When polymers are exposed to high shear stress, heat, water, or transition metal ions, polymer degradation chain reactions begin. Antioxidants protect plastics and other materials against thermally induced oxidation.

A plastic, as it oxidizes, loses properties over time and will begin to exhibit some defects:

- Yellowing.
- Discoloration.
- Increase of MFI due to polymeric chain breakage and loss of mechanical properties.
- Decrease of MFI due to cross-linking of polymeric chains and appearance of gels.
- Loss of gloss and transparency.
- The appearance of cracks.

The family of antioxidant additives is very broad, but they can be grouped into two groups, primary and secondary antioxidants. Each of them acts at different times in the oxidation cycle of the polymer. Mixtures of primary and secondary antioxidant additives will also provide a synergistic effect. In other words, both act more efficiently together than separately.

- Protect polymers from oxidation, extending their useful life.
- They prevent degradation or cross-linking during the extrusion process.