Influence of down shifting particles on the photochemical behaviour of EVA copolymers.
Résumé
The influence of SrAl2O4: Eu2+, Dy3+ particles (10–30% w/w) on the oxidation of ethylene-vinyl acetate copolymer (EVA) (18 wt% of vinyl acetate) exposed to UV-light irradiation was studied. EVA is sensitive to UV light at wavelengths above 300 nm, as described in the literature. Light-induced oxidation results in the formation of carboxylic acids, and the infrared absorbance of the CO band at 1716 cm−1 was consequently used to follow the oxidation of the EVA polymer. Linear increases were observed in response to increases in the exposure time, and the rate of the photo oxidation of the host matrix EVA was higher for the composite. SrAl2O4: Eu2+, Dy3+ particles strongly absorb in a domain extending up to 455 nm. The absorption of the particles is sufficiently high to compete with the absorption by EVA. As a result, an inner filter effect was expected, but this effect was not observed. Moreover, experiments have been performed as “side experiment” in order to understand the relationship between the oxidation rate and the absorbed light intensity. Samples with different thicknesses ranging from 50 to 160 μm were irradiated. The oxidation rate varied linearly with the amount of absorbed light. The rates of the oxidation of EVA in the neat material and in the composite were compared for irradiations under monochromatic light at 365 nm. The obtained result showed that the rates were similar, although EVA absorbed less in the composite than in the neat material. This result could be attributed to the potential photocatalytic capacity of SrAl2O4: Eu2+, Dy3+ or the diffusion of light by the particles, which increased the optical pathway.