L. T. Bugaenko

On the Crosslinking of Cellulose under Exposure to Radiation

The effect of γ-irradiation of air-dry cotton cellulose on the degree of order of its supermolecular structure was studied at room temperature within a dose range of 0–2 MGy. The degree of order was evaluated by measuring the crystallinity index by the X-ray diffraction technique and the water-retaining capacity of irradiated cellulose upon both equilibrium saturation with water vapor and swelling in liquid water. The buildup of macroradicals in irradiated cellulose and their decay upon plasticization with water during a postradiation period were also studied. The complex behavior revealed was explained in terms of the effect of radiation-chemical crosslinks on the mobility of macrochains and on the submicroscopic capillarity of cellulose fiber structure.

Effect of Temperature on the Yields of Final Products in the γ-Radiolysis of Formaldehyde Solutions in C1–C3 Alkanols

The effect of temperature on the yields of 1,2-alkanediols in the γ-radiolysis of the methanol(or ethanol)–formaldehyde (0.9 M) systems and on the yields of 1,2-alkanediols, carbonyl compounds, methanol, and ethanol in the γ-radiolysis of the 1-propanol(or 2-propanol)–formaldehyde (1 M) systems was studied over the range 373–473 K. It was found that the temperature dependence of the yields of 1,2-butanediol and 2-methyl-1,2-propanediol exhibited maximums at 423 and 373 K, respectively.

Effect of Aromatic Protectors on the Radiolysis of Polyorganosiloxanes

The influence of phenyl and other aromatic groups on radiation crosslinking of polydimethylsiloxane and its mechanical blends and copolymers with polydiphenylsiloxane and polyphenylsilsesquioxane, radiation-induced gas evolution, and radical generation in these systems were considered. It was shown that radiation-chemical yields of crosslinking and gas evolution follow a simple exponential law over a wide concentration range of phenyl groups (at their content above 1 mol %). A similar dependence was observed for the radiation-chemical yield of hydrogen in ethylene copolymers with styrene. For the crosslinking processes, it was proved that the effect of phenyl groups is identical in the mechanical blends and copolymers of polyorganosiloxanes. The effect of retardation of radiation-chemical processes by phenyl groups was shown to be independent of whether one or two groups is linked to a silicon atom, it is their total amount that matters.

The sonolysis of methanol in diluted aqueous solutions : product yields

Abstract Diluted aqueous methanol solutions (0.001–0.5 M) were exposed to 724 kHz ultrasound irradiation under argon atmosphere at 26 ± 3°C. As measured with the argon-saturated Fricke dosimeter, the γ-equivalent dose rate of ultrasound in the sonochemical cell was 2.6 kGy/h (1.6 × 10 22 eV dm −3 h −1 ). The yields of the following products were measured: H 2 , H 2 O 2 , CO, CH 2 O, ethylene glycol, CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 . It was found that over the entire investigated concentration range the yield of methane was strictly proportional to the methanol concentration, the yields of CO and H 2 increased and that of H 2 O 2 decreased with increasing the concentration of methanol in the solutions. In very diluted solutions the yields of formaldehyde and ethylene glycol were measured to be, respectively, 1.5 and 0.64 molecules per 100 eV chemically active acoustic energy and did not depend upon the concentration of methanol unless that reached 0.02 M in case of formaldehyde and 0.1 M in case of ethylene glycol. On the further increase of the concentration their yields started to grow. An examination of the concentration dependences of the product yields leads to the assumption that in the sonolysis of methanol in very diluted aqueous solutions the H atoms and . OH radicals generated inside the imploding cavitation bubbles from thermal water decomposition causes the transformations of methanol. In doing so, H atoms pass into the bulk and react with methanol to form formaldehyde and ethylene glycol, whereas . OH radicals probably cannot escape from the hot region; they react there with methanol to give CO or recombine to give H 2 O 2 . At higher methanol concentrations the decomposition of methanol due to the thermolysis of its vapors in the cavitational hot-spots becomes significant. The experimental data are discussed in terms of distinction and similarity between the sonolysis and the radiolysis of methanol in aqueous solutions.

A Mössbauer Tin-119 Emission Spectroscopy Study on Electron Scavenging in Frozen Solutions

The effects of impurity ions on the yield of valence states of tin after the internal conversion isomeric transition of 119mSn in frozen alcohol solutions was studied. The ratios of rate constants for electron scavenging by the solutes H+, Cr+2, and Cu+2 were determined. Mössbauer emission spectra showed that, as the solute concentration increased, the yield of Sn+4 increased. The calculation of the electron scavenging rate constants in terms of various models (simple competitive reactions, the kinetics involving the epithermal electron, and the electron diffusion model) showed that metal ions have a higher electron scavenging ability. It was concluded that the presolvated electron takes part in reactions with the solutes.

Ethanol Conversion in an Aqueous Solution upon Aluminum Valve Anode Microdischarge Treatment

The conversion of 0.1–2.0 M aqueous ethanol solutions in the carbonate electrolyte by treatment with a microdischarge at an anode made of the AMg-6 aluminum–magnesium alloy was studied. It was shown that the microdischarge treatment leads to degradation of ethanol yielding hydrogen, carbon monoxide, С1–С4 hydrocarbons, methanol, formaldehyde, acetaldehyde, 1,2-propylene glycol, 2,3-butylene glycol, water, and acetic acid. The mechanism of relevant processes is discussed, which suggests a multiplicity of ethanol degradation pathways in vapor–gas bubbles.

Effect of Radiation on the Supermolecular Structure of Siloxane Block Copolymers with Different Compositions and Block Sizes

Abstractγ-Radiation-induced changes in the supermolecular structure of dimethylphenylsilsesquioxane block copolymers were studied with the use of electron microscopy. It was found that the supermolecular structure of the block copolymers was altered by irradiation. The character of changes depends on the size of a soft, dimethylsiloxane block, as well as on the total amount of the blocks in the copolymer molecule. A variation in the properties of block copolymers upon γ-irradiation was also detected by the technique of differential scanning calorimetry.

Degradation and crosslinking of dextran in aqueous solutions by γ-radiolysis: The effect of hydrogen ions

The conditions under which crosslinking or degradation of dextran macromolecules (PW= 930) is a predominant process upon γ-irradiation of acidic aqueous dextran solutions in the dose range 0–0.32 MGy were found using viscometry and gel chromatography. It was found that initial acidification of dextran solutions increased the role of crosslinking of macromolecules in the formation of the molecular-weight distribution of this polymer, whereas further acidification, in contrast, enhanced the degradation. The former is due to the transformation of hydrated electrons into hydrogen atoms, and the latter results from the catalytic effect of protons on the unimolecular decomposition of primary macroradicals accompanied by the rupture of glucosidic bonds. It was also found that radical centers can be transferred via macroradical-macromolecule reactions as the concentration of dextran increased. As a result of this, a macroradical capable of unimolecular decomposition, which results in degradation, is converted into a macroradical incapable of this transformation.

Reactions of thermalizing electrons in a condensed polar medium

Abstract The influence of electron acceptors on the yield of trapped electrons in frozen aqueous solutions is examined, and the results of picosecond radiolysis is discussed. It has been shown that the correlations observed cannot be explained if thermal electrons only take part in reactions occurring in such matrices, whereas they can be correctly interpreted assuming that epithermal electrons are also capable of reacting with acceptors in a condensed medium. Experimental data obtained are discussed on the basis of these concepts. The times needed for thermalization, solvation and capture have been evaluated, and the rate constants of the reactions of epithermal electrons computed.

γ-Induced single-step synthesis of ethylene glycol from methanol-formaldehyde solutions

A mechanism is developed for the initiated nonbranched-chain formation of ethylene glycol in methanol-formaldehyde solutions at formaldehyde concentrations of 0.1–3.1 mol dm−3 and temperatures of 373–473 K. At a formaldehyde concentration of 1.4 mol dm−3 and T = 473 K, the radiation-chemical yield of ethylene glycol is 139 molecules per 100 eV. The effective activation energy of ethylene glycol formation is 25 ± 3 kJ mol−1. The quasi-steady-state treatment of the reaction network suggested here led to a rate equation accounting for the nonmonotonic dependence of the ethylene glycol formation rate on the concentration of the free (unsolvated) form of dissolved formaldehyde. It is demonstrated that the peak in this dependence is due to the competition between methanol and CH2=O for reacting with the adduct radical HOCH2CH2O•.