Polymers are susceptible to thermo-oxidative degradation when exposed to oxygen and heat during processing or in service.

This degradation breaks chemical bonds within the polymer, altering the molecular structure. As a result, the material’s mechanical properties, colour and overall performance can be compromised, ultimately leading to premature product failure.

Thermo-oxidative degradation can be inhibited by antioxidant additives, which scavenge free radicals and protect polymer chains during both processing and the service life of the product.

The effectiveness of an antioxidant is influenced by its molecular structure. Antioxidants with multiple side groups are able to donate hydrogen atoms to neutralise free radicals and limit polymer chain scission. These are known as primary antioxidants, and they are particularly effective in improving the long-term thermal ageing resistance of thermoplastics.

Primary antioxidants are known to work synergistically with secondary antioxidants. Secondary antioxidants decompose hydroperoxide free radicals, converting them into stable, non-reactive products. Typically, both classes are used together to enhance polymer melt stability during processing and to extend long-term thermal stability.

The molecular structure of an antioxidant also affects its thermal stability, effective service temperature and volatility. These factors must be considered when selecting an appropriate stabilisation package for a given application. No single antioxidant is universally effective across all polymer chemistries. It is essential to choose an additive package that is compatible with the base polymer resin and stable at the processing temperatures of that material.