Growing trees have the following components: roots, trunk, branches, leaves. The root system of trees acts as a supplier of moisture and nutrients from the soil through the trunk and branches to the leaves. In addition, the roots hold the trees upright. Through the branches, moisture enters the leaves, in which the process of photosynthesis takes place - the conversion of the radiant energy of the sun into the energy of chemical bonds of organic substances with absorption from the air carbon dioxide and release of oxygen. It is no coincidence that forests are called the lungs of the planet. The products of photosynthesis from the leaves are transferred along the branches to the rest of the trees - the trunk and roots. Thus, the branches act as channels through which the exchange of substances takes place between the leaves and the rest of the tree.

Coniferous trees - pine, cedar, spruce, larch - have narrow leaves - needles, and hardwoods - wide leaves. As a rule, deciduous trees grow mainly in temperate and southern latitudes, while conifers grow in northern ones.

Depending on the species and climatic conditions of growth, trees have different heights and trunk diameters. However, they fall into three categories. The first includes trees of the first magnitude, which reach a height of 20 m or more. These are spruce, cedar, larch, pine, birch, aspen, linden, oak, ash, maple, etc.

In the tropics and subtropics, the height of individual trees reaches 100 m or more. The second category includes trees of the second magnitude, having a height of 10–20 m. These are, in particular, willow, alder, mountain ash, etc. The third category is trees of the third magnitude, whose height is 7–10 m. These are apple, cherry, juniper, etc. .

The diameter of the tree trunk varies mainly from 6 to 100 cm or more and depends on the species, age of the trees and climatic conditions of growth. In some cases, the diameter of a tree trunk can exceed 3 m - in oak, poplar and some other species.

Wood is obtained by cutting tree trunks after removing branches. In this case, the yield of wood is 90 or more percent of the volume of the tree trunk. At the initial stage of wood processing, a transverse, or end, section of the trunk is made.

On the cross section, the following are distinguished: the bark covering the trunk from the outside and consisting of the outer layer - the crust and the inner layer - the bast cambium - a thin layer invisible to the eye between the bark and the wood (during the growth of trees, the living cells of the cambium divide, and due to this the tree grows in thickness); sapwood - living zone of wood; the core, which is adjacent to the core of the trunk and is a dead central zone that does not participate in physiological processes; the core, located in the center and representing a loose tissue with a diameter of 2–5 mm or more (depending on the species and age of the tree).

In the timber industry in Russia, the main object of harvesting is tree trunks, and branches and branches are burned or used for firewood. In Canada, Sweden and Finland, all components of trees are recycled, so the loss of wood there is minimal, and the yield of paper, cardboard and other things is maximum.

2. Macroscopic structure of wood

With a cross section of a tree trunk, you can establish the main macroscopic features: sapwood, heartwood, annual layers, medullary rays, vessels, resin canals and medullary repetitions.

In young trees of all species, wood consists only of sapwood. Then, as they grow, the living elements around the core die off, and the moisture-conducting paths become clogged, and extractive substances gradually accumulate in them - resins, tannins, dyes. Some trees - pine, oak, apple and others -

the central zone of the trunk acquires a dark color. Such trees are called sound. In other trees, the color of the central zone and sapwood of the trunk is the same. They're called non-core.

Kernelless trees are divided into two groups: ripe-woody(linden, fir, beech, spruce), in which the humidity in the central part of the trunk is less than in the peripheral, and sapwood, in which the moisture content is the same across the cross section of the trunk (birch, maple, chestnut, etc.). Moreover, the mass of sapwood decreases from the top to the butt, as well as with an increase in the age of the tree.

The age of trees can be determined by the number of annual layers that grow one per year. These layers are clearly visible on the cross section of the trunk. They are concentric layers around the core. Moreover, each annual ring consists of an inner and outer layer. The inner layer is formed in spring and early summer. It is called early wood. The outer layer is formed by the end of summer. Early wood has a lower density than late wood and is lighter in color. The width of the annual layers depends on a number of reasons: firstly, on the weather conditions during the growing season; secondly, on the growing conditions of the tree; thirdly, from the breed.

On a cross section of trees, you can see the core rays extending from the center of the trunk to the bark. In hardwoods, they occupy up to 15% of the volume of wood, in conifers - 5-6%, and the more their number, the worse mechanical properties wood. The width of the core rays ranges from 0.005 to 1.0 mm, depending on the tree species. Softwood wood differs from hardwood wood in that it contains cells that produce and store resin. These cells are grouped into horizontal and vertical resin ducts. The length of the vertical passages ranges from 10–80 cm with a diameter of about 0.1 mm, and the horizontal resin passages are thinner, but there are a lot of them - up to 300 pieces per 1 cm 2.

Hardwood has vessels in the form of a system of cells for the transfer of water and minerals dissolved in it from the roots to the leaves. Vessels have the form of tubes with an average length of 10 cm and a diameter of 0.02-0.5 mm, and in trees of some species they are concentrated in the early zones of the annual layers. They are called annular.

In trees of other species, the vessels are distributed over all annual layers. These trees are called diffuse-vascular.

3. Microscopic structure of coniferous and hardwood wood

Coniferous wood has a certain microstructure, which can be established using microscopes, as well as chemical and physical research methods. Coniferous wood differs from hardwood in a relatively regular structure and simplicity. The structure of coniferous wood includes the so-called early and late tracheids.

As established by research, early tracheids function as conductors of water with minerals dissolved in it, which comes from the roots of the tree.

Tracheids are in the form of strongly elongated fibers with co-cut ends. Studies have shown that in a growing tree, only the last annual layer contains living tracheids, and the rest are dead elements.

As a result of the research, it was revealed that the core rays are formed by parenchymal cells, along which reserve nutrients and their solutions move across the trunk.

The same parenchymal cells are involved in the formation of vertical and horizontal resin ducts. Vertical resin canals in coniferous wood, found in the late zone of the annual layer, are formed by three layers of living and dead cells. Horizontal resin ducts were found in the medullary rays.

According to the research results of professor V. E. Vikhrova, Pine wood has the following microscopic structure:

1) cross section;

2) radial incision;

3) tangential cut.

Rice. 1. Sections of a tree trunk: P - transverse, R - radial, T - tangential

As established by research, the microstructure of hardwood compared to coniferous wood has a more complex structure.

In hardwood, vascular and fibrous tracheids serve as conductors of water with minerals dissolved in it. The same function is performed by other vessels of wood. The mechanical function is performed by libriform fibers and fibrous tracheids. These vessels are in the form of long vertical tubes, consisting of separate cells with wide cavities and thin walls, and the vessels occupy from 12 to 55% of the total volume of hardwood. The largest part of the volume of hardwood is made up of libriform fibers as the main mechanical fabric.

Libriform fibers are elongated cells with pointed ends, narrow cavities and powerful walls with slit-like pores. Fibrous tracheids, like libriform fibers, have thick walls and small cavities. In addition, it was found that the core rays of deciduous wood unite the main part of parenchymal cells, and the volume of these rays can reach 28–32% (this figure applies to oak).

4. Chemical composition of wood

The chemical composition of wood depends partly on its condition. The wood of freshly cut trees contains a lot of water. But in a completely dry state, wood consists of organic substances, and the inorganic part is only from 0.2 to 1.7%. During the combustion of wood, the inorganic part remains in the form of ash, which contains potassium, sodium, magnesium, calcium and, in small quantities, phosphorus and other elements.

The organic part of wood of all species has approximately the same elemental composition. Absolutely dry wood contains on average 49-50% carbon, 43-44% oxygen, about 6% hydrogen and 0.1-0.3% nitrogen. Lignin, cellulose, hemicellulose, extractive substances - resin, gum, fats, tannins, pectins and others - make up the organic part of wood. Hemicellulose contains pentosans and genxosans. Coniferous species have more cellulose in the organic part, while deciduous species have more pentosans. Cellulose is the main component of the cell walls of plants, and it also provides the mechanical strength and elasticity of plant tissues. As a chemical compound, cellulose is a polyhydric alcohol. When cellulose is treated with acids, it is hydrolyzed with the formation of ethers and esters, which are used for the production of films, varnishes, plastics, etc. In addition, during the hydrolysis of cellulose, sugars are formed, from which ethyl alcohol is obtained by fermentation. Wood pulp is a valuable raw material for paper production. Another component of the organic part of wood, hemicellulose, is polysaccharides of higher plants that are part of the cell wall. In the process of processing cellulose, lignin is obtained - an amorphous polymer substance of a yellow-brown color. The largest amount of lignin - up to 50% - is formed during the processing of coniferous wood, and its yield from hardwood is 20–30%.

Very valuable products are obtained during the pyrolysis of wood - dry distillation without air at temperatures up to 550 ° C - charcoal, liquid and gaseous products. Charcoal is used in the smelting of non-ferrous metals, in the production of electrodes, medicine, as a sorbent for cleaning Wastewater, industrial waste and for other purposes. Such valuable products as gasoline antioxidant, antiseptics - creosote, phenols for the production of plastics, etc. are obtained from the liquid.

In the organic part of coniferous wood there are resins that contain terpenes and resin acids. Terpenes are the main raw material for the production of turpentine. The resin secreted by the coniferous tree serves as a raw material for the production of rosin.

In the process of wood processing, extractive substances are obtained, including tannins, used for leather dressing - tanning. The main part of tannins are tannins - derivatives of polyhydric phenols, which, when processed, interact with their protein substances and form insoluble compounds. As a result, the skins acquire elasticity, resistance to decay and do not swell in water.

A characteristic feature of hardwood is the presence of vessels, or pores, that run along the trunk and are visible in the cross section in the form of holes.

In oak and ash, large vessels are located in a ring in the early part of the annual layer (annular vascular). In birch, aspen, beech and some other species, the vessels are scattered throughout the annual layer, and the boundary between the annual layers is difficult to distinguish (scattered-vascular).

In the central part of the trunks of oak, elm, poplar, ash and some others there is heartwood. It consists of dead cells and is dark in color. The core in hardwoods is formed when its vessels are overgrown with special parenchymal cells - tills, which clog the water supply system. However, the tills themselves are highly saturated with moisture, so the freshly cut wood of these species does not have a noticeable difference in the moisture content of the core and sapwood. In beech and linden, the vessels in the central part also overgrow, but its color remains unchanged (ripe woody species). The formation of the core and mature wood is accompanied by the simultaneous impregnation of the cells of the central part of the trunk with complex organic compounds. In heartwood, these substances are oxidized by air and darken, while in spelowood they remain colorless. When the vessels are clogged, the core and mature wood become impermeable to water and air, therefore, in some cases, timber prepared from this part of the trunk noticeably increases resistance to decay.

Birch, aspen, alder, hornbeam and maple do not clog vessels, and they consist only of sapwood.

Disproportionate development of vessels, the cross-sectional area of ​​​​which can be a hundred times larger cross section other elements of wood, displaces neighboring cells. Therefore, hardwood does not have the correct structure that is characteristic of conifers. The composition of hardwood includes: conductive elements - vessels and tracheids; mechanical - libriform fibers; storage core rays and woody parenchyma. These basic elements have a number of transitional forms that greatly complicate the structure of hardwoods.

Vessels are typical water-carrying elements of hardwoods and consist of a vertical row of short cells, the partitions of which are dissolved. The diameter of the vessels sometimes reaches 0.5 mm, and the length varies from 5 to 20 cm.

Vessels are connected to adjacent elements by bordered, semi-circumscribed or simple pores.

Hardwood tracheids are much smaller than conifers and are of two types - vascular and fibrous. They represent transitional forms from vessels to fibers. Vascular tracheids perform conductive functions, and fibrous - mechanical.

Libriform is the main part of hardwood. Libriform fibers, in accordance with the mechanical function they perform, have a spindle shape, thick walls and small strips. The length of the fibers ranges from 0.3 to 2 mm, and the diameter is 0.02-0.05 mm. The weight and strength of the wood depend on the amount of libriform and the wall thickness of the fibers.

Parenchymal cells in hardwoods form primarily core rays, which are much more developed than in conifers. Depending on the tree species, the rays have width and height from one to several tens of rows of cells.

Along with the core rays, the storage functions are performed by the so-called wood parenchyma, which is almost absent in conifers. Its cells are collected in vertical rows, located on the border of annual rings near the vessels or scattered over the annual layer.

The trunk wood in a growing tree performs three main functions: conductive, mechanical, and storage. Therefore, in the wood of coniferous and deciduous species, one can find anatomical elements that perform the listed functions.

The structure of coniferous wood

Coniferous wood has a fairly simple and monotonous structure. This can be easily seen from the scheme of the structure of pine wood, shown in Fig. 12. The composition of coniferous wood includes tracheids and parenchymal cells. The conducting function is performed by early tracheids, the mechanical function is performed by late tracheids, and the storage function is performed by parenchymal cells. tracheids represent co6 cells elongated in length with rounded or oblique ends; they occupy almost the entire volume of wood. In the early zone of the annual layer, large-cavity thin-walled cells are visible, most often with a square cross section - these are early tracheids, formed at the beginning of the growing season; early tracheids on their radial walls, mainly at the rounded ends, have bordered pores. On the radial section, the bordered pore has the form of two concentric circles, between which the third one sometimes shines through. At the end of the growing season, thick-walled narrow-cavity late tracheids. On the transverse section, they look like rectangles flattened in the radial direction. Late tracheids have sparsely spaced slit-like fringed pores found on radial and tangential walls. The zone of early tracheids within one annual layer gradually passes into the zone of late tracheids. A clear boundary is observed between the late wood of one annual layer and the early wood of another layer (the boundary of annual layers).

Parenchymal cells in the wood of all coniferous species, they are part of the core rays and, in some species, are surrounded by resin passages. core lines in conifers with the help of a microscope, they are found on all three sections. The core rays are visible on the transverse section as strips consisting of cells located perpendicular to the boundary of the annual layer. Radial section shows replacement rays and rather high stripes crossing tracheids at right angles. On a tangential section, the medullary rays are represented by chains of cells located along the tracheids. resin passages. In the wood of some coniferous species (pine, cedar, larch, spruce), more or less large vertical channels filled with resin - resin tunnels - are most often found in the late zone of the annual layer. Resin ducts are composed of three layers of cells: an inner layer of lining epithelial cells, dead cells filled with air, and cells of the (living) accompanying parenchyma. Vertical resin ducts on longitudinal sections look like a long canal parallel to the tracheids with adjoining parenchymal cells. In addition to the vertical ones, there are horizontal resin ducts, which consist only of the epithelium and a layer of dead cells and are located in multi-row (in width) medullary rays. Horizontal resin ducts can most often be observed in tangential sections.

Rice. 12. Scheme of the structure of pine wood: 1-year layer; 2- early tracheids; 3- late tracheids; 4- core beam; 5 - vertical resin passage; 6 - bordered pores; 7-beam tracheids.

The structure of hardwood

In hardwoods, which differ from conifers in a more complex structure, each function has two, and sometimes more, anatomical elements.

Conductive function in hardwoods perform vessels. Depending on the nature of the location of the vessels along the width of the annual layer, breeds with ring-vascular and diffuse-vascular wood are distinguished.

Fig.13. The scheme of the structure of oak wood. 1-year layer: 2'-large vessels; 2"-small vessels; 3- libriform fibers: 4'- narrow core beam; 4” - wide heart-shaped beam

Rice. 14. Scheme of the structure of birch wood: 1-year layers; 2- vessels; 3- libriform fibers; 4- core beams

Schemes of the microscopic structure of typical representatives of ring-vascular (oak) and scattered-vascular (birch) species are shown in fig. 13 and 14. Large vessels in ring-vascular breeds are located in the early zone in one or two rows. Small vessels are located in the late zone, they are collected in groups that create one or another characteristic pattern.

In scattered vascular rocks, the vessels are most often small and distributed evenly throughout the annual layer, sometimes they are collected in groups of two or more vessels.

Vessels are vertical tubes made up of segments of thin-walled wide-cavity cells. The lower and upper walls of these cells partially or completely dissolve. In this case, simple (with one or two holes) or stair perforations(number of slotted holes). A segment with a simple perforation is characteristic of large oak wood vessels. The perforation plate in this case is located almost perpendicular to the walls of the vessel. Staircase perforations are commonly found in birch and alder wood vessels.

Vessels communicate with each other through rounded or multifaceted bordered pores in the walls. The cavities of the vessel are sometimes clogged with tills - outgrowths of parenchymal cells. In addition to vessels in some species (for example, in oak), the conductive function is also performed vascular tracheids, representing a transitional element between typical tracheids and vascular segments.

Libriform fibers make up the bulk of hardwood and perform a mechanical function. Libriform fibers are highly elongated, narrow-striated, thick-walled cells with sparsely located simple slit-like pores. Sometimes meet fibrous tracheids(for example, a pear).

Libriform fibers, fibrous and vascular tracheids along appearance very similar. Paranchymal cells perform a storage function and form two systems - horizontal (core rays) and vertical (wood parenchyma). core rays in width may consist of one or more rows of parenchymal cells. Wide core beams of oak include up to 30 rows. In some species (alder, hornbeam) there are falsely wide core rays, which are a bundle of narrow rays, closely spaced from each other and separated only by libriform fibers or tracheids (there are no vessels between the narrow rays). In height, the core rays also include several (sometimes tens) rows of cells. On tangential sections, narrow single-row core rays are visible in the form of vertical chains of cells located along the fibers. Multi-row rays have the form of a spindle or lentils.

Wood parenchyma in hardwoods it is much better developed than in conifers. On longitudinal sections one can often see individual vertical rows of parenchymal cells; the extreme cells are pointed, and the whole set of cells is perceived as a fiber separated by partitions. This education is called strand of woody parenchyma. In addition, it occurs fusiform parenchyma, which differs from parenchymal cords in the absence of transverse partitions.

"Determination of the features of the microscopic structure of wood", methodological guide, Ulan-Ude, 2005

Chemical composition

Chemical composition certain types tree species, as well as their parts, is qualitatively similar, but there are significant differences in the quantitative content of individual components. There are also individual features in the quantitative content of individual components within one species, associated with age and growing conditions. Wood is made up of organic substances, which include carbon, hydrogen, oxygen and some nitrogen. Absolutely dry pine wood contains on average: 49.5% carbon; 6.1% hydrogen; 43.0% oxygen; 0.2% nitrogen.

In addition to organic substances, wood contains mineral compounds that produce ash during combustion, the amount of which varies between (0.2-1.7)%; however, in some species (saxaul, pistachio kernels), the amount of ash reaches (3--3.5)%. In the same breed, the amount of ash depends on the part of the tree, position in the trunk, age and growing conditions. More ash is given by the bark and leaves; Branch wood contains more ash than trunk wood; for example, birch and pine branches produce 0.64 and 0.32% ash during combustion, and stem wood - 0.16 and 0.17% ash. The wood of the upper part of the trunk gives more ash than the lower; this indicates a high ash content in young wood.

The composition of the ash includes mainly salts of alkaline earth metals. Pine, spruce and birch wood ash contains over 40% calcium salts, over 20% potassium and sodium salts, and up to 10% magnesium salts. Part of the ash from 10 to 25% is soluble in water (mainly alkalis - potash and soda). In former times, K 2 CO 3 potash, used in the production of crystal, liquid soap and other substances, was extracted from wood ash. Ash from the bark contains more calcium salts (up to 50% for spruce), but less salts of potassium, sodium and magnesium. The main chemical elements (C, H and O) included in the composition of wood and the above-mentioned basic chemical elements form complex organic substances.

The most important of them form a cell membrane (cellulose, lignin, hemicelluloses - pentosans and hexosans) and make up 90--95% of the mass of absolutely dry wood. The remaining substances are called extractive, that is, extracted by various solvents without a noticeable change in the composition of the wood; of these, tannins and resins are the most important. The content of basic organic substances in wood depends to some extent on the species. This can be seen from Table 2

Table 2 - The content of organic substances in wood of different species

On average, it can be assumed that coniferous wood contains (48--56)% cellulose, (26--30)% lignin, (23--26)% hemicelluloses containing (10--12)% pentosans and about 13 % hexosans; at the same time, hardwood contains (46--48)% cellulose, (19--28)% lignin, (26--35)% hemicelluloses containing (23--29)% pentosans and (3--6 ) % hexosans. Table 2 shows that coniferous wood contains an increased amount of cellulose and hexosans, while hardwood wood is characterized by a high content of pentosans. In the cell membrane, cellulose is in combination with other substances. A particularly close relationship, the nature of which is still not clear, is observed between cellulose and lignin. Previously, it was believed that lignin was only mechanically mixed with cellulose; however, in recent years, more and more people have come to believe that there is a chemical bond between them.

The chemical composition of early and late wood in the annual layers, that is, the content of cellulose, lignin and hemicelluloses, is almost the same. Early wood contains only more substances soluble in water and ether; this is especially true for larch. By stem height chemical composition wood changes little. So, in the composition of oak wood, no practically tangible differences were found in the height of the trunk. In pine, spruce and aspen at the age of maturity, a slight increase in the content of cellulose and a decrease in the content of lignin and pentosans in the middle part of the trunk were found. The wood of pine, spruce and aspen branches contains less cellulose (44--48)%, but more lignin and pentosans. However, no noticeable differences in the chemical composition of the wood of the trunk and large branches were found in the oak, only in small branches were found less tannins (8% in the trunk and 2% in the branches). The difference in the chemical composition of sapwood and summer oak heartwood can be seen from the data in Table 3.

Table 3 - The difference in the chemical composition of sapwood and pine kernel wood

As we see from the table, a noticeable difference was found only in the content of pentosans and tannins: there are more of them in the wood of the kernel (and less ash). The chemical composition of the cell membranes of the cambium, newly formed wood and sapwood varies greatly: the content of cellulose and lignin sharply increases in the elements of wood (in ash from 20.2 to 4.6% in cambium, to 58.3 and 20.9% in sapwood). ), but the content of pectins and proteins also sharply decreases (from 21.6 and 29.4% in cambium to 1.58 and 1.37% in sapwood). The influence of growing conditions on the chemical composition of wood has been little studied.

Cellulose is a natural polymer, a polysaccharide with a long chain molecule. General formula cellulose (C 6 H 10 O 5) n, where n is the degree of polymerization from 6000 to 14000. It is a very stable substance, insoluble in water and common organic solvents (alcohol, ether and others), white. Bundles of cellulose macromolecules - the thinnest fibers are called microfibrils. They form the cellulose framework of the cell wall. Microfibrils are oriented mainly along the long axis of the cell, between them there is lignin, hemicelluloses, and also water. Cellulose consists of long chain molecules formed by repeating units consisting of two glucose residues. Each pair of glucose residues linked together is called a cellobiose. Glucose residues are formed after the release of a water molecule when glucose molecules are combined during the biosynthesis of cellulose polysaccharide. In cellobiose, glucose residues are rotated by 180 0, the first carbon atom of one of them is connected to the fourth carbon atom of the neighboring unit.

Considering cellulose at the molecular level, we can say that its macromolecule has the form of an elongated non-planar chain formed by various link structures. The presence of various units is associated with weak intramolecular bonds between hydroxyl groups (OH-OH) or between a hydroxyl group and oxygen (OH-O).

Cellulose has 70% crystalline structure. Compared to other linear polymers, cellulose has special properties, which is explained by the regularity of the macromolecule chain structure and significant forces of intra- and intermolecular interaction.

When heated to the decomposition temperature, cellulose retains the properties of a glassy body, that is, it is characterized mainly by elastic deformations. Cellulose is a chemically stable substance; it does not dissolve in water and most organic solvents (alcohol, acetone, etc.). Under the action of alkalis on cellulose, physicochemical processes of swelling, rearrangement and dissolution of low molecular weight fractions proceed simultaneously. Cellulose is not very resistant to the action of acids, which is due to glucosidic bonds between the elementary units. In the presence of acids, hydrolysis of cellulose occurs with the destruction of chains of macromolecules. Cellulose is a white substance with a density of 1.54 to 1.58 g/cm 3 .

The concept of hemicellulose combines a group of substances that are similar in chemical composition to cellulose, but differ from it in the ability to easily hydrolyze and dissolve in dilute alkalis. Hemicelluloses are mainly polysaccharides: pentosans (C 5 H 8 O 4) n and hexosans (C 6 H 10 O 5) n with five or six carbon atoms in the main unit. The degree of polymerization of hemicelluloses (n = 60-200) is much less than that of cellulose, i.e., the chains of molecules are shorter. During the hydrolysis of hemicellulose polysaccharides, simple sugars (monosaccharides) are formed; hexosans are converted to hexoses, and pentosans to pentoses. Usually, hemicelluloses are not obtained from wood in the form of marketable products. However, in the chemical processing of wood, they are widely used to obtain many valuable substances. For example, when wood is heated with twelve percent hydrochloric acid, almost all pentosans (93-96)% are converted into simple sugars - pentoses - and after the removal of three water molecules from each monosaccharide molecule, furfural is formed - a product widely used in industry. In a growing tree, hexosans are reserve substances, and pentosans perform a mechanical function.

In addition to carbohydrates (cellulose and hemicellulose), the cell wall contains an aromatic compound, lignin, which has a high carbon content. Cellulose contains 44.4% carbon, and lignin (60--66)%. Lignin is less stable than cellulose, and easily goes into solution when wood is treated with hot alkalis, aqueous solutions of sulfurous acid or its acidic salts. This is the basis for obtaining technical cellulose. Lignin is obtained in the form of waste during the cooking of sulfite and sulfate pulp, during the hydrolysis of wood. The lignin contained in black alkalis is mainly burned during regeneration.

Lignin is used as a pulverized fuel, a substitute for tannins, in the production of binders for molding earths (in the foundry industry), plastics, artificial resins, to obtain activated carbon, vanillin and more. However, the question of the full qualified chemical use of lignin has not yet been resolved. Of the other organic substances contained in wood, the largest industrial use obtained resins and tannins.

Resin refers to hydrophobic substances soluble in neutral non-polar solvents.

This group of substances is usually divided into water-insoluble resins (liquid and solid) and gum resins containing water-soluble gums. Among liquid resins, the most important is resin, which is obtained from wood (sometimes from the bark) of conifers as a result of tapping. The tapping of pine and cedar is carried out as follows. In the fall, a vertical groove is made with special tools on a section of the trunk cleared of coarse bark, and with the onset of warm weather in the spring, strips of bark and wood directed at an angle of 30 ° to the groove are systematically removed and so-called podnovki are formed. The depth of the warp is usually (3--5) mm. The wound inflicted on a tree by tapping is called a karra.

From the cut resin passages, the resin, which is under pressure (10-20) atmospheres, flows into the shoes and goes along the groove to the receiver. After applying four to five new pieces, the resin is selected from the conical receiver with a steel spatula. To increase the yield of resin, chemical stimulants (chlorine or sulfuric acid) are used, which are used to treat the freshly opened wood surface.

Spruce tapping is carried out by applying carr in the form of narrow longitudinal strips. To obtain resin from larch, channels are drilled deep into the trunk until they encounter large resin "pockets", which often form in the lower part of the trunk. Larch resin is highly valued and used in the paint and varnish industry for the manufacture the best varieties varnishes and enamel paints. Fir resin is extracted from the "blisters" that form in the bark. The resin from the pierced "blisters" is squeezed out into portable receivers. Fir resin resembles Canadian balsam in its properties and is used in optics, microscopic technology, and the like.

Pine resin is extracted in the largest quantities, which is a transparent resinous liquid with a characteristic pine smell. In the air, resin hardens and turns into a brittle whitish mass - barras. The pine resin obtained as a result of tapping contains approximately 75% rosin and 19% turpentine, the rest is water. Gum can be considered as a solution of solid resin acids (rosin) in liquid turpentine oil (turpentine). Recycling resin is carried out at rosin-turpentine plants and consists in distillation with water vapor of the volatile part - turpentine. The remaining non-volatile part is rosin.

Turpentine and rosin can be obtained by extraction processing of stump resin - the heart part of pine stumps, enriched with resin due to rotting of low-resin sapwood. Gasoline is most often used as a solvent. The resulting extract is distilled. The solvent and turpentine are distilled off, and the rosin remains. Extraction products are inferior in quality to turpentine and rosin obtained from resin. Turpentine is widely used as a solvent in the paint and varnish industry, for the production of synthetic camphor and other products. Camphor is used in large quantities as a plasticizer in the production of celluloid, varnishes and film.

The main consumer of rosin is the soap industry, where it is used to make laundry soap. In large quantities, rosin glue is used for sizing papers. Glycerin ester of rosin is introduced into the composition of nitro-varnishes to give the film shine. Rosin is used for the preparation of electrical insulating materials, in the production of synthetic rubber, etc. industrial value has larch gum. Gum is extracted from crushed wood with acidic water (acetic acid concentration 0.2%) at a temperature of 30 °. After evaporation to a concentration of (60--70)%, a commercial product is obtained. It is used in the textile industry for the manufacture of paints, in the printing and paper industries.

The concept of tannins or tannins combines all substances that have the properties of tanning raw leather, giving it resistance to decay, elasticity, and the ability not to swell. The most rich in tannins is the wood of the oak core from 6 to 11% and chestnut from 6 to 13%. The bark of oak, spruce, willow, larch and fir contains from 5 to 16% tannins. The growths on oak leaves - galls contain from 35% to 75% tannins (one of the varieties of tannins). In the leaves and roots of bergenia, the content of tannins is (15-25)%.

Tannins are soluble in water and alcohol, have an astringent taste, when combined with iron salts they give a dark blue color, and are easily oxidized. Tannins are extracted with hot water from crushed wood and bark. The marketable product is either a liquid or dry extract, which is obtained after the solution has been evaporated in a vacuum apparatus and dried. Essential oils, lactoresins and dyes can also be obtained from woody plants.

Essential oils belong to the group of terpenoids (isoprenoids) - hydrocarbons built from a different number of isoprene units.

From needles and cones different types fir trees extract fir oil, which is a transparent, colorless aromatic liquid that quickly evaporates in air. The needles of the Siberian fir contain from 0.63 to 3%, and the needles of the Caucasian fir 0.2% fir oil. Fir oil is used in pharmaceutical production, in perfumery and for the preparation of varnishes. Volatile essential oils of coniferous species of pine, spruce, western arborvitae, have the properties of phytoncidity, i.e., the ability to kill microbes in the air or in water.

Pine buds contain essential oil, resins, starch, tannins, pinipicrin. The needles contain a lot of ascorbic acid, tannins, and also contain alkaloids, essential oil. Gum contains up to 35% essential oil and resin acids. In medicine, pine buds are used in the form of infusion, tincture, decoction, extract as an expectorant, diuretic, disinfectant, anti-inflammatory and antiscorbutic agent. Pine buds are integral part breast collection; in combination with coniferous needles in the form of infusion and extract, they can be used to prepare coniferous baths. Polyprenol - the active component of pine needles has an antiserotonergic effect. Coniferous needles are used to prepare concentrates and infusions used for scurvy, as well as for therapeutic baths. Pine bud extract has bactericidal properties against staphylococcus, shigella and Escherichia coli. Turpentine is part of the ointments, liniments used for neuralgia, myositis, for rubbing. It is prescribed orally and for inhalation for bronchitis, bronchiectasis. Tar has disinfectant and insecticidal properties, has a local irritant effect. It is used in the form of ointments to treat skin conditions and wounds. The bark contains tannins. Gum from the bark of cedar pine contains turpentine and rosin.

Lactoresins are the milky juices of some plants, close to resins. These include rubber and gutta-percha. Rubber is extracted from the bark of the Hevea brasiliensis tree and is a yellow to dark amorphous mass soluble in carbon disulfide, chloroform, ether and turpentine. Gutta-percha is obtained from some tropical tree species (for example, Isonandra gutta Hook and others). Of the Russian breeds, gutta-percha is contained in the root bark (up to 7%) of the warty and European euonymus. Purified gutta-percha is a brown solid mass, easily soluble in carbon disulfide, chloroform and turpentine. It is used to make cliches for drawings, insulation of electrical cables and more.

Coloring substances can be found both in wood and in the bark, leaves and roots. The wood contains dyes of red, yellow, blue and brown. Of the species growing in our country, for dyeing fabrics and yarn yellow, the local population in the Caucasus uses the wood of maclura, mulberry, skumpia, hornbeam bark, sumac and hop hornbeam, for dyeing red - dry buckthorn bark, brown - skumpia wood , walnut peel and more.

The chemical composition of tree bark differs sharply from the chemical composition of wood (xylem). It should also be noted that the inner and outer parts of the bark, which have different functional purposes and, accordingly, the structure, differ significantly from each other in composition. But quite often, the analysis of the chemical composition of the bark is done without dividing it into bast and crust.

A distinctive feature of the chemical composition of the bark is the high content of extractive substances and the presence of certain specific components that cannot be removed by neutral solvents. By successive extraction with solvents with increasing polarity, from 15 to 55% of its mass is extracted from the bark of different species. The next treatment with a 1% NaOH solution additionally dissolves from 20 to 50% of the mass. As a result of such successive treatments, the tree bark loses from 10 to 75% of its own weight. With all this, not only some of the hemicelluloses are removed from the bark, but also such specific components as suberin and polyphenolic acids of the bark, which cannot be classified as extractive substances. The features of the structure and chemical composition of the bark cause certain difficulties in its analysis and require modification of the methods developed for the analysis of wood, namely, the introduction of additional pretreatments with aqueous and alcoholic solutions and sodium foxide. Otherwise, the presence of suberin and polyphenolic acids can lead to a significant overestimation of the results of the determination of holocellulose and lignin. The bark, when compared with wood, contains more minerals (1.5-5.0)%. Sometimes this is due to the deposition of carbonate crystals in the crust. The ash content of the bark largely depends on the growing conditions of the tree (the composition and moisture content of the soil, etc.).

Mass fraction holocellulose in the bark is approximately two times less than in wood, while its content in the bast is higher than in the bark. Cellulose in the bark, as well as in wood, is the main polysaccharide, but unlike wood, it cannot be called the predominant component of the bark. In the literature, values ​​from 10 to 30% are given for the mass fraction of cellulose in unextracted bark samples.

As in wood, the main hemicelluloses in the bark of coniferous species are glucomannans and xylans, while those of hardwoods are xylans. In the walls of cork cells found glucan - callose. Callose also appears in the phloem as a substance that clogs the sieve plates. Attention is drawn to a rather large mass fraction of uronic acids in the bark, especially in the tissues of the bast, which is associated with a high content of pectin substances. This is consistent with a significantly higher amount of water-soluble polysaccharides in the bark compared to wood. The composition of pectin substances in the bark does not differ significantly from the composition of these substances in wood. Note only a higher content of arabinose.

As already emphasized, one should be cautious about the data available in the literature on the determination of lignin and other components in the bark. For example, for frankincense pine (Pinus taeda), the range of results for determining lignin in the bark is very wide: from 20.4 to 52.2%. The differences may be due to the introduction of different methods of preparing bark samples for analysis and conducting the analysis itself.

Lignin in bark tissues is less evenly distributed than in wood. The outer layer of the crust is more lignified than the inner one. The walls of stony cells are the most lignified. Lignin is also found in the walls of fibers and some types of parenchymal cells of the phloem and crust. The distribution of lignin among different types of cells in the cortex has strong species differences. The bark lignin is more condensed than in the wood of the same tree species, which is confirmed to some extent by the data on bark delignification. Bark is more difficult to delignify than wood.

A characteristic component of the outer layer of the bark is suberin, a product of copolycondensation, mainly of higher (C16-C24) saturated and monounsaturated aliphatic a, dicarboxylic acids with hydroxy acids (the latter can be additionally hydroxylated). Participation in the polycondensation of monomers with three or more multifunctional groups (carboxylic, hydroxyl) leads to the formation of a polyester with a network structure. Some researchers admit the existence of simple ether bonds. As a result, suberin cannot be isolated from the bark unchanged, since it cannot be extracted with neutral solvents, and ester bonds make it a very labile component. From the bark, suberin is isolated in the form of suberin monomers after saponification with aqueous or alcoholic solutions of alkali and decomposition of the resulting suberin soap with mineral acid.

Suberin is contained in the periderm, including the wound. It is localized in cork cells, being an integral part of the cell wall. The cork tissue of the cork oak contains (42-46)% suberin, the Brazilian tropical tree paosantha (Kielmeyera coriacea) - 45%, and the cork cells of the warty birch - 45% suberin. The mass fraction of suberin in the outer layer of the bark occasionally exceeds (2-3)%, but there are tree species that are characterized by a high content of suberin. In the above tree species, suberic monomers make up (2-40)% of the mass of the outer part of the bark. characteristic feature The cork tissue of birch - birch bark is the accumulation along with suberin of triterpene alcohol - betulin. The composition of suberic monomers is very diverse. In addition to the dicarboxylic and hydroxy acids mentioned above, the composition of suberic monomers includes monobasic fatty acids, monohydric higher fatty alcohols (up to 20% by weight of suberin), phenolic acids, dilignols (dimers of phenylpropane units) and others.

As already noted, the treatment of bark previously extracted with neutral solvents with a 1% aqueous solution of NaOH extracts up to (15-50)% of the material, which is a group of phenolic substances with acidic properties. This gave reason to call them polyphenolic acids. However, not carboxyl, but carbonyl groups were found in them. After precipitation from an alkaline solution by acidification with mineral acids, polyphenolic acids become partially soluble in water and polar organic solvents. In all likelihood, "polyphenolic acids" are polymeric substances of the flavonoid type, related to condensed tannins and therefore capable of undergoing rearrangement in an alkaline environment with the appearance of carbonyl groups.

Significant differences in the structure and chemical composition of bark and wood necessitate separate processing these constituent parts wood biomass from both technological and economic points of view. However existing methods removal of bark (barking) is associated with loss of wood. The debarking waste, along with the bark, contains a significant amount of wood, which complicates the chemical processing of such raw materials. The variety of chemical compounds present in the bark makes the idea of ​​extracting the most valuable components attractive. The development of this area of ​​bark utilization is constrained by the relatively low content of extractable components. As a result, the main areas of bark processing are still limited to its utilization as an organic material as a fuel, in agriculture and so on. Rare examples of the use of the bark of individual tree species for the extraction of tannins, the production of cork, the production of tar (from birch bark) and the isolation of fir balsam from the bark of growing fir trees, unfortunately, do not improve the overall picture of the inefficient use of valuable organic compounds contained in the bark.

The work was added to the site site: 2016-03-13

">№10 ">. The structure of coniferous wood

"\u003e Coniferous wood has a rather simple and uniform structure. This can be easily seen from the structure of pine wood shown in Fig. 12. The composition of coniferous wood includes tracheids and parenchymal cells. The conducting function is performed by early tracheids, mechanical - late tracheids and storage function - parenchymal cells. Tracheids are co6 cells elongated in length with rounded or oblique ends; they occupy almost the entire volume of wood. In the early zone of the annual layer, large-cavitated thin-walled cells are visible, most often with a square cross section. period; early tracheids on their radial walls, mainly at the rounded ends, have bordered pores. On the radial section, the bordered pore has the form of two concentric circles, between which the third is sometimes translucent. At the end of the growing season, thick-walled narrow-cavity late tracheids are formed. have the form of rectangles flattened in the radial direction. Late tracheids have sparsely spaced slit-like fringed pores found on radial and tangential walls. The zone of early tracheids within one annual layer gradually passes into the zone of late tracheids. A clear boundary is observed between the late wood of one annual layer and the early wood of another layer (the boundary of annual layers).

"> Parenchymal cells in the wood of all conifers are part of the core rays and in some species surround the resin passages. Core lines in conifers are detected using a microscope on all three sections. Core rays are visible on the cross section as strips consisting of cells located perpendicular to the boundary of the annual layer.On the radial section, the rays of replacement and the form of rather high stripes crossing the tracheids at right angles.On the tangential section, the core rays are represented by chains of cells located along the tracheids.Resin canals.In the wood of some coniferous species (pine, cedar, larch, spruce) most often in the late zone of the annual layer there are more or less large vertical channels filled with resin - resin passages.Resin passages consist of three layers of cells: the inner layer of the lining cells of the epithelium, dead cells filled with air, and cells (live) of the accompanying parenchyma. Vertical resin ducts on longitudinal sections look like a long canal parallel to the tracheids with adjoining parenchymal cells. In addition to the vertical ones, there are horizontal resin ducts, which consist only of the epithelium and a layer of dead cells and are located in multi-row (in width) medullary rays. Horizontal resin ducts can most often be observed in tangential sections.

">№11 ">. ">Structure of hardwood

"> In hardwoods, which differ from conifers in a more complex structure, each function has two, and sometimes more, anatomical elements.

"> The conductive function in hardwood wood is performed by vessels. Depending on the nature of the location of the vessels, along the width of the annual layer, breeds with ring-vascular and diffuse-vascular wood are distinguished.

"> Large vessels in ring-vascular breeds are located in the early zone in one or two rows. Small vessels are located in the late zone, they are collected in groups that create one or another characteristic pattern.

"> In scattered vascular rocks, the vessels are most often small and distributed evenly throughout the annual layer, sometimes they are collected in groups of two or more vessels.

"> Vessels are vertical tubes made up of segments of thin-walled wide-cavity cells. The lower and upper walls of these cells partially or completely dissolve. This forms simple (with one or two holes) or ladder perforations (a number of slit-like holes). A segment with a simple perforation is characteristic for large oak wood vessels.The perforation plate in this case is located almost perpendicular to the walls of the vessel.Ladder perforation is usually found in vessels in birch and alder wood.

"> The vessels communicate with each other through rounded or multifaceted bordered pores in the walls. The cavities of the vessel are sometimes clogged with tills - outgrowths of parenchymal cells. In addition to the vessels in some species (for example, oak), the vascular tracheids, which are a transitional element between typical tracheids and vascular segments.

"> Libriform fibers make up the bulk of hardwood and perform a mechanical function. Libriform fibers are narrow-banded cells with thick walls, strongly elongated along the length, in which there are sparsely located simple slit-like pores. Fibrous tracheids are sometimes found (for example, in a pear).

"> Libriform fibers, fibrous and vascular tracheids are very similar in appearance. Parenchymal cells perform a storage function and form two systems horizontal (core rays) and vertical (woody parenchyma). Core rays in width can consist of one or several rows of parenchymal cells The wide core rays of oak include up to 30 rows.In some species (alder, hornbeam) there are falsely wide core rays, which are a bundle of narrow rays, closely spaced from each other and separated only by libriform fibers or tracheids (there are no vessels between the narrow rays). core rays also include several (sometimes tens) rows of cells.On tangential sections, narrow single-row core rays are visible in the form of vertical chains of cells located along the fibers.Multi-row rays look like a spindle or lentil.

"> Woody parenchyma in hardwoods is much better developed than in conifers. On longitudinal sections one can often see individual vertical rows of parenchyma cells; the extreme cells are pointed, and the entire set of cells is perceived as a fiber separated by partitions. Such a formation is called a strand of woody parenchyma. In addition, there is a fusiform parenchyma, which differs from parenchymal strands in the absence of transverse septa.

">№13 ">. Like any organic substance, wood has its own chemical composition. Wood (completely dry) has the following chemical composition: oxygen 44.2%, carbon - 49.5% and hydrogen - 6.3%. Accordingly, from these chemical elements consist of complex organic substances that are part of the cellular tissue of wood, lignin, hemicellulose, cellulose, which make up 90-96% of the mass of absolutely dry wood. The remaining 4-10% remain in extractive substances, which are extracted from wood with various solvents. them tannins and resins.In addition, the wood contains 0.3-1.8% of the mass of inorganic substances that are produced from the ash after burning wood.These are salts of potassium, calcium, magnesium, sodium.Stem wood gives less ash than leaves and bark.

"> Cellulose from wood is obtained by separating it from lignin and hemicellulose. The process of separating cellulose from these substances is based on its high resistance to chemical compounds and, in particular, to solutions of acids and alkalis, in which less resistant lignin and hemicellulose pass into solution. Wood wood chips are boiled in boilers in an alkaline (sulphate method) or acidic (sulfite method) medium at high (130-180°C) temperature and high (0.6-1.1 MPa) pressure.After several hours of cooking, the pulp is washed, cleaned, bleached Cellulose is the starting material for the production of cotton wool, paper, artificial furs, artificial fibers (viscose silk, staple) and leather, photographic and film films, cellophane, varnishes, plastics, gunpowder and other materials.

"> Lignin and hemicellulose, which went into solution during cooking, after further hydrolysis and chemical processing, are used to produce fodder yeast, ethyl alcohol, carbon dioxide, vanillin, dry ice, furfural. Ethyl alcohol is the primary raw material for the production of vinegar, artificial rubber, ether.

"\u003e The resin in the trunk of conifers has a weak bond with the wood tissue, due to this property it is relatively easy to extract. Resin is extracted either by extraction of highly resinous wood or by tapping a growing tree. During the extraction processing of wood, resinous substances are first dissolved in gasoline, and then the resulting extract is dispersed into rosin and turpentine.When tapping, superficial wounds are made on the trunk of a living tree, from which resin flows out - oleoresin.As a result of the processing of oleoresin, rosin and turpentine are obtained.

"> Rosin is used for the manufacture of varnishes, the production of soap, paints, esters, linoleum, and is also used in many industries (tanning, cable, rubber, oil) industries. Turpentine is used in medicine, used as a solvent for varnishes and paints, and also as raw materials for the production of other products.

"> Tannins (tannins) - obtained from crushed bark and wood by extraction with hot water. Tannins are used in the leather industry for tanning leather, giving it flexibility, softness, resistance to decay and swelling. Tannins can be dissolved in alcohol and water when combined with salts of various metals, resulting in dyes of various shades from light yellow to blue-black, used for deep dyeing of wood.

">№5+6. "> The main features in determining the breed the presence of the core, the width of the sapwood and the degree of sharpness of the transition from the core to the sapwood; the degree of visibility of the annual layers, the difference between early and late wood; the presence and size of the core rays; the size of the vessels; the presence of resin passages, the size and number additional signs color, gloss, texture (pattern), density and hardness.

"> First you need to establish which group of tree species the this sample: coniferous, deciduous annular-vascular or scattered vascular.

"> Conifers include those in which the annual layers are clearly visible due to the fact that the late wood is darker than the early one. Conifers do not have vessels, the core rays are very narrow and not visible to the naked eye. Some conifers contain resin passages.

"> Deciduous annular-vascular species include rocks with clearly visible annual layers. In the early wood of the annual layers of these species, large vessels form a continuous ring of holes, clearly visible to the naked eye, in dense late wood, patterns formed by clusters of small vessels are visible. most breeds.These breeds are sound.

"> Deciduous scattered-vascular rocks include rocks in which the annual layers are poorly visible; the vessels in the transverse section do not form a continuous ring, but are evenly spaced across the entire width of the annual layer. In some species, core rays are visible.

"> The main macroscopic features in determining the type of wood are:

"> ■ ;font-family:"Cambria""> the presence of a kernel;

"> ■ ;font-family:"Cambria""> width of sapwood and degree of sharpness of transition from sapwood to heartwood;

"> ■ ;font-family:"Cambria""> degree of visibility of annual layers;

"> ■ ;font-family:"Cambria""> difference in coloration of early and late wood;

"> ■ ;font-family:"Cambria""> present"\u003e e and the dimensions of the core rays;

"> ■ ;font-family:"Cambria""> presence of core repetitions;

"> ■ ;font-family:"Cambria""> the size of the vessels and the nature of their grouping;

"> ■ ;font-family:"Cambria""> the presence of resin passages, their size and number

;font-family:"Cambria"">#8. ;font-family:"Cambria""> Types of wood cells.

;font-family:"Cambria"">The cells that make up wood are diverse in shape and size. There are two main types of cells: cells with a fiber length of 0.5-3 mm, a diameter of 0.01-0.05 mm, with pointed ends - prosenchymal and smaller cells, having the form of a polyhedral prism with approximately the same side sizes (0.01-0.1 mm), - parenchymal.

;font-family:"Cambria"">Parenchymal cells serve to store reserve nutrients. Organic nutrients in the form of starch, fats and other substances are accumulated and stored in these cells until spring, and in spring they are sent to the crown of the tree to form leaves. Rows of storage cells are located along the radius of the tree and are part of the core rays.Their number in the total volume of wood is insignificant: in conifers 1-2%, in hardwoods - 2-15%.

;font-family:"Cambria"">The bulk of wood of all species consists of prosenchymal cells, which, depending on the vital functions they perform, are divided into conductive and supporting, or mechanical. Conductive cells v of a growing tree serve to conduct from the soil to the crown of water with solutions of mineral substances; supporting ones create the mechanical strength of wood.

;font-family:"Cambria"">Wood fabrics.

;font-family:"Cambria"">Cells of the same structure, performing the same functions, form wood tissues. In accordance with the purpose and type of cells that make up the tissues, there are: storage, conductive, mechanical (support) and integumentary fabrics.

;font-family:"Cambria"">Storage tissues consist of short storage cells and serve to accumulate and store nutrients. Storage tissue consists of parenchymal cells, often referred to as arboreal parenchyma.

;font-family:"Cambria"">Conductive, or vascular, tissues consist of elongated thin-walled cells with wide internal gaps; cells located one above the other connect to each other, creating tube vessels through which moisture absorbed by the roots, passes to the leaves. The length of the vessels is on average about 100 mm; in some species, for example, in oak, the vessels reach 2-3 m in length. The diameter of the vessels ranges from hundredths of a millimeter (in small-vessel species) to 0.5 mm (in large-vessel species).

;font-family:"Cambria"">Mechanical (supporting) tissues consist of long thick-walled cells with small internal gaps, with long pointed ends. These tissues are able to resist mechanical stress. Mechanical tissue is the strongest and most resistant to decay. The more this fabrics, the wood is denser, harder, stronger.Mechanical fabrics are called libriform.

;font-family:"Cambria"">Integumentary tissues are located in the cortex and perform a protective role.

;font-family:"Cambria"">#12.;font-family:"Cambria""> Lignification, or lignification, is the process of lignification of the walls of some plant cells. Cell walls are impregnated with lignin (phenolic polymer). Lignification is characteristic of secondary xylem cells (conductive tissue), but can also occur in other cells and tissues.Thanks to lignin, the cell loses its plasticity, it becomes very strong.Tree trunks due to lignification can hold a lot of trees, etc. In woody plants, in many cacti, the bulk of lignified cells is located in the center of the stem and root.

;font-family:"Cambria""> Lignification is characteristic of sclerophytes (plants of arid habitats), water evaporation is minimized.

;font-family:"Cambria"">Suberinization, or suberinization, is the process of deposition of suberin in cell membranes. Suberin is a glyceride of fallonic and other saturated fatty acids.

;font-family:"Cambria""> When cell membranes are impregnated with suberin, the cells and tissues become impermeable to water, gases, fungal infection, etc. That is, suberinization is of great biological importance. Usually corked cells are confined to peripheral tissues stem and root, protect them from water loss, from fungi, viruses, bacteria, etc. In addition, corky cells are more plastic, which is necessary for some cactus stems during growth cessation, cork cells are easier to exfoliate, etc.

">№14 ">. Hydrolysis production is based on the property of polysaccharides, which make up about 70% of the mass of plants on land, to undergo hydrolytic cleavage to monosaccharides under the action of water in the presence of mineral acids.

"> Commercial products of hydrolysis production are: fodder protein yeast, furfural, ethyl alcohol, carbon dioxide, xylitol.

"> Wood hydrolysis is carried out with dilute sulfuric acid with a concentration of 0.2-1%, at a temperature of 180-190 ° C and a pressure of 1-1.5 MPa without acid regeneration.

"> Wood hydrolysis is carried out in stationary pressure hydrolysis apparatuses. In industry, hydrolysis apparatuses with a capacity of 18 to 160 m3, recently made of acid-resistant steel, are used. The hydrolysis apparatus is a vertical cylindrical steel vessel of welded construction with a spherical upper and a conical lower parts.

"> The process of wood hydrolysis consists of loading crushed raw materials into the apparatus, pumping acid, heating the contents of the apparatus, percolation itself, washing lignin with water, squeezing out the hydrolyzate residue and removing lignin from the hydrolysis apparatus.

">№15. "> Thermal decomposition (pyrolysis) of wood this is the decomposition of wood without air access under the influence of high temperature. As a result of this process, solid, liquid and gaseous products are obtained. Solid products remain in the form of charcoal in the apparatus in which pyrolysis is carried out, and liquid and gaseous products are separated together in the form of a gas-vapor mixture.The gas-vapor mixture is separated by cooling into condensate (liquid) and non-condensable gases.The liquor is processed into acetic acid, methyl alcohol, tar and other products (see chapters 46), and non-condensable gases are burned as fuel.

"> Wood has a low thermal conductivity, which depends on the nature of the porosity, the direction of the fibers, on the species and volumetric weight of the wood, humidity and temperature. The thermal conductivity of wood along the fibers is 1.8 times higher than across the fibers. The thermal conductivity of wood is its ability to conduct heat through the entire thickness from one surface to another.Cavities, intercellular and intracellular spaces in dry wood are filled with air, which is a poor conductor of heat.Due to the low thermal conductivity, wood has become widespread in construction.

"> It increases with an increase in its moisture content and bulk density, since the amount of air contained in the pores of wood decreases. On average, its thermal conductivity is 0.150.25 kcal / m * h * deg.

"> Dense wood conducts heat somewhat better than loose wood. The moisture content of wood increases its thermal conductivity, since water is a better conductor of heat than air. In addition, the thermal conductivity of wood depends on the direction of its fibers and species. For example, the thermal conductivity of wood along the fibers is about twice than across.

"> K \u003d S (1.39 + 0.028 MC) + 0.165

"> where K is the coefficient of thermal conductivity, S is density, and MC is the humidity level in%. That is, an increase in density and humidity level leads to an increase in thermal conductivity, or to a loss of thermal insulation qualities.

">№16. "> Extractive substances determine the color, smell, taste, resistance of wood to decay, fire resistance and moisture permeability (hygroscopicity). They serve as raw materials for many very necessary substances paints, essential oils, fats, etc. Depending on the species, growing conditions and harvesting, wood contains 5-30% of extractive substances. Ash-forming substances in wood are few 0.1 - 3%.

"> The main extractive substances of wood are resinous substances, tannins and gums.

"> The oleoresin flowing out during wounds of a pine tree is a transparent resinous liquid with a pleasant pine odor. It consists of resin acids, neutral substances, terpene hydrocarbons. The oleoresin is cleaned and processed into rosin and turpentine in rosin-terpentine production.

"> In the wood of felled trees, especially in stump resin (in stumps that have stood in the ground for several years after cutting trees), the composition of resinous substances differs significantly from the composition of resin. In addition to resin acids and terpene hydrocarbons, they contain their oxidation products (oxidized resin acids and terpene alcohols), as well as fatty acids. The extraction of resinous substances from resin with organic solvents (usually gasoline) and their processing into rosin and turpentine take place in the extraction industry. Extraction of resinous substances from resin can also be done with a dilute solution of caustic soda.

"\u003e Tannins. Many woody plants contain tannins in wood or in bark; from them, water extracts are obtained at tanneries - tannin extracts. Oak wood contains 46% tannins (tannins), oak and willow bark 814, spruce 712, larch 8 16%. In addition to tannins, non-tannins (non-tannins) also dissolve in water. The content of tannins in the extract, expressed as a percentage of the mass of the dry extract, is called its good quality. The good quality of oak and larch extract is 6070 %, willow and spruce 5060%.

"> To obtain tannic extracts, raw materials are crushed and extracted with hot water in a battery of diffusers (extractors) according to the counterflow principle. Tanning extracts can be produced in three types - liquid, pasty and solid. They are used in the leather industry to turn raw animal skin into leather, i.e. e. to give it flexibility, softness, resistance to decay and swelling in water.

"> The extracted bark has even higher humidity. At a number of factories it is pressed on presses and used as fuel. Gum. Gum is called wood polysaccharides, soluble in water. Larch gum has adhesive properties and is applicable in the textile, match and printing industries. It can be extracted from larch wood, crushed into small chips, with hot water at 80 ° C or with a 0.2% solution of acetic acid at 30 ° C in an extractor battery.The yield of gum, depending on the age of the trees and other conditions, is 8 20%, on average 12% of absolutely dry wood.

">№17. "> Density of wood - the ratio of the mass of wood to the volume Pw \u003d Mw / Vw

"> Density depends on the rock and humidity, usually determined from the table.

"> There is a close relationship between the density and strength of wood. Heavier wood is generally more durable.

"> The density value varies over a very wide range. According to the density at a moisture content of 12%, wood can be divided into three groups:

"> rocks with a low density (510 kg / m3 or less): pine, spruce, fir, cedar, poplar, linden, willow, alder, chestnut, walnut;

"> rocks of medium density (550 ... 740 kg / m3): larch, yew, birch, beech, elm, pear, oak, elm, elm, maple, plane tree, mountain ash, apple tree, ash;

"> rocks with high density (750 kg / m3 and above): white locust, iron birch, hornbeam, boxwood, saxaul, pistachio, dogwood.

"> a) The density of the wood substance pd.v., g / cm, i.e. the density of the material of the cell walls, is equal to: pd.v. \u003d md.v. / vd.v., where md.v. and vd. in. - respectively, the mass, g, and volume, cm3, of the wood substance.

"> b) The density of absolutely dry wood p0 is equal to: p0 = m0 / v0, where m0, v0 - respectively, the mass and volume of wood at W=0%.

"> c) Density of wet wood: pw \u003d mw / vw, where mw and vw are, respectively, the mass and volume of wood at moisture content W.

"> d) The partial moisture content of wood p`w characterizes the content (mass) of dry wood per unit volume of wet wood: p`w \u003d m0 / vw, where m0 is the mass of absolutely dry wood, g or kg; vw is the volume, cm3 or m3 , wood at a given moisture content W.

"> e) The basic density of wood is expressed by the ratio of the mass of an absolutely dry sample m0 to its volume at a moisture content equal to or higher than the saturation limit of cell walls Vmax: pB = m0 / vmax.

">№18 ">. Humidity is one of the main characteristics of wood. With an uneven distribution of moisture during the drying of wood, internal stresses can form in it, that is, stresses that occur without the participation of external forces. Internal stresses can cause changes in the size and shape of parts during the mechanical processing of wood.

"> Under the moisture content of wood is understood the ratio of the mass of water to the dry mass of wood, expressed as a percentage.

"\u003e The absolute moisture content of wood is the ratio of the mass of moisture in a given volume of wood to the mass of absolutely dry wood.

"> The relative humidity of wood is the ratio of the mass of moisture contained in wood to the mass of wood in a wet state.

"> There are two forms of water in the wood: bound and free. They add up the total amount of moisture in the wood. The bound (or hygroscopic) moisture is contained in the cell walls of the wood, and the free one occupies the cell cavities and intercellular space. Free water is removed more easily, than bound, and to a lesser extent affects the deformation and cracking of wood.

"> According to the degree of moisture, wood is distinguished into the following types:

"> - Wet wood. Its moisture content is more than 100%. This is only possible if the wood has been in water for a long time.

"> - Freshly cut. Its humidity ranges from 50 to 100%.

"> - Air-dry. Such wood is usually stored in the air for a long time. Its humidity can be 15-20%, depending on climatic conditions and the season.

"> - Room-dry wood. Its moisture content is usually 8-10%.

"> - Absolutely dry. Its humidity is 0%.

"> Methods for determining wood: Weight method, ">electric way, ">determination of wood moisture from sawdust, determination of wood moisture from chips, determination of wood moisture using an indelible pencil, determination of wood moisture by feeling the weight.

">№19 ">. Shrinkage is the process of reducing the linear dimensions and volume of wood with a decrease in humidity. Types of shrinkage:

"> 1) Absolute - change in the linear dimensions of lumber in terms of length or volume.

"> 2) Relative - the ratio of the absolute shrinkage to the dimensions of the raw lumber.

"\u003e 3) Complete shrinkage - a change in the size of lumber with a decrease in moisture content in wood from the saturation limit to 0.

"> 4) Partial shrinkage - a change in the size of lumber with a decrease in moisture content in wood from the saturation limit to a given final moisture content. Wood shrinkage is not the same in different directions: in the tangential direction it is 1.5 - 2 times more than in the radial direction.

"> Under the full shrinkage, or maximum shrinkage Bmax, we understand the decrease in the linear dimensions and volume of wood when the entire amount of bound water is removed.

"> The formula for calculating the total shrinkage,%, is:

"> Bmax = (amax - amin) / amax * 100,

"> where amax and amin are the size (volume) of the sample, respectively, at a moisture content equal to or higher than the saturation limit of the cell walls and in an absolutely dry state, mm (mm3).

"> Swelling is the process of increasing the linear dimensions and volume of wood with an increase in moisture content in wood. The processes of shrinkage and swelling are mutually inverse and are associated with the removal and absorption of only bound moisture.

"> Swelling is a negative property of wood, but in some cases it is beneficial, providing tight joints (in barrels, vats, ships, etc.)

"> Swelling occurs when wood is kept in humid air or water. This is a property that is the opposite of shrinkage, and obeys basically the same laws. Total swelling,%, is calculated by the formula: amax = (amax - amin) / amin * 100 , where amax and amin - the size (volume) of the sample, respectively, at a moisture content equal to or higher than the saturation limit of the cell walls, and in an absolutely dry state, mm (mm3) Just like shrinkage, the greatest swelling of wood is observed in the tangential direction across the fibers , and the smallest - along the fibers.

">№20. "> The electrical conductivity of wood is characterized by its resistance to the passage electric current. It depends on the species, temperature, direction of the fibers and the moisture content of the wood. The electrical conductivity of dry wood is negligible, which allows it to be used as an insulating material (sockets for plugs and switches).

"> The electrical strength of wood is important in technology when evaluating it as an electrically insulating material and is characterized by a breakdown voltage in volts per 1 cm of material thickness. The electrical strength of wood is low and depends on the species, humidity, temperature and direction. With increasing humidity and temperature, the electrical strength decreases ; along the fibers it is much lower than across.

">№21 ">. THERMAL PROPERTIES OF WOOD, a set of properties of wood, which include heat capacity, thermal conductivity, thermal diffusivity and thermal expansion. Indicators of these properties are, respectively, specific heat capacity c, thermal conductivity λ, thermal diffusivity a and temperature coefficient of linear expansion α.

"> The specific heat capacity c determines the amount of heat absorbed by a unit mass of wood when it is heated by 1 ° C, and is expressed in kJ / (kg X ° C). With an increase in humidity and temperature, the specific heat capacity increases, amounting to pe 20 ° C 1.82.0 and 2.63.0 kJ / (kg X ° C), respectively, for dry and freshly cut wood.Specific heat capacity does not depend on the type of wood.

"> Thermal conductivity λ characterizes the stationary transfer of heat in wood, i.e. its thermal insulation ability, and is expressed in W / (m X ° C). It increases with increasing humidity, temperature (if it is above 0 ° C) and the density of wood, and also depends on its structure (species) and the direction of the heat flow.The thermal conductivity along the fibers is approximately two times higher than across.The K value of wood across the fibers, for example pine with a conditional density of 400 kg / m3 at a temperature of 20 ° С, is 0.150.19 and 0.280.33 W / (m X ° С), respectively, for dry and freshly cut wood.

"> Thermal diffusivity a characterizes the non-stationary transfer of heat in wood, i.e., its thermal inertia when the temperature changes, and is expressed in m2 / s. It is related to other indicators of T. s.d. by the ratio: a \u003d λ / ( cQ), where Q is the density of wood in kg / m3. The value of the thermal diffusivity of wood across the fibers, for example pine with a conditional density of 400 kg / m3 at a temperature of 20 ° C, is (1.81.9) X 10- 7 and (1.51.8) X 10-7 m2/s, respectively, for dry and freshly cut wood.

"> Temperature coefficient of linear expansion a characterizes the thermal expansion of wood and is expressed in 1 / ° C. The range of change a along the fibers is (2.55.4) X 10-6 1 / ° C, and across the fibers by an order of magnitude higher, and in the tangential direction 1.51.8 times more than in the radial direction.

"\u003e Many indicators of T. s.d. when it is thawed (or frozen) change abruptly: for example, the specific heat capacity decreases, thermal conductivity and thermal diffusivity increase. This jump is the greater, the higher the moisture content of the wood.

">№22. "\u003e The sound conductivity of wood, characterized by the speed of propagation of the sound, is much greater than that of air; it depends on the species and direction; sound travels best along the fibers, much more slowly in the radial and even more slowly in the tangential direction.

"\u003e The sound conductivity of wood in the longitudinal direction is 16 times, and in the transverse direction it is 3 ... current distortion) is widely used in the manufacture of musical instruments.High moisture content of wood reduces its sound conductivity.

"> The ability of wood to resonate (to amplify sound without distorting the tone) is extremely important in the music industry and is used in the manufacture of soundboards of musical instruments from it. The ability of wood to resonate, according to the research of N. N. Andreev, depends on the resistance to sound radiation and internal friction: the higher the first value and the smaller the second, the higher the ability to resonate.

">№23 ">. The hardness of wood, that is, the ability to resist processing with a cutting tool and, in general, the penetration of another body into it, depends on the type of wood, its bulk density and moisture content. Its ability to resist abrasion depends on the hardness of wood. According to the degree of hardness, wood is divided into six classes:

"> 1 class - very hard rocks (boxwood, dogwood);

"> 2 class - solid (hornbeam, pear, ash);

"> Grade 3 - moderately hard (oak, beech, maple);

"> 4 class - moderately soft (birch, elm, larch);

"> 5 class - soft (pine, spruce, alder, chestnut);

"> 6th grade - very soft (linden, aspen).

"\u003e The strength of wood - its ability to resist acting forces depends on a number of reasons. Dense, heavy wood usually has great strength. With increasing humidity, strength decreases significantly, especially if there are defects in the wood.

" xml:lang="en-US" lang="en-US">Elasticity - the ability of wood to change its shape under the influence of external forces and return to its original shape after the termination of these forces.

" xml:lang="en-US" lang="en-US">Plasticity is the ability of wood to change (without destruction) under pressure (load) its shape and then retain this shape after the load is removed.

">Test methods:

"> Compression along the fibers.

"> Compression across the fibers.

"> Stretch along the fibers.

">Stretch across the fibers.

"> The strength of wood in static bending.

"> Shear strength of wood.

">№24. "> The shortcomings of individual sections of wood, which reduce its quality and limit the possibility of its use, are called wood defects. They can be the result of improper growth of wood, destruction of its tissues by fungi, insects, mechanical stress, and also caused by improper storage.

"> Natural defects (as opposed to processing defects) are formed during the growth of a tree due to adverse climatic conditions and places of growth, accidental mechanical damage, natural aging, the activity of microorganisms, pests and birds. The effect of a defect on the quality of wood is determined by its type , size, location and purpose of lumber.Many wood defects are used for decorative purposes, in the manufacture of furniture and other products.

"> Classification of defects according to GOST:

1. ">Knots
2. ">Cracks
3. "> Defects in the shape of the trunk
4. "> Defects in the structure of wood
5. ">Chemical stains
6. "> Mushroom lesions
7. ">Biological damage
8. ">Foreign inclusions, mechanical damage and processing defects
9. "> warp

">№25. "> Knot is the part of the branch enclosed in the wood of the trunk.

"> The main characteristics of knots: location, shape, degree of intergrowth with wood, condition of the knot wood, color.

"> The main groups of knots:

"> 1. Open knot. Knot exposed to the side surface of the round timber

"> 2. Round knot.

"> 3. Oval knot.

"> 4. Oblong knot.

"> 5. Formation knot.

"> 6. Edge knot.

"> 7. Rib knot.

">8, end knot.

"> 9. Stitch knot. Knot,

">10. Scattered knots.

"> 11. Group knots.

"> 12. Branched knots.

"> 13. Intergrown knot.

"> 14. Partially fused knot.

"> 15. Unjoined knot

"> 16. Drop knot.

"> 17. Healthy bitch.

">18. Light healthy knot.

">19. Dark healthy knot.

"> 20. Healthy knot with cracks

">21. Rotten knot

">22. Rotten knot

">23. Tobacco knot

">24. One-sided knot

"> 25. Through knot

"> 26. Overgrown knot

">№26. "\u003e Cracks are longitudinal ruptures of wood, which occur, as a rule, under the action of internal stresses that exceed its tensile strength across the fibers.

"> Metic crack or metic a radially directed crack in the core, extending from the core and having a significant length along the trunk, but not reaching its periphery. It goes from the butt to the zone of living knots. It occurs in a growing tree and increases during drying. If the metic goes inside the trunk in one plane, then it is called consonant, if it goes in a spiral and goes to the other end directed in a different way, then it is called inconsistent.

"\u003e A peeling crack or peeling crack a crack passing between the annual layers that occurs in the core of a growing tree due to the drying of the core and heating of the outer layers. It occurs in wood of all species, but is especially common in oak, aspen, poplar, fir, spruce. In lumber at the end it looks like a crack-hole, and on the side surfaces in the form of longitudinal cracks or longitudinal grooved depressions.

"> A frost crack or a frost hole occurs in a growing tree during frost as a result of uneven cooling of the soil and different layers of wood containing moisture and not containing it. A lightning strike can also be the cause of its formation. A young crack looks like a simple longitudinal crack from the outside, without a trace closing at warm temperatures; old like a roller along a tree with an opening or overgrown internal crack.

"> Shrinkage crack a radial crack that occurs in felled wood during drying, the length is shorter than that of metic and frost, usually no more than 1 m; the depth is also less.

"> Also, cracks are classified by length, depth and position on the lumber.

">№27. "\u003e The group of defects in the shape of the trunk includes tapering, butting, ovality, outgrowths and curvature. The diameter of the tree trunk gradually decreases from the butt to the top. Such a decrease is called a run. If the diameter decreases sharply, this is considered a defect.

"> Tapering a wood defect in which the diameter of a tree trunk decreases by more than 1 cm for every meter of trunk height.

">Buttiness is a sharp increase in the diameter of the lower part of the trunk. It makes it difficult to use the material, increases the amount of waste, causes the appearance of fiber inclination in lumber.

"> Ovality the shape of the cross-section of the end of a round tree trunk, in which the larger diameter is at least one and a half times the smaller one.

">Ovality increases the amount of waste when peeling.

"> Outgrowth a local thickening of a tree trunk, which can be smooth or with an uneven surface and a wrinkled structure of wood, which is called burls. Growths are considered a conditional defect. In wood used as a structural material, this is a defect. For artistic furniture decoration, serrated burls valuable piece of wood.

"> Curvature is the curvature of the tree trunk along the length. It reduces the useful yield of lumber and veneer.

">№28 ">. "> "> The group of defects in the structure of wood includes the following defects.

"\u003e Fiber inclination is a deviation of the direction from the longitudinal axis of the log or lumber. The inclination of the fibers can be tangential, clearly visible on the cylindrical surface of the debarked log (it is associated with a spiral arrangement of fibers in a growing tree) and radial, caused by trunk run-off and clearly visible on radial sawn lumber.The radial slope of the fibers depends on the structure of the wood and on the direction of the cut planes relative to the direction of the fibers when cutting.This wood defect reduces the strength of the lumber, increases shrinkage along the fibers and leads to winging during drying.The quality of the machining of wood blanks with a slope of the fibers deteriorates.

"> Curl" is a tortuous or disordered arrangement of fibers. Curl reduces tensile, compressive and bending strength and increases shear and impact strength. It creates a beautiful texture and is highly valued in decorative finishing, so it is considered a conditional defect.

"\u003e Curl local curvature of the fibers (most often near knots). The decrease in the strength of wood depends on the size and shape of the curl and the area of ​​\u200b\u200bthe material occupied by it.

"> Roll - abnormally enhanced development of the late zone of wood. It is formed in the compressed zone of curved trunks of coniferous wood. In hardwoods, a similar structure, found in the stretched zone of curved or inclined trunks, is called traction wood.

"> Eyes traces of dormant buds that have not developed into a shoot (overgrown in wood).

"> Pitching a piece of wood abundantly impregnated with resin. Usually pitching is formed as a result of injury to the trunk of coniferous wood. Pitched wood is more resistant to decay, but it finishes and sticks worse.

"> Pocket a cavity inside the trunk filled with resin. There are pockets in coniferous wood, most often in spruce. Resin flows out of an open pocket on the surface of lumber, forming cavities. With small sizes of parts and large sizes of the pocket, the strength of the wood is reduced by 10-15 % in tension and compression along the fibers.

"> Sprouting is a dead area of ​​wood or bark, partially or completely overgrown in a tree trunk. Sprouting violates the integrity of the wood and is accompanied by a curvature of the annual layers.

">№29. "> Fungi Infection - Biological damage caused by fungi.

"> Mushrooms are plants without chlorophyll that feed on organic substances. They can worsen the mechanical properties of wood or affect the appearance.

"> Microbes are fungi belonging to the class Ascomycetes, which have small spores.

"> Mushroom core spots - abnormally colored areas of the core without a decrease in the hardness of wood that occur in a growing tree under the influence of wood-staining and (or) wood-destroying fungi. It is observed on the ends in the form of spots of various sizes and shapes (holes, rings and a concentrated zone of continuous damage to the central part trunk, sometimes with access to the periphery) brown, reddish, gray and gray-violet; on longitudinal sections - in the form of elongated spots and stripes of the same colors.

"> Mold - mycelium and fruiting of mold fungi on the surface of wood, in the form of individual spots or a continuous coating.

"> Sapwood fungus stains - abnormally colored areas of sapwood without lowering the hardness of wood that occur in felled wood under the influence of wood-staining fungi that do not cause rot. They spread deep into the wood from the ends to the side surfaces.

"> Blue - gray color of sapwood with bluish or greenish tints, caused by fungi.

"> Colored sapwood spots - orange, yellow, pink (to light purple) and brown sapwood.

"> Browning - abnormally colored areas of sapwood of hardwoods of brown color of various shades, of varying intensity and uniformity, arising in felled wood as a result of the development of biochemical processes with or without the participation of fungi and causing a slight decrease in the hardness of the wood. It precedes sapwood rot. It spreads deep into the wood from the ends and side surfaces.It is observed only on cuts of wood: on the ends in the form of spots of various sizes, shapes (often wedged out to the center of the forest products) and continuous damage to the sapwood.

"> Rot - areas of wood that are abnormal in color without a decrease or with a decrease in hardness, texture and color, arising under the action of wood-destroying fungi.

"> Hollow - a cavity that occurs in a growing tree as a result of the complete destruction of wood by wood-destroying fungi.

">№30. " xml:lang="en-US" lang="en-US">Classification of wood products">:

"> Detail is a product made of a homogeneous material, made without the use of assembly operations (table leg, chair seat, etc.).

">assembly units are products, the components of which are to be connected to each other at the enterprise with spikes, bolts, screws, etc.

"> Complex is two or more products that are not connected by assembly operations, but perform interrelated functions (furniture for a bedroom, office, etc.).

"> A set is two or more products that are not connected by assembly operations, with a common operational and auxiliary character (a set of returnable packaging for furniture packaging, kitchen equipment, etc.).

">Roundwood:

"> Round timber these are pieces of wood trunks, debranched and sawn at right angles to the longitudinal axis. Round timber is divided by species (coniferous and deciduous), by purpose (used in a round form and for sawing (sawlog) and by thickness.

"> Lumber:

"> Lumber is obtained by longitudinal sawing of logs. Their range is characterized by the following types of products:

"> Plates sawn along the fibers into two equal parts of the log;

"> quarters logs sawn in two mutually perpendicular directions;

"> Boards sawn timber with a thickness of up to 100 mm and a width of more than double thickness, can be edged and unedged;

"> Bars their thickness is up to 100 mm, the width does not exceed double the thickness;

"> Bars large lumber, width and thickness from 100 to 250 mm, they can be two-edged (sawn on both sides) or four-edged (sawn on four sides);

"> Slab a narrow part of a log cut off during sawing, usually with bark.

">Semi-finished products and finished goods

"> Semi-finished products and finished products include the following range:

"> Plywood layered wood material glued together from three or more layers of peeled veneer sheets;

"> Decorative plywood lined with film or other decorative coatings;

"> Carpentry boards boards glued from slats of coniferous wood and birch and glued on both sides with two layers of peeled veneer;

"> Chipboards are obtained by hot pressing of wood particles with binders;

"> Fibreboard is made from softwood and hardwood, as well as from reed and flax fire with the addition of other fillers and binders.

">№31. "\u003e FOREST COMMERCIAL, a scientific discipline that studies the consumer properties of forest products (forest products, woodworking and cell paper, wood chemical industry and side-use forest products). T. l. develops a classification and standardization of forest products, factors , determining their quality, methods of accounting, control and evaluation of goods, regularities in the formation of the assortment and structure of forest products, conditions for improving the quality of forest complex products and their preservation in the process of transportation, operation and consumption.

"> Within the framework of standardization and qualimetry (quantitative methods for assessing the quality of products) of forest products, T. L. considers the issues of marking, acceptance, transportation, stacking, storage, measurement, accounting and quality control of round timber, sawmill products, plywood, wood-based panels and etc.

"> The main place among forest products is occupied by wood products, which can be divided into the following groups: products of the logging industry, sawmill industry, woodworking (including furniture), plywood industry; special products. products (match, ski, chipboard and fiberboard, etc.), products of cello-paper, wood-chemical and hydrolysis industries. , fruits and berries, mushrooms, sugary juices, honey, resin, medicinal and technical raw materials, fodder, etc.) T. L. pays attention to these types of forest products.

"> T.-l. is aimed at the rational, integrated use of forest resources, their every possible saving. To determine the quality indicators of forest products in T. l., the main arr. measuring and calculation methods are used, in some cases external inspection And expert review goods quality. For example, wood defects cannot always be accurately measured instrumentally, but can be established by inspection. Scientific researches in the field of T. l. lead such institutes as VNIILM, MLTI, LenNIILKh, LTA, etc.

">№32. "> STANDARDIZATION OF WOOD MATERIALS, development and application of standards that determine the rational standard sizes and quality of timber produced by the industry, taking into account the requirements of the national economy and the prospects for its development.

"\u003e Timber of a certain established purpose is called an assortment. The quality of a particular assortment means a set of properties that meet certain requirements in accordance with its purpose. The more fully the assortment satisfies the requirements imposed on it by GOST, the higher its quality.

"> In the standards for different kinds round timber reflects the following those. assortment requirements: mandatory wood species, dimensions, tolerances and allowances for nominal dimensions, processing quality, grade, wood defects and their allowable dimensions, technical properties the wood itself (without defects). In addition, GOST 2292 (ST SEV 813) regulates the rules for marking, sorting, transportation, measurement, accounting and acceptance of timber. Timber storage is carried out in accordance with the requirements of GOST 9014.0.

"> By quality, round timber is divided by unified standards into four grades. Within each grade, the norms for tolerance of wood defects are given, which are common for all assortments, which facilitates the work of markers, crosscutters and scrapers and contributes to a more rational crosscutting of logs and improving the quality of products. Homogeneity of quality features within each grade for many assortments, it allows logging enterprises to better maneuver the stocks of wood available in the warehouse during its shipment.If the species composition, sizes, grades and prices match, some assortments can be replaced by others.

">№33. "> Standards should provide:

"> - correct understanding and unambiguous interpretation of special terms,

"> related to timber;

"> - an accurate statement by buyers of requirements for timber;

"> - perhaps a more complete description by sellers useful properties

"> sold timber;

"> -correct recognition and accurate measurement of features used in

"> quality control of timber;

"> - the use of methods for measuring dimensions and volume, providing close to

"> true value and economical use of wood in processing.

"> Quality class A

">First-class lumber, basically corresponding to butt logs with clean wood without blemishes or with minimal defects and with minimal restrictions on use.

"> Quality class B

"> Timber from medium to first quality without special requirements for clean wood, knots are allowed to the extent that is average for each species.

"> Quality class C

"> Timber of medium to low quality, values ​​of all quality characteristics slightly lower than normal values ​​are allowed.

">Quality class D

"> Timber that can be sawn with useful use of wood that does not meet classes A, B, C.

"> No. 34. Round timber with a thickness of 14 cm or more (stroyles, poles for power transmission line supports, sawlogs) must be marked individually in accordance with GOST 2292-88.

"> The marking is applied to the upper (thin) end of the timber with waterproof paints or weather-resistant crayons. The marking must contain the designation of the grade and thickness of the timber.

"> The variety is affixed with Arabic (1, 2, 3) or Roman (I, II, III) numerals.

"> The diameter of the timber is indicated Arabic numerals

"> 0 corresponds to a diameter of 20, 30, 40 cm, etc.

"> 2 corresponds to a diameter of 22, 32, 42 cm, etc.

"> 4 corresponds to a diameter of 14, 24, 34 cm, etc.

"> 6 corresponds to a diameter of 16, 26, 36 cm, etc.

"> 8 corresponds to diameter 18, 28, 38, etc.

">№35 ">. Quantification timber products is to determine the volume of accepted wood and its composition in terms of size and number of units.

"> Most round timber is taken into account in volumetric measures. A cubic meter is taken as a unit of wood volume.

"> They distinguish between a dense cubic meter, which means the volume of one cubic meter of the wood itself, and a folding meter, that is, the amount of wood contained in one cubic meter of space. In a folding m3, there are always air spaces between individual pieces of wood, as if tightly we never laid them in. Therefore, there is always less wood in a folded m3 than in a dense one.

"> The volume of round timber obtained from the top part of the trunk with increased taper is determined according to table No. 4 of the same GOST.

"> In this work, these tables are given in abbreviated form in special tables.

"> The thickness of round timber is calculated as the arithmetic mean of the measurement results of two mutually perpendicular diameters at the upper end. If the measurement site of the diameter of the timber coincides with the local thickening caused by the location of branches or other defects in the wood, then the diameter is measured in two measurements at the same distance above or below from this place and calculated as the arithmetic mean of the measurements made.

"> Determination of the volume of firewood measured in a folding measure is carried out in accordance with GOST 3243-46

"> Firewood is measured in storage cubic meters (1 storage cubic meter is equal to 1x1x1 m).

"> The density of laying firewood in woodpile is checked in the same way as the density of laying round commercial timber up to 2 m long in a pile.

"> The full-wood factor for a large batch of firewood (1000 m3 or more) with an average length of 1 m is taken when they are taken into account in size: for coniferous species 0.70; for hardwood 0.68.

">№36. "> Sawmill production produces sawn products (sawn products). Sawn products are wood products obtained by longitudinally dividing logs into parts of the transverse and longitudinal cutting of the resulting parts. It is produced in the form of lumber: beams, bars, boards, sleepers, both floors.

"> According to the shape and size of the cross-section, sawmill products are divided into types with different names.

"> Beam sawn timber with a width and thickness of 100 mm or more. Two-edged beam a beam with two opposite layers that were processed by sawing or milling. Three-edged beam a beam that has three longitudinal surfaces processed by sawing or milling. sawn or milled surfaces.

"> Bar lumber up to 100 mm thick and not more than double thickness wide.

"> Board lumber, up to 100 mm thick and more than double thickness wide.

"> Obapol sawmill product, which is obtained from the side of the log and it has one sawn and the other unsawn or partially sawn surfaces.

"> Sawmill products by species are divided into softwood sawn products (pine, spruce, cedar, fir, larch) and hardwood sawn products (soft hardwood - birch, linden, poplar; hard hardwood - oak, beech, elm, hornbeam).

"> By size in accordance with GOST 24454 80 (for coniferous) and GOST 2695 83 (for hardwood lumber), gradations in thickness, width and length are established.

"> Grading is determined by a combination of wood defects and processing defects.

">№37 ">. The length of lumber and blanks is measured by the smallest distance between the ends in compliance with the gradation value; the width of edged lumber and blanks with parallel edges in any place along the length where there is no wane, but not closer than 150 mm from the end; the width of uncut lumber in the middle length (excluding bark) and is defined as half the sum of the width of the layers, while values ​​\u200b\u200bless than 5 mm are not taken into account, 5 mm or more are considered as 10 mm The thickness of lumber and blanks is measured anywhere along the length, but not closer than 150 mm from the end.

"> The volume of blanks of different sections provided for by the standards, and lumber (boards, bars, edged beams) is determined according to the tables of volumes (GOST 5306-64) in cubic meters of one piece or m; the volume of plates and quarters according to the tables of round timber (GOST 2708 -75) with a decrease of 2 or 4 times.

"> Lumber from a length of m and blanks of any length are subject to marking. A symbol of a grade or quality group is applied to one of the ends or to the face with a chipping mark or indelible paint. Vertical stripes are applied to the end of lumber and blanks up to 25 mm thick, with a greater thickness dots Special-purpose blanks are marked with the addition of the following letters: for wagon construction O, skis L, resonant R.

"> Accounting for lumber is made in cubic meters. When calculating the cubature of lumber, permissible deviations in size are not taken into account.

">№39. "> Antiseptics for wood protect wood from moisture, atmospheric influences, solar radiation, protect wood from rotting, mold, fungi, wood blue, destruction by wood insects. Antiseptics are used to protect wood (wood impregnation), to cover sawn and planed wooden surfaces from the outside and indoors.

"> Antiseptics for wood are divided into 4 groups:

">1. Water soluble(water based);

"> 2. Oily (oil-based);

"> 3. Based on organic solvents;

"> 4. Combined;

">№40. "> Flame retardant is a special component of varnishes and paints, which gives them high refractory properties. In modern construction of residential and industrial premises flame retardants are widely used.

"> Requirements for flame retardants:

"> - prevent burning and smoldering of the protected material;

"> - do not cause corrosion of metal parts;

"> - duration of action;

"> - do not increase the hygroscopic properties of wood;

"> - not be poisonous to humans and animals;

"> - do not affect paint coatings applied to impregnated wood;

"> - to ensure (independently or together with antiseptics introduced in the same solution) the biostability of the impregnated material;

"> - do not create difficulties in the mechanical processing of the material;

"> - do not affect the properties of the impregnated material;

"> - do not be scarce.