Carbon dioxide formation during initial stages of photodegradation of poly(ethyleneterephthalate) (PET) films

Carbon dioxide (CO(2)) generation by ultraviolet irradiation of poly(ethyleneterephthalate) (PET) films in oxygen was monitored by in situ Fourier transform infrared spectroscopy. Typically, the CO(2) absorbance increased by similar to 100 x 10(-4) in 180 min, with no evidence of hindrance by restricted diffusion of O(2) into, or CO(2) out of, the films. It was concluded that Fourier transform infrared spectrometry monitoring of CO(2) conveniently, reliably and rapidly measures PET films photostability.Quantitative analysis of the CO(2) evolved from progressively thinner films from successive stages of the biaxial film drawing process indicated that CO(2) was generated within a few microns of the film surface and that the same amounts were generated from the irradiated surface of 540 mu m cast, 150 mu m uniaxially drawn and 85 mu m biaxially drawn films. Although drawing increased film crystallinity, photoreactivity appeared to be unchanged. However, total CO(2) formation followed the pattern PET cast<PET uniaxial<PET biaxial because ultraviolet irradiation attenuation reduced photo generation at the rear of thick films.