Sun radiation and temperature impact at different periods of the year on the photooxidation of polyethylene films

Analysis of the IR spectra of weathered films exposed at different periods of the year reveals that, the main regions of the IR spectrum affected by solar irradiation and temperature variation are the complex carbonyls and unsaturations composite absorption bands. Their respective kinetics vary in different manner according to the period at which the exposure is started. Curve fitting has been performed to refine the analysis of the IR spectra and to identify all the chemical species constituting the complex absorption bands. The analysis of the results let appears that whatever the exposure period of the year is, it does not affect the type of developing products, but it has strong effect on their kinetic rate of formation. The warm season is the more effective in terms of carbonyl formation and crystallinity index. This indicates that the Norrish type I (NI) process is very important in this season and it adds to the Norrish type II (NII) process. Both contribute to the carbonyl and vinyl groups formation via chain scission reactions; however the NII process is active during all the period of the year.