Pro-oxidant activity of biocompatible catechin stabilizer during photooxidation of polyolefins

Abstract

Polymer plaques made of high-density polyethylene (HDPE) or cycloolefin copolymer (COC) were stabilized with natural phenolic stabilizer (+)-catechin (CAT) and aged using accelerated weathering technique (WOM; accelerated photooxidation). The efficiency of the phenolic stabilizer was compared with a well-established hindered amine stabilizer (HAS) Tinuvin®770 (Tin770). In pursuit of the stabilization and identification of short-living radicals generated in the process of photooxidation of the polymers, a spin trapping agent 2,4,6-tri-tert-butylnitrosobenzene (TTBNB) was added to selected samples. Profiles of oxidation products and crystallinity inside the HDPE plaques were determined by IR microspectroscopy, oxidation products in COC copolymers were identified using ATR spectroscopy, concentration profiles of radicals generated inside polymer plaques during WOM exposure were determined by ESRI, the changes of local mechanical properties at the surface of polymer plaques were characterized using microindentation hardness testing (MHI), and the surface morphology changes were studied by light and/or scanning electron microscopy. All methods are in accordance with the conclusion that the natural phenolic stabilizer CAT exhibited pro-oxidant activity during accelerated photooxidation of both polymers, i.e. higher concentration of oxidation products, bigger changes of local mechanical properties and/or more microcracks on the exposed surfaces in comparison with non-stabilized systems and systems stabilized with Tin770.