ESR STUDIES ON γ-IRRADIATED CELLULOSE

Abstract

The types of free radicals formed by γ-irradiation in cellulose I and II were studied. The ESR spectra obtained with the γ-irradiated cellulose I and II were changed by contacting the fibers with water, and also the spectra for these fibers after immersion in water were varied by orientations of fiber axes to the magnetic field. These spectra seem to be related to the free radicals generated in the highly ordered regions inaccessible to water in irradiated cellulosic fibers. And the spectral differences between cellulose I and II may be due to the differences in the molecular conformation in the crystal lattices. As a model of typical amorphous regions in cellulose, decrystallized cellulose was prepared. The ESR spectrum of irradiated decrystallized cellulose was simple. When the sample was contacted with moisture, the ESR spectrum changed to a narrow singlet, which gradually decreased the intensity until the spectrum completely disappeared. By subtracting the spectrum of free radicals remaining in decrystallized cellulose after contacting with moisture from the spectrum of decrystal-lized cellulose, it was found that the types of free radicals formed in the decrystallized cellulose consisted of the overlap of narrow singlet (line width 8G, g-value 2.0050) and doublet (splitting 10G, g-value 2.0045) spectra. The singlet spectrum is attributed to alkoxyl radical formed by the rupture of glycosidic linkage at C1 or C4 position, and the doublet spectrum is ascribed to the radical formed by hydrogen abstraction from C1 position. When the ESR spectra of free radicals formed in the highly ordered regions of the irradiated cellulose I and II were added to the spectra of the singlet and doublet in adequate ratio, the constructed spectra were similar to the spectra of free radicals scavenged by water in cellulose I and II. From these facts the spectra generated by free radicals in the amorphous regions accessible to water in the irradiated cellulose I and II are considered to be composed of the ringlet and doublet formed by free radicals in the typical amorphous regions, and the spectra of other types of radicals, which are similar to the spectra for free radicals formed in crystal regions inaccessible to water. It is considered that the radicals are generated mainly in the typical amorphous regions in cellulose, since the contribution of the doublet spectrum is great in these constructed spectra for both cellulose I and II.