Polymer stabilisation almost always uses two types of antioxidant together. Understanding the difference explains why — and helps you build the right package.
Primary antioxidants (radical scavengers)
Primary antioxidants are hindered phenolics such as Irganox 1010 and Irganox 1076. They interrupt the oxidation chain by donating a hydrogen atom to free radicals, giving long-term thermal protection throughout the polymer's service life.
Secondary antioxidants (hydroperoxide decomposers)
Secondary antioxidants are phosphites such as Irgafos 168. They decompose hydroperoxides into stable, non-radical products, protecting the polymer mainly during high-temperature processing and helping preserve colour.
Why use both?
The two chemistries are synergistic: the phosphite protects the melt and regenerates/spares the phenolic, while the phenolic delivers long-term stability. A typical polyolefin package pairs a phenolic (e.g. Irganox 1010 or 1076) with a phosphite (Irgafos 168) at a chosen ratio. For a worked example see how to choose an antioxidant for polypropylene.
| Primary (phenolic) | Secondary (phosphite) | |
|---|---|---|
| Mechanism | Scavenges radicals | Decomposes hydroperoxides |
| Protects mainly | Long-term service life | Melt / processing |
| Examples | Irganox 1010, 1076 | Irgafos 168 |