Thermal degradation at 393 K of poly(acrylonitrile-butadiene-styrene) (ABS) containing a hindered amine stabilizer: a study by 1D and 2D electron spin resonance imaging (ESRI) and ATR–FTIR

Abstract

Electron spin resonance imaging (ESRI) was developed in our laboratory as a method for spatial and spectral profiling of radicals formed during polymer degradation. We present the application of this approach to the study of thermal degradation at 393 K of poly(acrylonitrile-butadiene-styrene) (ABS) containing 1 or 2% w/w Tinuvin 770 as the hindered amine stabilizer (HAS). The spatial distribution of the HAS-derived nitroxide radicals, obtained by 1D ESRI, was homogeneous at short treatment times but became heterogeneous after treatment times ⩾ 70 h. The spatial variation of the ESR line shapes with sample depth was visualized by 2D spectral–spatial ESRI. Nondestructive (“virtual”) slicing of the 2D images resulted in a series of ESR spectra along the sample depth, which were used to deduce the relative intensity of nitroxide radicals present in two distinct sites. The two sites represent radicals located in butadiene-rich and SAN-rich domains, respectively. Taken together, 1D and 2D ESRI allowed the determination of the extent of degradation within morphologically-distinct domains as a function of sample depth and treatment time. The conclusions from the ESRI experiments were substantiated by attenuated total reflectance (ATR) FTIR spectroscopy of the outer layer (500 μm thick) of the polymer. Comparison of the two techniques suggested that the advantage of the ESRI method is its ability to provide mechanistic details on the early stages of the ageing process. ESRI and FTIR data indicated that the larger Tinuvin 770 content in the polymer, 2%, leads to less efficient stabilization.