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 investigated under accelerated conditions (using a Weather-O-meter and a SEPAP 12-24 units) and natural conditions (at Dakar, Senegal, and at Tsukuba, Japan). Qualitative and quantitative measurements of the products of photo degradation were carried out by the FT-IR technique coupled with chemical treatments (SF4 and NO). The comparison of the yields of several oxidation products under these four modes of UV irradiation gave unexpected results. Whatever the mode of irradiation, carboxylic acid, sec-alcohol and ester species are produced 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 assertion 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 break. (C) 2000 Elsevier Science Ltd. All rights reserved.