Photostabilising action of Ni(II) bis(1-phenyl-3-methyl-4-decanoyl-5-pyrazolate), sanduvor NPU, in a polypropylene matrix

The photostabilising action of the metal chelate nickel(II) bis(1-phenyl-3-methyl-4-decanoyl-5-pyrazolate) in polypropylene is examined using normal and second-order derivative ultraviolet, infrared and phosphorescence spectroscopic techniques and hydroperoxide analysis. Although the chelate quenched the phosphorescence emission of a powerful sensitiser, benzophenone, there was no photoprotective action when the samples containing the chelate and the sensitiser were irradiated. In the case of anthraquinone there was no quenching and no photoprotection. Processing history plays a major role in controlling the photostabilising performance of the chelate. The effect of photosensitised oxidation with 365 nm light is examined. While the initial hydroperoxide concentration appears to control the onset of carbonyl growth in the polymer, the rate of photodecomposition of the chelate shows no dependence on hydroperoxide concentration. Furthermore, the rates of photooxidation under polychromatic irradiation follow the same trends as those obtained under monochromatic irradiation. The results are explained in terms of hydroperoxide inhibition during processing, stabiliser consumption during photooxidation and macroalkyl radical (P·) scavenging.