The chemical effects of near ultraviolet light (equivalent to that in terrestrial sunlight) on polypropylene and on poly(ethylene terephthalate) are described in some detail with particular emphasis on identification of the important primary bond-breaking reactions. It is shown that the critical processes are a Norrish Type I, a Norrish Type II, and polymer hydroperoxide formation and photolysis in the case of both these thermoplastics. The degradative changes result in the buildup of polar groups and polymer end groups primarily on or near the surfaces of irradiated films.

Surface growing fungus tests do not indicate microbial susceptibility for films of commercial-grade polypropylene, poly(ethylene terephthalate), or several other common thermoplastics. Even after extensive photodegradation, which might be expected to enhance biodegradability, these materials do not appear to support significant surface growth.