Why Antioxidants?
Plastics and elastomers are essential materials in various industries, such as the automotive, electrical and electronics, and packaging industries. To ensure their quality and durability, primary and secondary antioxidants are frequently added to these materials. Here, the different mechanisms of action of primary and secondary antioxidants, as well as their combinations in plastics and elastomers, are explained.
Primary Antioxidants
Primary antioxidants, also known as “radical scavengers,” are compounds capable of intercepting free radicals and halting their chain reactions. Free radicals are formed through oxidation reactions, where oxygen molecules strip electrons from other molecules, creating unstable compounds. Free radicals can trigger chain reactions that lead to the degradation of plastics and elastomers.
Primary antioxidants work by reacting with the free radicals and converting them into stable molecules. This process stops the chain reaction and prevents the degradation of plastics and elastomers. Primary antioxidants are added during the polymerization process and also during the further processing of polymers.
Examples of primary antioxidants include phenol-based compounds such as Butylated Hydroxyanisole (BHA) and Butylated Hydroxytoluene (BHT).
Secondary Antioxidants
Secondary antioxidants, also known as “heat stabilizers,” are compounds that prevent the degradation of plastics and elastomers caused by heat and light. Secondary antioxidants function by inhibiting the formation of peroxides and other unstable compounds that can occur at high temperatures.
Secondary antioxidants are added after the polymerization of plastics and elastomers during further processing to enhance their stability and durability. They can also be combined with primary antioxidants to achieve a synergistic effect.
Examples of secondary antioxidants include phosphites like Distearylthiodipropionat (DSTDP), phosphonates like Bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite (AO-168), and thioesters like Dilaurylthiodipropionat (DLTDP).
