Softened wood and method for producing the same

Abstract

To provide a novel production method for softened lumber.SOLUTION: A production method for softened lumber includes an impregnation step for impregnating lumber with ionic liquid and an acquiring step for acquiring softened lumber through a heating step for heating the lumber impregnated with the ionic liquid.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to softened wood and a method for producing the same. [Background technology]

[0002] Wood obtained from forest resources has been attracting attention as a sustainable resource with low energy production that can fix CO2 in the atmosphere, and is widely used for construction and civil engineering, as well as as a raw material for paper, etc. However, with the declining population, demand for these is expected to decrease, and because Japan's forest accumulation is increasing, there is a need to expand demand by developing new functions and uses for wood.

[0003] In recent years, various techniques for softening wood by chemical treatment have been reported. For example, Non-Patent Document 1 reports that extremely light wood is treated at high temperature in a sodium hydroxide solution, and then freeze-dried to destroy the wood tissue and turn it into a spongy wood.

[0004] However, conventional methods for producing softened wood have been limited in their simplicity and versatility because they require the use of relatively light wood and the softening treatment to be carried out under harsh conditions (such as the use of dangerous reagents such as strong acids and strong alkalis at high temperatures) that can significantly destroy the wood structure. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] ACS Nano 2018, 12, 10365-10373 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a novel method for producing softened wood. [Means for solving the problem]

[0007] As a result of intensive research in view of the above problems, the present inventor has found that the above problems can be solved by a method for producing softened wood including an impregnation step of impregnating wood with an ionic liquid and an acquisition step of obtaining softened wood through a heating step of heating the wood impregnated with the ionic liquid. Based on this finding, the present inventor further conducted research and completed the present invention. That is, the present invention includes the following aspects.

[0008] Item 1. An impregnation step of impregnating wood with an ionic liquid, and an acquisition step of obtaining softened wood through a heating step of heating the wood impregnated with the ionic liquid. A method for producing softened wood, comprising the above steps.

[0009] Item 2. The production method according to Item 1, further including a curing step of curing the obtained wood in a wet atmosphere after the heating step to soften the wood.

[0010] Item 3. The production method according to Item 2, wherein the wet atmosphere is an atmosphere with a humidity of 40% or more.

[0011] Item 4. The production method according to any one of Items 1 to 3, further including a liquid impregnation step of impregnating the wood or the softened wood with a liquid after the heating step or the acquisition step.

[0012] Item 5. The production method according to any one of Items 1 to 4, wherein the heating temperature in the heating step is 40°C or higher.

[0013] Item 6. The production method according to any one of Items 1 to 5, wherein the heating temperature in the heating step is 80°C or higher.

[0014] Item 7. The production method according to any one of Items 1 to 6, wherein the ionic liquid is 1-butyl-3-methylimidazolium acetate.

[0015] Item 8. The production method according to any one of Items 1 to 7, wherein the latewood rate of the wood is 5% or more.

[0016] Item 9. The manufacturing method according to any one of Items 1 to 8, wherein the cell wall swelling rate of the softened wood to be manufactured is 12% or more.

[0017] Item 10. Softened wood obtained by the manufacturing method according to any one of Items 1 to 9.

[0018] Item 11. Softened wood having a cell wall swelling rate of 12% or more.

[0019] Item 12. The softened wood according to Item 11, which has resilience.

[0020] Item 13. The softened wood according to Item 11 or 12, wherein the compression rate when a compression force of 0.5 MPa is applied is 2 times or more the compression rate when a compression force of 0.5 MPa is applied to the control wood.

[0021] Item 14. The softened wood according to any one of Items 11 to 13, wherein the recovery rate when compressed by 20% is 80% or more.

[0022] Item 15. The softened wood according to any one of Items 11 to 14, wherein the compression force at a compression rate of 20% is 1.3 times or less the compression force at a compression rate of 10%.

[0023] Item 16. The softened wood according to any one of Items 11 to 15, which has latewood.

Advantages of the Invention

[0024] According to the present invention, a novel manufacturing method of softened wood can be provided.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0026] In this specification, the expressions "containing" and "comprising" include the concepts of "containing", "comprising", "substantially consisting of", and "consisting only of".

[0027] 1. Method for manufacturing softened wood In one aspect of the present invention, it includes an impregnation step of impregnating wood with an ionic liquid, and an acquisition step of obtaining softened wood through a heating step of heating the wood impregnated with the ionic liquid (in this specification, it may also be referred to as "the manufacturing method of the present invention"). This will be described below.

[0028] 1-1. Impregnation process The wood that is the target of the impregnation process is not particularly limited as long as it is a material made from felled trees, and various woods can be adopted regardless of the type of woody plant used as the raw material and the presence (and degree) of sawn timber. The wood may be made from one type of woody plant as the raw material, or may be made from a combination of two or more types of woody plants as the raw material.

[0029] As for woody materials, there is no particular limitation as long as they can be used as wood materials. For example, softwood, hardwood, etc. can be mentioned. More specifically, for example, cedar, Japanese red pine, Korean pine, black pine, thujopsis dolabrata, dwarf pine, Japanese larch, Japanese chestnut, Japanese beech, oak, Japanese hemlock, spruce, fir, Japanese cypress, Japanese larch, elm, Japanese maple, Japanese red pine, elm, Japanese maple, oak, hard maple, hickory, pecan, white ash, white oak, white birch, red oak, acacia, eucalyptus, etc. can be mentioned. In addition, either sapwood or heartwood can be used as the wood material.

[0030] The type of wood is not particularly limited as long as it can be impregnated with ionic liquid. For example, logs, square timbers, boards, solid wood, wood materials, glued laminated timber, laminated veneer lumber, plywood, wood-based boards, particle boards, fiber boards, particulate wood (chips, particles, etc.), fibrous wood, etc. can be mentioned. In addition, as the wood, either green wood or dried wood can be used.

[0031] The wood preferably has a latewood part. The latewood ratio of the wood is, for example, 1% or more, 2% or more, 5% or more, 7% or more, 10% or more, 12% or more, 14% or more, or 15% or more. The upper limit of the latewood ratio is usually less than 100%, for example, 70%, 60%, 50%, 40%, 30%, or 20%. The wood usually has an earlywood part (= the part other than the latewood part).

[0032] The latewood ratio of the wood is determined as follows. The latewood part on the surface of the cross-section of the wood is determined based on Mork's definition, and the latewood ratio (= (latewood width / annual ring width) × 100 (%)) is obtained.

[0033] Further, the wood may be wood that retains a solvent by being treated with the solvent. The solvent in this case is not particularly limited as long as it is a solvent that can be replaced with an ionic liquid. Specific examples of the solvent include alcohol, water, acetone, acetonitrile, benzene, and toluene. Further, the wood can be one that retains a chemical agent.

[0034] The method for causing the wood to retain the solvent is not particularly limited, and examples thereof include a method of immersing the wood in the solvent.

[0035] The immersion in the solvent may be in any mode as long as the solvent can penetrate into the wood. Examples thereof include a mode in which part or all of the wood is immersed in the solvent. The immersion may be performed under reduced pressure, under pressure, or under atmospheric pressure. The immersion temperature is not particularly limited as long as the solvent can penetrate into the wood. The immersion temperature can be, for example, 0 to 40°C, preferably 15 to 25°C. The immersion time is not particularly limited as long as the solvent can penetrate into the wood, and is appropriately selected according to the size of the wood, the pressure and temperature during immersion, and the like. For example, the immersion time under atmospheric pressure and at room temperature can be 4 to 24 hours, preferably about 6 to 16 hours.

[0036] The wood may be used alone or in combination of two or more.

[0037] The ionic liquid is not particularly limited as long as it is a salt composed of a cation and an anion and is in a liquid state at normal temperature. Specific examples of the salt in a liquid state at normal temperature include salts having a melting point of 40°C or lower, preferably 25°C or lower, more preferably 10°C or lower, and even more preferably -20°C or lower. The ionic liquid may be used alone or in combination of two or more.

[0038] The cation is not particularly limited as long as it can be a cation constituting the ionic liquid. Specific examples of the cation include imidazolium ions represented by the general formula (1), pyridinium ions represented by the general formula (2), ammonium ions represented by the general formula (3), pyrrolidinium ions represented by the general formula (4), phosphonium ions represented by the general formula (5), and sulfonium ions represented by the general formula (6). Preferred are imidazolium ions represented by the general formula (1), phosphonium ions represented by the general formula (5), etc. Particularly preferred are imidazolium ions represented by the general formula (1). The cation may be used alone or in combination of two or more.

[0039]

Chemical formula

[0040] In the general formula (1), R 1 and R 2 are the same or different and each represents an optionally substituted alkyl group (preferably an unsubstituted alkyl group) or a hydrogen atom (provided that R 1 and R 2 are not simultaneously hydrogen atoms). The alkyl group is not particularly limited as long as the cation can form an ionic liquid. The alkyl group may be branched or linear, but is preferably linear. Examples of the alkyl group include an alkyl group having 1 to 8 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms, and more specifically, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group.

[0041] Preferred embodiments of the general formula (1) include the embodiment where R 1 is an alkyl group having 1 to 2 carbon atoms and R 2 is an alkyl group having 3 to 5 carbon atoms, and the embodiment where R 1 is an alkyl group having 1 to 2 carbon atoms and R 2Examples of such a case include an alkyl group having 1 to 2 carbon atoms. As the imidazolium ion represented by the general formula (1), preferably 1-butyl-3-methylimidazolium ion, 1-ethyl-3-methylimidazolium ion, etc. are mentioned, and particularly preferably 1-butyl-3-methylimidazolium ion is mentioned.

[0042] In the general formula (2), R 3 represents an optionally substituted alkyl group (preferably an unsubstituted alkyl group). The alkyl group is not particularly limited as long as the cation can form an ionic liquid. The alkyl group may be either branched or linear, but is preferably linear. Examples of the alkyl group include an alkyl group having 1 to 5 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms, and more specifically, a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group, etc. are mentioned.

[0043] In the general formula (3), R 4 ~R 7 are the same or different and represent an optionally substituted alkyl group (preferably an unsubstituted alkyl group) or a hydrogen atom (however, R 4 ~R 7 are not hydrogen atoms at the same time). The alkyl group is not particularly limited as long as the cation can form an ionic liquid. The alkyl group may be either branched or linear, but is preferably linear. Examples of the alkyl group include an alkyl group having 1 to 5 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms, and more specifically, a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group, etc. are mentioned.

[0044] In the general formula (4), R 8 and R 9 are the same or different and represent an optionally substituted alkyl group (preferably an unsubstituted alkyl group) or a hydrogen atom (however, R 8 and R 9(provided that they are not hydrogen atoms at the same time). The alkyl group is not particularly limited as long as the cation can form an ionic liquid. The alkyl group may be either branched or linear, but is preferably linear. Examples of the alkyl group include alkyl groups having 1 to 8 carbon atoms, preferably alkyl groups having 1 to 6 carbon atoms, and more specifically, methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, and the like.

[0045] In general formula (5), R 10 ~R 13 are the same or different and each represents an optionally substituted alkyl group (preferably an unsubstituted alkyl group) or a hydrogen atom (provided that R 10 ~R 13 are not hydrogen atoms at the same time). The alkyl group is not particularly limited as long as the cation can form an ionic liquid. The alkyl group may be either branched or linear, but is preferably linear. Examples of the alkyl group include alkyl groups having 1 to 5 carbon atoms, preferably alkyl groups having 1 to 3 carbon atoms, and more specifically, methyl group, ethyl group, propyl group, butyl group, pentyl group, and the like.

[0046] In general formula (6), R 14 ~R 16 are the same or different and each represents an optionally substituted alkyl group (preferably an unsubstituted alkyl group) or a hydrogen atom (provided that R 14 ~R 16 are not hydrogen atoms at the same time). The alkyl group is not particularly limited as long as the cation containing a radically polymerizable group can form an ionic liquid. The alkyl group may be either branched or linear, but is preferably linear. Examples of the alkyl group include alkyl groups having 1 to 5 carbon atoms, preferably alkyl groups having 1 to 3 carbon atoms, and more specifically, methyl group, ethyl group, propyl group, butyl group, pentyl group, and the like.

[0047] In general formulas (1) to (6), examples of the substituent of the alkyl group include a hydroxyl group, a carbonyl group, a methoxy group, an amino group, a carboxyl group, an aryl group, and a radical polymerizable group. Further, instead of a hydrogen atom, a radical polymerizable group can also be adopted. The radical polymerizable group is not particularly limited as long as it can be addition-polymerized by a radical and a radical polymerizable group-containing cation can form an ionic liquid. Specific examples of the radical polymerizable group include a vinyl group, an allyl group, an isopropenyl group, an acryloyl group, a methacryloyl group, and a maleoyl group, etc., and preferably a vinyl group, an allyl group, an acryloyl group, etc.

[0048] The anion is not particularly limited as long as it can be an anion constituting the ionic liquid. Specific examples of the anion include organic carboxylic acid ions (for example, organic carboxylic acid ions having 1 carboxyl group and 1 to 8 carbon atoms (preferably 2 to 4, more preferably 2 to 3)), halide ions, dialkyl phosphate ions, tetrafluoroborate ions (BF4 - ), BF3CF3 - , BF3C2F5 - , BF3C3F7 - , BF3C4F9 - , hexafluorophosphate ions (PF6 - ), bis(trifluoromethanesulfonyl)imide ions ((CF3SO2)2N - ), perchlorate ions (ClO4 - ), tris(trifluoromethanesulfonyl)carbonate ions ((CF3SO2)3C - ), trifluoromethanesulfonate ions (CF3SO3 - ), dicyanamide ions ((CN)2N - ), trifluoroacetate ions (CF3COO - ), and amino acid-derived ions, etc. The anion is preferably an organic carboxylic acid ion, a halide ion, etc., and particularly preferably an organic carboxylic acid ion. The anion may be used alone or in combination of two or more.

[0049] Ionic liquids can be produced according to known methods (see, for example, Chem. Lett., 2000, p. 922, J. Phys. Chem. B, 103, 1999, p. 4164, etc.). In the present invention, ionic liquids produced according to known methods may be used, or commercially available products may be used.

[0050] In the impregnation step, the liquid used to impregnate wood with an ionic liquid (impregnation liquid) is not particularly limited as long as it contains an ionic liquid, and it may consist only of an ionic liquid, or may contain other solvents and other components in addition to the ionic liquid. From the viewpoint of easily adjusting the viscosity etc. of the impregnation liquid to an appropriate level, it is preferable for the impregnation liquid to contain other solvents.

[0051] Examples of other solvents include water and various organic solvents. Examples of organic solvents include alcohols, acetone, acetonitrile, benzene, and toluene, etc. Water is preferable as the other solvent. When containing other solvents (preferably water), the total content ratio of the ionic liquid and other solvents (preferably water) is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and even more preferably 95% by mass or more. The other solvents may be used alone or in combination of two or more.

[0052] Since the production method of the present invention is not aimed at destroying wood tissue to make it spongy as in the prior art, it is preferable not to use strong acids such as sulfuric acid or strong alkalis such as sodium hydroxide in the impregnation step (and also in other steps described later).

[0053] Other components are not particularly limited, and examples include various wood treatment agents (for example, preservatives, termite repellents, insect repellents, flame retardants, non-combustible agents, etc.).

[0054] The content ratio of the ionic liquid in the agent of the present invention is not particularly limited. The content ratio is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, still more preferably 20 to 40% by mass, and even more preferably 25 to 35% by mass.

[0055] In the impregnation process of the present invention, the impregnation of the ionic liquid into the wood can be carried out by any method as long as the ionic liquid can be impregnated into the wood. For example, a method of immersing the wood in an impregnating liquid containing the ionic liquid, or a method of injecting the impregnating liquid into the raw wood using an injector can be mentioned.

[0056] The impregnation of the ionic liquid by immersion may be carried out under atmospheric pressure, but it can be carried out by changing the pressure (combining reduced pressure, increased pressure and atmospheric pressure states), and a method of alternately repeating the reduced pressure and atmospheric pressure states for impregnation is preferred. The temperature of the ionic liquid to be immersed may be any temperature at which the ionic liquid is a liquid. For example, 0 to 40°C is preferred, and 15 to 30°C is more preferred. Also, the immersion time of the wood may be any time as long as the wood is sufficiently impregnated with the ionic liquid, and it is appropriately selected according to conditions such as the size of the wood, the pressure and temperature during immersion. For example, about 12 to 120 hours is preferred, and about 24 to 96 hours is more preferred.

[0057] After impregnating the wood with the ionic liquid, it is also possible to further dry the wood impregnated with the ionic liquid (i.e., holding the ionic liquid). The drying method is not particularly limited as long as it does not correspond to a heating process, and a known wood drying method can be adopted. The drying method is usually natural drying.

[0058] 1-2. Heating process In the heating step, the wood obtained in the impregnation step (wood impregnated with an ionic liquid) is heated. As the heating temperature in the heating step, from the viewpoint of enhancing the softening of the wood and further expressing and enhancing the restorability, 40°C or higher is preferable, 60°C or higher is more preferable, 80°C or higher is further preferable, 90°C or higher is even more preferable, and 100°C or higher is particularly preferable. Also, the upper limit of the temperature range is not particularly limited, but 200°C is preferable, 150°C is more preferable, and 120°C is further preferable. The heating time depends on the heating temperature. For example, 6 hours or more is preferable, 12 hours or more is more preferable, 24 hours or more is further preferable, and 36 hours or more is particularly preferable. The upper limit of the heating time is, for example, 2 months, 1 month, 15 days, 10 days, or 5 days.

[0059] 1-3. Acquisition process In the acquisition step, softened wood is obtained through the heating step. Immediately after the heating step, the wood is hard and not in a softened state. In the acquisition step, the wood obtained by the heating step is softened. Specific methods of softening include a method of adsorbing or impregnating a liquid into the wood obtained in the heating step. Thus, in one aspect of the present invention, the manufacturing method of the present invention preferably includes a curing step of curing the obtained wood in a humid atmosphere after the heating step to soften the wood, or a liquid impregnation step of impregnating the wood or the softened wood with a liquid after the heating step. These will be described below.

[0060] 1-3-1. Curing process The humid atmosphere is not particularly limited as long as the humidity is a certain level or higher. The humidity is, for example, 40% or higher, preferably 50% or higher, more preferably 55% or higher. The upper limit of the humidity is not particularly limited and is, for example, 100%, 90%, 80%, or 70%.

[0061] The temperature of the humid atmosphere is not particularly limited as long as it does not repel the adsorption of moisture to the wood. The temperature is, for example, less than 40°C, preferably 35°C or lower, more preferably 30°C or lower, and even more preferably 25°C or lower. The lower limit of the temperature is not particularly limited and is, for example, 0°C, 5°C, or 10°C.

[0062] The time for conditioning is not particularly limited as long as it is sufficient for the wood to soften. The time is, for example, 5 hours or more, preferably 10 hours or more, more preferably 15 hours or more, still more preferably 20 hours or more. The upper limit of the time is not particularly limited, but from the viewpoint of the production efficiency of the softened wood, it is preferably 1 week, more preferably 3 days, still more preferably 2 days, and even more preferably 36 hours.

[0063] 1-3-2. Liquid impregnation process The liquid is not particularly limited as long as it is a solvent other than an ionic liquid that can be replaced with an ionic liquid. Specific examples of the solvent include alcohol, water, acetone, acetonitrile, benzene, toluene, polyethylene glycol, and the like. The solvent may be used alone or in combination of two or more. The solvent preferably contains water. Further, the liquid may contain a drug.

[0064] The impregnation may be carried out by any method as long as the liquid can be impregnated into the wood. For example, a method of immersing the wood in the liquid or a method of injecting the liquid into the raw wood using an injector can be mentioned.

[0065] The impregnation of the liquid by immersion may be carried out under atmospheric pressure, but it can be carried out by changing the pressure (combining reduced pressure, increased pressure, and atmospheric pressure states), and a method of alternately repeating the reduced pressure and atmospheric pressure states for impregnation is preferred. The temperature of the ionic liquid to be immersed is not particularly limited as long as the ionic liquid is in a liquid state. For example, 0 to 40 degrees is preferred, and 15 to 30 °C is more preferred. Further, the immersion time of the wood is not particularly limited as long as the ionic liquid is sufficiently impregnated into the wood, and it is appropriately selected according to conditions such as the size of the wood, the pressure and temperature during immersion. For example, about 12 to 120 hours is preferred, and about 24 to 96 hours is more preferred.

[0066] After impregnating with a liquid, if the treatment is carried out under conditions where the impregnated liquid volatilizes, the degree of softening and restoration of the wood may be reduced. Therefore, as the liquid to be impregnated, it is preferable to use a liquid that is difficult to volatilize, such as polyethylene glycol or the like.

[0067] Note that the liquid impregnation step can also be performed on the softened wood after the acquisition step.

[0068] 2. Softened wood By the production method of the present invention, softened wood can be obtained. The softened wood produced by the production method of the present invention can be easily compressed. The softened wood (air-dried) from which the ionic liquid has been removed after the heating step can be compressed more easily than the untreated wood (air-dried) before impregnation with the ionic liquid. In one aspect, the present invention relates to the softened wood obtained (or obtained) by the production method of the present invention.

[0069] The softened wood of the present invention is characterized in that the cell wall is swollen, and this is considered to be one of the reasons for softening the wood. The cell wall swelling rate in the softened wood is, for example, 12% or more, preferably 14% or more, more preferably 16% or more, and still more preferably 17% or more. The upper limit of the cell wall swelling rate is not particularly limited, and is, for example, 50%, 40%, 30%, or 25%. The cell wall swelling rate is measured according to the method described in Test Example 2. From this viewpoint, in one aspect, the present invention relates to softened wood having a cell wall swelling rate of 12% or more. The softened wood maintains the swollen state of the cell wall even after undergoing a drying treatment (in a dry state).

[0070] According to the production method of the present invention, the wood can be softened without dissolving and thinning the cell wall. Further, according to the production method of the present invention, it is also possible to maintain the woodiness (grain, color tone, etc.) as it is without discoloring the wood white as in the prior art (strong acid, strong alkali treatment).

[0071] The softened wood of the present invention has, for example, a compression ratio when a compressive force (compressive stress) of 0.5 MPa is applied, which is at least twice, preferably at least three times, more preferably at least five times the compression ratio when a compressive force of 0.5 MPa is applied to untreated wood (control wood) before impregnation with an ionic liquid. Further, the softened wood impregnated with an ionic liquid or other solvent can be compressed more easily than the untreated wood impregnated with water.

[0072] The softened wood of the present invention has, for example, a compression ratio when a compressive force of 1.2 MPa, preferably 1.0 MPa, more preferably 0.5 MPa, still more preferably 0.3 MPa, and even more preferably 0.2 MPa is applied, which is preferably 20% or more, more preferably 30% or more, and still more preferably 50% or more.

[0073] The softened wood of the present invention has restorability. For example, when the softened wood is compressed by 20%, preferably 50%, more preferably 75%, the restoration rate is preferably 80% or more, more preferably 85% or more, still more preferably 90% or more, and particularly preferably 95% or more.

[0074] The softened wood of the present invention can be compressed more with a certain compressive force. For example, the compressive force at the time of a compression ratio of X% (X = 10, 15, 20, 25, or 30) is preferably 1.6 times or less, more preferably 1.5 times or less, still more preferably 1.4 times or less, even more preferably 1.3 times or less, particularly preferably 1.2 times or less, and particularly even more preferably 1.1 times or less the compressive force at the time of a compression ratio of (X - Y)% (Y = 5, 10, 15, 20, 25 (provided that (X - Y) is 5 or more)).

[0075] The softened wood of the present invention preferably has a latewood portion. The softened wood of the present invention can exhibit the above characteristics particularly with respect to the force in the direction perpendicular to the lines constituting the latewood portion. On the other hand, it cannot exhibit the above characteristics with respect to the force in the direction parallel to the lines constituting the latewood portion.

Examples

[0076] The present invention will be described in detail below based on examples, but the present invention is not limited by these examples.

[0077] Example 1. Manufacturing of softened wood 1 The ionic liquid aqueous solutions used were as follows. As ionic liquids, four types, 1-ethyl-3-methyl imidazolium chloride ([EtMeIm]Cl), 1-butyl-3-methyl imidazolium chloride ([BuMeIm]Cl), 1-ethyl-3-methyl imidazolium acetate ([EtMeIm]OAc), and 1-butyl-3-methyl imidazolium acetate ([BuMeIm]OAc), were used. The ionic liquids were prepared to a concentration of 30% by mass with pure water.

[0078] The test specimens used were as follows. The sapwood of Cryptomeria japonica D. don, which was cut out continuously to a thickness of 5 mm in the fiber direction from an air-dried rod-shaped test specimen having a square end face of 15 mm × 15 mm, was used as the test material (15 mm × 15 mm × 5 mm). These test specimens were dried to a completely dry state. In addition, the latewood portion on the surface of the end face of the test specimen was determined based on Mork's definition, and when the latewood ratio (=(latewood width / annual ring width)×100(%)) was obtained, the average value was 16.2%.

[0079] The test specimens were immersed in beakers filled with four types of ionic liquid aqueous solutions, and reduced pressure and normal pressure were repeated at room temperature to sufficiently impregnate the test specimens (impregnation step). After the test specimens sufficiently impregnated with the ionic liquid were naturally dried for about one day, heat treatment was performed in an environment of 105°C for two days (heating step). Immediately after the heat treatment, the wood was hard and not in a state where it could be said to be softened wood. After the heat treatment, it was cured in an environment of a temperature of 20°C and a relative humidity of 60% for about one day (curing step). For 4 days The present invention will be described in detail below based on examples, but the present invention is not limited by these examples.

[0080] For the test pieces obtained in the health preservation project, a compression test was carried out using a precision universal testing machine (AG-110kN manufactured by Shimadzu Corporation). Figure 1 shows the relationship between the compression ratio and the compression stress. In addition, as controls, the results of untreated test pieces in the dry state (air-dried state) and untreated test pieces impregnated with pure water are also shown together.

[0081] Also, the dimensions of the test piece immediately after unloading were measured, and the return rate (recovery rate) was measured. The return rate was obtained by the following formula: Return rate (%) = (dimension of the test piece in the compression direction immediately after unloading) / (dimension of the test piece in the compression direction before compression) × 100.

[0082] As shown in Figure 1, for the control test pieces in the air-dried state, the compression stress was around 3 MPa, and for the control test pieces impregnated with pure water, it was around 1.5 MPa, about half of that, when the compression ratio was increasing (the compression ratio was constant). In contrast, for the test pieces impregnated with ionic liquid, the compression ratio increased at a weak compression stress of 1 MPa or less. The lowest compression stress was when [BuMeIm]OAc was used, about 0.1 to 0.2 MPa, softened to about 1 / 10 of that of the control test piece impregnated with pure water, and could be easily compressed even by finger pressure.

[0083] For the case of using [BuMeIm]OAc, the compression stress at each compression ratio is shown in Table 1.

[0084]

Table 1

[0085] As shown in Table 1, even when the compression ratio increased, the increase in compression stress was gentle.

[0086] The return rate after unloading was 97% or more at a 50% compression ratio and 87% even when the compression ratio was increased to 75% in the case of using [BuMeIm]OAc, which had the lowest compression stress.

[0087] Example 2. Analysis of the structure of softened wood [BuMeIm]OAc was used as the ionic liquid, and softened wood test pieces were obtained in the same manner as in Example 1. Electron micrographs of the surface were acquired, and in the photographic images, four arbitrary portions were selected in the latewood part where cells (substantially rectangular) were arranged continuously (measurement sites 1 to 4). The length of 5 to 13 cells (12 cells for measurement site 1, 13 cells for measurement site 2, 11 cells for measurement site 3, and 5 cells for measurement site 4) was measured starting from the center of one side of a certain cell. For the untreated test pieces before immersion in the ionic liquid aqueous solution, four measurements were also made so that the number of cells to be measured was the same as above. The cell wall swelling ratio was calculated according to the following formula: Cell wall swelling ratio = (measured value of the softened wood test piece / measured value of the untreated test piece) × 100 (wherein, for both measured values, the number of cells to be measured is the same).

[0088] An example of the electron micrographic image of the measurement site is shown in Fig. 2. Also, the measured values, cell wall swelling ratios, and the average value of the cell wall swelling ratios at the four measurement sites are shown in Table 2.

[0089]

Table 2

[0090] As shown in Table 2, the cell walls of the softened wood were swollen.

[0091] Example 3. Manufacturing of softened wood 2 [BuMeIm]OAc was used as the ionic liquid, and the test pieces were impregnated with the ionic liquid in the same manner as in Example 1. After allowing such test pieces to air-dry for about one day, heat treatment was performed for 2 days in environments of 40 °C, 60 °C, and 105 °C. After the heat treatment, curing was carried out for about one day in an environment of temperature 20 °C and relative humidity 60%. In addition, test pieces according to a comparative example in which treatment was performed for 2 days in an environment of 20 °C instead of the heat treatment were manufactured.

[0092] The compression test was performed in the same manner as in Example 1. Fig. 3 shows the relationship between the compression ratio and the compression stress. In the comparative example at 20 °C, the compression stress was about the same as that of the test piece impregnated with pure water, but as the treatment temperature (heating temperature) increased, the compression stress decreased in order and softened.

[0093] Example 4. Manufacturing of softened wood 3 [BuMeIm]OAc was used as the ionic liquid, and softwood test pieces were obtained in the same manner as in Example 1. Subsequently, the test pieces were immersed in a beaker filled with pure water and stirred for 3 days using a stirrer to replace the ionic liquid with pure water. The test pieces were dried and weighed to confirm that no ionic liquid remained. Thereafter, air-dried test pieces and test pieces impregnated with pure water again were produced for the test pieces.

[0094] The compression test was conducted in the same manner as in Example 1. Fig. 4 shows the relationship between the compression ratio and the compression stress.

[0095] Compared with the air-dried control test piece in Fig. 1, the compression stress of the air-dried test piece from which the ionic liquid was removed in Example 4 decreased to about 1 / 2. Furthermore, when pure water was injected again into this test piece, the compression stress was comparable to that of the test piece in Example 1 in which the ionic liquid was not removed, and the return rate after unloading also showed a similar tendency. That is, it was revealed that even if the ionic liquid was removed, the softened state could be maintained as long as it was filled with moisture, and it would return to its original shape after unloading unless it was significantly compressed.

Claims

1. An impregnation step of impregnating wood with an ionic liquid, wherein the latewood rate of the wood is 5% or more; An acquisition step of obtaining softened wood through a heating step of heating the wood impregnated with the ionic liquid; A curing step of curing the obtained wood for 20 hours or more in a humid atmosphere with a humidity of 40% or more after the heating step to soften the wood; comprising: wherein the heating step is a step of heating the wood at 80°C or higher for 36 hours or more; A method for manufacturing softened wood.

2. The manufacturing method according to claim 1, wherein the heating temperature in the heating step is 90°C or higher.

3. The manufacturing method according to claim 1 or 2, wherein the heating temperature in the heating step is 100°C or higher.

4. The manufacturing method according to any one of claims 1 to 3, wherein the ionic liquid is 1-butyl-3-methylimidazolium acetate.

5. The manufacturing method according to any one of claims 1 to 4, wherein the cell wall swelling rate of the manufactured softened wood is 12% or more.

6. Softened wood obtained by the manufacturing method according to any one of claims 1 to 5.

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