Pro-oxidant activity of .alpha.-tocopherol during photooxidative degradation of polyolefins. ESRI and IR microspectroscopy studies

0472352 - ÚMCH 2018 RIV NL eng J - Journal Article
Pilař, Jan - Šlouf, Miroslav - Michálková, Danuše - Šloufová, I. - Vacková, Taťana - Dybal, Jiří
Pro-oxidant activity of .alpha.-tocopherol during photooxidative degradation of polyolefins. ESRI and IR microspectroscopy studies.
Polymer Degradation and Stability. Roč. 138, April (2017), s. 55-71. ISSN 0141-3910. E-ISSN 1873-2321
R&D Projects: GA MZd(CZ) NV15-31269A; GA MŠMT(CZ) LM2015064; GA ČR(CZ) GA14-17921S; GA MŠMT(CZ) LO1507
Institutional support: RVO:61389013
Keywords : polymer photooxidation * stabilization * HAS
OECD category: Polymer science
Impact factor: 3.193, year: 2017

Photooxidation processes inside high-density polyethylene (HDPE) and cyclic olefin copolymer (COC) poly(ethylene-co-norbornene), both stabilized with biological antioxidant alpha-tocopherol (alpha-T-OH), has been investigated. Plaques made of the polymers stabilized with alpha-T-OH were subjected to long-term accelerated weathering in a Weather-Ometer (WOM). Concentration profiles of radicals generated in the plaques in dependence on WOM exposure time were determined by electron spin resonance imaging (ESRI). Concentration profiles of oxidation products and stabilizer, together with local crystallinity profiles inside the polymer plaques were determined by infrared (IR) microspectroscopy. The ESRI and IR profiles, supplemented by light microscopy (LM) and microindentation hardness measurements (MH), revealed the heterogeneity of the oxidation process and, surprisingly, the pro-oxidative activity of alpha-T-OH. Increasing concentration of products of polymer oxidation was found in the surface layers of the plaques stabilized with alpha-T-OH since the beginning of WOM treatment unlike the same control experiments with polymer plaques stabilized with HAS Tinuvin® 770, where no oxidation products were observed after the same treatment before HAS depletion. We have confirmed that alpha-T-OH exhibits antioxidant activity during thermooxidation but it acts as a pro-oxidant agent during photooxidation.
Permanent Link: http://hdl.handle.net/11104/0270672