In determining the adhesive-self-adhesive interaction of particles of disperse fibre-forming polymers, it is necessary to consider the nature of the forces that cause it, the structural and mechanical properties of the contacting surfaces (roughness and possibility of deformation in the contact zone, which affect the contact area of the polymer particles with the surface; the porosity of the materials; the existence of a gap between contiguous bodies, the radii of curvature of the contacting bodies), as well as the shape of the processed particles.The adhesive-self-adhesive properties (ADSP) that determine the interaction of contiguous condensed bodies are important in modern manufacturing processes. In chemical fibre production technology and in processing fibre-forming polymers, adhesive-self-adhesive properties are important in extruder processes, operation of dust-removal hopper systems, loading and unloading units, drying of polymers, etc. In particular, it is necessary to consider the ADSP of the processed materials, i.e., the effects of sticking to the walls of the unit, caking, etc., which prevent the normal evolution of drying of disperse fibre-forming polymers, to correctly select the dryer and equipment design, especially the feeders and batchers. Disperse fibre-forming polymers were classified to evaluate ADSP, and ADSP was taken into account through the adhesive-cohesive coefficient (K a ), related to the angle of repose of a disperse material [1][2][3][4][5]. The corresponding equation iswhere ƒ is the internal friction coefficient. For practical use, rating of K a , evaluated in points (from 1 to 5) characterizing the degree of friability or stickiness of the material (an ideally friable material, the sand in hourglasses, for example, has K a = 1, and for a sticky, wet, paste, wet clay, for example, K a = 5), is taken into account.At a certain stage in the evolution of manufacturing and production processes, this classification undoubtedly played an important role. However, it includes gradation of the treated materials, primarily by the organoleptic method, and does not reveal the mechanism of the adhesive-self-adhesive interaction of disperse particles and does not allow numerically determining the strength of the adhesive-self-adhesive interaction of contacting bodies. For this reason, the need for a theoretical approach to the numerical evaluation of ADSP of processed materials, including disperse fibre-forming polymers, is increasing.The adhesive-self-adhesive interaction on contact of particles (with the walls of the unit and with each other) is due to forces of different natures [6,7] which are a function of the surface properties of the fibre-forming polymers and the contact area. Self-adhesion, which determines the strength of the interaction between homogeneous particles that cause the particles to stick to the processed materials (caking), can be considered as adhesion of the second kind, which is not manifested on a surface of a different nature (for example, particles sticking to the w...
Different approaches to classifying fibre-forming polymers as objects of drying are examined. A classification based on their sorption and structural characteristics with consideration of the adhesive and autoadhesive properties is presented. Examples of the polymers in the classification groups are reported.Wet disperse polymer materials as objects of drying can be characterized by the process properties (acceptable heating temperature, toxicity, explosion hazard), aggregate state (solids, pastes, suspensions, solutions), and chemical composition. However, these characteristics were insufficient for selecting a rational type of drying unit. Research on classification of polymers was conducted at the Scientific-Research and Design Institute for Chemical Machine Building, based on the characteristic values of the Biot heat-and mass-exchange numbers (Bi, Bi′) and Fourier heat-and mass-exchange numbers (Fo, Fo′), which determine the type of heat-and mass-exchange problem. Based on the values of the Lykov number (Lu), all materials are divided into three types (I Lu = 0.1-0.5; II Lu = 0.02-0.1; III Lu = 0.005-0.02), which in term are divided into five classes based on the values of the Bi, Fo, and Bi′, Fo′ numbers. The corresponding drying equipment is recommended for each class of product [1][2][3][4].A slightly different approach has also been developed [5][6][7], where the problems of interphase heat and mass exchange are divided into external, internal, and balance, and the external and internal problems are delimited by the values of the Bi number (thermal or diffusion) obtained from the boundary conditions. At Bi, Bi′ > 20, the problem is considered to be an internal problem, and when Bi, Bi′ < 0.1, it is an external problem.A drawback of the classification of materials of the thermophysical problem type is that the parameters used as determining (thermal diffusivity a, thermal diffusion coefficient a′, heat transfer coefficient α, and mass transfer coefficient β) are not only a function of the nature of the material but also the treatment method and conditions.The classification based on factors determined by the nature and properties of the material that affect the kinetics of heat-and mass-exchange processes in drying and are not dependent on its parameters is the most rational. Elaboration of this principle, based on classification of the forms of binding of moisture with the material proposed by Rebinder [8] allowed working it out in some detail with respect to chemical materials.In the classification based on the energy principle, all materials are divided into four classes [9]. The first class refers to materials, primarily bulk materials, which are similar to capillary-porous bodies and retain liquid in undetermined ratios by a physicomechanical form of binding. The products in the second class retain adsorption-bound liquid as well as liquid with a physicochemical form of binding. This class of products is subdivided into two subgroups. Materials that retain the liquid by the forces of physical (van de...
The basic elements of a comprehensive analysis of fibre-forming polymers as objects for drying are examined. The basic characteristics and indexes of their effect on the drying process are identified.A classification of materials subject to drying based on a comprehensive analysis of them as objects of drying is necessary for developing highly efficient standard dryers. Such an analysis requires knowledge of the characteristics of the wet materials and methods of determining them.The basic characteristics of wet materials can be divided into five groups [1-4]:sorption-structural (sorptiondesorption isotherms, pore radius distribution curves), responsible for internal diffusion resistance during drying; thermal (thermal conductivity, thermal resistivity, heat capacity), responsible for thermal resistance during drying; hygrothermal (drying thermograms, heat of wetting), which determine the types and energy of binding moisture with the materials; structural-mechanical (adhesive-autoadhesive properties, particle size and shape), which affect selection of the hydrodynamic conditions of drying and design of loading-unloading devices; process (acceptable temperature of heating the material, fire-and explosion-hazard properties), which frequently play the role of limiting parameters in selecting the drying method and equipment design.A comprehensive analysis of the most important characteristics of fibre-forming polymers as objects for drying is conveniently performed on the example of suspension polyvinyl chloride (PVC), which is widely and variously used in the textile, food, electrotechnical, and other industries and in the construction industry. SORPTION AND STRUCTURAL CHARACTERISTICSThe adsorption method based on processing experimentally obtained sorptiondesorption isotherms should be considered the most rational of the existing methods (statistical processing of photomicrographs, mercury porosimetry, electron microscopy, capillary impregnation, etc.) for studying the intrapore structure of materials. This method makes it possible to evaluate not the geometric dimensions of the real pores in the material but the features of the structure of the material as an object of drying with consideration of the types of binding of moisture with the material and effect of changing the pore structure of the material on the mechanism of mass transfer. The experimental isotherms can be used to determine the sorption-structural characteristics of polymer materials (critical pore radius, pore volume, pore size distribution curves).In evaluating the pore structure by the adsorption method, we assumed that the pore shape was cylindrical or conical. The pores of real disperse materials naturally do not have a true cylindrical or conical shape. The characteristics of a real porous material (pore size and volume) obtained by this method are conditional and effective, characterizing the diffusion resistance, which is the pore structure of the material in drying.Moscow State Textile University.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.