Powder manufacturing method and powder

Abstract

To provide a technique for improving durability when a powder is re-dispersed in water.SOLUTION: There is provided a method of producing a powder containing a cellulose fiber which comprises a step of spray-drying a slurry, wherein the slurry comprises a cellulose fiber having an anionic group, a solvent including an organic solvent and a cross-linking agent which reacts with an anionic group, the anionic group includes a carboxy group and the cellulose fiber is dispersed in a solvent. A powder containing a cellulose fiber having an anionic group has a crosslinked structure by a crosslinking agent bonded to an anionic group, the anionic group includes a carboxy group, the surface specific area is 50 m2 / g or more and 400 m2 / g or less and the total pore volume is 0.1 cm3 / g or more and 0.85 cm3 / g or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing powder and the powder. [Background technology]

[0002] Cellulose is a biodegradable, naturally occurring material known for its versatility and relatively high chemical and thermal stability. Because cellulose is resistant to nonspecific interactions and adsorption with biological substances such as proteins, it is used as a packing material for purification and separation columns, as well as a carrier, adsorbent, and membrane material for immobilizing enzymes, microorganisms, and cells.

[0003] Fine fibrous cellulose, also known as cellulose nanofibers, are nano-order cellulose fibers obtained by defibrating cellulosic raw materials such as wood. Research results have been reported on the adsorption properties of cellulose nanofibers toward biological substances such as proteins. For example, Non-Patent Document 1 describes the adsorption properties of proteins toward TEMPO-oxidized cellulose nanofibers. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Ramon Weishaupt, and 8 others “TEMPO-OxidizedNanofibrillated Cellulose as a High Density Carrier for Bioactive Molecules”, Biomacromolecules, 2015, 16, 11, 3640-3650 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the cellulose nanofibers described in Non-Patent Document 1 do not have sufficient protein adsorption capacity, and there is room for improvement. The present inventors have therefore discovered that a powder with excellent protein adsorption capacity can be produced by spray-drying a slurry containing cellulose fibers and a solvent. However, the present inventors have found that there is room for improvement in the durability of the powder when redispersed in water. Therefore, there is a need for the development of a technology that can improve the durability of the powder when redispersed in water. [Means for solving the problem]

[0006] The present invention can be realized in the following aspects.

[0007] (1) According to one aspect of the present invention, there is provided a method for producing a powder containing cellulose fibers, comprising spray-drying a slurry, the slurry containing cellulose fibers having anionic groups, a solvent containing an organic solvent, and a cross-linking agent reactive with the anionic groups, the anionic groups containing carboxy groups, and the cellulose fibers dispersed in the solvent.

[0008] (2) In the powder manufacturing method of the above aspect, the slurry may contain the crosslinking agent in an amount of 0.05 equivalents or more and 0.5 equivalents or less relative to the anionic groups of the cellulose fibers.

[0009] (3) According to another aspect of the present invention, there is provided a powder containing cellulose fibers having anionic groups. This powder has a crosslinked structure formed by a crosslinking agent bonded to the anionic groups, the anionic groups containing carboxy groups, and a specific surface area of ​​50 m 2 / g or more 400m 2 / g or less, and the total pore volume is 0.1 cm 3 / g or more 0.85cm 3 / g or less.

[0010] (4) In the powder of the above form, the cellulose fibers may be TEMPO-oxidized cellulose nanofibers.

[0011] (5) The powder in the above form may be used for adsorbing proteins.

[0012] The present invention can be realized in various forms, for example, as a protein adsorbent, a column packing material, an immobilization carrier, and the like. [Effects of the Invention]

[0013] According to the manufacturing method of this embodiment, it is possible to manufacture a powder that has excellent durability when redispersed in water. Furthermore, according to the powder of this embodiment, the durability when redispersed in water is excellent. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the present invention will now be described in detail.

[0015] The method for producing a powder containing cellulose fibers according to the present embodiment includes a step of spray-drying a slurry containing cellulose fibers having anionic groups, a solvent containing an organic solvent, and a crosslinking agent reactive with the anionic groups, the anionic groups containing carboxy groups, and the cellulose fibers dispersed in the solvent.

[0016] According to the manufacturing method of this embodiment, a powder having excellent durability when redispersed in water can be manufactured. The mechanism by which this effect is achieved is unclear. However, one presumed mechanism is that the anionic groups of the cellulose fibers react with the crosslinking agent when the slurry is heated during the spray drying process, resulting in a powder having a crosslinked structure. The inclusion of a crosslinked structure in the powder can prevent the powder from losing its shape when redispersed in water, which is thought to result in increased durability. In this specification, the durability of a powder when redispersed in water is also referred to as "water resistance."

[0017] [Cellulose fiber] The cellulose fibers used in this embodiment have anionic groups. The presence of anionic groups can enhance the protein adsorption ability. Furthermore, the inclusion of at least a carboxyl group as anionic groups allows efficient formation of a crosslinked structure by reaction with a crosslinking agent.

[0018] The anionic group other than the carboxy group is not particularly limited, and examples thereof include at least one selected from the group consisting of a phosphate group, a sulfonic acid group, a nitrate group, a borate group, and a sulfate group. In this specification, the term "carboxy group" is not limited to the acid form (-COOH) but also encompasses the salt form, i.e., a carboxylate group (-COOX, where X is a cation that forms a salt with a carboxylic acid), and the acid form and the salt form may be mixed. Similarly, the term "phosphate group, sulfonic acid group, nitrate group, borate group, sulfate group, and the like is not limited to the acid form but also encompasses the salt form, and the acid form and the salt form may be mixed. The salt is not particularly limited, and examples thereof include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as magnesium salts and calcium salts, onium salts such as ammonium salts and phosphonium salts, and amine salts such as primary amines, secondary amines, and tertiary amines.

[0019] The cellulose fibers containing carboxy groups are not particularly limited, but examples include oxidized cellulose fibers formed by oxidizing hydroxyl groups of glucose units in cellulose molecules, carboxymethylated cellulose fibers formed by carboxymethylating hydroxyl groups of glucose units in cellulose molecules, etc. In one embodiment, the cellulose fibers may be a mixture of cellulose fibers containing carboxy groups as anionic groups and cellulose fibers containing anionic groups other than carboxy groups.

[0020] The amount of anionic groups in cellulose fibers is not particularly limited, but is preferably 0.5 to 3.0 mmol / g, and more preferably 1.5 to 2.0 mmol / g, relative to the dry mass of the cellulose fibers. For example, in the case of carboxy groups, the amount of anionic groups can be determined by preparing 60 mL of a 0.5 to 1% by mass slurry using cellulose fibers whose dry mass has been precisely weighed, adjusting the pH to approximately 2.5 with a 0.1 mol / L aqueous hydrochloric acid solution, adding a 0.05 mol / L aqueous sodium hydroxide solution dropwise, measuring the electrical conductivity, and continuing until the pH reaches approximately 11. The amount of sodium hydroxide (V) consumed during the neutralization stage of the weak acid, where the electrical conductivity changes slowly, can be used to determine the amount of anionic groups according to the following formula: Sulfate groups can also be measured by similar electrical conductivity measurements. Other anionic groups can also be measured by known methods. Amount of anionic group (mmol / g) = V (mL) × [0.05 / mass of cellulose fiber (g)]

[0021] The cellulose fibers used in this embodiment preferably have a type I crystal structure. Type I cellulose crystals are the crystalline form of natural cellulose, and the type I crystal structure makes the cellulose fibers water-insoluble, suppresses swelling in water, and increases durability. Therefore, by using cellulose fibers with a type I crystal structure, it is possible to provide a powder that has excellent protein adsorption capacity and higher durability.

[0022] The fact that cellulose fibers have a type I crystal structure can be identified, for example, by the presence of typical peaks at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°, in a diffraction profile obtained by wide-angle X-ray diffraction image measurement.

[0023] As the cellulose fibers, for example, fine fibrous cellulose (cellulose nanofibers) having an average fiber diameter of 3 nm to 500 nm may be used. The average fiber diameter of the fine fibrous cellulose is more preferably 3 nm to 100 nm, and even more preferably 3 nm to 30 nm.

[0024] The average fiber diameter of cellulose fibers can be measured as follows. Specifically, an aqueous dispersion of cellulose fibers with a solid content of 0.05 to 0.1% by mass is prepared, and the aqueous dispersion is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for observation with a transmission electron microscope (TEM). When fibers with large diameters are included, scanning electron microscope (SEM) images of the surface cast onto glass may be observed. The sample for observation may also be negatively stained, for example, with 2% uranyl acetate. Then, electron microscope images are observed at magnifications of 5,000x, 10,000x, or 50,000x, depending on the size of the fibers. In this case, an arbitrary axis of vertical and horizontal width is assumed within the obtained image, and the sample and observation conditions (magnification, etc.) are adjusted so that at least 20 fibers intersect with the axis. After obtaining an observation image that satisfies these conditions, two random axes are drawn vertically and horizontally per image, and the fiber diameters of the fibers intersecting the axes are visually determined. In this way, at least three non-overlapping images of the surface area are taken with an electron microscope, and the fiber diameter values ​​of the fibers intersecting each of the two axes are read (thus, information on the diameters of at least 20 fibers x 2 x 3 = 120 fibers is obtained). The arithmetic mean of the fiber diameters obtained in this way is taken as the average fiber diameter.

[0025] The average aspect ratio of the cellulose fibers is not particularly limited, but is preferably 50 or more and 1,000 or less, more preferably 100 or more and 800 or less, and even more preferably 200 or more and 500 or less.

[0026] The average aspect ratio of cellulose fibers can be measured as follows. Specifically, the average fiber diameter is calculated according to the method described above. The average fiber length of the cellulose fibers is also calculated from the same observation image. Specifically, the length from the start point to the end point of at least 10 fibers (fiber length) is visually read. The arithmetic mean of the fiber lengths thus obtained is calculated as the average fiber length. These values ​​are then used to calculate the average aspect ratio according to the following formula: Average aspect ratio = average fiber length (nm) / average fiber diameter (nm)

[0027] The fine fibrous cellulose may be obtained by a defibration treatment. The defibration treatment may be carried out after or before the introduction of anionic groups. The defibration treatment is not particularly limited, but may be carried out by treating an aqueous dispersion of cellulose fibers using, for example, a homomixer rotating at high speed, a high-pressure homogenizer, an ultrasonic dispersion processor, a beater, a disk refiner, a conical refiner, a double-disc refiner, a grinder, or the like, to obtain an aqueous dispersion of fine fibrous cellulose.

[0028] A preferred embodiment of the fine fibrous cellulose is oxidized fine fibrous cellulose in which the hydroxyl group at the C6 position of the glucose unit in the cellulose molecule is selectively oxidized to a carboxyl group. Oxidized fine fibrous cellulose can be obtained by oxidizing natural cellulose, such as wood pulp, with a co-oxidant in the presence of an N-oxyl compound and then defibrating (fine-graining) it. The N-oxyl compound is a compound having a nitroxy radical, which is commonly used as an oxidation catalyst, such as piperidine nitroxyoxy radical. Preferred N-oxyl compounds are 2,2,6,6-tetramethylpiperidinooxy radical (TEMPO) or 4-acetamido-TEMPO. Fine fibrous cellulose oxidized with TEMPO is generally referred to as TEMPO-oxidized cellulose nanofiber (hereinafter also referred to as TOCN). In this embodiment, the cellulose fiber is preferably fine fibrous cellulose, more preferably oxidized fine fibrous cellulose, and even more preferably TOCN. The oxidized fine fibrous cellulose may have an aldehyde group or a ketone group in addition to a carboxy group, but preferably does not substantially have an aldehyde group or a ketone group.

[0029] [solvent] The solvent in this embodiment includes an organic solvent. The organic solvent is not particularly limited, but examples thereof include alcohols, ketones, ethers, esters, etc. Examples of alcohols include methanol, ethanol, isopropanol, 1-propanol, etc. As the organic solvent, alcohols are preferably used from the viewpoint of having a relatively high dielectric constant and suppressing aggregation of cellulose fibers in the slurry, and methanol or ethanol is more preferably used. Furthermore, ethanol is particularly preferably used from the viewpoint of improving the protein adsorption ability of the powder obtained after spray drying. Furthermore, the solvent may contain water together with the organic solvent. One type of organic solvent may be used alone, or two or more types may be mixed and used. By including an organic solvent in the solvent, the pore state in the powder formed by spray drying can be maintained in an appropriate state.

[0030] The concentration of the organic solvent in the solvent is not particularly limited, but is preferably 75% by mass or more and 100% by mass or less, more preferably 80% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less, with the remainder of the solvent being water.

[0031] [Crosslinking agent] The crosslinking agent used in this embodiment forms a crosslinked structure by bonding to anionic groups contained in the cellulose fibers. Examples of the crosslinking agent include, but are not limited to, amino resins, epoxy compounds, aziridine compounds, carbodiimide compounds, oxazoline compounds, and polyisocyanate compounds. From the viewpoint of efficiently forming the crosslinking reaction, it is preferable to use a carbodiimide compound, an oxazoline compound, or an epoxy compound as the crosslinking agent.

[0032] [slurry] The slurry contains cellulose fibers having anionic groups dispersed in a solvent containing an organic solvent, and also contains a crosslinking agent that reacts with the anionic groups. A slurry in which the cellulose fibers are dispersed in the solvent can be obtained by mixing and stirring the solvent and the cellulose fibers. The crosslinking agent may be added to the slurry after dissolving it in water or the like, or, if soluble in the slurry solvent, may be added when mixing and stirring the solvent and the cellulose fibers. The content of the cellulose fibers relative to the total mass of the slurry is not particularly limited, but is preferably, for example, 0.01% by mass to 0.50% by mass, and more preferably 0.05% by mass to 0.40% by mass, calculated as solids. Setting the content above the lower limit can improve production efficiency. Setting the content below the upper limit can prevent the viscosity of the slurry from increasing excessively, thereby preventing nozzle clogging during spray drying and, as a result, preventing a decrease in production efficiency.

[0033] The amount of crosslinking agent added to the slurry is not particularly limited. The slurry preferably contains 0.05 to 0.5 equivalents of crosslinking agent relative to the anionic groups of the cellulose fibers contained in the slurry, more preferably 0.1 to 0.5 equivalents, and even more preferably 0.15 to 0.45 equivalents. Here, "equivalent" refers to molar equivalent. By setting the amount above the lower limit, the number of crosslinked structures formed by the reaction between the anionic groups of the cellulose fibers and the crosslinking agent can be increased, thereby further improving the water resistance of the powder. Furthermore, by setting the amount below the upper limit, the number of crosslinked structures in the powder can be prevented from becoming excessively large, thereby preventing a decrease in protein adsorption ability.

[0034] [Spray drying] The powder production method according to this embodiment includes a step of dispersing cellulose fibers having anionic groups in a solvent containing an organic solvent and spray-drying a slurry containing a crosslinking agent. By spray-drying the slurry containing the crosslinking agent, the crosslinking reaction can be promoted by the heat of the spray drying. Therefore, compared to when the crosslinking reaction is carried out in a separate step, the powder production process can be prevented from becoming complicated.

[0035] The spray drying method is not particularly limited, but may be, for example, a nozzle method such as a two-fluid or four-fluid method for spray drying, or a rotating disk method. The inlet temperature during spray drying is not particularly limited, but is preferably 100°C to 200°C, and more preferably 120°C to 180°C. By setting the temperature within the above range, the protein adsorption capacity of the powder obtained after spray drying can be further improved. Furthermore, by setting the temperature above the lower limit, the reaction between the anionic groups of the cellulose fiber and the crosslinker can be further promoted. In this specification, the "inlet temperature during spray drying" refers to the temperature measured at the junction between the drying chamber of the spray drying apparatus and the piping for introducing gas into the drying chamber. The slurry flow rate during spray drying is not particularly limited, but is preferably 1 mL / min to 10 mL / min when using, for example, a BUCHI Mini Spray Dryer B-290. The gas flow rate during spray drying is not particularly limited, but is preferably 1 L / min to 10 L / min. Examples of gases that can be used for spray drying include rare gases and nitrogen gas.

[0036] [powder] The above-mentioned production method can produce a powder containing cellulose fibers having anionic groups. This powder has a crosslinked structure formed by a crosslinking agent bonded to the anionic groups, the anionic groups containing carboxyl groups, and a specific surface area of ​​50 m 2 / g or more 400m 2 / g or less, and the total pore volume is 0.1 cm 3 / g or more 0.85cm 3 / g or less.

[0037] The crosslinking agent is not particularly limited, but examples thereof include the crosslinking agents described above. The crosslinked structure is not particularly limited, but at least includes a crosslinked structure formed by a crosslinking agent bonded to a carboxy group. That is, the powder has at least a crosslinked structure represented by the following general formula (1): In the formula, X represents a crosslinking agent.

[0038] [ka]

[0039] The specific surface area of ​​the powder is 50m 2 / g or more 400m 2 / g or less is more preferable, and 100m 2 / g or more 300m 2 / g or less is more preferable. By setting the specific surface area at or above the lower limit, the protein adsorption capacity can be improved. Furthermore, by setting the specific surface area at or below the upper limit, the physical strength of the powder can be imparted. In this specification, "specific surface area" means the nitrogen adsorption specific surface area determined by the BET method. The specific surface area of ​​the powder can be determined by measuring the nitrogen adsorption isotherm at 77K using a capacitance measuring device.

[0040] The total pore volume of the powder is 0.1 cm 3 / g or more 0.85cm 3 / g or less is more preferable, and 0.2 cm 3 / g or more 0.75cm 3 / g or less is more preferable. By setting the adsorption capacity at or above the lower limit, the protein adsorption capacity can be improved. Furthermore, by setting the adsorption capacity at or below the upper limit, the physical strength of the powder can be imparted. In this specification, "total pore volume" means the sum of the volumes of all pores. The total pore volume of a powder can be measured by converting the amount of adsorbed gas into a liquid when the relative pressure is sufficiently close to 1.

[0041] The average particle size of the powder is not particularly limited, but is more preferably 0.1 μm or more and 100 μm or less, and even more preferably 1 μm or more and 50 μm or less. By setting the size above the lower limit, dusting during handling of the powder can be suppressed. Furthermore, by setting the size below the upper limit, the loading amount during handling of the powder can be increased. The average particle size of the powder can be confirmed by observing a scanning electron microscope (SEM) image. In this specification, the "average particle size" can be calculated by measuring the maximum diameter of at least 20 particles using an SEM image and calculating the average value.

[0042] [Protein adsorption method, etc.] The powder according to this embodiment has excellent protein adsorption ability and excellent water resistance, and therefore can be suitably used for protein adsorption. The powder according to this embodiment can be suitably used, for example, as a protein adsorbent, column packing material, immobilization carrier, etc. The method for adsorbing protein to the powder according to this embodiment is not particularly limited, and for example, the powder may be immersed in a solution containing the protein, or stirring or shaking may be performed. Furthermore, for example, the protein may be adsorbed to the powder by pouring a solution containing the protein into a container containing the powder according to this embodiment.

[0043] In this embodiment, the protein to be adsorbed is not particularly limited, and examples thereof include various proteins such as enzymes, antibodies, hormones, etc. Furthermore, the solvent in which such proteins are contained is also not particularly limited, and various buffer solutions (phosphate buffer, citrate buffer, Tris, HEPES, etc.) are preferably used. [Example]

[0044] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0045] [Raw materials] TOCN: TEMPO-oxidized cellulose nanofiber (Rheocrysta I-2SX, Daiichi Kogyo Seiyaku Co., Ltd., cellulose concentration: 2% by mass, cellulose type I crystal structure: "present," number-average fiber diameter: 4 nm, average aspect ratio: 280, carboxyl group content: 1.9 mmol / g) Cellulose particles (comparison example): Cellufine c-500 (manufactured by JNC Corporation) ·ethanol Carbodiimide crosslinking agent (Carbodilite V-02-L2, manufactured by Nisshinbo Chemical Inc.) Oxazoline crosslinking agent (Epocross WS-700 (Epocross is a registered trademark), manufactured by Nippon Shokubai Co., Ltd.)

[0046] [Powder preparation] TOCN and a crosslinker were added to 50 mL of 100% ethanol as a solvent, and the mixture was stirred for 60 minutes using a disperser (IKA Homogenizer T10 basic) at 70 W, Power 6, and 30,000 rpm to prepare a slurry in which cellulose fibers were dispersed in the solvent. Sample 1 did not contain a crosslinker, Samples 2 to 4 contained a carbodiimide compound as a crosslinker, and Sample 6 contained an oxazoline compound as a crosslinker. The amount of crosslinker contained in the slurry was the equivalent weight relative to the anionic group (carboxy group) of TOCN, as shown in Tables 1 and 2 below. The TOCN concentration relative to the total mass of the slurry was 0.08% by mass in terms of solids content. The slurry was spray-dried using a spray dryer (BUCHI Mini Spray Dryer B-290). Spray drying was performed under the following conditions: an inlet temperature of 120 °C, a liquid feed rate of 2.5 mL / min, a gas flow rate of 6 L / min, and droplet diameters of 10 to 200 μm. This resulted in a powder containing TOCN in which some of the carboxylic acids were cross-linked.

[0047] The specific surface area (BET value), total pore volume, and lysozyme adsorption amount of the powder obtained by spray drying were measured. The specific surface area, total pore volume, and lysozyme adsorption amount of general-purpose cellulose particles (sample 5) were also measured. The zeta potential was also measured for the slurry solution before spray drying and for solutions in which the powder obtained by spray drying and the general-purpose cellulose particles were each dispersed in water. The water resistance of the powder obtained by spray drying was also evaluated.

[0048] [Measurement and evaluation methods] Specific surface area (BET value) Specific surface area (m 2 / g) was measured by measuring the nitrogen adsorption isotherm at 77 K using a capacitance measuring device (BEL, BELSORP28SA).

[0049] Total pore volume Total pore volume (cm 3 / g) was measured using a volumetric capacity measuring device (BEL, BELSORP28SA) as the liquid equivalent of the amount of gas adsorbed when the relative pressure was sufficiently close to 1.

[0050] Lysozyme adsorption amount The amount of lysozyme adsorption (mg Lys / g TOCN) was measured using the following method. Chicken egg white lysozyme (MP Biomedical, zeta potential: 7.8 mV, size: 4.5 × 3.0 × 3.0 nm, isoelectric point: 11) was used. First, 10–40 mg of lysozyme was added to 50 mL of water and stirred for 30 minutes using a shaker. Then, 10 mg of the powder, TOCN, or cellulose particles was added and stirred for 120 minutes using a shaker. The mixture was then centrifuged (15,000 rpm, 5 minutes). The absorbance of the supernatant was measured using UV-Vis-NIR spectroscopy (281 nm). The amount of free protein in the supernatant was quantified by comparing it with a separately prepared calibration curve. The mass of lysozyme adsorbed to the sample was calculated by subtracting the amount of free protein in the supernatant from the mass of lysozyme added. The amount of lysozyme adsorption (mg Lys / g TOCN) was defined as the mass of lysozyme adsorbed per solid mass of cellulose fiber in the sample.

[0051] Zeta potential The zeta potential (mV) was measured using a Malvern Zetasizer nano zs. The measurement was carried out in pure water at pH 7.0, with a powder concentration of 0.2 mg / mL, at a temperature of 25°C.

[0052] Water resistance rating The dry powder was redispersed in water at a concentration of 5% by mass, and the state after standing for 6 hours was visually observed, and the water resistance was evaluated according to the following evaluation criteria.

[0053] ○: Powder shape maintained △: The powder shape is partially collapsed ×: Gel-like

[0054] [Measurement and evaluation results] Table 1 shows the measurement results, and Table 2 shows the evaluation results.

[0055] [Table 1]

[0056] [Table 2]

[0057] As shown in Table 1, the powder obtained by spray-drying the slurry had a larger specific surface area, total pore volume, and lysozyme adsorption capacity than the cellulose particles used as a comparative example. This indicates that a powder with excellent protein adsorption properties was obtained. Furthermore, the absolute value of the zeta potential of the solution in which the powder obtained by spray-drying was dispersed in water was higher than that of the slurry solution before spray-drying. This suggests that the powder obtained by spray-drying disperses well in water. Furthermore, when the concentration of cross-linking agent in the slurry was high, the absolute value of the zeta potential of the aqueous dispersion of the powder obtained by spray-drying was small. This suggests that the cross-linking agent reacted with the anionic groups of the cellulose fibers during spray-drying to form a cross-linked structure, resulting in a decrease in the number of anionic groups in the powder.

[0058] As shown in Table 2, when the concentration of cross-linking agent in the slurry is high, the powder shape can be prevented from collapsing when redispersed in water, and as a result, the water resistance of the powder is improved.

[0059] The present invention is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit of the present invention. For example, the technical features in the embodiments and examples corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

Claims

1. A method for producing a powder containing cellulose fibers, comprising: spray drying the slurry; The slurry is A method for producing a cellulose fiber fibrous composition comprising: a cellulose fiber having an anionic group; a solvent containing an organic solvent; and a crosslinking agent reactive with the anionic group; the anionic group comprises a carboxy group, The cellulose fibers are dispersed in the solvent. Powder manufacturing method.

2. The method for producing powder according to claim 1, The method for producing a powder, wherein the slurry contains the crosslinking agent in an amount of 0.05 equivalents or more and 0.5 equivalents or less relative to the anionic groups of the cellulose fibers.

3. A powder containing cellulose fibers having anionic groups, having a crosslinked structure formed by a crosslinking agent bonded to the anionic group, the anionic group comprises a carboxy group, Specific surface area is 50m ２ / g or more 400m ２ / g or less, and the total pore volume is 0.1 cm ３ / g or more 0.85cm ３ / g or less.

4. The powder according to claim 3, A powder, wherein the cellulose fibers are TEMPO-oxidized cellulose nanofibers.

5. The powder according to claim 3 or claim 4, A powder used to adsorb proteins.

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