Лесотехнически Университет

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Thermally modified wood is a unique natural material with special properties, that have been received after heat treatment of natural wood. All these properties are the result of changes in the chemical composition and structure of the wood. The paper aims to identify gaps in the structure of natural and thermally modified wood. The changes in the structure of the wood after its heat treatment were discussed.

We examined the specimens of pine, spruce, summer oak, hornbeam and birch wood. Microscopic preparations were made from the wood specimens before and after heat treatment. The three main sections of wood at different zoom were observed. There have been noticed differences in the construction of anatomical elements.

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Many conditions need to be met for producing quality musical instruments. One of them is to have a consistency of structure and properties of wood. It is often difficult, especially for instruments in large dimensions. It is required to be cut large diameter trees.

The article examines variations in the density, compressive strength and flexural strength and modulus of elasticity in the radius of the stem of the spruce. A section for the manufacture of musical instruments is studied in the factory „Kremona AD” – Kazanluk. A section has stayed in dry and heated place more than 12 years. The differences in the properties of the test pieces of juvenile, central and peripheral wood have been established.

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The oaks are one of the most important species for our Dendroflora. This study of hardness complements the knowledge of the properties of their wood. Wood is a non-homogeneous material and its properties differ in different parts of the stem. Hardness is a property that is directly related to the construction of the wood. That is why knowledge of this property will be an important step towards more rational use of oak wood.

The work presents data on the hardness of the wood of pedunculate oak (summer) and sessile oak (winter oak). The influence of the habitat and the radius of the stem is examined. In order to compare the individual samples, the qualitative hardness coefficient was determined.

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The density is assumed to be a complex parameter of quality wood. On the one hand, it depends on the anatomical structure of the wood, the other largely determine all other mechanical properties and influence the processing and use of wood.

Work considered the density of oak wood, sourced from different habitats in the country and its distribution in the radius of the stem. The influence of age, the width of the annual ring, habitat and altitude.

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The distribution of the vessels in wood is largely genetically staked for each species. Many of the features available are permanent and unique to each species. The size and density of the vessels depend to a large extent by the site conditions and the location in stem.

The article examines the distribution of the vessels of some tropical tree species. The vessels were examined in cross-section. From the next few cells are formed the figures such as loops. Attitude lap / area (V/S) of these figures is discussed.

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Betula pendula Roth has a wide natural area stretching from the forest to steppe zones in the Ukraine. Understanding the term „wood quality“ was focused on the industrial importance of the end-use of the wood product. Small-sized timbers of Silver birch growing in the Carpathian Agroforestry were mostly used for the chemical industry. In order to produce the valuable birch timbers was proposed a pruning at the stand height exceeding about 8-10 m with the pruning height of 5–6 m using clippers. The basic wood density varied from 419 till          631 kg∙m^-3 with the mean value of 463–509 kg∙m^-3. The coefficient of variation was almost equal to accepted reference value, because of many wood specimens from this birch stand were characterized by false core. The variables of wood shrinkage were ranged from 7.9 till 9.9% and from 4.6 till 6.6% in the tangential and radial sections respectively. The accuracy values of research results were under accepted reference value of 3.0%. It was discovered that the false core mostly reduced the wood properties of Silver birch. Two groups regards basic wood density less 499 kg∙m^-3 with wood defects „false core“ and more 500 kg∙m^-3 without any wood discoloration were recommended for the industrial timber scaling and the weight method of timber volume measuring.

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Wood is a product of woody plants, formed by a complex of tissues - conductive, mechanical, reserve and secretory. However, it is not just a mechanical mixture of chemical compounds, but a complex biological and physico-chemical system composed of polymers, monomers, made up of cell walls and cell cavities (lumens). The knowledge of its structure allows the tree species to be determined, the conditions under which it is formed, as well as its behavior under different loads.

The paper examines the variation of the quantitative indicators of individual tissues and the possibility of using it to classify individual species.

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The structure of wood can be examined at several qualitatively different levels of consideration (macro, meso, micro and nano). Each of these levels can be considered as a separate, single and relatively independent subsystem in the wood structure. They are determined by the characteristics of the species, the ecology of the global, regional and local habitats. Each of these levels requires a separate, more precise and comprehensive classification. If the quantities and distribution of the main tissues are known, the tree species can be grouped in groups of construction and conclusions can be made about its physical and mechanical properties.

This work examines the possibility for a more in-depth formal-analytical description of the individual tree species and a theoretical representation of wood structure that more adequately reflects its characteristic features.

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In recent years, more and more systems for computer recognition of tree species are entering, which show good results in solving a certain group of problems. Some of them have already proven themselves in solving such tasks as quality control of wood materials. Studies also show that the classifications of tree species used so far do not allow to solve more general problems of structural wood science. The approaches, methods and means used in computer recognition for modeling the structure of the wood presuppose such a classification of the tree species, which should be based on a more general view on the structure of the wood in comparison with the methods used so far. This would allow to study and describe in a single formalized classification scheme all the anatomical elements that are observed with the corresponding increase in the samples of tree species. In addition, it is necessary to specify the term "texture", applicable in the computer structural anatomy of wood for the purposes of using the methods of computer vision.

The paper discusses the initial results of research related to the application of the requirements of computer modeling in solving some problems of wood anatomy. In particular, recommendations have been made for the quantitative characteristics of the study region in the wood samples and for the description of the anatomical elements making up the wood that will fall into this region and can be examined with sufficient accuracy.

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The construction of wood can be represented by both quantitative and qualitative characteristics. Each anatomical element has quantitative indicators. These are the size of the cell gap (lumen), the thickness of the cell wall, the diameter and the length of the cell. The arrangement of these cells relative to each other is very characteristic of each species and varies relatively slightly. It is a qualitative characteristic that can also be represented by quantitative methods. Although the structure of wood varies under the influence of environmental conditions and location in the stem, the most characteristic structures remain relatively constant.

The article considers the possibility of using a formal-analytical description of the wood structure, applying abstract measurement methods. The obtained data are identical and can be processed by different mathematical methods. The proposed abstract methods give different classifications of the wood structure. Thus, a tree species in one method falls into one group with some species, in another – with others.

Резюме

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.