RU2768389C1 - Fire-protective agent for wood (options) - Google Patents

Abstract

FIELD: fire protection.SUBSTANCE: group of inventions relates to the field of fire protection of wood. The product obtained by liquid-phase catalytic oxidation of crushed lignocellulose biomass of coniferous wood is used as a fire-protective agent for wood. Fire-protective agent for wood is a composition of a product obtained by liquid-phase catalytic oxidation of crushed lignocellulose biomass of coniferous wood, with an inorganic component selected from the group: silicon dioxide, borax, zinc chloride, with an inorganic component content from 5.0 to 15.0 g in 1 liter of the specified product.EFFECT: fire hazard of wood decreases, the effectiveness of protecting wood from fungal microorganisms increases.8 cl, 5 tbl, 2 dwg

Description

The invention relates to the field of bio-fire protection of wood and can be used to reduce the fire hazard of wood and protect it from the destructive action of fungal microorganisms.

The widespread use of building materials and wood products makes it necessary to use products that protect wood from burning and reduce its fire hazard. On the other hand, it is known that the main biological factor in the destruction of wood and building structures made from it and other products exposed to environmental factors are damage caused by microscopic fungi using cellulose, lignin and other wood components as a nutrient medium. The development of fungal infections can not only reduce the consumer properties of wood, but can also be dangerous for human health, because. micromycetes and their metabolic products can cause serious allergic reactions.

Although there is a wide range of fire retardant and bioprotective agents for wood on the market, including organic and inorganic compounds or their mixtures of various compositions, the most attractive from a consumer point of view are agents that have a combined protective effect, which simultaneously protect wooden products and structures from fire and the destructive action of fungal microorganisms. As a rule, manufacturers do not disclose the chemical composition of such products, see, for example, [https://leroymerlin.ru/catalogue/antiseptiki-dlya-dereva/ognebiozashchita/]. As a rare exception, we can cite information about preparations based on sodium pentachlorophenolate, borax and boric acid, in which, according to the manufacturer, pentachlorophenolate plays the role of an antiseptic, and the 6opa compound plays the role of a fire retardant [https://whitestrip.ru/ognezashhitnaja-i- antisepticheskaja-obrabotka/].

Known patent documents describing the means of combined use, designed for fire bioprotection of wood. For example, in the invention [RU 2157822, C1, publ. 20.10.2000] describes a flame retardant antiseptic, which is the reaction products of the interaction of phosphorous acid and an aqueous solution of ammonia 3-25%, taken in a volume ratio of 1:1-7. The subject of the invention [RU 2430829 C1, publ. 10.10.2011] is a fire antiseptic for wood, which is a mixture of esters of perfluorocarboxylic acids in the form of a 15-20% solution in lower aliphatic alcohols. Fire and bioprotective compositions for wood based on the natural product of bischofite are proposed. For example, in the invention according to the patent [RU 2497662 C1, publ. 11/10/2013] describes the composition, which is obtained by electrolysis of a bischofite solution using zinc electrodes. During the electrolytic oxidation of a solution of natural bischofite, chlorites, hypochlorites, hypobromites of magnesium and zinc are formed, the mutual action of which creates a synergistic effect, thereby enhancing the fungicidal, bactericidal activity of the final antiseptic fire retardant product. It should be noted that halogen-containing additives, especially hypochlorites and hypobromides, release free halogens into the environment under operating conditions, which contributes to the formation of toxic chlorine(bromine)-substituted dioxins.

Current trends focused on "green" environmentally friendly technologies make technical solutions that do not harm the environment preferable. In [A.V. Khvatov et al "Study of antiseptic properties of the flame retardant solution provided by oxidized plant waste with regard to wood staining and mold micromycetes", 2019 IOP Conf. Ser.: Mater. sci. Eng. 525 012103], taken by us as a prototype, it is shown that previously known as a fire retardant, an aqueous solution of a mixture of products of the catalytic oxidation of the substrate, including as a starch-containing component from 20 to 80 wt. % of crushed rice grain, and wood flour as a source of cellulose and lignin, also exhibits the properties of an antiseptic for wood. The product has undoubted advantages over most known drugs in terms of environmental aspects of its production and use, however, in terms of fungicidal activity, the product can only be classified as a medium-effective antiseptic.

The present invention solves the technical problem of expanding the arsenal of environmentally friendly fire and bioprotective agents for wood. The problem is solved by the proposed product options, which simultaneously reduce the fire hazard of wood and more effective than the prototype, protect wood from fungal microorganisms.

The essence of the invention is illustrated by the following illustrations.

On FIG. 1 shows the IR spectra of the ARBOXID product (spectrum 1) and composite products containing 15, 10 and 5 g of borax per 1 liter of the ARBOXID product (spectra 2, 3 and 4, respectively). The spectra were taken on a Tensor 37 spectrometer (Bruker) by the method of frustrated total internal reflection infrared spectroscopy (FTIR) with Fourier transform.

On FIG. 2 shows the results of differential scanning calorimetry (DSC) analysis of the ARBOXID product and composite products based on it. Curve 1 - ARBOXID product, curve 2 - composite product containing 10 g of silicon dioxide per 1 liter of product, curve 3 - composite product containing 10 g of borax per 1 liter of product, curve 4 - composite product containing 5 g of zinc chloride per 1 g of the product.

The proposed technical solution is based on the fact that we discovered, which consists in the fact that the exclusion of the starch-containing component from the composition of the oxidized initial substrate makes it possible to obtain a mixture of oxidation products that retain high fire-retardant efficiency and, at the same time, exhibit significantly higher fungicidal activity than the prototype product.

Based on this, one solution to the problem is that as a fire and bioprotective agent to reduce the fire hazard and increase the biostability of wood, a product obtained by liquid-phase catalytic oxidation of crushed lignocellulosic biomass of coniferous wood (hereinafter referred to as the “ARBOXID product”) is used. Previously described the use of the product ARBOXID as a means for flame retardant treatment of various combustible materials [RU 2425069 C2, publ. 27.07.2011], as well as in compositions for the production of low-flammability polyester binders [RU 2674210 C1, publ. 12/05/2018]. The mechanisms of the fire-retardant action of the ARBOXID product, as an intumescent flame retardant, are described in [S.M. Lomakin et al. “Investigation of the mechanism of the fire-retardant action of a bioantipyrene obtained on the basis of oxidized compounds of cellulose-containing biomass”, Chemical Physics, 2020, vol. 39, no. 11, p. 58-61].

As a second solution to the problem, a fire and bioprotective agent for wood is proposed, which is a composition of the specified product obtained by liquid-phase catalytic oxidation of crushed lignocellulosic biomass of coniferous wood, with an inorganic component selected from the group: silicon dioxide, borax, zinc chloride, with an inorganic component content of from 5.0 to 15.0 g in 1 liter of the indicated product.

EFFECT: variants of fire-bioprotective agents for wood are proposed, which provide a reduction in its fire hazard indicators and have a bioprotective efficiency higher than the agent according to the prototype.

According to GOST 12.1.044-89, the fire hazard of materials is a set of properties that characterize their ability to initiate and spread combustion. The fire hazard of wood samples treated with the proposed variants of fire bioprotective agents, in comparison with control samples not treated with protective agents, as well as in comparison with samples treated with a prototype agent, was characterized according to the method ISO 5660-1 "Behavior during tests for fire hazard - Heat dissipation, smoke emission and mass loss rate. Part 1: Heat release rate (cone calorimeter method) and smoke formation rate (measurements in dynamics)”. Test results show that all proposed products have the ability to reduce the fire hazard of wood, and more effectively than the prototype product.

Under the bioprotective action in the context of this invention refers to the ability of the proposed products to protect wood from fungal attack. Bioprotective properties, characterized by indicators of antifungal activity, are determined according to GOST 30028.4-2006 “Protective means for wood. Express method for evaluating the effectiveness against wood-destroying and mold fungi ”It is shown that all the proposed products are highly effective wood fungicides, significantly surpassing the prototype product in terms of protective effectiveness.

The ARBOXID product is a water-soluble fraction of the reaction products of the liquid-phase catalytic oxidation of crushed lignocellulosic biomass in an alkaline medium, obtained after separating solid reaction products insoluble in an aqueous alkaline medium. As lignocellulosic biomass, the use of wood flour from coniferous wood is optimal, however, raw materials of a lower degree of grinding, for example, sawdust, can be used. Oxidation is carried out with oxygen at a pressure of 2-3 atm. in the presence of copper salts at a temperature of 60-70°C for 8-10 hours. ARBOXIDE is a translucent brown liquid, well absorbed by the wood surface. The total dry matter content in the product is 15-20 wt. %. Along with the products of catalytic oxidation of the initial lignocellulosic substrate, ARBOXID contains alkali and a water-soluble copper salt used as a catalyst.

The mixture of soluble products of oxidation of woody biomass has a complex, incompletely established multicomponent composition. It includes salts of polyhydroxyphenolic compounds that are products of incomplete oxidative depolymerization of lignin, low molecular weight hydroxyphenolic compounds and secondary products of their condensation, hydrocarbons, products of oxidative decomposition of cellulose, etc. According to GC-MS analysis, it includes terpenes, hydroxy acids, resin and fatty acids and their salts, as well as the products of their interaction with each other [S.M. Lomakin et al. “Investigation of the mechanism of the fire-retardant action of a bioantipyrene obtained on the basis of oxidized compounds of cellulose-containing biomass”, Chemical Physics, 2020, vol. 39, no. 11, p. 58-61]. Unlike the prototype, ARBOXID does not contain products of incomplete hydrolysis and oxidation of starch, which can serve as a favorable environment for the development of fungal cultures. Perhaps the presence of these compounds is one of the reasons for the relatively low fungicidal efficacy of the prototype product.

The possibility of using the ARBOXID product not only as a flame retardant, but also as an antiseptic for wood, expands the potential for its practical application as a universal agent that provides comprehensive wood protection. ARBOXID is obtained by practically waste-free technology under the conditions of conventional chemical production using standard equipment and available materials. Its use as a fire bioprotective agent for wood not only does not harm the environment, but also contributes to solving an important environmental problem - the disposal of large-tonnage waste from woodworking and woodworking industries.

It was shown that the introduction of a number of inorganic components into the ARBOXID product, such as silicon dioxide, or borax, or zinc chloride in the amount of 5-15 g per 1 liter of the product, makes it possible to obtain composite products that are superior in fungicidal activity to the prototype product, and at the same time reduce performance. wood fire hazard.

The use of inorganic boron compounds in fire bioprotective agents for wood is known from the prior art. So, for example, in the application [RU 2000126027 A, publ 08/10/2002] calcium and sodium tetraborate hydrates are used as bioprotective additives in combination with calcium sulfate and phosphate and magnetammonite phosphate as a fire retardant. In the patent [RU 2501761 C1, publ. 12/20/2013] for fire and bioprotection of heat-insulating material based on wood fiber, sodium tetraborate and boric acid, as well as a phosphorus-nitrogen-containing component in the form of amidophosphate or disubstituted ammonium phosphate, were used. The composition of these compositions includes inorganic compounds that do not enter into chemical interaction with each other. The observed protective effect is due to the addition of flame retardant and antiseptic properties of individual components.

In contrast to these examples, in the complex compositions we offer, which include a large number of organic compounds in combination with inorganic components, chemical interactions take place, leading to the formation of new products that can make their non-additive contribution to the manifestation of fire-bioprotective properties of these composite materials. This is indicated by the data of spectral and DSC analysis.

The IR spectra of dried samples obtained by the interaction of sodium tetraborate with the products of liquid-phase oxidation of coniferous wood flour were obtained on a Bruker Tensor 37 spectrometer by the method of frustrated total internal reflection infrared spectroscopy (FTIR) with Fourier transform. On FIG. Figure 1 compares the IR spectra of the ARBOXID product and composite products containing various amounts of borax as an inorganic component (spectrum 1 - ARBOXID product, spectra 2, 3, 4 - products containing, respectively, 15, 10 and 5 g of borax in 1 liter of the mixture) . An increase in the quantitative content of sodium tetraborate in the mixture is accompanied not only by a quantitative but also by a qualitative change in the spectrum, which indicates the presence of chemical interactions in the solution. This is evidenced by the appearance of a broad signal with a maximum at 1024 cm ^-1 , consisting of a set of poorly resolved bands, while an increase in the intensity of the band at 1589 cm ^-1 is observed. Absorption in this region (1510-1635 cm ^-1 ) corresponds to asymmetric stretching vibrations of the -COONa groups that are part of the dicarboxylic acids formed during the oxidation of lignin, which is part of the raw wood. An increase in the content of sodium tetraborate to 15 g/l leads to a noticeable change in the spectrum - the signals corresponding to the absorption bands of the ARBOXID product disappear, and at the same time broad bands appear at 1183, 1101 and 932 cm ^-1 , which can be attributed to compounds based on borax, since in this area there are no absorption bands belonging to the product ARBOXIDE. This suggests that "excess" sodium tetraborate does not interact with organic products of lignin oxidation and does not participate in a non-additive increase in the fire and bioprotective efficiency of the product.

DSC studies of the proposed products were carried out on a NETZSCH DSC 204 Fl Phoenix differential scanning calorimeter in an argon atmosphere, under dynamic conditions, with a heating rate of 100/min. The mass of samples is about 5 mg. The results shown in FIG. 2 indicate that in the case of the ARBOXID product, the thermal effects of the endothermic processes are related to dehydration and water evaporation. When borax or silicon dioxide or zinc chloride is added to the initial product, the picture changes: an exothermic peak appears on the DSC curves in the range of 207–225°C with heat values of the exothermic effect from 90.9 to 289 J/g. Previously, we found that the chemical mechanism of intumescent fire protection of the ARBOXID product is described by two successive stages: at the first stage, up to 200°C, reactions of dehydration and decarboxylation of aliphatic hydroxy acids, which are components of the amorphous phase of cellulose and hemicellulose, occur. Further, at a temperature exceeding 200°C, exothermic polycondensation/crosslinking reactions occur, accompanied by the release of carbon dioxide and water. A significant increase in exo-effects is due to the participation of inorganic additives in the processes of crosslinking and carbonization of the products of oxidation of the original lignocellulosic raw materials: sodium tetraborate is a part of intermediate oxyborate complexes, silicon dioxide is a promoter of the catalytic polycondensation of oxidation products, zinc chloride, as a Lewis acid, is a catalyst for condensation processes. Thus, the results of DSC analysis indicate a non-additive effect of inorganic additives on the ability of the proposed composite products to reduce the fire hazard of wood by accelerating the reactions of crosslinking/carbonization of oxidation products through solid-phase catalysis.

An increase in the content of inorganic components in the composite product to more than 15.0 g/l of the product is undesirable, since it does not lead to an additional protective effect, but it can lead to an increase in the toxicity of the agent and undesirable side effects. For example, it is known that an excess of zinc chloride can contribute to the destruction of the surface layer of wood and have a negative effect on human health. An excess of silica can lead to an undesirable increase in the viscosity of the solution and to a deterioration in its absorption by the wood. The use of inorganic additives in amounts less than 5 g/l does not give a positive effect.

Tests of the fungicidal action of the products were carried out in accordance with GOST 30028.4-200 “Protective means for wood. Express method for evaluating the effectiveness against wood-destroying and mold fungi. It has been shown that 15 days after the start of testing under standard conditions, the average area of fungal infection of wood samples treated with ARBOXID or liquid composite products based on it is less than 10%, while during the same period the damage to control samples not treated with the drug , averages 26%. At the same time, the score on the damage scale, which characterizes the stage of development of the fungus, for the tested products is 2-3 points out of 6 possible, which corresponds to a relatively low stage of development of the fungal infection. In the control, the defeat score is 3-4 points. Thus, all the proposed products have pronounced fungicidal properties and, according to GOST 30028.4-2006, are effective fungicidal agents. In terms of bioprotective effectiveness, they are more than five times superior to the prototype agent, for which the affected area, determined under the same standard conditions, is, according to published data, 50.4%.

Thus, the exclusion of the starch-containing substrate from the composition of the oxidizable biomass makes it possible to significantly increase the fungicidal activity of the resulting product and obtain composite products based on it, which also exhibit high bioprotective efficiency. As will be shown below, the treatment of wood with these products also reduces its fire hazard.

Below are specific examples of obtaining the claimed products, not covering, however, all possible options.

Example 1 Preparation of the product ARBOXID from wood flour.

15 liters of hot water at a temperature of 60°C are placed in a steel vertical sealed reactor with a volume of 0.04 m ³ , 18 g of copper sulfate (CuSO ₄ ⋅5H ₂ O) and 2.25 kg of softwood flour are added. The mixture is stirred with a mechanical overhead stirrer for 2 minutes at a speed of 50 rpm, then add 1.2 kg of sodium hydroxide. Next, the stirring speed is increased to 140 rpm, the reactor is sealed, and gaseous oxygen is fed into the reactor from above at a rate of 0.2 l/min under a pressure of 2 atm. The oxidation is carried out at a temperature of 65°C. Reaction time 8 hours. During the reaction, the concentration of free alkali in the solution decreases from 1.25 to 0.5 M. The reaction mixture is filtered on a nylon filter to separate the product from solid impurities. A brown liquid translucent product is obtained. The content of solids in 1 liter of the resulting product is 150 g.

Example 2. Obtaining the product ARBOXID from sawdust

1000 ml of water is added to a 3 liter glass reactor, heated to 70°C, 1 g of CuCl ₂ ⋅H ₂ O and 150 g of sawdust from softwood are added. The mixture is stirred with a mechanical stirrer for 2 minutes, then 50 g of NaOH are added and oxygen is fed into the reactor from above at a rate of 0.3 l/min. During the reaction maintain a constant temperature of 70°C, oxygen pressure of 2 atm. Reaction time 10 hours. During the reaction, the concentration of free alkali in the solution decreases from 1.25 to 0.5 M. The reaction mixture is filtered to separate the product from solid impurities. A brown liquid translucent product is obtained. The content of solids in 1 liter of the product is 170 g.

Example 3. Obtaining a combined product based on the ARBOXID product with the addition of zinc chloride.

7.5 g of zinc chloride are gradually added to 1 l of the ARBOXID product obtained in example 1 at room temperature with stirring. (ZnCl ₂ "RusKhim"). A cream-coloured liquid opaque product is obtained.

Example 4. Obtaining a combined product based on the ARBOXID product with the addition of silicon dioxide.

To 1 liter of the ARBOXIDE product obtained in Example 1, 15 g of silicon dioxide are gradually added at room temperature with stirring. (AEROSIL 300 with specific surface area (BET), 300±30 m ² /g, average primary particle size 7 nm, bulk density 50 g/l, Evonik Degussa GmbH). Get liquid opaque product of light cream color.

Example 5. Obtaining a combined product based on the ARBOXID product with the addition of borax.

To 1 l of the ARBOXID product obtained in example 1, at room temperature, with stirring, gradually add 15 g of borax. (Na ₂ B ₄ O ₇ ⋅10H ₂ O, "RusKhim") Get a liquid opaque light brown product.

Methods and results of testing the bioprotective effectiveness of the proposed products

Tests of the bioprotective properties of the ARBOXID product and combined products based on it were carried out in accordance with GOST 30028.4-2006 “Protective means for wood. Express method for evaluating effectiveness against wood-staining and mold fungi, which establishes an express method for testing their protective ability against wood-staining and mold fungi. The method includes a 15-day exposure of wood samples, the surface of which is impregnated with the test agent, in humid chambers operating on the principle of "closed space - moisture reserve" with a large evaporation surface, under conditions most favorable for the activity of biological agents, followed by determination of the average affected area surfaces of specimens and stages of development of the fungus. The tests were carried out on three groups of fungi shown in Table. one.

Reseeding, cultivation, storage of mushroom cultures were carried out in accordance with safety requirements (GOST 9.048). A suspension of spores obtained from pure cultures of fungi grown in bacteriological test tubes on slant agar wort was used. To prepare the suspension of spores, cultures of fungi aged from 14 to 28 days (counting from the moment of reseeding) were used, the colonies of which filled the entire surface of the agar and had well-developed sporulation. Spore suspension is prepared separately for each species of fungus by washing the spores into beakers containing 25 cm ^{3 of} distilled water. The number of fungal spores in suspension is counted using a Goryaev counting chamber. The concentration of spores in the suspension is (N±0.001)×10 ⁶ spores/ml. Next, a working suspension of fungi is prepared for infecting sawdust in desiccators, taking into account the concentration of spores by mixing suspensions of individual fungi species that are part of a certain group. To prepare a working suspension, a calculated amount is taken from each suspension of individual types of fungi to ensure the content of 10 ⁶ spores in a calculated volume of 1 ml. Measured volumes of suspensions of each fungus species are added to a beaker and diluted with distilled water to a volume of (100±1) ml. The shelf life of the suspension does not exceed 1 hour from the moment of preparation.

For the preparation of samples, wood with a production time of more than 24 hours after removal from the storage chamber is used. The tests are carried out on wood samples in the form of a parallelepiped with dimensions of 10×55×75 mm (the latter dimension is indicated by the length of the fibers). The samples were made from straight-grained freshly sawn pine sapwood with an air-dry density of 0.48-0.52 g/cm ³ . Samples are impregnated by immersion in a solution in which the samples are kept for 1 min. Control samples are immersed in water. After impregnation, the samples are kept in open desiccators at room temperature for 2 hours.

The absorption of the protective agent solution P (g/m ² ) is calculated by formula (1) with an error not exceeding 5% of its average value:

where m ₁ and m ₂ - the mass of the sample, respectively, after processing and before processing, g; - mass of the sample after processing, g; S is the surface area of the sample, m, which is 0.01085 m ² . The results are shown in Table. 2.

The data in the table show that the proposed products are somewhat worse absorbed by wood than the product of the prototype, however, as will be shown below, this does not adversely affect their fungicidal effectiveness.

The protective effectiveness of the test samples is determined as the percentage of the surface area of the sample, averaged over several repetitions, affected by fungal infection, to the total surface area of the sample, equal to 0.01085 m ² . The state of the samples is assessed visually in dynamics after 5, 10 and 15 days by the “palette” method with a grid step of 5 × 5 mm. The degree and stage of damage to the samples evaluated on the scale shown in Table. 3.

The test results of the samples obtained in examples 1.3-5 are shown in Table. 4.

As can be seen from the table, for all tested products, the average area of wood samples affected by fungi is less than 10%, while in control it is more than 26%. The degree of damage, estimated at 3-4 points for control samples, does not exceed 3 points for tested samples, and 2 points for the most effective ones. Thus, both the original ARBOXID product and composite products based on it, in accordance with GOST 30028.4-2006, are effective antiseptic protective agents for wood and are superior in fungicidal effectiveness to the prototype product, for which the affected area is more than 50%.

In Table. 5 shows the results of testing the proposed products for the ability to reduce the fire hazard of wood. Tests to determine the indicators of fire danger were carried out by the method of con-calorimetry according to ISO 5660-1 under the influence of a heat flux with a power of 35 and 50 kW/m ² . Wood samples with dimensions of 10 × 10 cm and a thickness of 0.5-1 cm are placed horizontally on the holder using a fixing frame.

As can be seen from the above data, the treatment of wood with the proposed products significantly reduces, compared with the control, the average heat release rate and the total smoke emission index with an increase in the amount of coke residue after combustion, which characterizes the fire resistance of the material.

Thus, the proposed products not only protect wood from fungal infections, but also have a pronounced ability to reduce the fire hazard of wood, showing in most cases greater efficiency than the prototype product.

The method of using the products includes a single or multiple application to the surface of wood with drying of each layer in air or impregnation of products according to known technologies, followed by drying in air.

The products can be used both for wood processing and for incorporation into wood-based materials or for their surface treatment in order to increase their fire resistance under operating conditions.

Treatment of wood with ARBOXIDE and compositions based on it does not impair its strength characteristics and gives the products a deeper color, the shades of which vary depending on the content of inorganic additives. The use of the ARBOXID product and compositions based on it as a protective agent for wood meets modern environmental requirements, since the products are obtained using a waste-free technology that ensures the disposal of large-tonnage waste from woodworking and woodworking industries.

Claims (8)

1. The use of a product obtained by liquid-phase catalytic oxidation of crushed lignocellulosic biomass of coniferous wood as a fire bioprotective agent for wood. 2. Use according to claim 1, characterized in that the crushed lignocellulosic biomass is softwood wood flour. 3. Use according to claim 1, characterized in that the crushed lignocellulosic biomass is softwood sawdust. 4. Application according to claim 1, characterized in that it is carried out by surface treatment of wood, followed by air drying. 5. Application according to claim 1, characterized in that it is carried out by impregnation of wood, followed by air drying. 6. Fire bioprotective agent for wood, which is a composition of the product obtained by liquid-phase catalytic oxidation of crushed lignocellulosic biomass of coniferous wood, with an inorganic component selected from the group: silicon dioxide, borax, zinc chloride with an inorganic component content of 5.0 to 15.0 g in 1 liter of the indicated product. 7. The agent according to claim 6, characterized in that it is used by surface treatment of wood, followed by air drying. 8. Means according to claim 6, characterized in that it is used by impregnation of wood, followed by air drying.

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