Voprosy khimii i khimicheskoi tekhnologii (Issues of Chemistry and Chemical Technology)

11-17

Authors: Yu.N. Bespalko, M.A. Sinel'nikova, E.N. Shved

The kinetics of the curing reactions of epoxy ED-20 with succinic acid and isomethyltetrahydrophthalic, phthalic and succinic anhydrides catalyzed by fatty aromatic amines or anilines–boron trifluoride complexes are studied at the temperatures of 303–373 K. The observed effect of the ratio of epoxy resin to acid reagent on the reaction activation parameters indicates a change of the rate-determining step. It is found that the curing rate increases with decreasing the nucleophilicity of amine in the amine-BF3 complexes. The possible interactions of initial reagents in the system, the mechanisms of activation and epoxide ring-opening are estimated on the basis of quantum chemical calculations. It is suggested that the curing mechanism can mainly involve an electrophilic activation of epoxide by the amine-BF3 complexes. In case of anhydride excess, the contribution of side processes, e.g. with secondary alcohol, increases and affects the experimental activation enthalpy. The contribution of boron trifluoride activation increases with decreasing the nucleophilicity of amine and depends on the degree of complexes dissociation in the system.

26-34

Authors: I. Krutko, I. Danylo, V. Kaulin

The kinetics of decomposition of azodicarbonamide, an exothermic chemical blowing agent, which is used for obtaining solid foams, was investigated. It was shown that the modified coal tar pitch can be used as a polymer matrix to produce foamed pitch composite materials. The decomposition temperature of azodicarbonamide is approximately 200–210C. Such a decomposition temperature is too high to foam a modified coal tar pitch due to a change in its rheological properties. The azodicarbonamide decomposition temperature can be reduced by adding initiators. Zn stearate, Ca stearate, their mixture and polyvinylchloride were used as initiators. The influence of the initiators on the kinetics of azodicarbonamide-initiator decomposition at temperatures of 130–150C was investigated. The induction period, the time of reaching the maximum decomposition degree and the decomposition rate of the azodicarbonamide-initiator have been determined as a function of the temperature and the initiator amount. A maximum rate of mixture decomposition was observed in the case of Zn stearate; the addition of binary initiator Zn stearate/Ca stearate decelerates the process. The use of polyvinylchloride as an initiator is characterized by very low rates. The comparison of the decomposition degree for various initiators in isothermal conditions revealed that Zn stearate is the most active initiator. It has been established that there is a line of the optimal Zn stearate amount to reach the maximum decomposition degree at temperatures of 130–150C for the complex blowing agent azodicarbonamide-Zn stearate. The gas number of the complex blowing agent, azodicarbonamide-Zn stearate with an optimal composition has been determined at 140 and 150C.

42-48

Authors: A.A. Ovcharenko, A.A. Golichenko, A.V. Shtemenko

Two methods for the synthesis of dirhenium derivatives were developed. Depending on the initial products, complex compounds of two structural types, octachlorodirhenate(III) and cis-tetrachlorodi--carboxylate of dirhenium(III) with threonine, were synthesized for the first time. The preparation of (ThrН)2Re2Cl8 (І) was performed in a mixture of H2O and HCl (conc). LiReO4 and threonine were used as starting compounds, SnCl22Н2О was used as a reducing agent. As a result of the interaction of (NBu4)2Re2Cl8 with threonine in a mixture of acetone and acetonitrile, cis-[Re2(Thr)2Cl42CH3CN]Cl2 (ІІ) was synthesized. The composition and structure of the obtained substances were proved using elemental analysis, measurements of molar conductivity, infrared spectroscopy and electron absorption spectroscopy. The electron absorption spectra recorded for the solutions of the obtained compounds showed the presence of characteristic absorption bands which are related to the *-electron transition of the Re–Re quadruple bond; thus, the presence of octachlorodirenate(III) anion Re2Cl82- and cis-tetrachlorodi--aminocarboxylate of dirhenium(III) can be unambiguously established for I and II, respectively. According to the IR-spectrum of compound I, there is an intense vibration band, which refers to the vibrations of the non-ionized free carboxyl group (C=O), and a band of the protonated NH3+-group, confirming the conclusion that the amino acid is a cation in this compound. In the IR spectrum of compound II, there is no characteristic band of the uncoordinated CO–group, but there is an intense, weakly split band, which belongs to the s(CO) coordinated carboxylate group, the presence of which indicates the bridging coordination of this group of the ligand to the binuclear Re26+ fragment.

61-66

Authors: V.S. Protsenko, L.S. Bobrova, T.E. Butyrina, F.I. Danilov

Electrocatalytic activity of chromium-carbon electrodes towards hydrogen evolution reaction was studied in this work. Chromium-carbon coatings were electrodeposited from a trivalent chromium plating bath on the basis of a deep eutectic solvent. The plating electrolyte contained choline chloride, chromium(III) chloride and water. The electrocatalytic behavior was studied by means of linear voltammetry method and electrochemical impedance spectroscopy in an alkali medium (1 M NaOH). Our findings showed that the exchange current density of the hydrogen evolution reactions for Cr–C electrodeposited electrocatalysts was higher than that for Cr coatings. The results of linear voltammetry and electrochemical impedance spectroscopy revealed that the electrochemical reduction (i.e. Volmer step) is a rate-determining step of the hydrogen evolution reaction occurring on Cr and Cr–C electrodes in an alkaline solution. The changes in the electrocatalytic properties may be associated with the changes in the electronic structure. Thus, the electrodeposited chromium-carbon coatings fabricated from a deep eutectic solvent seem to be very promising to develop new electrocatalysts in the hydrogen evolution reaction for water-splitting devices.

73-79

Authors: L.M. Yashchenko, N.V. Iarova, T.F. Samoilenko, O.O. Brovko

The interaction of the components both in the model systems and in the epoxy-urethane matrix, based on the polyisocyanate, epoxy resin ED-20 and sodium silicate, as well as in the filled composite based on the epoxy-urethane matrix was investigated by the FTIR spectroscopy method. It was shown that trimerization of isocyanate groups occurs during the formation of the epoxyurethane polymer matrix in the system simultaneously with the reaction of urethane formation at the interaction of isocyanate groups of polyisocyanate with hydroxyl groups, isocyanurate fragments being formed as additional cross-links units of a three-dimensional network. The influence of the temperature of the reaction medium on the course of chemical reactions of epoxy-urethane matrix formation was studied. On the basis of synthesized epoxy-urethane matrix, the polymer composite material containing hemp chaff as a fiber filler was prepared. Hemp chaff is a source of cellulose fiber suitable for strengthening of polymers and as rapidly renewable natural resource, which is characterized by cheapness, ease of working and recycling. The interaction between the functional groups of the epoxy-urethane matrix and hydroxyl groups of hemp chaff was shown. Almost complete conversion rates of isocyanate and epoxy groups in the pressed sample of the filled composite material was revealed. It was determined that the optimal temperature of polymer composite material forming is 160°С.

86-91

Authors: V.Yu. Kramarenko, A.V. Serhieieva, H.D. Neskorozhena

The study is dedicated to determination of a simple method for recalculation of discharge time of paint-and-lacquer materials when using funnels with different parameters of outlet holes. To this end, the analysis of the dependences of kinematic coefficient of viscosity on the values of discharge time has been performed for the viscometer VZ-246 and the funnels that are used in compliance with the international standard ISO 2431. The causes of significant differences in the values of discharge time for the funnels with different nozzle geometry have been established, the differences being observed for viscometers even when the values of their volume and the diameter of their capillary part are equal. The coefficients of the basic equation, which was applied according to ISO 2431, have been determined for the viscometer VZ-246 which is widely used in domestic practice. It has been found that this equation can also be used for the description of correlation dependences of discharge time when using the funnels with different nozzle geometry. The alignment charts are plotted and the coefficients of correlation dependences are determined for different types of viscometers. The analysis of the errors associated with the use of the proposed approach shows its acceptability within the limits of the repeatability and reproducibility values specified by ISO 2431.

100-106

Authors: V.O. Kucherenko, Yu.V. Tamarkina, V.O. Saberova

We studied the porous structure of thermolysis solid products (TSP) fabricated from brown coal by the process of thermal shock alkaline (KOH, 1 g/g coal) activation which includes the following stages: (1) a rapid introduction of impregnated coal into the reactor preheated up to the temperature of thermal shock (tТS), varied within the interval of 400–850C, and (2) an isothermal exposure for 1 hour at tТS. Based on the 2D-NLDFT calculations of nitrogen adsorption-desorption isotherms (77 K), we determined the total specific surface area S (m2/g), the pore volume V (cm3/g), the surface (Smi) and the volume (Vmi) of microporous, the surface (S1nm) and the volume (V1nm) of subnanopores (i.e. pores with an average width of W1 nm). The integral and differential dependences of S and V on the average pore width were calculated. An increase in tTS from 400C to 850C results in an increase in the values of S (from 14.7 m2/g to 2414 m2/g) and V (from 0.124 to 1.04 cm3/g), the yield of TSP being decreased from 67 to 17%. The SΣ value increases with the temperature tTS due to the subnanopore surface development (from 0 to 2230 m2/g); its portion is dominant (S1nm/S0.86) in the pore structure of TSP prepared at tTS of 600 to 850C. The mutual action of KOH and heat shock was found to develop predominantly the pore surface with W5 nm. The specific surface area distribution by pore width as dS/dW vs. W relationship is characterized by peaks corresponding to subnanopores (dS1), micropores with W=1–2 nm (dS2) and mesopores with W=3–5 nm (dS3). With increasing tTS, the dS1 value increases exponentially (from 0 to 7000 m2/gnm) and well obeys the Arrhenius equation that allows valuating the parameter E(S1)=56.1 kJ/mol being formally similar to the "classical" activation energy. The parameter E(S1) characterizes the influence of tTS on the increment of specific surface area of subnanopores with increasing their width. An increase in the heat shock temperature was suggested to promote the subnanopores formation which is limited by the diffusion of the activator (i.e. KOH or K-atoms as the products of K+-ions reduction) within the formed three-dimensional framework of the brown-coal porous material.

116-122

Authors: I.V. Trembus, N.V. Sokolovska, V.V. Halysh, J.V. Nosachova, Т.А. Overchenko

It is necessary to reduce the negative impact of the pulp and paper industry on the environment and to expand the raw material base. This problem can be solved by the development of new environmentally friendly methods of the production of pulp and cellulose from wastes of agriculture to fabricate different types of cardboard and paper products. This work is devoted to the investigation of the effect of reagents consumption, catalysts application and duration of delignification in a medium of acetic and formic acids on the quality indices of straw cellulose. Pulp of high quality was obtained with the yield in the range of 51.7 to 63.1% and with the content of residual lignin of 5.2 to 12.9%. The indices of selectivity of lignin removal during organosolv delignification of wheat straw stems were calculated. The positive influence of Na2WO42H2O, MoWO42H2O and TiO2 on the delignification of non-wood material with the use of a mixture of organic acids was shown. The physical-mechanical indices of organosolv straw cellulose were determined; they are not inferior to kraft cellulose which indicates the possibility of the use of organosolv straw cellulose in the production of paper and cardboard.