In the manufacture, molding and use of plastics, heat sources at different temperatures, such as the contact points between the polymerization catalyst and the carbon chain, trigger different degrees of oxidation reactions. The mechanism of this oxidation reaction can be summarized as a spontaneous oxidation cycle in the form of free radicals.

The best way to prevent thermal aging is to capture various free radicals and peroxides generated in the spontaneous oxidation cycle, especially the long-lived peroxy free radicals and peroxides. Products that can capture free radicals are called primary antioxidants, and products that can capture peroxides are called secondary antioxidants.