Antioxidant 168 and Irganox 1010: How Phosphite and Phenolic Antioxidants Work Together
In polymer stabilisation, the two most important antioxidants are of fundamentally different types. Antioxidant 168 (Irgafos 168, a phosphite) is a secondary antioxidant; Irganox 1010 (a hindered phenol) is a primary antioxidant. Used together, they form the stabiliser system behind an enormous share of the world’s polyolefins. This article explains why the combination works and how to think about the balance between them.
For the full background on the phosphite, see our main article on antioxidant 168 (CAS 31570-04-4).
The Two Roles
Polymer oxidation is a chain reaction, and the two antioxidants attack it at different points.
| Antioxidant | Type | What it does | When it matters most |
|---|---|---|---|
| Antioxidant 168 (phosphite) | Secondary | Decomposes hydroperoxides (ROOH) into non-radical products | Melt processing: heat, shear, oxygen |
| Irganox 1010 (hindered phenol) | Primary | Traps peroxy radicals before they propagate | Long-term service ageing |
Why They Are Better Together
Each antioxidant compensates for the weakness of the other:
- The phosphite protects the phenol. Without a phosphite, a phenolic antioxidant has to deal with the hydroperoxides that form during processing, which consumes it and reduces how much is left for long-term protection. The phosphite removes those hydroperoxides first, preserving the phenol for the years of service that follow.
- The phenol covers what the phosphite cannot. Phosphites are strong during processing but do not on their own provide the long-term radical-trapping that keeps a polymer stable in service. The phenol supplies that.
- Colour. Phosphites contribute very little colour and can even help prevent the yellowing associated with phenolic oxidation, which is why the pair gives a better colour profile than a phenol alone.
The result is a system that protects the polymer both during the violent conditions of melt processing and through the long, slow oxidation of service life — which is why the combination is so widely used in polypropylene and polyethylene.
How the Balance Is Set
The ratio of phosphite to phenol is not fixed; it is tuned to the polymer and the duty. Factors that shift the balance include:
| Factor | Effect on the balance |
|---|---|
| Processing severity (temperature, shear, dwell time) | Harsher processing favours more phosphite |
| Required service life | Longer life favours more phenol |
| Polymer type | PP (chain scission) generally benefits strongly from a phosphite; PE behaves differently |
| Colour requirements | Light-coloured articles favour phosphite for colour control |
| Food-contact / regulatory limits | Set an upper bound on total and individual additive levels |
| Cost | Phosphite and phenol have different costs; the ratio trades performance against cost |
Because of these factors, there is no single universal ratio. Suppliers of one-pack stabiliser blends offer a range of phosphite-to-phenol combinations, and the formulator selects or tailors one by trial against the target process and service conditions.
Practical Formulation Notes
- One-pack blends. Antioxidant 168 and a phenol such as Irganox 1010 are frequently supplied pre-blended, which simplifies dosing, improves dispersion and reduces dust.
- Dosing. Total stabiliser levels are low; the split between phosphite and phenol is what the formulator adjusts.
- Dispersion. Good dispersion matters because a poorly dispersed additive protects unevenly; masterbatches and pre-dispersed forms help.
- Hydrolysis. Because the phosphite is moisture-sensitive, one-pack blends must still be stored dry and used in rotation.
- Interaction with other additives. The stabiliser package must be balanced with light stabilisers, acid scavengers and pigments, which can interact with either antioxidant.
Choosing and Substituting
Antioxidant 168 is the reference phosphite, and Irganox 1010 the reference hindered phenol. Substituting either component requires care:
- Match the function, not just the name. Replacing a phosphite with another phosphite changes the hydrolysis and colour profile; replacing a phenol with a phosphite changes the long-term protection entirely.
- Re-validate. Any change in the stabiliser system should be re-validated against the actual processing and service tests.
- Check regulatory limits. The individual and total additive levels are regulated for food-contact and other uses, so a change may affect compliance.
Frequently Asked Questions
Why use antioxidant 168 and Irganox 1010 together?
Because one is a secondary antioxidant that protects the melt and the other is a primary antioxidant that protects long-term service life. Together they cover the full life cycle of the polymer.
Which one is the primary antioxidant?
Irganox 1010, the hindered phenol, is the primary (radical-trapping) antioxidant. Antioxidant 168, the phosphite, is the secondary (hydroperoxide-decomposing) antioxidant.
Can I use only antioxidant 168?
It gives good processing and colour stability but weaker long-term protection on its own; in demanding applications it is normally paired with a phenolic antioxidant.
Can I use only a phenolic antioxidant?
Yes, but it will do more work during processing and the result is often less colour-stable and less cost-effective than the phosphite-plus-phenol combination.
How do I set the ratio?
By trial against your process and service requirements; there is no single ratio. Processing severity, service life, polymer type, colour and regulatory limits all influence it.