Antioxidants for Polyethylene: 5 Antioxidant Classes, Dosage and Selection

Antioxidants for polyethylene are radical-trapping and hydroperoxide-decomposing additives, mainly hindered phenols and phosphites, that are compounded into PE at about 0.05-0.4 wt% to stop oxygen from crosslinking and discolouring the polymer during extrusion and service. Unlike polypropylene, polyethylene reacts to oxidation by crosslinking and forming gels, so which antioxidant class suits film, pipe, cable or recyclate?

Antioxidants are one of the stabilizer groups of plastic additives, and commercial PE, PP and PVC packaging typically contains Irganox 1010 or Irganox 1076 together with Irgafos 168. This page covers why PE oxidizes by crosslinking rather than chain scission, the 5 antioxidant classes and how a phenol and a phosphite cooperate, grade and dosage by application, interaction with other additives, OIT and multipass testing, food and drinking-water clearance, and suppliers.

Key figures

• 0.05-0.4 wt% Irganox 1010 in polyolefins (BASF technical data)
• 1:1 to 4:1 phosphite:phenol ratio in standard PE packages
• OIT of at least 20 minutes at 210 °C for PE pressure-pipe compounds (EN 12201-1 / ISO 4427-1)
• 5 antioxidant classes used in PE: hindered phenols, phosphites and phosphonites, thioesters, metal deactivators, carbon-radical scavengers

Why Does Polyethylene Need Antioxidants?#

Polyethylene needs antioxidants because heat, shear and oxygen during extrusion start a self-accelerating radical chain reaction that crosslinks PE, forms gels in film and shortens the service life of pipes, cables and mouldings. This reaction, autoxidation, is autocatalytic: once a small number of hydroperoxide groups form, they split into new radicals and the reaction rate increases on its own until an antioxidant interrupts the cycle. The hub on antioxidants for plastics compares the same 5 classes across every polymer family, from PVC heat stabilizers to polypropylene phenolics.

How does polyethylene oxidize during processing and use?#

Polyethylene oxidizes through autoxidation: heat and shear in the extruder create alkyl radicals, oxygen turns them into peroxyl radicals, and the hydroperoxides they form split into new radicals that keep the chain reaction running. J. L. Bolland and G. Gee at the British Rubber Producers' Research Association described this cycle in the 1940s, and it still carries their name.

The autoxidation cycle of polyethylene runs in 4 steps.

1. Initiation: heat, shear or catalyst residues abstract hydrogen from the chain (RH → R•); copper, iron, manganese and cobalt ions accelerate this by redox cycling.
2. Oxygen addition: the alkyl radical reacts with dissolved oxygen, diffusion-controlled at about 1 x 10^7 to 1 x 10^9 L mol⁻¹ s⁻¹, forming a peroxyl radical (R• + O2 → ROO•).
3. Hydrogen transfer: the peroxyl radical abstracts hydrogen from another chain, forming a hydroperoxide and a new alkyl radical (ROO• + RH → ROOH + R•). Smith, Aitken and Coote (Accounts of Chemical Research, 2018) showed this transfer is disfavoured on saturated backbones and favourable mainly at unsaturated defect sites.
4. Branching and termination: the hydroperoxide splits into alkoxyl and hydroxyl radicals (ROOH → RO• + •OH), each starting a new chain, until two radicals combine and terminate.

Crosslinking and chain scission compete throughout this cycle in PE, and HDPE made with chromium (Phillips) catalysts is particularly prone to crosslinking. Rate constants and the modern revision of the cycle are on polymer oxidation and antioxidant mechanisms.

What are the signs of oxidation in polyethylene?#

Oxidized polyethylene shows 6 typical signs: gels and fisheyes in film, a falling melt flow rate, yellowing or pinking, a shorter oxidation induction time, surface cracking and embrittlement.

• Gels and fisheyes in film, from degraded or crosslinked polymer, unmelted resin or poor concentrate dispersion (Ampacet technical notes).
• A falling melt flow rate, measured at 190 °C / 2.16 kg, as crosslinking raises the polymer's effective molecular weight.
• Yellowing or pinking of white PE, where an over-oxidized phenolic antioxidant converts to coloured quinones.
• A shorter oxidation induction time on DSC, signalling depletion of the residual phenolic antioxidant.
• Surface cracking, a general sign only (our source library has no PE-specific crack-growth data).
• Embrittlement and loss of elongation in long-term service, illustrated by the retention criteria that GRI-GM13 uses to judge remaining antioxidant reserve.

Does polyethylene degrade differently from polypropylene?#

Yes: polyethylene tends to crosslink and form gels when it oxidizes, so its melt flow rate falls, whereas polypropylene chain-scissions at its tertiary carbons, so its melt flow rate rises. The two commodity polyolefins therefore need antioxidant packages tuned to opposite failure modes, even though both use the same phenol and phosphite chemistry.

What Are the 5 Types of Antioxidants for Polyethylene?#

The 5 types of antioxidants used in polyethylene are hindered phenols, phosphites and phosphonites, thioesters, metal deactivators and carbon-radical scavengers, and a hindered phenol plus a phosphite is the standard package in most PE grades. Aminic antioxidants, the primary class used in rubber, are not used in PE because they discolour the polymer.

1. Hindered phenols (primary antioxidants)#

Hindered phenols are primary antioxidants that donate a hydrogen atom to peroxyl radicals and so break the oxidation chain; each phenol group traps about 2 radicals before it ends as a coloured quinone methide. This reaction (ArOH + ROO• → ArO• + ROOH) is why phenols are called chain-breaking donors, and the stoichiometric factor of roughly 2 radicals per phenol group sets the theoretical dosage floor.

Commercial phenolic antioxidants for PE range in molecular weight from about 300 to 1,000 g/mol; the low end favours faster reaction but greater volatility, and the high end favours permanence at the cost of melt solubility. All commercial phenolic antioxidants (hindered phenols) are compared by molecular weight and melting range on the class hub. Irganox 1010 (CAS 6683-19-8, MW 1,177.6 g/mol), invented at Ciba-Geigy (M. Dexter et al., priority date 5 January 1962), remains the volume leader today.

Irganox 1010 is the volume leader among phenolic antioxidants, and full CAS, regulatory and dosage data for the substance are on its own page.

Vitamin E (alpha-tocopherol) in polyethylene#

Vitamin E (alpha-tocopherol) is a natural-type phenolic antioxidant that melt-stabilizes polyethylene at only 100-300 ppm, a level well below typical synthetic phenol dosages measured in wt%. Sahar Al-Malaika's group at Aston University has published extensively on vitamin E as a bio-based stabilizer for polyolefins, and in one three-pass extrusion trial on HDPE, 200 ppm vitamin E retained melt flow index where 200 ppm Irganox 1010 did not.

Vitamin E causes inherent yellowing in PE, so formulators add a phosphite in colour-sensitive HDPE grades. The EU lists alpha-tocopherol under FCM 110 with no SML, and the US treats tocopherols as GRAS under 21 CFR 182.3890. Irganox E 201 (BASF, CAS 10191-41-0 for the DL form; also 59-02-9, natural RRR form) is the main trade name. Grades and implant data are on Vitamin E (alpha-tocopherol) as a polymer antioxidant, a substance page not yet published.

2. Phosphites and phosphonites#

Phosphites and phosphonites are secondary antioxidants that reduce hydroperoxides to harmless alcohols while being oxidized to phosphates, which is why they protect the melt flow and colour of polyethylene during extrusion. Their reactivity ranks phosphonites above alkyl phosphites, which in turn rank above aryl and hindered aryl phosphites, and because they act mainly during melt processing rather than long-term service, they contribute little to outdoor or long-term heat ageing on their own.

Hydrolysis data for all phosphite and phosphonite antioxidants sit on the class hub. Irgafos 168 (CAS 31570-04-4, MW 646.9 g/mol, mp 183-186 °C) is hydrolytically stable, used in polyolefins at 0.05-0.2 wt%. Ultranox 626 (also Irgafos 126 or ADK STAB PEP-24, CAS 26741-53-7) offers higher activity but lower hydrolytic stability. P-EPQ (CAS 119345-01-6, about 70 % active) is a phosphonite that reduces gel counts in LLDPE, and ADK STAB PEP-36 is a further spiro diphosphite used in olefin copolymer film.

Irgafos 168 is the hydrolytically robust reference phosphite most competing grades are benchmarked against. Weston 705, a nonylphenol-free liquid phosphite marketed as a TNPP replacement, is named here without its unverified supplier performance claims.

Why phosphite hydrolysis matters in PE processing#

Phosphite hydrolysis matters because a phosphite that has taken up moisture turns acidic, feeds poorly and can leave black specks in PE film, so high-activity spiro diphosphites such as Ultranox 626 are sold in hydrolysis-buffered forms. Aryl phosphites hydrolyse at 150-180 °C to phenols and hydrogen phosphites, and this acidity causes the feeding and spotting problems.

Doverphos S-9228 is a second-generation phosphite with better hydrolysis resistance than earlier spiro diphosphites. Songwon sells Songnox 6280 as a 93:7 blend of Songnox 6260 with hydrotalcite to buffer this risk, and ships its phosphite grades in aluminium-coated bags to keep moisture out before use.

3. Thioesters (thiosynergists)#

Thioesters such as DSTDP and DLTDP are secondary antioxidants for the long-term heat ageing of polyethylene at about 100-150 °C, used mainly in HDPE and XLPE power cable compounds rather than for melt protection. They oxidize to sulfoxides and sulfones as they decompose hydroperoxides, and this sulfur chemistry antagonises HALS.

DSTDP (CAS 693-36-7, MW 683.2 g/mol, melting point 63.5-68.5 °C) is used in HDPE and XLPE cable compounds, though our source library has no sourced PE dosage for it. Under EU 10/2011, DLTDP (FCM 294), DSTDP (FCM 368) and ditetradecyl thiodipropionate (FCM 894) share group restriction 14, a combined SML(T) of 5 mg/kg including oxidation products; in the US they are prior-sanctioned under 21 CFR 181.24. DLTDP, DSTDP and DMTDP are compared on the thioester antioxidants class page.

4. Metal deactivators#

Metal deactivators such as Irganox MD 1024 and Naugard XL-1 bind copper and other catalytic metal ions that would otherwise accelerate the oxidation of polyethylene cable insulation. Titanium, aluminium and copper are the main catalytic metals in polymer compounds, and cable insulation is the critical case, since copper conductors sit in direct contact with the PE or XLPE jacket.

Irganox MD 1024 (CAS 32687-78-8) combines a hindered phenol with a hydrazide copper deactivator in one molecule and is used in PE and PP wire and cable insulation that touches copper; in one accelerated-ageing study, PP and recycled XLPE blends stabilized with it retained mechanical properties over 6,000 hours at 105 °C. Its EU listing is FCM 675, SML 15 mg/kg. Naugard XL-1 (CAS 70331-94-1), a phenol oxamide, combines the same two functions. How metal deactivators chelate copper across polymer families is explained on the family hub.

5. Carbon-radical scavengers: hydroxylamines and benzofuranones#

Carbon-radical scavengers such as the benzofuranone Irganox HP-136 and the hydroxylamine Irgastab FS 042 trap alkyl radicals before oxygen reaches them, and they are used at low levels in processing blends and phenol-free PE systems. The reaction of an alkyl radical with oxygen is diffusion-fast, at roughly 1 x 10^7 to 1 x 10^9 L mol⁻¹ s⁻¹, so scavenging the alkyl radical itself is difficult, and this is the gap lactones and hydroxylamines fill.

Irganox HP-136 (CAS 181314-48-7) traps carbon- and oxygen-centred radicals; the EU lists it under FCM 26, SML 5 mg/kg, and the FDA allows up to 0.1 % in olefin polymers for listed food types, dropping to 50 µm thickness in PE below 0.94 g/cm3 for other food types. Irgastab FS 042 (CAS 143925-92-2) is used at 0.05-0.15 % with a phosphite in phenol-free systems; the EU caps polyolefin use at 0.1 % (fatty foods excluded), and the FDA caps it at 0.075 % in HDPE of density 0.94 g/cm3 or above.

Phenolic and Phosphite Antioxidants in Polyethylene: How Do They Work Together?#

Phenolic and phosphite antioxidants work together in polyethylene because the phenol traps peroxyl radicals and the phosphite destroys the hydroperoxides this reaction leaves behind, so blends at a phosphite:phenol ratio of 1:1 to 4:1 protect PE better than either antioxidant alone. Ready-made ratios are listed under antioxidant blends and synergy: Irganox B 215 supplies Irgafos 168 to Irganox 1010 at 2:1 (67/33), B 225 supplies the same pair at 1:1, and B 900 supplies Irgafos 168 to Irganox 1076 at 4:1 (80/20).

Not every antioxidant class suits polyethylene. Aminic antioxidants are avoided because they stain and discolour the polymer. BHT (MW 220.35 g/mol) is too volatile for most high-temperature PE extrusion and has been replaced by Irganox 1076 in most plastics. TNPP, covered under the regulatory section below, is a REACH substance of very high concern being phased out in favour of nonylphenol-free phosphites. Thioesters should stay out of outdoor PE that also carries a HALS, since the two classes antagonise each other.

Which Antioxidant Is Best for Each Polyethylene Application?#

The best antioxidant for polyethylene depends on processing temperature, service temperature, contact with copper, water or food, and film thickness: a phenol plus a phosphite for film and mouldings, high-molecular-weight phenols for pipe and geomembranes, a metal deactivator for cable, and vitamin E for implants. The table below sets the recommended system, example grades and dosage level for 10 PE applications.

Supplier and literature ranges; FDA percentages are legal maxima, not dosages. Trials decide the final level.

LDPE and LLDPE film#

LDPE and LLDPE film is usually stabilized with Irganox 1076 or Irganox 1010 plus Irgafos 168, because the film must leave the die free of gels and keep its colour through blown or cast extrusion. LDPE has a density around 0.924 g/cm3 and LLDPE ranges from 0.916 to 0.940 g/cm3, and both are prone to gels and fisheyes from degraded or crosslinked polymer, unmelted resin or poor masterbatch dispersion (Ampacet technical notes). Lower melt temperature, higher throughput, adjusted screw design and tighter screen packs are the standard remedies once the antioxidant package is confirmed adequate.

Irganox 1076 is the monofunctional phenol most used in PE film. In one Songwon gel-count chart for recycled LLDPE, 0.1 % P-EPQ cut the gel count from about 210 to about 150 gels per 1,525 cm2. FDA rules cap Irgafos 168 at 0.2 % in ethylene polymers, with LDPE film above 0.051 mm further limited to 0.062 mg/in2 or conditions E-G; ADK STAB PEP-36 is capped at 0.05 % in olefin copolymer film up to 100 µm. Slip, antiblock and antifog packages are on additives for packaging film.

HDPE pressure pipe#

HDPE pressure pipe uses high-molecular-weight phenols such as Irganox 1330 or Irganox 1010 with a phosphite, so that the compound reaches an oxidation induction time of at least 20 minutes at 210 °C (EN 12201-1 / ISO 4427-1) and resists chlorinated drinking water. A PE pressure-pipe compound also carries 2.0-2.5 wt% carbon black with a primary particle size of 10-25 nm for UV screening. Carbon black, UV and drinking-water rules for pipe are on the additives for plastic pipes page.

High-molecular-weight phenols resist extraction better than low-molecular-weight grades, which matters because chlorine dioxide at 4 ppm and 90 °C consumes antioxidant about 4 times faster than plain chlorinated water at the same temperature. No standardised accelerated test for chlorine dioxide exposure exists yet, so pressurised loop tests that replicate actual service conditions remain the most reliable way to validate a pipe formulation. The phosphonite P-EPQ is on the EU drinking-water positive list (Implementing Decision (EU) 2024/367, entry 0667), and that positive-list regime applies from 31 December 2026.

HDPE geomembranes#

HDPE geomembranes need the most durable antioxidant package in polyethylene: GRI-GM13 requires a standard OIT of at least 100 minutes or a high-pressure OIT of at least 400 minutes, and most of it must survive 90 days of oven ageing at 85 °C. GRI-GM13 Rev. 16 (17 March 2021) sets carbon black at 2.0-3.0 % and PE density at 0.940 g/ml or above, and requires the compound to retain at least 55 % of its Std-OIT or at least 80 % of its HP-OIT after that 90-day, 85 °C oven test, plus at least 50 % of its HP-OIT after 1,600 hours of UV exposure.

The high-pressure method, ASTM D5885, detects HALS as well as phenolic antioxidant, while the standard method, ASTM D8117, does not. The full GRI-GM13 property table is on the additives for geomembranes and geosynthetics page.

PE and XLPE wire and cable insulation#

PE and XLPE cable insulation combines a phenolic antioxidant with a metal deactivator such as Irganox MD 1024, because copper conductors catalyse oxidation and XLPE runs continuously at 90-105 °C. In emergency overload conditions, XLPE cable can reach 130-140 °C, raising the demand on the package further. HFFR and LSZH packages for cable are compared on additives for wire and cable compounds.

Peroxide-crosslinked and silane-grafted compounds need antioxidants that do not interfere with the cure: in one silane-grafted POE/LLDPE study, 0.3 wt% antioxidant can cut cure time from 14-16 hours to 8 hours. Irganox 1035, a thioether-bridged phenol, and DSTDP are both used in PE and XLPE power cable compounds. A reference HFFR EVA/LLDPE formulation from Huber pairs 0.75 phr Ethanox 310 with 0.25 phr Ethaphos 368 for 1.0 phr total antioxidant, alongside 160 phr aluminium trihydrate flame retardant. Peroxide and silane crosslinking routes are compared on XLPE: crosslinked polyethylene.

HDPE mouldings and rotomoulded PE#

HDPE blow- and injection-moulded parts use the standard phenol-plus-phosphite package with a metal stearate, while rotomoulded PE needs a heat-stable powder package because the polymer spends long periods in an oven at about 300 °C. Blow-moulded bottles and IBCs and injection-moulded crates and caps carry the antioxidant alongside calcium or zinc stearate as acid scavenger and lubricant.

Rotomoulding uses powder-grade HDPE at a density around 0.961 g/cm3, with 1 to 2 cycles per hour, oven air around 300 °C and an internal part temperature reaching about 180 °C at the end point. More than 80 % of material processed by rotomoulding worldwide is polyethylene, which is why heat-stable powder packages are a distinct category from pellet-grade PE stabilizers.

UHMWPE medical implants#

UHMWPE hip and knee implants are stabilized with vitamin E, generally below 0.3 wt%, because radiation crosslinking leaves free radicals that would otherwise oxidize the bearing surface. Radiation doses used to crosslink UHMWPE for wear resistance also generate long-lived free radicals, and without stabilization these continue reacting with oxygen for years after implantation.

Vitamin E can be blended into the resin before consolidation or diffused into the finished implant after irradiation; studies covering 0.1-1.0 wt% report that it preserves oxidation resistance while keeping the wear resistance and fatigue strength irradiation crosslinking is meant to provide, an alternative to older post-irradiation remelting. ASTM F2695 is the standard test method for vitamin E-stabilized UHMWPE. Sterilization stability for medical devices generally is covered under additives for medical plastics.

Recycled polyethylene#

Recycled polyethylene needs fresh antioxidant because its original stabilizer is partly consumed: recycled HDPE is typically restabilized with 0.1-0.3 wt% of a phenol/phosphite blend such as Irganox 1010 with Irgafos 168. Rudolf Pfaendner, formerly of Ciba and now at Fraunhofer LBF, reviewed this restabilization concept in "Restabilization: 30 years of research for quality improvement of recycled plastics" (Polymer Degradation and Stability, volume 203, 2022).

Songwon's multipass data at 220 °C support the 0.1-0.3 wt% range for recycled HDPE using 1010/168 binary blends, and P-EPQ at 0.05-0.1 wt% targets processing stability and gel reduction in recycled LLDPE. Closed-loop recycling that adds antioxidant every cycle can lead to build-up over repeated loops (Knoben et al., 2025), and contamination matters too: 5 % polypropylene carried into recycled HDPE can cut slow-crack-growth resistance by up to 40 %. Dosing rules for PCR-PE and PCR-PP are on restabilization of recycled plastics; the Packaging and Packaging Waste Regulation (EU) 2025/40 adds recycled-content targets of 10 % and 35 % for plastic packaging from 2030, pushing restabilization further up the value chain.

How Much Antioxidant Does Polyethylene Need?#

Polyethylene needs about 0.05-0.4 wt% of a hindered phenol and 0.05-0.2 wt% of a phosphite, with the level set by the number of heat histories, the service temperature, contact with copper or chlorinated water, and the OIT the specification requires. Irganox 1076 runs slightly higher at 0.1-0.4 wt%, vitamin E melt-stabilizes PE at only 100-300 ppm, and recyclate restabilization typically falls in the 0.1-0.3 wt% band.

Four factors drive the final dosage in any given PE formulation.

• Number of heat histories, meaning how many extrusion or moulding passes the resin sees, since each pass consumes part of the antioxidant reserve.
• Service temperature, since cable insulation running continuously at 90-105 °C needs a more robust package than an ambient-temperature film.
• Contact with copper, chlorinated water or food, each of which either accelerates oxidation or restricts which antioxidants may be used at all.
• Part thickness and the OIT the specification requires, since thin film and thick pipe wall dilute or concentrate a given weight percentage differently across the finished part.

FDA percentages in 21 CFR 178.2010 are legal maxima, not recommended dosages: the regulation limits use to the amount reasonably required for the technical effect. As a worked example, a masterbatch containing 10 wt% active antioxidant, let down at 2 %, delivers 0.10 x 0.02 = 0.002, or 0.2 wt% antioxidant in the finished film. Check the arithmetic in the let-down ratio calculator.

How Do Antioxidants Interact with Other Additives in Polyethylene?#

Antioxidants in polyethylene interact most with acid scavengers, TiO2, HALS, crosslinking agents and nitrogen oxides from the air: acid scavengers protect the phosphite, while TiO2 and NOx can turn over-oxidized phenols pink or yellow. Ziegler-Natta and chromium catalyst residues leave acidic species in the resin, and a PE package normally includes calcium or zinc stearate or hydrotalcite specifically to neutralise them before they attack the phosphite.

Calcium stearate and hydrotalcite are compared under acid scavengers for polyolefins. Calcium stearate is used at 0.05-0.20 % as an acid scavenger in polyolefins, up to about 1,000 ppm; in a 2025 study, Espelage and colleagues found that its presence in a PP formulation meant more Irgafos 168 was retained after compounding, since less phosphite was lost to acid-catalysed hydrolysis. Hydrotalcite plays the same role in PP and PE and also protects UV stabilizers in greenhouse film.

Pinking and yellowing of white or pigmented PE share this chemistry: an over-oxidized phenolic antioxidant converts to coloured quinones, aggravated by low-treated TiO2, NOx gas fading, high-pH additives such as some UV stabilizers, moisture and dark storage. Zinc stearate forms colourless zinc-quinone complexes and so reduces pinking, while weathering-grade TiO2 pairs poorly above 232 °C. Direct gas-fired ovens are unsuitable for phenolic-only packages because of NOx exposure. Causes and fixes for yellowing, pinking and gas fading are on the troubleshooting page.

How Is Antioxidant Performance in Polyethylene Tested?#

Antioxidant performance in polyethylene is tested by oxidation induction time on a DSC, by repeated extrusion with melt flow, gel and colour measurements, and by long-term oven or water ageing. Each method targets a different failure mode, from residual phenolic antioxidant to accumulated processing damage to years of service exposure.

Oxidation induction time (OIT)#

Oxidation induction time (OIT) is the time a polyethylene sample, held at a constant 190-220 °C, survives in pure oxygen before it starts to oxidize, and it measures how much active phenolic antioxidant is left. The test heats the sample under nitrogen to the target temperature, switches the atmosphere to oxygen, and times the onset of the exotherm; ASTM D3895-19, ISO 11357-6:2018 and EN 728 all describe versions of this method, and the first two are not technically equivalent. Test conditions and limitations of oxidative induction time (OIT) are on the testing page.

High-pressure OIT (ASTM D5885, 3.4 MPa oxygen, 150 °C) is used only where the standard test would run beyond 30 minutes. OIT has real limitations: it mostly detects residual phenolic antioxidant, a volatile antioxidant can read low yet still perform in service (a caveat ASTM D3895 itself notes), phosphites and thioesters contribute little at 200 °C, and OIT does not predict service life at the 60-110 °C temperatures PE actually sees in use.

Multiple-pass extrusion: melt flow rate, gels and yellowness#

Multiple-pass extrusion tests how well an antioxidant package survives repeated heat histories: PE is extruded several times and melt flow rate at 190 °C / 2.16 kg, gel count and yellowness index are measured after each pass. Songwon runs its multipass restabilization trials for recycled HDPE at 220 °C, which is closer to the heat history a reprocessed resin actually experiences.

• Melt flow rate, measured under ISO 1133-1 or ASTM D1238-26 at 190 °C / 2.16 kg (also reported at 5 kg for some PE grades), reported in g/10 min.
• Gel count, counted per unit film area to track crosslinked or degraded particles.
• Yellowness index, measured under ASTM E313-20 (R2025); the older ASTM D1925 method was withdrawn in 1995 and should never be cited as current.

A falling melt flow rate signals crosslinking in PE, the opposite of the rising melt flow rate that signals chain scission in polypropylene.

Long-term heat ageing and chlorinated-water exposure#

Long-term performance of an antioxidant in polyethylene is tested by oven ageing to embrittlement and, for pipe, by exposure to hot chlorinated or chlorine-dioxide water, which consumes the antioxidant about 4 times faster at 4 ppm chlorine dioxide and 90 °C than plain chlorinated water at the same temperature. Oven ageing to embrittlement, following methods such as ISO 188 and UL 746B, tracks days of exposure before mechanical failure, the regime in which thioesters, acting at about 100-150 °C, make their main contribution.

Geomembrane specifications add their own clause, requiring the compound to hold its OIT reserve through 90 days at 85 °C. No standardised accelerated test for chlorine dioxide exposure exists, so pressurised loop testing that reproduces actual service conditions remains the most reliable way to validate a pipe package. Oven methods and the related thermal index are on the long-term heat aging page.

How antioxidant content in PE is measured#

Antioxidant content in polyethylene is measured to ASTM D6953: the additives are extracted with isopropanol for PE below 0.94 g/cm3 or cyclohexane for PE above 0.94 g/cm3 and quantified by liquid chromatography down to about 2 ppm. The method covers primary and secondary antioxidants, and slip agents such as erucamide are quantified alongside them by the same extraction and LC-UV procedure.

Because Irgafos 168 degrades in service to its phosphate (AO168=O) and to 2,4-di-tert-butylphenol, analysts must separate these degradation products from the parent phosphite to report an accurate residual level.

Which Antioxidants Are Allowed in Food-Contact and Drinking-Water Polyethylene?#

In the EU, food-contact polyethylene may contain only antioxidants listed in Regulation (EU) No 10/2011, each within its specific or overall migration limit; in the US, 21 CFR 178.2010 lists substances with polymer-specific limits, several of which depend on whether the PE density is above or below 0.94 g/cm3. Values here are checked against the consolidated EU 10/2011 text of 16 March 2025; later amendments have not been checked.

Antioxidants cleared under 21 CFR 178.2010 are correctly described as "authorised" or "listed", never as "FDA approved". All polymers, not just PE, are covered under food contact antioxidants.

EU 10/2011 and FDA 21 CFR 178.2010 limits for PE#

Irgafos 168 shows how the two systems differ for polyethylene: the EU lists it without a specific migration limit (FCM 671), while the US caps it at 0.2 % in ethylene polymers and restricts it further in LDPE film thicker than 0.051 mm. The EU 10/2011 overall migration limit of 10 mg/dm2 (60 mg/kg for infant food) applies to every substance that has no numeric SML of its own.

FDA limits are maximum use levels, not recommended dosages. Check food type and condition of use in 21 CFR 178.2010. EU values as consolidated on 16 March 2025.

SML and OML rules are explained on EU 10/2011. Food types and conditions of use for the American system are decoded on the 21 CFR 178.2010 regulation page.

Degradation products and NIAS: 2,4-DTBP and oxidized Irgafos 168#

The main non-intentionally added substances (NIAS) from polyethylene antioxidants are the oxidized phosphate of Irgafos 168 and 2,4-di-tert-butylphenol (2,4-DTBP), which has been measured at up to about 46 mg/kg in BOPP and LDPE food-contact products. Neither compound is on the EU 10/2011 Union list, so their presence is assessed as migration from a permitted starting substance, not as use of an authorised additive.

A 2018 PubMed survey (record 30517180) measured 2,4-DTBP at up to 45.568 ± 31.513 mg/kg in BOPP and LDPE food-contact products. A 2023 FDA safety assessment by Markley and colleagues set an acceptable daily intake of 1 mg/kg body weight per day for Irgafos 168, and a cumulative estimated daily intake for Irgafos 168 plus its phosphate of 0.09 mg/kg body weight per day.

Restricted antioxidants: TNPP and Antioxidant 2246#

TNPP and Antioxidant 2246 are the two antioxidants a PE formulator in the EU should review first: both are on the REACH Candidate List of substances of very high concern, TNPP since 16 July 2019 and Antioxidant 2246 since 17 January 2022. Neither substance is banned and neither requires authorisation to remain in use; Candidate List status is a hazard flag and a disclosure trigger, not a prohibition.

TNPP (CAS 26523-78-4) was listed on 16 July 2019 under Article 57(f) for grades with 0.1 % or more 4-nonylphenol, updated 21 January 2025 to also cover its intrinsic endocrine-disrupting properties; it retains its EU 10/2011 listing, FCM 69, SML 30 mg/kg. Alternatives, including nonylphenol-free Weston 705, are listed on the TNPP (tris(nonylphenyl) phosphite) substance page.

Antioxidant 2246 (CAS 119-47-1) was listed on 17 January 2022 as toxic for reproduction under Article 57(c), harmonised as Repr. 1B, H360F. It stays authorised under EU 10/2011 FCM 285, group restriction 13, combined SML(T) 1.5 mg/kg shared with FCM 163, a figure that should never be written as "no SML". The reproductive-toxicity classification is detailed on the Antioxidant 2246 (DBMC) substance page.

Who Supplies Antioxidants for Polyethylene?#

Antioxidants for polyethylene come from BASF (Irganox and Irgafos), Songwon (Songnox), Adeka (ADK STAB), Clariant (Hostanox), SI Group (Ethanox and Weston), Dover Chemical (Doverphos) and Everspring (Evernox and Everfos), and the main grades are sold by several of them under different trade names. Sumitomo Chemical also supplies phenolic and phosphite grades as Sumilizer, and Songwon has grown into the world's number-two producer of polymer stabilizers by volume.

Plants and grades by company are in the directory of polymer antioxidant manufacturers. US Chemical Data Reporting figures for 2023 put Irganox 1010 and Irgafos 168 each at 40 to under 55 million pounds of production and import volume, and Irganox 1076 at 25 to under 40 million pounds. Buyers should compare grades by CAS number and food-contact status, not by trade name.

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What Other Additives Does Polyethylene Need?#

Polyethylene needs a complete additive package in which antioxidants are only the first layer, next to acid scavengers and, depending on the product, UV stabilizers, slip and antiblock agents, processing aids or carbon black. The full package for the polymer is on additives for polyethylene.

Film formulations typically add erucamide or oleamide slip agents at 0.05-0.12 % and antiblock agents at 2,500-10,000 ppm, alongside processing aids, antifog and antistatic additives as the application requires. Pipe compounds add carbon black for UV screening, and acid scavengers protect the phosphite in every PE grade made with Ziegler-Natta or chromium catalyst residues.

UV stabilizers for polyethylene#

Outdoor polyethylene adds a hindered amine light stabilizer to its antioxidant package, typically 0.1-1.0 wt% in LDPE and LLDPE film and 0.05-0.6 wt% in thick sections. Chimassorb 944-type HALS grades are common in agricultural and geomembrane film, and because thioesters antagonise HALS, formulators avoid combining the two classes in a single outdoor PE product. Film and pipe grades are on UV stabilizers for polyethylene.

Antioxidants for polypropylene compared#

Polypropylene uses the same phenol-plus-phosphite chemistry as polyethylene but needs it more urgently, because its tertiary carbons make it the most oxidation-sensitive commodity polyolefin, and PP takes 34.68 % of plastic antioxidant revenue (Mordor Intelligence, 2025). Commodity PP grades carry less than 400 ppm phenolic antioxidant according to a 2023 Fraunhofer LBF study, a lower loading than the wt%-level dosages typical of PE, and PP formulations lean more heavily on a thioester such as DSTDP paired with a high-molecular-weight phenol for pipe and under-hood automotive parts. Dosage by PP grade is on antioxidants for polypropylene.

Is BHT used as an antioxidant in polyethylene?#

BHT is rarely used in modern polyethylene compounds because at 220.35 g/mol it is volatile and raises fogging, so higher-molecular-weight phenols such as Irganox 1076 have replaced it in most plastics. BHT is not a REACH substance of very high concern, though it remains on ECHA's Community Rolling Action Plan for suspected endocrine disruption, and it is not on California Proposition 65. The FDA published a Request for Information on BHT on 13 May 2026 (docket FDA-2026-N-2526), a data-gathering step, not a restriction. Regulatory status is tracked on BHT (butylated hydroxytoluene) as an antioxidant for plastics.

Are antioxidants in polyethylene safe?#

The main polyethylene antioxidants, Irganox 1010, Irganox 1076 and Irgafos 168, carry no EU harmonised hazard classification, and food-contact use is limited by the migration limits of Regulation (EU) No 10/2011. Self-classifications submitted to ECHA for these three substances vary by notifier, but none has a harmonised CLP classification in force. The FDA's acceptable daily intake for Irgafos 168 is 1 mg/kg body weight per day; Antioxidant 2246 is the main exception among common PE antioxidants, carrying a harmonised reproductive-toxicity classification. Broader questions about plastic toxicity and microplastics sit outside the additive-specific scope of this page.

Can natural antioxidants replace synthetic ones in polyethylene?#

Vitamin E already replaces synthetic phenols in some polyethylene grades, mainly food and medical film and UHMWPE implants, while other bio-based candidates such as sinapic acid esters are still at study stage. A 2023 Fraunhofer LBF study found sinapic acid stearyl ester gave processing stability in polypropylene comparable or superior to Irganox 1076, though that result is from a PP study and has not been confirmed for PE.

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