The gloss retention of a coating depends in part on the grade of TiO_2 used. Traditionally, the TiO_2 contribution to gloss retention has been attributed to the fact that TiO_2 is a photocatalyst, and that gloss retention differences between different grades of pigment are due to different levels of TiO_2 photocatalytic activity. However, there is poor correlation between photoactivity and gloss retention performance. In addition, there is commonly very poor correlation between exterior exposure rankings of TiO_2 pigments and accelerated exposure rankings in the same coating. In this paper we describe a second property of TiO_2 - beyond photoactivity - that explains these observations and allows us to better predict both exterior and accelerated gloss retention results.
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