Processing Stability

Polymers usually undergo several processing steps from manufacture to the final article. Polymer degradation occurs as a consequence of heat, shear, impurities and oxygen. The mechanical properties and the color of the polymer may change upon processing.

Polymer degradation through processing
Polymer degradation is initiated during processing, which is carried out under shear and heat. Free radicals are generated, which react rapidly with oxygen to form peroxy radicals. These peroxy radicals may further react with the polymer chains leading to the formation of hydroperoxides (ROOH). Cleavage of hydroperoxides on exposure to heat or light procues additional radicals that reiinitiate the process. Besides this degradation by radicals, some polymers (e.g. polyesters) undergo also hydrolytic degradation during melt processing. This kind of degradation is well avoided by polymer chain extenders.

Polymer stability through processing stabilizers
Polymer degradation during processing can be prevented by using processing stabilizers. These are antioxidants that are incorporated into the polymer. Optimal polymer stability is achieved when the initial molecular weight or/and the initial color of the polymer is maintained.Ciba® IRGAFOS® processing stabilizers, Ciba® IRGANOX® antioxidants, Ciba®  IRGAMOD® chain extender and Ciba® IRGASTAB® blends of syngergistic antioxidants are recommended to ensure processing and thermal stability. The required processing stabilizer depends on the application and the polymer.

Thermal Stability

Polymers are subjected to oxidation at every stage in their life cycle - during manufacture and processing as well as during storage and end use. Polymer Degradation through oxidation can change the aesthetic appearance and can destroy functional properties.

Polymer Degradation through oxidation Polymeric materials react with molecular oxygen in a process called "autoxidation". Autoxidation can be initiated by heat, UV light, mechanical stress, catalyst residues or through reaction with other impurities. Free radicals are generated, which react rapidly with oxygen to form peroxy radicals. These peroxy radicals may further react with the polymer chains leading to the formation of hydroperoxides (ROOH). Cleavage of hydroperoxides on exposure to heat or light produces additional radicals that reinitiate the process.

Polymer stability through antioxidants

Antioxidants prevent polymer degradation through oxidation by controlling molecular weight changes that lead to a loss of physical,  and aesthetic properties. Light stabilizers prevent polymer degradation initiated by exposure to sun light.Thermal stability of polymers is provided by Ciba® IRGANOX® B and Ciba® IRGASTAB® blends.