Influence of titanium dioxide pigments on the photodegradation of poly(vinyl chloride)

A nanocrystalline rutile powder, an anatase white pigment and a photoactive as well as a photostable futile pigment were examined for their influence on the photodegradation of poly(vinyl chloride), compared to blanc fire as an inert filler. By UV-VIS spectroscopy, the intermediate transfer of oxygen from the TiO2 surface to the polymer was proved. From the gloss losses during dry irradiation and full weathering, by the Weibull statistical model of failure the rates of PVC photooxidation were calculated. So for each TiO2 pigment the individual balance of UV-protective and photocatalytic properties could be quantified. Gloss losses were correlated with surface roughness measurements and electron microscopic images to elucidate the underlying morphological changes. In dry irradiation, the photooxidation of PVC comes to a standstill when the irradiation intensity is reduced by only 50%. Thus the space of W-protective influence around a rutile pigment particle is much larger than its ideal UV extinction sphere calculated from electromagnetic theory. (C) 2000 Elsevier Science Ltd. All rights reserved.