Съдържание

Vol. XIV, Issue 2 2025

STUDY OF THE DEPENDENCIES BETWEEN THE ANATOMICAL STRUCTURE AND PROPERTIES OF DOUGLAS WOOD

Автори: Martina Todorova

Резюме

The wood of coniferous tree species is mainly made up of tracheids. Abstractly viewed in cross-section, these tracheids can be considered as elements of some structure. In early wood, tracheids are larger in size and have thinner walls. In late wood, they are smaller in size and thicker cell walls. All this implies an uneven structure. 
The paper examines the distribution of tracheids within the annual rings. The Douglas wood is examined in a cross-section. The number of cells in the early and late wood is measured. Tangential stripes of tracheids have been examined. These stripes are arranged in a radial sequence, gradually moving away from the axis of the stem. Dependencies between the anatomical elements in the areas of early and late wood with different widths of the growth rings are sought. A correlation analysis has been made between the structure and some physical properties of the wood. The coefficient of unevenness is determined. 

Ключови думи: Douglas, anatomical structure, unevenness coefficient, shrinkage, swelling, density

EN Version

OPTIMIZATION OF THE CNC MILLING PROCESS VIA MODIFYING SOME PARAMETERS OF THE CUTTING MODE WHEN PROCESSING QUERCUS ROBUR L.

Автори: Alexander Doichinov

Резюме

This article examines certain cutting regime parameters that influence the quality of milled surfaces of oak wood (Quercus robur L.) parts processed on a CNC woodworking milling-drilling center. The present study aims to determine the combined effect of key cutting parameters such as spindle speed (n), feed rate (Vf) and depth of cut (h). The evaluation of the milled surfaces was conducted based on the roughness parameter Rz, with measurements taken using an electronic profilometer model Surftest SJ-210 (Mitutoyo, Japan). As a result of the conducted experiments, graphical dependencies were derived, illustrating the degree of influence of the studied factors on the surface roughness of the machined parts. 

Ключови думи: Surface quality, oak, milling, CNC machines, spindle speed, feed rate, depth of cut

EN Version

FROM FIELD RESIDUE TO BIO-BASED PANELS: INDUSTRIAL HEMP SHIVES IN PARTICLEBOARD AND FIBREBOARD PRODUCTION – A COMPREHENSIVE REVIEW

Автори: Viktor Savov, Georgi Ivanov

Резюме

Industrial hemp cultivation generates large quantities of stems and shives (hurd) that remain underutilised despite their attractive characteristics as a renewable lignocellulosic resource. In recent years, hemp shives have been increasingly explored as a partial or full substitute for wood particles and fibres in particleboards, medium-density fibreboards (MDF) and related panel products. This review synthesises the current state of knowledge on the use of industrial hemp stems and shives in bio-based wood panels, covering raw material properties, pre-treatments, panel manufacturing parameters and resulting performance. Particular attention is given to the influence of particle granulometry, density profile, adhesive type (UF, MF including UF/MF blends, pMDI and emerging bio-based binders) and processing conditions on mechanical properties, dimensional stability, thermal and hygric behaviour. The review compares hemp-based and conventional wood-based panels in terms of bending strength, internal bond, screw withdrawal resistance, water absorption and thickness swelling, as well as thermal conductivity and moisture buffering capacity relevant to building applications. Environmental and techno-economic aspects, including resource availability, lightweight design and potential for circular construction, are also briefly discussed. Finally, the paper identifies critical research gaps related to long-term durability, fire performance, interface optimisation between hemp particles and novel binders, upscaling from laboratory to industrial production, and standardisation of testing protocols for hemp-based panels. These gaps are used to outline future research directions and innovation pathways needed to fully valorise industrial hemp stems and shives as a reliable feedstock for next-generation bio-based particleboards and fibreboards. 

Ключови думи: industrial hemp; hemp shives; bio-based panels; particleboard; fibreboard; MDF; lignocellulosic composites; moisture buffering; thermal insulation

EN Version

PROPERTIES OF THREE-LAYER ASPEN (POPULUS TREMULA L.) PARTICLEBOARDS WITH LAYERED INCLUSION OF TURKEY OAK (QUERCUS CERRIS L.) PARTICLES

Автори: Rosen Grigorov

Резюме

The production of particleboard is influenced by various technological and technical factors that affect both quality and economic performance. Among these, board density is particularly important-higher density enhances mechanical properties but increases production costs. Therefore, medium-density particleboards are typically manufactured from softwood species, whose low density provides favorable strength characteristics. In contrast, hardwood species often reduce mechanical performance, limiting their proportion in the mixture to 20–30%. However, in the Republic of Bulgaria, 32% of forested areas are covered with oak species, including 9% with turkey oak (Quercus cerris L.), making its exclusion from production impractical. This study explores the potential for greater use of turkey oak in three-layer particleboards made from aspen. Layers of turkey oak particles were added to the face layers at 10%, 20% and 30%. In two additional panels, turkey oak was included in the core layer at 10% and 20%, resulting in a total content of 40% and 50%. The panels were manufactured under laboratory conditions at 180°C, 2.3 MPa and 330 seconds, with a target density of 640 kg·m⁻³. The results showed consistently high values of modulus of rupture and modulus of elasticity at all levels of turkey oak inclusion. 

Ключови думи: three-layer particleboards; separate layers; turkey oak particles; aspen; physical and mechanical properties

EN Version

INVESTIGATION OF ATMOSPHERE SUSTAINABILITY OF PROTECTIVE- DECORATIVE COATINGS

Автори: Vladimir Mihailov, Desislava Hristodorova

Резюме

The strength of bonding between protective-decorative coatings and the surface of wood materials, plays a major role in the durability of the wooden products, exposed to atmospheric conditions in the open area. This article analyzes the effects, that has the protective-decorative coatings, like durability of the natural oils and synthetic lacquer products used for protective layer of wood and the surface condition, after stay under the environmental impacts. To achieve this aim, an experimental stand was built according to standard EN 350:2016 and mounted in the territory of Yundola, Velingrad municipality. By the determined 12 months under review time period it is followed the change of surface of different types of natural oils and synthetic lacquer products used for protection of wood exposed to open area. The change in color is reflected, the damage to the surface of the used protective-decorative coatings, the mold formation, and the moisture resistance of the protective coatings. The results are analyzed and graphically presented. 

Ключови думи: atmosphere sustainability, lacquer gloss, wood protection, coatings, oils, aging

EN Version

PRESSURE EFFECTS ON POLYVINYL ACETATE JOINTS IN HEMP-SHIVE PARTICLEBOARDS – A COMPARATIVE STUDY

Автори: Desislava Hristodorova, Viktor Savov, Vladimir Mihailov, Galina Kutova

Резюме

This work presents one of the first systematic, ISO-aligned assessments of PVAc-bonded joints in laboratory-made hemp shive particleboards, benchmarked directly against industrial P2 particleboard under identical processing conditions (adhesive type and spread, surface preparation, and three nominal pressing pressures). By holding all bonding variables constant and varying only the substrate and pressure, the study isolates the effect of the substrate on shear strength. It offers actionable data for furniture construction with emergent hemp-based panels. 
The key achievement is a consistent approximately 45% increase in PVAc shear strength for hemp shive panels across the tested pressures, with mean values rising from 1.23 to 1.53 N/mm², compared to 0.68 to 0.83 N/mm² for P2 (ISO 6237:2017). This result demonstrates that hemp shive particleboards can deliver markedly stronger adhesive joints without changing adhesive type or application rate, directly supporting their use as a higher-performance alternative in PVAc-bonded furniture assemblies. The observed variability at the highest pressure level highlights a practical optimization window for balancing pressure with adhesive spread and substrate permeability. 

Ключови думи: hemp-shive particleboards; shear strength; furniture joints; PVAc bonding; ISO 6237

EN Version

COMPOSITE PACKAGING AND THE ROLE OF ECO-DESIGN IN THEIR RECYCLING

Автори: Alexsandra Kostadinova-Slaveva, Еkaterina Todorova

Резюме

The beginning of composite packaging was laid in 1930, when ordinary paper rubbed with paraffin was used for packaging liquid and other “wet” products. According to the modern understanding of “composite packaging”, it is made of different materials that cannot be separated manually and none of them represents more than 95% of the weight of the package. Since composite packaging consists of many different materials, it cannot be recycled directly without being separated, which creates several difficulties and often leads to landfilling or incineration. In this regard, to improve the possibility of implementing a circular economy for composite packaging waste, innovative solutions are required for the separation and recovery of recyclable materials, but above all innovations in their design and eco-design, which would facilitate their subsequent treatment and recycling. 

Ключови думи: composite packaging, eco-design, circular economy, recovery

EN Version

TEMPORARY COMMERCIAL SPACES IN SOFIA: TYPES AND POTENTIAL

Автори: Carmella Lombardi

Резюме

This article examines the phenomenon of temporary commercial spaces as a dynamic and increasingly popular format in the modern urban environment. The introduction presents the essence of these spaces, their main characteristics and functions, drawing on existing research and perspectives of leading authors in the field. Based on the literature review, the article offers an author's classification of the types of temporary commercial spaces, consistent with their functions, duration and form of implementation. 
The empirical part includes an analysis of two different types of bazaars in Sofia, studied through personal observations and interviews with organizers and participants.  
In conclusion, possible improvements for the future development of temporary commercial spaces in Sofia are formulated. 

Ключови думи: temporary commercial spaces, bazaar, pop-up, Sofia

EN Version

VIDEOCLIP MARATHONS – A PROVEN EDUCATIONAL APPROACH IN TEACHING "THEORY OF COMPOSITION” AT THE UNIVERSITY OF FORESTRY

Автори: Stela Tasheva

Резюме

The study examines young designers’ results in a specific task involving production of themed short “video clips”. It follows works of third-year students, majoring in the field of “Engineering design” in the Faculty of Forest Industry. The clip demonstration (on an internally organized marathon) has been held annually for more than a decade in the Sofia University of Forestry. 
The aim of the study is to reveal the benefit of the event as a learning tool and to trace the evolution of the clips, such as storylines and graphic tools applied by the students. The used research methods include selection of key examples, comparative analysis and classification. The expected results are in the field of design and art theory, contemporary design and architecture.

Ключови думи: Engineering design” students, composition, training, video clip, short movie,Department Interior and furniture design

EN Version

TRANSFORMING TRADITIONAL TEACHING METHODS THROUGH ARTIFICIAL INTELLIGENCE TECHNOLOGIES

Автори: Melina Neykova, Adelina Ivanova

Резюме

Today's educational institutions are facing constant challenges related to the avalanche of developments in the process of integrating digitalization technologies and forming "smart" e-learning environments, including those based on artificial intelligence (AI). The advent of AI technologies has had a profound impact on educational processes, precipitating a paradigm shift in conventional teaching methodologies. In this context, AI can be regarded as a valuable instrument capable of executing a multitude of operations intrinsic to university activities. 
Unfortunately, the dynamism of this process is very high, and the speed at which AI platforms have been generated has been increasing rapidly in recent years, while educational institutions still lack the practices, skills and readiness to operate and implement the various AI tools successfully. In this regard, the presented study provides an overview and comparative analysis of various specialized online AI-platforms that are available online and can be used both by teachers in their professional and pedagogical activities and by students, supporting the process of choosing and integrating AI-based technologies in teaching and educational activities. 

Ключови думи: Higher Education, Digital Education, Artificial Intelligence (AI), Information Technologies (IT), Digitalization, Digital Transformation

EN Version