Rapid measurement of polymer photo-degradation by FTIR spectrometry of evolved carbon dioxide

The method was then used to probe mechanistic aspects of the photo-oxidation of pigmented polyethylene (PE) film. For unpigmented polymer the photo-degradation was sensitive to changes in the small fraction of incident UV below 300 nm, but for pigmented films this was much less important. This is because unpigmented film degrades by direct photochemical attack whereas, for pigmented film, photocatalysis by TiO2, which absorbs in the 300-400 nm region, is important. For films whose photo-oxidation was dominated by photocatalysis by the TiO2 the rate of oxidation was shown to vary as the square root of the UV intensity. By contrast, for unpigmented films the rate of direct photochemical oxidation was linearly proportional to UV intensity. The difference is a consequence of the controlling role of electron-hole recombination in photocatalytic processes. For both unpigmented and pigmented films the rate of oxidation was shown to increase with increasing humidity and oxygen content of the atmosphere.