Modified pulp

Abstract

To provide a novel modified pulp having chirality.SOLUTION: The modified pulp of the present invention is a modified pulp in which at least some of hydroxyl groups of cellulose are substituted with sulfate ester groups, characterized by having chirality.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to modified pulp. [Background technology]

[0002] Chiral separation by chromatography has traditionally attracted attention in many fields, including analytical chemistry, organic chemistry, medicine, and pharmacology, and many chiral compounds have been reported. These compounds are used as chiral separating agents, chromatographic packing materials such as chiral column carriers, and the like (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5540368 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there have been no reports of modified pulp with chirality.

[0005] Therefore, an object of the present invention is to provide a new modified pulp having chirality. [Means for solving the problem]

[0006] In order to achieve the above object, the modified pulp of the present invention is A modified pulp in which at least a portion of the hydroxyl groups of cellulose are substituted with sulfate ester groups, It is characterized by having chirality. [Effects of the Invention]

[0007] In view of the above problems, the present inventors have conducted a series of studies and have found that chiral pulp exists among modified pulps in which at least a portion of the hydroxyl groups of cellulose have been substituted with sulfate ester groups. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a flow chart showing an example of a method for producing modified pulp of the present invention. [Figure 2-1] FIG. 2-1 is a graph showing the results of measuring the circular dichroism (CD) spectra of the aqueous dispersions of the modified pulps of Examples 1 to 6. [Figure 2-2] FIG. 2-2 is a graph showing the results of measuring the circular dichroism (CD) spectra of the aqueous dispersions of the modified pulps of Examples 7 to 10. [Figure 3] FIG. 3 is a graph showing the results of measuring the circular dichroism (CD) spectra of the aqueous dispersions of the modified pulps of Comparative Examples 1 to 5. DETAILED DESCRIPTION OF THE INVENTION

[0009] The modified pulp of the present invention is one in which at least a portion of the hydroxyl groups of cellulose has been substituted with sulfate ester groups.

[0010] The modified pulp is a fibrous material composed of a plurality of cellulose fibers, in which at least a portion of the hydroxyl groups (-OH groups) of the cellulose (a chain polymer in which D-glucose is linked via β(1→4) glycosidic bonds) constituting the cellulose fibers contained therein have been substituted with sulfate ester groups represented by formula (1).

[0011] (-OSO3 - ) r Z r+ (1) In formula (1), r is an independent natural number between 1 and 7, Z r+When r=1, is at least one selected from the group consisting of a hydrogen ion, an alkali metal ion, a monovalent transition metal ion, an ammonium ion, an aliphatic ammonium ion, an aromatic ammonium ion, and a cationic polymer; when r=2 or more, is at least one selected from the group consisting of an alkaline earth metal ion, a polyvalent metal ion, and a compound containing two or more cationic functional groups (e.g., diamine) in the molecule.

[0012] <Physical properties of modified pulp> The physical properties of the modified pulp, excluding the chirality described below, are not particularly limited, but are, for example, as follows.

[0013] <Amount of sulfate ester groups introduced> The amount of sulfate ester groups introduced per 1 g (solid mass) of the modified pulp is preferably adjusted to, 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.

[0014] Although there is no particular upper limit, from the viewpoint of suppressing fiber breakdown and cost increases resulting from decreased crystallinity, for example, the amount of sulfate ester groups introduced per 1 g (solid mass) of the modified pulp is 9.9 mmol / g or less, or 5 mmol / g or less.

[0015] <Method for measuring the amount of sulfate ester groups introduced> The amount of sulfate ester groups introduced into the modified pulp can be evaluated by the amount of sulfur introduced due to the sulfate ester groups, or by directly measuring the sulfate ester groups. For example, the amount of sulfate ester groups introduced into the modified pulp can be measured using a CHNS / O elemental analyzer. Alternatively, the amount of sulfate ester groups introduced into the modified pulp can be calculated by measuring electrical conductivity.

[0016] <Crystal structure> The modified pulp may have, for example, a cellulose type I crystalline structure, or a cellulose type II crystalline structure, or may contain both a cellulose type I crystalline structure and a cellulose type II crystalline structure.

[0017] <How to confirm the crystal structure> The crystalline structure of the modified pulp can be confirmed, for example, using an X-ray diffraction device.

[0018] <Average fiber length> The average fiber length of the 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.

[0019] <Short fiber rate (%)> The modified pulp may also include modified pulp with short fiber length as follows. Examples of modified pulp with short fiber length (hereinafter referred to as "short fiber") include modified pulp with a fiber length distribution of 0.04 mm or more and 0.2 mm or less. The content (%) of short fibers in the modified pulp (i.e., short fiber ratio (%)) is, for example, 10% or more, 15% or more.

[0020] From the viewpoint of handleability, the modified pulp has a short fiber content (%) (i.e., short fiber ratio (%)) of, for example, 10% to 70%, 10% to 60%, 10% to 50%, 10% to 45%, or 15% to 45% in terms of fiber length distribution.

[0021] <Average fiber width> The average fiber width of the modified pulp is not particularly limited, and is, for example, 5 μm to 100 μm, 10 μm to 50 μm, 20 μm to 40 μm, or 20 μm to 30 μm.

[0022] <Method for measuring average fiber length, average fiber width, and fiber distribution> The average fiber length and average fiber width of the modified pulp can be measured, for example, using a fiber tester or fiber length distribution measuring instrument manufactured by Lorentzen & Wettley in accordance with ISO 16065-2: 2007. The fiber length distribution and fiber width distribution of the modified pulp can be measured, for example, using a fiber length distribution measuring instrument in accordance with ISO 16065-2: 2007.

[0023] <Viscosity> The viscosity of a dispersion (solid content concentration 1% by mass) obtained by dispersing the modified pulp in water is, for example, 1000 mPa·s or more, 5000 mPa·s or more, or 10000 mPa·s or more. In particular, if the average fiber length of the modified pulp is 1 mm or less, the viscosity of the dispersion tends to increase.

[0024] <Viscosity measurement method> The viscosity (mPa·s) of the modified pulp can be measured, for example, using a B-type viscometer at a measurement temperature of 20°C, with measurements being performed at rotation speeds of 6 rpm and 60 rpm, and the thixotropy index (TI) value can also be calculated from each viscosity value. TI value = (viscosity at 6 rpm) / (viscosity at 60 rpm)

[0025] The TI value can be adjusted as appropriate, and when a high TI value is required, the lower limit of the TI value is, for example, 3 or more, 4 or more, or 5 or more. The upper limit of the TI value is, for example, 10 or less, 8 or less, 6 or less, or 5 or less. On the other hand, when a low TI value is preferred, the lower limit is, for example, 1 or more, and the upper limit is, for example, 3 or less, or 2.5 or less.

[0026] <Chirality> The modified pulp has chirality, which can be confirmed, for example, by the circular dichroism (CD) spectrum of the modified pulp.

[0027] The modified pulp can be obtained by, for example, the following method, but is not limited to this method.

[0028] In summary, this method involves chemically treating pulp (e.g., wood-based pulp (hereinafter simply referred to as "wood pulp")) to produce the modified pulp. This chemical treatment step includes a contacting step in which the pulp is contacted with a sulfate ester group-donating compound (described below) and at least one of urea and a urea derivative (hereinafter referred to as "urea, etc." Examples of the urea derivative include thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, benzoleinurea, and hydantoin, and one type may be used alone or two or more types may be used in combination), and a reaction step in which the pulp after the contacting step is heated to substitute at least a portion of the hydroxyl groups of the cellulose constituting the pulp with sulfate ester groups.

[0029] In the present invention, pulp refers to a fibrous material comprising a plurality of cellulose fibers. These cellulose fibers are comprised of a plurality of fine fibers (e.g., microfibrils). These fine fibers are comprised of a plurality of cellulose molecules (hereinafter, simply referred to as "cellulose"), which are chain-like polymers in which D-glucose is linked via β(1→4) glucoside bonds. It is preferable to wash the pulp beforehand. For example, filtration and dehydration using water on a 200-mesh or 235-mesh sieve can remove excessively fine fibers and debris, which is desirable because it improves handling during preparation. In other words, pulp is a collection of cellulose fibers of a size that can become residue on a 200-mesh or 235-mesh sieve. While the water may be tap water, it is preferably ion-exchanged water or pure water, as will be the case hereinafter.

[0030] Examples of the pulp include wood pulp, dissolving pulp, cotton pulp such as cotton linter, non-wood pulp such as wheat straw, bagasse, paper mulberry, mitsumata, hemp, kenaf, and fruit, and recycled paper pulp prepared from recycled newspapers, magazines, cardboard, etc. One type of pulp may be used alone, or two or more types of pulp may be used in combination. From the viewpoint of availability, wood pulp is the most commonly used pulp.

[0031] There are various types of wood pulp, and there are no particular limitations on their use. Examples include paper pulp such as softwood kraft pulp (NBKP), hardwood kraft pulp (LBKP), and thermomechanical pulp (TMP).

[0032] In the production of the modified pulp according to this example, an alkali treatment step of immersing the pulp in an alkaline alkali metal solution may be carried out prior to the chemical treatment step, as shown in Figure 1. Details of the method for producing the modified pulp according to the example shown in Figure 1 are, for example, as follows.

[0033] <Alkali treatment process> First, the pulp is immersed in an alkaline alkali metal solution (step S1).

[0034] The alkaline alkali metal solution may be, for example, a solution containing one or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide as a solute.

[0035] The solvent for the alkali metal solution is not particularly limited, and examples thereof include 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); and nonpolar solvents such as diethyl ether, benzene, toluene, hexane, chloroform, and 1,4-dioxane. One type of solvent may be used alone, or two or more types may be used in combination. Water is particularly preferred because it is easy to handle and inexpensive.

[0036] The amount of alkali metal in the total amount of the alkali metal solution (alkali metal ratio) is, for example, 2% by mass to 15% by mass. When the alkali metal ratio is within this range, modified pulp having chirality is easily obtained.

[0037] The ratio of the mass of the alkali metal solution to the mass of the pulp to be immersed therein is not particularly limited, but may be, for example, a ratio of about 5 g of the pulp to 100 g of the alkali metal solution.

[0038] The time for which the pulp is immersed in the alkali metal solution is not particularly limited, and may be, for example, about 1 hour.

[0039] <Cleaning process after alkaline treatment process, etc.> The alkali treatment step may be followed by a washing step of washing the pulp. This washing step is not particularly limited as long as it can wash the alkali metal solution from the pulp. For example, a method of washing the pulp on a sieve (e.g., 45 μm (300 mesh) mesh) with pure water may be used. The washed pulp may be dehydrated using a dehydrator (e.g., Model RC-001 manufactured by Bell-Ross Co., Ltd.). The dehydration may be performed by squeezing, air drying, or the like, in addition to using a dehydrator. The solids concentration of the pulp after dehydration is not particularly limited and may be, for example, about 25% by mass. The dehydrated pulp may be stored at room temperature or refrigerated in a refrigerator (e.g., 4°C).

[0040] <Contact process> Next, the pulp after the alkali treatment step is brought into contact with a reaction liquid containing a sulfate ester group-donating compound, urea, etc. (step S2).

[0041] The sulfate ester group-donating compound is not particularly limited as long as it is a compound capable of donating sulfate ester groups to the pulp, and examples thereof include sulfamic acid, sulfamic acid 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. The sulfate ester group-donating compound is preferably sulfamic acid because it has lower acidity than sulfuric acid and the like, has a high efficiency of introducing sulfate ester groups, is inexpensive, and is highly safe. Hereinafter, an example will be described in which sulfamic acid is used as the sulfate ester group-donating compound and urea is used as the urea.

[0042] This step is not particularly limited as long as it is a method that can cause the contact. For example, the pulp may be immersed in a reaction solution in which sulfamic acid and urea are dissolved in a solvent, thereby impregnating the pulp with the reaction solution, or the reaction solution may be applied to the pulp. Alternatively, sulfamic acid and urea may be separately applied to, impregnated into, or sprayed onto the pulp. Among these methods, the method of immersing the pulp in the reaction solution to impregnate the pulp with the reaction solution makes it easier to uniformly contact the pulp with sulfamic acid and urea.

[0043] The solvent for dissolving sulfamic acid and urea is not particularly limited, and examples thereof include 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); and nonpolar solvents such as diethyl ether, benzene, toluene, hexane, chloroform, and 1,4-dioxane. One of the solvents may be used alone, or two or more may be used in combination. Water is particularly preferred because it easily dissolves sulfamic acid and urea.

[0044] The pulp in this state that has been brought into contact with sulfamic acid and urea in this step is sometimes referred to as "reaction liquid-impregnated pulp."

[0045] <Contact amount of reaction solution> The reaction solution is preferably contacted with the pulp so that the sulfamic acid and urea in the reaction solution are present in a predetermined ratio relative to the pulp. Specifically, the reaction solution is contacted so that the amounts of sulfamic acid and urea in the reaction solution relative to the pulp in the reaction solution-impregnated pulp when the pulp is subjected to the reaction step are appropriate. More specifically, the amount of sulfamic acid contacted relative to the pulp (solid mass, which is the dry mass) in the reaction solution-impregnated pulp immediately before the heating reaction in the reaction step is adjusted to be equal to or greater than the amount of urea contacted.

[0046] For example, the reaction liquid is prepared so that the mixing ratio of sulfamic acid and urea is such that the value (sulfamic acid / urea) obtained by dividing the parts by mass of sulfamic acid per 100 parts by mass of the solid content of the pulp in the reaction liquid-impregnated pulp immediately before being subjected to the heating reaction by the parts by mass of urea per 100 parts by mass of the solid content of the pulp in the reaction liquid-impregnated pulp immediately before being subjected to the heating reaction is 0.8 or more, 0.85 or more, or 1 or more.

[0047] Furthermore, for example, the contact amount of sulfamic acid is adjusted to be 70 parts by mass or more, 100 parts by mass or more, or 200 parts by mass or more per 100 parts by mass of the solid content of the pulp in the reaction liquid-impregnated pulp immediately before being subjected to the heating reaction.

[0048] Furthermore, for example, the contact amount of urea, i.e., the contact amount of urea relative to the mass of solids of the pulp in the reaction solution-impregnated pulp immediately before being subjected to the heating reaction, is adjusted to 20 parts by mass or more, 30 parts by mass or more, or 50 parts by mass or more per 100 parts by mass of the solids of the pulp while maintaining the above-mentioned relationship with sulfamic acid. The upper limit of the contact amount of urea is not particularly limited, and is, for example, 350 parts by mass or less, 300 parts by mass or less, or 250 parts by mass or less per 100 parts by mass of the solids of the pulp.

[0049] The contact amounts of sulfamic acid and urea per 100 parts by mass of the solid content of the pulp can be calculated appropriately depending on, for example, the state of the reaction liquid-impregnated pulp to be subjected to the reaction step.

[0050] <State of pulp impregnated with reaction liquid> The state of the reaction liquid-impregnated pulp to be subjected to the above-mentioned next reaction step may be, for example, the reaction liquid-impregnated pulp as it is, i.e., a state in which the pulp is in contact with the reaction liquid without actively removing water, or a state in which the water has been actively removed from the pulp in contact with the reaction liquid.

[0051] The former reaction liquid-impregnated pulp (in a state where water is not actively removed) includes pulp in a state where the pulp is in contact with the reaction liquid (including, for example, a slurry state), and pulp prepared by removing the pulp from a state where the pulp is in contact with the reaction liquid and leaving it to stand.

[0052] On the other hand, the latter reaction liquid impregnated pulp (in a state where water has been actively removed) refers to pulp that has had water intentionally removed from the state where the pulp has been in contact with the reaction liquid. Examples include pulp that has been prepared by removing the pulp from the state where the pulp has been in contact with the reaction liquid and then naturally drying it by air drying or the like, pulp that has been prepared by filtering and dehydrating the pulp that has been in contact with the reaction liquid, pulp that has been filtered and dehydrated and further air-dried, pulp that has been filtered and dehydrated and further dried using a circulating air dryer, pulp that has been filtered and dehydrated and further dried using a heated dryer, pulp that has been contacted with the reaction liquid and then dried using a circulating air dryer or a heated dryer, and the like.

[0053] Thus, the reaction solution-impregnated pulp to be subjected to the reaction step may be one that has not been subjected to the aforementioned active water removal, or one that has had a certain amount of water removed by active water removal. Furthermore, when removing water by drying, there is no particular problem even if the moisture content after drying is about 1%. In particular, the latter method can reduce the moisture content in the reaction solution-impregnated pulp to be subjected to the reaction step, thereby shortening the reaction time for the heating reaction in the reaction step. This has the advantage of improving the productivity of the modified pulp. Furthermore, the dehydration method has the advantage of enabling the reaction solution-impregnated pulp to be prepared more efficiently than when treating a large amount of reaction solution.

[0054] When an active drying method is used, the reaction solution-impregnated pulp may be dried until its moisture content reaches about 1%, or the moisture may be removed by drying it until it reaches an absolutely dry state with a moisture content significantly lower than 1%.

[0055] In this specification, the term "wet state" refers to a reaction solution-impregnated pulp that has a moisture content of 1% or more and is not in an absolute dry state. For example, the term "wet state" may refer to pulp that is still impregnated with the reaction solution, pulp that has been dehydrated to a certain extent, or pulp that has been dried to a certain extent.

[0056] In addition, in this specification, bone-dry means a state in which the moisture content is reduced to less than 1%, for example, by reducing the pressure in a desiccator containing a desiccant such as calcium chloride or diphosphorus pentoxide, or by subjecting the material to a long-term heat drying treatment.

[0057] Therefore, when the latter method (reaction method in a state where active moisture removal is performed) is used, the moisture content of the reaction solution-impregnated pulp may be brought to a non-bone-dry state or to a bone-dry state, but it is preferable to use the method in which the moisture content is brought to a non-bone-dry state.

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

[0059] The solids mass (g) of the reaction solution-impregnated pulp in the above formula refers to the dry mass of the reaction solution-impregnated pulp. Specifically, this refers to the dry mass adjusted to a constant weight by drying the sample using a dryer or other device. For example, by placing the reaction solution-impregnated pulp in a dryer and drying it under specified drying conditions (e.g., 105°C for 2 hours) and measuring the mass, the mass of the reaction solution-impregnated pulp after moisture removal (i.e., the mass of the reaction solution-impregnated pulp that remains after the drying conditions are met, including the pulp and reagents in the reaction solution) can be calculated. Furthermore, "constant mass" refers to a state in which moisture in the atmosphere and the raw materials in the treatment facility no longer appears to move in or out. Specifically, after drying for a set period of time (e.g., 2 hours), the change in mass between two consecutive measurements is within 1% of the mass at the start of drying (however, the second mass measurement should be at least half the drying time required for the first measurement).

[0060] The state of the pulp when it is brought into contact with the reaction liquid is not particularly limited, and may be, for example, a dry state or a wet state (i.e., a moist state).

[0061] <Pre-drying process in the contact process> In the above example, the method for preparing reaction solution-impregnated pulp in this step was described as a method for preparing reaction solution-impregnated pulp in a state in which moisture has been actively removed. However, when using a method for removing moisture while heating (pre-drying step) in this method (for example, when directly heating and drying the pulp in a state in which the reaction solution has been contacted, or when heating and drying the dehydrated pulp), it is desirable to adjust the heating temperature to a predetermined temperature or lower. The drying temperature in this pre-drying step is not particularly limited, but is preferably adjusted to a temperature that can remove moisture contained in the reaction solution-impregnated pulp and ambient moisture and does not allow the reaction to 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 the temperature to 50°C or higher. Therefore, the drying temperature in the pre-drying step in the contact step is preferably 50°C to 100°C, or 70°C to 100°C.

[0062] <Moisture adjustment process in contact process> This process may include a moisture adjustment step in which the moisture content of the pulp to be contacted with the reaction solution is adjusted to fall within a predetermined range. This moisture adjustment step involves drying or humidifying the pulp so that it has a predetermined moisture content. By including this moisture adjustment step, the moisture content in the pulp when contacted with the reaction solution or the like can be made somewhat uniform, which may improve product stability in continuous operation. Furthermore, drying the pulp to a certain extent to reduce the moisture content (for example, to a moisture content of 1% to 10%) has the advantage of improving storage stability.

[0063] <Reaction process> Next, sulfate ester groups are introduced into at least a portion of the hydroxyl groups of the cellulose constituting the pulp after the contacting step (step S3). This step involves reacting cellulose fibers contained in the reaction solution-impregnated pulp provided from the contacting step with sulfamic acid and urea to substitute 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. That is, this step is a step of carrying out a reaction to substitute at least a portion of the hydroxyl groups in the cellulose fibers contained in the reaction solution-impregnated pulp with sulfate ester groups.

[0064] This step is not particularly limited as long as it is a method capable of substituting at least a portion of the hydroxyl groups of the cellulose fibers in the reaction solution-impregnated pulp with sulfate ester groups, and for example, a method in which the reaction is accelerated by heating the reaction solution-impregnated pulp can be used. Hereinafter, the reaction will be described taking as an example a case in which the reaction is carried out by this heating method.

[0065] <Reaction temperature in the reaction process> The reaction temperature in this step is not particularly limited, but is preferably a temperature at which sulfate ester groups can be introduced into the cellulose fibers that make up the pulp while suppressing thermal decomposition and hydrolysis of the fibers. For example, the ambient temperature of the reaction solution-impregnated pulp subjected to this step 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 less, thermal decomposition and discoloration of the fibers can be suppressed.

[0066] The heater or the like used in this step is not particularly limited, and for example, one that can directly or indirectly heat the reaction solution-impregnated pulp after the contact step while satisfying the above-mentioned requirements can be used, and known dryers, reduced pressure dryers, microwave heating devices, autoclaves, infrared heating devices, hot pressing methods using heat presses (e.g., AH-2003C manufactured by AS ONE Corporation), etc. can be used. In particular, from the viewpoint of operability, it is preferable to use a circulating air dryer because gas may be generated in this step.

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

[0068] By carrying out the above steps, the modified pulp can be produced.

[0069] <Cleaning process after reaction process> The reaction process may be followed by a washing process for washing the modified pulp. The modified pulp has an acidic surface due to the influence of sulfamic acid (a sulfate ester group-donating compound). Furthermore, unreacted reaction liquid is still present. Therefore, by providing a washing process for completely terminating the reaction and removing excess reaction liquid to neutralize the pulp, handling can be improved.

[0070] This washing step is not particularly limited, and may be performed, for example, so long as the modified pulp is substantially neutral. For example, a method of washing the modified pulp with pure water or the like until it becomes neutral may be used. Alternatively, neutralization washing using an alkaline solution or the like may be performed. When performing such neutralization washing, examples of the alkaline compound contained in the alkaline solution include inorganic alkaline compounds and organic alkaline compounds. Examples of inorganic alkaline compounds include hydroxides, carbonates, and phosphates of alkali metals. Examples of organic alkaline compounds include ammonia, aliphatic amines, aromatic amines, aliphatic ammonium, aromatic ammonium, heterocyclic compounds, and hydroxides of heterocyclic compounds.

[0071] The method for separating the modified pulp in the washing step is not particularly limited, and may be any method that allows the modified pulp to be separated from the wash water by filtration. For example, the modified pulp after the reaction can be washed using a stainless steel sieve with a mesh size of 243 μm (70 mesh) to 20 μm (635 mesh), 132 μm (120 mesh) to 45 μm (300 mesh), or 75 μm (200 mesh) to 45 μm (300 mesh).

[0072] The modified pulp can be used in a wide range of fields, for example, as a separating agent for optical isomers used in chromatography. [Example]

[0073] Example 1 <Contact process> Eight grams (2 g solids) of bleached softwood kraft pulp (NBKP) (hereinafter sometimes simply referred to as "pulp") was immersed in the reaction solution for 10 minutes to impregnate the pulp with the reaction solution. The reaction solution was prepared by adding 3.59 g (0.037 mol) of sulfamic acid and 1.80 g (0.030 mol) of urea to 12 g of pure water and stirring at room temperature (23°C). The bleached softwood kraft pulp (NBKP) manufactured by Marusumi Paper Co., Ltd. (25% solids by mass, the remaining 75% was water) and the sulfamic acid and urea manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. were used, as in Example 3 below.

[0074] The pulp impregnated with the reaction solution was spread thinly and uniformly on an acrylic plate and dried at 85°C for 3 hours using a thermostatic dryer (Yamato Scientific Co., Ltd., DKN602).

[0075] <Reaction process> The pulp impregnated with the reaction solution was subjected to a heating reaction at a reaction temperature of 140° C. for a reaction time (heating time) of 30 minutes.

[0076] <Cleaning process after reaction process> The pulp after the reaction step was neutralized on a 635 mesh sieve and washed with pure water to obtain modified pulp. An aqueous solution of sodium bicarbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the neutralizing agent. The obtained modified pulp was prepared into a 0.2% by mass aqueous dispersion using pure water and then stored in a refrigerator (4°C).

[0077] Example 2 Modified pulp was obtained in the same manner as in Example 1, except that the amounts of sulfamic acid and urea in the reaction solution were changed as shown in Table 1.

[0078] Example 3 <Alkali treatment process> 20 g (5 g solids) of bleached softwood kraft pulp (NBKP) (hereinafter simply referred to as "pulp") was immersed in 100 g of a 2% by mass aqueous solution of sodium hydroxide for 1 hour. The sodium hydroxide used was manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0079] <Cleaning process after alkaline treatment process, etc.> After immersion in the sodium hydroxide solution, the pulp was washed with pure water on a 300-mesh sieve. The washed pulp was placed in a homemade net using nylon mesh (manufactured by AS ONE Corporation, model number: PA-46μ, mesh size 46μm, 300 mesh), dehydrated for 2 minutes using a dehydrator (manufactured by Versos Corporation, model number: RC-001) until the solid content reached 25% by mass, and then stored in a refrigerator (4°C).

[0080] <Contact process, etc.> 8 g of the pulp (containing 2 g of the pulp after the alkali treatment step) that had been dewatered to a solids concentration of 25% by mass was immersed in the reaction solution for 10 minutes, thereby impregnating the pulp after the alkali treatment step with the reaction solution. The reaction solution used was the same as in Example 1. Thereafter, a modified pulp was obtained in the same manner as in Example 1.

[0081] Examples 4 to 8 Modified pulp was obtained in the same manner as in Example 3, except that the concentration of the aqueous sodium hydroxide solution used in the alkali treatment step (amount of sodium hydroxide blended) was changed as shown in Table 1.

[0082] Example 9 Modified pulp was obtained in the same manner as in Example 3, except that in the alkali treatment step, a 7% by mass aqueous solution of lithium hydroxide was used instead of a 2% by mass aqueous solution of sodium hydroxide, and the amounts of sulfamic acid and urea in the reaction solution were changed as shown in Table 1. Lithium hydroxide manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was used.

[0083] Example 10 Modified pulp was obtained in the same manner as in Example 3, except that in the alkali treatment step, a 7% by mass aqueous potassium hydroxide solution was used instead of a 2% by mass aqueous sodium hydroxide solution, and the amounts of sulfamic acid and urea in the reaction solution were changed as shown in Table 1. Potassium hydroxide manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was used.

[0084] (Comparative Examples 1 and 2) Modified pulp was obtained in the same manner as in Example 1, except that the amounts of sulfamic acid and urea in the reaction solution were changed as shown in Table 1.

[0085] (Comparative Examples 3 to 5) Modified pulp was obtained in the same manner as in Example 3, except that the concentration of the aqueous sodium hydroxide solution used in the alkali treatment step (amount of sodium hydroxide blended) was changed as shown in Table 1.

[0086] Table 1 shows the type and amount (concentration) of alkali metal in the alkali metal solution used in the alkali treatment step of Examples 3 to 10 and Comparative Examples 3 to 5, and the amount of sulfamic acid and urea in the reaction solution used in producing the modified pulp of Examples 1 to 10 and Comparative Examples 1 to 5.

[0087] [Table 1]

[0088] Figures 2-1, 2-2, and 3 show circular dichroism (CD) spectra of aqueous dispersions of modified pulps from Examples 1 to 6, Examples 7 to 10, and Comparative Examples 1 to 5. The CD spectra were measured using a circular dichroism spectrometer (JASCO Corporation, J-1500) over the range of 200 nm to 800 nm, with pure water as the baseline, in a quartz cell (optical path length 10 mm). As can be seen from these figures, Examples 1 to 10 exhibited a positive Cotton effect near 680 nm and a negative Cotton effect near 320 nm and 480 nm, confirming the presence of chirality. On the other hand, Comparative Examples 1 to 5 exhibited flat CD spectra, confirming the absence of chirality.

[0089] Although the present invention has been described above with reference to the embodiments and examples, the present invention is not limited to the above-described embodiments and examples. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

[0090] <Additional Notes> Some or all of the above embodiments and examples may be described as, but are not limited to, the following supplementary notes. (Appendix 1) A modified pulp in which at least a portion of the hydroxyl groups of cellulose are substituted with sulfate ester groups, A modified pulp characterized by having chirality. (Appendix 2) an alkali treatment step of immersing the pulp in an alkaline alkali metal solution; a contacting step of contacting the pulp after the alkali treatment step with a reaction solution containing a sulfate ester group-donating compound and at least one of urea and a urea derivative; a reaction step of introducing sulfate ester groups into at least a portion of the hydroxyl groups of the cellulose constituting the pulp after the contact step, A method for producing modified pulp having chirality, wherein the amount of alkali metal in the total amount of the alkali metal solution is 2% by mass to 15% by mass.

Claims

[Claim 1] A modified pulp in which at least a portion of the hydroxyl groups of cellulose are substituted with sulfate ester groups, A modified pulp characterized by having chirality.

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