Лесотехнически Университет

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In modern design, non-standard approach is encouraged and there are many unique design solutions. Here however, another approach will be considered which pertains to certain standards – canons – in design. An individual iconostasis project was developed for the needs of the Orthodox Church, in accordance with all the canons and meeting the requirements of the church board. This project also preserves the national cultural heritage by employing the dying craft of woodcarvers. The iconostasis was designed for the church in the village of Vladimirovo, respecting the canons and the traditions in wood carving. A project for a bishop’s throne was also created.

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Determining the economic efficiency of entire enterprises or of certain processes in the use of resources is a topic of constant relevance. Bulgaria's forest industry is a specific sector that provides employment to the population in all regions of the country. So far, many studies have been done on the economic efficiency of the forestry sector in the country. Human resources in the sector, as well as labor costs, were also investigated. In the present study, a methodology is applied that determines the economic efficiency of employment compared to the salaries paid. In this way, the study determines the optimality in the ratio of employment / wages and answers the question to what extent in each of the regions of the country companies have managed to provide productive jobs with good pay.

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Joints made with staples and gusset plates are widely used in the wood frame construction of various types of furniture, due to the quick and easy production and the availability of simple technology. In this regard, their good knowledge of bending loads would help furniture designers in the design process. The investigation aims to summarize the data from the specialized literature on the values of parameters characterizing the behavior of joints with staples and gusset plates of details in wood frame, as well as to establish the influence of some key factors such as the detailed thickness, the angle between wood details of the joints, thickness and type of material of the gusset plates on their strength and stiffness under bending load.

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When the water content changes, the wood undergoes serious changes in its dimensions and volume. The processes of shrinkage and swelling are mutually reciprocal and associated with large energy changes in the different directions of the stem. These changes are due to the fact that wood is formed from polymers that contain hydroxyl groups. Dimensional changes during drying of raw wood begin when the water content falls below the fibre saturation point. Shrinkage is different for different wood species. Shrinkage is also different in different directions of the wood.

The article examines research conducted on different wood species and at different levels of the chemical composition and anatomical structure of the wood, with the aim of explaining the processes of drying and swelling.

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At present, polycondensation urea-formaldehyde (UF) resins are the most widely used wood gluing adhesives, but their main disadvantage is their low resistance to water and moisture, which causes the subsequent release of formaldehyde emissions from finished products. The aim of the study was to reduce the release of formaldehyde from wood materials by developing and testing new, more effective modifiers that bind formaldehyde or form more stable methylene bonds during polycondensation. Research was focused on the biopolymer collagen and keratin. For this study collagen samples were modified with hardener RODA M 210 (manufacturer Duslo Šaľa) and sulphur additive. From biopolymer keratin, which can be found in hair, feather, wool, nails, hoofs, horns, etc., were prepared samples by thermal heating during for 1 hour at various temperatures from 150°C to 197°C. XPS Ray photoelectron spectroscopy analyse was used to identify changes in their surface chemical structure. The XPS spectrum of keratin samples has been shown to depend on the temperature of their thermal degradation, with the total amount of carbon, nitrogen and sulphur increasing with increasing temperature. For sulphur, the total amount of its reduced form expressed as sulphide also increases, while the total amount of oxygen decreases with increasing temperature. Technical applications have focused on the application of keratin samples to modify mixtures of UF resins to reduce the release of formaldehyde from glued wood-based panels. Formaldehyde emissions were assessed from five-layer plywood according to EN ISO 12460-4. Measured values of extinctions of tested samples confirmed the decrease of formaldehyde emissions for each concentration of collagen and keratin samples in comparison with the reference sample.

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Esters are used in the industry. The rapid increase in demand for esters in the food, cosmetics and pharmaceutical industries makes it mandatory to find alternative ways of synthesis instead of low-yield, expensive, energy-intensive and prolonged reactions.

The production process for the synthesis of esters is based on chemical esterification of fatty acids with alcohol in the presence of inorganic catalysts at high temperatures. However, these chemical processes are non-selective and consume a large amount of energy. In this regard, the current situation of environmental degradation requires the development of efficient and environmentally friendly methods in terms of energy consumption and waste reduction. The synthesis of esters by sonication is also an economical and effective method of performing esterification with broad practical application.

The article presents a review of research and modern engineering solutions based on "green technologies" for the synthesis of esters. Significant advantages of the method of transesterification of methyl caprate with sucrose, leading to esters with potential biological activity such as antifungal and antimicrobial agents, are highlighted.

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The main advantages of the technology for producing Medium Density Fibreboards (MDF) are the reduced requirements for wood raw material, the possibility of fabricating that type of product from sawmill residues and the potential of including other non-wood lignocellulosic raw materials in the composition of the panels.

Such lignocellulose raw materials are residues from agriculture. In our country and worldwide, there are many successful studies for at least partial replacement of wood raw material with agricultural residues. Sunflower plantations are the second largest in our country, which is why they would be a significant source of non-wood lignocellulosic raw material.

Another significant problem in MDF production is the presence of formaldehyde emissions from the panels. One of the main directions for solving this problem is replacing the traditional binders with alternative ones without formaldehyde emissions. These alternative binders should not significantly increase the cost of board production, maintain their performance, and, most importantly, not be hazardous to human health. This binder includes the so-called bio-based binders, of which lignin-based products are the most promising. A typical representative of such an alternative bio-based binder is lignosulfonate (methylated lignin).

That leads to the relevance of a study on the possibility of partially replacing wood raw material with sunflower stalks and reducing the number of synthetic binders used in MDF by adding lignosulfonate in the adhesive system.

As a result of the research on the influence of urea-formaldehyde resin content, lignosulfonate content, and pulp from sunflower stalks on the properties of thin MDF, the main conclusions were deduced, and recommendations were made on the practical use of these alternative raw materials.

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The radio-frequency discharge plasma (RFDP) has been used to improve the wetting and adhesive properties of beech (Fagus Sylvatica L.) wood. The pre-treatment of wood surface using discharge plasma is attractive for various wood applications, mainly because of its high efficiency and low production cost. Moreover, a significant increase of the polar component of wood surface energy after modification by RFDP has been identified, while the polar component of the surface energy is associated with the presence of acid-base forces (electron donor–acceptor bonds). The surface energy of beech wood pre-treated by RFDP during 120 s in air significantly decreased. The shear strength of adhesive joint beech wood-polyurethane adhesive increased non-linearly from 5.2 MPa (native beech wood) up to 7.8 MPa. FTIR-ATR results confirm the increase of the beech wood polarity during RFDP treatment due to growth in –OH polar groups amount. The enhancement of the wood wettability is a necessary condition to promote a better adhesion with a water-based adhesives and coatings, which is currently being studied.

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The barrier discharge plasma (BDP) modification represents an appropriate method for the polarity increasing of the wood surfaces. The surface properties of various wood species (beech, maple, birch) were pre-treated using BDP at atmospheric pressure in air were evaluated by contact angle measurements. The FTIR spectrum of the three tested species of wood is a mixed spectrum (composition) of cellulose and lignin with characteristic peaks corresponding to –OH bonds (with a maximum at about 3400 cm^-1) and fingerprints assigned to the –CO, –COO and –CH₂– bonds typical for polysaccharides.

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In the conditions of a global economy and an explosion of digital and online technologies, educational institutions must respond adequately by producing well-trained professionals with both professional and digital competencies. The digital competences of each person are an indicator of his successful realization in the professional sphere. The report provides an overview of training at the Forestry University in Sofia, Bulgaria. To assess the extent to which second-year Engineering Design (Interior and Furniture Design) students possess the necessary skills and digital professional competencies when working with unfamiliar online software, they were given the task of creating a 3D design of an apartment consisting of a living room with kitchenette and bathroom using Roomstyler's 3D planning tool. In the process of work, the student's digital knowledge and skills are evaluated. Participants in the assignment were also asked to complete an anonymous online survey to examine their satisfaction and attitude to work with novel software.