Basic Reactions in the Photodegradation of Some Important Polymers

It has been known for hundreds of years that native organic materials like textile fibers from cotton and flax are degraded in sunlight and lose strength by outdoor exposure. This phenomenon was studied in the 1800s when fibers and textiles were bleached to increase their whiteness. The molecular mechanisms involved were not known at that time. The chain structure of cellulose was established much later through the macromolecular concept, formulated by Herman Staudinger in 1920, and generally accepted by scientists in the 1930s. On a macromolecular basis, important advances in understanding the chemical reactions involved in photodegradation of polymeric materials have been made since about 1940. Plastics, rubber, fibers, paint, and lacquers are all degraded in sunlight by basically the same free radical mechanisms extensively studied for 50 years [1]. Polymers show different inherent photostabilities when they are used as materials. Depending on their resistance to photodegradation, polymers can be divided into groups showing different degrees of stability [2].