aminic antioxidants.

Phenol-free stabilization: hydroxylamines and lactones#

Phenol-free stabilization replaces the hindered phenol with a hydroxylamine such as Irgastab FS 042, used at 0.05-0.15 % with a phosphite, when white polypropylene fibre or TPO must not gas-fade. The lactone Irganox HP-136 traps carbon-centred radicals rather than peroxyl radicals, giving it a complementary role. Hydroxylamine and lactone systems are on the phenol-free stabilization page.

Metal deactivators#

Metal deactivators bind copper and other metal ions that speed up hydroperoxide decomposition, and 2 of them, Irganox MD 1024 and Naugard XL-1, are hindered phenols at the same time. Chelating chemistries are compared under metal deactivators.

Are phenolic antioxidants toxic?#

Most phenolic antioxidants used in plastics carry no harmonised EU hazard classification; the exception among common grades is Antioxidant 2246, classified as toxic for reproduction (Repr. 1B), and none is listed as a carcinogen in our source library. ADK STAB AO-80 carries a harmonised Acute Tox. 4 (H312) classification for dermal exposure. BHT is not on California's Proposition 65 list, though the related compound BHA is; the Prop 65 status of the other phenolic grades has not been verified for this page. Irganox 1076's FDA margin of exposure of about 850, cited above, is the most detailed exposure figure our source library holds for any grade.

Is BHT banned in plastics?#

No: BHT is not banned in plastics; it is listed in EU 10/2011 with an SML of 3 mg/kg and prior-sanctioned in the US under 21 CFR 181.24, although the FDA opened a Request for Information on it on 13 May 2026.

Are phenolic antioxidants in plastics the same as dietary polyphenols?#

No: phenolic antioxidants for plastics are synthetic hindered phenols such as Irganox 1010, designed for melt temperatures of 150-320 °C, whereas dietary polyphenols are plant compounds; vitamin E is the one molecule used in both worlds.

What are phenolic resins, and are they antioxidants?#

Phenolic resins are thermoset polymers made from phenol and formaldehyde, not antioxidants; the word "phenolic" on this page refers only to hindered phenol additives.

Who invented the modern hindered phenol antioxidant?#

The modern hindered phenol antioxidant dates from 5 January 1962, the priority date of the Geigy patent by M. Dexter and co-workers for Irganox 1010, which is still the highest-volume antioxidant in plastics. The synthesis route is a Michael addition of methyl acrylate to 2,6-di-tert-butylphenol, followed by transesterification with pentaerythritol. The underlying autoxidation chemistry that this antioxidant interrupts was first described by Bolland and Gee at the British Rubber Producers' Research Association in the 1940s.

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

PlasticAdditives.net Editorial Team

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