PHOTOCATALYTIC DEGRADATION OF POLYETHYLENE FILM BY INCORPORATED EXTRA-FINE PARTICLES OF TITANIUM-DIOXIDE

Low-density and high-density polyethylene (PE) films (thickness 50-170-mu-m) containing 0.125-1.0 wt% of titanium dioxide (TiO2) 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 TiO2 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 TiO2 or a rise in termperature reduced P(i). Transmission electron microscopic measurement revealed that voids around the TiO2 particles, which are predominantly located in the amorphous region of PE rather than the crystalline region, were produced by TiO2-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 TiO2, molecular oxygen, and photoirradiation.