MECHANISMS OF PHOTOSTABILIZATION OF POLYOLEFINS WITH N-ALKYL(METHYL)HALS

There is still controversy over the relative efficiency and stabilization mechanisms of secondary and tertiary HALS. In this study the performance of secondary HALS is compared with that of corresponding hindered amines bearing various substituents at the sterically hindered nitrogen atom. The bulk of the stabilization data concerns unpigmented polypropylene and the comparison of N-H and N-methyl derivatives. It is found that in PP films, PP multifilaments, PP tapes and injection molded PP plates the secondary HALS and the corresponding N-methyl derivatives give the same performance within experimental error. The results available, so far, with PE-HD films, PE-HD tapes and PE-LD films lead to the same conclusion. Saturated alkyl groups other than methyl show also comparable performance. The effect of unsaturated groups such as allyl and benzyl and of oxygen atoms (nitroxyl radicals) varies. Depending on the particular polypropylene batch used, the performance can be comparable, superior or inferior to that of the corresponding NH/N-methyl compounds.