Spectral profiling by 1D and 2D electron spin resonance imaging: Nitroxideradicals in UV and thermal degradation of poly(acrylonitrile-butadiene-styrene) containing a hindered amine stabilizer

Thermal and UV oxidative degradation of poly(acrylonitrile-butadiene-styren e) (ABS) containing a hindered amine stabilizer (HAS) was studied by electr on spin resonance (ESR) spectroscopy and ESR imaging (ESRI). The imaging te chnique allowed digital (nondestructive) spectral profiling of the HAS-deri ved nitroxide radicals: Their intensity profile was determined by 1D ESRI, and the spatial variation of the ESR line shapes was determined by 2D spect ral-spatial ESRI. The UV light was provided by fluorescent lamps with maxim um intensity in the range 290-320 nm (UVB) or by a Xe are that closely rese mbled the solar spectrum. Upon UVB irradiation the nitroxide signal was ini tially strong only on the irradiated side and increased with time through t he sample. These results were taken as evidence for extensive damage on the irradiated side and slower thermal degradation in the entire sample. The e ffect of UVB radiation was in marked contrast with that of a Xe source; aft er Xe irradiation the nitroxide radicals were detected at both the irradiat ed side and the opposite side, and their intensity was negligible in the sa mple interior. Spatial variation of the ESR line shapes was observed for ir radiation with both UV sources. The spatial distribution of the nitroxide r adicals was, however, homogeneous during thermal degradation at 318 and 333 K, and there was no spatial variation of the ESR line shapes. The results allowed mapping of the line shape and intensity of nitroxide radicals withi n the sample as a function of treatment time and provided mechanistic detai ls on the early stages of the degradation process. This study suggested a h ierarchical variation of the HAS-derived nitroxide concentration: within mo rphological domains in ABS on the scale of a few micrometers and within the sample depth on the scale of millimeters.