Why are antioxidants added to rubber compounds?

Antioxidants are added to rubber compounds to retard deterioration caused by exposure to oxygen and ozone. These additives function by disrupting the free-radical oxidation reactions that occur as rubber ages.12

Without these protective chemicals, oxidation can lead to molecular rupture and softening, or conversely, increased interlinking and hardening, both of which result in a loss of elasticity. By reacting with chain carriers—the free radicals that sustain the oxidative chain reaction—antioxidants effectively terminate the process.23

Commonly used antioxidants include amines, which are powerful retarders of oxidation, and hindered phenols, which are often preferred when staining must be avoided. Because certain metals like copper, manganese, and iron can catalyze these destructive reactions, sequestering agents are also employed to block their influence. By incorporating these compounds, manufacturers can significantly extend the lifespan and maintain the physical integrity of rubber products.21