Novel wood protection method and wood product manufactured by this method

Abstract

This document discloses an environmentally friendly method for protecting wood against biological deterioration, such as damage by fungi, bacteria, and insects, and non-biological wood deterioration, such as weathering. The method involves contacting the wood with an aqueous solution of a zirconium salt prior to a heat treatment step, providing durable wood protection against biodegradation and improving several other properties of the treated wood.

Description

Technical Field

[0001] The present invention relates to an environmentally friendly wood protection method against biological deterioration such as damage caused by fungi, bacteria, and insects, and non-biological wood deterioration such as weathering. The method includes contacting the wood with an aqueous solution of a zirconium salt before a heat treatment step, providing wood protection that is durable against biodegradation, and improving some other properties of the treated wood.

Background Art

[0002] Structurally, wood can be regarded as a porous, fibrous, hydrophilic and rigid biocomposite mainly composed of cellulose, hemicellulose and lignin. Due to its properties, wood is susceptible to environmental degradation including both physical and microbiological factors. Conventionally, various biocides and insecticides have been used to preserve and protect wood against decay, fungi, and insects. These compounds very often have an adverse effect on human health and the environment. For this reason, new methods for preventing attacks from decay, fungi, and insects have attracted considerable attention among researchers. In particular, when protecting wood under harsh conditions such as contact with the ground, solutions for wood modification with improved resistance to biodegradation are sought without adversely affecting nature and human health. Regarding wood, protection against fungi, decay, and insects that destroy wood is not only a very important property, but also properties such as low water absorption, excellent dimensional stability, high mechanical strength, and enhanced protection against natural weathering are very important factors contributing to the expanded use of wood as a building material, for example.

[0003] Regarding both economic and environmental impacts, various protection technologies exist with different protection efficiencies. Current technologies can be classified into "surface" and "depth direction" protection. Among other problems, surface protection technologies such as organic coatings have problems of anisotropic protection and lack of protection mechanisms for the whole and inside of wood, and surface protection is vulnerable to physical damage to thin surface coatings.

[0004] The "depth direction" protection technology is either "chemical impregnation" or "heat treatment". However, most of the existing "depth direction" protection technologies have significant drawbacks. As an example, there is a category of technologies based on "chemical impregnation" that use various biocides (e.g., ammoniacal copper quinate with boron (ACQ - B), copper azole with boron (CBA), chromated copper arsenate (CCA), and similar chemicals) that cause significant environmental problems. Other technologies known as environmentally friendly technologies also have drawbacks such as the complex / expensive manufacturing of acetylated and furfurylated wood and the reduction of mechanical properties in heat - treated wood.

[0005] Zirconium, the 20th most abundant element in the earth's crust, belongs to Group IVB of the periodic table. Zirconium exhibits a preferred oxidation state of 4, and the redox chemistry under these conditions is unknown. Zirconium has a high charge to radius ratio, and when dissolved in water, it hydrolyzes to form polymeric species where zirconium atoms are bonded and cross - linked by hydroxyl groups. Further hydrolysis polymerization of these polymeric species can occur by aging, heating, or a decrease in acidity, forming polymers with charged or neutral properties.

[0006] The polymeric species of zirconium in aqueous solution can act chemically and physically with various functional groups of organic polymers. The reactions of aqueous zirconium species are known, for example, with carboxyl groups, hydroxyl groups, and amine groups. The reaction of zirconium with the functional groups of organic polymers can be significantly controlled by changing the temperature, pH, and chelating agent. Zirconium polymer species based on the usage amount, physical parameters, and the degree and type of functionality in the organic polymer can induce cross - linkages, improve the adhesion of the treated object and the surface, and enhance the resistance to heat, scrubbing, water / solvent.

[0007] Zirconium salts have been previously proposed as agents for preventing the microbial decomposition of wood products (see U.S. Patent Application Publication No. 2011 / 250359, International Publication No. 98 / 45053, British Patent No. 809766, U.S. Patent No. 3547688, and U.S. Patent No. 5612094). However, none of these disclosures describe a method by which zirconium salts can be further used to improve other important properties of wood.

[0008] U.S. Patent No. 5612094 describes a method of contacting an aqueous composition containing one or more zirconium salts with wood and drying the wood. It is important to note that the document describes drying at low temperatures. Drying wood at low temperatures is common in the industry because it is known that drying at high temperatures deteriorates the mechanical properties and impairs the color properties.

[0009] Therefore, there is still a need for a method of modifying wood that provides high resistance to biological degradation without impairing the mechanical properties of the wood.

Summary of the Invention

Problems to be Solved by the Invention

[0010] An object of the present invention is to provide wood protection using a zirconium composition that has a long protection duration against biological degradation and very little leakage.

[0011] Another object of the present invention is to provide wood protection using a zirconium composition that improves the mechanical properties of wood.

[0012] An object of the present invention is also to provide wood protection using a zirconium composition that increases the hydrophobicity of the treated wood, reduces the moisture content, and thereby contributes to the dimensional stability of the wood.

[0013] Yet another object of the present invention is to provide wood protection using a zirconium composition that prevents discoloration of wood and maintains compatibility with conventional coating materials. **Means for Solving the Problems**

[0014] In one general aspect, the present invention relates to a method for preparing a wood product, comprising the steps of contacting an aqueous composition containing one or more zirconium salts with wood, and heat-treating the wood at a temperature of 100 to 220 °C, more preferably 115 to 200 °C, and most preferably 135 to 185 °C.

[0015] Surprisingly, by drying the wood treated with an aqueous composition containing one or more zirconium salts at a high temperature, wood with improved resistance to biodegradation can be obtained, and it has been found that the mechanical properties of the wood are improved. Without being bound by theory, it is considered that the high temperature enables an effective chemical bond between the zirconium salt and the hydroxyl and carboxyl groups of the wood. Thereby, by suppressing the decomposition mechanism, the strength loss of the heat-treated wood due to the decomposition of hemicellulose and amorphous cellulose is reduced or eliminated.

[0016] The zirconium salt is preferably selected such that the protonated counter ion of zirconium in the salt has a boiling point lower than the temperature of the heat treatment step.

[0017] Examples of zirconium salts having various anionic counterions soluble in water include, but are not limited to, zirconium acetate, ammonium zirconium carbonate, zirconium bromide, zirconium chloride, zirconium hydroxy nitrate, zirconium nitrate, zirconium oxide diperchlorate octahydrate, zirconium oxychloride, zirconium oxy nitrate, zirconium sulfate, zirconium sulfate tetrahydrate, zirconyl chloride, zirconium acetate hydroxide, zirconium orthosulfate, and zirconium sulphamate.

[0018] In one aspect of the method of the present invention, the composition contains zirconium ions from one or more zirconium salts in an amount of 0.01 to 30% (w / w), preferably 0.1 to 15% (w / w), and more preferably 0.2 to 6% (w / w), and preferably the zirconium salt is zirconium acetate.

[0019] In one aspect of the method of the present invention, the composition has a pH value of 2 to 13, preferably 2 to 11, and more preferably 2 to 9.

[0020] In one aspect of the method of the present invention, the contacting step is carried out by dipping, impregnating, padding, foularding, dipping, spraying, brushing, coating, rolling, foam coating, and is preferably carried out by vacuum pressure impregnation.

[0021] In one aspect, the method includes a step of drying the wood to a moisture content of less than 20% before heat-treating (i.e., curing) the wood.

[0022] In one aspect, the method includes a pretreatment step of drying the wood product to a moisture content of less than 40% before contacting it with the aqueous composition.

[0023] In one embodiment, the method includes a pretreatment step in which the wood product is heated to a temperature of from 5 to 250° C. prior to contacting with the aqueous composition.

[0024] In one embodiment, the method includes heating the aqueous composition to less than 100° C. prior to contacting the wood.

[0025] In one embodiment, the method includes heating both the wood product and the aqueous composition prior to the contacting step.

[0026] In another general aspect, the invention relates to a wood product treated according to any of the aforementioned methods.

[0027] Preferably, wood products treated with the method of the present invention have chemical bonds between zirconium atoms and hydrophilic functional groups selected from hydroxyl and carboxyl groups of hemicellulose, cellulose, or lignin in the treated wood.

[0028] The wood product of the present invention preferably has a lower crystallinity index (CrI) compared to the same heated wood product that has not been contacted with an aqueous composition comprising one or more zirconium salts. The crystallinity index Crib is calculated from a 13C CPMAS NMR spectrum having a peak area X from a chemical shift in the range of 86-92 ppm representing crystalline cellulose and a peak area Y from a chemical shift in the range of 79-96 ppm representing amorphous cellulose, and the CrI is calculated according to the formula (X / X+Y)*100.

[0029] The wood products of the present invention generally have improved resistance to heat, decay, fungi, mold, bacteria, insects, and weathering.

[0030] In one embodiment, when a wood product is prepared by the method of the present invention from pine sapwood wood, its CrI is lower than the CrI of pine sapwood wood that has been heat treated at the same temperature but has not been contacted with the aqueous composition.

[0031] In the wood products of the present invention, the zirconium salt forms a chemical / physical bond between the impregnated zirconium salt and the chemical components within the cell wall of the wood and / or the cellulose itself, thereby leading to the treated wood being protected against microbiological and bioenvironmental factors such as decay, weathering, moisture dimensional changes, and attacks by mold / mildew, as well as similar decomposition phenomena.

[0032] The aqueous composition used in the method and product of the present invention generally comprises one or more zirconium salts, water, and optionally at least one of an antifoaming agent, a preservative, a rheology modifier, a wetting agent, and a UV stabilizer. The components of the liquid composition of the present invention may have the aforementioned chemicals in any proportion. One of the most important features of the aqueous composition (for protection against decay, fungi, and insects) is that it remains in the wood and is supported by any of the aforementioned additives to prevent leaching.

[0033] Regarding the zirconium salt, the present invention relates to an environmentally friendly impregnation liquid formulation of a water-soluble zirconium salt having a pH value of 2 to 13, preferably 2 to 11, and more preferably 2 to 9, where the weight percentage of zirconium ions from the zirconium salt ranges from 0.01 to 30% (w / w), preferably 0.1 to 15% (w / w), and more preferably 0.2 to 6% (w / w).

[0034] According to the present invention, the wetting agent can refer to any surfactant, thickener, or stabilizer. The surfactant can be ionic or non-ionic. The surfactant is defined as a non-ionic emulsifier having an HLB value of 1 to 41 and can be selected from the types of surfactants having wettability in wood. In one embodiment, the emulsifier does not affect the reactivity of the zirconium oxide function and the hydrophobicity of the wood after heat treatment. In a preferred embodiment of the present invention, the wetting agent is used in an amount of less than 7 w / w%, preferably 0.01 to 4 w / w%, more preferably 0.1 to 3 w / w%. Examples of wetting agents include, but are not limited to, Lutensol TO5 from BASF, Lutensol TO7 from BASF, Brij S10 from CRODA, and the like.

[0035] The defoaming agent in the composition used in the present invention reduces foaming during production and application. Examples of suitable defoaming agents include, but are not limited to, EO / PO type defoaming agents, silicones, tributyl phosphate, alkyl phthalates, emulsion type defoaming agents, fatty acid based defoaming agents, etc. In a preferred embodiment, Dispelair CF 56 (Oy Chemec Ab) is used.

[0036] The dyes and pigments of the present invention refer to any dyes and pigments used to induce a color different from the color of the raw wood. The dyes and pigments can be organic or inorganic. In a preferred embodiment of the present invention, the dyes and pigments are used in an amount of less than 7 w / w%, or 0.01 to 4 w / w%, most preferably 0.1 to 3 w / w%.

[0037] The rheology modifier can be used to change the rheology profile and adapt it to a specific type of application method. Various types of rheology modifiers include, for example, fumed hydrophobic silica nanoparticles (Wacker HDK H30RM) and hydrophilic silica nanoparticles (Wacker HDK V15) (Wacker chemie AG), starch and its derivatives, or cellulose derivatives such as carboxymethyl cellulose. A suitable concentration of the rheology modifier in the aqueous composition of the present invention may be, for example, 0.5% to 5% (w / w).

[0038] In the composition used in the present invention, the UV stabilizer can refer to any molecule that absorbs / scatters UV radiation and reduces the UV degradation (photooxidation) of wood. The UV stabilizer can be organic or inorganic. In a preferred embodiment of the present invention, the UV stabilizer is used in an amount of less than 7 w / w%, or 0.01 to 4 w / w%, most preferably 0.1 to 3 w / w%.

[0039] The aqueous composition used in the present invention is a stable formulation and preferably has a shelf life of more than one month at a temperature below room temperature or in the range of 0 to 65 °C.

[0040] In the method of the present invention, the aqueous composition can be applied to wood using a non-pressure impregnation method including brushing and spraying, dipping, immersion, diffusion method, Boucherie method (sap replacement), warm and cold bath (see Richardson 1978, Tsoumis 1991, Walker 2006). Alternatively, an impregnation method combining vacuum and pressure, Bethell method (full-cell), vacuum method (full-cell), Rueping method (empty-cell), double Rueping method (empty-cell), Lowry method (empty-cell), vibration pressure method, cascade method, Nordheim method, Cellon or Drilon method, pressure-stroke method, Boulton method, Poulain method, etc. (see Ille 1959, Richardson 1978, Tsoumis 1991, Walker 2006) can be used to apply the aqueous composition to wood. The most preferred method of impregnation is the vacuum / pressure impregnation method. The time, temperature, and pressure are adjusted according to the type of wood until essentially sufficient impregnation is achieved.

[0041] The wood used in the present invention can be selected from spruce, pine, birch, oak, redwood, cedar, or composite materials such as plywood, fiberboard, particleboard, or pulp-based materials such as paperboard, cardboard, gypsum-grade paperboard, special paper, or molded pulp products.

[0042] After the drying process, before entering the heat treatment (curing) process in the wood treatment process, the wood preferably has a moisture content of less than 20%. The drying process is carried out at room temperature or below, or at a high temperature of 15 to 135 °C, particularly 25 to 105 °C.

[0043] The drying method of the present invention can be carried out using any drying technology such as microwave, IR, pulse, induction, air drying, kiln drying, dehumidification, vacuum drying, solar kiln, water seasoning, boiling or steam drying, chemical or salt drying, electric drying, and similar methods. The method can be carried out essentially until dry, preferably until the moisture content is less than 20%, in the absence or presence of a vacuum, an inert atmosphere, steam, or an atmospheric atmosphere.

[0044] The heat treatment (curing) according to the method of the present invention can be carried out under various atmospheric conditions using any heating technology such as the Westwood method, the Thermowood method, the Plato method (Ruyter 1989; Boonstra, Tjeerdsma and Groeneveld 1998), the Retification method (Vernois 2000), the Les Bois method, the thermal vacuum method (Vacwood), microwave, IR, pulse, induction, air drying, kiln drying, and similar methods. Non-limiting examples of the atmospheric conditions that can be used are inert atmospheres such as nitrogen atmosphere, steam and atmospheric atmosphere or reduced atmospheric atmosphere. The heat treatment can be carried out under various program cycles, heating rates, and heating times. Preferably, the curing / heat treatment step is carried out for 1 to 72 hours. The whole heat treatment may include two steps. Drying is carried out in the first step and curing is carried out in the second step. The drying temperature, time program, and method can be selected differently for the purpose of the moisture content of the wood reaching 20% or less. And the mild curing step of the present invention can be adjusted to 100 to 220 °C, more preferably 115 to 200 °C, and most preferably 135 to 185 °C.

[0045] Here, as an example, the present invention will be described with reference to the accompanying drawings.

Brief Description of the Drawings

[0046]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0047] One of the most important features of the impregnating liquid (protection against decay fungi and insects) is to remain in the wood under natural / accelerated weathering conditions and to be prevented and minimized from leaching. This is a very important feature for extending the service life of the treated wood. The inventors have found that heat treatment (curing) of the impregnated wood is necessary to form physical and chemical bonds between the zirconium salt and the hydroxyl and carboxyl groups of the wood. To elucidate the reaction between the zirconium salt and the wood, a model reaction (Figure 1) was devised in which zirconium acetate (water-soluble) was reacted with extracted wood hemicellulose (water-soluble) at a molar ratio of 1:1 (monosaccharide: Zr) and then cured at 135 °C. As a result, a product that was no longer water-soluble was produced by the chemical reaction between zirconium acetate and the reactive groups (hydroxyl groups, carboxyl groups, and the like) of hemicellulose. From this, it became clear that there was a cross-linking between the structures. Therefore, in the wood impregnated with zirconium acetate and heat-treated, it can be expected that the reactive groups in the chemical components (cellulose, hemicellulose, and lignin) of the wood react with the zirconium salt and the same phenomenon occurs.

[0048] <General procedures for preparing Compositions 1 to 2 according to the present invention>

[0049] Method 1 Step a) Mix the zirconium salt composition and water in any order of addition, Step b) Add a deformer, a wetting agent, and other optional components to the mixture obtained in Step a, where the mixture obtained in Steps a to b is optionally mixed and / or optionally homogenized.

[0050] Method 2 Step a) Mix a deformer, a wetting agent, and other optional components in water, Step b) Add a zirconium salt to the mixture obtained in Step a, where the mixture obtained in Steps a to b is optionally mixed and / or optionally homogenized.

[0051] The apparatus for preparing the aqueous composition is any kind of experimental or industrial apparatus that uses low shear force and / or high shear force to produce the homogeneous composition of the present invention. This includes an overhead stirrer equipped with a magnetic stirrer, a propeller or a disperser, etc., a high-pressure or non-high-pressure homogenizer, an in-line homogenizer or an external homogenizer, an extruder, a vibrating device, a mortar and pestle, a blender-type device, any kind of mixer (static mixer, micromixer, vortex mixer, industrial mixer, ribbon blender, V blender, continuous processor, cone screw blender, screw blender, double cone blender, double planetary, high-viscosity mixer, counter-rotating, double and triple shaft, vacuum mixer, high-shear rotor stator, dispersing mixer, paddle, jet mixer, mobile mixer, drum mixer, intermix mixer, planetary mixer, Banbury mixer, etc.), a French press, a crusher, a mill (grinding by a bead mill, a colloid mill, a hammer mill, a ball mill, a rod mill, a self-grinding mill, semi-autogenous grinding, a pebble mill, a high-pressure grinding roll, a buhrstone mill, a vertical shaft impactor mill, a tower mill, etc.), ultrasonic treatment, a rotor-stator mechanical device, any kind of propeller or mixer, a high-temperature and / or high-pressure bitumen emulsifier, or a combination of the above may be used.

[0052] Table 1 below summarizes the examples showing the present invention in the following sections of this specification.

[0053]

Table 1

[0054] The described structural changes in wood due to the reaction with zirconium salts under curing conditions have some influence on the properties of the wood. These are illustrated in the following examples.

[0055] Example 1 Reduction of hydrophilicity of wood by reaction of zirconium salts with hydrophilic functional groups in wood

[0056] As shown in Figure 1, a water-soluble component hemicellulose and zirconium acetate were mixed and cured at 135 °C to produce a turbid / opaque dispersion (not water-soluble). This property may be due to the chemical bond between zirconium acetate and the hydrophilic functional groups (hydroxyl, carboxylic acid, and the like) of hemicellulose and the cross-linking of monosaccharide-based molecules.

[0057] Example 2 Figure 2 shows the high hydrophobicity and low moisture sorption of wood. As shown in Figure 2, due to the hydrophobicity of the modified product, wood impregnated with zirconium acetate and heat-treated at 185 °C shows a lower equilibrium moisture content at the same relative humidity compared to the original / untreated reference wood.

[0058] Example 3 Figure 3 shows the high hydrophobicity and low moisture content of wood by immersion in water. The amount of water absorbed in wood impregnated with zirconium acetate and heat-treated at 185 °C is much less than that in untreated wood and wood treated only by heat treatment.

[0059] Example 4 Generally, when heat-treating wood, discoloration of the wood may occur, which may be related to the amount of decomposition occurring in the wood during the heat-treatment process. Evaluation of the discoloration of wood due to heat-treatment was carried out using untreated wood and wood impregnated with zirconium salts. In the zirconium salt-impregnated wood, there was basically no discoloration before and after heat-treatment. It was also proven that the presence of more zirconium salts can protect the wood against discoloration during heat-treatment at a given temperature. Wood impregnated with 3% and 10% zirconium acetate and heat-treated at 185 °C was subjected to sensory panel evaluation. The sensory panel used individuals who were trained to compare wood products and evaluate discoloration. Brown was ranked on a scale from 0, indicating no brown color, to 5, indicating a very dark brown color. Untreated wood was ranked 0. Wood heat-treated without impregnation was ranked 3. From the results shown in Table 1 below, it is clear that wood impregnated with a 10% zirconium acetate solution had less discoloration and thus less decomposition of the wood during heat-treatment at 185 °C. The presence of zirconium salts in the wood during the heat-treatment process clearly has a certain protective role against thermal decomposition. Table 2 below shows the discoloration evaluation of the heat-treated wood.

[0060]

Table 2

[0061] Example 5 To further evaluate the present invention, a 1-dimensional ((1D) 1 H→ 13 C CPMAS spectrum was recorded using a solid-state 400 MHz NMR spectrometer. For solid-state NMR recording, fine powders of all samples of untreated wood, heat-treated wood, and zirconium salt-impregnated and heat-treated wood were prepared. Figure 4 shows the 13 C CPMAS NMR spectrum and signal assignments of Scots pine wood, where Cr means crystalline, am means amorphous, and h means hemicellulose.

[0062] Figure 5 shows the recorded 13 C CPMAS NMR spectra of Japanese red pine sapwood, "Japanese red pine sapwood + heat treatment at 185°C", and "Japanese red pine sapwood impregnated with 3% zirconium acetate + heat treatment at 185°C". First, the chemical components of the wood were qualitatively identified. The 13 C CPMAS NMR spectra of the wood samples are dominated by signals attributed to cellulose. Further studies of hemicellulose in the wood matrix are more complex due to the significant overlap of signals attributed to hemicellulose and cellulose, but the lignin signals show little interference (due to different chemical properties). 13 C CPMAS NMR spectra of Japanese red pine sapwood, "Japanese red pine sapwood + heat treatment at 185°C", and "Japanese red pine sapwood impregnated with 3% zirconium acetate + heat treatment at 185°C" are shown. First, the chemical components of the wood were qualitatively identified. The 13 C CPMAS NMR spectra of the wood samples are dominated by signals attributed to cellulose. Further studies of hemicellulose in the wood matrix are more complex due to the significant overlap of signals attributed to hemicellulose and cellulose, but the lignin signals show little interference (due to different chemical properties).

[0063] During the heat treatment of wood, acetic acid is produced from the hydrolysis of acetyl esters in xylan. Hemicellulose is depolymerized into oligomeric and monomeric units, and further dehydrated to aldehydes under acidic conditions, resulting in wood with fewer hydroxyl groups and lower hygroscopicity. The effect of heat treatment on the depolymerization of cellulose is rather limited, and instead, the crystallinity of cellulose increases slightly. Lignin is the least active component and can only be cleaved at high temperatures to form phenolic groups. Therefore, generally, the changes in wood properties, similar to the strength loss of heat-treated wood, are considered to be mainly the result of the thermal decomposition of hemicellulose via an acidic autocatalytic reaction.

[0064] To conduct a comparative decomposition study between different treatments, the crystallinity of cellulose, determined as the crystallinity index (CrI), was calculated by deconvolving the area X of the C-4 signal of crystalline cellulose (86 - 92 ppm) and the area Y of the C-4 signal of amorphous cellulose (79 - 86 ppm) (Wikberg, Hanne. 2004. Advanced Solid State NMR Spectroscopic Techniques. PhD thesis, Helsinki, Finland: University of Helsinki).

[0065]

Equation

[0066] More decomposition of the amorphous region is associated with a higher crystallinity CrI of the sample (Table 2 and Figure 6). Quantitative 13 C solid NMR shows that the cellulose crystallinity (the ratio of peak integration of "crystalline + amorphous" cellulose to "crystalline cellulose") of the pine sapwood impregnated with zirconium acetate and heat-treated at 185 °C is lower than that of the pine sapwood heat-treated at 185 °C. This means that when the wood is impregnated with zirconium acetate, the decomposition of hemicellulose and amorphous cellulose is less.

[0067] Quantitative 13 C solid NMR shows that the cellulose crystallinity (the ratio of peak integration of "crystalline + amorphous" cellulose to "crystalline cellulose") of the pine sapwood impregnated with zirconium acetate and heat-treated at 185 °C is lower than that of the pine sapwood heat-treated at 185 °C. This means that when the wood is impregnated with zirconium acetate, the decomposition of hemicellulose and amorphous cellulose is less.

[0068] Example 6 The weight loss of the wood during heat treatment as a result of the thermal decomposition of the biopolymer into low-molecular / volatile molecules is another sign indicating the degree of decomposition. The weight analysis of the wood sample and the amount of low-molecular-weight volatile molecules released during the heat treatment process were evaluated by weighing the dry wood before and after the heat treatment at 185 °C. The results show that the wood impregnated with 3% zirconium acetate exhibits controlled decomposition and a mass loss of approximately 2%, which is almost the same as that of the unimpregnated wood.

[0069] As another evidence of less decomposition of the wood structure into low molecules, the amount of the leached substance after the leaching test (EN84) was measured. It can be concluded that the heat-treated (185 °C) zirconium-impregnated wood has less leaching than the heat-treated (185 °C) but unimpregnated wood (see Figure 7).

[0070] Example 7 Table 3 below shows the improvement of the water contact angle. As shown, when water was used, a higher contact angle (CA) could be measured in the wood impregnated with the Zr salt and heat-treated, compared to the wood treated only with heat.

[0071]

Table 3

[0072] Example 8 Table 4 below shows the dimensional expansion of the pine sapwood immersed in water for 4 days. The chemical changes and the introduced hydrophobicity of the zirconium-impregnated heat-treated wood were able to reduce the dimensional change of the wood sample, compared to the reference wood and the wood treated only with heat.

[0073]

Table 4

[0074] Example 9 Soft rot protection is carried out in accordance with CEN TS 15083-2 (SS-ENV 807:2009). The soft rot test carried out using the standard SS-ENV 807:2009 showed that the moisture content of the zirconium-impregnated / heat-treated wood was lower compared to the raw wood and the wood treated only with heat at the same temperature (see Figure 8). This low moisture content can further reduce the damage caused by biological wood degradation and biodeterioration. The reduction in mass loss of the zirconium-impregnated / heat-treated wood compared to the raw wood and the wood treated only with heat demonstrated the effectiveness of the heat-treated zirconium-impregnated wood against soft rot, which can be attributed to both the low moisture content of the wood and the low availability of digestible food sources. See Figure 9.

[0075] Example 10 The aqueous solution of the soluble zirconium salt has a minimum incompatibility with wood and makes the impregnation process very efficient. For example, the impregnation of wood with a 3% zirconium acetate solution at 11 bar took only 3 hours to reach 327 kg / m 3Impregnation water absorption up to this point occurred, which means that almost all of the sapwood parts of the impregnated wood were saturated with the zirconium salt aqueous solution (see Table 5). The deep penetration depth of the zirconium solution will bring about protection in the depth direction of the final product and longer durability. This experiment confirms the industrial feasibility of the present invention.

[0076]

Table 5

[0077] Example 11 To evaluate the state of the zirconium salt aqueous solution after being used in a large number of impregnation cycles, the aged and reused (10 impregnation cycles) liquid was examined. It was confirmed by observation that minimal chemical and physical changes occurred (there was no or minimal leaching from the wood substrate into the zirconium solution, the solution was not unstable, and there was no pH change in the liquid). This observed compatibility will further enhance production efficiency.

[0078] Example 12 Generally, when wood is heat-treated, a loss of flexural modulus and strength is expected. This is also related to the decomposition in wood, which is evident from the discoloration, mass loss, and leaching characteristics of the wood as described above. To further emphasize the advantages obtained from the present invention, a three-point bending test was conducted on untreated pine sapwood (raw material), pine sapwood heat-treated at 135°C, and pine sapwood impregnated with 5% zirconium acetate + heat-treated (135°C). As expected, the mechanical properties (both flexural modulus and flexural strength) decreased in the heat-treated wood. On the other hand, it was concluded that for the wood impregnated with zirconium and heat-treated, the wood maintained or improved its mechanical properties compared to the untreated wood or the heat-treated wood (see Figure 10).

[0079] Example 13 When the samples treated according to the present invention were subjected to EN84 / EN113 and classified according to SS-EN 350-1, good protection was confirmed against both white rot (Coriolus versicolor) and brown rot (Coniophora puteana and Gloeophyllum trabeum) (see Tables 6 and 7). The pine sapwood impregnated with a 10% zirconium acetate solution and then heat-treated at 135°C showed a natural durability class 1 (very durable).

[0080] [Table 6]

[0081] [Table 7]

[0082] Example 14 The paintability and further modification with other coatings were evaluated. The Zr-impregnated wood heat-treated according to the present invention generally showed very good compatibility with commercially available coatings / paints. The wood impregnated with 10% zirconium acetate powder, heat-treated at 135°C, further coated with one and two layers of a commercially available alkyd paint, and aged outdoors for one year still had very good quality / characteristics.

[0083] Example 15 The present invention was evaluated for protection against mold and fungal staining (blue staining) in wood. When the treated samples of the present invention and comparative wood samples were subjected to natural weathering conditions for one year, intensive fungal growth was observed on the surface and deep inside the untreated comparative samples, while it was confirmed that the 10% zirconium acetate impregnated + 135°C heat-treated wood samples received much less attack.

[0084] The present invention, generally described and exemplified as above, has the following advantages. The present invention is environmentally friendly, that is, it does not contain halogen, does not contain boric acid compounds, does not contain phosphorus, does not contain heavy metals, does not contain pesticides, and does not contain biocides. Chemical substances that are non-toxic, pose no health risks, and have no environmental hazard pictograms are used. No organic solvents are used, and only water is used. The present invention provides protection against decay and protection from rot / mildew (wood does not turn gray on the surface and deep inside so quickly when exposed to outdoor climate). Furthermore, the present invention provides hydrophobicity (increased dimensional stability, less shrinkage and swelling, fewer cracks), and although it is hydrophobic, it is still paintable and compatible with water-based coatings. Furthermore, the wood products of the present invention have minimal leakage of active ingredients, little decomposition during heat treatment, and are controlled, and their mechanical properties are improved. Finally, only industrially available chemical substances are used, and the method with the lowest risk of composition preparation, together with high durability / recyclability of the composition during efficient wood impregnation / processing and manufacturing cycles, is adopted. Aspects according to the present disclosure also include the following aspects. <1> a) contacting an aqueous composition containing one or more zirconium salts with wood, and b) heat-treating the wood at a temperature of 100 to 220 °C, more preferably 115 to 200 °C, and most preferably 135 to 185 °C A method for preparing a wood product, comprising: <2> The method according to <1>, wherein the composition contains 0.01 to 30% (w / w), preferably 0.1 to 15% (w / w), and more preferably 0.2 to 6% (w / w) of zirconium ions from one or more zirconium salts, and preferably the zirconium salt is zirconium acetate. <3> The method according to <1> or <2>, wherein the composition contains 70 to 99.99% (w / w) of water and optionally at least one of a wetting agent, an antifoaming agent, a preservative or a biocide, a dye, a pigment, a rheology modifier, and a UV stabilizer. <4> The method according to any one of <1> to <3>, wherein the pH value of the composition is 2 to 13, preferably 2 to 11, and more preferably 2 to 9. <5> The method according to any one of <1> to <4>, wherein the contacting step is carried out by dipping, impregnating, padding, foularding, dipping, spraying, brushing, coating, rolling, or foam coating, and preferably by vacuum pressure impregnation. <6> The method according to any one of <1> to <5>, further comprising a step of drying the wood to a moisture content of less than 20% before heat-treating the wood. <7> The method according to any one of <1> to <6>, further comprising a pretreatment step of drying the wood product to a moisture content of less than 40% before contacting it with the aqueous composition. <8> The method according to any one of <1> to <7>, further comprising a pretreatment step of heating the wood product to a temperature of 5 to 250 °C before contacting it with the aqueous composition. <9> The method according to any one of <1> to <8>, further comprising heating the aqueous composition to less than 100 °C before contacting it with the wood. <10> The method according to <8> and <9>, further comprising heating both the wood product and the aqueous composition. <11> A wood product prepared by the method according to any one of <1> to <10>. <12> The wood product according to <11>, comprising a chemical bond between a zirconium atom and a hydrophilic functional group selected from the hydroxyl groups and carboxyl groups of hemicellulose, cellulose, or lignin in the treated wood.

Claims

1. a) contacting a wood with an aqueous composition containing one or more zirconium salts and no biocide, and b) heat-treating the wood at a temperature of 115 to 200 °C A method for preparing a wood product, comprising: The method, wherein the zirconium salt forms physical and chemical bonds with the hydroxyl groups and / or carboxyl groups of the wood.

2. The method according to claim 1, comprising heating the wood at a temperature of 135 to 185 °C.

3. The method according to claim 1, wherein the composition contains 0.01 to 30% (w / w) of zirconium ions from one or more zirconium salts.

4. The method according to claim 3, wherein the zirconium salt is zirconium acetate.

5. The method according to claim 3 or claim 4, wherein the composition contains 0.1 to 15% (w / w) of zirconium ions from one or more zirconium salts.

6. The method according to claim 3 or claim 4, wherein the composition contains 0.2 to 6% (w / w) of zirconium ions from one or more zirconium salts.

7. The method according to any one of claims 1 to 6, wherein the composition contains 70 to 99.99% (w / w) of water.

8. The method according to claim 7, wherein the composition further contains at least one of a wetting agent, an antifoaming agent, a preservative, a dye, a pigment, a rheology modifier, and a UV stabilizer.

9. The method according to claim 1, wherein the pH value of the composition is 2 to 13.

10. The method according to claim 9, wherein the pH value of the composition is 2 to 9.

11. The method according to claim 1, wherein the contacting step is performed by dipping, impregnation, padding, foularding, dipping, spraying, brushing, coating, rolling, or foam coating.

12. The method according to claim 11, wherein the contacting step is performed by vacuum pressure impregnation.

13. The method according to claim 1, comprising a step of drying the wood to a moisture content of less than 20% before heat-treating the wood.

14. The method according to claim 1, comprising a pretreatment step of drying the wood product to a moisture content of less than 40% before contacting it with the aqueous composition.

15. The method according to claim 1, comprising a pretreatment step of heating the wood product to a temperature of 5 to 250 °C before contacting it with the aqueous composition.

16. The method according to claim 1, comprising heating the aqueous composition to less than 100 °C before contacting the wood.

17. The method according to claim 15 or claim 16, comprising heating both the wood product and the aqueous composition.

18. Comprising a chemical bond between a zirconium atom and a hydrophilic functional group selected from the hydroxyl and carboxyl groups of hemicellulose, cellulose, or lignin in the treated wood Having a low crystallinity (CrI) compared to the same heated wood product that is not in contact with the aqueous composition containing one or more zirconium salts A wood product prepared by the method according to any one of claims 1 to 17

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