ESR Spectra of Gamma-Irradiated Cotton Cellulose I and II

Abstract

Irradiation of purified fibrous cotton cellulose I and cotton cellulose II (mercerized) with γ-radiation from Co"" gave products containing relatively stable free radicals, easily shown in electron spin resonance (ESR) spectra. The ESR spectrum of irradi ated cellulose I consisted ,of three, lines, and the spectrum of irradiated cellulose II consisted of five lines. The principal lines of both spectra occurred at about the free electron value, and the symmetry of the spectra indicated equal interaction of hydrogen nuclear spins with the free radical. In the case of the three-line spectrum of irradiated cellulose I, this could occur on the formation of a free radical on the cleavage of the H atom from C5, cleavage of the OH group from C6, or cleavage of the H atom from the OH group of C6. The principal line of the spectra for each of these radicals would probably occur at ahout the same value, but the interaction of the equivalent hydrogens on C6 with either of the radicals would result in a different line width splitting. C5 is the most likely site of the free radical due to the delocalizing effect of the oxygen atom to which it is attached. In the case of the observed five-line spectrum of irradiated cellulose II this could occur on the formation of two free radicals which individually yield three lines. The principal lines of the spectra of these radicals would occur at about the same value and the less intense lines, due to equivalent hydrogen interactions of each spectrum, would occur at different line widths. One radical would likely form at C5 as described for cellulose I and the second radical at C6 on the same anhydroglucose unit or on another anhydroglucose unit in the same unit cell by either H atom or OH group cleavage. The formation of this second radical in cellulose II, compared with one radical in cellulose I. is further, evidence of differences in the internal forces in the unit cell on change of the lattice type from I to II, This could, be interpreted as a rearrangement in hydrogen bonding in the unit cell of cellulose II, compared with cellulose I, through the —CH 2OH (C6) group of the anhydroglucose unit. This bond ing would have a delocalizing effect on C6, thereby increasing the chances of forming a second radical.

Free radical generation upon plasma treatment of cotton fibers and their initiation efficiency in surface-graft polymerization

“…In case of mercerized cotton, which has been extensively investigated, radicals at C(1), C(4), C(5), and C(6) (see Fig. 1) have been postulated [45][46][47][48]. De Jesus et al obtained similar results from the hard seed covers of citrus seeds [49,50], showing that the lineshape is a resultant of the superposition of lines belonging to at least four different paramagnetic species.…”

“…The superposition of two triplets has been attributed to H-cleavage at C(5) or to cleavage of the OH group at C(6) [51]. According to Arthur et al [46], a single-line spectrum can also result from homolytic C-H bond cleavage at C(1) or C(4). Anyway, a quartet of hyperfine splitting constants of about 13 ± 1 G and a g value of 2.0044 ± 0.0004 due to the interaction of an unpaired electron with three hydrogen atoms have also been found [52].…”

Analysis of Relaxation Behavior of Free Radicals in Irradiated Cellulose Using Pulse and Continuous-Wave Electron Spin Resonance

“…Even though cellulose and starch have similar chemical formulas, their radical formation process may differ due to their structures (Rånby, 1977). It has been reported that the triplet ESR spectrum of cellulose (pure cotton) is due to the equal interaction of the two hydrogen atoms at the C6 position with the unpaired electron formed by the removal of the hydrogen atom at the C5 position of the glucose unit (Rånby, 1977;Arthur, 1971;Arthur & Hinojosa, 1971;Arthur et al, 1966;Baugh et al, 1967) (see Fig. 1 B).…”

“…The side signals are a part of the triplet. Some interaction between the two protons and the unpaired electron sites at the C2, C3, and C4 positions of the glucose unit are possible, and can be predicted in the cellulose structure (Rånby, 1977;Arthur et al, 1966;Baugh et al, 1967). One needs to consider the physical three-dimensional structure and energy levels of cellulose bond sites.…”

Use of the environmental scanning electron microscope for the observation of the swelling behaviour of cellulosic fibres

“…The exact mechanism of the damage is not fully understood, although it is widely believed to involve free radicals. Arthur et al (1966Arthur et al ( ,1971) studied the effects of high-energy radiation on various cellulose samples. They found radiation-sample interactions to produce radicals, ultimately resulting in dehydrogenation, dehydroxylation, and depolymerisation of the cellulose molecular chain.…”