Method for producing polybasic acid salt-modified cellulose and polybasic acid salt-modified cellulose composition

Abstract

The present invention provides a method for easily obtaining a high-quality polybasic acid salt-modified cellulose when producing the polybasic acid salt-modified cellulose by use of a raw material composition containing cellulose, a polybasic acid, and / or an acid anhydride thereof. The present invention is a method for producing polybasic acid salt-modified cellulose comprising a step in which polybasic acid-modified cellulose is obtained by use of a raw material composition containing cellulose, a polybasic acid, and / or an acid anhydride thereof and a step in which the polybasic acid-modified cellulose is neutralized, said method for producing polybasic acid salt-modified cellulose being characterized in that: in the raw material composition, the mass ratio of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine is less than 5000 ppm; and the mass ratio of an ionic liquid containing imidazolium ions is less than 5000 ppm.

Description

Method for producing polybasic acid salt-modified cellulose and polybasic acid salt-modified cellulose composition

[0001] The present invention relates to a method for producing polybasic acid salt-modified cellulose and a polybasic acid salt-modified cellulose composition. More specifically, the present invention relates to a method for producing polybasic acid salt-modified cellulose and a polybasic acid salt-modified cellulose composition that can be used in various industrial products such as sanitary materials and detergents.

[0002] Conventional hydrophilic polymers derived from petrochemicals have been suitably used as raw materials for various industrial products for use in sanitary materials, detergents, etc. In particular, water-absorbent resins (SAP / Super Absorbent polymers) having a structure in which hydrophilic polymers are crosslinked can be used as water-swellable polymer gelling agents, and among them, polyacrylic acid (salt)-based water-absorbent resins are widely used in applications requiring water absorption and water retention, such as absorbent articles such as disposable diapers and sanitary napkins, agricultural and horticultural water retention agents, and industrial water-stopping agents.

[0003] On the other hand, in recent years, in order to reduce the environmental burden and realize a sustainable society, there has been a demand for hydrophilic polymers to be made from biomass-derived raw materials or to be biodegradable. Under these circumstances, methods for obtaining hydrophilic polymers by modifying cellulose, a polysaccharide that exists in large quantities in nature, have been investigated (see, for example, Patent Documents 1 and 2, and Non-Patent Documents 1 and 2). Although not a method for obtaining hydrophilic polymers, a method for obtaining cellulose nanofibers (CNFs) by modifying cellulose and then defibrating it has been disclosed (see, for example, Patent Document 3).

[0004] Starch is a biomass-derived material known to be used as a hydrophilic polymer raw material, similar to cellulose. Starch exhibits high dispersibility and solubility in certain solvents, such as water and dimethyl sulfoxide, making it easy to modify. However, starch is an edible material, raising concerns about competition with food applications. Cellulose, on the other hand, is a nonedible material and does not compete with food applications. However, its crystallinity is significantly higher than that of starch and other polysaccharides. Therefore, it is necessary to ensure dispersibility and solubility in solvents during modification reactions. Therefore, modification reactions have typically been carried out using high-boiling organic solvents or ionic liquids, which can dissolve cellulose but are toxic and have a strong odor, or organic catalysts, which are toxic and have a strong odor, to increase reactivity.

[0005] Patent Publication No. 2012-12462 International Publication No. 2023 / 282534 Chinese Patent Application Publication No. 115819630

[0006] Journal of Applied Polymer Science, Vol. 99, 3251-3256 (2006)Journal of Hazardous Materials 169 (2009) 831-837

[0007] When polybasic acid salt-modified cellulose is produced using a raw material composition containing cellulose and a polybasic acid and / or an acid anhydride thereof, a method for easily obtaining high-quality polybasic acid salt-modified cellulose has been desired.

[0008] The present invention has been made in view of the above-described current situation, and an object of the present invention is to provide a method for easily obtaining high-quality polybasic acid salt-modified cellulose when polybasic acid salt-modified cellulose is produced using a raw material composition containing cellulose and a polybasic acid and / or an acid anhydride thereof.

[0009] The present inventors conducted extensive research into methods for easily obtaining high-quality polybasic acid salt-modified cellulose when producing polybasic acid salt-modified cellulose using a raw material composition containing cellulose and a polybasic acid and / or its acid anhydride, and focused on solvents. The inventors then discovered that in a method for producing polybasic acid salt-modified cellulose, which includes a step of obtaining polybasic acid-modified cellulose using a raw material composition containing cellulose and a polybasic acid and / or its acid anhydride, and a step of neutralizing the polybasic acid-modified cellulose, high-quality polybasic acid salt-modified cellulose can be easily obtained by providing the raw material composition with a mass proportion of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine of less than 5000 ppm and a mass proportion of an ionic liquid having an imidazolium ion of less than 5000 ppm. This finding led to the present invention, which successfully solved the above-mentioned problems.

[0010] That is, the present invention (1) is a method for producing polybasic acid salt-modified cellulose, comprising the steps of obtaining polybasic acid-modified cellulose using a raw material composition containing cellulose and a polybasic acid and / or an acid anhydride thereof, and neutralizing the polybasic acid-modified cellulose, wherein the raw material composition contains less than 5000 ppm by mass of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine, and the mass proportion of an ionic liquid having an imidazolium ion is less than 5000 ppm. The above "the mass proportion of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine is less than 5000 ppm" means that the total mass proportion of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine in the raw material composition is less than 5000 ppm. The mass proportions of some or all of these components in the raw material composition may be 0 ppm.

[0011] The present invention (2) is the method for producing polybasic acid salt-modified cellulose according to the present invention (1), characterized in that the raw material composition contains at least one functional group selected from the group consisting of a sulfoxide group, a pyridyl group, and an amide group, and the mass proportion of the organic solvent that is liquid at 20°C and 1 atmosphere is less than 5000 ppm.

[0012] The present invention (3) is the method for producing polybasic acid-modified cellulose according to the present invention (1) or (2), characterized in that the raw material composition contains at least one functional group selected from the group consisting of a sulfoxide group, a pyridyl group, and an amide group, and the mass proportion of the liquid organic solvent in the step of obtaining the polybasic acid-modified cellulose is less than 5000 ppm.

[0013] The present invention (4) is the method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (3), characterized in that the starting material composition contains at least one functional group selected from the group consisting of a sulfoxide group, a pyridyl group, and an amide group and has a molecular weight of 130 or less, and the mass proportion of the organic solvent and / or the organic catalyst is less than 5,000 ppm.

[0014] The present invention (5) is the method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (4), wherein the raw material composition contains an ionic liquid having at least one ion selected from the group consisting of ammonium, phosphonium, pyridinium, and imidazolium in an amount of less than 5,000 ppm by mass.

[0015] The present invention (6) is the method for producing a polybasic acid-modified cellulose according to any one of the present inventions (1) to (5), characterized in that the step of obtaining the polybasic acid-modified cellulose is carried out using less than 30% by mass of a base catalyst relative to 100% by mass of the polybasic acid and / or its acid anhydride.

[0016] The present invention (7) is the method for producing polybasic acid salt-modified cellulose according to the present invention (6), wherein the base catalyst is a solid alkaline compound.

[0017] The present invention (8) relates to the method for producing polybasic acid salt-modified cellulose according to the present invention (7), wherein the solid alkali compound is at least one selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal hydrogencarbonates.

[0018] The present invention (9) is the method for producing a polybasic acid-modified cellulose according to any one of the present inventions (1) to (8), characterized in that the step of obtaining the polybasic acid-modified cellulose is carried out at a temperature exceeding 120°C.

[0019] The present invention (10) is the method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (9), characterized in that the mass proportion of the polybasic acid and / or its acid anhydride in the raw material composition is 50 mass% or more relative to 100 mass% of the mass of the cellulose.

[0020] The present invention (11) is the method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (10), characterized in that the cellulose has an average particle size of 400 μm or less.

[0021] The present invention (12) is the method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (11), wherein the cellulose has a crystallinity of 75% or less.

[0022] The present invention (13) is the method for producing polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (12), characterized in that the polybasic acid anhydride is a cyclic polybasic acid anhydride.

[0023] The present invention (14) is the method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (13), wherein the polybasic acid and / or its acid anhydride is a polybasic carboxylic acid and / or its acid anhydride.

[0024] The present invention (15) is the method for producing polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (14), characterized in that the polybasic acid and / or its acid anhydride is a dibasic acid and / or its acid anhydride.

[0025] The present invention (16) is the method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (15), wherein the polybasic acid and / or its acid anhydride is succinic acid and / or its acid anhydride.

[0026] The present invention (17) is the method for producing a polybasic acid-modified cellulose according to any one of the present inventions (1) to (16), characterized in that the polybasic acid-modified cellulose is a polybasic acid monoesterified cellulose.

[0027] The present invention (18) is the method for producing a polybasic acid-modified cellulose according to any one of the present inventions (1) to (17), characterized in that the polybasic acid-modified cellulose has an average degree of substitution of cellulose with a polybasic acid per glucose residue of 1 or more.

[0028] The present invention (19) is a method for producing crosslinked polybasic acid-modified cellulose, comprising the steps of obtaining polybasic acid-modified cellulose using a raw material composition containing cellulose and a polybasic acid and / or an acid anhydride thereof, neutralizing the polybasic acid-modified cellulose, and crosslinking the polybasic acid-modified cellulose, wherein the raw material composition contains less than 5000 ppm by mass of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine, and the mass proportion of an ionic liquid having an imidazolium ion is less than 5000 ppm.

[0029] The present invention (20) is a polybasic acid salt-modified cellulose composition comprising a polybasic acid salt-modified cellulose, in which the mass proportion of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine is less than 5000 ppm, and the mass proportion of an ionic liquid having an imidazolium ion is less than 5000 ppm.

[0030] The present invention (21) relates to the polybasic acid salt-modified cellulose composition of the present invention (20), characterized in that the polybasic acid salt-modified cellulose has an average degree of substitution of cellulose with a polybasic acid salt per glucose residue of 1 or more.

[0031] The present invention (22) is a crosslinked polybasic acid salt-modified cellulose composition comprising a crosslinked polybasic acid salt-modified cellulose, in which the mass proportion of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine is less than 5000 ppm, and the mass proportion of an ionic liquid having an imidazolium ion is less than 5000 ppm.

[0032] The present invention (23) is a crosslinked polybasic acid salt-modified cellulose composition, which is a crosslinked product of the polybasic acid salt-modified cellulose composition of the present invention (20) or (21).

[0033] The present invention (24) is the polybasic acid salt-modified cellulose composition of the present invention (20) or (21), or the crosslinked polybasic acid salt-modified cellulose composition of the present invention (22) or (23), which is used as a raw material for sanitary materials, agricultural and horticultural supplies, cosmetics, or detergents.

[0034] The method for producing polybasic acid salt-modified cellulose of the present invention has the above-mentioned configuration and can easily produce high-quality polybasic acid salt-modified cellulose.

[0035] 1 is a diagram illustrating an example of a reaction formula between cellulose and a polybasic acid anhydride in the production method of the present invention. 2 is a diagram illustrating each step in the production method of the present invention.

[0036] The present invention will be described in detail below. Note that a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

[0037] [Method for producing polybasic acid salt-modified cellulose] Hereinafter, a method for producing polybasic acid salt-modified cellulose will be described in detail.

[0038] (Polybasic acid salt-modified cellulose) The polybasic acid salt-modified cellulose obtained by the production method of the present invention is composed of modified cellulose in which the cellulose molecules are densely modified with polybasic acid salts by the production method of the present invention, and in which part or all of the cellulose is soluble in water at the molecular level.

[0039] In addition, general cellulose nanofiber (CNF) manufacturing methods, including the method for producing highly charged nanocellulose described in Patent Document 3, require surface modification of microfibrils, the smallest fiber units constituting cellulose raw materials, followed by separation into individual microfibrils for uniform dispersion in water. This defibration process requires the use of energy-intensive techniques such as ultrasonic application or high-speed shearing, which can significantly increase production costs. Furthermore, although microfibrils have a structure in which multiple cellulose molecules are bundled together, the interior of the microfibrils is unmodified, resulting in a low overall average degree of substitution. Therefore, their hydrophilicity is lower than that of conventional hydrophilic polymers derived from petrochemicals. Therefore, they are unsuitable for applications requiring high charge density, such as sanitary materials and detergents, and their use as a substitute for hydrophilic polymers derived from petrochemicals is difficult.

[0040] On the other hand, the polybasic acid salt-modified cellulose obtained by the production method of the present invention has individual cellulose molecules constituting the microfibrils modified with polybasic acid salts, and has a high overall charge density. Furthermore, due to electrostatic repulsion between the modified cellulose molecules resulting from the high charge density, the cellulose has the property of being uniformly dispersed or dissolved in water without defibration. Another characteristic of the polybasic acid salt-modified cellulose obtained by the production method of the present invention is that the crystallinity within the microfibrils is lost due to the modification of the individual cellulose molecules constituting the microfibrils, resulting in a low degree of crystallinity.

[0041] For these reasons, the polybasic acid salt-modified cellulose obtained by the production method of the present invention is more hydrophilic than conventional cellulose, and can be produced at low cost as an alternative to the above-mentioned hydrophilic polymers derived from petrochemicals.

[0042] The degree of modification of modified cellulose molecules can be evaluated by several techniques, including the disappearance of the crystalline peak derived from microfibrils in the cellulose raw material, the average degree of substitution, which represents the amount of modifier bound per glucose residue in the cellulose molecule, and the proportion of modified cellulose molecules that have become molecular and dissolved in water. For the aforementioned evaluation, for example, crystallinity measurement by X-ray diffraction, pH titration, gel permeation chromatography (GPC), etc. are used. The average degree of substitution of cellulose molecules that are highly hydrophilic is generally 1 or greater. The methods for measuring and calculating the average degree of substitution are described in detail in the Examples.

[0043] <Step of Obtaining Polybasic Acid-Modified Cellulose> The production method of the present invention includes a step of obtaining polybasic acid-modified cellulose using a raw material composition containing cellulose and a polybasic acid and / or its acid anhydride. In this specification, the step of obtaining polybasic acid-modified cellulose is also referred to as a reaction step.

[0044] (Solvent) In the reaction step, the raw material composition contains at least one organic solvent selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine in a mass proportion of less than 5,000 ppm, and contains an ionic liquid having an imidazolium ion in a mass proportion of less than 5,000 ppm. By substantially not using the solvent in the reaction step, the operation of removing the solvent after the reaction step can be omitted. Furthermore, this prevents the solvent, which may be toxic or have a strong odor, from remaining in the resulting polybasic acid salt-modified cellulose, thereby enabling the production of high-quality polybasic acid salt-modified cellulose with sufficient coloration prevention. In this specification, when the raw material composition contains two or more specified organic solvents, the mass proportion of the organic solvents refers to the total mass proportion of the organic solvents. Furthermore, when the raw material composition contains two or more specified ionic liquids, the mass proportion of the ionic liquid refers to the total mass proportion of the organic solvents. The raw material composition may not contain the specified organic solvent or the specified ionic liquid. For example, the raw material composition may be one that does not contain any of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, 4-dimethylaminopyridine, or an ionic liquid having an imidazolium ion. The mass ratios are measured as described in the examples or methods equivalent thereto, and are mass ratios relative to the raw material composition.

[0045] In one preferred embodiment of the present invention, the raw material composition contains less than 5,000 ppm by mass of an organic solvent that contains at least one functional group selected from the group consisting of a sulfoxide group, a pyridyl group, and an amide group and is liquid at 20°C and 1 atmosphere. Another preferred embodiment of the present invention is that the raw material composition contains less than 5,000 ppm by mass of an organic solvent that contains at least one functional group selected from the group consisting of a sulfoxide group, a pyridyl group, and an amide group and is liquid in the step of obtaining polybasic acid-modified cellulose. Another preferred embodiment of the present invention is that the raw material composition contains less than 5,000 ppm by mass of an organic solvent that contains at least one functional group selected from the group consisting of a sulfoxide group, a pyridyl group, and an amide group and has a molecular weight of 130 or less. The lower limit of the molecular weight of the organic solvent is not particularly limited, but is usually 70 or more. In another preferred embodiment of the present invention, the raw material composition contains less than 5000 ppm by mass of an organic solvent that contains at least one functional group selected from the group consisting of a sulfoxide group, a pyridyl group, and an amide group and has a boiling point of 110° C. or higher at 1 atmospheric pressure. There is no particular upper limit for the boiling point of the organic solvent at 1 atmospheric pressure, but it is usually 300° C. or lower.

[0046] In one preferred embodiment of the present invention, the raw material composition contains less than 5,000 ppm by mass of an organic solvent that contains sulfur atoms and / or nitrogen atoms and is liquid at 20°C and 1 atmosphere. Another preferred embodiment of the present invention is that the raw material composition contains less than 5,000 ppm by mass of an organic solvent that contains sulfur atoms and / or nitrogen atoms and is liquid in the step of obtaining polybasic acid-modified cellulose. Another preferred embodiment of the present invention is that the raw material composition contains less than 5,000 ppm by mass of an organic solvent that contains sulfur atoms and / or nitrogen atoms and has a molecular weight of 130 or less. The lower limit of the molecular weight of the organic solvent is not particularly limited, but is usually 70 or more. Another preferred embodiment of the present invention is that the raw material composition contains less than 5,000 ppm by mass of an organic solvent that contains sulfur atoms and / or nitrogen atoms and has a boiling point of 110°C or higher at 1 atmosphere. The upper limit of the boiling point of the organic solvent at 1 atmosphere is not particularly limited, but is usually 300° C. or lower.

[0047] The mass proportion of the organic solvent is preferably 4000 ppm or less, more preferably 3000 ppm or less, even more preferably 2000 ppm or less, and particularly preferably 1000 ppm or less. Furthermore, the mass proportion is most preferably below the detection limit. For example, the raw material composition may be free of the organic solvent, and the mass proportion of the organic solvent may be 0 ppm.

[0048] In one preferred embodiment of the present invention, the raw material composition has a mass proportion of the ionic liquid containing at least one ion selected from the group consisting of ammonium, phosphonium, pyridinium, and imidazolium ions of less than 5000 ppm.

[0049] The mass proportion of the ionic liquid is preferably 4000 ppm or less, more preferably 3000 ppm or less, even more preferably 2000 ppm or less, and particularly preferably 1000 ppm or less. Furthermore, the mass proportion is most preferably below the detection limit. For example, the raw material composition may be free of the ionic liquid, and the mass proportion of the ionic liquid may be 0 ppm.

[0050] The method for detecting the organic solvent and ionic liquid is not particularly limited, but common detection methods include nuclear magnetic resonance, gas chromatography, liquid chromatography, ultraviolet-visible spectroscopy, Raman spectroscopy, infrared spectroscopy, etc. Among these, detection methods using liquid chromatography are preferred from the standpoint of quantitativeness and simplicity of the measurement technique, and common devices can be used to perform measurements with a detection limit of less than 1000 ppm.

[0051] Furthermore, in the above reaction step, the presence of water not only reduces the concentration during the reaction and reduces the reaction efficiency, but also accelerates decomposition of the cellulose skeleton, ester bonds, and acid anhydrides. Therefore, it is preferable that the amount of water added as a solvent be less than 5,000 ppm.

[0052] (Organic Catalyst) In the reaction step, the raw material composition contains at most 5,000 ppm by mass of at least one organic catalyst selected from the group consisting of pyridine and 4-dimethylaminopyridine. By substantially not using the organic catalyst in the reaction step, the procedure for removing the organic catalyst after the reaction step can be omitted. Furthermore, the organic catalyst, which has a strong toxicity and odor, can be prevented from remaining in the resulting polybasic acid salt-modified cellulose, thereby enabling the production of high-quality polybasic acid salt-modified cellulose with sufficient coloration prevention. While pyridine and 4-dimethylaminopyridine can also be used as organic solvents to dissolve cellulose and / or its derivatives at temperatures above their melting points, it is preferable not to use them for either purpose. In this specification, when the raw material composition contains two or more specified organic catalysts, the mass percentage of the organic catalysts refers to the combined mass percentage of the organic catalysts.

[0053] In another preferred embodiment of the present invention, the raw material composition contains less than 5000 ppm by mass of an organic catalyst that contains at least one functional group selected from the group consisting of a sulfoxide group, a pyridyl group, and an amide group and has a molecular weight of 130 or less. The lower limit of the molecular weight of the organic catalyst is not particularly limited, but is usually 70 or more.

[0054] In another preferred embodiment of the present invention, the raw material composition contains less than 5,000 ppm by mass of an organic catalyst that contains sulfur atoms and / or nitrogen atoms and has a molecular weight of 130 or less. The lower limit of the molecular weight of the organic catalyst is not particularly limited, but is usually 70 or more.

[0055] The mass proportion of the organic catalyst is preferably 4000 ppm or less, more preferably 3000 ppm or less, even more preferably 2000 ppm or less, and particularly preferably 1000 ppm or less. Furthermore, the mass proportion is most preferably below the detection limit. The method for detecting the organic catalyst is not particularly limited, but typical detection methods include nuclear magnetic resonance, gas chromatography, liquid chromatography, ultraviolet-visible spectroscopy, Raman spectroscopy, and infrared spectroscopy. Among these, detection methods using liquid chromatography are preferred in terms of quantitativeness and ease of measurement, and typical devices can achieve a detection limit of less than 1000 ppm.

[0056] In the reaction step, the raw material composition contains cellulose and a polybasic acid and / or its acid anhydride, and may further contain an organic solvent, an organic catalyst, and an ionic liquid, so long as the mass proportion of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine is less than 5000 ppm, and the mass proportion of an ionic liquid having an imidazolium ion is less than 5000 ppm. For example, the raw material composition may contain an organic solvent other than the six compounds described above, ethyl acetate, an organic catalyst other than the pyridine and 4-dimethylaminopyridine described above, or an ionic liquid other than the ionic liquid described above. In particular, the raw material composition preferably contains the organic solvent, organic catalyst, and ionic liquid in a total mass proportion of less than 5000 ppm. The total mass proportion of the organic solvent, organic catalyst, and ionic liquid is preferably 4000 ppm or less, more preferably 3000 ppm or less, even more preferably 2000 ppm or less, and particularly preferably 1000 ppm or less. Furthermore, the total mass proportion is most preferably below the detection limit. For example, the raw material composition may not contain an organic solvent, an organic catalyst, or an ionic liquid, and the total mass proportion of the organic solvent, organic catalyst, and ionic liquid may be 0 ppm. Furthermore, even when the organic solvent and the organic catalyst are used in combination, they are counted as one substance when added together.

[0057] The reaction step is preferably carried out at a reaction temperature exceeding 120° C. The reaction step is also preferably carried out at a reaction temperature exceeding the melting point of the polybasic acid and / or its acid anhydride. The upper limit of the reaction temperature is not particularly limited, but is usually 200° C. or lower, preferably 180° C. or lower.

[0058] The reaction time in the reaction step is preferably 10 minutes or more, more preferably 20 minutes or more, and even more preferably 30 minutes or more, and is, for example, 12 hours or less, preferably 6 hours or less, and more preferably 3 hours or less.

[0059] The reaction step can be suitably carried out by kneading the raw material composition using a ball mill, rod mill, bead mill, roller mill, roll mill, planetary mixer, pan mixer, kneader, blender, or the like. The reaction vessel may be continuous or batch-type. In particular, a kneader with multiple rotors can powerfully knead the entire raw material composition, and can easily improve production efficiency by continuous or large-scale operation. Therefore, it is preferable to use a multi-screw kneader (kneader) with two or more rotors for the reaction step. The number of rotors can be two, three, four, or eight. Examples of batch-type multi-screw kneaders include a double-arm kneader, a pressure kneader, a Banbury mixer, and an internal mixer. Examples of continuous kneaders include a twin-screw kneader extruder, a twin-screw kneader, and a twin-screw extruder. The kneading tank in which the reaction composition is kneaded may be open or closed. The rotors of the kneader may be tangential or intermeshing, but intermeshing is preferred due to its powerful kneading properties. Specific kneading machines include a CKH-type continuous kneader (Honda Iron Works Co., Ltd.), a twin-screw extruder TEX (The Japan Steel Works, Ltd.), a twin-screw extruder TEXαIII (The Japan Steel Works, Ltd.), a continuous kneader (CONTINUOUS KNEADER, Dalton Co., Ltd.), a KRC hybrid reactor (KRC HYBRID REACTER, Kurimoto Iron Works Co., Ltd.), a KRC kneader (KURIMOTO-READCO CONTINUOUS KNEADER, Kurimoto Iron Works Co., Ltd.), a KEX extruder (KEX EXTRUDER, Kurimoto Iron Works Co., Ltd.), and a KEXD extruder (KEXD Examples of such extruders include a twin-screw extruder (TEX-EXTRUDER, Kurimoto Iron Works Co., Ltd.), a twin-arm kneader-ruder (KNEADER-RUDER, Moriyama Corporation), a twin-screw kneader extruder TEX-SSG (Toshiba Machine Co., Ltd.), a twin-screw kneader extruder TEX-CS (Toshiba Machine Co., Ltd.), a twin-screw kneader extruder TEX-SX (Toshiba Machine Co., Ltd.), a twin-screw kneader extruder TEX-DS (Toshiba Machine Co., Ltd.), a twin-screw kneader extruder TEX-A (Toshiba Machine Co., Ltd.), a twin-screw kneader extruder TEX-B (Toshiba Machine Co., Ltd.), a twin-screw kneader extruder TEX-BS (Toshiba Machine Co., Ltd.), a four-screw or eight-screw kneader extruder WDR series (Technovel Corporation), and the like. Therefore, in a preferred embodiment of the present invention, the apparatus used in the reaction step is a continuous multi-screw extruder.

[0060] The raw material composition may be charged all at once into a reaction apparatus such as a reaction tank, or may be supplied to the reaction apparatus continuously or intermittently. The raw materials may be charged by sequentially charging each raw material, charging a plurality of raw materials at once, or charging premixed raw materials in a separate apparatus.

[0061] (Cellulose) Examples of the cellulose include pulp derived from plants such as cotton and wood, compressed pulp, bacterial cellulose, lignocellulose, regenerated cellulose (regenerated fibers such as cellophane, cupra, and lyocell), and microcrystalline cellulose. The cellulose may be modified by esterification such as acetylation, etherification such as carboxyalkylation, phosphorylation, sulfation, phosphate cross-linking, enzyme treatment, or the like, but is preferably unmodified. Furthermore, since cellulose raw materials are strong and can be regenerated through recycling, recycled cellulose raw materials may be used to reduce environmental impact. From the perspective of realizing a sustainable society, one preferred embodiment of the present invention is the use of recycled pulp obtained from used pulp raw materials regenerated from sanitary materials such as waste paper and diapers. Alternatively, cellulose raw materials derived from agricultural waste or food waste may be used. The raw cellulose may be compressed into a plate or flake shape, a fibrous form, or a powder, with the powder form being preferred. Furthermore, cellulose raw materials are hygroscopic, but the moisture contained in the cellulose raw materials is distinct from the water added separately as a solvent during the reaction. The presence of water reduces the concentration during the reaction, reducing the reaction efficiency, and also promotes decomposition of the cellulose skeleton, ester bonds, and acid anhydrides, so it is preferable that the cellulose raw materials be dry. The drying method is not particularly limited, but natural drying at room temperature or forced drying by heating can be suitably carried out.

[0062] From the viewpoint of improving the reaction efficiency in the reaction step, it is desirable that the cellulose be microparticulated on the micrometer scale. Microparticulation increases the surface area, which is expected to improve the reaction efficiency during modification. Furthermore, even on the nanometer scale, it is preferable that the cellulose does not have a microfibril structure in which multiple cellulose molecules are bundled together, and in the reaction step, it is preferable that the cellulose has a low degree of crystallinity and is amorphous, as described below. In other words, it is preferable that the cellulose is not fibrous. Furthermore, in the reaction step, it is preferable that the cellulose molecules and polybasic acid-modified cellulose molecules of the cellulose and the polybasic acid-modified cellulose molecules generated by the progress of the reaction are uniformly dissolved or dispersed in the raw material composition, and it is desirable that the microfibril structure of the cellulose be collapsed after the reaction.

[0063] The cellulose preferably has an average particle size of 400 μm or less. The average particle size is more preferably 300 μm or less, even more preferably 200 μm or less, and particularly preferably 150 μm or less. The lower limit of the average particle size is not particularly limited, but is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. The average particle size is a mass-average particle size, and is measured by the method described in the Examples.

[0064] The cellulose preferably has a crystallinity of 75% or less. A low crystallinity increases the number of highly reactive amorphous sites, allowing the modification reaction to proceed more efficiently. The crystallinity is more preferably 73% or less, and even more preferably 70% or less. The lower limit of the crystallinity is not particularly limited, but is usually 1% or more. The crystallinity is measured by the method described in the Examples.

[0065] (Polybasic Acid and / or Acid Anhydride Thereof) Examples of polybasic acids and / or acid anhydrides thereof include dibasic acids such as succinic acid, maleic acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, methyltetrahydrophthalic acid, methylhexahydrophthalic acid, endomethylenetetrahydrophthalic acid, methylendomethylenetetrahydrophthalic acid, and itaconic acid; polybasic acids such as trimellitic acid, citric acid, butanetetracarboxylic acid, and phosphoric acid; dibasic acid anhydrides such as succinic anhydride (also known as succinic anhydride), maleic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride, and itaconic acid; and polybasic acid anhydrides such as trimellitic anhydride, citric anhydride, butanetetracarboxylic acid anhydride, and phosphoric anhydride. In this specification, acid anhydrides having a structure in which two or more molecules of a monobasic acid are condensed, such as acetic anhydride, are not considered to be polybasic acid anhydrides, since they are anhydrides of monobasic acids. In the production method of the present invention, the polybasic acid and / or its acid anhydride can also function as a solvent and can dissolve the polybasic acid-modified cellulose produced by the reaction.

[0066] The polybasic acid and / or its acid anhydride is preferably a polybasic acid anhydride, more preferably a cyclic polybasic acid anhydride. The polybasic acid anhydride is preferably in the form of an acid anhydride when added. Another preferred embodiment involves heating the polybasic acid in the system during modification to prepare a polybasic acid anhydride or a cyclic polybasic acid anhydride. In this case, the reaction efficiency can be improved by adding an inorganic catalyst that promotes the production of acid anhydrides, such as sodium hypophosphite, in addition to the base catalyst. It is also preferable that the polybasic acid and / or its acid anhydride is a polybasic carboxylic acid and / or its acid anhydride. Furthermore, the polybasic acid and / or its acid anhydride is preferably a dibasic acid and / or its acid anhydride, more preferably succinic acid and / or its acid anhydride.

[0067] In the raw material composition, the mass proportion of the polybasic acid and / or its acid anhydride is preferably 50% by mass or more relative to 100% by mass of the cellulose. The mass proportion of the polybasic acid and / or its acid anhydride is more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 150% by mass or more. The mass proportion of the polybasic acid and / or its acid anhydride is not particularly limited to an upper limit, but is usually 2000% by mass or less, preferably 1000% by mass or less, more preferably 550% by mass or less, and even more preferably 400% by mass or less.

[0068] In the reaction step, the molar ratio of glucose residues in the cellulose to the polybasic acid can be set as appropriate, but is preferably, for example, 1 / 1 to 1 / 1000. A blending ratio within this range is preferred from the standpoint of yield and economy. More preferably, it is 2 / 3 to 1 / 500, even more preferably 1 / 2 to 1 / 300. Particularly preferably, it is 1 / 3 to 1 / 100.

[0069] (Base Catalyst) The step of obtaining the polybasic acid-modified cellulose is preferably carried out using a base catalyst. The base catalyst is not particularly limited as long as it has the effect of accelerating the modification reaction, and inorganic base catalysts can be used. Specific examples include hydroxides such as potassium hydroxide, sodium hydroxide, lithium hydroxide, calcium hydroxide, thallium hydroxide, tin hydroxide, lead hydroxide, and nickel hydroxide; carbonates such as potassium carbonate, sodium carbonate, rubidium carbonate, cesium carbonate, lead carbonate, zinc carbonate, and nickel carbonate; and bicarbonates such as potassium bicarbonate, sodium bicarbonate, rubidium bicarbonate, and cesium bicarbonate. One or more of these can be used. Among these, carbonates and bicarbonates are preferred.

[0070] The base catalyst is preferably a solid alkali compound, which further improves the reactivity of cellulose. In one preferred embodiment of the present invention, the base catalyst is a solid alkali compound alone.

[0071] Examples of the solid alkali compound include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali metal carbonates such as sodium carbonate and potassium carbonate, and alkali metal bicarbonates such as sodium bicarbonate and potassium bicarbonate, and these may be used alone or in combination. Of these, alkali metal carbonates and alkali metal bicarbonates are preferred.

[0072] The amount of base catalyst used is preferably 0.1 mol% to 200 mol% in terms of base molar equivalent relative to the polybasic acid and / or its acid anhydride used as the modifying agent, more preferably 1 mol% to 100 mol%, even more preferably 2 mol% to 50 mol%, and particularly preferably 5 mol% to 25 mol%. The base molar equivalent here refers to the amount of base catalyst used corrected for its base valence, e.g., 1 mol% for 1 mol% of sodium hydroxide, a monovalent base catalyst, and 2 mol% for sodium carbonate, a divalent base catalyst. If the amount of base catalyst used is too small, the reaction efficiency of the reaction composition decreases, resulting in a longer reaction time and a lower degree of substitution. If the amount of base catalyst used is too large, unwanted side reactions may occur in the reaction composition, or the viscosity of the reaction composition may increase, resulting in a lower mixing uniformity, which may result in a longer reaction time, a lower degree of substitution, and overload or damage to the kneader, which is undesirable. It has also been found that the optimum amount of base catalyst used varies depending on the amount of polybasic acid and / or its acid anhydride used as the modifying agent. The amount of base catalyst used changes the viscosity of the reaction composition, which in turn changes the kneading uniformity of the reaction composition and the applied shear force, which is thought to change the optimum amount. Therefore, it is preferable to adjust the amount of base catalyst used based on the amount of polybasic acid and / or its acid anhydride added. When two or more types of base catalysts are used, the above mass ratio refers to the total mass ratio of the base catalysts.

[0073] The raw material composition may further contain other components such as an antioxidant, a catalyst other than the base catalyst, etc. The mass proportion of the other components in the raw material composition is preferably 5 mass% or less, more preferably 1 mass% or less, and even more preferably 0.1 mass% or less.

[0074] (Polybasic acid-modified cellulose) In the production method of the present invention, polybasic acid-modified cellulose is produced by reacting cellulose with a polybasic acid and / or its acid anhydride. The polybasic acid-modified cellulose is preferably polybasic acid monoesterified cellulose. Monoesterification refers to a state in which only one of the multiple acid groups present in the polybasic acid is bonded to a hydroxy group of the cellulose, and the others are free acids or acid neutralized salts.

[0075] The polybasic acid-modified cellulose preferably has an average degree of substitution of polybasic acid per glucose residue constituting the cellulose of 1 or more. The average degree of substitution is more preferably 1.2 or more, and even more preferably 1.5 or more. In the reaction step, the average degree of substitution can be further increased by using a carbonate, a bicarbonate, or the like as a base catalyst. The average degree of substitution is usually 3 or less. The average degree of substitution is measured by the method described in the Examples. Furthermore, the average degree of substitution of polybasic acid-modified cellulose can be converted, as necessary, into the mass percentage of the modifier relative to the cellulose, the mass percentage relative to the total mass, or the number of charges relative to the total mass. Conversion can be performed using a general calculation method, and an example is described below. Furthermore, since the following calculation method can be used regardless of whether neutralization is performed or not, conversion can also be performed using the same calculation for polybasic acid-modified cellulose. The mass percentage y of the modifier relative to the cellulose １ (Conversion to mass%) Mass percent of modifier relative to total mass y ２ (Conversion to mass%) The number of charges y derived from the acid group of the modifier relative to the total mass ３ Conversion to (mmol / g or meq) where x is the average degree of substitution, y １ ~y ３ is the converted value, N is the degree of neutralization, M ｓ (g / mol) is the molecular weight of the glucose residue that constitutes cellulose, M ｍ (g / mol) is the molecular weight of the modifier, M ｉ(g / mol) is the mass per charge of the counter cation resulting from the neutralization reaction between the acid group introduced into the cellulose by the modifying agent and a base catalyst, and m is the valence of the modifying agent. The molecular weight of the hydrogen ion was set to 1 (g / mol). For example, when the polybasic acid-modified cellulose is a sodium partially neutralized salt of succinic acid-modified cellulose, M ｓ is 162, m is 2, M ｍ is 100, M ｉ is 23, and in the case of a partially neutralized salt of magnesium, which is a divalent cation, M ｉ is 24 / 2 = 12. When multiple types of cations are used for neutralization, the degree of neutralization can be calculated by using the sum of the values ​​calculated from the degree of neutralization for each cation and the molar mass per charge, in the same way as in the calculation of the degree of substitution by pH titration described below.

[0076] The polybasic acid-modified cellulose preferably has a cellulose-derived crystallinity of 45% or less. The crystallinity is more preferably 40% or less, even more preferably 35% or less, even more preferably 30% or less, even more preferably 25% or less, and particularly preferably 20% or less. The lower limit of the crystallinity is not particularly limited, and may be 0% or more, and is typically 5% or more. The crystallinity can be further reduced by using a carbonate, bicarbonate, or the like as a base catalyst in the reaction step. The crystallinity is measured by X-ray diffraction, and is measured by the Segal method described in the Examples.

[0077] <Step of purifying polybasic acid-modified cellulose> The method for producing polybasic acid salt-modified cellulose of the present invention preferably includes a step of purifying the polybasic acid-modified cellulose after the reaction step. The purification step is not particularly limited, but examples include raw material recovery, catalyst recovery, neutralization, filtration, decantation, extraction, washing, evaporation, distillation, and column chromatography. Each of the above operations can be performed alone or in combination of two or more. Among these, purification by filtration and washing is particularly preferred. In the washing operation, organic solvents or water that have a low boiling point (e.g., 100°C or less) and are easy to remove can be used as appropriate. In the purification step, the time and temperature can be appropriately set. The pressure is not particularly limited, and may be normal pressure, increased pressure, or reduced pressure, but normal pressure or reduced pressure is preferred.

[0078] <Step of Neutralizing Polybasic Acid-Modified Cellulose> The method for producing polybasic acid-modified cellulose of the present invention includes a separate step of neutralizing the polybasic acid-modified cellulose obtained in the reaction step described above after the reaction step. This allows polybasic acid-modified cellulose to be obtained. By performing this neutralization step, some or all of the polybasic acids bonded to the cellulose become ionizable salts, which ionize in water and generate electrostatic repulsion between the modified cellulose molecules. This results in high hydrophilicity, allowing the cellulose to be uniformly dispersed or dissolved in water without defibration. The polybasic acid-modified cellulose may be a fully neutralized salt or a partially neutralized salt. In one preferred embodiment of the present invention, the fully neutralized salt or partially neutralized salt is a neutralized product with a monovalent cation. Examples of monovalent cations include alkali metal salts such as sodium and potassium, and ammonium salts. The step of neutralizing the polybasic acid-modified cellulose can be carried out appropriately using a metal compound, ammonia, an organic amine, or the like. Preferred examples of metal compounds include compounds containing alkali metals such as lithium, sodium, and potassium; and compounds containing Group 2 elements of the periodic table such as beryllium, calcium, barium, and magnesium. Specific examples include hydroxides, carbonates, bicarbonates, silicates, phosphates, and aluminates of these metals. In particular, since decomposition of the ester bonds of the modified cellulose progresses when the solution becomes strongly alkaline during neutralization, it is preferable to use sodium carbonate and / or potassium carbonate as the base. In the neutralization step, the time, temperature, and pressure can be appropriately set. The neutralization step can be carried out under solvent-free conditions or in water. From the perspective of productivity, a high concentration of the polybasic acid-modified cellulose during neutralization is desirable, preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, particularly preferably 20% by mass or more, and most preferably 30% by mass or more. The degree of neutralization achieved in the neutralization step is preferably 30% or more, more preferably 50% or more, even more preferably 60% or more, and even more preferably 70% or more, since it is desirable that the liquid after neutralization be as close to neutral as possible. The upper limit of the degree of neutralization is preferably 100%.

[0079] <Step of Crosslinking Polybasic Acid Salt-Modified Cellulose> The production method of the present invention preferably further includes a step of crosslinking the polybasic acid salt-modified cellulose. The crosslinking step can produce crosslinked polybasic acid salt-modified cellulose. The crosslinked polybasic acid salt-modified cellulose is a water-swellable, water-absorbent polymer having the above-mentioned polybasic acid salt-modified cellulose in its main chain. One suitable application of crosslinked polybasic acid salt-modified cellulose is a water-absorbent resin derived from water-swellable, crosslinked polybasic acid salt-modified cellulose. Here, "water-absorbent resin derived from crosslinked polybasic acid salt-modified cellulose" refers to a water-swellable crosslinked polymer obtained by crosslinking a hydrophilic polymer having a polybasic acid salt-modified cellulose as its main chain skeleton, and "water-swellable" means that the absorption capacity under no load (also referred to as centrifuge retention capacity (CRC)) as defined in NWSP 241.0. R2(15) is 5 g / g or more.

[0080] The reaction carried out in the crosslinking step can be a reaction commonly used for crosslinking modified cellulose such as carboxymethylated cellulose. It can be a reaction that bonds functional groups of the polybasic acid salt-modified cellulose together, such as by ester condensation between carboxylic acid (salt) groups derived from the polybasic acid and / or its acid anhydride added in the reaction step and hydroxy groups derived from cellulose, or a reaction that forms a bond with a crosslinking agent, or a reaction that bonds crosslinking agents bound to functional groups of the polybasic acid salt-modified cellulose together, or a method that generates hydrogen bonds between acid groups and hydroxy groups by adjusting the degree of neutralization, or a method that combines multiple techniques. The acid (salt) group represents an acid group and / or an acid-base group. Examples of the acid group include a carboxylic acid group, a sulfonic acid group, a sulfate group, and a phosphate group. Examples of the acid-base group include metal salts such as alkali metal salts, alkaline earth metal salts, and transition metal salts of the acid group, as well as organic amine salts and ammonium salts.

[0081] Specific reactants and reaction modes include ester formation of functional groups derived from polybasic acid salt-modified cellulose in an equivalent reaction using a condensing agent such as a carbodiimide, e.g., dicyclohexylcarbodiimide; ester formation by dehydration condensation of functional groups derived from polybasic acid salt-modified cellulose in a catalytic reaction using inorganic acids, e.g., sulfuric acid and hydrochloric acid, organic acids, e.g., citric acid, Lewis acids, e.g., boron trifluoride, and metal salts, e.g., titanium salts; and ester formation by dehydration condensation of functional groups derived from polybasic acid salt-modified cellulose in an equivalent reaction using an epoxy structure, e.g., (poly)ethylene glycol diglycidyl ether, glycerol diglycidyl ether, oxetane structure, and oxalate structure. Crosslinking agents with multiple highly active functional groups such as sazoline structures or isocyanate structures, ester formation by reaction of polybasic acid anhydrides such as carboxylic acid anhydrides such as succinic anhydride or maleic anhydride, or inorganic acid anhydrides such as polyphosphoric acid with functional groups of polybasic acid salt-modified crosslinked cellulose, acetal formation of hydroxyl groups with compounds with multiple aldehyde groups such as glutaraldehyde or glyoxal, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, 1,4-butanediol, pentaerythritol, ethylenediamine, ethylenediaminetetraacetic acid ... crosslinking by radical polymerization of the multiple bonds derived from the crosslinking agent; crosslinking by reacting a silane coupling agent having a functional group reactive with a functional group derived from the polybasic acid salt-modified cellulose, such as an epoxy group or an amino group, with a silane coupling agent; hydrogen bonding of an acid group derived from the polybasic acid salt-modified cellulose and a hydroxy group by adjusting the degree of neutralization by adding an inorganic acid such as sulfuric acid or hydrochloric acid or an inorganic acid such as citric acid; and complex formation by a polyvalent metal salt such as a titanium salt, an aluminum salt or a zirconium salt with an acid group derived from the polybasic acid salt-modified cellulose.

[0082] Since the crosslinking step can proceed by the ester condensation even without a crosslinking agent, the crosslinking may proceed in the drying step after the reaction step or the neutralization step. That is, the crosslinking step may be an independent step, or may be carried out simultaneously with the reaction step or the drying step, or may be both.

[0083] The crosslinking agent may be used alone or in combination with two or more other crosslinking agents. Alternatively, a polybasic acid and / or anhydride thereof different from the polybasic acid and / or anhydride thereof used in the reaction step may be added separately as a crosslinking agent.

[0084] The amount of the crosslinking agent used is, for example, preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, relative to 100% by mass of the polybasic acid salt-modified cellulose. The amount used is, for example, preferably 10% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0085] The amount of crosslinking agent used is, in terms of substance amount, preferably 0.01 mol% or more, more preferably 0.05 mol% or more, and even more preferably 0.1 mol% or more, relative to the glucose residues of the polybasic acid salt-modified cellulose. The amount used is, for example, preferably 10 mol% or less, more preferably 3 mol% or less, and even more preferably 1 mol% or less. When two or more crosslinking agents are used, the above amount used is the total amount used. In the crosslinking step, the time, temperature, and pressure can be appropriately set. When crosslinking by hydrogen bonding by adjusting the degree of neutralization, the degree of neutralization may be adjusted by the amount of base added in the neutralization step, or by adding an acid separately.

[0086] <Step of Drying Crosslinked Polybasic Acid Salt-Modified Cellulose> The production method of the present invention preferably further comprises a step of drying the crosslinked polybasic acid salt-modified cellulose. The drying temperature in the drying step is preferably 40 to 200°C, more preferably 60 to 180°C, even more preferably 80 to 160°C, and particularly preferably 100 to 140°C. The drying time in the drying step is preferably 3 minutes to 24 hours, more preferably 5 minutes to 12 hours, even more preferably 7 minutes to 6 hours, even more preferably 10 minutes to 3 hours, and particularly preferably 15 to 90 minutes. In the drying step, the pressure can be appropriately set, but normal pressure or reduced pressure is preferred. Drying methods include various methods such as heat drying, hot air drying, reduced-pressure drying, infrared drying, microwave drying, drum dryer drying, band drying, and high-humidity drying using high-temperature steam.

[0087] <Step of Powdering Crosslinked Polybasic Acid Salt-Modified Cellulose> In the production method of the present invention, it is desirable to powder the dried crosslinked polybasic acid salt-modified cellulose. The powdering method is not particularly limited, and may include forming a crosslinked polybasic acid salt-modified cellulose solution into particles before drying and then drying, pulverizing the dried product during drying, or pulverizing after drying. In other words, the powdering step may be an independent step, may be performed simultaneously with a drying step, or may be a combination of multiple steps. The powdered polybasic acid salt-modified cellulose may be used as is, or may be classified to a specific particle size. Classification to a specific particle size allows for the impartation of desirable physical properties depending on the application, such as adjusting the dissolution rate in the case of an uncrosslinked product, or improving the absorption rate, liquid permeability, and other physical properties in the case of a crosslinked product for use as a water-absorbent resin. Uncrosslinked polybasic acid salt-modified cellulose may also be dried and powdered in the same manner as described above.

[0088] <Step of Surface-Crosslinking Powdery Crosslinked Polybasic Acid Salt-Modified Cellulose> In the production method of the present invention, it is preferable to include a step of surface-crosslinking the powdery crosslinked polybasic acid salt-modified cellulose. The surface-crosslinking step is a step in which a surface-crosslinking agent is added that reacts with the functional groups of the powdery crosslinked polybasic acid salt-modified cellulose (particularly the acid (salt) groups derived from the polybasic acid and / or its acid anhydride added in the reaction step and the hydroxyl groups derived from the cellulose) to additionally crosslink the surfaces of the crosslinked powder particles. This step is distinct from the step of crosslinking the entire uncrosslinked polybasic acid salt-modified cellulose. The crosslinking agent and reaction method used for surface crosslinking are not particularly limited, but the reactions described in the step of crosslinking polybasic acid cellulose can be suitably used. Furthermore, the reaction used for surface crosslinking may be a single agent or a combination of multiple reactions. The crosslinking agent used for surface crosslinking may be the same as the crosslinking agent used for crosslinking the entire polybasic acid salt-modified cellulose, or a different agent may be used. The addition of a surface cross-linking agent for forming surface cross-linking and the method for forming surface cross-linking are not particularly limited, and may be a method of processing a polybasic acid salt-modified cellulose molded into a powder before the entire cross-linking, a method of carrying out surface cross-linking simultaneously with the entire cross-linking, a method of carrying out surface cross-linking separately after the entire cross-linking, a method of carrying out an independent step, a method of carrying out a step simultaneously with another step, or a method of combining a plurality of steps. Surface cross-linking makes it possible to appropriately adjust physical properties depending on the application, and particularly in water-absorbent resin applications, it makes it possible to impart preferable physical properties such as strengthening the particle strength before and / or after swelling, and improving or suppressing the swelling ratio, absorption rate, liquid permeability, etc.

[0089] <Step of processing cellulose used in the reaction step> The production method of the present invention may include a step of previously shredding, defibrating, or pulverizing the cellulose used in the reaction step to process it into a form suitable for modification. In the processing step, the cellulose is treated with a processing machine such as a screw extruder (e.g., pelletizer, shredder, kneader, or meat chopper), a ball mill, a cutter mill, or a jet mill to change the shape and density and process it into an optimal form. Examples of the form of cellulose after processing include chips, pellets, fibers, and powder. Note that this processing step does not necessarily have to be performed. It is preferable to perform the processing step to convert the cellulose into a powder and adjust the average particle size to within the above-mentioned preferred range.

[0090] <Step of recovering and regenerating impurities removed by the purification step> In the production method of the present invention, the impurities removed by the purification step (for example, the unreacted polybasic acid and / or its acid anhydride as raw materials) can be recovered as needed and recycled as reaction raw materials, etc. Furthermore, the solvent used in the purification can also be recovered as needed and recycled as a solvent. A distillation step can be suitably used for the recovery and regeneration. The conditions for the distillation step can be set appropriately. For example, the solvent can be recovered by distillation. Furthermore, for example, after removing a solvent having a boiling point lower than that of the polybasic acid and / or its acid anhydride by distillation, the polybasic acid and / or its acid anhydride can be recovered by vacuum distillation, etc.

[0091] The production method of the present invention may include other steps, etc., as long as it includes the above-mentioned reaction step. For example, the production method of the present invention may include a step of separating the base catalyst and the neutralizing agent.

[0092] [Polybasic Acid Salt-Modified Cellulose Composition] The present invention also relates to a polybasic acid salt-modified cellulose composition comprising a polybasic acid salt-modified cellulose, in which the mass proportion of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine is less than 5000 ppm, and the mass proportion of an ionic liquid having an imidazolium ion is less than 5000 ppm.

[0093] The polybasic acid salt-modified cellulose composition of the present invention may be free of the above-mentioned dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine, and may also be free of the above-mentioned ionic liquid. For example, the polybasic acid salt-modified cellulose composition of the present invention may be free of any of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, 4-dimethylaminopyridine, and an ionic liquid having an imidazolium ion. The polybasic acid salt-modified cellulose composition of the present invention contains sufficiently reduced amounts of toxic and strongly odorous solvents and organic catalysts, and is therefore highly safe and suitable for use in sanitary materials and detergents that come into contact with the human body.

[0094] The polybasic acid salt-modified cellulose composition of the present invention comprises a polybasic acid salt-modified cellulose as a primary component, and may further contain an organic solvent, an organic catalyst, and an ionic liquid, so long as the mass proportion of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine is less than 5,000 ppm, and the mass proportion of an ionic liquid having an imidazolium ion is less than 5,000 ppm. For example, the polybasic acid salt-modified cellulose composition of the present invention may contain an organic solvent other than the six compounds described above, or may contain ethyl acetate or an ionic liquid other than the ionic liquids described above. In particular, the polybasic acid salt-modified cellulose composition of the present invention preferably contains an organic solvent, organic catalyst, and ionic liquid in a total mass proportion of less than 5,000 ppm. For example, the polybasic acid salt-modified cellulose composition of the present invention may be free of organic solvent, organic catalyst, or ionic liquid, and the total mass proportion of the organic catalyst, organic solvent, and ionic liquid may be 0 ppm.

[0095] The polybasic acid salt-modified cellulose composition of the present invention preferably has a soluble component ratio of 1% or more. The soluble component ratio is more preferably 2% or more, even more preferably 5% or more, even more preferably 10% or more, and particularly preferably 20% or more. The upper limit of the soluble component ratio is not particularly limited, but is preferably 100% or less, more preferably 90% or less, and even more preferably 80% or less. The soluble component ratio is determined by the method in the Examples.

[0096] The preferred average degree of substitution of polybasic acid salts per glucose residue in the polybasic acid salt-modified cellulose of the present invention is the same as the preferred average degree of substitution of polybasic acid salts per glucose residue in the above-mentioned polybasic acid-modified cellulose.

[0097] The preferred crystallinity of the polybasic acid salt-modified cellulose of the present invention is the same as the preferred crystallinity of the polybasic acid-modified cellulose described above. That is, the polybasic acid salt-modified cellulose of the present invention preferably has a crystallinity of 45% or less as cellulose. The crystallinity is more preferably 40% or less, even more preferably 35% or less, even more preferably 30% or less, even more preferably 25% or less, and particularly preferably 20% or less. The lower limit of the crystallinity is not particularly limited, but is usually 0% or more, preferably 5% or more. The crystallinity is determined by the method described in the Examples.

[0098] The preferred mass proportions of the organic solvent, organic catalyst, and ionic liquid in the polybasic acid salt-modified cellulose composition of the present invention are the same as the preferred mass proportions of the organic solvent, organic catalyst, and ionic liquid in the above-mentioned raw material composition.

[0099] Fig. 1 is a diagram showing an example of the reaction formula between cellulose and a polybasic acid anhydride according to the production method of the present invention, in which succinic anhydride is used as the polybasic acid anhydride.

[0100] Fig. 2 is a diagram illustrating each step in the production method of the present invention. Fig. 2 schematically shows a production method for a water-absorbent resin, in which cellulose SAP 6 is obtained through step 2, in which pulp raw material (compressed form) 1 is defibrated and pulverized to amorphize it, step 3, in which it is modified with a polybasic acid and / or its acid anhydride (reactant) under solvent-free conditions, step 4, in which impurities including the reactant are separated, and step 5, in which it is neutralized, crosslinked, and dried. Furthermore, it is also possible to recover and regenerate the reactant and solvent separated as impurities in step 4 by distillation step 7, and reuse the reactant in step 3 or reuse the solvent in step 4 for purifying it.

[0101] The polybasic acid salt-modified cellulose obtained using the production method of the present invention can be suitably used as a raw material for various products, including industrial materials and products, agriculture, forestry, and fisheries, food and feed, daily necessities, and medical and biotechnology applications. For example, uncrosslinked polybasic acid salt-modified cellulose can be used as a physical property adjuster such as a thickener, a binder, a dispersant, a stabilizer, a metal sealant, a film-forming agent, and other structure control agents, making it suitable for a variety of applications, including uncrosslinked polyacrylic acid (salt)-based hydrophilic resins. Specific application fields include material processing and structure formation applications such as papermaking, paints, building materials, adhesives, pressure-sensitive adhesives, ceramics, civil engineering, and textiles; nutritional product applications such as livestock feed and food; pharmaceutical applications; agricultural and horticultural applications; daily necessities applications such as cosmetics and detergents; and electronic materials. In addition, crosslinked polybasic acid salt-modified cellulose has characteristics such as water absorption, water retention, suction swelling, gelling properties, and thickening properties, making it suitable for a variety of further applications, including crosslinked polyacrylic acid (salt)-based water-absorbent resins. Specific applications include hygiene materials; agriculture and horticulture; food; distribution; civil engineering and construction; cosmetics; daily necessities; medical care; electronic materials; paints, etc., and more specifically, in hygiene material applications, sanitary products, disposable diapers, breast pads, toilet absorbents, and absorbents for pet sheets; in agriculture and horticulture applications, soil water retention agents, seedling raising sheets, seed coating agents, artificial sphagnum moss, disintegration aids for pesticides, mushroom culture media, and seed gelling agents; in food applications, freshness-preserving agents, drip absorbents, dehydrating agents, and anti-condensation agents; in the distribution field, ice packs; and in civil engineering and construction applications, anti-condensation agents. , water retention agents for spraying, concrete curing materials, lost circulation prevention agents, sealants, cement admixtures, sludge solidification agents, excavation lubricants, drilling agents, antifriction agents, gelling agents for sandbags; gel fragrances, sweat absorbents, thickeners in cosmetics; body warmers in the field of daily necessities; dressings, absorbents for tampons, drug delivery agents, gelling agents for waste blood, and poultices in the medical field; waterproofing agents and gelling agents for battery electrolytes; thickeners, water swelling absorbents, and emulsion stabilizers in paint applications.Among these, water-absorbent resins produced using polybasic acid salt-modified cellulose as a raw material can be particularly suitably used for applications requiring water absorption or water retention, such as sanitary material applications such as disposable diapers, sanitary products, adult incontinence products (incontinence pads, etc.), and pet sheets, as well as for applications requiring water absorption or water retention, such as daily necessities (detergents, etc.), agriculture and horticulture (soil water retention agents, etc.), food (water-absorbent sheets, etc.), cosmetics (thickeners, etc.), and industrial applications (water-stopping agents, etc.). In particular, compared to conventional polyacrylic acid-based products that are highly residual in the environment and pose problems of fuel consumption and carbon dioxide emissions when incinerated, the polybasic acid salt-modified cellulose obtained by the present invention has high biodegradability and therefore has the advantage of causing little load on the environment throughout its entire life cycle, from raw material to disposal.

[0102] The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention should not be construed as being limited to these examples, and examples obtained by appropriately combining the technical means described in each example are also included in the scope of the present invention. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

[0103] [CRC (absorbency without load)] The CRC (absorbency without load) in a 0.9% by mass sodium chloride aqueous solution (hereinafter referred to as saline) was measured in accordance with NWSP 241.0.R2(15). Specifically, 0.2 g of sample was placed in a nonwoven bag and immersed in a large excess of saline for 30 minutes to allow the sample to freely swell. The sample was then dehydrated using a centrifuge (centrifugal force: 250 G), and the CRC (absorbency without load) (unit: g / g) was measured. Pure water CRC was also measured using pure water instead of saline. When measuring pure water CRC, pure water was used instead of saline, and the sample amount was changed from 0.2 g to 0.1 g, but the measurement was otherwise performed using the same procedures as for saline CRC.

[0104] [Calculation of the residual solvent ratio or residual modifier ratio in a sample] The residual solvent ratio or residual modifier ratio in a sample was quantified as the mass ratio of the residual solvent or residual modifier relative to the total sample mass by calculating from the area value of the peak detected in the differential refractive index (hereinafter RI) chromatogram of high performance liquid chromatography (hereinafter HPLC). When the sample injection amount in HPLC is the same, the peak area value detected by the RI detector is proportional to the mass concentration of the sample in the measurement solution. Therefore, the amount of residual solvent or residual modifier in the sample can be calculated from the relationship between the mass concentration of the residual solvent determined by calibration in advance and the peak area value. Furthermore, when a polybasic acid anhydride is used as the modifier and HPLC measurement is performed with the eluent described below, the modifier is detected as a hydrolyzed free acid.

[0105] (Sample Preparation) A measurement solution was prepared according to the following procedure. The entire sample to be measured was pulverized so as to pass through a JIS standard sieve with a mesh size of 300 μm. Then, 0.1 g of the sample was weighed into a 100 mL glass beaker equipped with a 30 mm long magnetic stirrer, 10 g of pure water was added, and stirring was initiated at 350 rpm using a magnetic stirrer at room temperature (20°C to 25°C). After 30 minutes of stirring, 40 g of a 0.25% by mass aqueous phosphoric acid solution was added to the beaker, and stirring was continued for 30 minutes to obtain a 0.2% by mass sample dispersion. The sample dispersion was then passed through a filter (Membrane Solutions, PTFE syringe filter, hydrophilic 25A, pore size 0.22 μm) to obtain a measurement solution.

[0106] (HPLC measurement conditions) Measurement was carried out using a Waters Alliance HPLC. The device configuration was an apparatus equipped with an ion exclusion chromatography column and an RI detector. The measurement device and measurement conditions were as follows. Pump / autosampler: Waters Alliance HPLC Guard column: Shim-pack SCR (H) guard column (Shimadzu GLC) Column: Shim-pack SCR-101H (Shimadzu GLC) RI detector: 2414 differential refractometer (Waters) Eluent: 0.4% phosphoric acid aqueous solution Flow rate: 1 mL / min Injection amount: 50 μL Measurement temperature: 35° C. A sufficient amount of eluent was allowed to flow through the device during measurement, and the measurement was carried out when the baseline of the detector was stable. Data collection from the RI detector and analysis of the RI chromatogram were performed using Empower3 software manufactured by Waters. The area values ​​of the peaks derived from the impurities, such as the remaining solvent or the remaining modifier, were obtained from the RI chromatogram and used to calculate the remaining ratio.

[0107] (Calculation of Residual Solvent Ratio or Residual Modifier Ratio) The solvent or modifier alone was measured using the same procedure as in the sample measurement, and the relationship between the RI peak area value and the concentration of the residual solvent or modifier was calculated. Specifically, the solvent or modifier was diluted 10,000 times with a 0.4 mass% aqueous phosphoric acid solution and then filtered to prepare a measurement solution with a concentration of 0.01 mass%, which was then measured by HPLC. The elution time and RI peak area value of the residual solvent or modifier were obtained from the RI chromatogram. The obtained RI peak area value was divided by the mass concentration of the measurement solution to calculate the coefficient C [1 / mass%] of the solvent or modifier concentration in the measurement solution and the RI peak area value. The coefficient C was used to calculate the concentration of the residual solvent or modifier in the measurement solution from the RI peak area value of the measurement solution, and the product of this value and the dilution factor of the sample was obtained to calculate the proportion of the residual solvent or modifier in the sample. Here, x is the proportion of the remaining solvent or modifier in the sample [mass %], A is the RI peak area value detected from the measurement solution of the sample, and c is the mass concentration of the sample in the measurement solution [mass %].

[0108] [Calculation of the proportion of soluble components] The proportion of soluble components in a sample was determined by calculation from the value detected in the RI chromatogram of gel permeation chromatography (hereinafter referred to as GPC).

[0109] (Sample Preparation) A solution was prepared by diluting the sample to be measured so that the concentration of the sample to be measured was 0.1 mass % relative to the solid content, and the diluted solution was filtered through a filter (manufactured by Membrane Solutions, PTFE syringe filter, hydrophilic 25A, pore size 0.22 μm) to obtain a measurement solution. GPC measurement of this solution was performed under the following conditions.

[0110] (GPC Measurement Conditions) Measurement was carried out using a Viscotek TDA305 manufactured by Malvern Panalytical. The instrument was equipped with a gel permeation chromatography column, an RI detector, a light scattering detector, and a capillary viscometer. The measurement instrument and measurement conditions were as follows: Pump / autosampler: GPCmax manufactured by Viscotek; Guard column: OHpak SB-G (manufactured by Showa Denko); Column: Two OHpak SB-806MHQ (manufactured by Showa Denko) connected in series; Detector: Viscotek TDA305 manufactured by Malvern Panalytical (system temperature maintained at 30°C); Eluent: 60 mM sodium dihydrogen phosphate dihydrate, 20 mM disodium hydrogen phosphate dodecahydrate, and 400 ppm sodium azide aqueous solution (pH 6.35 to 6.38); Flow rate: 0.5 mL / min; Injection volume: 100 μL; Measurement temperature: 30°C. Ultrapure water purified using a Millipore Simplicity UV (manufactured by Merck) was used for the measurement. Furthermore, measurements were performed after a sufficient amount of eluent had flowed through the instrument and the detector baseline had stabilized. In particular, measurements were performed without noise peaks in the light scattering detector. Instrument calibration was performed using polyoxyethylene glycol (weight average molecular weight (Mw) 22,396, molecular weight distribution (Mw / Mn = 1.0), refractive index increment with concentration (dn / dc) = 0.132, solvent refractive index 1.33) as a standard sample. The differential refractive index of the polymer being analyzed was measured using the value of dextran, a polysaccharide commonly used in GPC ((dn / dc) = 0.147, solvent refractive index 1.33). Data collection and analysis of RI, light scattering intensity, and viscosity (DP) were performed using Malvern Panalytical's OmniSEC 5.3 software. The molecular weight of the dissolved components versus elution time was calculated from the RI and light scattering intensity (7° angle) data obtained from the LALS and viscometer, and the RI area value of peaks present at molecular weights of 1,000 or more was obtained from the RI chromatogram. The proportion of soluble components in the measurement object (modified cellulose) in GPC was calculated using the following formula.Carboxymethylcellulose sodium salt (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), a completely water-soluble polymer with a cellulose backbone, was used as a standard substance, and the RI peak area obtained by GPC measurement under the same conditions was used as the standard to calculate the proportion of soluble components. To correct the proportion of soluble components, the proportion of residual solvent measured by HPLC was excluded from the calculation. where x is the proportion of dissolved components [mass %], A ｐ is the RI peak area value of the measured sample with a molecular weight of 1000 or more, A ｃ is the RI peak area value detected in the measurement of carboxymethyl cellulose sodium salt, which is a standard substance; s is the remaining solvent proportion [mass %] calculated from the HPLC measurement results; and a is the remaining modifier proportion [mass %] calculated from the HPLC measurement results.

[0111] [Calculation of Average Degree of Substitution by pH Titration] The average degree of substitution in a sample was measured by measuring the amount of acid in the modified product by pH titration. The measurement solution was prepared as follows: After the entire sample to be measured was crushed so that it passed through a 300 μm JIS standard sieve, 0.1 g of the sample was placed in a 100 mL glass beaker, diluted with 50 g of 0.9% by mass sodium chloride aqueous solution, and a 30 mm magnetic stirrer was placed inside. Subsequently, to improve the uniformity of the measurement, a process was carried out to increase the degree of neutralization of the sample and disperse it in water. Specifically, an appropriate amount of 0.1 mol / L sodium hydroxide aqueous solution was added, and the mixture was stirred at 350 rpm for 1 hour at room temperature (20°C to 25°C) using a magnetic stirrer. The pH of the solution was measured using a handheld pH meter. The amount of sodium hydroxide aqueous solution added was adjusted so that the pH of the solution after stirring was 5.5 to 7. If the pH of the solution was 5.5 or lower, additional sodium hydroxide aqueous solution was added, followed by stirring for another hour. This process was repeated until the pH of the solution after stirring reached 5.5 to 7. On the other hand, if the pH of the solution was 7 or higher, the test solution was prepared again. A pH titrator manufactured by HIRANUMA (formerly Hiranuma Sangyo) was used with the following configuration: pH automatic titrator: Tight Station TS-980; additional burette: B-900; burette head: H-900; automatic cycler: C-912; control and analysis software: COM-2500; acid titration solution: 0.1 mol / L hydrochloric acid-base titration solution: 0.1 mol / L sodium hydroxide aqueous solution manufactured by Kanto Chemical. The test solution was titrated using an automatic titrator. The test solution was first titrated with sodium hydroxide aqueous solution until the pH reached 10.5, and then with hydrochloric acid until the pH reached 2.8, and the amount of titration solution required for each titration was recorded. In addition to the sample measurement solution, a similar blank measurement was also performed without adding the sample, and the amount of acid or base required for each neutralization was calculated from the difference in the amount of titration solution added between the sample measurement and the blank measurement. The amount of acid in the modified cellulose comes from the modifier bonded by half-esterification and the modifier in the free acid form remaining in the sample, and when the modifier is an acid anhydride, the following equation holds: where x is the average degree of substitution, W is the weight of the sample used in the pH titration [g], s is the proportion of the remaining solvent in the sample [mass %] calculated from the HPLC measurement results, a is the proportion of the remaining modifier in the sample [mass %], M ｓ is the molar mass per glucose unit of cellulose [g / mol], M １ is the molar mass of the acid anhydride of the modifying agent [g / mol], M ２ is the molar mass of the remaining free acid form of the modifier [g / mol], m ｉ is the molar mass per charge of the cationic species i [g / mol] derived from the base catalyst added during the modification reaction or the base used for neutralization, n is the acid valence of the modifier, N ｉ is the degree of neutralization derived from the cationic species i of the sample, Σ is the summation symbol indicating that the calculations for each cationic species involved in neutralization are summed up, A is the amount of hydrochloric acid [mL] required for the acid titration of the sample, A ｂ is the amount of hydrochloric acid [mL] required for the blank acid titration. The molar mass of hydrogen ions was set to 1 g / mol. When succinic anhydride is used as the modifier, M １ is 100 g / mol, M ２ is 118 g / mol and n is 2. In the case of cellulose, the repeating unit is a glucose unit, so M ｓ In the case of polybasic acid-modified cellulose using only potassium carbonate as a base catalyst, the cationic species involved in neutralization is only potassium, and m Ｋ is the molar mass of potassium, 39 g / mol, and the degree of neutralization N Ｋ can be determined from the results of pH titration. If sodium carbonate is then used for neutralization after purification to obtain polybasic acid salt-modified cellulose, the cationic species involved in the neutralization will be potassium and sodium. Ｎａ is 23 g / mol, and the degree of neutralization by potassium N Ｋ is the value calculated by the measurement before neutralization, and the neutralization rate by sodium N Ｎａ is the degree of neutralization of the entire sample calculated by pH titration, N to N ＫThe degree of neutralization N of the entire sample can be calculated by subtracting the total amount B [mL] of the aqueous sodium hydroxide solution required to adjust the pH of the sample solution, the total amount B [mL] of the aqueous sodium hydroxide solution required for base titration by the titrator, and the total amount B [mL] of the aqueous solution required for titration of the blank measurement. ｂ It can be calculated from [mL] using the following formula: The above formula was transformed to calculate the average degree of substitution x using the following formula: In addition, when a polybasic acid having a free acid group is used as the modifying agent instead of an acid anhydride, M １ Subtract the molecular weight of water, 18, from M ２ This can be calculated by adding 18 to the above.

[0112] [Calculation of Mass Average Particle Diameter (D50)] The mass average particle diameter (D50) of the cellulose raw material was calculated using the Rosin-Rammler equation, which is commonly used to determine the particle size distribution of pulverized particles. The Rosin-Rammler equation is expressed by the following formula. Here, d [μm] is the particle diameter of the powder, R(d) is the mass fraction of particles with a particle diameter of d or more, c [μm] is the particle diameter corresponding to R(c) = 0.368, and n is an equality number. n is an index representing the particle size distribution, and the larger the value, the narrower the distribution, i.e., the more uniform the particle size of the powder. Transforming both sides of this Rosin-Rammler equation yields the following equation: Since this equation has a linear relationship between ln(d) and (ln(1 / R(d))), it is possible to calculate R(d) at particle diameter d by obtaining values ​​of R(d) for multiple particle diameters d and creating an approximate straight line for the above equation using the least squares method. Furthermore, from the relationship of the above equation, the slope of the approximate straight line becomes the equality number n. Classification when calculating the Rosin-Rammler equation was performed as follows. 3 g of the cellulose raw material was placed on a stack of JIS standard sieves (manufactured by Iida Seisakusho Co., Ltd., frame diameter 75 mm) with specified mesh openings at room temperature and a humidity of 50% RH, and the classification was performed by shaking for 5 minutes in a sieve shaker (manufactured by Iida Seisakusho Co., Ltd., sieve shaker model ES-65). The sieve opening size was varied depending on the particle size being processed. Particles with particle sizes between 850 and 150 μm were classified using sieves with opening sizes of 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 250 μm, and 180 μm, while particles with particle sizes of 150 μm or less were classified using sieves with opening sizes of 125 μm, 106 μm, 90 μm, 75 μm, and 45 μm. After shaking, the mass of the powder remaining on each sieve was measured. The mass of the powder remaining on each sieve with opening size and on the sieve with larger opening sizes was summed to obtain the mass fraction R(d) of particles with a particle size of d or greater. The values ​​of d and R(d) for each sieve were logarithmically transformed twice to obtain the values ​​of ln(d) and ln(ln(R(d))), and an approximate straight line was created using the least squares method. Then, the value of d at which R(d)=0.5 (50% by mass in percentage) was calculated from the approximation line to obtain the mass average particle diameter D50 [μm].

[0113] [Measurement of Cellulose Crystallinity] The cellulose I-type crystallinity is calculated from the diffraction intensity value obtained by X-ray diffraction by the Segal method, and is defined by the following formula. where x is the cellulose I type crystallinity [%], I ２２．６ is the diffraction intensity of the lattice plane (002 plane) (diffraction angle 2θ = 22.6°) in X-ray diffraction, I １８．５indicates the diffraction intensity of the amorphous portion (diffraction angle 2θ = 18.5°). The diffraction angle is a value measured using an X-ray source of Cu / Kα (wavelength 0.154 nm), and if the X-ray source is changed, the angle can be calculated by appropriately correcting the angle according to the wavelength. X-ray diffraction was performed using an apparatus with the following configuration. Measuring apparatus: Aeris manufactured by Malvern Panalytical X-ray source: Cu / Kα (0.154 nm) Tube voltage: 40 kV Tube current: 15 mA Measurement range: diffraction angle 2θ = 5 to 50° X-ray scan speed: 1.67° / min

[0114] The degree of crystallinity is derived from the structure of the cellulose raw material, and it is thought that the degree of crystallinity decreases when the inside of the crystal is modified with carboxylic acid. Therefore, it is thought that the degree of crystallinity does not change substantially by neutralization after purification. Therefore, in some examples, the crystallinity of the product was judged from the results of X-ray diffraction before neutralization. Furthermore, although not described in the examples of this patent, when cellulose of type II crystal is used as the raw material, the degree of crystallinity of type I is judged from the results of X-ray diffraction before neutralization. ２２．６ I ２０．０ (diffraction intensity at diffraction angle 2θ=20.0°), I １８．５ I １５．０ (diffraction intensity at diffraction angle 2θ=15.0°) can be calculated in the same way.

[0115] [Preparation of Fibrous Pulp] A commercially available softwood pulp board was defibrated using a vertical cutter mill to prepare fibrous pulp.

[0116] [Preparation of powdered pulp using a planetary ball mill] The fibrous pulp was pulverized in a planetary ball mill for 1 hour to obtain powdered pulp, which was then classified using sieves with 850 μm and 150 μm openings. The powder remaining on the 150 μm sieve was obtained as powdered pulp with a particle size of 850 to 150 μm, and the powder that passed through the 150 μm sieve was obtained as powdered pulp with a particle size of 150 μm or less.

[0117] Example 1 (Solventless Modification of Fibrous Pulp and Measurement of Dissolved Component Ratio) A double-arm kneader was used as the kneading device, and the kneading tank was heated to 125°C using a jacket through which thermal oil was passed. 100 parts by mass (25 g) of fibrous pulp, 300 parts by mass of succinic anhydride, and 15 parts by mass of potassium carbonate were added to the kneader and kneaded for 1 hour. The kneaded product was removed and pulverized using a force mill manufactured by Osaka Chemical Co., Ltd. The pulverized product was added to acetone in an amount five times the mass of the pulverized product and stirred at room temperature (20°C to 25°C). The unreacted succinic anhydride was then removed by vacuum filtration and acetone washing. The product was then vacuum dried at 45°C to obtain succinic acid-modified cellulose, which is a polybasic acid-modified cellulose. HPLC analysis and pH titration were performed to calculate the residual solvent ratio and average degree of substitution. The crystallinity was measured by X-ray diffraction, confirming a decrease from 73% in the raw material to 21%. One part of this succinic acid-modified cellulose was added to 1,000 parts of the same sodium phosphate buffer solution used in the GPC measurement, and neutralization was carried out by thoroughly stirring until uniform, yielding a 0.1% by mass solution of neutralized succinic acid-modified cellulose. Because the amount of disodium hydrogen phosphate was in excess relative to the carboxylic acid of the succinic acid-modified cellulose, a 100% neutralized product was obtained. GPC measurement was performed using this dispersion, and the proportion of dissolved components was calculated. Because the buffer solution had a pH around neutral, hydrolysis of the succinic acid cellulose did not occur during neutralization with the buffer solution, the values ​​before neutralization were used for the crystallinity, residual solvent proportion, and average degree of substitution.

[0118] [Comparative Example 1] (Measurement of the proportion of soluble components in polybasic acid-modified cellulose) Neutralization with sodium phosphate buffer was not performed, and 1 part of succinic acid-modified cellulose was added to 1,000 parts of pure water and stirred uniformly. The same procedure as in Example 1 was performed, except that neutralization with sodium phosphate buffer was not performed, and the proportion of soluble components in the unneutralized succinic acid-modified cellulose was measured.

[0119] [Comparative Example 2] (Modification in DMF and Measurement of Dissolved Component Ratio) 100 parts by mass (0.3 g) of fibrous pulp, 300 parts by mass of succinic anhydride, 15 parts by mass of potassium carbonate, and 2000 parts by mass of DMF were added to a test tube equipped with a magnetic stirrer and stirred at 125 ° C. for 1 hour. After completion of the reaction, acetone was added in an amount five times the total volume of the reaction composition, and the mixture was stirred at room temperature (20 ° C. to 25 ° C.) to precipitate succinic acid-modified cellulose. Unreacted succinic anhydride was removed by vacuum filtration and acetone washing. The mixture was then vacuum dried at 45 ° C. under 10 hPa to obtain unneutralized succinic acid-modified cellulose. HPLC measurement and pH titration were performed to calculate the residual solvent ratio and average degree of substitution. 1 part by mass of this succinic acid-modified cellulose was added to 1000 parts by mass of the same sodium phosphate buffer solution used in the GPC measurement, and neutralization was carried out by stirring thoroughly to homogenize, yielding a 0.1% by mass solution of neutralized succinic acid-modified cellulose. This dispersion was subjected to GPC measurement, and the proportion of dissolved components was calculated.

[0120] Comparative Example 3 (Modification in DMSO and Measurement of Dissolved Component Ratio) The same procedure as in Comparative Example 2 was carried out except that DMF was changed to DMSO, and the soluble component ratio, average substitution degree, and residual solvent ratio of the modified product in DMSO were measured. In Example 1 and Comparative Example 1 in Table 1, no residual solvent was observed because both were solvent-free modifications. On the other hand, almost no soluble components were detected in Comparative Example 1, whereas the amount of soluble components increased significantly in Example 1, which was neutralized, confirming the effect of neutralization on improving hydrophilicity. Example 1 and Comparative Examples 2 and 3 all achieved high soluble component ratios and average degrees of substitution, but in Comparative Examples 2 and 3, which were modified in a solvent, the solvent was not completely removed even after acetone washing and vacuum drying, and remained in the sample.

[0121] Example 2 (Solventless Modification of Fibrous Pulp and SAP Preparation) A double-arm kneader was used as the kneading device, and the kneading tank was heated to 125°C using a jacket through which thermal oil was passed. 100 parts by mass (25 g) of fibrous pulp, 200 parts by mass of succinic anhydride, and 10 parts by mass of potassium carbonate were added to the kneader and kneaded for 1 hour. The kneaded product was removed and pulverized using a Force Mill FM-1 manufactured by Osaka Chemical Co., Ltd. The pulverized product was added to 5 times the mass of acetone and stirred at room temperature. Unreacted succinic anhydride was then removed by vacuum filtration and acetone washing. The product was then vacuum dried at 45°C to obtain unneutralized succinic acid-modified cellulose. HPLC measurement and pH titration were performed to calculate the residual solvent ratio and average degree of substitution. X-ray diffraction measurement revealed that the crystallinity had decreased to 25%. This modified product was neutralized and dried by heating to prepare an SAP. The amount of base required to achieve a degree of neutralization of 90% was calculated from the pH titration results. One part (0.4 g) of purified succinic acid-modified cellulose was diluted with 19 parts of pure water, and then a 2% by mass aqueous solution of sodium hydroxide was added dropwise with stirring to achieve the required amount of base, thereby neutralizing the mixture. The neutralized product was dried by heating at 120°C for 1 hour in a blower dryer, and the dried product was pulverized to obtain an SAP. The CRC of this SAP was measured. X-ray diffraction analysis of this SAP also revealed that the degree of crystallinity was 21%, with almost no change before and after neutralization.

[0122] Comparative Example 4 (Modification in DMF and SAP Preparation) 100 parts by mass (0.3 g) of fibrous pulp, 200 parts by mass of succinic anhydride, 10 parts by mass of potassium carbonate, and 2,000 parts by mass of DMF were added to a test tube equipped with a magnetic stirrer and stirred at 125°C for 1 hour. After completion of the reaction, acetone was added in an amount five times the total volume of the reaction composition, and the mixture was stirred at room temperature to precipitate succinic acid-modified cellulose. Unreacted succinic anhydride was removed by vacuum filtration and acetone washing. The mixture was then vacuum dried at 45°C to obtain unneutralized succinic acid-modified cellulose. HPLC measurement and pH titration were performed to calculate the average degree of substitution. Subsequently, the mixture was neutralized with aqueous sodium hydroxide and dried by heating in the same manner as in Example 2 to obtain SAP, and the residual solvent content was measured by CRC and HPLC.

[0123] Comparative Example 5 (Modification in DMSO and Preparation of SAP) The same procedures as in Comparative Example 4 were carried out except that DMF was replaced with DMSO, and the residual solvent ratio and average degree of substitution of unneutralized succinic acid-modified cellulose, as well as CRC measurement of SAP and measurement of the residual solvent ratio were carried out. The CRC of SAP, the average degree of substitution at the stage of unneutralized succinic acid-modified cellulose, and the proportion of remaining solvent at the SAP stage are shown in Table 2. In a comparison between Example 2 and Comparative Examples 4 and 5, both showed water absorption and swelling, but the products that underwent reaction in a solvent still contained residual solvent even after purification and heat drying, confirming strong residua.

[0124] (Effects of Reaction Temperature and Base Catalyst) [Example 3] 100 parts by mass (0.5 g) of fibrous pulp, 1,000 parts by mass of succinic anhydride, and 10 parts by mass of potassium carbonate were added to a test tube equipped with a magnetic stirrer and stirred at 125°C for 1 hour. During the reaction, the succinic anhydride was melted, and the entire mixture was in a paste state. After removing the reaction product, it was crushed, washed with acetone, and vacuum dried in the same manner as in Example 1 to obtain unneutralized succinic acid-modified cellulose. HPLC measurement, pH titration, and X-ray diffraction were performed to calculate the residual solvent ratio, average degree of substitution, and degree of crystallinity. Neutralization was performed with a sodium phosphate buffer solution, and the proportion of dissolved components was measured.

[0125] Example 4 The same procedures as in Example 3 were carried out except that potassium carbonate was not added, and succinic acid-modified cellulose was produced and the proportion of dissolved components, average degree of substitution, proportion of remaining solvent, and degree of crystallinity were measured.

[0126] [Example 5] The same procedures as in Example 3 were carried out to produce succinic acid-modified cellulose, and measurements of the proportion of dissolved components, average degree of substitution, proportion of remaining solvent, and degree of crystallinity were carried out, except that the reaction temperature was 110° C. During the modification reaction, succinic anhydride was not melted, and the entire product had a solid appearance.

[0127] Example 6 The same procedures as in Example 5 were carried out except that potassium carbonate was not added, and succinic acid-modified cellulose was produced and the proportion of dissolved components, average degree of substitution, proportion of remaining solvent, and degree of crystallinity were measured. The results of Examples 3 and 4 and Examples 5 and 6 in Table 3 show that the addition of potassium carbonate as a base catalyst increased the soluble component ratio and the average degree of substitution. In addition, a comparison of Examples 3 and 5 shows that an increase in the reaction temperature also increased the soluble component ratio, indicating that both the addition of a base catalyst and an increase in reaction temperature had the effect of accelerating the modification reaction.

[0128] [Example 7] Using a twin-screw kneader comprising a Laboplastomill 3S150 manufactured by Toyo Seiki Seisaku-sho, Ltd. connected to a roller mixer, the inside of a reaction vessel was heated to 125°C with an electric heating jacket, and then 100 parts by mass (3 g) of fibrous pulp, 200 parts by mass of succinic anhydride, and 10 parts by mass of potassium carbonate were charged into the kneader and kneaded for 30 minutes. After removing the kneaded product, it was pulverized, washed with acetone, dried, diluted with pure water, and neutralized with an aqueous sodium hydroxide solution in the same manner as in Example 2, and the crystallinity and average degree of substitution before neutralization, as well as the CRC and residual solvent ratio of the crosslinked SAP were measured.

[0129] [Example 8] The same operations as in Example 7 were performed, except that 10 parts by mass of potassium carbonate was replaced with 7 parts by mass of potassium hydrogencarbonate, which was the equimolar amount, to prepare succinic acid-modified cellulose, and the CRC, average degree of substitution, proportion of residual solvent, and degree of crystallinity were measured.

[0130] [Example 9] The same operations as in Example 7 were performed, except that 10 parts by mass of potassium carbonate was replaced with 6 parts by mass of sodium hydrogencarbonate, which was the equimolar amount, to prepare succinic acid-modified cellulose, and the CRC, average degree of substitution, proportion of residual solvent, and degree of crystallinity were measured. The results of Examples 7, 8, and 9 in Table 4 show that all of them had similar average degrees of substitution, and that the reaction proceeded in the same manner even when the base catalyst was changed to another alkali metal catalyst.

[0131] (Effect of Amorphization) [Example 10] A succinic acid-modified cellulose neutralized with a sodium phosphate buffer solution was obtained by the same procedure as in Example 1, except that, in the kneading in the kneader, powdery pulp having a particle size of 150 μm or less obtained by pulverizing fibrous pulp in a planetary ball mill was used instead of the fibrous pulp. Subsequently, the proportion of dissolved components, the average degree of substitution, the proportion of residual solvent, and the degree of crystallinity were measured.

[0132] Comparing Example 1 and Example 10, the cellulose having a smaller average particle size, lower crystallinity, and a higher degree of amorphousness was used as the raw material, resulting in a higher proportion of dissolved components and a more hydrophilic modified product.

[0133] Example 11 The same procedure as in Example 1 was carried out up to the stage of obtaining unneutralized succinic acid-modified cellulose. HPLC analysis confirmed no residual solvent. One part (2.2 g) of succinic acid-modified cellulose was diluted with 7.5 parts of pure water, and then 1.5 parts of a 4.8% by weight aqueous solution of sodium hydroxide was added dropwise while stirring to obtain a dispersion of neutralized succinic acid-modified cellulose. Three parts of a 0.05% by weight aqueous solution of Denacol EX-810 (manufactured by Nagase ChemteX) as a crosslinking agent were added to 100 parts (4.5 g) of this dispersion. The mixture was stirred until homogeneous, and then heated and dried in a 120°C fan oven for 45 minutes to obtain a crosslinked solid. CRC measurements revealed a CRC of 13.5 g / g in saline and 23.5 g / g in pure water.

[0134] 1: Pulp raw material (compressed form) 2: Process of defibrating, pulverizing and amorphizing 3: Reaction process of modifying with reactant under solvent-free conditions 4: Purification process of separating reactant 5: Process of neutralizing, crosslinking and drying 6: Cellulose SAP 7: Distillation process

Claims

1. A method for producing polybasic acid salt-modified cellulose, comprising the steps of obtaining polybasic acid-modified cellulose using a raw material composition containing cellulose and a polybasic acid and / or its acid anhydride, and neutralizing the polybasic acid-modified cellulose, wherein the raw material composition contains less than 5,000 ppm by mass of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine, and the mass proportion of an ionic liquid having an imidazolium ion is less than 5,000 ppm.

2. A method for producing polybasic acid salt-modified cellulose as described in claim 1, characterized in that the raw material composition contains at least one functional group selected from the group consisting of a sulfoxide group, a pyridyl group, and an amide group, and the mass proportion of an organic solvent that is liquid at 20°C and 1 atmosphere is less than 5000 ppm.

3. A method for producing polybasic acid-modified cellulose as described in claim 1 or 2, characterized in that the raw material composition contains at least one functional group selected from the group consisting of a sulfoxide group, a pyridyl group, and an amide group, and the mass proportion of the liquid organic solvent in the process of obtaining the polybasic acid-modified cellulose is less than 5000 ppm.

4. A method for producing polybasic acid salt-modified cellulose described in any one of claims 1 to 3, characterized in that the raw material composition contains at least one functional group selected from the group consisting of a sulfoxide group, a pyridyl group, and an amide group, has a molecular weight of 130 or less, and has a mass proportion of an organic solvent and / or an organic catalyst of less than 5,000 ppm.

5. A method for producing polybasic acid salt-modified cellulose described in any one of claims 1 to 4, characterized in that the raw material composition has a mass proportion of an ionic liquid having at least one ion selected from the group consisting of ammonium, phosphonium, pyridinium, and imidazolium ions of less than 5000 ppm.

6. A method for producing polybasic acid-modified cellulose according to any one of claims 1 to 5, characterized in that the step of obtaining the polybasic acid-modified cellulose is carried out using less than 30% by mass of a base catalyst relative to 100% by mass of the polybasic acid and / or its acid anhydride.

7. The method for producing polybasic acid salt-modified cellulose according to claim 6, wherein the base catalyst is a solid alkaline compound.

8. The method for producing polybasic acid salt-modified cellulose according to claim 7, wherein the solid alkaline compound is at least one selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal hydrogen carbonates.

9. A method for producing polybasic acid-modified cellulose according to any one of claims 1 to 8, characterized in that the step of obtaining the polybasic acid-modified cellulose is carried out at a temperature exceeding 120°C.

10. A method for producing polybasic acid salt-modified cellulose described in any one of claims 1 to 9, characterized in that the mass proportion of the polybasic acid and / or its acid anhydride in the raw material composition is 50 mass% or more relative to 100 mass% of the mass proportion of the cellulose.

11. A method for producing a polybasic acid salt-modified cellulose according to any one of claims 1 to 10, characterized in that the cellulose has an average particle size of 400 μm or less.

12. A method for producing a polybasic acid salt-modified cellulose according to any one of claims 1 to 11, characterized in that the cellulose has a crystallinity of 75% or less.

13. A method for producing polybasic acid salt-modified cellulose according to any one of claims 1 to 12, characterized in that the polybasic acid anhydride is a cyclic polybasic acid anhydride.

14. A method for producing polybasic acid salt-modified cellulose according to any one of claims 1 to 13, characterized in that the polybasic acid and / or its acid anhydride is a polybasic carboxylic acid and / or its acid anhydride.

15. A method for producing polybasic acid salt-modified cellulose according to any one of claims 1 to 14, characterized in that the polybasic acid and / or its acid anhydride is a dibasic acid and / or its acid anhydride.

16. A method for producing polybasic acid salt-modified cellulose according to any one of claims 1 to 15, characterized in that the polybasic acid and / or its acid anhydride is succinic acid and / or its acid anhydride.

17. A method for producing a polybasic acid-modified cellulose according to any one of claims 1 to 16, characterized in that the polybasic acid-modified cellulose is a polybasic acid monoesterified cellulose.

18. A method for producing polybasic acid-modified cellulose according to any one of claims 1 to 17, characterized in that the polybasic acid-modified cellulose has an average degree of substitution of cellulose with polybasic acid of 1 or more per glucose residue.

19. A method for producing crosslinked polybasic acid-modified cellulose, comprising the steps of obtaining polybasic acid-modified cellulose using a raw material composition containing cellulose and a polybasic acid and / or its acid anhydride, neutralizing the polybasic acid-modified cellulose, and crosslinking the polybasic acid-modified cellulose, wherein the raw material composition contains less than 5000 ppm by mass of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine, and the mass proportion of an ionic liquid having an imidazolium ion is less than 5000 ppm.

20. A polybasic acid salt-modified cellulose composition comprising a polybasic acid salt-modified cellulose, in which the mass proportion of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine is less than 5000 ppm, and the mass proportion of an ionic liquid having an imidazolium ion is less than 5000 ppm.

21. The polybasic acid salt-modified cellulose composition according to claim 20, characterized in that the polybasic acid salt-modified cellulose has an average degree of substitution of cellulose with polybasic acid salt of 1 or more per glucose residue.

22. A crosslinked polybasic acid salt-modified cellulose composition comprising crosslinked polybasic acid salt-modified cellulose, in which the mass proportion of at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, and 4-dimethylaminopyridine is less than 5000 ppm, and the mass proportion of an ionic liquid having an imidazolium ion is less than 5000 ppm.

23. A crosslinked polybasic acid salt-modified cellulose composition, which is a crosslinked product of the polybasic acid salt-modified cellulose composition according to claim 20 or 21.

24. A polybasic acid salt-modified cellulose composition according to claim 20 or 21, or a cross-linked polybasic acid salt-modified cellulose composition according to claim 22 or 23, which is used as a raw material for sanitary materials, agricultural and horticultural products, cosmetics, or detergents.

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