Non-isothermal Dehydration Kinetics of Some Cationites

The kinetic parameters of dehydration were determined under non-isothermal conditions for different polystyrenedivinylbenzene sulfonic acid type cationites (DVB) and their dependence on the degree of cross-linking granulation, porosity, specific surface, content of SO₃M groups (M=Li, Na, K, Rb), nature of the alkali metal in partially neutralized -SO₃H groups and heating rate was investigated. This revised version was published online in July 2006 with corrections to the Cover Date.     

The study of non-isothermal degradation of acrylic ion-exchange resins

Summary The thermal behavior under non-isothermal conditions of some low-acidity carboxylic cationites with acrylic-divinylbenzene (DVB) matrix was investigated in air and nitrogen atmosphere up to 600°C. Thermal analysis (TG/DTG) combined with Mass Spectrometry (MS) and Fourier Transform Infrared Spectroscopy (FTIR) was used to characterize the resins decomposition steps and the degradation products. Five decomposition steps were observed. The first step is due to elimination of osmotic and bound water. The second decomposition step is due to dehydration of neighboring (-COOH) groups. The third and fourth mass-loss steps correspond to decarboxylation of the polyanhydrides and to some depolymerization of the polymeric matrix. The last decomposition step is associated with total degradation of the polymeric matrix. The shape and the temperature for each decomposition steps depend on the experimental conditions (heating rate and degradation atmosphere) and on the sample properties (i.e. granulation, cross-linking degree, porosity and physical form).     

The enthalpy of interaction between an aqueous solution of methionine and carboxyl cationites in the copper form

The influence of acidity of aqueous solutions of methionine on their interaction with carboxyl cationites in the copper form was studied by the calorimetric, sorption, and spectroscopic methods. The distribution of methionine between aqueous solutions and sorbents with the formation of Cu(II) cation complexes in both phases was observed over the pH range 5–12. The enthalpies of interaction between methionine and KB-2 and Kb-4 cationites in the copper form were determined at various pH.     

The temperature dependence of the exchange enthalpy of calcium and sodium ions on polymethacrylic and polyacrylic cationites

The influence of temperature on the exchange of calcium and sodium ions from solutions of 2.3–2.8 g-equiv/l concentrations on KB-2e4 gel polyacrylic cationite, KB-4P2 and KB-4 gel polymethacrylic cationites, and Purolite C104 polyacrylic cationite was studied over the temperature range 273–400 K. It was shown that, simultaneously with a substantial increase in selectivity with respect to calcium ions, the differential enthalpy of the ion exchange reaction increased linearly on all polyacrylic and polymethacrylic cationites as the temperature grew.     

The enthalpy of sorption of glycine from aqueous solutions by carboxyl cationites in the copper and mixed forms

The influence of glycine solution acidity on glycine interactions with carboxyl cationites in the copper and mixed sodium-copper forms was studied by the calorimetric, sorption, and IR spectroscopy methods. The enthalpies of sorption of glycine on KB-2 and KB-4 at various pH were determined.     

Heterogeneous soft acid catalysis of the sucrose hydrolysis

Using a micro-calorimetrical DSC we have compared the acid-catalyzed inversion of sucrose in homogeneous and heterogeneous systems. Acetic acid was chosen as catalyst for homogeneous system, and several carboxylic cationites were used as heterogeneous catalysts. The kinetic apparent parameters (A, E, k _ap) for all the systems were calculated from DSC data with Friedmann’s method and catalytic constant, k₃₂₃^cat, was further inferred. We found that the specific catalyst efficiency, q _cat, in heterogeneous system is over 5000 times higher than in case of homogeneous ones. The activity of heterogeneous carboxylic systems is still about 30 times larger than those of a strong mineral acid in homogeneous catalysis. The results indicate the high efficiency of heterogeneous systems for soft acid catalysis of the sucrose hydrolysis.     

Diffusion kinetics of the ion exchange of benzocaine on sulfocationites

The theory of the ion exchange kinetics on strong acid cationites with the participation of weak electrolytes is discussed. The kinetics of desorption of benzocaine in the protonated and molecular forms from strong acid cationites, sulfonated polycalixarene, and KU-23 30/100 sulfocationite, is studied experimentally. It is shown that the flow of protonated benzocaine from cationite upon desorption proceeding by the ion-exchange mechanism is more intense than upon desorption of nonionized benzocaine molecules. It is established that the diffusion coefficient of benzocaine cations is (1.21 ± 0.23) × 10^?12 m²/s in KU-23 30/100 sulfocation and (0.65 ± 0.06) × 10^?13 m²/s in sulfonated polycalixarene, while the diffusion coefficient of benzocaine molecules is (0.65 ± 0.15) × 10^?14 m²/s in sulfonated polycalixarene.     

应用搅拌棒吸附萃取-热脱附-气相色谱-质谱分析烟用香料的化学成分

应用搅拌棒吸附萃取法(SBSE)提取烟用香料的化学成分,并利用热脱附(TD)和色谱-质谱联用(GC-MS)进行分析。对影响萃取效果的因素(萃取时间和氯化钠的加入量)进行了考察,并采用正交试验法对影响热脱附的3个主要因素(脱附温度、脱附时间和冷阱温度)进行了优化,得到了较优的实验条件。对方法的重现性进行了考察,同一样品6次测定所得30个组分的峰面积的相对标准偏差（RSD）平均值小于10%,说明所建立方法的重现性较好。在样品中鉴别出酯类、酮类和醛类等30种不同化学组分,这些物质反映了该香料的香气特点。实验证明SBSE和TD适用于烟用香料的快速分析测定。     

A kinetic study on the thermal behaviour of chitosan

The thermal behaviour of chitosan was studied by means of thermogravimetry, mass spectrometry and infrared spectrometry. Kinetic parameters were obtained by advanced kinetic evaluation (differential isoconversional analysis) from DSC curves, in non-isothermal conditions, at several heating rates, between 5 and 30°C min⁻¹. The results showed that the decomposition of chitosan does not follow a single mechanism because both the activation energy and the pre-exponential factor are not constant during the course of the reaction. A comparison with the results obtained by applying different conventional calculating methods is also shown.     

The state of Gd<Superscript>3+</Superscript> ions in sulfo-and sulfophenol-containing ion exchange polymers according to the EPR data

The KU-2 and KU-1 universal cationites were found to exhibit partly selective properties with respect to Gd³⁺ ions. As distinct from the transition group cations studied earlier, gadolinium ions formed centers with SO ₃ ^? functional groups even in sulfo resin matrices hydrated to the greatest extent, and the fraction of these complexes increased as free water was removed from ionite matrices. The EPR spectra of gadolinium aquacomplexes in hydrated polymers were similar to their spectra in aqueous solutions. The strong crystal field condition (D

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hv) with the presence of axial and rhombic components was fulfilled for fixed complexes. The spectra corresponded to complexes of two types. The effective g-factors and λ = E/D parameters were calculated to describe the spectra of systems with spin S = 7/2 quantitatively. The correlation times of rotational motion of aquacomplexes in hydrated cationites were determined. These times were found to be longer (1.5 to 3 times) than in aqueous solutions. Dipole-dipole interactions between gadolinium ions were studied to estimate the local concentrations of sorbed ions in large-sized pores.

     

Study of Cryostructuring of Polymer Systems: 23. Composite Poly(vinyl alcohol) Cryogels Filled with Dispersed Particles Containing Ionogenic Groups

Composite poly(vinyl alcohol) cryogels containing particles of cross-linked dextran gels (Sephadexes and their ion-exchange derivatives with different ionogenic groups) as fillers were prepared and studied. It was shown that mechanical and thermal-physical properties of such composites were affected by the presence of ionogenic groups on the particles of dispersed fillers: as the ionite concentration increases, less rigid (than in the case of unmodified Sephadex particles) filled cryogels were formed. The properties of composite cryogels depend on the nature and concentration of counterion added with the ionite. Substantial increase in the rigidity and melting point of composites was observed when using strong anionites in the OH^–-form and strong cationites in the H⁺-form as fillers.     

Estimation of Flame Retardancy Effect by Thermal Analysis Using Kinetic Parameters Obtained under Non-Isothermal Conditions in Air

A series of compounds obtained from urea, phosphoric acid and inorganic salts of Zn, Ni and Ca, were tested in respect of their flame‐retardancy behavior. The estimation criteria were the kinetic parameters obtained in air, under non‐isothermal conditions, on a Perkin‐Elmer Diamond device, at heating rates of 5, 10, 12 and 15 deg·min^?1. The flame‐retardancy effect was assigned to the significant endothermic decomposition at relatively low temperature (150–200°C). The quantitative estimation of the thermal behavior was performed by comparison of the kinetic data obtained by Flyn‐Wall‐Ozawa, Friedman and NPK (Sempere‐Nomen) methods. The kinetic homogeneity and a very good quality of the model are arguments in favour of the NPK method. The Ni containing material exhibited the best flame‐retardancy behavior, i.e. higher activation energy and mass loss, respectively a single decomposition step with both physical and chemical processes. The results were validated by fire resistance tests.     

Thermal Degradation of Natural Polymers

The thermal degradation of sodium hyaluronate, xanthan and methylcellulose was evaluated by thermogravimetric and infrared analysis. Kinetic parameters such as activation energy and pre-exponential factor were determined considering the Ozawa and Freeman–Carroll methods. The results suggest changes in the degradation mechanism with the fraction of mass loss for both the studied polysaccharides. The activation energy values determined by the Freeman–Carroll method are higher than those obtained by the Ozawa method under the same conditions, probably because in the first method a first order reaction was assumed and the thermal history effects were eliminated since only one TG curve was used to determine the kinetic parameters. Low thermal stability was observed for polyanions e.g. sodium hyaluronate (Na-Hy) and xanthan(XT) in comparison with methylcellulose (MC) which is a neutral polysaccharide. By infrared spectroscopy, it was observed that at low temperatures there occured only the scission of the exocyclic groups for both polysaccharides and that the scission of strong links in the backbone occurred at high temperatures, in agreement with the kinetic parameters determined for the degradation reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal degradation studies of polystyrene sulfonic and polyacrylic carboxylic cationites

The thermal degradation of polyacrylic carboxylic and polystyrene sulfonic cationites was investigated using thermal analysis (TG) combined with Scanning Electron Microscopy (SEM). Fourier Transform Infrared Spectroscopy (FTIR) was used to characterize the resins degradation steps. The carboxylic cationite undergoes degradation through dehydration forming polyanhydrides, decomposition of polyanhydrides through decarboxylation with elimination of CO₂ and CO. The sulfonic cationite undergoes degradation through dehydration, followed by decomposition of sulfonic acid functional groups liberating SO₂. It was observed that strong acid (−SO₃H⁺) cationite shows small mass loss of 55%, as against 88% mass loss shown by low-acidity carboxylic cationite. The possible reason for small mass loss of sulfonic cationite is discussed. The text was submitted by the authors in English.     

Thermal Decomposition Kinetics of High Impact Polystyrene/Organo Fe‐montmorillonite Nanocomposites

In this article, high impact polystyrene/organo Fe‐montmorillonite (HIPS/Fe‐OMT) nanocomposites were prepared by melting intercalation. The thermal stability of HIPS/Fe‐OMT nanocomposites increased significantly compared to that of HIPS examined in thermal degradation conditions. Kinetic evaluations were performed by Kissinger, Flynn‐Wall‐Ozawa, Friedman methods and multivariate nonlinear regression. Apparent kinetic parameters for the overall degradation were determined. The results showed that the activation energy of HIPS/Fe‐OMT nanocomposites was higher than that of HIPS. A very good agreement between experimental and simulated curves was observed in dynamic conditions. Their decomposition reaction model was a single‐step process of an nth‐order reaction.     

The kinetics of cation exchange in network calyxarene-containing polymers: the nanoreactor effect

The kinetics of cation exchange from aqueous solutions of electrolytes in network calyxarene-containing polymers with sulfo acid and phenol ionic groups was studied. It was shown that the interaction of the polymers with aqueous solutions of LiCl, NaCl, AgNO₃, LiOH, NaOH, and (CH₃)₄NOH was controlled by ion diffusion in the polymer phase. The nanoreactor effect, that is, a significant increase in the ion exchange rate in sulfonated calyxarene-containing polymers, was observed. The spherical layer model was used to obtain an analytic dependence of conversion on the interdiffusion coefficient and ion exchange duration in bifunctional cationites.     

Some Remarks on the Methodology of Thermal Analysis of Clay Minerals

The influence of certain experimental conditions on the courses of the thermal curves (DTA and DTG) of selected clay minerals was studied. The thickness of the sample layer, the sample mass, the type of sample holder and the parameters of the air atmosphere were varied in thermal analyses of 13 samples of clay minerals. Comparison of the results obtained on different clay samples analysed under different experimental conditions may serve as the basis for the improvement of the thermal analysis methodology applied for the study of clay minerals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of thermal treatment on potato starch evidenced by EPR,XRD and molecular weight distribution

Effect of heating of the potato starch on damages of its structure was investigated by quantitative electron paramagnetic resonance (EPR) spectroscopy, X‐ray diffraction and determination of the molecular weight distribution. The measurements were performed in the temperature range commonly used for starch modifications optimizing properties important for industrial applications. Upon thermal treatment, because of breaking of the polymer chains, diminishing of the average molecular weights occurred, which significantly influences generation of radicals, evidenced by EPR. For the relatively mild conditions, with heating parameters not exceeding temperature 230 °C and time of heating equal to 30 min a moderate changes of both the number of thermally generated radicals and the mean molecular weight of the starch were observed. After more drastic thermal treatment (e.g. 2 h at 230 °C), a rapid increase in the radical amount occurred, which was accompanied by significant reduction of the starch molecular size and crystallinity. Experimentally established threshold values of heating parameters should not be exceeded in order to avoid excessive damages of the starch structure accompanied by the formation of the redundant amount of radicals. This requirement is important for industrial applications, because significant destruction of the starch matrix might annihilate the positive influence of the previously performed intentional starch modification. Copyright © 2015 John Wiley & Sons, Ltd.     

The interaction of erythromycin with polymeric sorbents adjusted to the antibiotic molecule

Cross-linked carboxylic cationites adjusted to sorption of the antibacterial antibiotic erythromycin were obtained by radical copolymerization of methacrylic acid, erythromycin methacrylate, and ethylene glycol dimethacrylate as a cross-linking agent. Studies of the sorption and desorption of erythromycin showed that adjusted sorbents had favorable equilibrium and kinetic characteristics of sorption and the ability to reversibly desorb the antibiotic. Original Russian Text ? O.A. Pisarev, N.M. Ezhova, I.S. Garkushina, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 1, pp. 142–146.     

La Decomposition Thermique de Quelques Thiobenzpiperidides

The thermal decomposition of thiobenzpiperidides and some derivatives containing substituents on the benzene nucleus was studied. By thermal analysis was put in evidence the influence of the nature and position of the substituents on the decomposition process. Kinetic parameters in non-isothermal and quasi-isothermal conditions (CRTA) were calculated. The chromatographic analysis, associated with mass spectrometry, proved that the initiation of the complex decomposition process is the result of the polar bond break. This revised version was published online in July 2006 with corrections to the Cover Date.