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TiO 2 ‐, ZnO‐, and CdS‐photocatalyzed oxidation of ethylene‐propylene thermoplastic elastomers

1987; Wiley; Volume: 25; Issue: 10 Linguagem: Inglês

10.1002/pola.1987.080251015

1099-0518

Jacques Lacoste, Raj Pal Singh, Jacques Boussand, René Arnaud,

Photopolymerization techniques and applications

Abstract The ZnO‐, TiO 2 ‐, and CdS‐photocatalyzed oxidations of an amorphous ethylene‐propylene copolymer ( EP copolymer) containing 75% w/w of ethylene are described. In solid films exposed under polychromatic (λ > 300 nm) or monochromatic (λ = 365 nm) UV light, it is observed that the introduction of pigment (0.5–5% w/w) strongly modified the course of the photooxidation of a transparent sample. Ketonic and lactonic groups accumulate in the polymer matrix without being converted photochemically into acidic, ester, and vinyl groups. In the kinetic study it is pointed out that the variations of the rate of formation of carbonyl groups depend on the nature of the pigment. With highly photoactive pigments (ZnO and untreated TiO 2 RL11A), the rate is at first a decreasing function of the pigment percent, then an increasing function. With poorly photoactive pigments (treated TiO 2 RL90 and CdS), the rate of formation of carbonyl groups is a decreasing function of the pigment content. It is therefore emphasized that, at a low pigment content, the inner filter effect prevails over the photocatalytic influence with any pigment. It is also observed that the rate of formation of vinyl groups, photoproducts formed from the excited ketones, is a monotonously decreasing function of the pigment content. The complete inhibition of the ketone photochemistries is observed with ZnO in conditions in which the light is not absorbed by the pigment, suggesting that the carbonyl groups formed are adsorbed on the pigment.