Ivanovo State Polytechnic University

In the context of the global transition to the circular economy principles, arbolite as a composite material with a high content of secondary organic resources is of particular importance. However, the arbolite widespread usage is hindered by the insufficient study of non-stationary heat and mass transfer processes during the raw blocks drying, which leads to structural defects formation and product quality decrease. The purpose of this work is to develop a mathematical model of moisture transfer in arbolite products for three drying schemes: on the permeable, impermeable, and partially permeable base. Based on the nonlinear diffusion equation for capillary-porous media, an analytical solution of the non-stationary mass conductivity problem was obtained for an uneven initial moisture distribution and second-kind boundary conditions using the Fourier and Kirpichev dimensionless criteria. The microprocess method allowed for the consideration of the mass flows temporal non-stationarity at the computational domain boundaries with an approximation error of no more than 3–5%. The modeling showed that drying on the impermeable base forms the asymmetric moisture profile with a maximum in the bottom zone, increasing the shrinkage defects risk, while the partially permeable flooring scheme reduces the drying time by 25–30% with maintaining structural homogeneity. The proposed model provides a basis for optimizing thermal treatment modes and developing a digital twin for the production of arbolite products.

The quality of dry construction mixtures is determined by their homogeneity, which directly depends on the efficiency of the mixers, among which vibration mixers are used for gentle and intensive mixing of loose materials of various density and dispersion. However, the process is complicated by the phenomenon of particle segregation and the need to take into account the random characteristics of the materials and the parameters of the vibration effect. To describe the mixing process, the authors of the article propose a probabilistic approach using the convective diffusion equation. An effective way to solve this equation is to use the mathematical framework of Markov chain theory, which implements stochastic modeling. The mixing vessel is represented as an array of ideal mixing cells, and the movement of components is governed by a transition probability matrix. The model allows for the prediction of the distribution of components in the mixture, taking into account random factors. Simulation modeling has confirmed the adequacy of the description of the processes of vibro-liquefaction and mixing, including the diffusion and segregation mechanisms. The method for determining the stochastic coefficients of the model has been tested on a virtual simulation setup, a digital computer model of a periodic-action vibrating apparatus. The proposed approach allows for the quantification of the effectiveness of vibratory mixing. The model can be used for the design of technological lines and the control of the quality of construction mixtures. Further research should focus on the consideration of the actual rheological properties of materials.

The aim of the study was to compare the effectiveness of flax shive modification with alkaline solutions of sodium bisulfite and hydroxymethylsulfinate in relation to solving current problems of sorption treatment of wastewater from divalent metal ions and cationic organic compounds. Using methods of selective extraction and photometry of polycarbohydrates, scanning electron microscopy, and low-temperature nitrogen adsorption, changes in the polymer composition of the shives, the state of the xylem cell walls, and the distribution of the specific surface area by pore size were assessed. The elements of the development of the pore system of the substrate are shown with the achievement of a specific surface area of more than 170 m2/G. Using the method of Fourier-transform IR spectroscopy with decomposition of overlapping signals, the functionalization of lignin macromolecules was traced, and the complex occurrence of reactions of reduction, hydrolysis, sulfonation and demethylation under the action of sodium hydroxymethylsulfinate was confirmed, which provide a content of grafted sulfo groups four to five times higher than treatment with a sodium bisulfite solution, with an increase of 6.6–8.6 times in the absorption of phenolic hydroxyls. The sorption properties of native and modified botrytis samples were studied in a steady state with respect to Cu2+ ions, methylene blue dye, and the cationic detergent cetylpyridinium chloride. The most adequate description of the sorption kinetics is provided by the pseudo-second-order kinetic model. The chemisorption indices on native pectin and on transformed lignin in modified samples were differentiated and compared, confirming the significant advantages of replacing the sorption-active biopolymer when treating the shives with a sodium hydroxymethylsulfinate solution.

The dynamics of the polymer composite materials market demonstrate a remarkable rate of adoption of organic fiber-reinforced plastics in major industrial sectors, medicine, sports and household equipment, and household goods. Natural fibers, particularly flax fibers, are of practical interest because of their low cost, environmental friendliness, biodegradability, acceptable mechanical properties, and availability. The expanding use of flax in composite materials imposes new requirements on the quality of flax fiber products. This progress highlights the need for broader studies and deeper knowledge of the possibilities for modifying the physical and mechanical properties of reinforced polymers through fiber pretreatment and selection of treatment conditions with consideration of the required characteristics and operating conditions of composite products. The objective is to analyze recent literature, published mainly over the past three years, addressing the principal issues that hinder the widespread use of flax fiber in the composite industry. Preservation and rational utilization of the natural potential of technical flax fiber in long-fiber forms of reinforcing fillers eliminates the adverse effect of anisotropy in the geometric and mechanical properties of elementary flax fibers. We analyze experience in the use of chemical treatments to overcome the natural porosity and hydrophilicity of flax materials, identify unresolved problems, and search for effective biomimetic approaches to overcoming these difficulties. Information on the structure and functions of the object of biomimicry, the xylem of the flax stem, provides the key to developing moisture-resistant composite materials based on advanced two-stage molding methods using different types of binders.

The article presents a comprehensive analysis of the thermophysical and operational properties of highly porous thermally bonded polyester-based nonwovens to justify their use as an effective functional layer in multifunctional removable and detachable thermal protective coatings for pipeline systems. Laboratory tests of samples of nonwovens with different surface and bulk densities have been carried out. Their effective coefficients of thermal conductivity are determined. An approach to a fibrous material as a continuous porous medium is used to model heat transfer. The heat resistance and parameters of the insulating layer are calculated according to classical methods for multilayer walls. It has been established that nonwoven fabric has elasticity, shape stability, ease of installation, UV resistance and safety.It has been scientifically proven that polyester-based highly porous nonwovens present a highly efficient, technologically advanced and durable alternative to traditional insulating materials (e.g. mineral wool) for creating energy-efficient thermal insulation coatings. The calculated dependences obtained make it possible to optimise the design of thermal insulation structures.