AbstractTitanium dioxide, zinc oxide, and other white pigments are widely used in protective coatings and textile applications. An undesirable property of such pigments is their behavior as photo‐oxidation catalysts. As a measure of the activities of various pigments, quantum yields were determined for the photo‐oxidation of isopropyl alcohol to acetone in a system where the pigment was the only absorbing species. An absolute quantum yield of 0.5 was found for reagent‐grade anatase; relative quantum yields were determined for various commercial anatase and rutile titanium dioxides, zinc oxide, barium sulfate, and barium tungstate. A good correlation was found between the photodegradation rates of pigmented polypropylenes, the photodegradation rates of the dyes in pigmented cellulose acetate butyrate, and the activities of the pigments determined by the isopropyl alcohol oxidation m
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