SynopsisThe ESR spectra of microcrystalline cellulose and purified cotton cellulose reacted with ceric ammonium nitrate in nitric acid were determined. The effects of the concentration of ceric ion, atmosphere, temperature, and graft copolymerization with acrylonitrile on the rates of formation and decay of radicals in the cellulose molecule were determined under both static and dynamic conditions. Under static conditions, after the desired conditions of reaction, the samples were frozen at -100 or -16OoC., and then the concentration of free radicals was determined. Under dynamic conditions ceric ion solution was continuously flowed through the celluloses while these determinations were being made a t 25OC. In the presence of oxygen the rate of decay of free radicals was decreased. On initiation of copolymerization reactions with acrylonitrile, there was an increase in radical concentration, then a decrease. Apparently, during graft copolymerization the radical site initially on the cellulose molecule was retained on the end of the growing polymer chain. Then additional ceric ion coordinated with the hydroxyl groups of the cellulose, leading to the formation of additional radical sites. An Arrhenius interpretation of the effect of temperature on the formation of these additional radical sites gave apparent activation energies for radical formation on cotton cellulose as 34 kcal./mole and on microcryst,alline cellulose as 29 kcal./mole.
Two series of samples of purified cotton were irradiated in oxygen and nitrogen atmospheres with gamma rays at six dosage levels ranging from 100.000 to 100.000.000 roentgens. Some of the chemical and physical properties of the irradiated cellulose were determined by means of various widely used techniques of cellulose chemistry. It was found that high energy gamma irradiation of cotton resulted in carbonyl group formation, carboxyl group formation, and chain cleavage in the approximate ratio of 20 : 1 : 1 ; increased solubility in water and in dilute alkali ; decrease in tensile strength of the fibers ; small but unusual changes in moisture regain: relatively unchanged infrared absorption spectra ; and the same type of degradation in a nitrogen atmosphere as in an oxygen atmosphere, with oxygen producing only slight enhancement of the reaction.
SynopsisIt was demonstrated by ESR spectroscopy that the Fe+2/Hz0z syst,em gave a reactive species which generated an ESR triplet spectrum or sorbitol similar to that generated by hydroxyl radicals from the Ti+3/Ha03 system. An ESR spectrum was obtained for the hydroxyl radicals generated by the latter system. However, the lifetime of hydroxyl radicals, generated by the Fe+2/Hz0z system, was apparently very short, and an ESR spectrum for the hydroxyl radicals, generated by this system, was not observed. The Fe+z/HzOz system also generated triplet spectra with cotton cellulose I, cotton cellulose 11, and microcrystalline cellulose, suggesting that a hydrogen at.om had been abstracted from the hydroxyl group on carbon C , or possibly the hydrogen atom on carbon Cg.The ESR spectrum generated on microcrystalline cellulose was less intense than those generat,ed on cellulose I and 11. On initiation of graft polymerization of the activated celluloses with acrylonitrile, the triplet spectrum disappeared and was replaced by two strong singlet spectra. One of the singlet spectra was likely generated on carbon C1 or C, on depolymerization of the cellulose molecule, and the other was probably generated on the end of the growing polyacrylonitrile molecular chain. The absence of a triplet spectrum gave direct evidence for the order in which the acrylonitrile monomer was being grafted onto the cellulose molecule. The mechanisms proposed by Haber and Weiss for the reactions generated in the Fe + 2 / H~0 z system were generally supported.
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