[REFRESH] Irgafos 168: Uses, Benefits & Specifications

Irgafos 168 (CAS 31570-04-4) is a phosphite secondary antioxidant, a processing stabilizer that protects molten plastic from heat damage during extrusion, molding, and recycling. Sold as Antioxidant 168 and under names such as Alkanox 240, it pairs with a primary phenolic antioxidant like Irganox 1010 to keep polyolefins from yellowing and losing strength. This guide covers its chemical identity, how it works, dosage by polymer, food-contact compliance, and how to verify quality before you buy.

What Is Irgafos 168?

Among phosphite stabilizers, Irgafos® 168 is the most commonly used secondary antioxidant in the plastics industry. Marketed as Irgafos 168 by BASF, it’s chemically tris(2,4-di-tert-butylphenyl) phosphite, a trivalent-phosphorus compound the producer describes as a “hydrolytically stable phosphite processing stabilizer.” It does its work during the melt-processing window rather than in the finished part, which is what makes it a secondary, not a primary, antioxidant.

Used as an AO (antioxidant) for decades, it belongs to the class of secondary antioxidants: additives that don’t stop oxidation on their own but instead protect the polymer, and the primary antioxidant, during the high-heat processing steps of compounding, extrusion, and molding.

You will see the same molecule sold under several names, which causes confusion at the buying stage. “Antioxidant 168,” “AO-168,” “Alkanox 240,” and “Songnox 1680” all refer to CAS 31570-04-4. The name “Irganox 168” is a frequent misspelling, the BASF trade name for this phosphite is Irgafos 168, while the Irganox family is the company’s primary phenolic antioxidants. Getting that name wrong is a real sourcing risk, not a typo: a buyer who orders “Irganox 168” expecting a phosphite can be shipped a phenolic instead, because the two families do opposite jobs, and the mistake usually surfaces only after the melt yellows on the production line at 230 °C. Wellt’s in-house QC cross-checks every inquiry against CAS 31570-04-4, the ≥99% assay, and the FDA food-contact status before quoting, whichever trade name a customer uses. If you are sourcing, treat all of these as the same active and compare on assay and grade rather than brand. Wellt supplies it as Irgafos 168 (Antioxidant 168) within its phosphite ester range.

Chemical Identity & Key Properties

Data below is drawn from the BASF technical data sheet and cross-checked against the PubChem database and peer-reviewed literature; spectral identification (FTIR and 31P-NMR) is what confirms the structure on a Certificate of Analysis. These are the numbers a buyer need to read a Certificate of Analysis (COA) or fill a material spec sheet.

Two properties explain why this particular phosphite dominates the market. First, it resists hydrolysis: many cheaper phosphites react with moisture and break down in the bag or the feed throat, forming acids and gels. Irgafos 168 holds up, which is why it ships and stores reliably. Second, it has low volatility, so it stays in the melt at processing temperatures instead of fuming off. Together these traits let it deliver, in BASF’s words, “high performance at low concentration levels.”

How Irgafos 168 Works: The Secondary Antioxidant Mechanism

To understand where Irgafos 168 fits, start with what goes wrong. When a polymer is heated during processing, autoxidation initiated by oxygen, shear, and metal catalyst residues kicks off. The chain reaction produces hydroperoxides (ROOH) inside the melt. Left alone, those hydroperoxides split into new radicals that cut polymer chains (chain scission) or link them (crosslinking) — the result is lower molecular weight, lost strength, and yellowing.

A melt-flow-rate shift of 20–50% is common in unstabilized polypropylene after a single extrusion pass at 230 °C, because the autoxidation chain keeps cutting molecules, which is why processors treat this as a real production problem and a warranty risk, not a cosmetic one.

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A primary antioxidant such as Irganox 1010 mops up the radicals. But it can’t neutralize the hydroperoxides themselves. That’s the secondary antioxidant’s job. Trivalent phosphorus in Irgafos 168 reacts during processing with hydroperoxides, converting each one to a harmless alcohol (ROH) while the phosphite itself is oxidized to a phosphate, a reaction that help reduce degradation of the polymer. It works inside polymers preventing process-induced degradation, and in doing so it removes the fuel before it can ignite a new radical cycle. When you combine the phosphite with the phenolic, the phosphite is effectively extending the performance of primary antioxidants, which is why the two are almost always used together. The spent phosphite also leaves behind well-characterized degradation species that we cover in a companion guide.

Irgafos 168 vs Irganox 1010: Why You Need Both (The 1:2 Rule)

This is the single most common question buyers ask, and the answer drive most antioxidant formulations. Irganox 1010 and Irgafos 168 aren’t competitors, they do different jobs at different stages. Treating them as interchangeable is the classic formulation mistake: dose only the phenolic and the melt is left unprotected during extrusion; dose only the phosphite and the finished part can fail early in service, because neither one covers the other’s window. In practice Wellt ships the two together as the pre-blended 1:2 B215 package, so a compounder dosing a typical 0.15% total (per the dosage table below) gets both windows covered without weighing two powders.

The 1:2 Rule. As a default starting point, the industry uses two parts of the phosphite for every one part of the phenolic. That ratio is exactly what the ready-made blend Irganox B215 contains: one part Irganox 1010 to two parts Irgafos 168. If you would rather dose a single pre-mixed pellet than weigh two powders, buy the blend; if you want to tune the ratio for a specific resin, dose them separately.

What is the difference between Irgafos 168 and Irganox 1010?

Irganox 1010 is a primary (chain-breaking) hindered-phenol antioxidant that protects the finished part over its service life; Irgafos 168 is a secondary phosphite that protects the melt during processing by decomposing hydroperoxides. Using only the phenolic leaves the melt under-protected during extrusion; using only the phosphite leave the part exposed in service. A combination, typically the 1:2 blend, covers both windows, which is why almost every polyolefin antioxidant package contains a phenolic and a phosphite.

Applications by Polymer: PP, PE, ABS, PC & More

You’ll find Irgafos 168 in nearly all melt-processed thermoplastics, but the reason it’s added changes with the resin. Polyolefins are the largest market because they oxidize readily at processing temperatures, a use documented in the patent literature on phosphite additives in polyolefins.

What plastics is Irgafos 168 used in?

Irgafos 168 is used mainly in polyolefins, polypropylene, HDPE, and LLDPE, plus polycarbonate, polyamide, ABS and other styrenics, EVA, polybutene, elastomers, adhesives, and waxes. It’s also used in high-bake powder and coil coatings. In every case it’s a processing-stage stabilizer, so it appears wherever a polymer is melt-processed, extruded, molded, or reprocessed during recycling.

Recommended Dosage, Grades & Handling

There’s no single dose. The right level depend on the resin, how many heat cycles it sees, and whether a primary antioxidant is present. The four application bands below give practical starting points; confirm with your own processing trials.

The 4-Tier Dosage Matrix

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Grades and handling. Commercially, the product ships as a standard powder or as a low-dust granular “FF” grade; the granular form feed more cleanly and reduces airborne dust on the compounding line. Store it sealed in its original packaging between 5 °C and 40 °C. Because it resists hydrolysis better than most phosphites, it tolerates normal warehouse conditions, but prolonged exposure to heat and humidity should still be avoided. A patented dust-free, improved-flow form is the origin of the granular grade most plants prefer.

Food-Contact Compliance & Safety

Because Irgafos 168 is so widely used in food packaging, the hazard profile behind its food-contact use has been studied closely. In its updated safety assessment, the U.S. Food and Drug Administration reviewed the dietary exposure and oral toxicity of Irgafos 168 (referred to as I-168) and its main degradant. The exposure assessment included both I-168 and its degradants, and its conclusions on the use of I-168 underpin the headline numbers compliance teams cite.

Since the CEDI (0.09 mg/kg bw/day) sits well below the ADI (1 mg/kg bw/day), the FDA concluded there is no safety concern at current authorized use levels. In the European Union, Irgafos 168 appears on the Regulation (EU) No 10/2011 Union list of substances authorized for plastic food-contact articles and materials, with the list reviewed and updated periodically through 2025–2026. This long food-contact regulatory history means most buyers can document compliance quickly, but always confirm the current entry and any specific migration limit for your application.

“There is no safety concern for its current authorized use levels, and the degradants of I-168 do not appear to pose a safety concern for neurotoxicity.”

Markley et al., FDA Center for Food Safety and Applied Nutrition (2021)

Is Irgafos 168 safe for food contact?

Yes, within authorized use levels. The FDA’s assessment found the cumulative estimated daily intake (0.09 mg/kg bw/day) is roughly ten times below the acceptable daily intake of 1 mg/kg bw/day, and it dismissed the neurotoxicity concern raised about the phosphate degradant. Irgafos 168 is also listed under EU Regulation 10/2011 for plastic food-contact materials. For regulated applications, request food-contact documentation and any migration-limit data from your supplier.

A Limitation Worth Knowing: Migration

One counterintuitive finding is worth flagging, because it surprises buyers who assume a stabilizer stays locked in the part. Peer-reviewed migration studies show that Irgafos 168 actually migrates out of polyolefins more than Irganox 1010 does, and the release rate climbs at higher temperatures. In fact, the additive is so common that analysts find it as a background contaminant in laboratories, which complicates leaching measurements.

How to Source & Verify Irgafos 168

Because the same molecule is sold by many producers at very different quality levels, the COA, not the brand, tells you what you’re buying. Use this checklist when you request a quote and again when the material arrives.

• ✔ Assay (purity) stated as ≥99% on the COA
• ✔ Phosphorus content near the ~4.8% theoretical value
• ✔ Melting range within 181–186 °C
• ✔ Grade confirmed, powder vs low-dust granular (FF) — to match your feeder
• ✔ CAS 31570-04-4 and equivalence to Irganox 168 / Alkanox 240 stated explicitly
• ✔ Food-contact documentation (FDA / EU 10/2011) and an animal- and ethanol-free statement where relevant

If you’re comparing offers, ask each supplier for the same COA fields and a small sample for a processing trial before you commit to volume. Wellt sources Irgafos 168 (Antioxidant 168) with quality documentation and can quote alongside the matching Irganox 1010 or the pre-mixed B215 blend. For background on the wider additive family, see our guide to plastic antioxidants.

Request an Irgafos 168 quote & COA →

Supply & Regulatory Outlook

Two forces shape sourcing decisions for Irgafos 168 buyers right now, and neither is the headline market-size figure. First, the FDA’s reaffirmation that the additive raises no safety concern at authorized food-contact levels removes a question mark that once slowed adoption in food packaging, it gives compounders firmer footing to specify it. Second, recycling is pushing demand for processing stabilizers: every additional heat cycle a recycled polyolefin sees consumes more antioxidant, so reprocessed streams need more phosphite, not less. For a production line compounding 30% recycled polypropylene at 2 ton/h, that can mean stepping Irgafos 168 from 0.10% to 0.18% just to hold melt-flow stability, because the recyclate arrives part-spent, a real cost-and-supply risk, and a stockout problem if a single source falls short. Wellt keeps two qualified sources on the shelf for exactly this reason.

On the supply side, capacity for phosphite antioxidants has grown among Chinese producers, which means more qualified Antioxidant 168 equivalents are available at competitive prices. For background, market trackers put the phosphite auxiliary antioxidant segment in the low single-digit billions with mid-single-digit annual growth, but those figures vary by source and should be read as directional context only. The practical takeaway for buyers: qualify two or three sources on COA quality now, so recycled-content and food-contact projects aren’t held up by a single-supplier bottleneck later.

Frequently Asked Questions