Evaluation of the adhesive-self-adhesive properties of disperse fibre-forming polymers

Abstract

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...

Effect of continuous modification of dielectric order in grain

“…In general, bulk grain represents a two-component disperse system, where the air is a disperse medium and separate kernels are disperse particles. In a low-frequency electromagnetic field with a wavelength λ, which significantly exceeds grain kernel dimensions, the dielectric permittivity ε g of such a system can be described by the Reynolds-Hough formula [9][10][11][12][13]:…”

“…where v is the volume fraction of kernels in bulk material, K is the ratio of the mean electric field magnitude inside kernels and field magnitude in the substance volume [9][10][11][12][13] and ε k is the dielectric permittivity of separate kernels. This value is supposed to be averaged out over the whole volume of kernels, as well as the kernel density ρ k .…”

“…It is a simple and good approximation taking into consideration the field of multiple diffraction by all particles at small distances among themselves. Therefore, the expressions obtained in electrostatics for particles of a given shape in a homogeneous electric field [14] are usually applied for this ratio [9][10][11][12][13]. As an example, for a sphere (in the same designations)…”

“…where F and S are the values, which have the sense of coefficients that take into account the shape of kernels and its relative size with respect to the electromagnetic radiation wavelength. For mixtures with high component concentration, like bulk grain, the effective dielectric permittivity ε eff is supposed to be equal to the dielectric permittivity of the whole mixture ε g [10][11][12][13]. In the case of a very great wavelength of radiation, one should expect the size coefficient S being close to 1 and shape indicator F ranging from 0 to 1/2.…”

“…In this case the organic substance of kernels is a disperse medium, but air microcapillaries and formations of absorbed water, that fill the medium, are disperse particles [17]. Commonly, the dielectric permittivity of such systems is described by the Lichtenecker's power law of mixing [9][10][11][12][13]:…”