Method for producing polybasic acid salt modified cellulose

Abstract

The purpose of the present invention is to provide a method for efficiently producing a polybasic acid salt modified cellulose that has a low organic solvent content and a high degree of substitution with a polybasic acid and / or an acid anhydride. The present invention is a method for producing a polybasic acid salt modified cellulose, said method comprising a reaction step for using a raw material composition that contains cellulose, an alkali catalyst, and a polybasic acid and / or an acid anhydride thereof to obtain a polybasic acid modified cellulose, and a neutralization step for neutralizing the polybasic acid modified cellulose, said method being characterized in that the reaction step is carried out using a kneader.

Description

Method for producing polybasic acid salt-modified cellulose

[0001] The present invention relates to a method for producing polybasic acid salt-modified cellulose, and more particularly to a method for producing polybasic acid salt-modified cellulose 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 sanitary materials, detergents, etc. In particular, water-absorbent resins (SAP / Super Absorbent Polymers) having a structure in which a hydrophilic polymer is 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 to 5). 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 known as a biomass-derived material that can be used as a hydrophilic polymer raw material, similar to cellulose. Starch exhibits high dispersibility and solubility in water and certain solvents such as dimethyl sulfoxide, making it easy to modify. However, starch is an edible raw material, raising concerns about competition with food applications. Cellulose, on the other hand, is a non-edible raw material and does not compete with food applications, but it has significantly higher crystallinity than starch and other polysaccharides, and its dispersibility and solubility in water and solvents are low. For this reason, it has generally been very difficult to uniformly modify it to produce a hydrophilic polymer.

[0005] Japanese Patent Application Publication No. 60-137001 Japanese Patent Application Publication No. 2009-293167 Chinese Patent Application Publication No. 115819630 International Publication No. 2012 / 064741 Special Publication No. 2017-525784

[0006] As described above, methods for obtaining hydrophilic polymers and cellulose nanofibers by modifying cellulose have been reported, but because cellulose has low reactivity, it is not easy to obtain modified cellulose with a high degree of substitution in which a compound that imparts hydrophilicity has been sufficiently reacted. Furthermore, when polybasic acid salt-modified cellulose obtained by modifying cellulose with a polybasic acid and / or its acid anhydride is used as a raw material for water-absorbent resins and the like, a polybasic acid salt-modified cellulose with a low content of organic solvents that have adverse effects on the human body, such as toxicity and odor, is required. Therefore, a method for producing polybasic acid salt-modified cellulose with a low content of organic solvents and a high degree of substitution with a polybasic acid and / or its acid anhydride is needed.

[0007] The present invention has been made in view of the above-mentioned current situation, and an object of the present invention is to provide a method for efficiently producing polybasic acid salt-modified cellulose which has a low organic solvent content and a high degree of substitution with a polybasic acid and / or its acid anhydride.

[0008] The present inventors have investigated a method for efficiently producing polybasic acid salt-modified cellulose that contains a small amount of organic solvent and has a high degree of substitution with a polybasic acid and / or its acid anhydride. They have found that by using a raw material composition containing cellulose, a polybasic acid and / or its acid anhydride, and an alkali catalyst, and reacting the cellulose with the polybasic acid and / or its acid anhydride in a kneader, the modification reaction of cellulose with the polybasic acid and / or its acid anhydride can proceed in a short time without using a solvent, thereby producing polybasic acid-modified cellulose that is highly substituted with a polybasic acid and / or its acid anhydride. They have also found that neutralizing the resulting polybasic acid-modified cellulose can efficiently produce polybasic acid salt-modified cellulose that does not contain an organic solvent and has a high degree of substitution with a polybasic acid and / or its acid anhydride. Furthermore, the present inventors focused on the amount of alkali catalyst added and discovered that the average degree of substitution of cellulose after modification is closely related to the amount of alkali catalyst added relative to the amount of polybasic acid and / or its acid anhydride used as the modifying agent. They also found that by appropriately setting the amount of alkali catalyst added, it is possible to easily obtain polybasic acid salt-modified cellulose that serves as a high-quality hydrophilic polymer. These findings led to the realization of a brilliant solution to the above-mentioned problems, and led to the completion of the present invention. Patent Documents 1 and 3 describe the addition of an alkali catalyst to promote modification, but do not describe the effects of the amount ratio relative to the polybasic acid and / or its acid anhydride, making it difficult to envision the present invention.

[0009] That is, the present invention (1) is a method for producing polybasic acid-modified cellulose, which comprises a reaction step of obtaining polybasic acid-modified cellulose using a raw material composition containing cellulose, a polybasic acid and / or an acid anhydride thereof, and an alkali catalyst, and a neutralization step of neutralizing the polybasic acid-modified cellulose, wherein the reaction step is carried out using a kneader.

[0010] 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 1.5 to 5.5 parts by mass of a polybasic acid and / or anhydride thereof per part by mass of cellulose.

[0011] The present invention (3) is the method for producing polybasic acid salt-modified cellulose according to the present invention (1) or (2), characterized in that the raw material composition contains a base catalyst in an amount of 0.1 to 200 mol % in terms of base molar equivalents relative to the polybasic acid and / or its acid anhydride.

[0012] 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 raw material composition contains 0.025 to 0.5 parts by mass of a base catalyst per 1 part by mass of the polybasic acid and / or its acid anhydride.

[0013] 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), characterized in that the kneader is a multi-screw kneader.

[0014] The present invention (6) is the method for producing polybasic acid salt-modified cellulose according to the present invention (5), wherein the multi-screw kneader has an intermeshing structure.

[0015] The present invention (7) is the method for producing polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (6), characterized in that the reaction step is carried out at a temperature equal to or higher than the melting point of the polybasic acid and / or its acid anhydride.

[0016] The present invention (8) is the method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (7), characterized in that the reaction step is carried out using a raw material composition in an amount such that a filling rate in a kneader is 30% or more.

[0017] The present invention (9) is the method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (8), characterized in that the raw material composition has a total content of the organic solvent, the organic catalyst, and the ionic liquid of less than 10% by mass, based on 100% by mass of the raw material composition.

[0018] The present invention (10) is the method for producing polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (9), characterized in that the polybasic acid anhydride is a cyclic polybasic acid anhydride.

[0019] 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 polybasic acid and / or its acid anhydride is a polybasic carboxylic acid and / or its acid anhydride.

[0020] The present invention (12) is the method for producing polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (11), characterized in that the polybasic acid and / or its acid anhydride is a dibasic acid and / or its acid anhydride.

[0021] The present invention (13) is the method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (12), wherein the polybasic acid and / or its acid anhydride is succinic acid and / or its acid anhydride.

[0022] The present invention (14) is the method for producing a polybasic acid-modified cellulose according to any one of the present inventions (1) to (13), characterized in that the polybasic acid-modified cellulose is a polybasic acid monoesterified cellulose.

[0023] The present invention (15) is the method for producing a polybasic acid-modified cellulose according to any one of the present inventions (1) to (14), wherein the polybasic acid-modified cellulose has an average degree of substitution of polybasic acid per glucose residue of 1 or more.

[0024] 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), characterized in that the cellulose is regenerated pulp.

[0025] The present invention (17) is the method for producing polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (16), wherein the base catalyst is one or more selected from the group consisting of sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

[0026] The present invention (18) is a method for producing the polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (17), characterized by crosslinking the polybasic acid salt-modified cellulose.

[0027] The present invention (19) 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, the mass proportion of an ionic liquid having an imidazolium ion is less than 5000 ppm, and the average degree of substitution of the cellulose with the polybasic acid salt per glucose residue is 1 or more.

[0028] The present invention (20) is the polybasic acid salt-modified cellulose composition of the present invention (19), which is used as a raw material for sanitary materials, agricultural and horticultural supplies, cosmetics, or detergents.

[0029] The method for producing polybasic acid salt-modified cellulose of the present invention is a useful method for producing polybasic acid salt-modified cellulose with a high degree of substitution with a polybasic acid and / or its acid anhydride without using an organic solvent, and can be suitably used as a method for producing a raw material for a biomass-derived water-absorbent resin.

[0030] FIG. 1 is a diagram showing an example of a conceptual diagram of a cutaway side of a continuous co-rotating intermeshing twin-screw kneader according to the production method of the present invention. FIG. 2 is a diagram showing an example of a conceptual diagram of a cross section of a sealed structure part in a plane perpendicular to the rotation axes of a continuous co-rotating intermeshing twin-screw kneader according to the production method of the present invention. FIG. 3 is a diagram showing an example of a conceptual diagram of a cutaway side of a continuous co-rotating tangential twin-screw kneader according to the production method of the present invention. FIG. 4 is a diagram showing an example of a conceptual diagram of a cross section of a sealed structure part in a plane perpendicular to the rotation axes of a continuous co-rotating tangential twin-screw kneader according to the production method of the present invention. FIG. 5 is a diagram showing an example of a reaction formula between cellulose and a polybasic acid anhydride according to the production method of the present invention. FIG. 6 is a diagram illustrating each step according to the production method of the present invention.

[0031] 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.

[0032] [Method for Producing Polybasic Acid Salt-Modified Cellulose] <Reaction Step for Obtaining Polybasic Acid Salt-Modified Cellulose> The production method of the present invention includes a reaction step for obtaining polybasic acid-modified cellulose using a raw material composition containing cellulose, a polybasic acid and / or its acid anhydride, and an alkali catalyst. Mixing the raw material composition containing cellulose, a polybasic acid and / or its acid anhydride, and an alkali catalyst through strong mechanical kneading using a kneader allows these three components to be thoroughly mixed without the use of a solvent, and the reaction between cellulose and the polybasic acid and / or its acid anhydride can be sufficiently promoted to obtain polybasic acid-modified cellulose with a high degree of substitution. Note that, because basicity is generally referred to as alkalinity, the base catalyst may also be referred to as an alkali catalyst in this specification. In other words, the terms base catalyst and alkali catalyst are treated as synonyms.

[0033] (Cellulose) Examples of the cellulose include cotton, wood-derived pulp, compressed pulp, bacterial cellulose, lignocellulose, regenerated cellulose (regenerated fibers such as cellophane, cupra, and lyocell), and microcrystalline cellulose. 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 in the form of a compressed plate or flake, a fibrous form, or a powder. Furthermore, while cellulose raw materials are hygroscopic, the moisture contained in the cellulose raw material is distinguished from water added separately as needed 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. Therefore, it is preferable that the cellulose raw material 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. 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.

[0034] 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.

[0035] 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.

[0036] The average particle size and crystallinity can be adjusted, for example, by previously defibrating or pulverizing the cellulose used in the reaction step. The defibrating step is not particularly limited, and can be performed, for example, using a cutter mill or the like. The pulverizing step is not particularly limited, and can be performed, for example, using a screw extruder such as a kneader or a meat chopper, or a pulverizer such as a ball mill. The defibrating step and the pulverizing step may each be performed continuously or intermittently. The defibrating time and the pulverizing time can be set as appropriate. The average particle size and crystallinity can also be adjusted as appropriate by classifying the cellulose using a sieve or a fluid such as a liquid or airflow, or by using other steps (for example, a granulation step, a decomposition step).

[0037] (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 anhydride, 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.

[0038] The polybasic acid anhydride is preferably a cyclic polybasic acid anhydride. The polybasic acid is preferably succinic acid or maleic acid. By heating a polybasic acid, a polybasic acid anhydride or a cyclic polybasic acid anhydride can be prepared. The polybasic acid and / or its acid anhydride is preferably 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, and more preferably succinic acid and / or its acid anhydride.

[0039] The raw material composition preferably contains 1.5 to 5.5 parts by mass of a polybasic acid and / or its acid anhydride per 1 part by mass of cellulose. More preferably, it contains 1.8 to 4 parts by mass, and even more preferably, it contains 2 to 3.5 parts by mass, per 1 part by mass of cellulose. By using a raw material composition containing a polybasic acid and / or its acid anhydride in such a ratio, it is possible to obtain polybasic acid-modified cellulose with a higher degree of substitution with a polybasic acid and / or its acid anhydride, while suppressing increases in costs due to an excess of polybasic acid and / or its acid anhydride and preventing decreases in reactivity due to phase separation of excess modifier from the kneaded product.

[0040] In the reaction step, the molar ratio of glucose units in the cellulose to the polybasic acid can be set as appropriate, but is preferably, for example, 1 / 1 to 1 / 10. A blending ratio within this range is preferred from the standpoint of yield and economy. More preferably, it is 2 / 3 to 1 / 8, and even more preferably, it is 1 / 2 to 1 / 7. Particularly preferably, it is 1 / 3 to 1 / 5.

[0041] (Base Catalyst) The base catalyst used in the production method of the present invention 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 sodium carbonate, potassium carbonate, rubidium carbonate, cesium carbonate, lead carbonate, zinc carbonate, and nickel carbonate; and bicarbonates such as sodium bicarbonate, potassium bicarbonate, rubidium bicarbonate, and cesium bicarbonate. One or more of these can be used. Among these, carbonates and bicarbonates are preferred.

[0042] 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.

[0043] 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.

[0044] The amount of base catalyst used is preferably 0.1 to 200 mol % in terms of base molar equivalent relative to the polybasic acid and / or its acid anhydride as the modifying agent, more preferably 1 to 100 mol %, even more preferably 2 to 50 mol %, and particularly preferably 5 to 25 mol %. The base molar equivalent here refers to the amount of base catalyst used corrected for its valence as a base. For example, the base molar equivalent is 1 mol % for 1 mol % of sodium hydroxide, a monovalent base catalyst, and 2 mol % for 1 mol % of sodium carbonate, a divalent base catalyst. If the amount of base catalyst added 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, unnecessary side reactions may occur in the reaction composition, or the viscosity of the reaction composition may increase, resulting in a decrease in kneading uniformity, which may result in a longer reaction time, a lower degree of substitution, or overload or damage to the kneader, which is undesirable. It has also been found that the optimal amount of base catalyst used varies depending on the amount of polybasic acid and / or its acid anhydride as the modifying agent. It is believed that the viscosity of the reaction composition changes depending on the amount of base catalyst used, and that the optimum point changes as a result of changes in the kneading uniformity of the reaction composition and the applied shear force. Therefore, it is preferable to adjust the amount of base catalyst used based on the amount of polybasic acid and / or its acid anhydride used. When two or more types of base catalysts are used, the above-mentioned substance amount ratio is the total substance amount ratio.

[0045] Furthermore, the raw material composition preferably contains 0.025 to 0.5 parts by mass of the base catalyst per 1 part by mass of the polybasic acid and / or its acid anhydride as the modifying agent, more preferably 0.03 to 0.4 parts by mass, even more preferably 0.04 to 0.3 parts by mass, and particularly preferably 0.05 to 0.2 parts by mass. 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, unnecessary side reactions may occur in the reaction composition, or the viscosity of the reaction composition may increase, resulting in a lower kneading uniformity, which may result in a longer reaction time, a lower degree of substitution, or overload or damage to the kneader, which is undesirable. Furthermore, in the present invention, it has been found that the optimal amount of base catalyst used varies depending on the amount of the polybasic acid and / or its acid anhydride as the modifying agent. It is believed that the viscosity of the reaction composition changes depending on the amount of base catalyst used, and that the optimum point changes as a result of changes in the kneading uniformity of the reaction composition and the applied shear force. Therefore, it is preferable to adjust the amount of base catalyst added based on the amount of polybasic acid and / or its acid anhydride used. When two or more types of base catalysts are used, the above mass ratio is the mass ratio of their total.

[0046] (Solvent, Organic Catalyst) The reaction step can be carried out without using a solvent or an organic catalyst, and is preferably carried out without using a solvent or an organic catalyst. However, either or both of a solvent and an organic catalyst may be used. Here, the solvent refers to a substance having a melting point below the temperature at which the reaction step is carried out. When the reaction step is carried out using a solvent, examples of the solvent include water, organic solvents, ionic liquids, and combinations thereof. Among these, one or more of organic solvents containing sulfur atoms and / or nitrogen atoms, and ionic liquids containing at least one ion selected from the group consisting of ammonium, phosphonium, pyridinium, and imidazolium, can be preferably used. When an organic catalyst is used, an organic catalyst containing sulfur atoms and / or nitrogen atoms can be preferably used. Note that some organic catalysts can also be used as organic solvents that dissolve cellulose and / or its derivatives at temperatures above the melting point, but it is preferable not to use them for either role.

[0047] Even when a solvent is used in the reaction step, the amount of solvent used is preferably small, preferably less than 10% by mass of 100% by mass of the raw material composition used in the reaction step. More preferably, it is 5% by mass or less of 100% by mass of the raw material composition, and even more preferably, it is 1% by mass or less of 100% by mass of the raw material composition. The raw material composition may not contain a specified organic solvent or an ionic liquid. When the solvent is water, the amount of water used refers to water optionally added separately from other raw materials, and does not include water resulting from elimination by thermal condensation of cellulose and acid, or water present in undried raw materials.

[0048] Furthermore, the raw material composition preferably has a total content of the organic solvent, organic catalyst, and ionic liquid of less than 10% by mass relative to 100% by mass of the raw material composition. More preferably, the total content is less than 0.5% by mass (5000 ppm), even more preferably less than 0.4% by mass (4000 ppm), particularly preferably less than 0.3% by mass (3000 ppm), particularly preferably less than 0.2% by mass (2000 ppm), and most preferably less than 0.1% by mass (1000 ppm). Even when a compound serves both as a solvent and a catalyst, the total content is calculated as one substance. The raw material composition may not contain one or more of the specified organic solvent, organic catalyst, and ionic liquid. Such a raw material composition can prevent the residue of toxic or strongly odorous solvents and prevent coloration, resulting in a higher quality polybasic acid salt-modified cellulose.

[0049] 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.

[0050] (Kneader) The kneader used in the production method of the present invention is not limited as long as it can knead the raw material composition containing cellulose, a polybasic acid and / or its acid anhydride, and an alkali catalyst. The use of a kneader makes it possible to increase the concentration and shorten the reaction time, thereby significantly improving production efficiency. Specifically, any device that can knead the raw material composition while applying mechanical shear force, such as a ball mill, rod mill, bead mill, roller mill, roll mill, planetary mixer, pan mixer, kneader, or blender, can be suitably used. The kneader may be of either a continuous or batch type. An example of a single-screw continuous kneader is the Buss Kneader (manufactured by Buss Corporation), which is a single-screw reciprocating continuous kneader.

[0051] A multi-screw kneader is preferred as the kneader used in the production method of the present invention. The use of a multi-screw kneader allows for the application of stronger mechanical shear and compression forces to the raw material composition via multiple kneading shafts, thereby more effectively kneading the raw material composition and accelerating the modification reaction. This allows for more thorough reaction between cellulose and a polybasic acid and / or its acid anhydride, resulting in the production of polybasic acid-modified cellulose with a higher degree of substitution. Examples of multi-screw kneaders include twin-screw, triple-screw, quadruple-screw, and eight-screw kneaders. 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 either an open or closed type. The rotors of the kneader may be tangential or intermeshing, with intermeshing being preferred due to the powerful kneading capabilities. The tangential type is a type in which the rotors are arranged so that their movable ranges do not overlap, while the intermeshing type is a type in which the rotors are arranged so that their movable ranges overlap and they intermesh. Figures 2 and 4 show conceptual cross-sections of the sealed structure parts of a tangential twin-screw kneader and an intermeshing twin-screw kneader, taken on a plane perpendicular to the rotation axes.Specific examples of the kneading machine include a CKH-type continuous kneader (manufactured by Honda Iron Works Co., Ltd.), a twin-screw extruder TEX (manufactured by The Japan Steel Works, Ltd.), a twin-screw extruder TEXαIII (manufactured by The Japan Steel Works, Ltd.), a continuous kneader (manufactured by Dalton Co., Ltd.), a KRC hybrid reactor (manufactured by Kurimoto Iron Works, Ltd.), a KRC kneader (Kurimoto-Readco Continuous Kneader (manufactured by Kurimoto Iron Works, Ltd.)), a KEX extruder (manufactured by Kurimoto Iron Works, Ltd.), and a KEXD extruder (manufactured by Kurimoto Iron Works, Ltd.). Examples of the multi-screw extruder include the twin-screw extruder TEX-SSG (manufactured by Toshiba Machine Co., Ltd.), the twin-screw extruder TEX-CS (manufactured by Toshiba Machine Co., Ltd.), the twin-screw extruder TEX-SX (manufactured by Toshiba Machine Co., Ltd.), the twin-screw extruder TEX-DS (manufactured by Toshiba Machine Co., Ltd.), the twin-screw extruder TEX-A (manufactured by Toshiba Machine Co., Ltd.), the twin-screw extruder TEX-B (manufactured by Toshiba Machine Co., Ltd.), the twin-screw extruder TEX-BS (manufactured by Toshiba Machine Co., Ltd.), and the four-screw and eight-screw extruders WDR series (manufactured by Technovel Corporation). A twin-screw extruder is more preferred as the multi-screw extruder. The twin-screw kneader is advantageous in that it is possible to procure a large-sized machine, which makes it easy to expand the scale of production, and it also allows for continuous production. Therefore, in a preferred embodiment of the present invention, the apparatus used in the reaction step is a continuous twin-screw kneader.

[0052] (Multi-shaft kneader) In one example of the manufacturing method according to the present invention, a multi-shaft kneader having an inlet, a main body incorporating multiple rotors, and a discharge outlet is used, as shown in Figures 1 and 2. Each rotor has a kneading means. In particular, the multi-shaft kneader shown in Figure 1 is a continuous type, in which raw material compositions continuously fed into the main body from the inlet are kneaded by the kneading means of each rotor and continuously removed from the discharge outlet. In the present invention, the main body means the body part in which multiple rotors and pulverizing means are installed, and is also called a barrel, trough, casing, etc.

[0053] In order to maintain the reaction temperature, the multi-shaft kneader preferably has a heating means and / or a heat-retaining means. The heating means and / or the heat-retaining means are not particularly limited, and examples thereof include a heating means using direct heat transfer by convection and / or indirect heat transfer by heat conduction from the heating surface (surface in contact with the kneaded material, heat source part) of the multi-shaft kneader heated by a heat medium, and specific examples thereof include a ventilation heating type for direct heat transfer and an outer wall heating type for indirect heat transfer. Furthermore, a heat medium can also be circulated inside the multiple rotating bodies to serve as a heating means and / or a heat-retaining means.

[0054] The multi-shaft kneader used in the production method according to the present invention may be a vertical type (the direction of travel of the kneaded material is the up-down direction), or a horizontal or horizontal type (the direction of travel of the kneaded material is the left-right direction or the horizontal direction). In addition, both vertical and horizontal multi-shaft kneaders may be inclined at an angle of 0° to 90° with respect to the horizontal direction.

[0055] The shape of the rotor is not particularly limited as long as the effects of the present invention can be obtained. Generally, the type of grinding means possessed by the rotor can be changed by replacing part or all of the rotor. Depending on the kneading machine, the shape of the rotor can be changed by attaching multiple disks to a rod-shaped rotating shaft. By changing the type of disk, the compression and shearing action on the kneaded material can be changed, thereby changing the grinding effect. Disks may also be called chips, paddles, elements, kneading elements, rotors, etc. The shape of the disk is not particularly limited and can be appropriately selected from disks, approximately elliptical shapes, approximately triangular shapes, etc. It is also possible to use a combination of disks of different shapes, and their arrangement is appropriately adjusted from the perspective of the shear force and energy required for the reaction.

[0056] The rotation direction of the multiple rotors may be a synchronous type, where each rotor rotates in the same direction, or a counter-rotating type, where each rotor rotates in the opposite direction. A synchronous type device can be expected to have self-cleaning properties, while a counter-rotating type device can be expected to have strong shearing forces. The rotation direction of each rotor is appropriately selected in combination with the arrangement (disk pattern) of the grinding means described below.

[0057] A structure in which the cross section of the main body perpendicular to the rotation axis of the rotor surrounds the rotation axis is called a sealed structure, while a structure in which part or all of the cross section of the main body perpendicular to the rotation axis is open is called an open structure. In a sealed structure, shear forces and pressure are generated between the rotor and the main body wall, generally resulting in stronger kneading than in an open structure, promoting the reaction. Therefore, it is preferable that part or all of the main body of the kneader has a sealed structure. For example, a pressure kneader without an inlet has an entirely sealed structure. In a continuous multi-shaft kneader such as that shown in FIG. 1, the inlet 102, the chemical inlet 112, and the outlet 108 are open structures, but the main body cross section between them has a sealed structure as shown in FIG. 2, allowing for powerful kneading. In the case of the main body of a multi-shaft kneader, the proportion of the sealed structure portion in the multi-shaft kneader can be evaluated by the ratio of the length of the sealed structure portion of the rotary shaft to the total length of the rotary shaft of the rotor part that comes into contact with the kneaded material and has a disk or the like attached, excluding parts that do not come into contact with the kneaded material, such as bearings. For example, in a continuous multi-shaft kneader having a rotor with a length of 100 cm at the portion where the disk is attached, if the length of the rotor shaft of the open-structured portion such as the inlet and outlet is 40 cm and the length of the closed-structured portion is 60 cm, the closed-structure proportion is 60%. The total proportion of the closed-structured portion in the entire multi-shaft kneader is arbitrary, but a higher proportion of the closed-structured portion enables more powerful kneading. Furthermore, while the proportion of the closed-structured portion can be up to 100%, in the case of a continuous multi-shaft kneader with an inlet perpendicular to the rotor, the inlet is an opening, so the proportion of the closed-structured portion is less than 100%. Therefore, the closed-structured portion of the entire body length is preferably 50% to less than 100%, more preferably 60% to 99%, more preferably 70% to 98%, and even more preferably 80% to 97%.

[0058] In a kneader having a sealed structure, the filling rate can be defined as the volume ratio of the material to be kneaded to the capacity inside the main body. A higher filling rate makes it easier for pressure to be generated during kneading, kneading the material more strongly and promoting reaction. In addition, a high filling rate prevents the material from rotating together with the rotating body, resulting in insufficient kneading. Therefore, a higher filling rate is preferable. The filling rate V [%] can be calculated using the following formula (1): Filling rate V = A / B x 100 ... formula (1) Where, A [m ３ ] is the volume of the kneaded material, and B [m ３ ] is the internal volume of the main body excluding the volume of the rotor and the portions corresponding to the inlet and outlet. The kneaded material volume A and the volume B of the main body may be either calculated or measured values. In addition, when calculating the kneaded material volume A, if there is no significant change in volume due to gasification during the reaction, etc., it is desirable to derive the kneaded material volume A from the sum of the volumes of the raw materials before being added in order to simplify the calculation. In addition, in a continuous multi-shaft kneader, the filling rate can be calculated by using the volume of the kneaded material remaining inside the kneader at a certain time as A and the internal volume of the main body excluding the portions corresponding to the inlet and outlet as B.

[0059] 1 and 2 show conceptual diagrams of a continuous, co-rotating, intermeshing twin-screw kneader as an example. FIG. 1 is a cutaway side view of a twin-screw kneader 100, and is equipped with an inlet 102, a main body 104, two rotors 106, an outlet 108, a drive unit 110, and a chemical inlet 112 for use during kneading. The main body 104 is also referred to as a barrel. FIG. 2 is a cross-sectional view of the sealed structure portion of the twin-screw kneader 100, taken along a plane perpendicular to the rotation axis, and is equipped with the sealed main body 104 and two intermeshing rotors 106, which rotate in the same direction to knead the raw material composition.

[0060] The reaction step in the production method of the present invention is preferably carried out using an amount of raw material composition that results in a filling rate of 30% or more in the kneader. When the filling rate in the kneader is 30% or more, the raw material composition is more thoroughly kneaded in the kneader by the movement of the kneading shaft of the kneader. The filling rate in the kneader is more preferably 40% or more, and even more preferably 60% or more. Furthermore, the filling rate in the kneader is preferably 100% or less. If the filling rate in the kneader is too high, there is little void space in the kneader, which hinders the flow of the raw material composition and prevents it from being thoroughly kneaded, which may result in the generation of portions that are insufficiently kneaded. The filling rate in the kneader is more preferably 90% or less.

[0061] In the reaction step of the production method of the present invention, the power can be calculated from the motor's power consumption and the raw material composition in the kneading device. The power per 1 g of raw material composition in the kneading device is preferably 0.01 to 1000 W / g. More preferably, it is 0.1 to 100 W / g, and even more preferably, it is 1 to 100 W / g. Kneading under such power conditions allows the raw material composition to be kneaded more efficiently while suppressing deterioration due to overheating, and allows the reaction between cellulose and a polybasic acid and / or its acid anhydride to proceed in a short period of time. The power per 1 g of raw material composition can be calculated by (power consumption of the motor during kneading [W] × motor efficiency during kneading − power consumption of the motor during idling [W] × motor efficiency during idling) / weight [g] of the raw material composition in the kneader.

[0062] The reaction step in the production method of the present invention is preferably carried out at a reaction temperature exceeding 120°C. It is also preferable that the reaction step be carried out at a reaction temperature exceeding the melting point of the polybasic acid and / or its acid anhydride. When the reaction is carried out at a reaction temperature exceeding the melting point of the polybasic acid and / or its acid anhydride, the polybasic acid and / or its acid anhydride function as a solvent in addition to functioning as a cellulose modifier in the kneader, making it easier to knead the entire raw material composition more uniformly, allowing the reaction between cellulose and the polybasic acid and / or its acid anhydride to proceed more efficiently. The upper limit of the reaction temperature is not particularly limited, but is usually 200°C or lower, preferably 180°C or lower.

[0063] 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.

[0064] The raw material composition may be charged into a reaction apparatus such as a reaction tank all at once, or may be supplied to the reaction apparatus continuously or intermittently.

[0065] (Polybasic acid-modified cellulose) In the reaction step of the production method of the present invention, cellulose is reacted with a polybasic acid and / or its acid anhydride to produce polybasic acid-modified cellulose. The polybasic acid-modified cellulose obtained in the reaction step is preferably polybasic acid monoesterified cellulose.

[0066] The polybasic acid-modified cellulose preferably has an average degree of substitution of polybasic acid per glucose residue 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 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 ~y３ 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.

[0067] <Neutralization Step for Neutralizing Polybasic Acid-Modified Cellulose> The production method of the present invention includes a step of neutralizing polybasic acid-modified cellulose. This allows for the production of polybasic acid-modified cellulose, a type of hydrophilic polymer. By carrying out this neutralization step, some or all of the polybasic acids bonded to the cellulose become ionizable salts, which ionize in water and cause electrostatic repulsion between the modified cellulose molecules. This results in high hydrophilicity, allowing the cellulose to be uniformly dispersed or dissolved in water without a defibration procedure. 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.

[0068] The step of neutralizing the polybasic acid-modified cellulose can be appropriately carried out 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, if the solution becomes strongly alkaline during neutralization, decomposition of the ester bonds of the modified cellulose progresses; therefore, 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. Considering 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, even more preferably 20% by mass or more, and particularly preferably 30% by mass or more. The degree of neutralization achieved in the neutralization step is not particularly limited, but since it is desirable that the liquid after neutralization be as close to neutral as possible, it is preferably 30% or more, more preferably 50% or more, even more preferably 60% or more, and particularly preferably 70% or more. The upper limit of the degree of neutralization is preferably 100% or less.

[0069] <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 obtained in the neutralization step. Crosslinking can produce crosslinked polybasic acid salt-modified cellulose. The crosslinked polybasic acid salt-modified cellulose is a water-swellable, water-absorbent polymer having the polybasic acid salt-modified cellulose in its main chain. One suitable use 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.

[0070] The reaction carried out in the crosslinking step can be a reaction commonly used for crosslinking modified cellulose such as carboxymethylated cellulose, and may be one 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 one that forms a bond with a crosslinking agent and reacts with it, or one that bonds crosslinking agents bound to functional groups of the crosslinked polybasic acid salt-modified cellulose together, or one that adjusts the degree of neutralization to form hydrogen bonds between acid groups and hydroxy groups, or a method that combines multiple techniques. The acid (salt) group represents an acid group and / or an acid-base group, and 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 acid groups, organic amine salts, and ammonium salts.

[0071] 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, oxazo structure, etc. Crosslinking agents having multiple highly active functional groups such as phosphorus 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 hydroxy groups with compounds having multiple aldehyde groups such as glutaraldehyde or glyoxal, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, 1,4-butanediol, pentaerythritol, ethylenediamine ... Examples of such crosslinking methods include ester and / or amide formation between a carboxylic acid and a crosslinking agent having multiple hydroxyl or amine groups, such as polyethylene carbonate, propylene carbonate, or polyethyleneimine; ester formation between a hydroxyl group and a polyacid crosslinking agent capable of forming multiple ester bonds, such as an organic acid such as succinic acid, maleic acid, trimellitic acid, or citric acid, or an inorganic acid such as phosphoric acid; crosslinking by binding a crosslinking agent having multiple bonds, such as acrylic acid, maleic acid, or vinylsilane, to the hydroxyl groups of polybasic acid salt-modified cellulose, followed 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 polybasic acid salt-modified cellulose, such as an epoxy group or an amino group, followed by condensation of the silane coupling agent; hydrogen bond formation between an acid group and a hydroxyl group derived from polybasic acid salt-modified cellulose by adjusting the degree of neutralization by adding an inorganic acid such as sulfuric acid or hydrochloric acid, or an organic acid such as citric acid; and ionic bond complex formation between a polyvalent metal salt, such as a titanium salt, an aluminum salt, or a zirconium salt, and an acid group derived from the polybasic acid salt-modified cellulose crosslinked product.

[0072] 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.

[0073] 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.

[0074] The amount of 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. The amount of substance is, for example, 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 refers to the total amount used. In the crosslinking step, the time, temperature, and pressure can be appropriately set. When crosslinking is performed by adjusting the degree of neutralization through hydrogen bonding, the degree of neutralization may be adjusted by adjusting the amount of base added in the neutralization step, or by separately adding an acid.

[0075] <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.

[0076] <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.

[0077] <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.

[0078] <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 the 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.

[0079] <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, 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 recycling.

[0080] The conditions for the distillation step can be appropriately set. For example, the solvent can be recovered by distillation. Alternatively, 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 or the like.

[0081] 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.

[0082] [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, wherein 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, the mass proportion of an ionic liquid having an imidazolium ion is less than 5,000 ppm, and the average degree of substitution of the cellulose with a polybasic acid salt per glucose residue is 1 or more. As described above, by using the method for producing polybasic acid salt-modified cellulose of the present invention, polybasic acid salt-modified cellulose can be produced without using a solvent or with a reduced amount of solvent, and therefore a polybasic acid salt-modified cellulose composition with a low solvent content can be obtained.

[0083] The polybasic acid salt-modified cellulose composition of the present invention may be free of the above-mentioned organic solvents or ionic liquids. For example, the hydrophilic polymer material of the present invention may be free of any of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, pyridine, 4-dimethylaminopyridine, and ionic liquids having imidazolium ions. The polybasic acid salt-modified cellulose composition of the present invention is highly safe, as it contains sufficiently reduced amounts of toxic and odorous solvents and organic catalysts. Furthermore, the polybasic acid salt-modified cellulose composition is a highly hydrophilic polymer material in which the average degree of substitution of cellulose with polybasic acid salts per glucose residue is 1 or more. Therefore, the composition is suitable for use in sanitary materials and detergents that come into contact with the human body.

[0084] The polybasic acid salt-modified cellulose composition of the present invention comprises a polybasic acid salt-modified cellulose as a main component, and may further contain water, an organic solvent, and an ionic liquid, so long as the mass proportion of at least one organic solvent 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 water, an organic solvent, and an 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 water, an organic solvent, and an ionic liquid, and the total mass proportion of water, an organic solvent, and an ionic liquid may be 0 ppm. The preferred mass proportions of water, organic solvent, and ionic liquid in the polybasic acid salt-modified cellulose composition of the present invention are the same as the preferred mass proportions of water, organic solvent, and ionic liquid in the above-mentioned raw material composition.

[0085] Fig. 5 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.

[0086] Fig. 6 is a diagram illustrating each step in the production method of the present invention. Fig. 6 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, pulverized, and amorphized, step 3, in which the pulp raw material is modified with a polybasic acid and / or its acid anhydride (reactant) under solvent-free conditions, step 4, in which the reactant is separated, and step 5, in which the cellulose SAP 6 is neutralized, crosslinked, and dried. Furthermore, by distillation step 7, the reactant separated in the purification step 4 and the solvent used in the purification step 4 can be recovered and recycled, and the reactant can be reused in the reaction step 3 or the solvent can be reused in the purification step 4.

[0087] 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.

[0088] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0089] [CRC (absorbency without load)] The CRC (absorbency without load) in a 0.9% by mass aqueous solution of sodium chloride (physiological saline) was measured in accordance with NWSP241.0.R2(15). Specifically, 0.2 g of a sample was placed in a nonwoven bag and immersed in a large excess of physiological 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. Furthermore, the CRC of pure water was also measured by replacing the physiological saline with pure water. The CRC of pure water was measured in the same manner as above, except that pure water was used instead of saline and the amount of sample was changed from 0.2 g to 0.1 g.

[0090] [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.

[0091] (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.

[0092] (HPLC measurement conditions) Measurement was performed 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 volume: 50 μl Measurement temperature: 35 ° C. During measurement, a sufficient amount of eluent was flowed into the device, and the measurement was performed when the detector baseline was stable. Data collection from the RI detector and analysis of the RI chromatogram were performed using Waters Empower3 software. The area values ​​of the peaks derived from the impurities, namely, the remaining solvent or the remaining modifier, were obtained from the RI chromatogram and used to calculate the remaining ratio.

[0093] (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 %].

[0094] [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).

[0095] (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.

[0096] (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 OHpakSB-806MHQ (manufactured by Showa Denko) connected in series; Detector: Viscotek TDA305 manufactured by Malvern Panaltytical (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. The water used in this measurement was ultrapure water purified using a Millipore Simplicity UV manufactured by Merck. Furthermore, measurements were performed with a sufficient amount of eluent flowing through the instrument and with the detector baseline 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)) and 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 configurations ((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 Panalytic'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.

[0097] [Calculation of Average Degree of Substitution by pH Titration] The average degree of substitution in the sample was measured by measuring the amount of acid in the modified product by pH titration. The measurement solution was prepared as follows.

[0098] (Preparation of Measurement Solution) After the entire sample to be measured was crushed to pass through a 300 μm JIS standard sieve, 0.1 g of 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 in which the sample was neutralized and dispersed 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 lower than 5.5, 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. If the pH of the solution exceeded 7, the measurement solution was prepared again.

[0099] (pH Titration Conditions) 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 aqueous sodium hydroxide solution manufactured by Kanto Chemical; titration of the test solution was carried out using the automatic titrator. The test solution was first titrated with aqueous sodium hydroxide until the pH reached 10.5, and then titrated 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 test solution, a similar blank measurement was also performed without the sample. 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 and blank measurements. The amount of acid in the modified cellulose comes from the partially esterified and bonded modifier and the free acid form of the modifier remaining in the sample. When the modifier is an acid anhydride, the following formula 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 Mｓ 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 Ｋ The 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.

[0100] [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].

[0101] [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 the value measured using a Cu / Kα X-ray source (wavelength 0.154 nm); 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 MalvernPanalytical 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. Since 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, it is thought that the degree of crystallinity does not change much with neutralization after purification. Therefore, in some examples, the crystallinity of the product was determined from the results of X-ray diffraction before neutralization. Furthermore, although not described in the examples of this patent, when type II crystalline cellulose was used as the raw material, I 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.

[0102] [Preparation of Fibrous Pulp] A commercially available softwood pulp board was defibrated using a vertical cutter mill to produce fibrous pulp. XRD measurement of this fibrous pulp was carried out, and the degree of crystallinity was calculated to be 73%.

[0103] [Preparation of powdered pulp using a planetary ball mill] 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. XRD measurement of this powdered pulp was performed, and the crystallinity was calculated to be 25%.

[0104] Example 1: A kneading machine, Kneader A (two-arm kneader), was used, which was a batch-type twin-screw kneader with an open top and a tangential rotor. The kneading machine 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 had a uniform, thermoplastic resinous appearance. 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 acetone in an amount five times the mass of the pulverized product and stirred at room temperature. Unreacted modifier (succinic anhydride) was removed by vacuum filtration and acetone washing. The mixture was then vacuum dried at 45°C to obtain succinic acid-modified cellulose. pH titration was performed, and the amount of base required to achieve a degree of neutralization of 90% was calculated. One part by mass (0.4 g) of purified succinic acid-modified cellulose was diluted with 19 parts by mass of pure water, and then a 10% by mass aqueous solution of sodium carbonate was added dropwise with stirring to achieve the required base amount, thereby neutralizing the mixture to obtain neutralized succinic acid-modified cellulose (1). An aqueous dispersion of the neutralized succinic acid-modified cellulose (1) was subjected to pH titration, HPLC measurement, and GPC measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 1. The mass of the sample was determined by the solids concentration determined by drying the aqueous dispersion at constant weight at 120°C.

[0105] Example 2: Kneader B, a batch-type twin-screw kneader with a completely sealed kneading tank and a tangential rotor, was used as the kneading apparatus. The kneading tank was heated to 125°C using an electrically heated jacket. 100 parts by mass (4 g) of fibrous pulp, 200 parts by mass of succinic anhydride, and 10 parts by mass of potassium carbonate were added to kneader B and kneaded for 15 minutes. At this time, the kneading apparatus was filled to 80%. After removing the kneaded product, the same operations as in Example 1 were performed to obtain neutralized succinic acid-modified cellulose (2). As in Example 1, the aqueous dispersion of neutralized succinic acid-modified cellulose (2) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 1.

[0106] Example 3: A batch-type twin-screw mixer C was used as the kneading apparatus. The mixer had a sealed structure covering 60% of the total length of the main body, excluding the sample inlet opening, and had intermeshing rotors. The mixing tank was heated to 125°C using an electric heating jacket. 100 parts by mass (12 g) of fibrous pulp, 200 parts by mass of succinic anhydride, and 10 parts by mass of potassium carbonate were added to the mixer C and mixed for 15 minutes. At this time, the mixing chamber was 80% full. After removing the mixed material, the same procedures as in Example 1 were repeated to obtain a neutralized succinic acid-modified cellulose (3). As in Example 1, the aqueous dispersion of the neutralized succinic acid-modified cellulose (3) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 1.

[0107] Comparative Example 1: In a stirring reaction procedure, 100 parts by mass (1 g) of fibrous pulp, 200 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 3 hours. At the end of the reaction, the reaction product was in the form of a heterogeneous mass with some fibrous structure remaining and showed no thermoplasticity. After removing the reaction product, the same procedure as in Example 1 was carried out to obtain neutralized succinic acid-modified cellulose (C1). As in Example 1, pH titration, HPLC measurement, and GPG measurement were carried out on the aqueous dispersion of neutralized succinic acid-modified cellulose (C1), and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 1.

[0108] Comparative Example 2: In a stirring reaction procedure, 100 parts by mass (0.5 g) of fibrous pulp, 1,000 parts by mass of succinic anhydride, and 100 parts by mass of potassium carbonate were added to a test tube equipped with a magnetic stirrer and stirred at 125°C for 60 minutes. At the end of the reaction, the reaction product was in the form of a dispersion in which a non-uniform solid was dispersed in molten succinic anhydride. After removing the reaction product, the same procedure as in Example 1 was repeated to obtain neutralized succinic acid-modified cellulose (C2). As in Example 1, the aqueous dispersion of neutralized succinic acid-modified cellulose (C2) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 1.

[0109]

[0110] As shown in Table 1, in Examples 1 to 3, in which the reaction was carried out using a batch twin-screw kneader, the degree of substitution was 1.5 or higher. In particular, in the open-top kneader A, the degree of substitution was 1.52 after a kneading time (reaction time) of 60 minutes. However, when kneading was carried out using kneaders B and C, which are capable of stirring in a sealed container, the degree of substitution was 2 or higher after a kneading time of 15 minutes, demonstrating that sealed systems can achieve higher substitution degrees at higher speeds. On the other hand, in the reaction using a stirring device without a kneading function (Comparative Example 1), the degree of substitution barely increased to 0.88 even when the reaction time was extended to 180 minutes. This demonstrates that the kneading in Examples 1 to 3 further accelerates the reaction. Furthermore, the results of Comparative Example 2 reveal that in order to achieve a degree of substitution similar to that achieved with the open-type kneader of Example 1 using a stirring device, a large excess of succinic anhydride (10 equivalents) relative to the cellulose raw material is required. From the above, it can be seen that the use of a kneading device makes it possible to significantly reduce the amount of succinic anhydride added and shorten the reaction time, which has a significant effect on improving production efficiency.

[0111] [Example 4] Neutralized succinic acid-modified cellulose (4) was obtained by the same procedure as in Example 2, except that powdered pulp obtained by pulverizing fibrous pulp in a planetary ball mill was used instead of the fibrous pulp used in Example 2. The particle size of the powdered pulp was 150 μm or less. As in Example 2, the aqueous dispersion of neutralized succinic acid-modified cellulose (4) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 2.

[0112] [Example 5] Neutralized succinic acid-modified cellulose (5) was obtained by the same procedure as in Example 3, except that powdered pulp obtained by pulverizing fibrous pulp in a planetary ball mill was used instead of the fibrous pulp used in Example 3. The particle size of the powdered pulp was 150 μm or less. As in Example 3, the aqueous dispersion of neutralized succinic acid-modified cellulose (5) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 2.

[0113]

[0114] As shown in Table 2, when powdered pulp was reacted in a kneader, kneader C, which has a structure in which the rotors intermesh, achieved a higher average degree of substitution than kneader B, which is a tangential kneader without an intermesh structure. This result shows that an intermeshing kneader allows for stable modification regardless of the sample shape.

[0115] [Example 6] The same procedure as in Example 3 was carried out, except that the amount of fibrous pulp added was 3 g and the filling rate in the kneader during kneading was 20%, to obtain neutralized succinic acid-modified cellulose (6). As in Example 3, the aqueous dispersion of neutralized succinic acid-modified cellulose (6) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 3.

[0116] [Example 7] The same procedure as in Example 3 was carried out, except that the amount of fibrous pulp added was 6 g and the filling rate in the kneader during kneading was 40%, to obtain neutralized succinic acid-modified cellulose (7). As in Example 3, the aqueous dispersion of neutralized succinic acid-modified cellulose (7) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 3.

[0117]

[0118] As shown in Table 3, the average degree of substitution tended to improve with an increase in the filling rate. It is believed that increasing the filling rate suppresses co-rotation, allowing the raw material composition to be efficiently kneaded, thereby improving the average degree of substitution.

[0119] [Example 8] The same procedure as in Example 3 was carried out, except that the amount of succinic anhydride added was 100 parts by mass and the amount of potassium carbonate added was 5 parts by mass, to obtain neutralized succinic acid-modified cellulose (8). The aqueous dispersion of neutralized succinic acid-modified cellulose (8) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 4.

[0120] [Example 9] The same procedure as in Example 3 was carried out, except that the amount of succinic anhydride added was 300 parts by mass and the amount of potassium carbonate added was 15 parts by mass, to obtain a neutralized succinic acid-modified cellulose (9). As in Example 3, the aqueous dispersion of the neutralized succinic acid-modified cellulose (9) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 4.

[0121] [Example 10] The same procedure as in Example 3 was carried out, except that the amount of potassium carbonate added was changed to 20 parts by mass, to obtain a neutralized succinic acid-modified cellulose (10). As in Example 3, the aqueous dispersion of the neutralized succinic acid-modified cellulose (10) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 4.

[0122] [Example 11] The same procedure as in Example 3 was carried out, except that the amount of succinic anhydride added was 500 parts by mass and the amount of potassium carbonate added was 25 parts by mass, to obtain a neutralized succinic acid-modified cellulose (11). As in Example 3, the aqueous dispersion of the neutralized succinic acid-modified cellulose (11) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 4.

[0123] Example 12 Neutralized succinic acid-modified cellulose (12) was obtained by the same procedure as in Example 3, except that the amount of succinic anhydride added was 600 parts by mass and the amount of potassium carbonate added was 30 parts by mass. As in Example 3, pH titration, HPLC measurement, and GPG measurement were performed on the aqueous dispersion of neutralized succinic acid-modified cellulose (12), and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 4. Furthermore, after the end of kneading, a phenomenon was observed in which a portion of the molten succinic anhydride was not completely mixed with the kneaded product and flowed out in liquid form.

[0124]

[0125] As shown in Table 4, the results of Examples 8 and 3 show that when the amount of succinic anhydride added was increased from 1 part by mass to 2 parts by mass, the average degree of substitution was significantly improved from 1.05 to 2.06. On the other hand, the results of Examples 11 and 12 show that when the amount of succinic anhydride added was increased from 5 parts by mass to 6 parts by mass, the average degree of substitution was reduced from 2.37 to 1.99. It is believed that the addition of a large amount of succinic anhydride reduced the viscosity of the kneaded product, thereby reducing the kneading efficiency and thereby reducing the average degree of substitution.

[0126] [Comparative Example 3] The same procedure as in Example 3 was carried out, except that potassium carbonate was not added, to obtain neutralized succinic acid-modified cellulose (C3). As in Example 3, the aqueous dispersion of neutralized succinic acid-modified cellulose (C3) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 5.

[0127] [Example 13] The same procedure as in Example 3 was carried out, except that the amount of potassium carbonate added was changed to 5 parts by mass, to obtain a neutralized succinic acid-modified cellulose (13). As in Example 3, the aqueous dispersion of the neutralized succinic acid-modified cellulose (13) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 5.

[0128] [Example 14] The same procedure as in Example 3 was carried out, except that the amount of potassium carbonate added was changed to 20 parts by mass, to obtain a neutralized succinic acid-modified cellulose (14). As in Example 3, the aqueous dispersion of the neutralized succinic acid-modified cellulose (14) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 5.

[0129] [Example 15] The same procedure as in Example 3 was carried out, except that the amount of potassium carbonate added was 30 parts by mass, to obtain a neutralized succinic acid-modified cellulose (15). As in Example 3, the aqueous dispersion of the neutralized succinic acid-modified cellulose (15) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 5.

[0130]

[0131] In Comparative Example 3 and Examples 13, 14, and 15, increasing the amount of potassium carbonate added increased the motor load of the kneader, and in Example 15, the motor reached the upper limit of its rated capacity, making it impossible to add potassium carbonate in amounts greater than those of Example 15.

[0132] [Example 16] The same procedure as in Example 9 was carried out, except that the amount of potassium carbonate added was 30 parts by mass, to obtain a neutralized succinic acid-modified cellulose (16). As in Example 9, the aqueous dispersion of the neutralized succinic acid-modified cellulose (16) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 6.

[0133]

[0134] [Example 17] The same procedure as in Example 11 was carried out, except that the amount of potassium carbonate added was 75 parts by mass, to obtain a neutralized succinic acid-modified cellulose (17). As in Example 11, the aqueous dispersion of the neutralized succinic acid-modified cellulose (17) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 7.

[0135] [Example 18] The same procedure as in Example 11 was carried out, except that the amount of potassium carbonate added was 100 parts by mass, to obtain neutralized succinic acid-modified cellulose (18). As in Example 11, the aqueous dispersion of neutralized succinic acid-modified cellulose (18) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 7.

[0136]

[0137] From Tables 5 to 7, it can be seen that there is an optimum amount of potassium carbonate added at which the average degree of substitution is maximized, and that the optimum amount of potassium carbonate added increases as the amount of succinic anhydride increases.

[0138] [Example 19] The same procedure as in Example 9 was carried out, except that 9 parts by mass of sodium hydroxide was added instead of potassium carbonate, which was the same base molar equivalent as that of succinic anhydride, to obtain a neutralized succinic acid-modified cellulose (19). As in Example 9, the aqueous dispersion of the neutralized succinic acid-modified cellulose (19) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 8.

[0139] [Example 20] The same procedure as in Example 9 was carried out, except that 12 parts by mass of sodium carbonate was added instead of potassium carbonate in Example 9, which was the same base molar equivalent as that of succinic anhydride, to obtain a neutralized succinic acid-modified cellulose (20). As in Example 9, the aqueous dispersion of the neutralized succinic acid-modified cellulose (20) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 8.

[0140] [Example 21] The same procedure as in Example 9 was carried out, except that 18 parts by mass of sodium bicarbonate was added instead of potassium carbonate in the same base molar equivalent relative to succinic anhydride, to obtain neutralized succinic acid-modified cellulose (21). As in Example 9, the aqueous dispersion of neutralized succinic acid-modified cellulose (21) was subjected to pH titration, HPLC measurement, and GPG measurement, and the average degree of substitution and the proportion of soluble components were calculated. The results are shown in Table 8.

[0141]

[0142] As shown in Table 8, regardless of which base catalyst was used, modified cellulose with a high average degree of substitution of 1.8 or more was obtained.

[0143] Example 22 To 100 parts by mass (4.0 g, solids content 10% by mass) of the aqueous dispersion of the neutralized succinic acid-modified cellulose (9) obtained in Example 9, 0.4 parts by mass of a 0.1% by mass aqueous solution of Denacol EX-810 (manufactured by Nagase ChemteX Corp.) as a crosslinking agent was added and stirred until homogeneous. The mixture was then heated and dried in a 120°C fan oven for 45 minutes to obtain a crosslinked solid. CRC measurement revealed a CRC of 9.4 g / g and a pure water CRC of 17.0 g / g.

[0144] Example 23 A continuous kneading device was used, which was a continuous twin-screw kneader with an intermeshing rotor and a structure in which 60% of the total length of the main body was sealed, excluding the sample inlet opening. The barrel was heated to 125°C using a heat medium jacket. Raw materials were continuously fed into kneader D while maintaining a rate of 10 g per minute (100 parts by mass of fibrous pulp, 300 parts by mass of succinic anhydride, and 30 parts by mass of potassium carbonate), and kneaded for 60 minutes. After discarding the kneading discharged material during the first 30 minutes until the barrel was filled with the raw material composition and the process reached a steady state, the kneaded material discharged between 31 and 60 minutes was recovered. The recovered kneaded material was subjected to the same procedures as in Example 1 to obtain neutralized modified cellulose. As in Example 1, pH titration, HPLC measurement, and GPG measurement were performed on an aqueous dispersion of neutralized modified cellulose. The average degree of substitution and the soluble component ratio were calculated to be 1.99 and 29%, respectively. After the kneading was completed, the volume of the kneaded material remaining inside the barrel was measured, and the volume was divided by the volume of the voids inside the barrel to calculate the filling rate, which was 65%.

[0145] [Example 24] A crosslinked solid was prepared using the aqueous dispersion of neutralized modified cellulose obtained in Example 23 in the same manner as in Example 21, and the CRC was measured. The CRC was 12.9 g / g, and the pure water CRC was 25.1 g / g.

[0146] 100: Continuous co-rotating intermeshing twin-screw kneader 102: Inlet 104: Main body 106: Two intermeshing rotors 108: Discharge outlet 110: Drive unit 112: Chemical inlet 200: Continuous co-rotating intermeshing twin-screw kneader 202: Inlet 204: Main body 206: Two tangential rotors 208: Discharge outlet 210: Drive unit 212: Chemical inlet 1: Pulp raw material (compressed form) 2: Process for defibrating, pulverizing and amorphizing 3: Reaction process for modifying with reactant under solvent-free conditions 4: Purification process for separating reactant 5: Process for neutralizing, crosslinking and drying 6: Cellulose SAP 7: Distillation process

Claims

1. A method for producing polybasic acid-modified cellulose, comprising: a reaction step of obtaining polybasic acid-modified cellulose using a raw material composition containing cellulose, a polybasic acid and / or its acid anhydride, and an alkali catalyst; and a neutralization step of neutralizing the polybasic acid-modified cellulose, wherein the reaction step is carried out using a kneader.

2. The method for producing polybasic acid salt-modified cellulose according to claim 1, characterized in that the raw material composition contains 1.5 to 5.5 parts by mass of polybasic acid and / or its acid anhydride per 1 part by mass of cellulose.

3. A method for producing polybasic acid salt-modified cellulose according to claim 1 or 2, characterized in that the raw material composition contains 0.1 to 200 mol% of a base catalyst in terms of base molar equivalent relative to the polybasic acid and / or its acid anhydride.

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 0.025 to 0.5 parts by mass of a base catalyst per 1 part by mass of a polybasic acid and / or its acid anhydride.

5. A method for producing polybasic acid salt-modified cellulose according to any one of claims 1 to 4, characterized in that the kneader is a multi-screw kneader.

6. The method for producing polybasic acid salt-modified cellulose according to claim 5, wherein the multi-screw kneader has an intermeshing structure.

7. A method for producing polybasic acid salt-modified cellulose according to any one of claims 1 to 6, characterized in that the reaction step is carried out at a temperature equal to or higher than the melting point of the polybasic acid and / or its acid anhydride.

8. A method for producing polybasic acid salt-modified cellulose described in any one of claims 1 to 7, characterized in that the reaction process is carried out using an amount of raw material composition that results in a filling rate of 30% or more in the kneader.

9. A method for producing polybasic acid salt-modified cellulose described in any one of claims 1 to 8, characterized in that the total content of the organic solvent, organic catalyst, and ionic liquid in the raw material composition is less than 10 mass% based on 100 mass% of the raw material composition.

10. A method for producing polybasic acid salt-modified cellulose according to any one of claims 1 to 9, characterized in that the polybasic acid anhydride is a cyclic polybasic acid anhydride.

11. A method for producing polybasic acid salt-modified cellulose according to any one of claims 1 to 10, characterized in that the polybasic acid and / or its acid anhydride is a polybasic carboxylic acid and / or its acid anhydride.

12. A method for producing polybasic acid salt-modified cellulose according to any one of claims 1 to 11, characterized in that the polybasic acid and / or its acid anhydride is a dibasic acid and / or its acid anhydride.

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 and / or its acid anhydride is succinic acid and / or its acid anhydride.

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

15. A method for producing polybasic acid-modified cellulose according to any one of claims 1 to 14, characterized in that the polybasic acid-modified cellulose has an average degree of substitution of polybasic acid per glucose residue of 1 or more.

16. A method for producing polybasic acid salt-modified cellulose according to any one of claims 1 to 15, characterized in that the cellulose is regenerated pulp.

17. A method for producing polybasic acid salt-modified cellulose according to any one of claims 1 to 16, characterized in that the base catalyst is one or more selected from sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

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

19. A polybasic acid salt-modified cellulose composition comprising a polybasic acid salt-modified cellulose, wherein 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, the mass proportion of an ionic liquid having an imidazolium ion is less than 5000 ppm, and the average degree of substitution of the cellulose with the polybasic acid salt per glucose residue is 1 or more.

20. The polybasic acid salt-modified cellulose composition according to claim 19, which is used as a raw material for sanitary materials, agricultural and horticultural supplies, cosmetics, or detergents.

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