The Photooxidative Degradation of Polypropylene. Part I. Photooxidation and Photoinitiation Processes

All unstabilized organic polymers are degraded upon exposure to terrestrial sunlight in the presence of oxygen. However, the rates of photooxidative deterioration vary enormously with polymer structure, and range from a few months outdoor lifetime for polypropylene (PPH) and poly(l,3-phenylene isophthalamide) up to several years for poly(ethylene terephthalate), poly(methyl methylacrylate), and poly-(tetrafluoroethylene). Despite its high photosensitivity, PPH is now widely exploited in the form of films, fibers, and moldings. Current PPH capacity in the United States is rated at ∼1.2 × 106 metric tons, of which −30% is used as thin films and fibers [1].