A spectroscopic study of the interaction between hindered amines and high molecular weight phenols during the natural weathering of polypropylene films

The interaction between three commercial hindered amines, viz. Tinuvin 144, Cyasorb UV 3346 and Tinuvin 622 and two commercial hindered phenols, viz. Hostanox 03 and Cyanox 1790, has been examined during the natural weathering of polypropylene films, using second-order derivative ultra-violet (UV)-visible and Fourier-transform infra-red (IR) spectroscopy. Unstabilised polypropylene samples show signs of oxidative degradation after only 1 week, and the hindered phenols, as expected, offer little or no protection to environmental damage. On the other hand, Cyasorb UV 3346 and Tinuvin 144 give a seven and tenfold increase in the polymer lifetime, respectively while Tinuvin 622 offers very little protection (similar to the phenols). Both antagonistic and synergistic effects are observed when the hindered amines and the phenols are used in conjunction. The effects are attributed to physical interaction, i.e. when the antioxidant is protected by the amine through reaction of the latter with radical species from the polymer, and to chemical interaction, i.e. direct reaction of the phenol and the amine. The results are explained in terms of the mechanistic action of these compounds.