Softened lumber and production method therefor

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 is a low-energy production sustainable material that can fix CO2 in the atmosphere. Wood has been attracting attention as a sustainable resource and is widely used for construction and civil engineering, as well as for the raw material of 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 describes a technique in which extremely light wood is treated at high temperature in a sodium hydroxide solution and then freeze-dried. It has been reported that wood can be made sponge-like by heating the wood to destroy its wood tissue.

[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, which 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. 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. The production method.

[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 softwood to be manufactured is 12% or more.

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

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

[0019] Item 12. The softwood according to Item 11, having resilience.

[0020] Item 13. The softwood 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 softwood 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 compression force at a compression rate of 20% is 1.3 times or less the compression force at a compression rate of 10%. The softwood according to any one of Items 11 to 14.

[0023] Item 16. The softwood according to any one of Items 11 to 15, having a latewood portion.

Advantages of the Invention

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

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0026] In this specification, expressions such as "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. That is, a method for producing softened wood (which may also be referred to as "the production method of the present invention" in this specification). This will be described below.

[0028] 1-1. Impregnation process The wood that is the target of the impregnation step is not particularly limited as long as it is a material made from felled trees as raw materials, and various woods can be adopted regardless of the type of woody plant used as the raw material and the presence (and degree) of lumbering. 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, coniferous woods, broad-leaved woods, etc. can be mentioned. More specifically, for example, sugi, ezomatsu, karamatsu, kuromatsu, todomatsu, himekomatsu, ichii, nezuko, harimomi, iramomi, inumaki, momi, sawara, togasawara, asunaro, hiba, tsuga, kometsuga, hinoki, ichii, inugaya, touhi, yellow cedar (Chamaecyparis nootkatensis), Lawson's cypress (Chamaecyparis lawsoniana), Douglas fir (Pseudotsuga menziesii), Sitka spruce (Picea sitchensis), radiata pine, eastern spruce, eastern white pine, western larch, western hemlock, western fir, tamarack, etc. of coniferous woods; aspen, American black cherry, yellow poplar, walnut, oaks, keyaki, sycamore, silver cherry, tama, teak, Chinese elm, Chinese maple, nara, hard maple, hickory, pecan, white ash, white oak, white birch, red oak, acacia, eucalyptus, etc. of broad-leaved woods, etc. can be mentioned. Also, either sapwood or heartwood can be used as wood materials.

[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, woody 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. Also, as wood, either green wood or dried wood can be used.

[0031] The wood preferably has a latewood portion. 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 portion (the portion other than the latewood portion).

[0032] The latewood rate 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 rate (= (latewood width / annual ring width) × 100 (%)) is obtained.

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

[0034] The method of 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. For example, a mode in which part or all of the wood is immersed in the solvent can be mentioned. 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 It can be. 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, etc. For example, under atmospheric pressure and at room temperature The immersion time can be, for example, 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 salts that are 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 still 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 an 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) and the like. Preferably, imidazolium ions represented by the general formula (1), phosphonium ions represented by the general formula (5), and the like are mentioned, and particularly preferably, imidazolium ions represented by the general formula (1) are mentioned. 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 and 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] A preferred embodiment of the general formula (1) is that 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 that R​1 is an alkyl group having 1 to 2 carbon atoms, and R 2 is an alkyl group having 1 to 2 carbon atoms. Examples of the imidazolium ion represented by the general formula (1) include preferably 1-butyl-3-methylimidazolium ion, 1- ethyl-3-methylimidazolium ion, etc., and particularly preferably 1-butyl-3- methylimidazolium ion.

[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 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.

[0043] In the general formula (3), R 4 to R 7 are the same or different and represent an optionally substituted alkyl group (preferably an unsubstituted alkyl group) or a hydrogen atom (provided that R 4 to R 7 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 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.

[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 (provided that R8 and R 9 (however, 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 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 6 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.

[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 (however, 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 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.

[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 (however, R 14 ~R 16 are not hydrogen atoms at the same time). The alkyl group is not particularly limited as long as the cation having a radically polymerizable group 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 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.

[0047] In the 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. A radical polymerizable group can also be used instead of a hydrogen atom. The radical polymerizable group is not particularly limited as long as it can be subjected to addition polymerization by a radical and the 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, and preferably a vinyl group, an allyl group, and an acryloyl group.

[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 carboxylate ions (e.g., an ion having one carboxy group, Organic carboxylate ions having 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 ion (PF6 - ), Bis(Tori Fluoromethanesulfonyl)imidate ion ((CF3SO2)2N - ), perchlorate ion (ClO4 - ), tris(trifluoromethanesulfonyl)carbonate ion ((CF3SO2)3C - ), Truffle Fluoromethanesulfonate ion (CF3SO3 - ), dicyanamide ion ((CN)2N - ), trifluoroacetate ion (CF3COO - ), and amino acid-derived ions. Examples thereof preferably include organic carboxylic acid ions, halide ions, etc., and organic carboxylic acid ions are particularly preferable. The anions may be used alone or in combination of two or more kinds.

[0049] The ionic liquid can be produced according to a known method (for example, see Chem. Lett., 2000, p. 922, J. Phys. Chem. B, 103, 1999, p. 4164, etc.). In the present invention, an ionic liquid produced according to a known method may be used, or a commercially available product may be used. In the impregnation step, the liquid (impregnation liquid) used for impregnating the wood with the ionic liquid is not particularly limited as long as it contains the ionic liquid, and it may consist only of the 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 degree, it is preferable that the impregnation liquid contains other solvents.

[0050] Examples of other solvents include water and various organic solvents. Examples of the organic solvent include alcohol, 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 kinds.

[0051] Since the production method of the present invention is not intended to break the wood tissue into a sponge-like state 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).

[0052]

[0053] ​Other components are not particularly limited, and examples thereof include various wood treatment agents (for example, preservatives, termite-proof agents, insect-proof agents, 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, even more preferably 25 to 35% by mass.

[0055] In the impregnation step of the present invention, the impregnation of the ionic liquid into the wood may 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 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, etc. For example, about 12 to 120 hours is preferred, and about 24 to 96 hours is more preferred.

[0057] After the wood is impregnated with the ionic liquid, the wood impregnated with the ionic liquid (that is, holding the ionic liquid) can be further dried. 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, and 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 still 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 curing time 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, and 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 the ionic liquid that can be replaced with the 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. Also 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 impregnated may be any temperature at which the ionic liquid is a liquid. For example, 0 to 40 degrees is preferred, and 15 to 30°C is more preferred. Also The impregnation time of the wood only needs to be a time when the ionic liquid sufficiently impregnates the wood, and it is appropriately selected according to conditions such as the size of the wood, the pressure and temperature during impregnation, etc. For example, it is about 12 to 120 hours. Preferably, it is about 24 to 96 hours, and more preferably about 24 to 96 hours.

[0066] After impregnating with the liquid, if it is processed under conditions where the impregnated liquid volatilizes, the degree of softening and restoration of the wood may be reduced. For this reason, as the liquid to be impregnated, it is preferable to use a liquid that is difficult to volatilize, such as polyethylene glycol.

[0067] Incidentally, 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 of the present invention, it relates to softened wood having a cell wall swelling rate of 12% or more. The softened wood maintains the cell wall swelling state even after undergoing a drying treatment (in a dry state).

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

[0071] The softened wood of the present invention, for example, has a compression ratio when a compressive force (compressive stress) of 0.5 MPa is applied that is 2 times or more, preferably 3 times or more, more preferably 5 times or more the compression ratio when a compressive force of 0.5 MPa is applied to the untreated wood (control wood) before impregnating with the ionic liquid. Also, 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, for example, has 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, even more preferably 0.2 MPa is applied that is preferably 20% or more, more preferably 30% or more, still more preferably 50% or more.

[0073] The softened wood of the present invention has resilience. For example, when the softened wood is compressed by 20%, preferably 50%, more preferably 75%, the recovery rate is preferably 80% or more, more preferably 85% or more, still more preferably 90% or more, 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, most preferably 1.2 times or less, particularly most 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 (however, (X - Y) is 5 or more)). is preferably 1.2 times or less, particularly most preferably 1.1 times or less.

[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 a force in a direction perpendicular to the lines constituting the latewood portion. On the other hand, it cannot exhibit the above characteristics with respect to a force in a direction parallel to the lines constituting the latewood portion.

Example

[0076] Hereinafter, the present invention will be described in detail 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 are as follows. As the 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 in pure water. Thereafter.

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

[0079] The test pieces were immersed in beakers filled with four types of ionic liquid aqueous solutions and left at room temperature. For 4 daysThe degree of reduced pressure and normal pressure were repeated to sufficiently impregnate the test piece (impregnation process). After allowing the test piece sufficiently impregnated with the ionic liquid to air-dry naturally for about one day, heat treatment was performed for two days in an environment of 105°C ( heating process). Immediately after the heat treatment, the wood was hard and not in a state where it could be called softened wood. After the heat treatment, it was cured for about one day in an environment of 20°C and 60% relative humidity (curing process).

[0080] Regarding the test piece obtained in the curing process, a compression test was performed using a precision universal testing machine (AG-110kN manufactured by Shimadzu Corporation). Fig. 1 shows the relationship between the compression ratio and the compression stress. In addition, as controls, the results of untreated test pieces in a 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 Fig. 1, in the control test piece in the air-dried state, the compression stress was around 3 MPa, and in the control test piece impregnated with pure water, it was around 1.5 MPa, about half of that, when the compression ratio increased (the compression ratio became horizontal). In contrast, in the test piece impregnated with the ionic liquid, the compression ratio increased with a weak compression stress of 1 MPa or less. The lowest compression stress was when [BuMeIm]OAc was used, which softened to about 0.1 to 0.2 MPa, about one-tenth of that of the control test piece impregnated with pure water, and could be easily compressed even by finger pressure.

[0083] Regarding the case where [BuMeIm]OAc was used, 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 the compression stress was gentle.

[0086] The recovery rate after unloading was over 97% at a 50% compression rate when [BuMeIm]OAc with the lowest compressive stress was used, and was 87% even when the compression rate was increased to 75%.

[0087] Example 2. Analysis of the structure of softened wood Using [BuMeIm]OAc as the ionic liquid, softened wood specimens were obtained in the same manner as in Example 1. An electron micrograph of the surface was acquired. In the photomicrograph, four arbitrary portions were selected in the latewood part where cells (substantially rectangular) were arranged continuously (measurement sites 1 to 4). From the center of one side of a certain cell, the lengths 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) were measured. For the untreated specimens 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 rate was calculated according to the following formula: Cell wall swelling rate = (measured value of the softened wood specimen / measured value of the untreated specimen) × 100 (provided that the number of cells to be measured is the same for both measurements).

[0088] An example of the electron micrograph image of the measurement site is shown in FIG. 2. Also, the measured values, cell wall swelling rates, and the average value of the cell wall swelling rates 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 Using [BuMeIm]OAc as the ionic liquid, the specimens were impregnated with the ionic liquid in the same manner as in Example 1. After such specimens were air-dried for about one day, they were placed in environments of 40 °C, 60 °C, and 105 °C for 2​​ A heat treatment was performed during the day. After the heat treatment, it was cured for about one day in an environment with a temperature of 20°C and a relative humidity of 60%. In addition, a test piece according to a comparative example in which the treatment was performed for 2 days in an environment of 20°C was manufactured instead of the heat treatment. .

[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 a temperature of 20°C, the compression stress was about the same as that of the test piece impregnated with pure water. However, as the treatment temperature (heating temperature) increased, the compression stress decreased and softened in order.

[0093] Example 4. Manufacturing of softened wood 3 [BuMeIm]OAc was used as the ionic liquid, and a softened wood test piece was obtained in the same manner as in Example 1. Next, the test piece was 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 piece was dried and weighed to confirm that no ionic liquid remained. Thereafter, an air-dried test piece and a test piece impregnated with pure water again were manufactured.

[0094] The compression test was performed 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 about the same as that of the test piece of Example 1 in which the ionic liquid was not removed , and the return rate after unloading also showed a similar tendency. That is, it became clear that even if the ionic liquid was removed, as long as it was filled with moisture, the softened state could be maintained 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, and An acquisition step of obtaining softened wood through a heating step of heating the wood impregnated with the ionic liquid. A method for manufacturing softened wood, comprising these steps.

2. The manufacturing method according to Claim 1, further comprising a curing step of curing the obtained wood in a humid atmosphere after the heating step to soften the wood.

3. The manufacturing method according to Claim 2, wherein the humid atmosphere is an atmosphere with a humidity of 40% or more.

4. The manufacturing method according to any one of Claims 1 to 3, further comprising a liquid impregnation step of impregnating the wood or the softened wood with a liquid after the heating step or the acquisition step.

5. The manufacturing method according to any one of Claims 1 to 4, wherein the heating temperature in the heating step is 40°C or higher.

6. The manufacturing method according to any one of Claims 1 to 5, wherein the heating temperature in the heating step is 80°C or higher.

7. The manufacturing method according to any one of Claims 1 to 6, wherein the ionic liquid is 1-butyl-3-methylimidazolium acetate.

8. The manufacturing method according to any one of Claims 1 to 7, wherein the latewood rate of the wood is 5% or more.

9. The manufacturing method according to any one of Claims 1 to 8, wherein the cell wall swelling rate of the manufactured softened wood is 12% or more.

10. Softened wood obtained by the manufacturing method according to any one of Claims 1 to 9.

11. Softened wood with a cell wall swelling rate of 12% or more.

12. The softened wood according to Claim 11, having resilience.

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

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

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

16. The softened wood according to any one of Claims 11 to 15, having a latewood portion.

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