Photoageing of rigid PVC - IV. Effects of titanium dioxide

The photoageing of unpigmented and TiO2 (5%) pigmented rigid PVC samples has been studied in reactors equipped with different types of fluorescent lamps. The changes in thickness distribution of carbonyl and conjugated polyene concentrations were followed by IR and UV spectrophotometry on microtomed slices (20 mu m) and discussed on the basis of kinetic results obtained on thin films (similar to 80 mu m) under the same conditions. In the presence of TiO2, the thickness of the degraded layer is divided by about 2 whereas the screen effect is multiplied by 5. From a comparison of photo-oxidation rates with sources of distinct spectra it is hypothesized that the observed penetration of photoageing could be due to a radiation wavelength of similar to 390 nm, close to the absorption cut-off of TiO2. (C) 1998 Elsevier Science Limited. All rights reserved.