Chemically modified pulp

Abstract

The present invention provides chemically modified pulp with host-guest properties. [Solution] A chemically modified pulp characterized in that at least a portion of the hydroxyl groups of cellulose are replaced with sulfate ester groups, and at least a portion of the remaining hydroxyl groups of the pulp are replaced with a cyclodextrin derivative.

Description

Technical Field

[0001] The present invention relates to chemically modified pulp.

Background Art

[0002] There has been proposed a regenerated cellulose fiber having host-guest properties, which is obtained by mixing cyclodextrin and a hydrophobic substance with viscose and spinning it (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, the regenerated cellulose fiber described in Patent Document 1 has host-guest properties obtained by mixing cyclodextrin and a hydrophobic substance with viscose and spinning it. In contrast, if there is a chemically modified pulp containing a cyclodextrin derivative and having host-guest properties, it is convenient because processes such as spinning are not required.

[0005] Therefore, an object of the present invention is to provide a chemically modified pulp containing a cyclodextrin derivative and having host-guest properties.

Means for Solving the Problems

[0006] In order to achieve the above object, the chemically modified pulp of the present invention is a pulp in which at least a part of the hydroxyl groups of cellulose is substituted with sulfate ester groups, and at least a part of the remaining hydroxyl groups of the pulp is substituted with a cyclodextrin derivative.

Effects of the Invention

[0007] According to the present invention, it is possible to provide a chemically modified pulp containing a cyclodextrin derivative and having host-guest properties. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a graph showing the transmittance of the infrared absorption spectrum in each example and comparative example. [Figure 2] Figure 2 is a graph showing the absorbance of the infrared absorption spectrum for each example and comparative example. [Figure 3] Figure 3 is a graph showing the host-guest properties of the chemically modified pulp in Example 1. [Figure 4] Figure 4 is a graph showing the calibration curve between toluene concentration and absorbance in Example 1. [Figure 5] Figure 5 is a graph showing the host-guest properties of the chemically modified pulp in Example 2. [Figure 6] Figure 6 is a graph showing a calibration curve between the concentration of γ-cyclodextrin and the decrease in the absorbance of phenolphthalein in Example 2. [Modes for carrying out the invention]

[0009] <Chemically modified pulp> The chemically modified pulp of the present invention is characterized in that at least a portion of the hydroxyl groups of cellulose are replaced with sulfate ester groups, and at least a portion of the remaining hydroxyl groups of the pulp are replaced with a cyclodextrin derivative.

[0010] The chemically modified pulp is a fibrous material formed by the aggregation of multiple cellulose fibers, wherein at least a portion of the hydroxyl groups (-OH groups) of the cellulose (a chain-like polymer in which D-glucose is linked by β(1→4) glycosidic bonds) constituting the cellulose fibers are substituted with sulfate ester groups represented by formula (1), and at least a portion of the remaining hydroxyl groups of the pulp are substituted with cyclodextrin derivatives.

[0011] (-OSO3 - ) r ·Z r+ (1) In formula (1), r is an independent natural number from 1 to 7, Z r+ is, when r = 1, at least one selected from the group consisting of hydrogen ions, alkali metal ions, monovalent transition metal ions, ammonium ions, aliphatic ammonium ions, aromatic ammonium ions, and cationic polymers; when r ≥ 2, at least one selected from the group consisting of alkaline earth metal ions, polyvalent metal ions, and compounds containing two or more cationic functional groups (such as diamine, etc.) in the molecule.

[0012] At least a part of the hydroxyl groups of the cyclodextrin derivative is bonded to at least a part of the remaining hydroxyl groups of the pulp substituted with sulfate ester groups by a condensation reaction. Specific examples of the cyclodextrin derivative will be described in the preparation method of the chemically modified pulp described later. The bond by the condensation reaction can be confirmed, for example, by observing the infrared absorption spectrum using an infrared spectrophotometer.

[0013] <Physical properties of chemically modified pulp> The physical properties of the chemically modified pulp are not particularly limited, but are, for example, as follows.

[0014] <Crystallinity> The chemically modified pulp has, for example, a cellulose I-type crystal structure as a crystal structure, and its crystallinity may be 75% or less. Also, from the viewpoint of maintaining the fiber shape, the crystallinity of the chemically modified pulp is preferably 30% or more. Furthermore, from the viewpoint of handling properties in the preparation of the chemically modified pulp, the crystallinity of the chemically modified pulp is, for example, 30% or more, 40% or more.

[0015] <Method for measuring crystallinity> The crystallinity of the chemically modified pulp can be measured using, for example, an X-ray diffractometer.

[0016] <Average fiber length> The average fiber length of the chemically modified pulp is not particularly limited and is, for example, 0.2 mm to 2 mm, 0.2 mm to 1.8 mm, 0.2 mm to 1.5 mm, or 0.2 mm to 1 mm.

[0017] <Method for measuring average fiber length> The average fiber length of the chemically modified pulp can be measured using, for example, a fiber tester manufactured by Lorenz & Betzler that complies with ISO 16065-2:2007 or a fiber length distribution measuring instrument.

[0018] <Amount of introduced sulfate ester groups> The amount of introduced sulfate ester groups per 1 g (dry solid mass) of the chemically modified pulp is preferably adjusted to be, for example, 0.6 mmol / g or more, 0.8 mmol / g or more, 1 mmol / g or more, or 1.2 mmol / g or more.

[0019] The upper limit is not particularly limited, but from the viewpoint of suppressing fiber disintegration and cost increase due to decreased crystallinity, for example, the amount of introduced sulfate ester groups per 1 g (dry solid mass) of the chemically modified pulp is 9.9 mmol / g or less or 5 mmol / g or less.

[0020] <Method for measuring the amount of introduced sulfate ester groups> The amount of introduced sulfate ester groups in the chemically modified pulp can be evaluated by the amount of introduced sulfur due to the sulfate ester groups or directly measuring the sulfate ester groups. For example, the amount of introduced sulfate ester groups in the chemically modified pulp can be measured using a CHNS / O elemental analyzer. Also, the amount of introduced sulfate ester groups in the chemically modified pulp can be calculated by measuring the electrical conductivity.

[0021] <Short fiber rate (%)> Furthermore, chemically modified pulp may also contain pulp with short fiber lengths, such as the following. Examples of this short fiber length pulp (hereinafter referred to as "short fiber") include pulp having a fiber length of 0.04 mm or more and 0.2 mm or less in its fiber length distribution. The short fiber content (%) (i.e., short fiber ratio (%)) in chemically modified pulp is, for example, 10% or more and 15% or more.

[0022] From the standpoint of ease of handling, the chemically modified pulp has a short fiber content (%) (i.e., short fiber ratio (%)) in the fiber length distribution that is, for example, 10% to 70%, 10% to 60%, 10% to 50%, 10% to 45%, and 15% to 45%.

[0023] <Average fiber width> The average fiber width of chemically modified pulp is not particularly limited, and can range from 5 μm to 100 μm, 10 μm to 50 μm, 20 μm to 40 μm, or 20 μm to 30 μm.

[0024] <Method for measuring average fiber width and fiber distribution> The average fiber width of chemically modified pulp can be measured, for example, using a fiber tester or fiber length distribution analyzer manufactured by Lorenzen & Bettley in accordance with ISO 16065-2:2007. Furthermore, the fiber length distribution and fiber width distribution of chemically modified pulp can be measured, for example, using a fiber length distribution analyzer in accordance with ISO 16065-2:2007.

[0025] <Amount of cyclodextrin derivative to be introduced> The amount of cyclodextrin derivative introduced per 1 g (solid content) of chemically modified pulp is preferably adjusted to, for example, 0.01 mmol / g or more, 0.015 mmol / g or more, 0.02 mmol / g or more, or 0.022 mmol / g or more. The upper limit of the introduced amount is not particularly limited.

[0026] <Method for measuring the amount of cyclodextrin derivative introduced> The amount of cyclodextrin derivative introduced into chemically modified pulp can be evaluated by directly measuring cyclodextrin. For example, the amount of cyclodextrin derivative introduced into chemically modified pulp can be calculated using a calibration curve of the concentration of the inclusion compound. Specifically, as shown in the examples below, it can be calculated using a calibration curve of toluene concentration or a calibration curve of the decrease in phenolphthalein absorbance.

[0027] <Host-Guest Characteristics> The host-guest properties of chemically modified pulp can be confirmed, for example, by measuring the UV-Vis absorbance when the chemically modified pulp is added to an aqueous solution containing toluene or phenolphthalein.

[0028] The chemically modified pulp can be obtained, for example, by the method shown below, but is not limited to this method.

[0029] The outline of this method is to produce the chemically modified pulp by subjecting cellulose-containing pulp (for example, wood-based pulp (hereinafter simply referred to as "wood pulp")) to a chemical treatment. This chemical treatment step includes a first contact step in which the pulp is brought into contact with a sulfate ester group donating compound described later and at least one of urea and urea derivatives (hereinafter referred to as "urea, etc."; for example, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, benzoleinurea, hydantoin, etc., and one type may be used alone or two or more types may be used in combination)); a second contact step in which the pulp is brought into contact with a cyclodextrin derivative donating compound; and a reaction step in which the pulp after these contact steps is subjected to a heating reaction to replace at least a portion of the hydroxyl groups of cellulose with sulfate ester groups and replace at least a portion of the remaining hydroxyl groups of the cellulose in the pulp with the cyclodextrin derivative.

[0030] <First contact process> The sulfate ester group donating compound is not particularly limited as long as it is a compound capable of donating sulfate ester groups to pulp. Examples include sulfamic acid, sulfamate salts, and sulfuryl compounds having a sulfonyl group with two oxygen atoms covalently bonded to sulfur. One of these compounds may be used alone, or two or more may be used in combination. Sulfamic acid is preferred as the sulfate ester group donating compound because it has lower acidity, higher efficiency in introducing sulfate ester groups, is inexpensive, and is highly safe compared to sulfuric acid. Hereafter, the explanation will take as an example the case in which sulfamic acid is used as the sulfate ester group donating compound and urea is used as the urea.

[0031] The first contact step is a step of bringing the pulp into contact with sulfamic acid and urea. This first contact step is not particularly limited as long as it is a method that can cause the contact to occur. For example, the pulp may be impregnated with the reaction solution by immersing it in a reaction solution in which sulfamic acid and urea are dissolved in a solvent, or the reaction solution may be applied to the pulp, or sulfamic acid and urea may be applied, impregnated, or sprayed onto the pulp separately. Of these, the method of immersing the pulp in the reaction solution to impregnate it is suitable for homogeneous contact between sulfamic acid and urea and the pulp.

[0032] The solvent used to dissolve sulfamic acid and urea is not particularly limited and can be any of the following: protic polar solvents such as water, ethanol, methanol, acetic acid, formic acid, 2-propanol, nitromethane, and aqueous ammonia; aprotic polar solvents such as acetone, ethyl acetate, tetrahydrofuran (THF), dimethylformamide (DMF), acetonitrile, dimethyl sulfoxide (DMSO), dimethyl sulfide (DMS), and dimethylacetamide (DMA); or nonpolar solvents such as diethyl ether, benzene, toluene, hexane, chloroform, and 1,4-dioxane. One solvent may be used alone, or two or more may be used in combination. Water is particularly preferred from the viewpoint of easily dissolving sulfamic acid and urea.

[0033] Furthermore, the pulp in which sulfamic acid and urea have been brought into contact through this first contact process is sometimes referred to as "reaction solution impregnated pulp."

[0034] <Amount of reaction solution in contact> When the reaction solution comes into contact with the pulp, it is preferable to ensure that the sulfamic acid and urea in the reaction solution are in predetermined proportions relative to the pulp. Specifically, the amount of sulfamic acid and urea in the reaction solution should be appropriate relative to the pulp in the reaction solution-impregnated pulp before the reaction process. More specifically, the amount of sulfamic acid in contact with the pulp (dry mass, which is the solid content mass) in the reaction solution-impregnated pulp immediately before the heating reaction of the reaction process should be adjusted to be about the same as or greater than the amount of urea in contact.

[0035] For example, the reaction solution is prepared such that the mixing ratio of sulfamic acid and urea is such that, in terms of mass ratio, the value obtained by dividing the mass of parts of sulfamic acid per 100 parts by mass of solid content of pulp in the reaction solution-impregnated pulp immediately before the heating reaction by the mass of parts of urea per 100 parts by mass of solid content of pulp in the reaction solution-impregnated pulp immediately before the heating reaction (sulfamic acid / urea) is 0.8 or higher, 0.85 or higher, and 1 or higher.

[0036] Furthermore, for example, the amount of sulfamic acid in contact with the pulp is adjusted to be 70 parts by mass or more, 100 parts by mass or more, and 200 parts by mass or more, based on 100 parts by mass of solid content of the pulp in the reaction solution-impregnated pulp immediately before being subjected to the heating reaction.

[0037] Furthermore, for example, the amount of urea in contact with the pulp, that is, the amount of urea in contact with the solid content of the pulp in the reaction solution-impregnated pulp immediately before being subjected to the heating reaction, is adjusted to be 20 parts by mass or more, 30 parts by mass or more, and 50 parts by mass or more per 100 parts by mass of solid content of the pulp, while maintaining the aforementioned relationship with sulfamic acid. The upper limit of the amount of urea in contact with the pulp is not particularly limited, but for example, it is 350 parts by mass or less, 300 parts by mass or less, and 250 parts by mass or less per 100 parts by mass of solid content of the pulp.

[0038] The amount of sulfamic acid and urea that come into contact with 100 parts by mass of solid content of the pulp can be appropriately calculated, for example, depending on the state of the reaction solution-impregnated pulp used in the reaction process.

[0039] <Second contact process> The cyclodextrin derivative donating compound can be any derivative chemically modified from cyclodextrin, and the compound used for chemical modification of cyclodextrin is not particularly limited, but examples include compounds having a sulfate group, a phosphate group, or a carboxyl group. Among these, from the viewpoint of solubility and cost, compounds having a carboxyl group are preferable for chemical modification, and citric acid is particularly preferable. In this step, either the compound used for chemical modification and cyclodextrin may be used, or the cyclodextrin derivative after chemical modification may be used. Among these, from the viewpoint of ease of handling, it is preferable to use cyclodextrin and the compound used for chemical modification in this step.

[0040] <Cyclodextrin> The cyclodextrin is not particularly limited, and examples include α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, methyl-β-cyclodextrin, and hydroxypropyl-β-cyclodextrin. Among these, β-cyclodextrin is preferable from the viewpoint of availability and ease of handling. Hereafter, the explanation will take the case in which β-cyclodextrin is used as the cyclodextrin and citric acid is used as the compound for chemical modification as an example.

[0041] The second contact step is a step of bringing the pulp into contact with β-cyclodextrin and citric acid. This second contact step is not particularly limited as long as it is a method that can bring about the contact. For example, the pulp may be impregnated with the reaction solution by immersing it in a reaction solution in which β-cyclodextrin and citric acid are dissolved in a solvent, or the reaction solution may be applied to the pulp, or β-cyclodextrin and citric acid may be applied, impregnated, or sprayed onto the pulp separately. Of these, the method of immersing the pulp in the reaction solution to impregnate it is suitable for homogeneously bringing β-cyclodextrin and citric acid into contact with the pulp.

[0042] The solvent used to dissolve β-cyclodextrin and citric acid is not particularly limited and can be any of the following: protic polar solvents such as water, ethanol, methanol, acetic acid, formic acid, 2-propanol, nitromethane, and aqueous ammonia; aprotic polar solvents such as acetone, ethyl acetate, tetrahydrofuran (THF), dimethylformamide (DMF), acetonitrile, dimethyl sulfoxide (DMSO), dimethyl sulfide (DMS), and dimethylacetamide (DMA); or nonpolar solvents such as diethyl ether, benzene, toluene, hexane, chloroform, and 1,4-dioxane. One solvent may be used alone, or two or more may be used in combination. Water is particularly preferred from the viewpoint of easily dissolving β-cyclodextrin and citric acid.

[0043] Furthermore, the pulp that has been in contact with β-cyclodextrin and citric acid through this second contact process is sometimes called "reaction solution impregnated pulp."

[0044] <Amount of reaction solution in contact> When the reaction solution comes into contact with the pulp, it is preferable to ensure that the β-cyclodextrin and citric acid in the reaction solution are in a predetermined ratio relative to the pulp. Specifically, the amount of β-cyclodextrin and citric acid in the reaction solution relative to the pulp in the reaction solution-impregnated pulp before the reaction process is adjusted to be appropriate. More specifically, the amount of β-cyclodextrin in contact with the pulp (dry mass, which is the solid content mass) in the reaction solution-impregnated pulp immediately before the heating reaction of the reaction process is adjusted to be about the same as or greater than the amount of citric acid in contact.

[0045] For example, the reaction solution is prepared such that the mixing ratio of β-cyclodextrin and citric acid is such that, in terms of mass ratio, the value obtained by dividing the mass of parts of β-cyclodextrin per 100 parts by mass of solid content of pulp in the reaction solution-impregnated pulp immediately before the heating reaction by the mass of citric acid per 100 parts by mass of solid content of pulp in the reaction solution-impregnated pulp immediately before the heating reaction (β-cyclodextrin / citric acid) is 1 or greater, 1.5 or greater, and 2 or greater.

[0046] Furthermore, for example, the amount of β-cyclodextrin in contact with the pulp is adjusted to be 1 part by mass or more, 5 parts by mass or more, and 10 parts by mass or more, based on 100 parts by mass of solid content of the pulp in the reaction solution-impregnated pulp immediately before the heating reaction.

[0047] Furthermore, for example, the amount of citric acid in contact with the pulp, that is, the amount of citric acid in contact with the solid content of the pulp in the reaction solution-impregnated pulp immediately before the heating reaction, is adjusted to be 0.5 parts by mass or more, 1 part by mass or more, and 1.5 parts by mass or more per 100 parts by mass of solid content of the pulp, while maintaining the aforementioned relationship with β-cyclodextrin. The upper limit of the amount of citric acid in contact with the pulp is not particularly limited, but for example, it is 100 parts by mass or less, 50 parts by mass or less, and 30 parts by mass or less per 100 parts by mass of solid content of the pulp.

[0048] The amount of β-cyclodextrin and citric acid in contact with 100 parts by mass of solid content of the pulp can be appropriately calculated, for example, depending on the state of the reaction solution-impregnated pulp used in the reaction process.

[0049] The first and second contact steps may be performed in any order. Alternatively, the first and second contact steps may be performed simultaneously, that is, sulfamic acid, urea, β-cyclodextrin, and citric acid may be dissolved in the same solvent and brought into contact with the pulp at the same time. Of these, from the viewpoint of ease of handling, it is preferable to dissolve sulfamic acid, urea, β-cyclodextrin, and citric acid in the same solvent and bring them into contact with the pulp at the same time.

[0050] <Condition of pulp impregnated with reaction solution> As mentioned above, the state of the reaction solution-impregnated pulp to be used in the next reaction step can include, for example, the reaction solution-impregnated pulp in its original state, that is, in a state where the pulp and reaction solution are in contact without active removal of moisture, or in a state where moisture has been actively removed from the pulp that has been in contact with the reaction solution.

[0051] The former (a state in which no active moisture is removed) refers to reaction solution-impregnated pulp, which includes pulp in a state where it is in contact with the reaction solution (for example, including a slurry state), and pulp that has been removed from a state where it is in contact with the reaction solution and then allowed to stand to prepare.

[0052] On the other hand, the latter type of reaction solution-impregnated pulp (in a state where moisture has been actively removed) refers to pulp from which moisture has been intentionally removed from a state in which it has been in contact with the reaction solution. For example, this includes pulp that has been removed from a state in which it has been in contact with the reaction solution and then air-dried, pulp that has been in contact with the reaction solution and then filtered and dewatered, pulp that has been filtered and dewatered and then air-dried, pulp that has been filtered and dewatered and then dried further using a circulating air dryer, pulp that has been filtered and dewatered and then dried further using a heated dryer, pulp that has been filtered and dewatered and then dried using a circulating air dryer or a heated dryer, and so on.

[0053] Thus, the reaction solution-impregnated pulp used in the reaction process may be in a state where no active moisture removal has been performed as described above, or in a state where some moisture has been removed by active moisture removal. Furthermore, when moisture is removed by drying, there is no particular problem even if the moisture content after drying is around 1%. In particular, using the latter method allows for a lower moisture content in the reaction solution-impregnated pulp used in the reaction process, thereby shortening the reaction time in the heating reaction of the reaction process. This has the advantage of improving the productivity of chemically modified pulp. In addition, using a dewatering treatment method has the advantage of allowing for more efficient preparation of reaction solution-impregnated pulp when processing large quantities of reaction solution.

[0054] Furthermore, when using an active drying method, the moisture content of the reaction solution-impregnated pulp may be dried to about 1%, or the moisture may be removed by drying to a completely dry state with a moisture content considerably lower than 1%.

[0055] In this specification, a non-dry state in which the moisture content of reaction solution-impregnated pulp is 1% or more is also referred to as a wet state. For example, in this specification, the term "wet state" may refer to pulp that has been left impregnated with the reaction solution, pulp that has been partially dehydrated, and even pulp that has been partially dried.

[0056] Furthermore, as used herein, "absolutely dry" means a state in which the moisture content is reduced to less than 1% by reducing the pressure in a desiccator containing a desiccant such as calcium chloride or phosphorus pentoxide, or by heat drying for a long period of time.

[0057] Therefore, when using the latter method described above (a reaction method in which moisture is actively removed), the moisture content of the reaction solution-impregnated pulp may be reduced to either a non-dry state or a completely dry state, but it is preferable to use the method that reduces it to a non-dry state.

[0058] The moisture content of the reaction solution-impregnated pulp in this specification is calculated using the following formula. Moisture content of reaction solution-impregnated pulp (%) = 100 - (Mass of solid content of reaction solution-impregnated pulp (g) / Mass of reaction solution-impregnated pulp at the time of moisture content measurement (g)) × 100 = {(Mass of reaction solution-impregnated pulp at the time of moisture content measurement (g) - Mass of solid content of reaction solution-impregnated pulp (g)) / Mass of reaction solution-impregnated pulp at the time of moisture content measurement (g)} × 100

[0059] In the above formula, the solid content mass (g) of the reaction solution-impregnated pulp refers to the dry mass of the reaction solution-impregnated pulp. Specifically, it refers to the dry mass obtained by drying the sample using a dryer or the like and adjusting it to a constant weight. For example, by placing the reaction solution-impregnated pulp in a dryer and drying it under predetermined drying conditions (e.g., 105°C for 2 hours) and measuring the mass, the mass of the dried material after the moisture has been removed from the reaction solution-impregnated pulp (i.e., what is not removed by the above drying conditions, for example, the pulp and reagents in the reaction solution) can be calculated.

[0060] The state of the pulp when it comes into contact with the reaction solution is not particularly limited; for example, it may be dry or wet (i.e., humid).

[0061] <Pre-drying process> In the above example, a method for preparing reaction solution-impregnated pulp was described in which moisture was actively removed. However, when using a method of removing moisture while heating (pre-drying step) in this method (for example, directly heating and drying the pulp in contact with the reaction solution, or heating and drying the dehydrated pulp), it is desirable to adjust the heating temperature to be below a predetermined temperature. The drying temperature in this pre-drying step is not particularly limited, but it is preferable to adjust it to a temperature that can remove moisture contained in the reaction solution-impregnated pulp and surrounding moisture, and at which point the reaction does not proceed. For example, the drying temperature in the pre-drying step can be adjusted so that the ambient temperature of the reaction solution-impregnated pulp is 100°C or lower. On the other hand, from the viewpoint of workability, it is preferable to adjust it to be 50°C or higher. Therefore, the drying temperature in the pre-drying step is preferably 50°C to 100°C or 70°C to 100°C.

[0062] <Moisture adjustment process> This method may include a moisture adjustment step to adjust the moisture content of the pulp that comes into contact with the reaction solution to fall within a predetermined range. This moisture adjustment step involves drying or humidifying the pulp to achieve a predetermined moisture content. Including this moisture adjustment step can make the moisture content in the pulp more uniform when it comes into contact with the reaction solution, potentially improving product stability during continuous operation. Furthermore, drying the pulp to a certain extent to reduce its moisture content (for example, to a moisture content of 1% to 10%) has the advantage of potentially improving its storability.

[0063] <Reaction Process> The reaction solution-impregnated pulp prepared as described above is subjected to the next reaction step. This reaction step involves reacting the cellulose fibers contained in the reaction solution-impregnated pulp with sulfamic acid and urea to replace at least a portion of the hydroxyl groups in the cellulose fibers with sulfate ester groups, thereby introducing sulfate ester groups into the cellulose fibers contained in the pulp. Furthermore, it involves reacting the cellulose fibers with β-cyclodextrin and citric acid to replace at least a portion of the remaining hydroxyl groups in the cellulose fibers with a cyclodextrin derivative, thereby introducing a cyclodextrin derivative into the cellulose fibers contained in the pulp. In other words, this reaction step involves replacing at least a portion of the hydroxyl groups in the cellulose fibers contained in the reaction solution-impregnated pulp with sulfate ester groups, and replacing at least a portion of the remaining hydroxyl groups in the cellulose fibers with a cyclodextrin derivative.

[0064] This reaction step is not particularly limited as long as it is a method capable of replacing at least a portion of the hydroxyl groups of the cellulose fibers in the reaction solution-impregnated pulp with sulfate ester groups, and replacing at least a portion of the remaining hydroxyl groups of the cellulose fibers with a cyclodextrin derivative. For example, a method of accelerating the reaction by heating the reaction solution-impregnated pulp can be used. The following explanation will take the case where the reaction is carried out by this heating method as an example.

[0065] <Reaction temperature during the reaction process> The reaction temperature in the reaction process is not particularly limited, but it is preferable that it is a temperature that can introduce sulfate ester groups and cyclodextrin derivatives into the cellulose fibers constituting the pulp while suppressing thermal decomposition and hydrolysis reactions of the fibers. For example, the ambient temperature of the reaction solution-impregnated pulp subjected to the reaction process is adjusted to 100°C to 200°C, 120°C to 200°C, 120°C to 180°C, or 120°C to 160°C. If the ambient temperature during heating is 200°C or lower, thermal decomposition and discoloration of the fibers can be suppressed.

[0066] The heaters used in the reaction process are not particularly limited. For example, any heater capable of directly or indirectly heating the reaction solution-impregnated pulp while satisfying the requirements can be used. Known dryers, vacuum dryers, microwave heating devices, autoclaves, infrared heating devices, and hot presses (e.g., AH-2003C manufactured by AS ONE Corporation) can be used. In particular, from the viewpoint of ease of operation, it is preferable to use a circulating air dryer because gas may be generated in the reaction process.

[0067] <Reaction time in the reaction process> When using the heating method described above as a reaction step, the heating time (i.e., reaction time) is not particularly limited, but for example, when the reaction temperature is adjusted to fall within the above range, it can be 1 minute or more, 5 minutes or more, 10 minutes or more, or 15 minutes or more, and from the viewpoint of operability and cost, it can be 5 minutes to 300 minutes or 5 minutes to 120 minutes.

[0068] By performing the above steps, chemically modified pulp can be prepared.

[0069] <Washing process after the reaction process> A washing step may be included after the reaction step to wash the chemically modified pulp. The surface of the chemically modified pulp is acidic due to the effects of sulfamic acid (a sulfate ester group donating compound) and citric acid. In addition, unreacted reaction solution is present. Therefore, by including a washing step to ensure that the reaction is completely finished and excess reaction solution is removed to bring the pulp to a neutral state, handling can be improved.

[0070] This washing process is not particularly limited; for example, it is sufficient to make the chemically modified pulp nearly neutral. For instance, washing with pure water until the chemically modified pulp becomes neutral can be used. Alternatively, neutralization washing using an alkaline solution may be performed. When such neutralization washing is performed, examples of alkaline compounds in the alkaline solution include inorganic alkaline compounds and organic alkaline compounds. Examples of inorganic alkaline compounds include alkali metal hydroxides, carbonates, and phosphates. Examples of organic alkaline compounds include ammonia, aliphatic amines, aromatic amines, aliphatic ammonium compounds, aromatic ammonium compounds, heterocyclic compounds, and hydroxides of heterocyclic compounds.

[0071] Furthermore, the separation of the chemically modified pulp in the washing process is not particularly limited; for example, any method that allows for filtration of the chemically modified pulp from the washing water is acceptable. For example, the washing of the chemically modified pulp after the reaction can be performed using stainless steel sieves with mesh sizes of 243 μm (70 mesh) to 20 μm (635 mesh), 132 μm (120 mesh) to 45 μm (300 mesh), and 75 μm (200 mesh) to 45 μm (300 mesh).

[0072] The chemically modified pulp of the present invention enables the production of functional pulps utilizing host-guest properties brought about by the introduction of cyclodextrin derivatives, as well as pulps capable of adsorbing contaminants. This pulp can be suitably used in a wide range of applications in various fields, including industrial, food, medical, and cosmetic industries. [Examples]

[0073] (Example 1) A reaction solution was prepared by completely dissolving 9 g of sulfamic acid, 4.5 g of urea, 90 mg of citric acid, and 540 mg of β-cyclodextrin in 30 g of pure water. The reaction solution was uniformly absorbed into 20 g (5 g solids) of bleached softwood kraft pulp (NBKP, hereinafter sometimes simply referred to as "pulp") placed in a plastic bag (Asahi Kasei Home Products Corporation, Ziploc®). The pulp was then spread thinly on an acrylic board and dried at 85°C for 3 hours. The dried material was then subjected to a heating reaction at 140°C for 30 minutes. The resulting reaction product was neutralized with an aqueous sodium bicarbonate solution to convert the counterions of the sulfate ester groups introduced into the pulp into sodium ions. The product was then washed with pure water on a 300-mesh sieve to obtain chemically modified pulp. For the bleached coniferous kraft pulp (NBKP), we used one manufactured by Marusumi Paper Co., Ltd. that had never been dried (25% solids by mass, the remaining 75% by mass being water). For the urea, we used one manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., with a purity of 99.0%, model number: Special Grade. For the citric acid, we used one manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., with a purity of 98.0+%, model number: Special Grade. For the β-cyclodextrin, we used one manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., with a purity of 98.0+%, model number: First Grade. For the sodium bicarbonate, we used one manufactured by Nacalai Tesque Ltd., Nacalai Standard First Grade.

[0074] (Example 2) Chemically modified pulp for Example 2 was obtained in the same manner as for Example 1, except that the cyclodextrin used was changed to γ-cyclodextrin, the amount used was changed to 2.1 g, and the amount of citric acid used was changed to 1.6 g. As for the γ-cyclodextrin, Tokyo Chemical Industries, Ltd., with a purity of >99.0% was used.

[0075] (Comparative Example 1) A chemically modified pulp for Comparative Example 1 was obtained in the same manner as the chemically modified pulp for Example 1, except that cyclodextrin and citric acid were not used.

[0076] (Measurement of chemical bonding in cyclodextrin derivatives) The chemical bonding between cyclodextrin derivatives and cellulose in chemically modified pulp was measured using infrared absorption spectroscopy. A Fourier transform infrared spectrophotometer (IRTracer-100, Shimadzu Corporation) was used for infrared absorption spectroscopy. The sample was prepared by freeze-drying chemically modified pulp.

[0077] (Host-Guest Characteristics) The host-guest properties of the chemically modified pulp in Example 1 were measured by absorbance. A UV-Vis spectrophotometer (Shimadzu Corporation, model number: UV-2600i) was used for absorbance measurement. The measurement solution was prepared by adding 5 g of 1.5% by mass chemically modified pulp to 30 ml of 10 ppm aqueous toluene solution, stirring for 24 hours, and then centrifuging under TAPPI No. 26 conditions. The supernatant was used. Toluene used was 99.5% purity, special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Centrifuge was performed using a benchtop centrifuge (Kokusan Co., Ltd., model number: H-36α).

[0078] The host-guest properties of the chemically modified pulp in Example 2 were measured in the same manner as in Example 1, except that a solution prepared by adding phenolphthalein to a 0.01 ml / l sodium hydroxide aqueous solution to a concentration of 10 ppm was used instead of 30 ml of a 10 ppm aqueous toluene aqueous solution. For the phenolphthalein, Fujifilm Wako Pure Chemical Industries, Ltd., purity 98.0%, model number; special grade was used, and for the sodium hydroxide aqueous solution, Fujifilm Wako Pure Chemical Industries, Ltd., purity 1 ml / l, model number; volumetric analysis equipment was used, diluted.

[0079] (Amount of cyclodextrin derivative introduced) The amount of cyclodextrin derivative introduced into the chemically modified pulp in Example 1 was calculated from the absorbance calibration curve of toluene aqueous solution. To create the calibration curve, aqueous solutions of toluene with concentrations of 0.0125 mmol / l, 0.025 mmol / l, 0.05 mmol / l, 0.1 mmol / l, and 0.2 mmol / l were used.

[0080] The amount of cyclodextrin derivative introduced into the chemically modified pulp in Example 2 was calculated from a calibration curve of absorbance reductions obtained by preparing phenolphthalein aqueous solutions by adding phenolphthalein to a 0.01 mol / l sodium hydroxide aqueous solution to a concentration of 10 ppm, and then adding γ-cyclodextrin at different concentrations and stirring for 24 hours. For the creation of the calibration curve, phenolphthalein aqueous solutions with γ-cyclodextrin concentrations of 0.01 mmol / l, 0.02 mmol / l, 0.08 mmol / l, and 0.16 mmol / l were used.

[0081] (Measurement results) Figure 1 is a graph showing the measured transmittance of the infrared absorption spectra of the chemically modified pulp for each example and comparative example. Figure 2 is a graph showing the measured absorbance of the infrared absorption spectra of the chemically modified pulp for each example and comparative example. Figure 3 is a graph showing the measured host-guest properties for Example 1 and Comparative Example 1. Figure 4 is a graph showing the calibration curve between toluene concentration and absorbance in Example 1. Figure 5 is a graph showing the measured host-guest properties for Example 2 and Comparative Example 1. Figure 6 is a graph showing the calibration curve between γ-cyclodextrin concentration and the decrease in phenolphthalein absorbance in Example 2.

[0082] As shown in Figure 1, the chemically modified pulp of each example and Comparative Example 1 was 1220 cm². -1 Absorption of sulfate ester groups was confirmed in the vicinity. Furthermore, as shown in Figure 2, the chemically modified pulps of Example 1 and Example 2 contained 1700 cm³. -1 Absorption of ester bonds was confirmed in the vicinity. In other words, it was confirmed that the chemically modified pulp obtained in Example 1 and Example 2 had cyclodextrin derivatives introduced into it.

[0083] As shown in Figure 3, it was confirmed that at wavelengths above 260 nm, the absorbance of toluene in the aqueous solution containing the chemically modified pulp of Example 1 was lower than that of toluene in the aqueous solution containing the chemically modified pulp of Comparative Example 1. Furthermore, from the decrease in absorbance in Figure 3 and the calibration curve between toluene concentration and absorbance in Figure 4, it was determined that the amount of cyclodextrin derivative introduced into the chemically modified pulp of Example 1 was 0.020 mmol / g. In other words, it was confirmed that the chemically modified pulp of Example 1 contained a cyclodextrin derivative and possessed host-guest properties.

[0084] As shown in Figure 5, it was confirmed that at wavelengths exceeding 500 nm, the absorbance of phenolphthalein in the aqueous solution containing the chemically modified pulp of Example 2 was lower than that of phenolphthalein in the aqueous solution containing the chemically modified pulp of Comparative Example 1. Furthermore, from the decrease in absorbance in Figure 5 and the calibration curve of the decrease in absorbance of phenolphthalein with respect to the concentration of γ-cyclodextrin in Figure 6, it was determined that the amount of cyclodextrin derivative introduced into the chemically modified pulp of Example 2 was 0.024 mmol / g. In other words, it was confirmed that the chemically modified pulp of Example 2 contained a cyclodextrin derivative and possessed host-guest properties.

[0085] Although the present invention has been described above with reference to embodiments and examples, the present invention is not limited to the above embodiments and examples. Various modifications to the configuration and details of the present invention can be understood by those skilled in the art within the scope of the present invention.

Claims

1. A pulp in which at least some of the hydroxyl groups of cellulose are replaced with sulfate ester groups, A chemically modified pulp characterized in that at least a portion of the remaining hydroxyl groups of the pulp are replaced with a cyclodextrin derivative.

2. The chemically modified pulp according to claim 1, characterized in that the cyclodextrin derivative includes a cyclodextrin derivative having a carboxyl group.

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