COMPARISON OF UV DEGRADATION CHEMISTRY IN ACCELERATED XENON) AGING TESTS AND OUTDOOR TESTS .2.

Compared with outdoor weathering, accelerated weathering of polyethyle ne (using a filtered xenon lamp) leads to a more rapid decrease in elo ngation at break, higher oxygen uptake and a higher CO/CO2 formation r ate, a faster decrease in the concentration of UV stabilizer (2-hydrox y-4-octoxybenzophenone) and faster changes in the IR spectra. The acce lerated degradation rate depends on the type of filter used to filter the xenon lamp. With an UV filter (wavelengths > 290 nm) degradation i s faster than with a glass filter (wavelengths > 310 nm). A comparison of the data for accelerated (with a glass filter and an UV filter) an d outdoor aging at the same degree of oxidation shows unexpected diffe rences, especially in the IR spectra. These differences are explained by assuming a change in the ratio between oxygen uptake by initiation due to charge transfer complexes (CTCs) and oxygen uptake due to norma l autooxidation. An increase in the cut-off wavelength of the filter f rom > 290 nm to > 310 nm causes a higher conversion of oxygen to carbo nyl. This is because the absorption of the CTCs above 290 nm decreases with increasing wavelength, which means that when a glass filter is u sed (wavelength > 310 nm) oxygen uptake via the CTC mechanism becomes less important and normal oxidation becomes more important. The conver sion of oxygen to carbonyl during outdoor weathering is even lower tha n that during accelerated weathering using an UV filter. This is proba bly because outdoor weathering takes place at a lower temperature than accelerated weathering, which results in a higher stability of the CT Cs, so that during outdoor weathering more oxygen is converted via the CTCs and less through normal oxidation.