Add time:07/16/2019         Source:sciencedirect.com

The effects of 4-substitution of a butoxy-4-amino-2,2,6,6-tetramethylpiperidinyl group on the thermal and photostabilising action of 2-hydroxybenzophenone have been studied in polypropylene (PP) and Zeigler and Philips grade high density polyethylenes (HDPE), and these effects have been compared with the corresponding activities of 2-hydroxy-4-n-octoxybenzophenone (Cyasorb UV 531). Using infra-red absorption absorption spectroscopy (FTIR), hydroperoxide analysis, differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) the former stabiliser is shown to exhibit both effective thermal (oven ageing and melt) and light stabilisation in the three polyolefin systems. Carbonyl and hydroperoxide growths in the polymers are consistent, with the degree of thermal and photostabilisation being dependent upon the initial hydroperoxide concentrations in the polymers as well as the polymer type and its processing histroy. Both the oven ageing and thermal analysis data correlate well, showing a relationship with the rates of thermal decomposition of the stabilizers themselves. In both cases processing history reduces the stability of the stabilisers and their stabilising effectiveness in the polymers due to the consequent formation of increased levels of hydroperoxides. The hindered piperidine stabiliser exhibits strong autoretardation on both thermal and photoageing, illustrating its behaviour as an effective photothermal antioxidant. Fourier transform infra-red analysis and weight loss from TGA indicate that the hindered piperidine stabiliser undergoes a primary mechanism of hydrogen atom abstraction at the methylene-amine link by active hydroxyl radicals produced from the homolysis of hydroperoxides and subsequent splitting of the carbon-nitrogen bond into alkyl and amino radicals. The latter then effectively scavenge oxygen, preventing further oxidative breakdown of the polymer. The ability of the hindered piperidine stabiliser to complex and react with oxygen is also implicated in the overall scheme.

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