Polymers naturally degrade over time because they react with oxygen, a process called autoxidation, which can be triggered by heat, light, mechanical stress, or even traces of heavy metals. Autoxidation cannot be avoided, so it needs to be controlled. This degradation involves the formation of free radicals in a chain reaction, causing polymers to become brittle, discolored, and less durable. 

Heat, light, or mechanical stress generate free radicals inside the material, triggering a chain reaction that weakens it. Oxygen transforms these radicals into even more reactive species, which continue to attack the polymer. Antioxidants help break this cycle: phenolic antioxidants directly neutralize the radicals, while phosphites eliminate hydroperoxides, unstable molecules that fuel the degradation process. 

To slow down this process, antioxidant additives are incorporated into polymers to act as protective barriers. Some, known as thermo-oxidation inhibitors, stop the free radical chain reactions that occur during processing or exposure to high temperatures. Others, such as photooxidation inhibitors and metal deactivators, neutralize unstable molecules formed under UV light or block the catalytic effect of metal residues. 

Although all these additives contribute to preventing oxidation, the term “antioxidants” most often refers specifically to thermo-oxidation inhibitors. By combining different antioxidant types, polymers benefit from stronger protection, helping them remain stable, resist ageing, and maintain their mechanical properties throughout their lifetime. By combining different antioxidant types, polymers benefit from stronger protection, helping them remain stable, resist ageing, and maintain their mechanical properties throughout their lifetime. 

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