ESR Studies of NR

Very few papers on ESR studies of NR composites and nanocomposites are available in the literature. 

This chapter reviews the ESR studies of natural rubber (NR) and some selective other polymer composites and nanocomposites based on literature surveys. 

In this chapter, ESR studies on NR composites and nanocomposites are extensively reviewed based on available published literatures. A very few ESR studies on rubbers were conducted due its complexity and specific natures. Interactions between both carbon black and silica particles with NR matrix were well established by conducting the ESR study. Variations of the ESR spectra and the concentration of the unpaired spins of NR/carbon black composites with carbon black concentration, milling time, types of carbon... 

The key feature of the isotopically asymmetric system is that an interaction of a polarized reactive free radical r with ( " N-0- N) results in three distinct polarized species with different sets of for each paramagnetic species and not overlapping spectra (Scheme 12.14) (r " N-0- N), ( " N-0- Nr) and ( " N-0- N). This situation is essentially different from the previously studied case of ( " N-0- " N), where the three basic components of the ESR spectrum of ( " N-0- " N) coincide with components of the adduct ( " N-0- " Nr) (see Fig. 12.9). The TR ESR spectra obtained with isotopically asymmetric ( " N-0- N) are presented in Fig. 12.10. 

Dubrovic et al. have studied the NR films crosslinked by y-irradiation under both relaxed and uniaxial deformation state by ESR. Figure 25.11 shows the ESR spectra of the spin probe dilfused non-irradiated and irradiated NR matrix at relaxed state. The intensity of the broad component is more pronounced and the narrow component is strongly reduced in case of the 200 kGy irradiation dose applied crosslinked NR films in comparison with the non-crosslinked NR films at unstretched condition. The ratio of intensity for narrow (7n) to broad (4) spectral lines reduces with application of irradiation, which is due to the decrease in sol components by irradiation induced cross-linking process. The amount of broad component is not pronounced at higher irradiation doses, which may be attributed to the heterogeneous distribution of... 

Baccaro et al. have investigated the ehemical interactions between N375 carbon black and NR matrix under eleetron beam irradiations. In their ESR studies, effects of radiation dose on free radical concentration were evaluated by applying 191 kGy, 499.5 kGy and 1 MGy irradiation doses to the compounds at 2 kGy/h dose rate. The results are shown in Figure 25.24(a). The shapes of the ESR spectra remain unchanged with different radiation doses, whereas intensity of the derivative peaks change with the radiation doses. It is assumed that the radiation-induced free radical concentration may be proportional to the peak-to-peak intensity signal. The intensity of the spectra lines increases up to 499.5 kGy and then decreases at 1 MGy radiation dose. The... 

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