Photocatalytic degradation of polyethylene film by incorporated extra-fine particles of titanium dioxide

Abstract

Low-density and high-density polyethylene (PE) films (thickness 50–170 μm) containing 0·125–1·0 wt% of titanium dioxide (TiO 2) particles were photoirradiated by a high-pressure mercury arc over a period up to 200 h at room temperature in air. During photoirradiation, the transparent film (transmittance of the unirradiated film with 0·5 wt% of TiO 2 was >65%) turned white together with decreases in weight and mechanical properties, e.g. elongation at break and tensile strength. This occurred after characteristic induction periods, while linear accumulation of carbonyl groups in the film was observed just after the commencement of photoirradiation. Carbon dioxide and carbon monoxide were detected as gaseous products. X-ray diffraction analyses revealed a decrease in the proportion of amorphous region in PE during the photocatalytic degradation. Increase in the amount of TiO 2 or a rise in termperature reduced P i . Transmission electron microscopic measurement revealed that voids around the TiO 2 particles, which are predominantly located in the amorphous region of PE rather than the crystalline region, were produced by TiO 2-photocatalytic oxidation, causing the whitening and the decrease of mechanical strength. Control experiments revealed that this type of degradation proceeds only in the copresence of extra-fine particles of TiO 2, molecular oxygen, and photoirradiation.