ABSTRACT
All commercial polyolefins will degrade eventually as they are not chemically “pure” materials: they contain several chemical impurities which are introduced at different stages of their life cycle (polymerization, processing, manufacturing, stor age, and upon environmental exposure in-service) [1]. Impurities such as metal ions, peroxides, unsaturation, and carbonyl compounds initiate oxidation of the polymer, and even stabilized polymers undergo eventual oxidation with the intro duction of a variety of carbonyl species, in particular carboxylic acids and esters [2] . Antioxidants contribute to prolonging the product outdoor lifetime; this aspect raises many environmental problems in the form of plastics litter and as hazards to animals. Plastics products in many applications, e.g., high volume packaging and agricultural, are often made to be too stable for their intended purpose. In response to these problems, manufacturers produced a number of polyolefin-based materials with enhanced degradability, and products based on these materials have been claimed to be photodegradable, biodegradable, or both, often without defining the conditions or the way in which the polymer product degrades. The lack of sufficient scientific evidence and objective criterion to test the manufacturer’s claims on the performance and degradability attributes of their products has raised public concern [3] . We report here some of the work carried out under the Brite-Euram collabora tive research program [4] which was set up to examine how chemical, physical, and biological factors affect the degradability of commercially available photo(biode gradable polyethylenes. Some of the issues addressed in this research program have already been reported [5]. Three classes of commercial degradable polyethylenebased materials were used throughout this work:
A. Photolytic polymers (A samples): In this class the photosensitizing group forms an integral part of the polymer chain. Two different types of polyethyl ene (PE) containing carbonyl groups are available commercially:
(i) The carbonyl is built in the polymer chain by copolymerizing carbon monoxide with ethylene, ECO system [6 ]; this is now used for specialized applications such as “six-collar packs” for beverage cans.
