Abstract
The effects of adding dispersed powders of various forms of titanium(IV) dioxide on the photodegradation of polyethylene have been examined from the following points of view: effect of crystal form, concentration of pigment, transition metal ion, dopant concentration, calcination temperature of pigment, and pigment coating. The rate of photodegradation of polyethylene is reduced by adding certain grades of TiO 2 such as coated TiO 2 particles or TiO 2 doped with small percentages of Cr or Mn ions. The rate is increased on adding TiO 2 doped with V and especially Mo or W ions. The anatase form of TiO 2 is more photoactive than the rutile form, and the effect of increasing the calcination temperature of the pigment is to reduce photoactivity by boosting the rutile fraction. The concentration dependences of the degradation rates are complex, but can be directly related to the percentage of anatase achieved after calcination. Even the most aggressive of the metal-doped pigments are less photoactive than the Degussa P25 material, containing both rutile and anatase.
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