Oxidation of polymers can lead to many undesirable effects including color changes, formation of rough surface morphology, changes in melt viscosity and reduction in mechanical properties, which can affect the service life of the polymer or the final product. Oxidation can occur at every stage of the polymer life cycle, during the production and storage of polymer resins, during high temperature melt processing operations, during the processing of resins into articles, and during the use of the articles. In addition, exposure to UV rays from sunlight also accelerates the oxidation process. Adding phenolic antioxidants for polymers can inhibit and delay the oxidation and degradation of polymer materials.
Antioxidants are generally divided into primary antioxidants and secondary antioxidants. Primary antioxidants work by scavenging peroxy free radicals formed during oxidation. The two main classes of primary antioxidants are hindered phenol antioxidants and aromatic amines. They are effective over a wide temperature range, improving material processing and long-term thermal stability.
Secondary antioxidants, such as phosphites and thioethers, work through the decomposition of hydroperoxides. Phosphites are most effective at the high temperatures of melt processing operations, while thioethers work best in the solid phase at long-term use temperatures.
TINTOLL hindered phenolic antioxidants have low volatility, high efficiency, resistance to air fading and hydrolysis, and can be implemented in a wide range of applications.
Hindered phenol stabilizers are the main antioxidant additives for plastics and act as hydrogen donors. They react with peroxy radicals to form hydroperoxides and prevent abstraction of hydrogen from the polymer backbone. Phenolic stabilizers are often used in combination with secondary antioxidants and come in a variety of molecular weights, product forms and functions. They are very effective during processing and long-term heat aging, and many are FDA-approved. These polymer stabilizers are generally less prone to staining or discoloration. However, they may form quinoid structures when oxidized, resulting in yellowing. PowerNoxTM Phenolic antioxidants include simple phenols, bisphenols, polyphenols and thiobisphenols.
PowerNoxTM 2640 (BHT) is the most commonly used primary antioxidant and is FDA-approved for food contact and is suitable as a long-term stabilizer in almost all cases. However, BHT is a relatively volatile material that is gradually being replaced by higher molecular weight antioxidants that resist migration.
Thiobisphenols also act as peroxide decomposers (secondary antioxidants), which are often used in higher temperature applications.