Most polymers go through oxidative degradation processes during manufacturing and subsequent compounding and processing. Oxidation and heat aging are major causes of degradation of plastics.
Exposure to heat and oxygen causes a chain reaction involving the formation of free-radicals, which inevitably leads to cleavage of the main chains in the polymer and degradation of the plastic. This is manifested in many difference ways including loss of shine and transparency, yellowing, surface cracking and odours. Oxidation can also result in loss of mechanical properties such as impact resistance, elongation and tensile strength.

Anti-oxidant masterbatch interrupt autoxidation in different ways according to their chemistry and molecular weight. Autoxidation occurs when polymers reacts with atmospheric oxygen. … Antioxidants are of great importance during the process stage, with long-term stability at ambient temperature
Polymer stabilizers are essential to practical use, since they maintain the inherent properties, color, and other characteristics of plastics by preventing the oxidative degradation caused by high temperature during processing, and ultraviolet exposure during use.
The oxidation resistance is measured according to DIN 53383 or other methods. Change of viscosity, mechanical properties and yellowish effect are parameters that are usually measured to check the antioxidant effect.