Varvara Evgenievna Rumyantseva

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 concepts of physical and chemical transformations occurring in cement concrete under conditions of microbiological deterioration can be used to control the processes of the destruction of cement concretes in order to ensure the required durability and to predict the service life of products. The study of changes in the structural and phase composition of cement stone made of Portland cement grade CEM I 42.5N in the process of fungal deterioration for 6 months when moistened, as well as a sample of a concrete wall exposed to fungal microorganisms for 20 years, was carried out. Diffractograms of the studied cement stone samples contain a large number of pronounced narrow peaks and indicate a highly crystalline structure of phases with the presence of an X-ray amorphous phase of calcium hydrosilicates and tobermorite gel in the cement stone. Changes in the structure of cement stone under the influence of fungi are confirmed by the data of a derivatographic analysis. A decrease in the content of calcium hydrosilicates and ettringite, as well as other crystalline phases in cement stone, leads to a decrease in compressive strength by about 15% over 6 months of fungal degradation. Similar changes after 20 years of exposure to microorganisms suggest deterioration in the strength characteristics of concrete.

The article discusses the aspects of obtaining red-colored phosphate coatings on the surface of steel at low temperatures. The solution for color phosphating is based on a modified composition based on the chemical «Majef» with sodium nitrite as an accelerator, organic additives of glycerin and Trilon B to improve the quality of precipitated phosphate coatings, and the preparation of OS-20 for emulsifying and wetting the surface. To precipitate red phosphate coatings, it is proposed to introduce copper salt into the composition of the phosphating solution. In the phosphating solution with the addition of copper salt, contact deposition of copper occurs before the formation of a phosphate film on the surface of the steel. This copper layer stains the resulting phosphate coating but does not adhere to the steel surface. To obtain a red phosphate coating of satisfactory quality, it is recommended to first soak the steel product in a modified cold phosphating solution for 15 min, and after the formation of a thin layer of phosphate film on the surface of the steel, introduce copper salt into the solution. Red phosphate coatings are inferior in their protective abilities to unpainted phosphate films; they have greater roughness and high porosity. Although red phosphate coatings have a protective ability, their anticorrosive properties should be improved by additional varnish treatment.

This review summarizes the results of research published in recent decades on the main directions in the functionalization of fibrous materials using surface modification. Methods for thepreliminary activation of the surface of fibrous materials are described, allowing increasing the adhesion of modifiers. The features of the formation of functionalizing coatings on fibrous materials in comparison with other substrates are analyzed. Some specific methods for evaluating the effectiveness of the surface modification inherent in fibrous materials are considered. Particular attention is paid to giving fibrous materials antimicrobial properties, photoactivity, the ability to protect against ultraviolet radiation, and hydrophobicity.

Wood processing soft waste is mainly used in the production of fuel briquettes, irrecoverable (non-recyclable) waste from spinning flax and cotton are incinerated or sent to dump. The development of methods for recycling non-recyclable cellulosic waste through the product manufacturing is relevant, both from the resource conservation perspective, as well as the environmental point of view. The issues of plant waste recycling through the manufacturing of various types of products are widely developed in the Russian and foreign scientific research practice. Researchers deal with the processing of wheat, rice straw, bamboo stalks, and other cellulosic materials. There is a plenty of published information on methods of soft wood waste recycling. However, no research on recycling irrecoverable waste of spinning flax and cotton fibers had been carried out before this paper. We propose to produce thermal insulation boards based on phenol-formaldehyde resol binder using flax and cotton spinning waste and soft wood processing waste. The wet production method used here involves mixing the filler with water, a precipitant solution and a binder. After spinning the material is dried. The paper presents the results of determining the physical and mechanical properties and thermal conductivity coefficient of boards made of plant waste. The research was carried out according to the B-plan of the second order. Adequate regression mathematical models of the dependences of physical and mechanical parameters of the boards on the varying factors of the production process were developed according to the experimental data processing results. Using the developed regression models we built the response surfaces of the composite parameters: the bending strength of the boards, the thickness swelling of the boards after 24 h of exposure in water and the thermal conductivity coefficient. Nomograms of the dependencies of board parameters on the values of varying factors have been developed based on the mathematical models analysis. The nomograms are the basis for the development of practical recommendations for determining the rational values of the parameters of insulation board materials production from irrecoverable waste of spinning flax and cotton and soft wood processing waste.

Снижение температуры отверждения фенолоформальдегидного связующего позволяет уменьшить затраты на производство целлюлозосодержащих материалов: фанеры ФСФ, теплоизоляционных плиточных композитов из растительных отходов. Однако низкотемпературный режим не обеспечивает достаточной степени отверждения фенолоформальдегидного связующего, это приводит к снижению водостойкости материала на основе данного компонента. В условиях низкотемпературного отверждения для уменьшения количества свободных гидроксиметилольных групп в связующем и для формирования более прочно сшитой структуры необходимо введение в фенолоформальдегидное связующее модификатора. В качестве модификатора нами использован пероксид водорода. Результаты подтвердили гипотезу о его влиянии на процесс структурообразования целлюлозосодержащих материалов на фенолоформальдегидном связующем. Модификация фенолоформальдегидного связующего пероксидом водорода позволила в условиях низкотемпературного отверждения (120 °С для фанеры ФСФ, 100 °С для теплоизоляционных композитов из растительных отходов) уменьшить продолжительность отверждения фенольного связующего и прессования фанеры ФСФ, а также улучшить физико-механические показатели фанеры ФСФ и теплоизоляционных композитов из целлюлозосодержащего наполнителя – мягких древесных отходов и невозвратных отходов прядения льна. При введении в связующее добавки 1,0 % Н₂О₂ продолжительность отверждения снижается на 43,6 %; прочность фанеры ФСФ при скалывании увеличивается на 4,4 %, при статическом изгибе – на 4,8 %, разбухание по толщине за 24 ч пребывания в воде снижается на 2 %; прочность теплоизоляционных композитов из целлюлозосодержащих отходов увеличивается на 5,2 %, разбухание по толщине за 24 ч снижается на 4,9 %. Результаты исследования позволяют рекомендовать для повышения прочностных показателей фанеры ФСФ и теплоизоляционных композитов из растительных отходов модифицирующую добавку Н₂О₂ к фенолоформальдегидному связующему в количестве 1,0 % от массы смолы. Для цитирования: Vakhnina T.N., Fedotov A.A., Susoeva I.V., Rumyantseva V.E. Plywood and Thermal Insulation Boards Based on the Modified Phenol Formaldehyde Binder // Изв. вузов. Лесн. журн. 2022. № 1. С. 155–165. DOI: 10.37482/0536-1036-2022-1-155-165

The article presents a method for obtaining white phosphate coatings on steel by cold method. The deposition of protective phosphate coatings was carried out from solutions based on the preparation “Majef”, consisting of manganese and iron phosphates. To obtain phosphate films of white color, it is proposed to introduce zinc and calcium nitrates into phosphating solutions at the rate of 25–30 g/L. The surface of phosphate coatings was studied using the SolverP47-PRO atomic force microscope images, and the average grain size was determined. The structural and phase composition of phosphate coatings was been studied using X-ray diffraction analysis. The protective properties of phosphate coatings were estimated by corrosion rate indicators calculated from corrosion diagrams. Fine-crystalline uniform coatings were obtained from modified phosphating solutions at room temperature on steel. The white color of phosphate coatings is due to the increased content of phosphophyllite, hopeite, and parascholzite in their structural and phase composition. By applying protective phosphate coatings of white color on a steel product, corrosion can be slowed down by 4–4.5 times. However, white phosphate coatings are inferior in protective properties to unpainted coatings. The index of change in the mass of samples with white phosphate coatings because of corrosion is 0.371–0.41 g/(m²·h), and with unpainted coatings is 0.128 g/(m²·h).

В статье рассмотрено действие нитратов, вводимых в цементную смесь на стадии изготовления, на степень повреждения цементного камня бетона жидкими хлоридсодержащими средами. В качестве ингибирующих добавок в цементное тесто вводились нитраты кальция, магния, натрия, цинка и калия, выбор которых обусловлен использованием для ускорения твердения бетона. Исследования проводились на образцах, изготовленных из портландцемента ЦЕМ I 42,5 Н с В/Ц = 0,3 с добавками нитратов 0,5 % от массы цемента. Образцы цементного камня в течение 150 суток подвергались воздействию жидких хлоридсодержащих сред: 2 %-ый раствор MgCl2, раствор HCl с рН = 5 и 0,1 %-ый раствор CaCl2. В ходе проведенных исследований установлено, что ингибиторы не оказывают значительного влияния на скорость растворения кальция из структуры бетона агрессивными средами на начальном этапе коррозии. Добавки оказывают положительное действие на прочность бетона в средах различной степени агрессивности. Нитраты не повышают прочностные характеристики бетона, но способствуют замедлению потери прочности под воздействием жидких хлоридсодержащих сред: в сильно агрессивных - в 1,3 раза; в средне агрессивных - в 1,4 раза; в слабо агрессивных - в 1,6...