Modern Ideas About Diffusion in Polymer Systems

Чалых, А. Е.; Zlobin, V.B.

doi:10.1070/rc1988v057n06abeh003367

Cited by 21 publications

(33 citation statements)

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“…Using standard processing of the initial segment of the sorption isotherm in coordinates of the BET equation [6], the sorption capacity of the investigated fibres was determined and its value was 41.5 mg H 2 O/g of cellulose. In current sorption theories, this characteristic is given the meaning of a quantity proportional to the total concentration of primary sorption sites accessible to water molecules [7].…”

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confidence: 99%

Structural dependence of the features of the sorption behavior of cotton cellulose in reacting with water

2008

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and A. P. MoryganovIt was shown that the increase in the accessibility of cotton cellulose to water in drying is due to perturbations of the long-range order in the surface layer of crystallites. The necessity of quantitatively considering the structural changes in calculations of sorption values was demonstrated. The correlation of some features of the sorption behavior of cellulose materials in processes that include frequently repeated wetting and drying operations with the probable character of formation of accessible sections in the surface layer of the crystalline phase was noted.Studying the cellulose-water system has sustained continuous interest for many years. Information on this is important not only because of its theoretical value, but it also has direct practical significance, since cellulose materials are in close contact with aqueous and water-vapor media, primarily with atmospheric moisture, in all stages of production, processing, and use. Valuable information on the reaction of the components of the system is obtained in analyzing the water-vapor sorption isotherms for cellulosic materials [1]. Calculations of the different sorption characteristics using these isotherms usually assume constancy of the content of sorbing regions in the cellulose during water absorption. Moreover, the effect of a change in the supramolecular structure of different cellulosic materials during wetting has been reliably established with different methods of investigation (x-ray structural analysis, IR spectroscopy, dilatometry) [1][2][3][4]. The important effect of the moisture content on the ratio of amorphous and crystalline phases in cellulose should undoubtedly be reflected in the equilibrium and kinetic characteristics of its reaction with water. In this research, we established the cause of the dependence of these features of the sorption behavior of cotton cellulose which are related to the structural rearrangements that take place when the moisture content changes.The sorption measurements were performed by vacuum gravimetry using a quartz spring. We investigated scoured and bleached cotton fabric; samples of this fabric had previously been used in x-ray diffraction studies [4,5]. This make it possible to use the established parameters of the supramolecular structure in calculations of the sorption characteristics.The reaction of oxidation of cellulose with atmospheric oxygen at 150°C was also used to study the character of the structural changes that take place when cotton cellulose is wet and dried. The degree of thermooxidative degradation of the samples of cotton fabric was evaluated with the yellowness parameter, defined as coordinate b of the color field of the CIE Lab colorimetric system. It was calculated with the spectral reflection curve of thermooxidized samples taken on a reflection spectrophotometer in the 400-700 nm wavelength range.The water-vapor sorption isotherm for the investigated fabric sample at 20°C is shown in Fig. 1. In determining such a sorption value as the average hydration numbe...

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confidence: 99%

Structural dependence of the features of the sorption behavior of cotton cellulose in reacting with water

2008

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“…Detailed data on the effect of liquid media and vapors on polymeric materials, including PFCM, are reported in [2,10,[192][193][194][195][196][197][198][199]. However, we note that the data on water absorption and water, oil, and gasoline resistance are preliminary and can differ strongly, since the properties of the components of PFCM and their reaction with the active media are very different.…”

Section: Polar Matrices (Binders) And/or Fibres Water Absorption and mentioning

confidence: 99%

“…The effect of active media on composites includes the following fundamental cases [2, 10, [192][193][194][195][196][197][198][199]: wetting of the surface by liquids; sorption of liquids by the material, accompanied by swelling and plasticization of the material; sorption of vapors, accompanied by swelling and plasticization of the material; chemical degradation under the effect of acid and basic media or, in rare cases, formation of additional intermolecular cross-links; biodegradation by microorganisms. As a result of the effect of active media, the properties of the material change: the mechanical properties change in swelling and plasticization without degradation of the components of the composite the strength decreases and the deformability increases (the deformation modulus decreases and the deformation at failure increases); when degradation processes predominate, the strength and deformability simultaneously decrease.…”

Section: Effect Of Active Media On Pfcmmentioning

confidence: 99%

Polymeric fibre composites, basic types, principles of fabrication, and properties. Part 5. Effect of performance effects on polymeric fibre composites; safety/hazardousness characteristics

Perepelkin

2006

Fibre Chem

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The principles of materials science of polymeric fibre composite materials (PFCM) containing different reinforcing fibrous fillers (short-cut fibres, paper, yarn, tow, sliver, fabrics, and nonwoven materials) and different matrices (thermoplasts and thermosets) are examined in an analytical review [Khim. Volokna, No. 4 and 5 (2005); No. 1, 4, and 6 (2006)]. The mutual effect and reaction of the components of PFCM (fibres and matrices) are analyzed. information is reported on the fabrication and properties of different kinds of composites: fibre-filled molding materials, pertinaxes, textolites, unidirectional composites, honeycomb plastics, etc. New types of composites with ultrahigh mechanical and thermal characteristics are examined. Testing methods and the functional properties of PFCM are examined: mechanical, thermophysical, electrophysical, optical. The mechanisms of the changes in the structure and properties of PFCM under external effects: thermal, photochemical, ionizing radiation, active media, and other factors, are analyzed. Performance reliability indexes are examined, including aging and the effect of extreme conditions. Safety/ hazardousness characteristics are very important in selection of PFCM and use of articles made from them: sanitary-hygienic and toxicological, combustibility and toxicity of products of combustion. The following features of polymeric fibre composites in comparison to other materials are summarized below based on the examination: Combination of different kinds of fibre fillers and matrices (binders) allows regulating the properties of PCM in a wide range, selecting the optimum indexes for items with a wide spectrum of applications.Items made of PFCM involve low specific consumption of materials and are easy to manufacture, process, and treat in comparison to many traditional materials, metals and ceramics in particular. Articles made from composites are reliable in use, almost not subject to corrosion, and do not require special protection or periodic painting of the surface. With respect to specific mass characteristics, PFCM can be many times better than items made of metals and other traditional materials. This is important for using them in vehicles, aircraft, rescue craft, and sporting goods. Due to the features of the properties and the positive performance characteristics, PFCM have a great future in the most varied areas of application. BASIC EFFECTS ON PFCM DURING USEPolymer fibre materials and items made from them are constantly exposed to the environment during use: high temperatures, insolation and radiation, atmospheric and microbiological effects, active liquid and gaseous media, and other factors. Usually several of these factors act simultaneously, potentiating each other [2, 10,[171][172][173]. Aging during use of PFCM takes place under the effect of external factors their structure and properties, evaluated by the change in the basic functional characteristics, primarily mechanical and physical, gradually change.St. Petersburg State University of Technology ...

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“…The interaction of water and water vapors with polymers in the general case is a combination of the processes of absorption, adsorption, capillary soaking, and chemisorption [4]. Predominance of a particular mechanism depends on the internal structure of the polymer, its compatibility with the sorbate, swelling, and many other factors.…”

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confidence: 99%

“…Depending on the drying time, all polymers can be broken down into three groups [1][2][3][4][5]. The first group includes polymers whose particle size ranges from dozens to hundreds of micrometers.…”

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Kinetics and Apparatus-Technological Arrangement of Convective Drying of Disperse Polymer Materials

Rudobashta

Dmitriev

2005

J Eng Phys Thermophys

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The laws of internal mass transfer under deep drying of granular polymers depending on their state have been considered. From the point of view of the system approach, the general problem of their drying kinetics has been decomposed into two basic levels: a micro-and a macroscopic one, and, in accordance with this, the questions of mathematical modeling have been analyzed. The experimental data on the diffusion and sorption properties and longitudinal mixing of the solid phase are presented and recommendations on the apparatus arrangement of the process are given.In many industries (chemical, food, pharmaceutical), as well as in farming production, various disperse materials -granular, grained, powdery -are dried. Their drying process entails considerable energy and material expenditures and also has an appreciable effect on the quality of the products, which places stringent requirements upon the apparatus-technological arrangement and accuracy of the kinetic calculation of the drying stage.The majority of polymer materials require thorough removal of water from the raw material in those processes where polymer melts are used as the basis. The presence of moisture in the polymer melt even in negligible quantities leads to serious consequences: destruction and hydrolysis of the melt, a decrease in the degree of crystallinity, mass foaming, deterioration of the strength properties, lowering of the quality of the surface of products, and local change in the chromaticity and inhomogeneity of their translucence. Moreover, for products made of sheeting and fibers, the dielectric indices worsen, the degree of uniaxial and biaxial orientation decreases, and cracks are formed.Practically all producers of polymers and polymer materials use the drying process both at the production stage and in processing into products. Polymers in various aggregate states are subjected to drying: solutions and suspensions, pasty, fine-grained, and granular polymers [1, 2]. The drying conditions strongly influence the quality of the polymeric granulate.Depending on the drying time, all polymers can be broken down into three groups [1-5]. The first group includes polymers whose particle size ranges from dozens to hundreds of micrometers. They contain mainly surface moisture that is easy to remove. The drying time of such materials measures seconds. The second group of polymers contains, besides the surface moisture, bound moisture, whose removal takes a few minutes. The third, the widest group, is represented by granular polymer materials whose particle sizes measure a few millimeters. It is characterized by a rather long drying time (a few hours) needed for the moisture diffusion inside the particles to their surface.In a number of features of the course of the mass-transfer process in drying, polymers differ markedly from the classical porous disperse materials. Drying at the stage of polymer production is carried out most frequently upon extraction of the low-molecular compounds in an aqueous medium or upon granulation. In so doing, main...

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Modern Ideas About Diffusion in Polymer Systems

Cited by 21 publications

References 0 publications

Structural dependence of the features of the sorption behavior of cotton cellulose in reacting with water

Structural dependence of the features of the sorption behavior of cotton cellulose in reacting with water

Polymeric fibre composites, basic types, principles of fabrication, and properties. Part 5. Effect of performance effects on polymeric fibre composites; safety/hazardousness characteristics

Kinetics and Apparatus-Technological Arrangement of Convective Drying of Disperse Polymer Materials

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