Method for producing modified wood

Abstract

A method for producing modified wood which comprises a step in which block-shaped wood is impregnated with an aqueous organic-acid solution containing an organic acid and a step in which the block-shaped wood impregnated with the aqueous organic-acid solution is dried and then heated in an inert atmosphere, the heating in the inert atmosphere being conducted at a temperature of 110-220°C.

Description

Modified wood manufacturing method

[0001] The present invention relates to a method for producing modified wood.

[0002] Since wood repeatedly swells and shrinks as it absorbs and desorbs moisture, changes in moisture content cause dimensional changes. Patent Document 1 discloses a method for suppressing such dimensional changes and imparting dimensional stability.

[0003] Patent Document 1 discloses a method for improving the mold and rot resistance of cellulose products and the dimensional stability of the products. Specifically, Patent Document 1 discloses drying cellulose products to a moisture content level of less than 15% and subjecting them to a heat treatment carried out at high temperature, in which after drying, the product is held in a moist oven supplied with steam at a temperature above 150°C under atmospheric pressure, and the treatment is continued until the product has lost at least 5% of its weight.

[0004] Patent No. 3585492

[0005] However, the method of simply drying wood and then treating it with high-temperature steam, as in Patent Document 1, has the problem of promoting the decomposition of cellulose, which is a skeletal component of wood, resulting in a decrease in the strength of the treated wood. If the heat treatment temperature of the wood is lowered to avoid this problem, the hemicellulose in the wood will not be sufficiently decomposed and modified, making it difficult to improve the dimensional stability of the treated wood.

[0006] The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a method for producing modified wood that has both excellent dimensional stability and mechanical strength.

[0007] In order to solve the above problems, a method for producing modified wood according to an embodiment of the present invention includes the steps of impregnating a block of wood with an organic acid aqueous solution containing an organic acid, drying the block of wood impregnated with the organic acid aqueous solution, and then heating it in an inert atmosphere, wherein the temperature during heating in the inert atmosphere is 110°C or higher and 220°C or lower.

[0008] Fig. 1 is an explanatory diagram showing an example of a method for producing modified wood according to the present embodiment. Fig. 2 is a graph showing the relationship between the dimensional change rate and the bending strength of the test pieces of the examples, reference examples, and comparative examples.

[0009] The modified wood manufacturing method according to the present embodiment will be described in detail below with reference to the drawings. Note that the dimensional proportions in the drawings are exaggerated for the sake of convenience and may differ from the actual proportions.

[0010] [First embodiment] The method for producing modified wood according to this embodiment includes the steps of impregnating a block of wood with an organic acid aqueous solution containing an organic acid, drying the block of wood impregnated with the organic acid aqueous solution, and then heating it in an inert atmosphere.

[0011] Figure 1 shows the flow of the modified wood manufacturing method according to this embodiment. In this manufacturing method, the first step is to impregnate a block of wood with an organic acid aqueous solution containing an organic acid. The wood may be in the shape of a block, for example, a board. The thickness of the board-shaped wood is not particularly limited, but can be, for example, 10 mm to 40 mm.

[0012] Examples of wood include wood from various tree species used for building materials such as floors, walls, and ceilings, fixtures, furniture, crafts, etc. The wood species is not particularly limited, and for example, at least one selected from the group consisting of cedar, larch, Douglas fir, rubber tree, birch, beech, oak, beech, oak, teak, hard maple, cherry, walnut, white ash, mahogany, and yellow birch can be used. These woods have a luxurious feel and are highly decorative, so by modifying these woods, they can be suitably used for building materials, fixtures, furniture, and crafts.

[0013] Furthermore, fast-growing trees, which grow to large diameters in a short period of time, primarily in Japan and Southeast Asia, can also be used. Specifically, at least one selected from the group consisting of China chinaberry, Chinese lantern tree, Japanese alder, tulip tree, eucalyptus, poplar, Acacia mangium, and falcata can be used. Fast-growing trees grow quickly and are relatively inexpensive, making them suitable for sufficient supply through plantation forestation. However, fast-growing trees have wide ring widths and large ring curvatures, resulting in anisotropic dimensional changes. Therefore, when fast-growing trees are dried, large localized shrinkage stresses occur, making them prone to drying cracks. However, as described below, organic acids and sugars have dimensional stabilizing effects, and impregnating the interior of fast-growing trees with these can suppress shrinkage. Therefore, fast-growing trees can also be suitably used as wood in this embodiment.

[0014] The wood may be in a green state with a high moisture content, or in a dried state with a low moisture content. Even when the moisture content of the wood is high, the moisture in the vessels can be replaced with the organic acid aqueous solution, allowing the wood to be impregnated with the organic acid aqueous solution. Artificially dried wood (KD wood), which has been artificially dried in a drying oven or the like to reduce its moisture content, may also be used. In this case, the moisture content of the KD wood is preferably 7 to 25%. The moisture content of wood can be measured based on Japanese Industrial Standard JIS Z2101 (Testing Methods for Wood).

[0015] Here, raw block-shaped wood (green lumber) may crack or discolor due to drying if stored at room temperature. Logs to be sawn into green lumber may also crack or discolor due to drying, so they are imported between winter and spring when temperatures are low. After sawn into green lumber, they must be stored frozen or refrigerated to prevent cracking and discoloration. In addition, because blocks of lumber are sawn from logs with a roughly circular cross section, yields are low. Furthermore, when logs are imported from overseas and sawn into blocks of lumber, waste is generated during sawing, meaning that the waste is included in the transport of the imported lumber. Therefore, when transporting green lumber and logs over long distances, transportation and storage costs tend to be high.

[0016] In contrast, dried wood (KD lumber) requires a drying process, but because it is in a dry state, there is a low risk of cracking or discoloration. Furthermore, KD lumber can be stored at room temperature. In this way, KD lumber can reduce transportation and storage costs.

[0017] In addition, if the logging site and the location where the manufacturing method of this embodiment is carried out are close to each other, there is no need to transport the logs over long distances. Therefore, in this case, it is preferable to use green lumber as the wood material, rather than KD lumber, which requires a drying process.

[0018] The organic acid aqueous solution to be impregnated into the wood can be prepared by dissolving the organic acid in water. As the organic acid, an organic compound can be used that can improve the dimensional stability and strength of wood impregnated with the organic acid aqueous solution by heat treating the wood in an inert atmosphere, as described below. Specifically, the organic acid is preferably at least one selected from the group consisting of carboxylic acids, sulfonic acids, and sulfinic acids.

[0019] The organic acid is preferably a carboxylic acid, more preferably a divalent or higher carboxylic acid. When wood impregnated with a carboxylic acid is heat-treated in an inert atmosphere, hemicellulose and lignin, which are constituent components of the wood, tend to deteriorate, thereby further promoting the modification of the wood.

[0020] The carboxylic acid is preferably at least one selected from the group consisting of citric acid, tartaric acid, malic acid, succinic acid, oxalic acid, adipic acid, malonic acid, phthalic acid, sebacic acid, maleic acid, fumaric acid, itaconic acid, glutaric acid (1,5-pentanedioic acid), gluconic acid, glutaconic acid, and pentenedioic acid. Furthermore, the carboxylic acid is more preferably at least one selected from the group consisting of citric acid, malic acid, and succinic acid. By using citric acid, malic acid, and succinic acid, modified wood with good dimensional stability and mechanical strength can be easily obtained. Furthermore, because these carboxylic acids can be obtained from naturally occurring materials, it is possible to reduce the environmental impact.

[0021] In the organic acid aqueous solution, the organic acid content is preferably 3 to 30% by mass, more preferably 3 to 20% by mass, and even more preferably 3 to 10% by mass. When the organic acid content in the organic acid aqueous solution is within this range, the organic acid can easily penetrate into wood, thereby achieving the effects of stabilizing the dimensions of wood and improving its strength.

[0022] It is preferable that the organic acid aqueous solution further contains a sugar. The organic acid aqueous solution contains both an organic acid and a sugar, which can enhance the dimensional stability and mechanical strength of wood. Specifically, by impregnating wood with an organic acid aqueous solution containing both an organic acid and a sugar, and then heat-treating the wood in an inert atmosphere, the dimensional stability and strength can be enhanced by the effect of the organic acid. Furthermore, sugars fill the microvoids in the cell walls of wood instead of water molecules, and can remain in these microvoids without evaporating even during drying. Furthermore, because sugars can maintain the cell walls in a swollen state, the so-called "bulk effect" can suppress shrinkage of the resulting modified wood.

[0023] The saccharide may be at least one selected from the group consisting of monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Examples of monosaccharides include fructose, xylose, ribose, arabinose, rhamnose, xylulose, and deoxyribose. Examples of disaccharides include sucrose, maltose, trehalose, turanose, lactulose, maltulose, palatinose, gentiobiulose, melibiulose, galactosucrose, rutinulose, and planteobiose. Examples of oligosaccharides include fructooligosaccharides, galactooligosaccharides, mannanoligosaccharides, and stachyose. Examples of polysaccharides include starch, agarose, alginic acid, glucomannan, inulin, chitin, chitosan, hyaluronic acid, glycogen, and cellulose.

[0024] Here, the sugar is preferably at least one selected from the group consisting of fructose, maltose, xylose, and sucrose. These sugars are easily available and, together with the organic acid, can further improve the dimensional stability of the modified wood.

[0025] The sugar content in the organic acid aqueous solution is preferably 3 to 30% by mass, more preferably 3 to 20% by mass, and even more preferably 3 to 10% by mass. When the sugar content in the organic acid aqueous solution is within this range, the sugars can easily penetrate into the wood, thereby achieving the dimensional stabilization effect of the modified wood with the sugars.

[0026] Since organic acids and sugars are highly soluble in water, the organic acid aqueous solution does not need to contain an organic solvent. Furthermore, the absence of an organic solvent in the organic acid aqueous solution reduces the environmental impact and increases safety for the human body.

[0027] There are no particular limitations on the method for impregnating a block of wood with an organic acid aqueous solution. For example, wood can be impregnated with the organic acid aqueous solution by immersing the wood in the organic acid aqueous solution and leaving it. In order to speed up the impregnation of the wood with the organic acid aqueous solution, it is preferable to place the wood in a pressure-resistant container filled with the organic acid aqueous solution and apply pressure. In this case, the pressure to be applied is not particularly limited, but is preferably 0.3 to 10.0 MPa, for example.

[0028] When wood is impregnated with the organic acid aqueous solution, the temperature of the organic acid aqueous solution is not particularly limited, but is preferably, for example, 80° C. or less. The temperature of the organic acid aqueous solution can also be room temperature.

[0029] To speed up the impregnation of wood with the organic acid aqueous solution, the wood may be placed in a pressure-resistant container, the pressure reduced, the air inside the wood removed, and then the wood immersed in the organic acid aqueous solution. This allows the organic acid aqueous solution to penetrate more easily into the vessels of the wood, allowing the wood to be quickly impregnated with the organic acid aqueous solution.

[0030] When impregnating a block of wood with an organic acid aqueous solution, it is preferable that the entire wood, i.e., the center of the wood, is impregnated with the organic acid aqueous solution. This allows the organic acid to modify the wood up to the center. However, it is not necessary to impregnate the center of the wood with the organic acid aqueous solution; it is sufficient to impregnate at least the portion of the wood to be modified with the organic acid aqueous solution.

[0031] In the manufacturing method of this embodiment, in the second step, the wood impregnated with the organic acid aqueous solution is dried to remove excess moisture from inside the wood. The drying conditions are not particularly limited, but natural drying can be used, for example. The wood may also be dried by heating, for example, at a temperature of 80°C or less, preferably 70°C or less, and more preferably 60°C or less. The drying atmosphere is also not particularly limited, and drying may be performed in the air, for example. The moisture inside the wood may also be removed by gradually decreasing the humidity in the drying atmosphere.

[0032] The drying process will be described in more detail. The drying process may be natural drying as described above, or the wood may be dried using a drying device. An example of such a drying device is a steam drying device that supplies steam to a heating tube in the drying device to gradually increase the temperature inside the drying device while gradually decreasing the humidity (relative humidity) inside the drying device. Alternatively, a dehumidifying drying device equipped with a heat pump dehumidifier or a reduced-pressure drying device that dries by reducing pressure and heating may be used as the drying device. Hot air or a radiant heater may be used during drying.

[0033] The moisture content of the wood dried in the drying step is not particularly limited, but can be, for example, 25% or less. The moisture content of the dried wood may also be 20% or less, or 15% or less. The moisture content of wood can be measured in accordance with JIS Z2101.

[0034] Since the organic acid and sugars remain in the microscopic spaces inside the wood, they can suppress shrinkage of the wood during drying and improve dimensional stability, so that even if wood impregnated with an aqueous organic acid solution is dried as described above, deformation and cracking of the wood can be suppressed.

[0035] In the manufacturing method of this embodiment, a high-temperature, high-pressure steam treatment is not performed between the step of impregnating wood with an organic acid aqueous solution and the step of drying the wood impregnated with the organic acid aqueous solution. Here, "high-temperature, high-pressure steam treatment" refers to treatment at a temperature of 110°C or higher and 160°C or lower, and at a pressure of saturated steam pressure at that temperature.

[0036] In the manufacturing method of this embodiment, the wood that has been subjected to the drying process is subjected to a heating treatment in an inert atmosphere as a third step. By subjecting the wood that has been impregnated with an organic acid to a heat treatment in an inert atmosphere, the decomposition and modification of hemicellulose can be promoted, and dimensional stability can be improved.

[0037] The heat treatment conditions under an inert atmosphere are preferably heating at 110°C or higher and 220°C or lower, and more preferably heating at 140°C or higher and 220°C or lower. The heating time is preferably adjusted depending on the type and size of the wood, but can be, for example, 12 to 72 hours. The inert atmosphere is an atmosphere with a reduced oxygen concentration, and can be, for example, a nitrogen gas atmosphere or a superheated steam atmosphere. Note that superheated steam is a gas obtained by heating saturated steam, and therefore contains almost no oxygen.

[0038] Here, when wood is heat-treated, a decomposition reaction occurs due to the high temperature treatment, which usually leads to volume shrinkage. However, in the modified wood manufacturing method of this embodiment, the wood is impregnated with an organic acid that has a dimensional stabilizing effect, so wood shrinkage can be suppressed even when heat-treated in an inert atmosphere. Furthermore, heat-treated wood generally becomes a material with reduced viscosity. This is because the non-crystalline regions of hemicellulose and other components that cause wood viscosity, i.e., areas that easily adsorb water, are decomposed. However, the modified wood of this embodiment is impregnated with at least an organic acid and may also be impregnated with sugars. It is believed that such organic acids and sugars penetrate between the cellulose fibers and impart flexibility to the wood. Therefore, it is believed that the modified wood of this embodiment can maintain viscosity and increase mechanical strength compared to general heat-treated wood.

[0039] As described above, modified wood according to this embodiment can be obtained by subjecting wood to the organic acid aqueous solution impregnation process, drying process, and heat treatment process. The resulting modified wood has high dimensional stability and mechanical strength, as described above. Furthermore, organic acids are often used as food additives and are highly safe. Therefore, the modified wood can be suitably used for a variety of applications, such as building materials, fixtures, furniture, and crafts.

[0040] The method for producing modified wood according to the present embodiment includes the steps of impregnating a block of wood with an organic acid aqueous solution containing an organic acid, drying the block of wood impregnated with the organic acid aqueous solution, and then heating the block of wood in an inert atmosphere at a temperature of 110° C. or higher and 220° C. or lower.

[0041] In the manufacturing method of this embodiment, the organic acid and heat treatment in an inert atmosphere promote the decomposition and modification of hemicellulose in the wood, thereby suppressing moisture adsorption and desorption and improving dimensional stability. Furthermore, the organic acid penetrates between the cellulose fibers in the wood and has the effect of imparting flexibility to the wood, allowing the modified wood of this embodiment to maintain toughness and increase mechanical strength. Furthermore, the organic acid exerts a catalytic effect that promotes the decomposition and modification of hemicellulose in the wood, allowing the heat treatment temperature to be lowered and the heat treatment time to be shortened.

[0042] Wood can deteriorate, such as by corrosion, depending on the environment in which it is used. This corrosion is primarily the result of the activity of decay fungi, and is further accelerated by environmental factors such as moisture and ultraviolet light. These decay fungi cause wood to decay by acting on the amorphous regions of wood, which are prone to decay initiation sites.

[0043] However, as described above, in the manufacturing method of this embodiment, the hemicellulose that forms the amorphous regions is decomposed by heat treatment of wood impregnated with an organic acid, and therefore the resulting modified wood has a reduced amount of amorphous regions, which improves decay resistance.

[0044] In this way, the modified wood obtained by the manufacturing method of this embodiment may be used as it is for various building materials (floors, walls, ceilings, fixtures, etc.), furniture, wood decks, etc. The modified wood can also be sliced ​​into thicknesses of 1 to 10 mm using a saw or the like, and then bonded to a substrate, to be used as a surface material for various products.

[0045] [Additional Notes] The above description of the embodiments discloses the following techniques.

[0046] (Technology 1) A method for producing modified wood, comprising the steps of: impregnating a block of wood with an organic acid aqueous solution containing an organic acid; drying the block of wood impregnated with the organic acid aqueous solution, and then heating the block of wood in an inert atmosphere; wherein the temperature during heating in the inert atmosphere is 110°C or higher and 220°C or lower.

[0047] This composition promotes the decomposition and modification of hemicellulose in wood, suppressing moisture absorption and desorption and improving the dimensional stability of wood. Furthermore, the organic acid penetrates between the cellulose fibers in wood, imparting flexibility to the wood. This allows for the production of modified wood with improved dimensional stability and mechanical strength.

[0048] (Technology 2) The method for producing modified wood according to Technology 1, wherein the organic acid aqueous solution further contains a sugar.

[0049] This structure allows the sugars to be impregnated into the cell walls of the wood, keeping them in a swollen state, which in turn reduces shrinkage of the resulting modified wood and improves its dimensional stability through the so-called "bulk effect."

[0050] (Technology 3) The method for producing modified wood according to Technology 1 or 2, wherein the organic acid is a divalent or higher carboxylic acid.

[0051] This configuration makes it possible to further promote the modification of wood by heat treating wood impregnated with carboxylic acid in an inert atmosphere, which makes it easier for the wood's constituent components, hemicellulose and lignin, to be altered.

[0052] (Technology 4) The method for producing modified wood according to Technology 3, wherein the carboxylic acid is at least one selected from the group consisting of citric acid, malic acid, and succinic acid.

[0053] This configuration allows the carboxylic acid to easily react with hemicellulose and other components of the wood, making it possible to easily obtain modified wood with good dimensional stability and mechanical strength.

[0054] (Technology 5) The method for producing modified wood according to any one of technologies 1 to 4, wherein the content of the organic acid in the organic acid aqueous solution is 3 to 30% by mass.

[0055] This configuration allows the organic acid to easily penetrate into the wood, thereby achieving the effects of stabilizing the dimensions of the wood and improving its strength.

[0056] (Technology 6) The method for producing modified wood according to Technology 2, wherein the sugar is at least one selected from the group consisting of fructose, maltose, xylose, and sucrose.

[0057] These sugars are readily available, and therefore can easily improve the dimensional stability of modified wood.

[0058] (Technology 7) The method for producing modified wood according to Technology 2 or 6, wherein the content of the sugar in the organic acid aqueous solution is 3 to 30% by mass.

[0059] This configuration allows the sugars to easily penetrate into the wood, thereby achieving the effect of stabilizing the dimensions of the wood modified with the sugars.

[0060] (Technology 8) A method for producing modified wood according to any one of technologies 1 to 7, wherein the inert atmosphere is a nitrogen atmosphere or a superheated steam atmosphere.

[0061] This configuration allows wood that has been impregnated with an organic acid and dried to be easily heat-treated in an inert atmosphere.

[0062] Hereinafter, the present embodiment will be described in more detail with reference to examples, reference examples and comparative examples, but the present embodiment is not limited to these examples.

[0063] [Preparation of Test Samples] (Examples and Reference Examples) First, four pieces of cedar wood, each 30 mm wide, 30 mm thick, and 200 mm long, were prepared. The wood was cut with the grain on all four sides. The length direction of the cedar wood was the fiber direction.

[0064] Next, citric acid, which is an organic acid, and water were mixed in the ratio shown in Table 1 to prepare aqueous solutions of Examples (Reference Examples).

[0065]

[0066] Next, the aqueous solution of the example was placed in a pressure-resistant container, and the four cedar lumber pieces were immersed in the aqueous solution. Then, while the cedar lumber was immersed in the aqueous solution, a pressure impregnation treatment was performed in which the atmospheric pressure was set at 0.7 MPa and maintained for 3 hours. After the pressure impregnation treatment, the cedar lumber was immersed in the aqueous solution and cured for 12 hours under atmospheric pressure. By curing the cedar lumber in this way while immersed in the aqueous solution, the organic acid can be reliably impregnated into the cell walls of the cedar lumber.

[0067] Next, the four pieces of cedar wood after the impregnation treatment were removed from the aqueous solution and then dried. The drying process was carried out using a steam dryer, with the drying conditions changing in the order of steps 1 to 7 shown in Table 2.

[0068]

[0069] Then, the four pieces of cedar wood that had been subjected to the drying process were subjected to heat treatments under conditions 1 to 4 shown in Table 3 using a pressure-resistant container. Each heat treatment under conditions 1 to 4 was performed on one piece of cedar wood. The cedar wood obtained in this way under condition 1 was used as the test sample for Example 1, the cedar wood under condition 2 was used as the test sample for Example 2, the cedar wood under condition 3 was used as the test sample for Example 3, and the cedar wood under condition 4 was used as the test sample for the reference example.

[0070]

[0071] (Comparative Example) First, four cedar lumber pieces, each 30 mm wide, 30 mm thick, and 200 mm long, were prepared, as in the Example. Next, only water was placed in a pressure-resistant container, and the four cedar lumber pieces were immersed in the water. Then, while the cedar lumber pieces were immersed in water, a pressure impregnation treatment was performed in which the atmospheric pressure was set to 0.7 MPa and maintained for 3 hours. After the pressure impregnation treatment, the cedar lumber pieces were cured for 12 hours under atmospheric pressure while still immersed in water.

[0072] Next, the four pieces of cedar wood after the impregnation treatment were removed from the water and then dried using a steam dryer. The drying process was carried out in the same manner as in the examples, with the drying conditions being changed in the order of steps 1 to 7 shown in Table 2.

[0073] The cedar lumber that had been subjected to the drying process was then subjected to heat treatments under conditions 1 to 4 shown in Table 3 using a pressure-resistant container. Each heat treatment under conditions 1 to 4 was performed on one cedar lumber. The cedar lumber obtained under condition 1 was used as the test sample for comparative example 1, the cedar lumber under condition 2 was used as the test sample for comparative example 2, the cedar lumber under condition 3 was used as the test sample for comparative example 3, and the cedar lumber under condition 4 was used as the test sample for comparative example 4.

[0074] [Evaluation] (Dimensional change rate measurement) Four test pieces were prepared for each of Examples 1 to 3, Reference Example, and Comparative Examples 1 to 4 by cutting each test sample to a width of 30 mm, a thickness of 30 mm, and a length of 5 mm. The length direction of each test piece was the fiber direction.

[0075] Next, the test piece of each example was kept under the following moisture absorption conditions to absorb moisture, and the dimensions in the width direction and thickness direction were measured. Next, the test piece of each example was kept under the following drying conditions to dry, and the dimensions in the width direction and thickness direction were measured. Moisture absorption conditions: temperature 40°C, relative humidity 90%, number of days 4 Drying conditions: temperature 70°C, relative humidity 25%, number of days 4

[0076] Next, the dimensional change rate in the width direction and the dimensional change rate in the thickness direction of the test piece of each example were calculated from the following Equations 1 and 2, and the sum of the dimensional change rate in the width direction and the dimensional change rate in the thickness direction was taken as the dimensional change rate of each test piece. The average value of the dimensional change rates of the four test pieces was taken as the dimensional change rate of each example. The dimensional change rates of each example are shown in Tables 4 and 5. [Equation 1] Width direction dimensional change rate (%) = [(Width direction dimension when hygroscopic) - (Width direction dimension when dry)] / [Width direction dimension when dry] x 100 [Equation 2] Thickness direction dimensional change rate (%) = [(Thickness direction dimension when hygroscopic) - (Thickness direction dimension when dry)] / [Thickness direction dimension when dry] x 100

[0077] (Measurement of bending strength) First, four test pieces were prepared for each of Examples 1 to 3, Reference Example, and Comparative Examples 1 to 4 by cutting each test sample to a width of 11 mm, a thickness of 5 mm, and a length of 90 mm. The length direction of each test piece was the fiber direction.

[0078] Next, the bending strength of each test piece was measured in accordance with the "bending test" in JIS Z2101:2009 (Testing methods for wood). At this time, the span (distance between supports) was 70 mm, and the load head speed was 10 mm / min. The average value of the bending strengths of the four test pieces for each example was taken as the bending strength of each example. The bending strengths of each example are shown in Tables 4 and 5.

[0079] (Measurement of Dissolution Rate) Two test pieces were prepared for each of Examples 1 to 3, Reference Example, and Comparative Examples 1 to 4 by cutting each test sample to a width of 30 mm, a thickness of 30 mm, and a length of 5 mm. The length direction of each test piece was the fiber direction.

[0080] Next, the test specimens of each example were left to stand at 100°C for two days to carry out initial drying. Next, the test specimens of each example that had been subjected to initial drying were immersed in water at 20°C for 24 hours. Thereafter, the immersed test specimens were left to stand at 100°C for four days to carry out post-immersion drying.

[0081] Next, the dissolution rate of each test piece was calculated using the following mathematical formula 3. The average value of the dissolution rates for the two test pieces was taken as the dissolution rate for each example. The dissolution rates for each example are shown in Tables 4 and 5. [Math 3] Dissolution rate (%) = [(mass of test piece after initial drying) - (mass of test piece after immersion and drying)] / [mass of test piece after initial drying] x 100

[0082]

[0083]

[0084] Figure 2 shows the relationship between the dimensional change rate and the bending strength for the test pieces of the Examples, Reference Examples, and Comparative Examples. As shown in Figure 2, it can be seen that, for the test pieces of the Comparative Examples, as the heat treatment temperature increases, the dimensional change rate decreases and the dimensional stability increases, but the bending strength also decreases significantly. In contrast, for the test pieces of the Examples, as the heat treatment temperature increases, the dimensional stability increases and the bending strength decreases, but the bending strength is less likely to decrease than for the Comparative Examples.

[0085] In other words, generally, when the heat treatment temperature is increased to improve the dimensional stability of wood, there is a trade-off between the two, in that the strength properties of the wood are significantly reduced. However, by impregnating the wood with an organic acid as in the examples, it is possible to suppress the reduction in the strength properties of the wood even when the heat treatment temperature is increased to improve the dimensional stability of the wood.

[0086] Furthermore, Tables 4 and 5 show that the test specimen of Example 1, which was heat-treated at 140°C, had improved dimensional stability and bending strength compared to the test specimen of Comparative Example 1. Furthermore, the test specimen of Example 2, which was heat-treated at 170°C, had a slightly lower bending strength than the test specimen of Comparative Example 2, but had a significantly improved dimensional stability. Furthermore, the test specimen of Example 3, which was heat-treated at 200°C, had improved dimensional stability and bending strength compared to the test specimen of Comparative Example 3, and in particular, had a significantly improved bending strength.

[0087] Furthermore, the dimensional change rate in Example 1 was 2.7%, but to obtain a similar dimensional change rate without using an organic acid, it is necessary to increase the heat treatment temperature to about 200°C as in Comparative Example 3. In this way, by using an organic acid, it is possible to lower the required heat treatment level and improve the efficiency of the heat treatment.

[0088] Table 4 shows that the elution rate of the test pieces of the examples decreases as the heat treatment temperature increases. This is thought to be because the heat treatment causes the organic acid to react with the wood components, immobilizing the organic acid inside the wood. Furthermore, the reaction between the organic acid and the wood components is thought to suppress the elution of the wood components.

[0089] In contrast, Table 5 shows that the elution rate of the test pieces of the comparative example increases when they are subjected to heat treatment. This is thought to be because heat treatment causes a decomposition reaction of wood components, resulting in the elution of decomposition products.

[0090] (Anti-rot performance test) For the test samples of Examples 1 to 3 and Comparative Examples 1 to 3, decay resistance was evaluated in accordance with "5.2 Anti-rot performance", "5.2.1 Indoor test", and "5.2.1.1 For injection treatment" of JIS K1571:2010 (Wood preservatives - Performance standards and test methods).

[0091] Specifically, each test sample of Examples 1 to 3 and Comparative Examples 1 to 3 was sliced ​​to prepare a plurality of treated specimens each having a width of 30 mm, a thickness of 30 mm, and a length of 4.4 mm. The length direction of the treated specimens in each example was the fiber direction. Next, in accordance with "5.2.1.1.3 Test" of JIS K1571:2010, the treated specimens in each example were subjected to weathering, antibacterial, and correction procedures.

[0092] Then, the mass loss rate of each treated specimen was calculated from the mass of the treated specimen before and after the antibacterial treatment or the correction treatment, based on Equation 4 and Equation 5. In other words, the mass loss rate of each treated specimen was calculated by subtracting the average mass loss rate (%) of the correction specimens from the mass loss rate (%) of the treated specimens after the antibacterial treatment was completed. The same evaluation was also performed on cedar sapwood as a control specimen. The evaluation results are summarized in Table 6. [Equation 4] Mass loss rate due to antibacterial treatment (%) = [(mass before antibacterial treatment) - (mass after antibacterial treatment)] / [mass before antibacterial treatment] x 100 [Equation 5] Mass loss rate due to correction treatment (%) = [(mass before antibacterial treatment) - (mass after correction treatment)] / [mass before correction treatment] x 100

[0093]

[0094] As shown in Table 6, when the test fungus was P. palustris, the average mass loss rate of the test samples in Example 1 was 28.7%, while the average mass loss rate of the test samples in Comparative Example 1 was 40.9%. Furthermore, the average mass loss rate of the test samples in Example 2 was 18.4%, while the average mass loss rate of the test samples in Comparative Example 2 was 37.8%. Furthermore, the average mass loss rate of the test samples in Example 3 was 8.5%, while the average mass loss rate of the test samples in Comparative Example 3 was 30.8%.

[0095] Similarly, when the test fungus was Coriolus versicolor, the average mass loss rate of the test samples in Example 1 was 13.9%, while the average mass loss rate of the test samples in Comparative Example 1 was 22.7%. Furthermore, the average mass loss rate of the test samples in Example 2 was 7.3%, while the average mass loss rate of the test samples in Comparative Example 2 was 22.9%. Furthermore, the average mass loss rate of the test samples in Example 3 was 2.4%, while the average mass loss rate of the test samples in Comparative Example 3 was 13.0%.

[0096] As described above, the test samples of Examples 1 to 3 have a significantly reduced mass reduction rate compared to the test samples of Comparative Examples 1 to 3, which indicates that the decay resistance is significantly improved.

[0097] Table 6 also shows that the decay resistance improves as the heat treatment temperature in an inert atmosphere increases. Furthermore, even though the treatment temperature in an inert atmosphere in Example 1 is 30°C lower than in Comparative Example 2, the decay resistance improved, which suggests that the organic acid accelerates the decomposition of the non-crystalline regions of the wood.

[0098] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment.

[0099] The entire contents of Japanese Patent Application No. 2022-114075 (filing date: July 15, 2022) are incorporated herein by reference.

[0100] According to the present disclosure, it is possible to provide a method for producing modified wood that has both excellent dimensional stability and mechanical strength.

Claims

1. A step of impregnating a block of wood with an organic acid aqueous solution containing an organic acid; a step of drying the block-shaped wood impregnated with the organic acid aqueous solution and then heating it under an inert atmosphere; Including, A method for producing modified wood, wherein the temperature during heating in the inert atmosphere is 110°C or higher and 220°C or lower.

2. The method for producing modified wood material according to claim 1 , wherein the organic acid aqueous solution further contains a sugar.

3. The method for producing modified wood material according to claim 1 or 2, wherein the organic acid is a divalent or higher carboxylic acid.

4. The method for producing modified wood material according to claim 3, wherein the carboxylic acid is at least one selected from the group consisting of citric acid, malic acid and succinic acid.

5. The method for producing modified wood material according to claim 1 or 2, wherein the organic acid content in the organic acid aqueous solution is 3 to 30 mass %.

6. The method for producing modified wood material according to claim 2, wherein the sugar is at least one selected from the group consisting of fructose, maltose, xylose and sucrose.

7. The method for producing modified wood material according to claim 2 or 6, wherein the content of the sugar in the aqueous organic acid solution is 3 to 30 mass%.

8. The method for producing modified wood material according to claim 1 or 2, wherein the inert atmosphere is a nitrogen atmosphere or a superheated steam atmosphere.