Mechanisms of breakdown of the structure of glass cloth during impregnation with polymer binders

The basic sources of worsening of the quality indexes of insulating glass cloth and the requirements for the properties of the cloth and binder during impregnation were determined: short pile, gas inclusions, thermodynamic characteristics of binder and monofilament on the binder—monofilament, binder—air, and air—monofilament interface, internal stresses in the structure of the cloth, weave geometry, and position of monofilaments in the complex fibre.Stekloplastik—Sertifikat Co., Moscow. Translated from Khimicheskie Volokna, No. 3, pp. 43–46, May–June, 1994.     

Determination of the Melting Point and Glass Transition Temperature of Polymers with the Lattice Model

The melting point and glass transition temperature of polymers is estimated with the lattice model of the bulk polymer phase. The good agreement of the predictions of the theory and the experimental findings on melting of polyethylene is demonstrated. The dependence between the melting point and glass transition temperature of polymers is obtained with the statistical thermodynamic theory and is in good agreement with the experimental data.__________Translated from Khimicheskie Volokna, No. 1, pp. 33–35, January–February, 2005.     

Na_2O-TeO_2系统玻璃形成液体脆性的研究

通过测量Na2 O -TeO2 系统玻璃转化区的热容曲线 ,对该系统不同成分玻璃形成液体的热力学和动力学脆性进行研究。结果表明 :该系统玻璃形成液体从热力学和动力学综合看脆性程度介于强弱之间 ,为中性偏脆性。随着氧化钠含量的升高 ,玻璃形成液体的脆性增强。用Kissinger方程和Ritland -Bartanev方程 ,得到的在玻璃转变区的结构松弛激活能十分接近。对该系统玻璃形成液体脆性参数的计算也得到该玻璃形成液体脆性分类的相同结果     

Environmental stress cracking and crazing in polymers in terms of irreversible thermodynamics

The processes in environmental stress cracking and crazing in polymers are analysed in terms of the irreversible thermodynamics. The thermodynamic potential of the system composed of the polymer matrix at a flaw tip region and its environmental liquid is constructed as a function of the concentration of the liquid migrated in the matrix and the dilative stress due to stress concentration. A state of the system is represented by a point in the thermodynamic potential diagram. The paths of the state shifts leading to failure in the diagram are governed by the shapes of the thermodynamic potential curves, the liquid concentrations giving the potentials a minimum, the critical concentration and the breakdown concentrations here introduced. Various kinetic data of environmental stress cracking in low density polyethylenes can be understood by the unified picture. The predictions of the theory are also consistent with the reported kinetic nature of crazing.     

The Method of Possible States and Its Application to the Chemical Thermodynamic Analysis of Nonequilibrium Processes in a Multicomponent Mixture of Reacting Gases under Isobaric Adiabatic Conditions

Subject to the laws of classical chemical thermodynamics on the basis of a method for representing a domain of possible states, a nonequilibrium process is considered in a closed system—a spatially homogeneous mixture of chemically reacting gases under isobaric adiabatic conditions. Using a vector representation of the rates of a set of basic reactions and analyzing entropy generation in the system, the path of the nonequilibrium process in the domain is determined without taking into account the factor of time, and relationships between the rates of the basic reactions as functions of the thermodynamic parameters of the system are established. The general form of an expression for the rates of the basic reactions is presented.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 3, 2005, pp. 269–277.Original Russian Text Copyright © 2005 by Smirnov.     

Refractory concretes of a new generation. Thermodynamic aspect of the technology

With allowance for the approach developed preferentially in the works of Tsimmermanis and Shtakel'berg, a set of fundamental regularities of the thermodynamics of irreversible processes (nonequilibrium thermodynamics) is used to analyze the processes of structure formation in manufacturing new refractory concretes. Structure formation and hardening of concretes is phenomenologically realized as the formation of a capillary-porous structure in the process of changes in the free surface energy of the system, which serves as a measure for the strength, elastic, and other properties of the material. In this approach to thermodynamic analysis of structure formation the watering potential of a disperse system is treated as an analog of the Gibbs chemical potential. The notions of structural affinity and the degree of completeness of structure formation are introduced by analogy with chemical affinity and the degree of completeness of a chemical reaction.Translated from Ogneupory, No. 1, pp. 2–7, January, 1995.     

Kinetic nature of the glass transition

A simple kinetic model is proposed to account for the behaviour of the specific heat of polymers near the glass transition. There is no need to assume any sudden changes of thermodynamic variables with temperature and the observed transition is attributed to a rapid but smooth change of the molecular relaxation time. The concept of a fictive temperature is introduced and is shown to be useful in understanding the behaviour of other thermodynamic quantities such as expansivity.     

Flexibility of Structure and Glass-Forming Ability: A Chemical Approach

Abstract[—The flexibility of the internal structure of solids stems from the free motion of their structural units without discontinuity of the structure as a whole. The flexibility is a necessary factor for the formation of a disordered glass structure and determines the glass-forming ability and sizes of glass formation regions in oxide systems. The glass transition phenomenon is a consequence and an indication of the high flexibility of glass structure. Crystallization of a multicomponent glass is governed, to a large extent, by structural–chemical factors. The sequence of the formation of different crystalline phases along the crystallization path with an increase in temperature corresponds to the sequence of liberation of glass structure components, which is determined by the strength of chemical bonds and the flexibility of glass structure.     

Mass-Transfer Equation in Multicomponent Mixtures

A multicomponent mass-transfer equation for the distillation of multicomponent mixtures is derived in terms of the thermodynamics of irreversible processes.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 3, 2005, pp. 337–344.Original Russian Text Copyright © 2005 by Serafimov, Timoshenko.     

Fragments of Heterocyclic Copolyamide Phase Diagrams

Fragments of a ternary phase diagram of the system heterocyclic copolyamide—DMAA/LiCl—precipitant (H₂O and isobutanol) are obtained. The temperature—concentration boundary of the phase transition for sulfuric-acid solutions of the heterocyclic copolyamide in the region of the existence of isotropic and anisotropic phases is determined. A hypothesis is advanced concerning the relatively high thermodynamic rigidity of the copolyamide molecules, close to the rigidity of PABI but less than the rigidity of PPTA.     

Vitrification, Properties, and Structure of Lead-Tellurite Borate Glasses

The vitrification, structure, and physicochemical properties of glasses in the PbO – ZnO – B₂O₃ – TeO₂ system are studied. The dual role of the lead ions in the glass structure is confirmed. It is demonstrated that the coordination transition of boron ions correlates with the concentration of PbO in glass. A nonlinear dependence of properties on the glass composition is due to the structural modifications in glass.     

A reaction order functional relationship with the Williams–Landel–Ferry equation in curing kinetics

A methodology is presented to obtain a kinetic model for curing reactions, from conversion against time and the glass‐transition temperature versus conversion data. Isothermal runs for a cyanate ester resin from 140 to 190°C, reported previously, were evaluated. The approach utilizes the conversion measurement time derivatives that allow following the estimated parameters' trends: the rate constant and the reaction order, in this case. An autocatalytic model was found, and the rate constants were truly constant along the experiments; thus, their Arrhenius parameters were evaluated. The methodology allowed constructing a master curve relating the variable reaction order with a temperature difference (reaction and glass transition) explained by the Williams–Landel–Ferry (WLF) equation. Four parameters describing the reaction order variation, two related to an exponential‐like behavior and two required by the WLF equation, allowed describing the whole experimental set accurately. POLYM. ENG. SCI., 54:1900–1908, 2014. © 2013 Society of Plastics Engineers     

The state of Tin on Pt–Sn/Nb2O5 catalysts

The effect of tin addition on niobia supported catalysts was studied and compared to the properties of alumina supported bimetallic Pt–Sn catalysts. The catalyst surfaces were probed by methylcyclopentane conversion, showing that both the presence of Sn and the reduction of the support caused a decrease in hydrogenolysis activity, favoring the ring enlargement reaction. The thermodynamics of reduction of these systems, evaluated by following the reduction step (temperature programmed reduction — TPR) with a differential scanning calorimeter (DSC), and irreversible H₂ and CO uptakes, allowed to conclude that a Pt–Sn alloy is formed on niobia supported catalysts.     

Thermodynamics of the chemical reactions between clay minerals and iron oxides

The thermodynamics of chemical reactions between clay minerals and iron oxides is considered within the framework of phase diagrams for multicomponent systems. Dominant reactions are identified featuring a thermodynamic probability higher than that of clay mineral dehydration.Translated from Steklo i Keramika, No. 12, pp. 21–23, December, 1996.     

Kinetics of solid-phase prepolycondensation of demonomerized polycaproamide

A variant of solid-phase prepolycondensation of PCA that takes place in conditions of an irreversible reaction is examined and a relation that satisfactorily describes the kinetics of the process in the case of an excess of terminal groups of one kind in the polymer is obtained. It was found that passage of solid-phase prepolycondensation of PCA from conditions of a reversible to conditions of an irreversible reaction is accompanied by an almost two-fold increase in the kinetic nonequivalence parameter of the reaction sites while the maximum rate constant remains almost unchanged. It is shown that at 453–483 K, depolymerization of demonomerized PCA takes place at a rate which is low in terms of the decrease in the yield of polymer, but is relatively high from the point of view of the necessity of recovering the caprolactam separated.Translated from Khimicheskie Volokna, No. 6, pp. 11–15, November–December, 2004.     

Analysis of a Two-Phase Perfectly Mixed Reactor under the Condition of a Phase Equilibrium

A mathematical model is formulated for a gas–liquid perfectly mixed flow reactor under the condition that the two-phase flow at the reactor outlet is at thermodynamic equilibrium. The phase equilibrium is calculated using the Redlich–Kwong–Soave equation of state. The set of nonlinear algebraic equations of the model is numerically solved by the efficient algorithm of the homotopy method. The steady-state modes of reactor operation are analyzed for liquid-phase benzene hydrogenation. It is shown that, under isothermal isobaric conditions, there can be a multiplicity of steady-state solutions, which is, on the one hand, due to the nonlinearity of the kinetic law and, on the other, due to the deviation of the properties of the reaction mixture from the properties of an ideal system. The stability of the steady-state solutions is analyzed, and the causes of the multiplicity and instability are explained.     

A study of the thermodynamics of precipitation of a polyheteroarylene using low-molecular models

Conclusions On the basis of colloid-chemical, thermodynamic, and spectral studies of the process of precipitation of PBITA and its low-molecular analogs, models have been constructed of the solvation phenomena in precipitation of PBITA.Types of complexes and their behavior in polymer (or model)—solvent—electrolyte systems in the presence of a precipitant have been examined.It has been found that the benzamide unit is responsible for the precipitation of the models and of PBITA.Values of the thermodynamic characteristics of precipitation of the models have been discussed; these additionally support an effect of precipitation mixture composition on precipitate morphology.Translated from Khimicheskie Volokna, No. 2, pp. 18–21, March–April, 1986.