Method for producing polybasic acid modified cellulose

Abstract

This invention provides a simple method for obtaining high-quality polybasic acid-modified cellulose when reacting cellulose with a polybasic acid and / or its acid anhydride to produce polybasic acid-modified cellulose. [Solution] The present invention relates to a method for producing polybasic acid modified cellulose, comprising the steps of reacting cellulose with a polybasic acid and / or its acid anhydride to obtain polybasic acid modified cellulose, and neutralizing the polybasic acid modified cellulose, wherein the cellulose has an average particle diameter of 150 μm or less.

Description

[Technical Field]

[0001] This invention relates to a method for producing polybasic acid-modified cellulose. More specifically, it relates to a method for producing polybasic acid-modified cellulose used in various industrial products such as sanitary materials and detergents. [Background technology]

[0002] Conventional hydrophilic polymers derived from petrochemicals have been suitably used as raw materials for various industrial products, such as sanitary materials and detergents. In particular, polyacrylic acid (salt)-based superabsorbent polymers are widely used in applications requiring water absorption and retention, including sanitary materials such as disposable diapers and sanitary products, as well as in agriculture, horticulture, food processing, and industrial sectors.

[0003] In recent years, in order to reduce environmental impact and realize a sustainable society, there has been a demand for hydrophilic polymers to be made from biomass-derived raw materials or to be made biodegradable. Under these circumstances, methods for obtaining hydrophilic polymers by modifying cellulose, which is abundant in nature, have been investigated (see, for example, Patent Documents 1 and 2, and Non-Patent Documents 1 and 2). In addition, although it is not a method for obtaining hydrophilic polymers, a method for obtaining cellulose nanofibers (CNF) by modifying cellulose and then defibrating it has been disclosed (see, for example, Patent Document 3).

[0004] Starch is a biomass-derived raw 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. On the other hand, 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 stronger crystallinity than starch and other polysaccharides, resulting in low dispersibility and solubility in water and solvents. Therefore, uniform modification to create a hydrophilic polymer has been extremely difficult. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2012-12462 [Patent Document 2] International Publication No. 2023 / 282534 [Patent Document 3] Chinese Patent Application Publication No. 115819630 Specification [Non-patent literature]

[0006] [Non-Patent Document 1] Journal of Applied Polymer Science, Vol. 99, 3251-3256 (2006) [Non-Patent Document 2] Journal of Hazardous Materials 169 (2009) 831-837 [Overview of the project] [Problems that the invention aims to solve]

[0007] When producing polybasic acid-modified cellulose by reacting cellulose with polybasic acids and / or their acid anhydrides, there has been a need for a simple method to obtain high-quality polybasic acid-modified cellulose.

[0008] This invention has been made in view of the above-mentioned circumstances, and aims to provide a method for easily obtaining high-quality polybasic acid-modified cellulose when producing polybasic acid-modified cellulose by reacting cellulose with a polybasic acid and / or its acid anhydride. [Means for solving the problem]

[0009] When the present inventors were producing polybasic acid salt-modified cellulose by reacting cellulose with a polybasic acid and / or its acid anhydride, they conducted various studies on a method for easily obtaining high-quality polybasic acid salt-modified cellulose, and focused on the average particle size of the cellulose. Then, the present inventors found that in a method for producing polybasic acid salt-modified cellulose including a step of reacting cellulose with a polybasic acid and / or its acid anhydride to obtain polybasic acid-modified cellulose, and a step of neutralizing the polybasic acid-modified cellulose, when the cellulose has an average particle size of 150 μm or less, the reactivity of the cellulose is greatly improved, and high-quality polybasic acid salt-modified cellulose can be easily obtained. Further, the present inventors found that even when the crystallinity of the cellulose is 30% or less, high-quality polybasic acid salt-modified cellulose can be easily obtained, and conceived that the above problems can be perfectly solved, thus arriving at the present invention.

[0010] That is, the present invention (1) is a method for producing polybasic acid salt-modified cellulose including a step of reacting cellulose with a polybasic acid and / or its acid anhydride to obtain polybasic acid-modified cellulose, and a step of neutralizing the polybasic acid-modified cellulose, wherein the cellulose has an average particle size of 150 μm or less.

[0011] The present invention (2) is a method for producing polybasic acid salt-modified cellulose according to the present invention (1), wherein the cellulose has a crystallinity of 30% or less.

[0012] The present invention (3) is a method for producing polybasic acid salt-modified cellulose according to the present invention (1) or (2), wherein the step of obtaining the polybasic acid-modified cellulose is carried out at a temperature exceeding 120°C.

[0013] The present invention (4) is a method for producing polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (3), wherein the polybasic acid anhydride is a cyclic polybasic acid anhydride.

[0014] The present invention (5) is a method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (4), characterized in that the polybasic acid and / or its acid anhydride is a polybasic carboxylic acid and / or its acid anhydride.

[0015] The present invention (6) is a method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (5), characterized in that the polybasic acid and / or its acid anhydride is a dibasic acid and / or its acid anhydride.

[0016] The present invention (7) is a method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (6), characterized in that the polybasic acid and / or its acid anhydride is succinic acid and / or its acid anhydride.

[0017] The present invention (8) is a method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (7), characterized in that the polybasic acid-modified cellulose is a polybasic acid monoesterified cellulose.

[0018] The present invention (9) is a method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (8), characterized in that the step of obtaining the polybasic acid-modified cellulose is carried out using a base catalyst of less than 30% by mass with respect to 100% by mass of the polybasic acid and / or its acid anhydride.

[0019] The present invention (10) is a method for producing a polybasic acid salt-modified cellulose according to any one of the present inventions (1) to (9), characterized in that the base catalyst is a solid alkali compound.

[0020] The present invention (11) is a method for producing a polybasic acid salt-modified cellulose according to the present invention (10), characterized in that the solid alkali compound is at least one selected from the group consisting of an alkali metal hydroxide, an alkali metal carbonate, and an alkali metal bicarbonate.

[0021] The present invention (12) is a method for producing polybasic acid modified cellulose according to any of the present inventions (1) to (11), characterized in that the polybasic acid modified cellulose has an average degree of substitution of polybasic acids per glucose unit of 1 or more.

[0022] The present invention (13) is a method for producing polybasic acid modified cellulose according to any of the present inventions (1) to (12), characterized in that the above production method further includes a step of crosslinking the polybasic acid modified cellulose obtained in the above neutralization step.

[0023] The present invention (14) is a method for producing polybasic acid modified cellulose, comprising the steps of reacting cellulose with a polybasic acid and / or its acid anhydride to obtain polybasic acid modified cellulose, and neutralizing the polybasic acid modified cellulose, wherein the cellulose has a degree of crystallinity of 30% or less. [Effects of the Invention]

[0024] The present invention provides a method for producing polybasic acid-modified cellulose, comprising the above-described configuration, which allows for the easy production of high-quality polybasic acid-modified cellulose. [Brief explanation of the drawing]

[0025] [Figure 1] This figure shows an example of a reaction equation between cellulose and a polybasic acid anhydride according to the manufacturing method of the present invention. [Figure 2] This figure illustrates each step in the manufacturing method of the present invention. [Modes for carrying out the invention]

[0026] The present invention will be described in detail below. Furthermore, combinations of two or more of the individual preferred embodiments of the present invention described below are also preferred embodiments of the present invention.

[0027] [Method for producing polybasic acid modified cellulose] The following describes in detail the method for producing polybasic acid-modified cellulose.

[0028] (Polybasate-modified cellulose) The polybasic acid-modified cellulose obtained by the manufacturing method of the present invention is composed of modified cellulose in which the cellulose molecules are densely modified with polybasic acid salts as a result of the manufacturing method of the present invention, and which is partially or entirely soluble in water at the molecular level.

[0029] Furthermore, general cellulose nanofiber (CNF) manufacturing methods, including the method for producing highly charged nanocellulose described in Patent Document 3, require the modification of the surface of microfibrils, which are the smallest units of fibers constituting the cellulose raw material, and then the subsequent uniform dispersion in water, thus necessitating the separation of individual microfibrils. This defibrillation process requires the use of energy-intensive methods such as ultrasonic application or high-speed shearing, which can lead to a significant increase in production costs. In addition, although microfibrils have a structure in which multiple cellulose molecules are bundled together, the inside of the microfibrils is not modified, and the overall average degree of substitution is small. Therefore, their hydrophilicity is lower compared to conventional hydrophilic polymers derived from petrochemicals. Consequently, they are unsuitable for applications requiring high charge density, such as sanitary materials and detergents, and are difficult to use as a substitute for the aforementioned petrochemical-derived hydrophilic polymers.

[0030] On the other hand, the polybasic acid-modified cellulose obtained by the production method of the present invention is in which the individual cellulose molecules constituting the microfibrils are modified by polybasic acid salts, and as a whole it has a high charge density. Furthermore, due to the electrostatic repulsion between the modified cellulose molecules caused by the high charge density, it has the property of being able to disperse or dissolve uniformly in water without performing a defibrillation operation. In addition, the polybasic acid-modified cellulose obtained by the production method of the present invention has the characteristic of having a low degree of crystallinity because the crystallinity within the microfibrils is lost as the individual cellulose molecules constituting the microfibrils are modified.

[0031] Based on these findings, the polybasic acid-modified cellulose obtained by the manufacturing method of the present invention is highly hydrophilic compared to conventional products, and can be produced at low cost as a substitute for the hydrophilic polymers derived from petrochemicals mentioned above.

[0032] Furthermore, the degree of modification of modified cellulose molecules can be evaluated using several methods, including the disappearance of crystal peaks derived from microfibrils of the cellulose raw material, the average degree of substitution representing the amount of modifying agent bound per glucose residue of the cellulose molecule, and the measurement of the proportion of modified cellulose molecules that have become molecular and dissolved in water. For the aforementioned evaluations, for example, crystallinity measurement by X-ray diffraction, pH titration, and gel permeation chromatography (GPC) are used. The average degree of substitution of cellulose molecules that become highly hydrophilic is generally 1 or higher. The methods for measuring and calculating the average degree of substitution will be described in detail in the examples.

[0033] <Process for obtaining polybasic acid-modified cellulose> The present invention provides a manufacturing method that includes a step of reacting cellulose with a polybasic acid and / or its acid anhydride to obtain polybasic acid-modified cellulose. In this specification, the step of obtaining polybasic acid-modified cellulose is also referred to as the reaction step.

[0034] (cellulose) Examples of the cellulose mentioned above include plant-derived pulp such as cotton and wood, compressed pulp, bacterial cellulose, lignocellulose, regenerated cellulose (regenerated fibers such as cellophane, cupro, and lyocell), and microcrystalline cellulose. The cellulose may be modified by esterification such as acetylation, etherification such as carboxyalkylation, phosphorylation, sulfation, phosphate crosslinking, enzymatic treatment, etc., but it is preferable that it is not modified. Furthermore, since cellulose raw materials are tough and can be recycled, recycled cellulose raw materials may be used to reduce environmental impact. From the viewpoint of realizing a sustainable society, one preferred embodiment of the present invention is to use recycled pulp obtained from used pulp raw materials, such as recycled paper and sanitary materials such as diapers. In addition, cellulose raw materials derived from agricultural waste and food residue may be used. The form of the raw material cellulose may be compressed into a plate or flake form, in a fibrous form, or in a powder form, but the powder form is preferred. Furthermore, although cellulose raw materials are hygroscopic, the moisture contained in the cellulose raw materials is distinct from the water added separately as a solvent during the reaction. The presence of water reduces the concentration during the reaction and decreases the reaction efficiency, as well as causing decomposition of the cellulose skeleton, ester bonds, and acid anhydrides. Therefore, it is preferable that the cellulose raw materials be dry. The means of drying are not particularly limited, but natural drying at room temperature or forced drying by heating can be suitably carried out.

[0035] From the viewpoint of increasing reaction efficiency in the above reaction process, it is desirable that the cellulose be micronized on a micrometer scale. Micronization increases the surface area, which is expected to improve the reaction efficiency during modification. Furthermore, even on a nanometer scale, it is preferable that the cellulose does not have a microfibril structure in which multiple cellulose molecules are bundled together, and in the above reaction process, it is preferable that the cellulose has a low degree of crystallinity and is amorphous, as will be described later. In other words, it is preferable that the cellulose is not fibrous. Moreover, in the above reaction process, it is preferable that the cellulose and the cellulose polybasic acid modified product produced by the progress of the reaction are uniformly dissolved or dispersed in the raw material composition, and it is desirable that the microfibril structure of the cellulose is broken down after the reaction.

[0036] The cellulose described above has an average particle diameter of 150 μm or less. Preferably, the average particle diameter is 130 μm or less, more preferably 110 μm or less, even more preferably 100 μm or less, even more preferably 90 μm or less, and particularly preferably 50 μm or less. The average particle diameter described above is not particularly limited in its lower limit, but is preferably 1 μm or larger, more preferably 5 μm or larger, and even more preferably 10 μm or larger. The average particle diameter mentioned above is the mass-average particle diameter, and is measured by the method described in the examples.

[0037] The cellulose described above preferably has a crystallinity of 30% or less. A lower crystallinity increases the number of highly reactive amorphous regions, allowing the modification reaction to proceed more efficiently. The degree of crystallinity is more preferably 28% or less, even more preferably 26% or less, even more preferably 24% or less, and particularly preferably 22% or less. The crystallinity level mentioned above does not have a particularly limited lower limit, but it is usually 1% or higher. The above degree of crystallinity is measured by the method described in the examples.

[0038] The average particle size and degree of crystallinity mentioned above can be adjusted, for example, by pre-fibrillating or grinding the cellulose used in the reaction process. The defibration process is not particularly limited, but for example, cellulose can be defibrated using a cutter mill or the like. The grinding process is not particularly limited, but for example, cellulose can be ground using a screw extruder such as a kneader or meat chopper, or a grinder such as a ball mill. The defibration and pulverization processes may be performed continuously or intermittently. The defibration and pulverization times can be set as appropriate. Furthermore, the average particle size and degree of crystallinity can be appropriately adjusted by classifying the cellulose using sieves, liquids, airflows, or other fluids, or by using other processes (for example, granulation processes, decomposition processes).

[0039] (Polybasic acids and / or their acid anhydrides) Examples of polybasic acids and / or their acid anhydrides include dibasic acids such as succinic acid, maleic acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, methyltetrahydrophthalic acid, methylhexahydrophthalic acid, endomethylenetetrahydrophthalic acid, methylendomethylenetetrahydrophthalic acid, and itaconic acid, as well as 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, as well as polybasic acid anhydrides such as trimellitic anhydride, citric acid anhydride, butanetetracarboxylic acid anhydride, and phosphoric acid anhydride. In this specification, acid anhydrides having a structure in which two or more monobasic acids, such as acetic anhydride, are condensed are not considered polybasic acid anhydrides, as they are monobasic acid anhydrides. In the production method of the present invention, polybasic acids and / or their acid anhydrides can also act as solvents and can dissolve the polybasic acid-modified cellulose produced by the reaction.

[0040] The polybasic acid and / or its acid anhydride described above is preferably a polybasic acid anhydride, more preferably a cyclic polybasic acid anhydride, and even more preferably succinic anhydride or maleic anhydride. Polybasic acid anhydrides and cyclic polybasic acid anhydrides can be prepared by heating the polybasic acid. Furthermore, it is also preferable that the polybasic acid and / or its acid anhydride is a polybasic carboxylic acid and / or its acid anhydride. Furthermore, it is preferable that the polybasic acid and / or its acid anhydride is a dibasic acid and / or its acid anhydride, and more preferably succinic acid and / or its acid anhydride.

[0041] The mass percentage of the polybasic acid and / or its acid anhydride is preferably 50% by mass or more relative to the mass percentage of the cellulose (100% by mass). More preferably, the mass percentage of the polybasic acid and / or its acid anhydride is 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 150% by mass or more. Furthermore, there is no particular upper limit to the mass percentage of the polybasic acid and / or its acid anhydride, but it is usually 2000% by mass or less, preferably 1000% by mass or less, more preferably 550% by mass or less, and even more preferably 400% by mass or less.

[0042] In the above reaction step, the molar ratio of glucose units in cellulose to polybasic acid can be set as appropriate, but is preferably, for example, 1 / 1 to 1 / 1000. A blending ratio within this range is preferable in terms of yield and economy. More preferably, it is 2 / 3 to 1 / 500, and even more preferably, 1 / 2 to 1 / 300. Particularly preferably, it is 1 / 3 to 1 / 100.

[0043] (Base catalyst) The process of obtaining the polybasic acid-modified cellulose described above is preferably carried out using a base catalyst. The base catalyst is not particularly limited as long as it has the effect of accelerating the modification reaction, but inorganic base catalysts can be used. Specifically, examples include hydroxides such as potassium hydroxide, sodium hydroxide, lithium hydroxide, calcium hydroxide, thallium hydroxide, tin hydroxide, lead hydroxide, and nickel hydroxide; carbonates such as potassium carbonate, sodium carbonate, rubidium carbonate, cesium carbonate, lead carbonate, zinc carbonate, and nickel carbonate; and bicarbonates such as potassium bicarbonate, sodium bicarbonate, rubidium bicarbonate, and cesium bicarbonate. One or more of these can be used. Among these, carbonates and bicarbonates are preferred.

[0044] The above-mentioned base catalyst is preferably a solid alkali compound. This further improves the reactivity of cellulose. In addition, one preferred embodiment of the present invention is that the above-mentioned base catalyst is solely a solid alkali compound.

[0045] Examples of the solid alkali compounds mentioned above 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. One or more of these can be used. Among these, alkali metal carbonates and alkali metal bicarbonates are preferred.

[0046] The amount of base catalyst used is preferably 0.1 mol% to 200 mol%, more preferably 1 mol% to 100 mol%, more preferably 2 mol% to 50 mol%, and more preferably 5 mol% to 25 mol%, relative to the polybasic acid and / or its acid anhydride, which are modifiers, in terms of base molar equivalent. Here, base molar equivalent is a value obtained by correcting the amount of substance of the base catalyst used by the valence of the base. For example, if sodium hydroxide is a monovalent base catalyst at 1 mol%, it is 1 mol%, and if sodium carbonate is a divalent base catalyst, it is 2 mol%. If the amount of base catalyst used is too little, the reaction efficiency of the reaction composition will decrease, resulting in a longer reaction time and a decrease in the degree of substitution. If the amount of base catalyst used is too much, unwanted side reactions will occur in the reaction composition, and the viscosity of the reaction composition will increase, leading to a decrease in kneading uniformity, which is undesirable as it can result in a longer reaction time, a decrease in the degree of substitution, and overload or damage to the kneader. Furthermore, it was found that the optimal amount of base catalyst used changes depending on the amount of polybasic acid and / or its acid anhydride used as a modifier. It is thought that the viscosity of the reaction composition changes depending on the amount of base catalyst used, and that the uniformity of mixing the reaction composition and the shear force imparted change, thereby changing the optimal amount. Therefore, it is preferable to adjust the amount of base catalyst used by adding the polybasic acid and / or its acid anhydride. Note that when two or more of the above base catalysts are used, the above mass ratio is the total mass ratio of the base catalysts.

[0047] (solvent) The above reaction process may be carried out using a solvent or under solvent-free conditions. When the above reaction step is carried out using a solvent, examples of solvents include water, organic solvents, ionic liquids, and combinations thereof. Among these, one or more types of solvents, such as organic solvents containing sulfur atoms and / or nitrogen atoms, or ionic liquids having at least one ion selected from the group consisting of ammonium, phosphonium, pyridinium, and imidazolium, can be suitably used. The mass percentage of the solvent can be adjusted as appropriate, but one preferred embodiment in this invention is, for example, 50% by mass or more of the raw material composition used in the reaction step (100% by mass). The upper limit of the mass percentage of the solvent is not particularly limited, but it is usually 95% by mass or less.

[0048] Furthermore, in the above reaction step, it is also a preferred embodiment of the present invention to set the mass percentage of the solvent to less than 50% by mass of 100% by mass of the raw material composition used in the reaction step. The above reaction step may also be carried out under solvent-free conditions, for example, the mass percentage of the solvent may be less than 5000 ppm. If the above reaction steps are 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 can also act as a solvent and dissolve cellulose and / or polybasic acid-modified cellulose produced by modification. Note that the mass proportion of the polybasic acid and / or its acid anhydride is not included in the mass proportion of the solvent. The above mass ratio is measured by the method described in the examples or by a similar method.

[0049] In the above reaction step, other components such as antioxidants and catalysts other than base catalysts may also be used. In the raw material composition used in the reaction process, the mass percentage of other components is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less.

[0050] The above reaction step is preferably carried out at a reaction temperature exceeding 120°C. This further improves the reactivity of cellulose. It is also preferable to carry out the above reaction step at a reaction temperature exceeding the melting point of the polybasic acid and / or its acid anhydride. The reaction temperature described above is not particularly limited in its upper limit, but is usually 200°C or lower, and preferably 180°C or lower.

[0051] The reaction time in the above reaction step is preferably 10 minutes or more. The above reaction time is more preferably 20 minutes or longer, and even more preferably 30 minutes or longer. The above reaction time is, for example, 12 hours or less, preferably 6 hours or less, and more preferably 3 hours or less.

[0052] The above reaction process can be suitably carried out by kneading the raw material composition using a roll mill, kneader, blender, or the like.

[0053] The raw material composition may be charged all at once into a reaction vessel such as a reaction tank, or it may be supplied to the reaction vessel continuously or intermittently.

[0054] (Polybasic acid-modified cellulose) In the manufacturing method of the present invention, polybasic acid-modified cellulose is produced by the reaction of cellulose with a polybasic acid and / or its acid anhydride. The polybasic acid-modified cellulose described above is preferably polybasic acid monoesterified cellulose.

[0055] In the above-mentioned polybasic acid-modified cellulose, it is preferable that the average degree of substitution of polybasic acids per glucose residue constituting the cellulose is 1 or more. The above average degree of substitution is more preferably 1.2 or higher, even more preferably 1.5 or higher, and particularly preferably 2.3 or higher. In the above reaction process, the degree of substitution can be further increased by using carbonates, bicarbonates, etc., as base catalysts. The average degree of substitution mentioned above is usually 3 or less. The average degree of substitution described above is measured by the method described in the examples. Furthermore, the average degree of substitution of polybasic acid-modified cellulose can be converted, if necessary, to 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 given below. Moreover, since the following calculation method can be performed regardless of whether neutralization has occurred, the same calculation can be used to convert polybasic acid-modified cellulose. Conversion of the mass percentage y1 (mass%) of the modifying agent relative to cellulose

number

number

number

[0056] The above polybasic acid-modified cellulose preferably has a cellulose-derived crystallinity of 45% or less. The above degree of crystallinity is more preferably 40% or less, even more preferably 35% or less, even more preferably 30% or less, even more preferably 25% or less, and particularly preferably 20% or less. The above degree of crystallinity does not have a particularly limited lower limit; it only needs to be 0% or higher, and is usually 5% or higher. In the above reaction process, the degree of crystallinity can be further reduced by using carbonates, bicarbonates, etc., as a base catalyst. The above degree of crystallinity is measured by X-ray diffraction, specifically by the Segal method described in the examples.

[0057] <Process for purifying polybasic acid-modified cellulose> The present invention's method for producing polybasic acid-modified cellulose preferably includes a step of purifying the polybasic acid-modified cellulose after the above reaction step. The purification process described above is not particularly limited, but examples include methods involving raw material recovery, catalyst recovery, neutralization, filtration, decantation, extraction, washing, evaporation, distillation, and column chromatography. Each of the above operations can be performed individually or in combination of two or more as appropriate. Among these, purification by filtration and washing is particularly preferred. In addition, organic solvents or water with low boiling points (e.g., below 100°C) that are easy to remove can be used as appropriate during the cleaning process. In the purification process, the time and temperature can be set as appropriate. The pressure is not particularly limited and may be atmospheric pressure, pressurized pressure, or reduced pressure, but atmospheric pressure or reduced pressure is preferred.

[0058] <Process for neutralizing polybasic acid-modified cellulose> The present invention provides a method for producing polybasic acid-modified cellulose, which includes a step of neutralizing the polybasic acid-modified cellulose after the above reaction step. This allows for the production of polybasic acid-modified cellulose. By performing this neutralization step, some or all of the polybasic acids bound to the cellulose become ionizable salts, which ionize in water, causing electrostatic repulsion between the modified cellulose molecules. This results in high hydrophilicity, allowing for uniform dispersion or dissolution in water without the need for defibrillation. The polybasic acid-modified cellulose may be a fully neutralized salt or a partially neutralized salt. In the present invention, one preferred form of the fully neutralized or partially neutralized salt is a neutralized product with a monovalent cation. Examples of monovalent cations include alkali metal salts such as sodium and potassium, and ammonium salts. The neutralization step of polybasic acid-modified cellulose can be carried out as appropriate using metal compounds, ammonia, organic amines, etc. Preferred metal compounds include, for example, 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. Specifically, examples include hydroxides, carbonates, bicarbonates, silicates, phosphates, and aluminates of these metals. In particular, since the decomposition of ester bonds in modified cellulose progresses when the solution is strongly alkaline during neutralization, it is preferable to use sodium carbonate and / or potassium carbonate as the base. In the neutralization process, time, temperature, and pressure can be set as appropriate. The neutralization process can be carried out under solvent-free conditions or in water. From the perspective of productivity, a higher concentration of polybasic acid-modified cellulose during neutralization is desirable, preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, particularly preferably 20% by mass or more, and most preferably 30% by mass or more. The degree of neutralization achieved in the above neutralization process is not particularly limited, but since it is desirable for the liquid to be close to neutral after neutralization, 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.

[0059] <Process for crosslinking polybasic acid-modified cellulose> The manufacturing method of the present invention preferably further includes a step of crosslinking polybasic acid-modified cellulose. Crosslinking can be used to obtain crosslinked polybasic acid-modified cellulose. Crosslinked polybasic acid-modified cellulose is a water-swellable superabsorbent polymer having the above-mentioned polybasic acid-modified cellulose as its main chain. One suitable application of crosslinked polybasic acid-modified cellulose is a water-swellable superabsorbent resin derived from crosslinked polybasic acid-modified cellulose. Here, "water-swellable superabsorbent resin derived from crosslinked polybasic acid-modified cellulose" refers to a water-swellable polymer crosslink obtained by crosslinking a hydrophilic polymer having polybasic acid-modified cellulose as its main chain skeleton, and "water-swellable" means that the absorption ratio under no pressure (also called the centrifugal capacity (CRC)) as defined in NWSP 241.0.R2(15) is 5 g / g or more.

[0060] The reaction carried out in the crosslinking process can be one of the reactions commonly used for crosslinking modified celluloses such as carboxymethylated cellulose. This reaction may involve esterification of carboxylic acid (salt) groups derived from polybasic acids and / or their acid anhydrides added in the reaction process with hydroxyl groups derived from cellulose, thereby bonding the functional groups of the polybasic acid modified cellulose crosslinked material together. Alternatively, it may involve bonding with the crosslinking agent, or bonding of crosslinking agents bonded to the functional groups of the polybasic acid modified cellulose crosslinked material together. The reaction may also involve adjusting the degree of neutralization to generate hydrogen bonds between acid groups and hydroxyl groups, or a combination of multiple methods may be used. Note that "acid (salt) group" refers to an acidic group and / or an acid-base. Examples of acidic groups include carboxylic acid groups, sulfonic acid groups, sulfate groups, and phosphoric acid groups. Examples of acid-bases include alkali metal salts, alkaline earth metal salts, transition metal salts, organic amine salts, and ammonium salts of acidic groups.

[0061] Specific reactants and reaction modes include: ester formation of polybasic acid-modified cellulose-derived functional groups via stoichiometric reactions using condensing agents such as carbodiimides (e.g., dicyclohexylcarbodiimide); ester formation via catalytic dehydration condensation of polybasic acid-modified cellulose-derived functional groups via condensation using inorganic acids such as sulfuric acid and hydrochloric acid, organic acids such as citric acid, Lewis acids such as boron trifluoride, and metal salts such as titanium salts; and epoxy structures such as (poly)ethylene glycol diglycidyl ether and glycerol diglycidyl ether, as well as oxetane structures and ox Crosslinking agents having multiple highly active functional groups such as sazolin structures and isocyanate structures; ester formation through reaction between the functional groups of polybasic acid anhydrides such as succinic anhydride and maleic anhydride, and polybasic acid anhydrides such as polyphosphate and other inorganic acid anhydrides; acetal formation of hydroxyl groups with compounds having multiple aldehyde groups such as glutaraldehyde and glyoxal; ethylene glycol, polyethylene glycol, propylene glycol, glycerin, 1,4-butanediol, pentaerythritol, ethylenediamine Examples of crosslinking methods include ester and / or amide formation between carboxylic acids and crosslinking agents having multiple hydroxyl or amine groups, such as mine, ethylene carbonate, propylene carbonate, and polyethyleneimine; ester formation between hydroxyl groups and polyacid crosslinking agents capable of forming multiple ester bonds, such as organic acids like succinic acid, maleic acid, trimellitic acid, and citric acid, and inorganic acids like phosphoric acid; crosslinking by radical polymerization of multiple bonds derived from the crosslinking agents after bonding a crosslinking agent having multiple bonds, such as acrylic acid, maleic acid, and vinylsilane, to the hydroxyl groups of polybasic acid-modified cellulose; crosslinking by condensing the silane coupling agent after reacting it with a silane coupling agent having a functional group that can react with functional groups derived from polybasic acid-modified cellulose, such as epoxy groups and amino groups; hydrogen bond formation between acid groups and hydroxyl groups derived from polybasic acid-modified cellulose by adjusting the degree of neutralization by adding inorganic acids such as sulfuric acid and hydrochloric acid, and organic acids such as citric acid; and complex formation between polyvalent metal salts such as titanium salts, aluminum salts, and zirconium salts and acid groups derived from polybasic acid-modified cellulose.

[0062] Furthermore, since the crosslinking process can proceed by the ester condensation described above even without a crosslinking agent, crosslinking may also occur during the reaction process or the drying process after the neutralization process. In other words, the crosslinking process may be an independent process, may be carried out simultaneously with the reaction process or drying process, or may be both.

[0063] Furthermore, since the crosslinking process can proceed by the ester condensation described above even without a crosslinking agent, crosslinking may also occur during the reaction process or the drying process after the neutralization process. In other words, the crosslinking process may be an independent process, may be carried out simultaneously with the reaction process or drying process, or may be both.

[0064] One crosslinking agent may be used, or two or more may be used. In addition, a different polybasic acid and / or acid anhydride from the one used in the reaction step may be added separately as a crosslinking agent.

[0065] The amount of crosslinking agent used is preferably, for example, 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, based on 100% by mass of polybasic acid modified cellulose. The amount used is preferably, for example, 10% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0066] The amount of crosslinking agent used is preferably, in terms of substance, 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 modified cellulose. The amount used is preferably, for example, 10 mol% or less, more preferably 3 mol% or less, and even more preferably 1 mol% or less. If two or more crosslinking agents are used, the above usage amounts refer to the total usage amounts. During the cross-linking process, time, temperature, and pressure can be set as appropriate. When adjusting the degree of neutralization to achieve crosslinking by hydrogen bonding, the degree of neutralization may be adjusted by changing the amount of base added during the neutralization process, or by adding an acid separately.

[0067] <Process for drying cross-linked polybasic acid modified cellulose> The manufacturing method of the present invention preferably further includes a step of drying the cross-linked polybasic acid modified cellulose. The drying temperature in the drying process 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 process 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 minutes to 90 minutes. During the drying process, the pressure can be set as appropriate, but it is preferable to use atmospheric pressure or reduced pressure. Various drying methods can be used, including heating drying, hot air drying, reduced pressure drying, infrared drying, microwave drying, drum dryer drying, band drying, and high-humidity drying using high-temperature steam.

[0068] <Process for powdering cross-linked polybasic acid modified cellulose> In the manufacturing method of the present invention, it is desirable to powderize the dried crosslinked polybasic acid modified cellulose. The powdering method is not particularly limited, but it may be a method in which the crosslinked polybasic acid modified cellulose solution before drying is formed into particles and then dried, or a method in which the dried material is pulverized during drying, or a method in which pulverization is performed after drying. In other words, the powdering step may be an independent step, may be performed simultaneously with the drying step, or a combination of multiple steps may be used. The powdered polybasic acid modified cellulose may be used as is, or it may be classified into a specific particle size. By classifying it into a specific particle size, it becomes possible to impart desirable physical properties according to the application, such as adjusting the dissolution rate if it is an uncrosslinked product, or improving physical properties such as absorption rate and liquid permeability in water-absorbent resin applications if it is a crosslinked product. Alternatively, polybasic acid-modified cellulose that has not undergone crosslinking may be dried and powdered in the same manner as described above.

[0069] <Process for surface crosslinking powdered crosslinked polybasic acid-modified cellulose> In the manufacturing method of the present invention, it is preferable that the powdered crosslinked polybasic acid modified cellulose includes a step of surface crosslinking. The surface crosslinking step is a step in which a surface crosslinking agent is added that reacts with the functional groups of the powdered crosslinked polybasic acid 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 cellulose), thereby further crosslinking the surface of the crosslinked powder particles, and is distinct from a step in which the entire uncrosslinked polybasic acid modified cellulose is crosslinked. The crosslinking agent and reaction mode used for surface crosslinking are not particularly limited, but the reaction described in the step for crosslinking polybasic acid cellulose is suitably usable. Furthermore, the reaction used for surface crosslinking may be a single reaction 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 modified cellulose, or a different agent may be used. The method for adding a surface crosslinking agent to form surface crosslinks and the method for forming surface crosslinks are not particularly limited. It may be a method of processing polybasic acid modified cellulose that has been molded into a powder before overall crosslinking, a method of performing surface crosslinking simultaneously with overall crosslinking, a method of performing surface crosslinking separately after overall crosslinking, an independent process, a process performed simultaneously with another process, or a combination of multiple processes. Surface crosslinking allows for appropriate adjustment of physical properties according to the application. In particular, in water-absorbent resin applications, it is possible to impart desirable physical properties such as strengthening particle strength before and / or after swelling, and improving or suppressing swelling ratio, absorption rate, and liquid permeability.

[0070] <Process for processing cellulose used in the reaction process> The manufacturing method of the present invention may include a step of pre-processing the cellulose used in the reaction step by shredding, defibrating, and pulverizing it to a form suitable for modification. In the processing step, cellulose is treated using processing machines such as pelletizers, shredders, kneaders, meat choppers, ball mills, cutter mills, and jet mills to change its shape and density and process it into the optimal form. The processed cellulose can take the form of chips, pellets, fibers, or powder. Note that this processing step is not required. It is preferable to process the cellulose to a powder and bring the average particle size within the preferred range described above.

[0071] In the manufacturing method of the present invention, impurities removed by the purification process described above (for example, polybasic acids and / or their acid anhydrides, which are raw materials) can be recovered as needed and recycled as reaction raw materials, etc. Furthermore, the solvents used in the reaction and purification can also be recovered as needed and recycled as solvents. A distillation process can be suitably used for recovery and recycling. The conditions for the distillation process can be set as appropriate. For example, the solvent can be recovered by evaporation through distillation. Alternatively, for example, the solvent with a lower boiling point than the polybasic acid and / or its acid anhydride can be removed by evaporation through distillation, and then the polybasic acid and / or its acid anhydride can be recovered by evaporation through vacuum distillation.

[0072] The manufacturing method of the present invention may include other steps, etc., as long as it includes the above-mentioned reaction step. For example, the manufacturing method of the present invention may include a step of separating the base catalyst and the neutralizing agent.

[0073] The present invention relates to a method for producing polybasic acid-modified cellulose, comprising the steps of reacting cellulose with a polybasic acid and / or its acid anhydride to obtain polybasic acid-modified cellulose, and neutralizing the polybasic acid-modified cellulose, wherein the cellulose is characterized in that its degree of crystallinity is 30% or less. The present invention provides a method for producing polybasic acid-modified cellulose that significantly improves the reactivity of cellulose, enables highly uniform modification, and allows for the easy production of high-quality polybasic acid-modified cellulose.

[0074] [Polybasate-modified cellulose] The polybasic acid-modified cellulose obtained by the manufacturing method of the present invention is of high quality and can be easily obtained.

[0075] The polybasic acid-modified cellulose obtained by the production method of the present invention preferably has a dissolved component ratio of 1% or more. More preferably, the dissolved component ratio is 2% or more, even more preferably 5% or more, even more preferably 10% or more, and particularly preferably 20% or more. The above-mentioned proportion of dissolved components is not particularly limited to an upper limit, but is preferably 100% or less, more preferably 90% or less, and even more preferably 80% or less. The proportion of dissolved components is determined by the method described in the examples.

[0076] The preferred average degree of substitution of polybasic acid per glucose residue in the polybasic acid modified cellulose of the present invention is the same as the preferred average degree of substitution of polybasic acid per glucose residue in the polybasic acid modified cellulose described above.

[0077] The preferred degree of crystallinity of the polybasic acid-modified cellulose of the present invention is the same as the preferred degree of crystallinity of the polybasic acid-modified cellulose described above. That is, the polybasic acid-modified cellulose of the present invention preferably has a degree of crystallinity of 45% or less as cellulose. The degree of crystallinity is more preferably 40% or less, even more preferably 35% or less, even more preferably 30% or less, even more preferably 25% or less, and particularly preferably 20% or less. The crystallinity described above is not particularly limited in its lower limit, but is usually 0% or higher, and preferably 5% or higher. The degree of crystallinity is determined by the method described in the examples.

[0078] Figure 1 shows an example of a reaction equation between cellulose and a polybasic acid anhydride according to the manufacturing method of the present invention. In Figure 1, succinic anhydride is used as the polybasic acid anhydride.

[0079] Figure 2 illustrates each step in the manufacturing method of the present invention. Figure 2 schematically illustrates a method for producing superabsorbent polymer (SAP) by obtaining cellulose SAP6 through a process involving defibration and pulverization of pulp raw material (compressed form) 1, reaction 3 in which polybasic acid and / or its acid anhydride (reactant) is modified, purification 4 in which the reactant is separated, and neutralization, crosslinking, and drying 5. Furthermore, a distillation step 7 allows for the recovery and regeneration of solvents used in reaction 3 and purification 4, as well as the reactant separated in purification 4, for reuse in reaction 3 and purification 4.

[0080] The polybasic acid-modified cellulose obtained using the manufacturing method of the present invention can be suitably used as a raw material for various industrial products such as sanitary materials and detergents. For example, the superabsorbent polymer obtained by crosslinking polybasic acid-modified cellulose can be suitably used in applications requiring water absorption and retention, including sanitary materials such as disposable diapers and sanitary napkins, as well as in agricultural, horticultural, food, and industrial fields. [Examples]

[0081] The present invention will be described more specifically with reference to the following examples and comparative examples, but the present invention is not limited to these, and examples obtained by appropriately combining the technical means described in each example are also included in the scope of the present invention. Unless otherwise specified, "parts" means "parts by mass" and "%" means "percent mass".

[0082] [Calculation of residual solvent percentage or residual modifier percentage in the sample] The percentage of residual solvent or residual modifier in the sample was quantified by calculating the area value of the peak detected in the differential refractive index (RI) chromatogram of high-performance liquid chromatography (HPLC) as the mass ratio of the residual solvent or residual modifier to the total sample mass. Since the peak area value detected by the RI detector is proportional to the mass concentration of the sample in the measurement solution when the sample injection volume in HPLC is the same, 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 prior calibration) 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 later, the modifier is detected as hydrolyzed free acid.

[0083] (Sample preparation) The measurement solution was prepared according to the following procedure. After grinding the entire sample to be measured so that it could pass through a JIS standard sieve with a mesh size of 300 μm, 0.1 g of the sample was weighed into a 50 mL glass beaker equipped with a 30 mm long magnetic stirrer, 10 g of pure water was added, and stirring was started at 350 rpm using a magnetic stirrer at room temperature (20°C to 25°C). Thirty minutes after stirring began, 40 g of a 0.25% by mass phosphoric acid aqueous solution was added to the beaker, and stirring was continued for another 30 minutes to obtain a 0.2% by mass sample dispersion. Subsequently, the sample dispersion was passed through a filter (Membrane Solutions, PTFE syringe filter, hydrophilic 25A, pore size 0.22 μm) to obtain the measurement solution.

[0084] (HPLC measurement conditions) Measurements were performed using a Waters Alliance HPLC system. The system configuration included an ion exclusion chromatography column and a radioisotope detector. The measurement equipment and conditions were as follows: Pump / Autosampler: Waters Alliance HPLC Guard column: Shim-pack SCR(H) Guard column (manufactured by Shimadzu GLC) Column: Shim-pack SCR-101H (manufactured by Shimadzu GLC) RI detector: 2414 Differential Refraction Detector (Waters) Eluent: 0.4% phosphoric acid aqueous solution Flow rate: 1mL / min Injection volume: 50μL Measurement temperature: 35℃ During the measurement, a sufficient amount of eluent was flowed into the apparatus, and the measurement was performed after the detector baseline had stabilized. Data acquisition from the RI detector and analysis of the RI chromatogram were performed using Waters Empower3 software. Area values ​​of peaks originating from impurities (residual solvent or residual modifier) ​​were obtained from the RI chromatogram and used to calculate the residual percentage.

[0085] (Calculation of residual solvent percentage or residual modifier percentage) The solvent or modifier was measured individually using the same procedure as for sample measurement, and the relationship between the concentration of the residual solvent or modifier and the RI peak area value was calculated. Specifically, the solvent or modifier was diluted 10,000 times with a 0.4 mass% phosphoric acid aqueous solution, filtered, and a 0.01 mass% concentration measurement solution was prepared, 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%] between the solvent or modifier concentration in the measurement solution and the RI peak area value. The concentration of residual solvent or modifier in the measurement solution was calculated using the coefficient C from the RI peak area value of the measurement solution. The product of this concentration and the dilution factor of the sample was then calculated to determine the proportion of residual solvent or modifier in the sample.

number

[0086] [Calculation of dissolved component ratio] The proportion of dissolved components in the sample was quantified from the values ​​detected by the RI chromatogram obtained by gel permeation chromatography (GPC).

[0087] (Sample preparation) A solution was prepared by diluting the sample to be measured to a concentration of 0.1% by mass relative to the solid content. This solution was then filtered using a filter (Membrane Solutions, PTFE syringe filter, hydrophilic 25A, pore size 0.22 μm) to obtain the measurement solution. GPC measurement of this solution was performed under the following conditions.

[0088] (GPC measurement conditions) Measurements were performed using a Viscotek TDA305 from Malvern Panalytical. The system consisted of a gel permeation chromatography column, an RI detector, a light scattering detector, and a capillary viscometer. The measurement equipment and conditions were as follows: Pump / Autosampler: Viscotec GPCmax Guard column: OHpak SB-G (manufactured by Showa Denko) Columns: Two OHpak SB-806MHQ columns (manufactured by Showa Denko) were connected in series. Detector: Viscotek TDA305 manufactured by Malvern Panalytical (system temperature maintained at 30°C) Eluent: 60 mM sodium disodium phosphate dihydrate, 20 mM disodium hydrogen phosphate dodecahydrate, 400 ppm sodium azide aqueous solution (pH 6.35 to 6.38) Flow rate: 0.5mL / min Injection volume: 100μL Measurement temperature: 30℃ For this measurement, ultrapure water purified using Merck's Millipore Simplicity UV was used. Furthermore, the measurement was performed by flowing a sufficient amount of eluent into the apparatus and ensuring a stable detector baseline. In particular, the measurement was performed without any noise peaks in the light scattering detector. Instrument calibration was performed using polyoxyethylene glycol (weight-average molecular weight (Mw) 22396, molecular weight distribution (Mw / Mn=1.0), refractive index increment with respect to concentration (dn / dc)=0.132, solvent refractive index 1.33) as a standard sample. The differential refractive index of the polymer to be analyzed was measured using the value of dextran ((dn / dc)=0.147, solvent refractive index 1.33), which is also a polysaccharide and commonly used in the composition of GPC. Data acquisition and analysis of radioisotopes (RI), light scattering intensity, and viscosity (DP) were performed using Malvern Panalytical's OmniSEC 5.3 software. From the RI, light scattering intensity (angle 7°) LALS, and viscometer data, the molecular weight of the dissolved component was calculated against the elution time, and the RI area values ​​for peaks present at molecular weights above 1000 were obtained from the RI chromatogram. The proportion of dissolved components in GPC of the sample (modified cellulose) was calculated using the following formula. As a standard substance, carboxymethylcellulose sodium salt (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), which has cellulose as its main backbone and is a completely water-soluble polymer, was used, and the proportion of dissolved components was calculated based on the area value of the RI peak obtained by GPC measurement under the same conditions. Furthermore, in order to correct for the proportion of dissolved components, the residual solvent proportion measured by HPLC was excluded from the calculation.

number

[0089] [Calculation of average degree of substitution by pH titration] The average degree of substitution in the sample was measured by determining the amount of acid in the modifier using pH titration. The measurement solution was prepared using the following procedure. After grinding the entire sample to be measured so that it could pass through a JIS standard sieve with a mesh size of 300 μm, 0.1 g of the sample was placed in a 100 mL glass beaker, diluted with 50 g of a 0.9 mass% sodium chloride aqueous solution, and a 30 mm long magnetic stirring bar was added. Next, to improve the uniformity of the measurement, a step was performed to increase the degree of neutralization of the sample and disperse it in water. Specifically, an appropriate amount of 0.1 mol / L sodium hydroxide aqueous solution was added, and the mixture was stirred at 350 rpm for 1 hour at room temperature (20°C to 25°C) using a magnetic stirrer, and the pH of the solution was measured with a handheld pH meter. The amount of sodium hydroxide solution added was adjusted so that the pH of the solution after stirring was between 5.5 and 7. If the pH of the solution was below 5.5, additional sodium hydroxide solution was added, and the mixture was stirred again for 1 hour. This process was repeated until the pH of the solution after stirring was between 5.5 and 7. On the other hand, if the pH of the solution was above 7, the measurement solution was prepared again. A pH titrator manufactured by HIRANUMA (formerly Hiranuma Sangyo) was used, and measurements were taken with the following configuration. pH automatic titrator: TightStation TS-980 Additional burette: B-900 Burette head: H-900 Automatic Cycling: C-912 Control and analysis software: COM-2500 Acid titration solution: 0.1 mol / L hydrochloric acid manufactured by Kanto Chemical Co., Ltd. Base titration solution: 0.1 mol / L sodium hydroxide aqueous solution manufactured by Kanto Chemical Co., Ltd. The measurement solution was titrated using an automatic titrator. First, the measurement solution was titrated with an aqueous sodium hydroxide solution until the pH reached 10.5, and then with hydrochloric acid until the pH reached 2.8. The amount of titrant used for each step was recorded. In addition to the sample measurement solution, a similar blank measurement was performed without the sample, and the required amount of acid or base for each neutralization was determined from the difference in the amount of titrant added between the sample measurement and the blank measurement. The amount of acid in modified cellulose originates from the semi-esterified and bonded modifying agent and the free acid form of the modifying agent remaining in the sample. When the modifying agent is an acid anhydride, the following equation holds true.

number

number

number

[0090] [Calculation of mass-average particle diameter (D50)] The mass-average particle size (D50) of the cellulose raw material was calculated using the Rosin-Rammler equation, which is commonly used to determine the particle size distribution of ground particles. The Rosin-Rammler equation is expressed as follows:

number

number

[0091] [Measurement of the crystallinity of cellulose] The degree of crystallinity of cellulose type I is calculated from the diffraction intensity values ​​obtained by X-ray diffraction using the Segal method and is defined by the following formula.

number

[0092] 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 as the carboxylic acid modifies the inside of the crystal, it is considered that the degree of crystallinity does not change much after neutralization following purification. Therefore, in some examples, the crystallinity of the product was determined from the results of XRD measurement before neutralization. Furthermore, although not described in the examples of this patent, if type II crystalline cellulose is used as the raw material, 22.6 to I 20.0 (Diffraction intensity at diffraction angle 2θ = 20.0°), I 18.5 to I 15.0 It can be similarly calculated by using (diffraction intensity at diffraction angle 2θ = 15.0°).

[0093] [Preparation of fibrous pulp] Commercially available softwood pulp board was defibrated using a vertical cutter mill to produce fibrous pulp.

[0094] [Preparation of powdered pulp using a planetary ball mill] Fibrous pulp was ground in a planetary ball mill for 1 hour to obtain powdered pulp. The powder was then classified using sieves with mesh sizes of 850 μm and 150 μm. The powder remaining on the 150 μm sieve was obtained as powdered pulp with a particle size of 850-150 μm, and the powder passing through the 150 μm sieve was obtained as powdered pulp with a particle size of 150 μm or less. A portion of the powdered pulp with a particle size of 150 μm or less was further classified using a sieve with a mesh size of 106 μm, and the powder passing through the sieve was obtained as powdered pulp with a particle size of 106 μm or less.

[0095] [Preparation of powdered pulp using a rolling ball mill] Fibrous pulp was crushed in a rolling ball mill for 24 hours to obtain powdered pulp. The powder was then classified using sieves with mesh sizes of 850 μm and 150 μm. 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.

[0096] (Comparison of modifications and dissolved component ratios in DMF) [Example 1] In a test tube equipped with a magnetic stirring bar, 100 parts by mass (0.3 g) of powdered pulp with a particle size of 106 μm or less, ground using a planetary ball mill, 300 parts by mass of succinic anhydride, 15 parts by mass of potassium carbonate, and 2000 parts by mass of DMF were added and stirred at 125°C for 1 hour. After the reaction was complete, 5 times the volume of the reaction composition in acetone was added, and the mixture was stirred at room temperature to precipitate succinic acid-modified cellulose. Unreacted succinic anhydride was removed by vacuum filtration and acetone washing. Then, the mixture was vacuum-dried at 45°C to obtain unneutralized succinic acid-modified cellulose. The average degree of substitution was calculated by HPLC measurement and pH titration. One part by mass of succinic acid-modified cellulose was added to 1,000 parts by mass of GPC sodium phosphate buffer and neutralized by thoroughly stirring until homogeneous. Since the amount of disodium hydrogen phosphate was in excess of the carboxylic acid of succinic acid-modified cellulose, a 100% neutralized product was obtained. GPC measurement was performed on the dispersion containing this neutralized succinic acid-modified cellulose, and the proportion of dissolved components was calculated. Since the pH of the buffer was around neutral and no hydrolysis of succinic acid cellulose occurred during neutralization with the buffer, the average degree of substitution was the value before neutralization.

[0097] [Example 2] The procedure was the same as in Example 1, except that powdered pulp with a particle size of 150 μm or less, which was milled using a planetary ball mill, was used instead of powdered pulp with a particle size of 106 μm or less, which was milled using a planetary ball mill. The proportion of dissolved components and the degree of substitution were then measured.

[0098] [Comparative Example 1] The procedure was the same as in Example 1, except that powdered pulp with a particle size of 850-150 μm, which was milled using a planetary ball mill, was used instead of powdered pulp with a particle size of 106 μm or less, which was milled using a planetary ball mill. The proportion of dissolved components and the degree of substitution were then measured.

[0099] [Example 3] The procedure was the same as in Example 1, except that powdered pulp with a particle size of 150 μm or less, ground using a rolling ball mill, was used instead of powdered pulp with a particle size of 150 μm or less, ground using a planetary ball mill. The proportion of dissolved components and the degree of substitution were then measured.

[0100] [Comparative Example 2] The procedure was the same as in Example 1, except that powdered pulp with a particle size of 850-150 μm, which was ground using a rolling ball mill, was used instead of powdered pulp with a particle size of 106 μm or less, which was ground using a planetary ball mill. The proportion of dissolved components and the degree of substitution were then measured.

[0101] [Table 1]

[0102] In the results of Examples 1 and 2 and Comparative Example 1, and Examples 3 and Comparative Example 2 in Table 1, the smaller D50 particles had a higher proportion of dissolved components, resulting in succinic acid-modified cellulose with higher hydrophilicity. In the results of Examples 2 and 3, Example 2, which had a lower degree of crystallinity, had a higher proportion of dissolved components, indicating that amorphization yielded succinic acid-modified cellulose with higher hydrophilicity.

[0103] (Comparison of modification and dissolved component ratio under solvent-free conditions) [Example 4] A dual-arm kneader was used as the mixing device, and the kneading tank was heated to 125°C using a jacket purified with heat transfer oil. 100 parts by mass (25 g) of powdered pulp with a particle size of 150 μm or less, pulverized by a planetary ball mill, 300 parts by mass of succinic anhydride, and 15 parts by mass of potassium carbonate were added to the kneader and kneaded for 1 hour. The kneaded material was removed and pulverized using a Force Mill manufactured by Osaka Chemical Co., Ltd. The material was stirred in acetone five times its mass at room temperature, filtered under reduced pressure, and then washed with acetone to remove unreacted succinic anhydride. The material was then vacuum dried at 45°C to obtain succinic acid-modified cellulose that had not been neutralized. HPLC measurement and pH titration were performed to calculate the average degree of substitution. One part of this succinic acid-modified cellulose was added to 1000 parts of GPC sodium phosphate buffer and neutralized by thoroughly stirring until homogeneous. Since the amount of disodium hydrogen phosphate was in excess of the carboxylic acid of the succinic acid-modified cellulose, a 100% neutralized product was obtained. GPC measurements were performed on the dispersion containing this neutralized succinic acid-modified cellulose, and the proportion of dissolved components was calculated.

[0104] [Comparative Example 3] The procedure was the same as in Example 4, except that powdered pulp with a particle size of 850-150 μm, which was milled using a planetary ball mill, was used instead of powdered pulp with a particle size of 150 μm or less, which was milled using a planetary ball mill. The proportion of dissolved components and the degree of substitution were then measured.

[0105] [Comparative Example 4] The procedure was the same as in Example 4, except that unground fibrous pulp was used instead of powdered pulp with a particle size of 150 μm or less, which was ground using a planetary ball mill. The proportion of dissolved components and the degree of substitution were measured. When the fibrous pulp was classified on an 850 μm sieve, the entire amount remained on the sieve. Therefore, it was determined that the mass-average particle size D50 was 850 μm or larger, and the uniformity number was not calculated. [Table 2]

[0106] From the results of Example 4 and Comparative Examples 3 and 4 in Table 2, Example 4, which had a lower D50 and crystallinity, showed a higher proportion of dissolved components and was a more hydrophilic modified product. [Explanation of Symbols]

[0107] 1: Pulp raw material (compressed form) 2: The process of defibration, pulverization, and amorphous formation. 3: Reaction step of modification with a reactant under solvent-free conditions 4. Purification process to separate the reactants. 5. Neutralization, cross-linking, and drying process 6: Cellulose SAP 7: Distillation process

Claims

1. A step of reacting cellulose with a polybasic acid and / or its acid anhydride to obtain polybasic acid-modified cellulose, and A method for producing polybasic acid modified cellulose, comprising a step of neutralizing the polybasic acid modified cellulose, The method for producing polybasic acid modified cellulose is characterized in that the cellulose has an average particle diameter of 150 μm or less.

2. The method for producing polybasic acid modified cellulose according to claim 1, characterized in that the cellulose has a degree of crystallinity of 30% or less.

3. The method for producing polybasic acid-modified cellulose according to claim 1 or 2, characterized in that the step of obtaining the polybasic acid-modified cellulose is carried out at a temperature exceeding 120°C.

4. The method for producing polybasic acid modified cellulose according to claim 1 or 2, characterized in that the polybasic acid anhydride is a cyclic polybasic acid anhydride.

5. The method for producing polybasic acid modified cellulose according to claim 1 or 2, characterized in that the polybasic acid and / or its acid anhydride is a polybasic carboxylic acid and / or its acid anhydride.

6. The method for producing polybasic acid modified cellulose according to claim 1 or 2, characterized in that the polybasic acid and / or its acid anhydride is a dibasic acid and / or its acid anhydride.

7. The method for producing polybasic acid modified cellulose according to claim 1 or 2, characterized in that the polybasic acid and / or its acid anhydride is succinic acid and / or its acid anhydride.

8. The method for producing polybasic acid modified cellulose according to claim 1 or 2, characterized in that the polybasic acid modified cellulose is polybasic acid monoesterified cellulose.

9. The method for producing polybasic acid modified cellulose according to claim 1 or 2, characterized in that the step of obtaining the polybasic acid modified cellulose is carried out using a base catalyst in an amount of less than 30% by mass per 100% by mass of the polybasic acid and / or its acid anhydride.

10. The method for producing polybasic acid modified cellulose according to claim 9, wherein the base catalyst is a solid alkali compound.

11. The method for producing polybasic acid modified cellulose according to claim 10, wherein the solid alkali compound is at least one selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal bicarbonates.

12. The method for producing polybasic acid modified cellulose according to claim 1 or 2, characterized in that the polybasic acid modified cellulose has an average degree of substitution of polybasic acid per glucose unit of 1 or more.

13. The method for producing polybasic acid modified cellulose according to claim 1 or 2, further comprising a step of crosslinking the polybasic acid modified cellulose obtained in the neutralization step.

14. A step of reacting cellulose with a polybasic acid and / or its acid anhydride to obtain polybasic acid-modified cellulose, and A method for producing polybasic acid modified cellulose, comprising a step of neutralizing the polybasic acid modified cellulose, A method for producing polybasic acid modified cellulose, characterized in that the cellulose has a degree of crystallinity of 30% or less.

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