The service life of polymers is limited by their degradation, which can be caused by a number of environmental factors, e.g. temperature, humidity, impurities, mechanical load, irradiation, microorganisms, chemicals and air. Degradation is an undesirable process in the majority of polymeric applications as it generally leads to changes in the chemical and physical structure of the polymer resulting in the loss of many useful properties, such as molecular weight, mechanical strength, impact resistance and color. The understanding of degradation mechanisms is further complicated by factors such as morphology, diffusion processes and interactions of additives