Comparison of formation of oxidation products during photo-oxidation of linear low density polyethylene under different natural and accelerated weathering conditions

The weathering behaviour of linear low density polyethylene was investigate d under accelerated conditions (using a Weather-O-meter and a SEPAP 12-24 u nits) and natural conditions (at Dakar, Senegal, and at Tsukuba, Japan). Qu alitative and quantitative measurements of the products of photo degradatio n were carried out by the FT-IR technique coupled with chemical treatments (SF4 and NO). The comparison of the yields of several oxidation products un der these four modes of UV irradiation gave unexpected results. Whatever th e mode of irradiation, carboxylic acid, sec-alcohol and ester species are p roduced to a closely related extent. The evolutions of sec-hydroperoxides, vinyls and, to a less extent, ketones were very sensitive to the mode of UV irradiation. These findings call into question the validity of the asserti on that photo-products arise from hydroperoxide decomposition. Alternative routes, based on radical recombination, to elucidate the formation of photo -products explain quite well the changes observed in the elongation at brea k. (C) 2000 Elsevier Science Ltd. All rights reserved.