Heterogeneity of Accelerated Photooxidation in Stabilized Bulk Commodity Polymers Studied by X-Band ESRI

Heterogeneity of photooxidation processes in plaques made of commodity polymers, high-density polyethylene, and cyclic olefin copolymer poly(ethylene- co -norbornene) (Topas ® 8007) stabilized with various hindered amine stabilizers; some of them in combination with UV stabilizers exposed to accelerated weathering were studied using electron spin resonance imaging (ESRI) and three independent microscopic-scale methods: scanning electron microscopy, infrared microscopy, and microhardness testing. Concentration profiles of nitroxides mapping photooxidation process inside polymer plaques along the direction of incident radiation (perpendicular to the irradiated surface of the plaques) were determined by ESRI technique in dependence on the duration of the accelerated photooxidation. ESRI data were complemented with profiles of oxidation products, crystallinity, and microhardness measured inside the plaques along the same direction. Selection of stabilizers in the study was completed with α-tocopherol that is considered as the most active component of excellent processing stabilizer vitamin E.