home Calculators Pressed wood effects. Boiling in alkali and pressing made the wood much stronger

Pressed wood effects. Boiling in alkali and pressing made the wood much stronger

The production and use of sliding friction parts from pressed wood makes it possible to improve specifications woodworking equipment and increase its efficiency.

Today, the main use of modified wood is the production of sliding friction parts for woodworking equipment. The practice of using pressed wood shows that the use of 1 ton of this material in friction units can replace 6–7 tons of bronze, 15–20 tons of cast iron and 6–8 tons of steel. Plain bearing shells operate reliably in abrasive, aqueous and corrosive environments, even without the installation of seals. At the same time, the cost of pressed wood is much less - compared to cast iron by three times, with steel by five times, with bronze by 20 times, and with textolite by 2.5 times. In addition, the use of pressed wood can significantly reduce the weight of the friction unit.

Creating production sites for the production of pressed wood does not require large investments. As a rule, their area does not exceed 30–50 m2, and wood waste, which is available not only at woodworking, but also at metalworking enterprises, can be used as raw material. Simple equipment for serial pressing equipment can be manufactured by local machine shops. The site can be serviced by two or three semi-skilled workers. One of the significant advantages of both solid and pressure-treated wood is the ability to absorb and retain grease, making it difficult for moisture to penetrate into it. At the same time, the hydrophobicity of pressed wood increases significantly, resulting in environment The reliability of the parts made from it increases.

The coefficient of friction of oil-impregnated pressed wood paired with steel ranges from 0.06–0.08 or less for various types lubricant. Also, pressed wood has high elastic compliance, which makes it a valuable material for the production of bushings, liners, and crowns of silent gears operating under shock and alternating loads. Today, in Russia and abroad, various methods have been developed for pressing and impregnating raw and dry wood, as well as for shaping blanks of friction unit parts (mainly bushings) by pressing and bending. But the most widely used method in the manufacture of sleeve bearings is uniaxial uneven pressing.

Main technological operations in the manufacture of bushings from pressed wood are: obtaining pressed wood sectors (by axial uneven pressing of natural wood blocks) and assembling a bushing with a ring cross-section from pressed wood sectors. This design of the sleeve guarantees the radial arrangement of all wood fibers, which allows the part to withstand the load and ensures its greatest wear resistance. The device for producing cylindrical sectors operates as follows. A matrix with a separating bar and a punch is installed on the support platform between the jaws of the mold. The mold is placed on the hydraulic press table. The punch is lifted and blocks of natural wood are placed on the supporting planes of the matrix. Then the punch is lowered until it comes into contact with the workpieces. After this, the wood is compacted to a given degree of compression. In the compressed state, the resulting sectors are kept under pressure and transferred for assembly of the bushing blank.

The technology for assembling a sleeve from pressed wood sectors is as follows. First, glue is applied to the joint surfaces of the sectors. After this, the sectors are assembled into a bushing blank by placing the sectors in a clamp. Next, the sleeve blank is repressed from the clamp into a cylindrical mold, where it is pressed in the axial direction to the required size. After this, the bushing blank is pressed out of the mold. However this technology labor-intensive and low-productivity both in terms of manufacturing individual sectors and in terms of assembling sectors (the number of which, for example, with an internal diameter of the sleeve of 150 mm is 12). Specialists of the St. Petersburg State Forestry University named after. CM. Kirov (SPbGLTU) a less labor-intensive and more productive method for the production of bushings from pressed wood elements has been developed to obtain final products higher quality.

To do this, a cylindrical blank is turned from natural wood, cut into it (for example, on milling machine with a dividing head) radially located grooves, the number and width of which are determined by the purpose of the sleeve. The depth of the groove is determined by the diameter of the depressions Dвп, which is selected smaller than the internal diameter of the future finished product Dvp.ed. Next, inserts made of pressed wood, lubricated with glue on opposite sides, are installed in the grooves, orienting the wood fibers of all inserts radially. Pressing of the liners to a given degree of pressing is carried out in advance. Moreover, pressing is carried out in the most technologically advanced way - axial compression of the liner blank bar across the fibers. This allows you to achieve the highest degree of wood compaction at the lowest cost. Internal stresses in a pressed liner with a rectangular cross-section are distributed more evenly in relation to the stress distribution in liners with a sector-shaped cross-section. In this case, the height of the liners b with the height of the grooves h is related by the dependence b=h+(Rн-Rк), where Rн, Rк are the initial and final radii of the workpiece.

Rice. 1. Device for manufacturing cylindrical sectors 1 – mold, 2 – punch, 3 – matrix, 4 – dividing bar, 5 – bar

Obviously, the difference (Rн-Rк) is related to the degree of compaction of the wood of the workpiece, which is set during the manufacture of the product. Then the workpiece with installed liners is subjected to radial pressing until the specified size Rк is obtained. The pressed workpiece is drilled to obtain the size Dvp.izd. In this case, the following condition is met: Dvp.ed. > Dvp. The finished product is placed in a bath of dehydrated mineral oil at room temperature and kept for 5–12 days (depending on the volume of the bushing wood). It is preferable to impregnate blanks for pressing sectors with oil before they are piezo-treated, since in this case the area of penetration of oil from the vessels through the pores into the intermicellar space of the wood will be maximum. However, preliminary impregnation complicates both the process of pressing the sectors (due to squeezing out oil onto the equipment) and the process of their subsequent gluing when placed in a clamp. Impregnation of the finished product made using the proposed technology is possible as a final operation, since in this case the liners (to a lesser extent) and the sectors located between them are impregnated. These sectors are the main oil reservoirs that provide lubrication of the rubbing surfaces of the friction unit during operation.

Rice. 2. Sequence of assembly of bushings with liners, a – workpiece with longitudinal slots, b – workpiece with installed pressed wood liners, c – workpiece with liners after radial pressing, d – product after drilling a hole

The implementation of the proposed technology for manufacturing bushings with liners in the form of pressed parallelepipeds is much cheaper and simpler than known technology assemblies of bushings from pressed sectors. It does not require the manufacture of separate molds for each standard size of bushings, allows you to maximize the density of pressed wood of the bushings, reduces internal stresses glued structure, improves lubrication conditions, which generally improves the performance characteristics of friction units. And the use of the method of installing embedded inserts into the body of a workpiece with cut grooves also makes it possible to produce shaped bushings, for example conical, as well as friction parts for sliders and guides.

Rice. 3. Shaped parts of friction units made of wood

Wood structure after processing

Researchers have learned to increase the strength of wood by boiling wooden blocks in an alkaline solution and pressing them. After this procedure, the bars become five times thinner and 11.5 times stronger, the magazine reports. Nature.

Not all materials scientists develop new materials from scratch, synthesizing them artificially. Some prefer to take existing natural materials as a basis and improve their characteristics different ways. Wood is often used as a base - one of the most common natural materials. For example, last year, scientists developed a composite analogue of spider webs, consisting of 90 percent cellulose nanofibers extracted from wood.

Researchers led by Liangbing Hu from the University of Maryland also took wood as a basis and developed a method that increases its strength by an order of magnitude. It consists of two main stages. First, the wooden blocks are placed in a boiling solution of sodium hydroxide and sodium sulfite and boiled for seven hours. After this, they are washed several times with boiling deionized water and the remaining solution is removed. This treatment leaves almost all cellulose fibers in the wood, but removes most lignin and hemicellulose surrounding them. Due to this, the wood becomes more porous and less rigid.

After this, the wood blocks are pressed at a temperature of 100 degrees Celsius. Tests by researchers on oak and linden bars showed that their thickness decreases five times and their density increases three times, while without removing lignin and hemicelluloses, the density changes much less.

Photos and microstructures of wood before and after treatment

Jianwei Song et al. / Nature, 2018

In addition, scientists tested mechanical properties processed wood. It turned out that after treatment, the strength of linden increases 11.5 times from 52 to 587 megapascals. The researchers were able to strengthen oak bars to similar values (608 megapascals), but their strength was initially twice as strong. This strength is comparable to many grades of stainless steel. In addition, the specific strength of such wood turned out to be noticeably higher than that of many alloys, for example, 1.7 times higher than that of the titanium alloy Ti-6Al-4V.

The scientists analyzed the structure using a scanning microscope and found that, unlike compressed wood, from which lignin and hemicelluloses were not removed, in treated wood, the cellulose structures become much closer and intertwined when pressed.

In 2016, this group of researchers developed a similar wood-based material. Instead of pressing the wood after cooking, they filled it with epoxy resin, which removed air from the cavities inside the wood and made it transparent.

Grigory Kopiev

structural material, wood subjected to compression perpendicular to the grain under pressure up to 30 Mn/m 2 (300 kgf/cm 2). Density D. p. 1200-1450 kg/m 3. Depending on the pressing method, a distinction is made between compaction produced by one-sided, two-sided and contour compaction. One-sided compaction is carried out by pressing blocks of wood across the grain in one direction, two-sided - in two directions. The second method achieves a higher density. Contour compaction is carried out by pressing a cylindrical piece of wood into a metal cylinder of a smaller diameter. The tensile strength of wood under static bending and compression along the fibers, as well as the hardness of the end surface, is 2-3 times higher than that of natural wood. In industry, it replaces ferrous and non-ferrous metals, textolite. Drivers for weaving machines, sliding bearings operating in an abrasive environment, etc. are made from D.

Lit.: Khukhryansky P.N., Wood pressing, 3rd ed., M., 1964; Plywood Manufacturer's Handbook, M., 1968.

A. N. Kirillov.

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Wood is a natural polymer composite material that changes its properties under mechanical and chemical influence. Knowing the patterns of material changes, you can create them purposefully, imparting the qualities required by the consumer. This is called wood modification process. It is necessary in the production of chipboard, MDF, OSB, WPC and other wood materials, where crushed wood mixed with a polymer binder is pressed to produce a homogeneous material of standard sizes.

The proposed wood modification technology changes the properties of wood in the massif, that is, to the entire depth of the processed material, without resorting to grinding it. This is achieved by the fact that the molecules of the modifier, i.e., a substance that helps change the properties of wood, are comparable in size to the molecules of the wood substance and less than the size of the intercellular spaces in it. Therefore, by diffusion or forced impregnation under pressure, the modifier penetrates the entire thickness of the impregnated product, and then, under the influence of temperature and pressure, reacts with natural chemicals found in the wood substance. Thus, the technology makes it possible not to chop wood, not to use expensive polymer binders, and to achieve the same effect that was achieved in the production of MDF, for example, but in a cheaper way. At the same time, the solid wood with all its positive properties is preserved, the texture stands out brighter, and the color can be changed (lamination is not required).

So, the modifier must, in a dissolved state, penetrate the cellular structures of wood, be chemically active for the components that make up the wood substance, and, reacting with these components, purposefully change the physical and operational properties of the material. The most suitable substance for this is urea, after all, in the previously mentioned MDF or OSB, the most applicable binders are urea. Urea is soluble in water, including that contained in a bound state in wood, which means that by saturating the wood with an aqueous solution of urea, we, paradoxically, “dry” it, “taking” part of the wood moisture onto hydrophilic urea. Urea or urea actively reacts with components of wood substances such as lignin, hemicelluloses, and extractives. And since polycondensation reaction occurs in the macromolecules of woody matter, the solid wood acquires new useful qualities specified by the manufacturer, while retaining the positive old ones. The urea solution is not harmful, chemically neutral, moreover, grade A urea according to GOST 6691-77 is used as a feed additive for livestock.

Urea-modified wood is certified (GOST 24329-80) and is mainly used under the Destam or Lignoferum trademarks in the production of bearing shells. In the production of construction and joinery products, thermally modified wood is currently also used, the technology of which is similar to that proposed, except that the chemical modification of the wood substance is carried out in the absence of urea due to the polycondensation of decomposition products of lignin, hemicelluloses, extractives and xylans. Due to thermal degradation, the physical and mechanical properties of thermally modified wood are partially reduced.

The technological process for producing mechanochemically modified wood consists of impregnating the original wood of any species and any moisture content with a modifier solution. Impregnation can be carried out using the “hot-cold bath” method - diffusion or in an autoclave - forced. Then drying is carried out, if necessary - with compaction (pressing), and heat treatment, which fixes the new properties of the wood. It should be noted that it is more economical to use low-value rocks, since their performance properties after modification are superior to those of expensive rocks (see table).

Properties (at 12% humidity)	Oak	Pine	Aspen	MD of unpressed aspen	MD pressed aspen
Color	light brown	yellow	white	From yellow to brown	Until black
Texture	expressive wife	weak	not expressed	Pronounced	Vividly expressed
Density	690	505	495	700	1200
Moisture absorption in 30 days. At air humidity 92%, %	24,5	19,5	19,0	14,6	14,9
Ultimate strength at: compression along the fibers; static bending, MPa	57,1103,0	50,482,0	44,777,4	100,0123,0	150,0250,0
Hardness across the fibers, MPa	52,0	26,0	18,5	73,0	100,0
Biostability: weight loss from exposure to mold in 45 days, %	27	27	27	4,0	3,5
Fire resistance: weight loss during combustion, %	18,3	36,2	19,6	5,0	3,3
Modulus of elasticity in bending, GPa	10,2	11,8	9,2	20,1	24,7
Impact strength, kJ/sq.m	76,3	41,3	45,0	54,0	110,0

The original wood treated in this way during drying is chemically compacted as a result of the removal of water and the reaction of the modifier with the wood substance: by 5-31% for coniferous species and by 12-35% for deciduous species. If greater compaction is required, hot pressing of dried wood is used with a compaction of 50-70%.

By using various additives to the modifier, from any type of original wood it is possible to obtain modified wood (WM) with increased strength properties, high hardness and abrasion, non-flammable or completely fireproof, with increased water and moisture resistance, not susceptible to the effects of biopests. And mechanochemically modified wood is transformed into a thermoplastic material, that is, it can be pressed, easily bent, and processed by thermal rolling, which opens up new technological possibilities for MD processing. The shape given by MD is preserved by heat treatment.

If you only need to obtain a log, beam or board from modified wood, which will subsequently be subjected to traditional woodworking, then the process can be carried out sequentially in impregnation baths or an autoclave, drying - in a conventional drying chamber, heat treatment - in a heat treatment chamber with temperatures up to 200 ° C. To combine these processes, a special wood modification unit (WMD) has been developed and tested.

Fig. 1 Pilot industrial sample of a plant for wood modification with a loading volume of 0.2 cubic meters

The installation allows impregnation with a modifier solution under pressure, accelerated drying of impregnated wood at variable pressure and temperature, and final heat treatment during one cycle. The installation also allows you to compact the MD or press out a special profile on the product using a thermocompression liner included in the UMD kit.

So a spruce log with a diameter of 150 mm and a length of 2.5 m in a freshly cut state with a humidity of 85%, a density of 450 kg/cub.m., with all the inherent disadvantages of this species (lounging knots, low bio-fire-moisture resistance) after 77 hours of processing in UMD has the following properties:

humidity 8%;
density 630 kg/cub.m.;
fire resistance is increased by 50%, and when using special additives to the modifying solution, the log does not support combustion at all;
moisture resistance is increased by 30% (more when using special additives to the modifier);
MD is not susceptible to biological pests (mold, fungi, bugs, etc.);
the protruding knots are pressed and fused;
During the drying process, a groove and a ridge can be pressed onto the log for articulation when assembling the log house (tested - 15 mm deep);
The texture of the wood is pronounced, the color can vary from golden to dark brown throughout the entire thickness.

Mechanochemically modified wood is processed on serial woodworking machines, taking into account its hardness when sharpening tools. Due to the increased deformability of MD before heat treatment, such types of processing as pressing in presses with heated plates, bending and rolling are used.

Fig. 2 Samples of wood processed in UMD: pine, birch, spruce logs, oak beams on the right, logs with pressed grooves for assembly

Pressing allows you to obtain a multi-level image (thread) with a depth of up to 10 mm and higher on the surface of an MD shield, as well as a flat image with a three-dimensional effect (holography). By the way, after hot pressing, no grinding operations are required, since the surface quality of the product is determined by polishing the mold. There is also no need for varnishing, since the modifying composition forms a protective film on the surface of the product during pressing.

Fig.3 Panels made of mechanochemical modified birch wood (relief on the left, flat on the right)

The area dimensions of the pressed product are determined by the dimensions of the heated plates of the pressing equipment, and the cost of the equipment itself also depends on these dimensions. To avoid this, when producing large-area products from mechanochemically modified wood, the thermocompression molding method is used.

The method is carried out as follows: a wooden blank in the form of a joinery and furniture board assembled from slats is placed in the lower part of a special mold (SPF), the contours of which correspond to the contours of the blank. A relief-forming stamp is placed on top, forming a decorative image on the surface of the workpiece under pressure. Between the upper and lower parts of the SPF there is a composite thermally expanding elastic molding insert, which, when heated, provides the necessary pressure of up to 30 MPa. The degree of deformation of the workpiece depends on the thickness of the liner. The dimensions of the pressed product are determined only by the dimensions of the SPF and the composite liner, which makes it possible to produce an entire tabletop or paneled door of any size.

Blanks for joinery and furniture panels are made from individual MD slats, which can be of different widths, but of the same thickness. The technical result is achieved by making calibrated holes in the original slats made of modified wood with a certain pitch, forming transverse channels coaxial with the subsequent slats of the shield, and longitudinal grooves are made on the side surfaces, forming an internal power reinforcing lattice, followed by filling the free channels with a mixture of urea resins with foaming agent and filler in the form of sawdust. The composition of the material of the power grid filler is the same type as the modifier, and additional transverse polymer bonds are created between them during the pressing process as a result of the polycondensation reaction. The power reinforcing grid ensures the solidity of the product during operation and eliminates warping of large panels. In the proposed method, when preparing slats from MD, the requirements for manufacturing accuracy are reduced compared to traditional methods of adhesive splicing, as a result of which it becomes possible to automate the process, and there is no need for careful selection textures and colors. Their partial discrepancy is compensated by the creation of a uniform color background and decorative pattern during hot pressing. In addition, this method involves a wide range of products using various types of wood, including non-business

The technological process of bending consists of through impregnation of the original wood with a modifying solution, drying to a certain humidity, heating the wood blank immediately before bending, bending itself with heat treatment of the curved product fixed on the template in a heat chamber. After heat treatment The dimensions of the product can only change when it is heated above 200°C. The greatest difficulties in the bending process arise when bending hardwood, since for beech and oak it is impossible to maintain the original color of the wood if large deformations are required. As a result, the oak becomes stained (black), and the beech becomes dark brown. Aspen bends best, and it acquires a golden hue. In small-scale, in the form of a trial batch, the production of frames for oval mirrors measuring 1410x410 mm was tested. Blank: beech strip 2m long, with a rectangular cross-section of 12x22mm, and it was necessary to bend according to the smallest cross-sectional dimension. The part was a U-shaped shell, with a cross-sectional size on the front side of 22mm, and a bendable side of 12mm. Bending was carried out without tires, since it is problematic to make them for such a small size (12mm), according to a template on which the workpiece was heat-treated in a fixed state. As a result, defects (chipping) occurred only when cut fibers emerged on the outer side (slanting). The results are in the photo.

Fig.4 Bent beech blank for shell

Drying and pressing of end blanks from mechanochemically modified wood has been tested. Pressing end-face blanks from MD has its own characteristics: MD is compacted in the axial direction, i.e., along the fibers, which implies the application of a lower specific pressure, but this pressure must be selected so as to avoid loss of stability of the deformed blank and the formation of cracks in it, since tangential and radial stresses arising during end pressing have opposite signs.

Fig.5 End blank made of MD pine

As a result of the conducted studies of the physical and mechanical properties of end-modified wood, it was established that the degree of deformation of the wood can be taken as a parameter characterizing both the pressing process itself and the resulting material. The pressing force depends on the initial density of the wood species used and the direction of pressing. To achieve the same density of MD of different species, the degrees of deformation differ significantly and depend on the initial density of the wood and its moisture content during the pressing process. It was also established that the maximum deformability of the end blanks of MD pine is 75%, and that of birch MD is 70%. However, with such large deformations, the modified wood fibers lose stability, which leads to the formation of chips and cracks on the front surface of the samples. Therefore, to eliminate these factors, it is necessary to limit the radial deformation of the MD, i.e., it is necessary to use molds with lateral pressing of the MD during the end pressing process.

Currently, barometer bodies are made from end-grain wood at Utes LLC; when used to modify the original large-sized blanks, it is planned to produce stools and tables of “rustic design”.

The intended consumers of MD products will be companies whose main activity is the construction and decoration of residential premises, since the properties of the manufactured product are unique. Thus, fireproof logs and beams are the most valuable material for the construction of houses, bathhouses, and outbuildings. Technologies and equipment have been developed to complete the entire facility under construction with MD products: logs and beams for the load-bearing frame, boards for the floor and ceilings, moldings and beams for door and window blocks, panels for the interior decorative finishing of the building. At the same time, product prices will not be significantly higher than the prices of products traditionally made from industrial wood, and the properties will be unique. Further development of the market is determined by the decorative properties of MD and the technological capabilities of its processing: compressibility, the possibility of bending and rolling. This determines the following circle of potential consumers: finishers, furniture makers, designers, parquet floorers.

Current experience shows that the creation of production sites for the production of modified wood does not require large costs and large areas. The equipment can be manufactured by the repair and mechanical services of the enterprise. The above allows us to say that the use of modified wood, the involvement in the production of cheap, underutilized soft hardwood wood will expand the areas of application of wood, reduce production costs and make fuller use

Modified is called solid wood with directionally modified physical or chemical methods and properties. According to GOST 23944-80 and GOST 24329 - 80, there are five main modification methods and corresponding types of products.

Thermomechanically modified wood is also called compressed wood (CP). When pressing pre-steamed or heated wood, usually in a plane across the fibers, a change in the macrostructure of the wood occurs, an increase in density and an improvement in the properties associated with it. Work on thermomechanical modification carried out by the Voronezh Forestry Engineering Institute (now VGLTA) and other organizations made it possible to propose various technological processes and techniques for producing densified wood.

It is advisable to obtain pressed wood using soft hardwoods, and in some cases coniferous and even hardwood. Requirements for raw materials for the manufacture of DP are regulated by GOST 23551 - 79. The brands, sizes and indicators of physical and mechanical properties of block and board type blanks, as well as cylinders, bushings, etc. from pressed wood are established by GOST 24588 - 81 and GOST 9629 - 81 DP density 800-1350 kg/m3.

Pressed wood has several times greater strength, hardness and impact strength than natural wood, has fairly good anti-friction properties and can be used to make bearings instead of bronze, babbitt and other metals. Pressed wood dampens vibrations well and has the ability to absorb abrasive particles, which protects shafts from damage. In water, pressed wood swells and delayed deformations return. However, in some cases, swelling and decompressing of DP may be useful, for example, in sealing devices of hydraulic machines. Pressed wood is used to make bushings for road wheels, gears, parquet and other purposes. Pressed wood can be further modified by filling it with oils, metals, and polymers, mainly to improve its properties as an anti-friction material.

In chemical-mechanical modification, wood is preliminarily (or simultaneously) treated with ammonia, urea or other substances, and then compacted. The Institute of Wood Chemistry of the Academy of Sciences of Latvia has developed a technology for producing lignamon, a material from wood that has been treated with ammonia, pressed and dried. Preliminary chemical treatment causes a change in the properties of cell walls, the wood is plasticized, it is easy to give new uniform. Wood plasticized with ammonia absorbs water, swells and compresses. Impact elevated temperature these disadvantages can be reduced. Indicators of the physical and mechanical properties of lignamon blanks are given in GOST 9629-81.

Furniture parts, parquet, musical instruments. Urea-modified compressed wood (destam) is used for flooring.

Thermochemically modified wood is a material obtained by impregnating wood with monomers, oligomers or resins and subsequent heat treatment for polymerization or polycondensation of the impregnating composition.

In some cases, chemical grafting of the modifier to the polymer components of wood is observed. Wood is most often impregnated with phenol-formaldehyde resins, for example, in the form aqueous solution phenolic alcohols, furan-type resins, polyester resins, etc. Work on thermochemical modification was carried out at BelTI, the Central Research Institute of Building Structures (TsNIISK) and other organizations.

Modification of wood with synthetic resins reduces its hygroscopicity, water absorption and permeability, reduces swelling, increases strength, stiffness and hardness, but often reduces impact strength. Resin formulations have been developed that make it possible to obtain the necessary improvement in properties without increasing the fragility of the material; low-flammability and bioresistant materials have been created. Thermochemically modified wood is used in building structures, furniture, and ski production.

When modifying wood by radiation-chemical methods, polymerization of substances introduced into wood occurs under the influence of ionizing radiation. Wood is impregnated with methyl methacrylate, styrene, vinyl acetate, acrylonitrile and other monomers, as well as mixtures thereof. Work carried out at the branch of the Physicochemical Institute named after. V. L. Karpov showed that this method of modification improves the dimensional stability, mechanical and operational properties of wood. Modified wood is used to make parquet, machine parts and other purposes.

In chemical modification, wood is treated with ammonia, acetic anhydride, or other substances that change its fine structure and chemical composition. Treatment with ammonia increases the pliability of wood; under its influence, wood self-compacts during drying and changes color. Treatment with acetic anhydride is carried out for the purpose of acetylation of wood, that is, the introduction of acetyl groups into the composition of its chemical components. In acetylated wood, the mechanical properties change slightly, but water and moisture absorption, swelling and shrinkage are significantly reduced. It is advisable to use acetylated wood for the manufacture of products with increased dimensional stability. Work in the field of wood acetylation was carried out at the Latvian Agricultural Academy.