Spectral Profiling by 1D and 2D Electron Spin Resonance Imaging: Nitroxide Radicals in UV and Thermal Degradation of Poly(acrylonitrile−butadiene−styrene) Containing a Hindered Amine Stabilizer

Abstract

Thermal and UV oxidative degradation of poly(acrylonitrile−butadiene−styrene) (ABS) containing a hindered amine stabilizer (HAS) was studied by electron spin resonance (ESR) spectroscopy and ESR imaging (ESRI). The imaging technique allowed digital (nondestructive) spectral profiling of the HAS-derived nitroxide radicals: Their intensity profile was determined by 1D ESRI, and the spatial variation of the ESR line shapes was determined by 2D spectral−spatial ESRI. The UV light was provided by fluorescent lamps with maximum intensity in the range 290−320 nm (UVB) or by a Xe arc that closely resembled the solar spectrum. Upon UVB irradiation the nitroxide signal was initially strong only on the irradiated side and increased with time through the sample. These results were taken as evidence for extensive damage on the irradiated side and slower thermal degradation in the entire sample. The effect of UVB radiation was in marked contrast with that of a Xe source; after Xe irradiation the nitroxide radicals wer...