Method for manufacturing decay-resistant timber

Abstract

The present invention provides a method for producing decay-resistant timber that does not require special equipment or excessive energy, and that improves physical properties such as dimensional stability while suppressing weakening. [Solution] Untreated wood is immersed in an aqueous solution of an inorganic salt that decomposes to generate acidic gas, with polyalkylene glycol added in combination. Next, the immersed wood is dried. Then, the dried wood is heated in a dry heat atmosphere within the range of 150°C to 200°C. As a result, the water-resistant swelling capacity (water absorption ASE) after water absorption is 40% or more, the bending strength (fracture coefficient: MOR) in the three-point bending test is improved by 15% or more compared to the bending strength in the comparative test, and the 5% strength of the side length in the partial compression test is improved by 20% or more compared to the 5% partial compressive strength of the side length in the comparative test.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing decay-resistant wood, and particularly to a method for manufacturing decay-resistant wood having excellent physical properties such as dimensional stability.

Background Art

[0002] Wood, plywood, etc. are widely used as building materials and the like, and due to their unique texture, they are widely used not only as structural materials but also as exterior and interior materials. However, when wood or the like is used as an exterior material or the like in a harsh environment such as outdoors, there are problems such as deterioration by wind and rain, corrosion by wood-decaying fungi, and further damage by termites. Therefore, conventionally, it has been common to perform antiseptic and insect-proof processing by applying or impregnating a preservative or resin to the wood. However, in recent years, due to the increasing environmental awareness and health awareness, the development of decay-resistant wood made of wood that does not use chemicals or in which no chemicals remain after processing has been desired.

[0003] Among the things developed in response to such demands, there is a high-temperature heat treatment technology for wood. As a typical technology that has been put into practical use, for example, there is ThermoWood (registered trademark) developed in Finland. This technology has succeeded in enhancing the decay resistance of wood and obtaining dimensional stability by heating the wood at a high temperature in a superheated steam atmosphere (Patent Document 1 below). Also, as a technology developed in Japan, there is Estec Wood (registered trademark). This technology is by the Miyagi Prefectural Industrial Technology Center, and similar results have been obtained by heating the wood at a high temperature in an inert gas nitrogen atmosphere (Patent Document 2 below).

[0004] Generally, JIS K 1571:2010 "Wood preservatives - Performance standards and test methods (5.2 Anti-corrosion performance)" is used as an index to evaluate the decay resistance of wood. To meet the performance standards for wood preservatives in JIS K 1571 using the above technology, a mass reduction of approximately 18% of the wood before and after treatment is required through heat treatment at 220°C or higher. However, wood has the property of releasing flammable gases above 180°C and igniting at around 250°C. Therefore, the above technology had the problem of requiring high-temperature heat treatment in an atmosphere with a low oxygen concentration, such as a water vapor atmosphere or an inert gas atmosphere of nitrogen.

[0005] Therefore, in order to prevent the burning of wood, a technique for processing it at a temperature of 200°C or lower, preferably 180°C or lower, was developed at the Nara Prefectural Forestry Technology Center, for example, in Patent Document 3 below, which describes a method for manufacturing highly durable wood. In this method, the wood is first impregnated with an aqueous solution of a salt that is nearly neutral to weakly acidic at room temperature, then dried, and then heat-treated. Furthermore, in the heat treatment method for wood described in Patent Document 4 below by the present inventors, the wood is first impregnated with a dilute aqueous solution of a salt that generates inorganic acids, and then heat-treated. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 3585492 [Patent Document 2] Special Publication No. 58-018205 [Patent Document 3] Japanese Patent Publication No. 2018-161802 [Patent Document 4] Japanese Patent Publication No. 2022-131431 [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, the methods described in Patent Documents 3 and 4 above allow processing at temperatures below 200°C using a conventional heat treatment apparatus. This makes it easier to control the temperature of the wood during the heat treatment stage, and allows for the production of decay-resistant wood while preventing combustion of the wood without removing oxygen from within the heat treatment apparatus. However, although the decay-resistant wood obtained by these methods has excellent decay resistance, it has the problem of becoming extremely brittle because the heat treatment is performed in combination with salts that exhibit weak acidity or salts that generate inorganic acids.

[0008] Therefore, the present invention aims to address the above problems by providing a method for manufacturing decay-resistant timber that does not require special equipment or excessive energy, and that can improve physical properties such as dimensional stability while suppressing weakening. [Means for solving the problem]

[0009] In order to solve the above problems, the inventors of the present invention, through diligent research, discovered that the above problems could be solved by performing a heat treatment using polyalkylene glycol in combination with an inorganic salt that decomposes to generate acidic gas, and thus completed the present invention.

[0010] In other words, according to the description in claim 1, the method for producing decay-resistant wood according to the present invention is as follows: The process involves immersing untreated wood in an aqueous solution of an inorganic salt that decomposes and generates acidic gas, in which polyalkylene glycol is used in combination. A drying step for drying the wood after the immersion step, The process includes a heating step in which the wood after the drying step is heated in a dry heat atmosphere within the range of 150°C to 200°C. The value of the water-resistant swelling capacity (water absorption ASE) after water absorption, calculated from the dimensional change of the decay-resistant wood from its completely dry state after the aforementioned heating process using a vacuum pressure injection can, is 40% or more. The bending strength (mortality of failure: MOR) of the three-point bending test, measured with the straight-grained surface of the wood facing upwards and downwards, was improved by 15% or more compared to the bending strength of the comparative test using only the inorganic salt without the use of polyalkylene glycol, and A method for producing decay-resistant timber, characterized in that the value of the 5% partial compressive strength of the side length in a partial compression test, measured with the tangential surface of the timber as the compression surface, is improved by 20% or more compared to the 5% partial compressive strength of the side length in a comparative test using only the inorganic salt without the use of polyalkylene glycol.

[0011] Furthermore, according to claim 2, the present invention relates to a method for producing decay-resistant wood as described in claim 1, The inorganic salt is characterized by being ammonium chloride.

[0012] Furthermore, according to claim 3, the present invention is a method for manufacturing decay-resistant wood as described in claim 1 or 2, The polyalkylene glycol is characterized by being polyethylene glycol or polypropylene glycol having a number average molecular weight of 200 to 2000.

[0013] Furthermore, according to claim 4, the present invention relates to a method for producing decay-resistant wood as described in claim 3, The polyalkylene glycol is characterized by being polyethylene glycol having a number average molecular weight in the range of 200 to 400.

[0014] Furthermore, according to claim 5, the present invention relates to a method for producing decay-resistant wood as described in claim 3, The polyalkylene glycol is characterized by being a polypropylene glycol having a number average molecular weight in the range of 200 to 400. [Effects of the Invention]

[0015] According to the above configuration, the method for manufacturing decay-resistant wood according to the present invention has an immersion step, a drying step, and a heating step. In the immersion step, untreated wood is immersed in an aqueous solution of an inorganic salt that decomposes to generate an acidic gas, with the combined use of a polyalkylene glycol. The drying step dries the wood after the immersion step. The heating step heats the wood after the drying step in a dry-heat atmosphere within the range of 150°C to 200°C.

[0016] The physical properties of the decay-resistant wood thus manufactured are as follows: For the decay-resistant wood after the heating step, the value of the anti-swelling ability after water absorption (water absorption ASE) calculated from the dimensional change from the fully dry state of the decay-resistant wood into which water is injected using a pressure-reducing and pressure-increasing injection tank is 40% or more. Also, the value of the bending strength (modulus of rupture: MOR) in the three-point bending test measured with the radial surface of the wood being vertical is improved by 15% or more compared to the bending strength in the comparative test manufactured only with an inorganic salt without the combined use of a polyalkylene glycol. Furthermore, the value of the 5% partial compression strength of the side length in the partial compression test measured with the flat surface of the wood being the compression surface is improved by 20% or more compared to the 5% partial compression strength of the side length in the comparative test manufactured only with an inorganic salt without the combined use of a polyalkylene glycol.

[0017] This enables the provision of a method for manufacturing decay-resistant wood that does not require special equipment or excessive energy, and that can improve physical properties such as dimensional stability and suppress embrittlement.

[0018] Also, according to the above configuration, the aqueous solution of the inorganic salt that decomposes to generate an acidic gas is preferably an aqueous solution of ammonium chloride. This can more specifically and effectively exhibit the above-described effects.

[0019] Also, according to the above configuration, the polyalkylene glycol used in combination with the aqueous solution of the inorganic salt is preferably polyethylene glycol or polypropylene glycol having a number average molecular weight of 200 to 2000. This can more specifically and effectively exhibit the above-described effects.

[0020] Further, according to the above configuration, the polyalkylene glycol used in combination with the aqueous solution of the inorganic salt is particularly preferably polyethylene glycol having a number average molecular weight in the range of 200 to 400, or polypropylene glycol having a number average molecular weight in the range of 200 to 400. By this, the above-described effects can be exhibited more specifically and effectively.

Brief Description of Drawings

[0021] [Figure 1] It is a graph showing the values (results of the first and third times) of the anti-swelling ability (water absorption ASE) of each test body obtained in Example 1. [Figure 2] It is a graph showing the values of the mass change rate of each test body obtained in Example 1. [Figure 3] It is a graph showing the values of the area change rate of each test body obtained in Example 1 in the fully dry state. [Figure 4] It is a graph showing the values of the flexural strength (modulus of rupture: MOR) of each test body obtained in Example 1. [Figure 5] It is a graph showing the values of the flexural Young's modulus (MOE) of each test body obtained in Example 1. [Figure 6] It is a graph showing the values of the 5% side length partial compression strength in the partial compression test of the plank surface of each test body obtained in Example 1.

Modes for Carrying Out the Invention

[0022] The method for manufacturing decay-resistant wood according to the present invention will be described according to embodiments. Note that the present invention is not limited only to the following embodiments.

[0023] First, let's explain the materials that serve as raw materials for the decay-resistant wood according to the present invention. Generally, lumber or planks cut directly to the required dimensions from a single log are called sawn timber or solid wood. On the other hand, materials made by collecting small pieces of wood or thin boards and gluing them together to form larger components are called wood-based materials. Examples include plywood (including veneer), laminated timber, LVL (laminated veneer lumber), particleboard, fiberboard, and MDF (medium-density fiberboard). In this invention, the above-mentioned sawn timber or solid wood and wood-based materials are defined as "wood, etc." as raw materials for the decay-resistant wood according to the present invention.

[0024] Next, we will describe inorganic salts that decompose to generate acidic gases. In this invention, wood becomes decay-resistant wood by being heat-treated in an atmosphere of the generated acidic gas, causing it to partially carbonize (also called semi-carbonization) without burning. Acidic gases include carbon dioxide, hydrogen chloride, and hydrogen sulfide, and any inorganic salt that decomposes to generate these gases can be used. Ammonium chloride is preferred as such an inorganic salt.

[0025] Polyalkylene glycols to be used in combination with aqueous solutions of these inorganic salts include polyethylene glycol, polypropylene glycol, and polybutylene glycol. Preferably, the number average molecular weight of these glycols is between 200 and 2000. Among these, polyethylene glycol with a number average molecular weight in the range of 200 to 400, or polypropylene glycol with a number average molecular weight in the range of 200 to 400, are particularly preferred. These may also be used in appropriate combinations.

[0026] The decay-resistant wood according to the present invention is manufactured through a soaking process, a drying process, and a heating process. Each process will be described below.

[0027] ≪Soaking process≫ First, the immersion solution is prepared by combining an aqueous solution of an inorganic salt such as ammonium chloride with a polyalkylene glycol such as polyethylene glycol. The concentration of the aqueous solution of the inorganic salt used should be adjusted as appropriate depending on the density of the wood or other material being treated. For example, the amount of inorganic salt such as ammonium chloride relative to the immersion solution can be in the range of 0.05% to 2.0% by mass, preferably 0.1% to 1.0% by mass, and more preferably 0.2% to 0.5% by mass. The amount of polyethylene glycol or the like used in combination can also be in the range of 0.5% to 20.0% by mass, preferably 2.0% to 15.0% by mass, and more preferably 5.0% to 10.0% by mass, relative to the immersion solution.

[0028] Next, the injection of the immersion solution into the wood can be carried out using the same equipment and procedures as in normal wood processing. Common wood injection methods include vacuum-pressure injection, vacuum injection, pressure injection, and hot / cold bath methods, but in the present invention, it is preferable to use the vacuum-pressure injection method. This is because by maintaining a vacuum state for a certain period of time before pressurizing the immersion solution into the wood, air present in the voids of the wood can be removed, and the amount of immersion solution injected under pressure can be increased. The degree of vacuum and pressure during vacuum or pressurization, processing time, and processing temperature are not particularly limited and should be appropriately selected depending on the type and size of the wood, the concentration of the immersion solution to be injected, etc.

[0029] ≪Drying process≫ In the drying process, operations similar to those for normal wood processing can be carried out. For example, the wood after the immersion process is dried in a temperature range of 50°C to 105°C. It is preferable that this drying process be carried out at a temperature that does not cause the injected inorganic salts to sublimate or decompose.

[0030] ≪Heating process≫ In this embodiment, a constant-temperature dryer and a stainless steel chamber are used as the heat treatment apparatus, as will be described later, but the invention is not limited to these. In the present invention, heat treatment is performed at a temperature of 200°C or lower to prevent combustion of wood, etc. In particular, the heat treatment temperature is in the range of 150°C to 200°C, and preferably in the range of 160°C to 180°C. At temperatures higher than 200°C, there is a risk of wood, etc. igniting. On the other hand, at temperatures lower than 150°C, sufficient decay resistance cannot be obtained. Furthermore, the heat treatment time can be appropriately adjusted depending on the type of wood, etc. being treated and the heating temperature.

[0031] The present invention will be described in detail below with reference to examples. Here, the dimensional stability and mechanical properties of test specimens of decay-resistant wood according to the present invention (Example 1 below) and conventional decay-resistant wood (Comparative Example 1 below) were evaluated. However, the present invention is not limited to the following examples. [Examples]

[0032] In this Example 1, cedar sapwood specimens measuring 30 mm x 30 mm at the end grain and 5.5 mm in the fiber direction (four pieces per condition) were prepared as test specimens to evaluate dimensional stability. Ammonium chloride (hereinafter referred to as "NH4Cl") was used as the inorganic salt that decomposes to generate acidic gas, and polyethylene glycols with number average molecular weights of 200, 400, 600, 1000, 1540, and 2000 (hereinafter referred to as "PEG200, PEG400, PEG600, PEG1000, PEG1540, PEG2000") and polypropylene glycol with a number average molecular weight of 400 (hereinafter referred to as "PPG400") were used in combination with ammonium chloride to process each test specimen. The polyalkylene glycols used in this Example 1 are shown in Table 1.

[0033] [Table 1]

[0034] ≪Soaking process≫ An immersion solution was prepared containing 0.5% by mass of NH4CL and 7.5% by mass of each PEG and PPG. Immersion was performed using a vacuum pressure tester, with the samples treated for 1 hour under a reduced pressure of 50 hPa, followed by 2 hours under a pressurized pressure of 1.0 MPa, until the same amount of treatment solution as the calculated maximum was injected into each specimen.

[0035] ≪Drying process≫ Each test specimen, to which the immersion solution was injected during the immersion process, was dried at 60°C for 2 days, and then at 105°C for 6 hours to obtain test specimens injected with NH4CL and each of the PEG and PPG compounds.

[0036] ≪Heating process≫ Each dried test specimen was placed at equal intervals inside a stainless steel chamber with an internal space of 150 mm wide x 250 mm deep x 20 mm high. This chamber was then placed inside a constant-temperature drying oven (Yamato Scientific Co., Ltd., DY300) and subjected to heat treatment. Thermocouple thermometers were set up to measure the internal temperature of both the chamber and the test specimens.

[0037] Each test specimen was subjected to heat treatment only after its total dry mass was measured before the immersion process and after the heating process, in order to measure the change in mass. In Example 1, the heat treatment temperature was set to 170°C, and after the internal temperature of the test specimen reached the set treatment temperature of 170°C, the heat treatment was carried out for two days to obtain decay-resistant wood (Examples 1-1 to 1-7) using each immersion solution. In parallel with this, conventional decay-resistant wood (Comparative Example 1) was obtained by heat treatment with NH4CL alone.

[0038] Next, the dimensional stability of each test specimen of the decay-resistant wood obtained in Example 1 (Examples 1-1 to 1-7) and conventional decay-resistant wood (Comparative Example 1) was evaluated. First, dimensional stability was evaluated by the anti-swelling ability (water absorption ASE).

[0039] ≪Anti-swelling ability (water absorption ASE)≫ Water absorption ASE is calculated by measuring the total swelling rate (rate of change in end grain surface area) from the completely dry state to the saturated state, and then using the following formula. ASE (%) = [(Su-St) / Su] × 100 Su: Volume swelling rate of the untreated test specimen St: Volume expansion rate of decay-resistant wood The ASE was calculated based on this.

[0040] First, the dimensions of the end grain (tangential and radial directions) of the test specimens immediately after the reaction were measured with a digital caliper to an accuracy of 1 / 100 mm while they were completely dry. Next, each test specimen was submerged in distilled water using a vacuum pressure injection can and treated for 2 hours under reduced pressure of 50 hPa. After returning to atmospheric pressure, the specimens were left to stand in water for 2 days, and the dimensions of the end grain in a saturated state were measured to determine the swelling rate. Subsequently, each test specimen was dried at 60°C for 1 day, and then at 105°C for 1 day to a completely dry state.

[0041] These operations were repeated up to three times (three cycles), with each cycle counting as one. The water absorption ASE was measured not only immediately after the reaction (first water absorption) but also during water absorption in the second and third cycles, and the changes associated with repeated water absorption and drying (decrease in dimensional stability) were also evaluated. Three cycles of water absorption and drying were performed because, including unreacted material, almost all water-soluble components would be leached out after three cycles, eliminating their contribution to dimensional stability, etc.

[0042] Figure 1 is a graph showing the anti-swelling ability (water absorption ASE) values ​​(results after 1 and 3 cycles) of each test specimen obtained in Example 1. In Figure 1, the ASE value evaluated after the first water absorption operation (1 cycle) was higher when polyalkylene glycol was used in combination. A tendency for the ASE to decrease as the number-average molecular weight of the polyalkylene glycol increased was observed. Furthermore, after repeating water absorption and drying three times (3 cycles), the decrease in ASE was greater for PEG with a number-average molecular weight of 400 (Example 1-2) or higher. PEG200 (Example 1-1) and PPG400 (Example 1-2) showed higher ASE values ​​than when no polyalkylene glycol was added (Comparative Example 1). Note that PEG400 (Example 1-2) was similar to Comparative Example 1, and PEGs with larger molecular weights actually showed lower ASE values. Good results were obtained for both 1 and 3 cycles for PPG400 (Example 1-2), and the decrease in ASE with repeated water absorption and drying was minimal.

[0043] <<Rate of Mass Change>> Next, the rate of change in mass of the test specimens will be explained. The mass of the test specimen in its completely dry state before treatment is used as the baseline (100), and the rate of change in mass after treatment and after water absorption and drying (+: heavier than before treatment, -: decreased) is shown. Figure 2 is a graph showing the values ​​of the rate of change in mass of each test specimen obtained in Example 1.

[0044] In Figure 2, when no polyalkylene glycol was added (Comparative Example 1), the mass decreased significantly due to heat treatment (-11.4%), but the mass decrease associated with repeated water absorption and drying was minor. Furthermore, with the combined use of polyalkylene glycol, in the case of PEG200 (Example 1), the mass decrease associated with heat treatment was offset, and there was almost no mass decrease. On the other hand, in the case of PEG400 to PEG2000 (Examples 1-2 to 1-6), the test specimen became heavier than before treatment. This is thought to be because the higher the molecular weight, the less evaporation occurs due to heat treatment. Also, in the case of PEG400 to PEG2000 (Examples 1-2 to 1-6), the mass decrease associated with repeated water absorption and drying was large, but it never fell below the mass of the original test specimen. At the time of complete drying after 3 cycles (at the time of the 4th complete drying), it is thought that almost all water-soluble components, including unreacted material, have leached out, so it is thought that a portion of each polyalkylene glycol reacts with the wood components in some way and becomes insoluble.

[0045] In Figure 2, PEG200 and PPG400 showed almost no mass change associated with heat treatment. However, this was 10% or more higher than the case without polyalkylene glycol (Comparative Example 1) (-11.4%), and this trend remained unchanged even after complete drying following three cycles (after the fourth complete drying). This suggests that PEG200 (Example 1-1) and PPG400 (Example 1-2), like other polyalkylene glycols, reacted with wood components.

[0046] ≪Area Change Rate≫ Next, we will explain the rate of change in the area of ​​the test specimens. The end grain area in the completely dry state before treatment is used as the baseline (100), and the rate of change in the end grain area after treatment and after water absorption and drying (+: expanded compared to before treatment, -: contracted) is shown. Figure 3 is a graph showing the values ​​of the rate of change in the area of ​​each test specimen in the completely dry state obtained in Example 1.

[0047] In Figure 3, when no polyalkylene glycol was added (Comparative Example 1), the area shrank by 3.7% due to heat treatment. With the addition of polyalkylene glycol, the shrinkage due to heat treatment was offset, and the area actually increased for all polyalkylene glycols. Furthermore, with PEG, the area change rate (increase rate) in the initial stage (immediately after the reaction) tended to be larger as the molecular weight increased. On the other hand, with PEG400 to PEG2000 (Examples 1-2 to 1-6), the decrease due to repeated water absorption and drying was large, but the area never became smaller than before treatment. With PEG200 (Example 1-1) and PPG400 (Example 1-7), the increase in area due to treatment was smaller than with other polyalkylene glycols, and the decrease due to repeated water absorption and drying was minor. Similar to other polyalkylene glycols, even after 3 cycles of water absorption and drying (4th complete drying), the area did not become smaller than before treatment.

[0048] In addition to evaluating the dimensional stability described above, mechanical properties were also evaluated in this Example 1. Mechanical properties were evaluated by bending tests and partial compression tests. First, 216 specimens were prepared, with 10 mm in the tangential and radial directions and 160 mm in the fiber direction. After conditioning at 20°C and 65% relative humidity, the bending Young's modulus (MOE) was measured, and the specimens were divided into 9 groups of 24 specimens per test condition so that the average MOE values ​​would be approximately the same. Of the 9 groups, 7 were prepared as the decay-resistant wood (Examples 1-1 to 1-7) related to this Example 1. One group was prepared as conventional decay-resistant wood (Comparative Example 1). For these 8 groups, after calculating the mass change associated with the treatment, they were conditioned at 20°C and 65% relative humidity along with one untreated specimen, and the following tests were conducted.

[0049] ≪Bending Test≫ In accordance with JIS Z2101:2009 "Testing Methods for Wood," bending tests were conducted with the quarter-sawn side facing up and down, with a span of 147 mm and a head speed of 5 mm / min, and the bending strength (MOR) and bending Young's modulus (MOE) were measured. Figure 4 is a graph showing the bending strength (fracture coefficient: MOR) values ​​for each test specimen obtained in Example 1. Figure 5 is a graph showing the bending Young's modulus (MOE) values ​​for each test specimen obtained in Example 1.

[0050] In Figure 4, the addition of polyalkylene glycol increased the maximum strain, resulting in a 15% or more improvement in flexural strength (fracture coefficient: MOR) compared to the sample without polyalkylene glycol (Comparative Example 1). On the other hand, in Figure 5, the flexural Young's modulus (MOE) was slightly lower compared to the sample without polyalkylene glycol (Comparative Example 1). Generally, MOR and MOE are considered to be proportional. However, in each test specimen of Example 1 (Examples 1-1 to 1-7), the MOE decreased while the MOR increased compared to the test specimen treated only with NH4Cl without polyalkylene glycol (Comparative Example 1).

[0051] The inventors believe the reason for this is as follows: When polyalkylene glycol was included in the treatment in Example 1, the fragility associated with heat treatment was mitigated compared to Comparative Example 1, which did not include polyalkylene glycol, and the amount of strain leading to bending fracture increased from 1.3 to 1.6 times. Therefore, the effect was greater than offsetting the decrease in MOE (from 0.82 to 0.92 times).

[0052] Partial Compression Test After the bending test, the non-destructive portion of the specimen was cut out, and the 5% partial compressive strength of the side length was determined in accordance with JIS Z2101:2009 "Testing Methods for Wood," with the tangential surface as the compression surface and a head speed of 1 mm / min. Figure 6 is a graph showing the 5% partial compressive strength of the side length of the tangential surface of each specimen obtained in Example 1.

[0053] In Figure 6, when the tangential surface was used as the compression surface, the combined effect of polyalkylene glycol was observed in all test specimens containing polyalkylene glycol (Examples 1-1 to 1-7), and an improvement in strength of more than 20% was observed compared to the specimen without polyalkylene glycol (Comparative Example 1).

[0054] As described above, in this embodiment 1, it is possible to provide a method for manufacturing decay-resistant timber that does not require special equipment or excessive energy, and that can improve physical properties such as dimensional stability while suppressing weakening.

Claims

1. The process involves immersing untreated wood in an aqueous solution of an inorganic salt that decomposes and generates acidic gas, in which polyalkylene glycol is used in combination. A drying step for drying the wood after the immersion step, The process includes a heating step in which the wood after the drying step is heated in a dry heat atmosphere within the range of 150°C to 200°C. The value of the water-resistant swelling capacity (water absorption ASE) after water absorption, calculated from the dimensional change of the decay-resistant wood from its completely dry state after the aforementioned heating process using a vacuum pressure injection can, is 40% or more. The bending strength (mortality of failure: MOR) of the three-point bending test, measured with the straight-grained surface of the wood facing upwards and downwards, was improved by 15% or more compared to the bending strength of the comparative test using only the inorganic salt without the use of polyalkylene glycol, and A method for producing decay-resistant timber, characterized in that the value of the 5% partial compressive strength of the side length in a partial compression test, measured with the tangential surface of the timber as the compression surface, is improved by 20% or more compared to the 5% partial compressive strength of the side length in a comparative test using only the inorganic salt without the use of polyalkylene glycol.

2. The method for producing decay-resistant wood according to claim 1, characterized in that the inorganic salt is ammonium chloride.

3. The method for producing decay-resistant wood according to claim 1 or 2, characterized in that the polyalkylene glycol is polyethylene glycol or polypropylene glycol having a number average molecular weight of 200 to 2000.

4. The method for producing decay-resistant wood according to claim 3, characterized in that the polyalkylene glycol is polyethylene glycol having a number average molecular weight in the range of 200 to 400.

5. The method for producing decay-resistant wood according to claim 3, characterized in that the polyalkylene glycol is polypropylene glycol having a number average molecular weight in the range of 200 to 400.

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