Nanocellulose and its dispersion

Abstract

To provide a nanocellulose that does not contain an N-oxyl compound and exhibits excellent dispersion stability in a dispersion medium.SOLUTION: Provided is a nanocellulose which is an oxide of a cellulose raw material by hypochlorous acid or a salt thereof, has an average fiber width of 1 nm to 200 nm, substantially does not contain an N-oxyl compound, and has a zeta potential of -30 mV or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to nanocellulose and its dispersion. More specifically, it relates to nanocellulose obtained by defibrating oxidized cellulose, which is produced by oxidizing a cellulosic raw material with an oxidizing agent, and to a nanocellulose dispersion containing the same. [Background technology]

[0002] Various technologies have been proposed for producing nanocellulose materials such as cellulose nanofibers (hereinafter also referred to as CNF) by oxidizing various cellulosic raw materials with an oxidizing agent and then micronizing the resulting oxidized cellulose (see, for example, Patent Document 1 and Patent Document 2).

[0003] Patent Document 1 discloses a method of oxidizing cellulose obtained by using hypochlorous acid or a salt thereof as an oxidizing agent and oxidizing a cellulosic raw material under high-concentration conditions where the effective chlorine concentration in the reaction system is 14 to 43% by mass, and then defibrating and nano-forming the oxidized cellulose. Patent Document 2 discloses a method of oxidizing cellulose obtained by using hypochlorous acid or a salt thereof as an oxidizing agent and oxidizing a cellulosic raw material while adjusting the pH to 5.0 to 14.0 with an effective chlorine concentration in the reaction system of 6 to 14% by mass, and then defibrating and nano-forming the oxidized cellulose. In these technologies, the oxidation treatment is performed without using N-oxyl compounds such as 2,2,6,6-tetramethyl-1-piperidine-N-oxyl radical (TEMPO) as a catalyst, so no N-oxyl compounds remain in the cellulose fibers, and therefore it is possible to manufacture nanocellulose materials while reducing the impact on the environment. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2018 / 230354 [Patent Document 2] International Publication No. 2020 / 027307 [Overview of the project] [Problems that the invention aims to solve]

[0005] Nanocellulose materials are sometimes used dispersed in a dispersion medium such as water or an organic solvent to facilitate mixing with other materials (e.g., resins). Alternatively, nanocellulose materials may be mixed with inorganic particles such as pigments and a dispersion medium to be used in a slurry state. In this case, the nanocellulose material is required to exhibit good dispersion stability in the dispersion medium.

[0006] This invention has been made in view of the above circumstances, and its main objective is to provide nanocellulose that does not contain N-oxyl compounds in the cellulose fibers and has excellent dispersion stability in a dispersion medium. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides the following means. [1] Nanocellulose which is an oxide of a cellulosic raw material with hypochlorous acid or a salt thereof, having an average fiber width of 1 nm or more and 200 nm or less, substantially free of N-oxyl compounds, and having a zeta potential of -30 mV or less. [2] Nanocellulose of [1], wherein the average fiber width is 1 nm or more and 5 nm or less. [3] Nanocellulose of [1] or [2] having an aspect ratio of 20 to 150. [4] Nanocellulose of any of [1] to [3], wherein the light transmittance in a mixture obtained by mixing with water to a solid content concentration of 0.1% by mass is 95% or more. [5] Nanocellulose which is an oxide of a cellulosic raw material made of hypochlorous acid or a salt thereof, which does not contain an N-oxyl compound and has an average fiber width of 1 nm or more and 5 nm or less. [6] Nanocellulose which is an oxide of a cellulosic raw material by hypochlorous acid or a salt thereof, having an average fiber width of 1 nm or more and 200 nm or less, not containing an N-oxyl compound, and having an aspect ratio of 20 or more and 150 or less. [7] Nanocellulose which is an oxide of a cellulosic raw material by hypochlorous acid or a salt thereof, having an average fiber width of 1 nm or more and 200 nm or less, not containing an N-oxyl compound, and having a light transmittance of 95% or more in a mixed solution obtained by mixing with water to a solid content concentration of 0.1% by mass. [8] A nanocellulose dispersion in which any of the nanocelluloses from [1] to [7] is dispersed in a dispersion medium. [Effects of the Invention]

[0008] According to the present invention, nanocellulose with excellent dispersion stability in a dispersion medium can be obtained. Furthermore, since it does not contain N-oxyl compounds, the impact on the environment can be reduced. [Modes for carrying out the invention]

[0009] Nanocellulose The nanocellulose disclosed herein (hereinafter also referred to as "this nanocellulose") is a fibrous nanocellulose obtained by defibrating oxidized cellulose, which is produced by oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof. Furthermore, the oxidized cellulose can also be described as an oxide of the cellulosic raw material due to hypochlorous acid or a salt thereof. This nanocellulose will be described in detail below. Furthermore, since "nanocellulose" is fibrous cellulose made by finely processing oxidized fibrous cellulose, it is also called "fine cellulose fiber."

[0010] Nanocellulose is substantially free of N-oxyl compounds because the cellulosic raw material is oxidized with hypochlorous acid or a salt thereof. Here, in this specification, "substantially free of N-oxyl compounds" means that the nanocellulose contains no N-oxyl compounds at all, or that the content of N-oxyl compounds is 2.0 ppm by mass or less, preferably 1.0 ppm by mass or less, relative to the total amount of nanocellulose. Furthermore, if the content of N-oxyl compounds is an increase from the cellulosic raw material, preferably 2.0 ppm by mass or less, more preferably 1.0 ppm by mass or less, it also means "substantially free of N-oxyl compounds." By substantially eliminating N-oxyl compounds, it is possible to suppress the residue of N-oxyl compounds, which are a cause for concern regarding their impact on the environment and human health, in nanocellulose. The content of N-oxyl compounds can be measured by known means. One known method is to use a trace total nitrogen analyzer. Specifically, the nitrogen component derived from N-oxyl compounds in nanocellulose can be measured as nitrogen content using a trace total nitrogen analyzer (for example, Mitsubishi Chemical Analytec Co., Ltd., instrument name: TN-2100H, etc.).

[0011] • First Embodiment [Fiber width] The average fiber width of this nanocellulose is 1 to 200 nm. When the average fiber width exceeds 200 nm, since the proportion of coarse nanocellulose is large, when the nanocellulose is dispersed in a dispersion medium to form a nanocellulose dispersion, there is a tendency for a large amount of precipitation of the nanocellulose and the quality to deteriorate. Also, since the quality of the nanocellulose dispersion is not uniform, for example, when it is made into a slurry (hereinafter also referred to as "nanocellulose-containing slurry") further containing solid particles such as pigments, the viscosity of the slurry is unstable, and there is a tendency for the handling property and coating property to be easily reduced. From these viewpoints, the average particle diameter of this nanocellulose is preferably 50 nm or less, more preferably 10 nm or less, and particularly preferably 5 nm or less. Further, when the average fiber width is less than 1 nm, it is close to the state of a single cellulose molecule, and the quality as nanocellulose tends to be non-uniform, and when made into a slurry, the viscosity stability, handling property, and coating property tend to be easily reduced. Therefore, the average fiber width is preferably 1.2 nm or more, and more preferably 1.5 nm or more.

[0012] In particular, when the average fiber width of this nanocellulose is 1 to 5 nm, in addition to the dispersion stability in the dispersion medium, when it is made into a nanocellulose-containing slurry, the viscosity stability, handling property, and coating property of the slurry can be made good, which is suitable.

[0013] [Aspect ratio] In this nanocellulose, the aspect ratio (average fiber length / average fiber width) represented by the ratio of the average fiber width to the average fiber length is preferably 20 to 150. When the aspect ratio is 150 or less, a network of fine cellulose is likely to be formed uniformly and densely in the dispersion medium, resulting in a stable structure, thereby improving the dispersion stability. Also, when it is made into a nanocellulose-containing slurry, a network of solid particles and fine cellulose is likely to be formed uniformly and densely, suppressing the aggregation of solid particles, and improving the dispersion stability. Furthermore, it can suppress the aggregation of solid particles and nanocellulose, or the aggregation of nanocellulose itself, improving the handling property of the slurry and suppressing uneven processing. From these viewpoints, the aspect ratio is more preferably 145 or less, still more preferably 130 or less, even more preferably 120 or less, and even more preferably 100 or less.

[0014] On the other hand, when the aspect ratio is too low, that is, when the shape of the nanocellulose is a thick rod shape rather than an elongated fibrous shape, it becomes difficult to form a network, aggregation occurs due to uneven distribution, and the viscosity stability of the slurry tends to decrease. Also, since the viscosity of the slurry increases, the handling property tends to decrease, and the slurry coating property may be inferior. Therefore, the aspect ratio is more preferably 30 or more, still more preferably 35 or more, and even more preferably 40 or more.

[0015] The average fiber width and average fiber length were calculated by mixing nanocellulose with water to a nanocellulose concentration of approximately 1 to 10 ppm, naturally drying the sufficiently diluted cellulose aqueous dispersion on a mica substrate, observing the shape of the nanocellulose using a scanning probe microscope, randomly selecting an arbitrary number of fibers from the obtained image, and calculating the fiber length by setting the cross-sectional height of the shape image as the fiber width and the perimeter ÷ 2 as the fiber length. Image processing software can be used to calculate the average fiber width and average fiber length in this way. In this case, the image processing conditions are arbitrary, but even with the same image, the calculated values ​​may differ depending on the image processing conditions. Preferably, the range of difference in values ​​due to image processing conditions is within ±100 nm for the average fiber length. Preferably, the range of difference in values ​​due to conditions is within ±10 nm for the average fiber width. A more detailed measurement method follows the method described in the examples below.

[0016] Preferably, this nanocellulose has a structure in which at least two of the hydroxyl groups of the glucopyranose ring constituting the cellulose are oxidized, and more specifically, a structure in which the hydroxyl groups at positions 2 and 3 of the glucopyranose ring are oxidized and carboxyl groups are introduced. Furthermore, it is preferable that the hydroxyl group at position 6 of the glucopyranose ring in this nanocellulose remains unoxidized and as a hydroxyl group. Note that the position of the carboxyl group on the glucopyranose ring of the nanocellulose is in solid form. 13 This can be analyzed using 1C-NMR spectroscopy. The above solid 13 In the 1C-NMR spectrum, the presence of peaks corresponding to the carboxyl groups at positions 2 and 3 of the glucopyranose ring indicates the presence of an oxidized structure. In this case, the peaks corresponding to the carboxyl groups at positions 2 and 3 may be observed as broad peaks in the range of 165 ppm to 185 ppm. The definition of a broad peak can be determined by the area ratio of the peaks. In other words, a baseline is drawn over the peaks in the NMR spectrum in the range of 165 ppm to 185 ppm, and the total area value is determined. Then, the ratio of the two peak area values ​​obtained by vertically dividing the area value at the peak top (larger area value / smaller area value) is calculated, and if this ratio of peak area values ​​is 1.2 or greater, it can be said that it is a broad peak. Furthermore, the presence or absence of the broad peak can be determined by the ratio of the baseline length L in the range of 165 ppm to 185 ppm to the length L' of the perpendicular from the peak top to the baseline. That is, if the ratio L' / L is 0.1 or greater, it can be determined that a broad peak exists. The ratio L' / L may also be 0.2 or greater, 0.3 or greater, 0.4 or greater, or 0.5 or greater. There is no particular upper limit to the ratio L' / L, but it is usually sufficient if it is 3.0 or less, 2.0 or less, or 1.0 or less.

[0017] Furthermore, the structure of the glucopyranose ring in this nanocellulose can also be determined by analysis according to the method described in Sustainable Chem. Eng. 2020, 8, 48, 17800-17806.

[0018] [Zeta potential] In one preferred embodiment of this disclosure, the nanocellulose has a zeta potential of -30mV or less. When the zeta potential is -30mV or less (i.e., an absolute value of 30mV or more), sufficient repulsion between microfibrils is obtained, making it easier to generate nanocellulose with a high surface charge density during mechanical defibrillation. This improves the dispersion stability of the nanocellulose, resulting in excellent viscosity stability, handling properties, and coating properties when used as a slurry. From the viewpoint of dispersion stability, there is no particular lower limit to the zeta potential. However, when the zeta potential is -100mV or more (i.e., an absolute value of 100mV or less), oxidative severance in the fiber direction associated with the progression of oxidation tends to be suppressed, so nanocellulose of uniform size can be obtained, and excellent coating properties can be achieved.

[0019] From the above viewpoint, the zeta potential of this nanocellulose is preferably -35mV or less, more preferably -40mV or less, and even more preferably -50mV or less. Furthermore, the lower limit of the zeta potential is preferably -90mV or more, more preferably -85mV or more, even more preferably -80mV or more, even more preferably -77mV or more, even more preferably -70mV or more, and even more preferably -65mV or more. The range of the zeta potential can be appropriately combined from the lower and upper limits described above. The zeta potential is preferably -90mV or more and -30mV or less, more preferably -85mV or more and -30mV or less, even more preferably -80mV or more and -30mV or less, even more preferably -77mV or more and -30mV or less, even more preferably -70mV or more and -30mV or less, even more preferably -65mV or more and -30mV or less, and even more preferably -65mV or more and -35mV or less. In this specification, the zeta potential is the value measured for a cellulose aqueous dispersion prepared by mixing nanocellulose and water to a nanocellulose concentration of 0.1% by mass, under conditions of pH 8.0 and 20°C. Specifically, it can be measured according to the conditions described in the examples below.

[0020] [Light transmittance] Nanocellulose dispersions, in which this nanocellulose is dispersed in a dispersion medium, exhibit high light transmittance due to reduced light scattering from cellulose fibers. Specifically, in one preferred embodiment, the nanocellulose, when mixed with water to a solid content concentration of 0.1% by mass, exhibits a light transmittance of 95% or more. Therefore, this nanocellulose and nanocellulose dispersions containing it can be widely applied and useful in applications requiring transparency. The light transmittance is more preferably 96% or more, even more preferably 97% or more, and even more preferably 99% or more. The light transmittance is the value measured at a wavelength of 660 nm using a spectrophotometer.

[0021] [Method for producing nanocellulose] Next, the method for producing this nanocellulose will be described. This nanocellulose can be produced by a method comprising step A, in which a cellulosic raw material is oxidized with hypochlorous acid or a salt thereof to obtain oxidized cellulose, and step B, in which the oxidized cellulose is defibrated. Furthermore, since "oxidized cellulose" is fibrous cellulose that has been oxidized, it is also called "oxidized cellulose fiber."

[0022] (Process A: Production of oxidized cellulose) Cellulosic raw materials are not particularly limited as long as they are primarily composed of cellulose. Examples include pulp, natural cellulose, regenerated cellulose, and fine cellulose obtained by depolymerizing cellulose through mechanical treatment. Commercially available cellulose-based raw materials such as crystalline cellulose made from pulp can be used as is. In addition, unused biomass containing a large amount of cellulose, such as okara (soy pulp) or soybean hulls, may also be used as raw materials. Furthermore, the cellulose-based raw materials may be pre-treated with an appropriate concentration of alkali to facilitate the penetration of the oxidizing agent into the pulp.

[0023] Examples of hypochlorous acid or its salts used for the oxidation of cellulosic raw materials include hypochlorous acid water, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and ammonium hypochlorite. Among these, sodium hypochlorite is preferred due to its ease of handling.

[0024] One method for producing oxidized cellulose by oxidation of cellulosic raw materials is to mix the cellulosic raw materials with a reaction solution containing hypochlorous acid or a salt thereof. Water is preferred as the solvent in the reaction solution because it is easy to handle and less likely to cause side reactions. The effective chlorine concentration of hypochlorous acid or a salt thereof in the reaction solution is preferably 6 to 43% by mass, more preferably 7 to 43% by mass, even more preferably 10 to 43% by mass, and still more preferably 14 to 43% by mass. When the effective chlorine concentration of the reaction solution is within the above range, the amount of carboxyl groups in the oxidized cellulose can be sufficiently increased, and the defibrillation of the oxidized cellulose can be easily performed when obtaining nanocellulose.

[0025] From the viewpoint of efficiently and sufficiently increasing the amount of carboxyl groups in oxidized cellulose, the effective chlorine concentration of the reaction solution is more preferably 15% by mass or more, even more preferably 18% by mass or more, and even more preferably 20% by mass or more. Furthermore, from the viewpoint of suppressing excessive decomposition of cellulose during defibration, the effective chlorine concentration of the reaction solution is more preferably 40% by mass or less, and even more preferably 38% by mass or less. The range of the effective chlorine concentration of the reaction solution can be appropriately combined from the lower and upper limits described above. The range of the effective chlorine concentration is more preferably 16 to 43% by mass, and even more preferably 18 to 40% by mass.

[0026] The effective chlorine concentration of hypochlorous acid or its salts is defined as follows. Hypochlorous acid is a weak acid that exists as an aqueous solution, and hypochlorites are compounds in which the hydrogen of hypochlorous acid is replaced by other cations. For example, sodium hypochlorite, which is a hypochlorite, exists in a solvent (preferably in an aqueous solution), so its concentration is measured as the amount of effective chlorine in the solution, not as the concentration of sodium hypochlorite. Here, regarding the effective chlorine of sodium hypochlorite, the oxidizing power of the divalent oxygen atoms produced by the decomposition of sodium hypochlorite is equivalent to two atomic equivalents of monovalent chlorine. Therefore, the bound chlorine atoms of sodium hypochlorite (NaClO) have the same oxidizing power as two unbound chlorine atoms (Cl2), and effective chlorine = 2 × (chlorine in NaClO). The specific measurement procedure is as follows: First, the sample is accurately weighed, water, potassium iodide, and acetic acid are added and left to stand, and the liberated iodine is titrated with sodium thiosulfate solution using starch aqueous solution as an indicator to measure the effective chlorine concentration.

[0027] The oxidation reaction of cellulosic raw materials with hypochlorous acid or its salt is preferably carried out while adjusting the pH within the range of 5.0 to 14.0. Within this range, the oxidation reaction of cellulosic raw materials can proceed sufficiently, and the amount of carboxyl groups in the oxidized cellulose can be sufficiently increased. This makes it easy to defibrillate the oxidized cellulose. The pH of the reaction system is more preferably 6.0 or higher, even more preferably 7.0 or higher, and even more preferably 8.0 or higher. The upper limit of the pH of the reaction system is more preferably 13.5 or lower, and even more preferably 13.0 or lower. Furthermore, the pH range of the reaction system is more preferably 7.0 to 14.0, and even more preferably 8.0 to 13.5.

[0028] The following will further explain the method for producing oxidized cellulose, using sodium hypochlorite as the hypochlorous acid or its salt as an example.

[0029] When oxidizing cellulosic raw materials using sodium hypochlorite, the reaction solution is preferably an aqueous sodium hypochlorite solution. Methods for adjusting the effective chlorine concentration of the aqueous sodium hypochlorite solution to the desired concentration (for example, target concentration: 6% to 43% by mass) include concentrating an aqueous sodium hypochlorite solution with an effective chlorine concentration lower than the target concentration, diluting an aqueous sodium hypochlorite solution with an effective chlorine concentration higher than the target concentration, and dissolving sodium hypochlorite crystals (for example, sodium hypochlorite pentahydrate) in a solvent. Among these, adjusting the effective chlorine concentration to act as an oxidizing agent by diluting the aqueous sodium hypochlorite solution or dissolving sodium hypochlorite crystals in a solvent is preferred because it results in less self-decomposition (i.e., less decrease in effective chlorine concentration) and is simpler to adjust.

[0030] The method for mixing the cellulose-based raw material and the sodium hypochlorite aqueous solution is not particularly limited, but from the viewpoint of ease of operation, it is preferable to add the cellulose-based raw material to the sodium hypochlorite aqueous solution and mix them.

[0031] To efficiently carry out the oxidation reaction of the cellulosic raw material, it is preferable to stir the mixture of the cellulosic raw material and the sodium hypochlorite aqueous solution during the oxidation reaction. Examples of stirring methods include a magnetic stirrer, stirring rod, stirrer with stirring blades (three-one motor), homomixer, disperser-type mixer, homogenizer, and external circulation stirring. Of these, it is preferable to use one or more types of shear-type stirrers such as homomixers and homogenizers, stirrers with stirring blades, and disperser-type mixers, as these allow the oxidation reaction of the cellulosic raw material to proceed smoothly and make it easy to adjust the degree of polymerization of the oxidized cellulose to a predetermined value or less. In particular, it is preferable to use a stirrer with stirring blades. When using a stirrer with stirring blades, a device equipped with known stirring blades such as propeller blades, paddle blades, and turbine blades can be used as the stirrer. Furthermore, when using a stirrer with stirring blades, it is preferable to stir at a rotational speed of 50 to 300 rpm.

[0032] The reaction temperature in the oxidation reaction is preferably 15°C to 100°C, and more preferably 20°C to 90°C. During the reaction, the pH of the reaction system decreases as carboxyl groups are generated in the cellulosic raw material by the oxidation reaction. Therefore, from the viewpoint of efficiently carrying out the oxidation reaction, it is preferable to add an alkaline agent (e.g., sodium hydroxide) or an acid (e.g., hydrochloric acid) to the reaction system to adjust the pH of the reaction system to the above preferred range. The reaction time for the oxidation reaction can be set according to the degree of oxidation, but it is preferably about 15 minutes to 50 hours. If the pH of the reaction system is 10 or higher, it is preferable to set the reaction temperature to 30°C or higher and / or the reaction time to 30 minutes or higher.

[0033] Furthermore, by adjusting the reaction time, reaction temperature, stirring conditions, etc., of the oxidation reaction, the fiber width and zeta potential of nanocellulose can be adjusted to desired values. Specifically, as the reaction time is increased and / or the reaction temperature is increased, oxidation of the cellulose microfibrils on the surface of the cellulosic raw material progresses, and the average fiber width tends to decrease due to increased repulsion between fibrils caused by electrostatic repulsion and osmotic pressure. In addition, the zeta potential tends to be increased by setting one or more of the oxidation reaction time, reaction temperature, and stirring conditions (for example, increasing the reaction time) to the side that promotes further oxidation (i.e., the side that increases the degree of oxidation).

[0034] The amount of carboxyl groups in the oxidized cellulose obtained by the above oxidation reaction is preferably 0.30 to 2.0 mmol / g. When the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more, the defibrillability of the oxidized cellulose can be sufficiently high, and nanocellulose with a uniform fiber width can be obtained. This makes it possible to homogenize the quality of the nanocellulose-containing slurry and improve the viscosity stability, handling properties, and coating properties of the slurry. On the other hand, when the amount of carboxyl groups is 2.0 mmol / g or less, excessive decomposition of cellulose during the defibrillation process can be suppressed, and nanocellulose with a low proportion of particulate cellulose and uniform quality can be obtained. From this viewpoint, the amount of carboxyl groups in the oxidized cellulose is more preferably 0.35 mmol / g or more, even more preferably 0.40 mmol / g or more, even more preferably 0.42 mmol / g or more, even more preferably 0.50 mmol / g or more, even more preferably more than 0.50 mmol / g, and even more preferably 0.55 mmol / g or more. The upper limit of the carboxyl group content may be 1.5 mmol / g or less, 1.2 mmol / g or less, 1.0 mmol / g or less, or 0.9 mmol / g or less. The preferred range for the carboxyl group content can be determined by appropriately combining the upper and lower limits described above. The carboxyl group content of this oxidized cellulose is more preferably 0.35 to 2.0 mmol / g, even more preferably 0.35 to 1.5 mmol / g, even more preferably 0.40 to 1.5 mmol / g, even more preferably 0.50 to 1.2 mmol / g, even more preferably more than 0.50 to 1.2 mmol / g, and even more preferably 0.55 to 1.0 mmol / g.

[0035] The amount of carboxyl groups (mmol / g) in oxidized cellulose can be calculated using the following formula by adding a 0.1 M hydrochloric acid solution to an aqueous solution containing oxidized cellulose to adjust the pH to 2.5, then adding a 0.05 N sodium hydroxide solution dropwise until the pH becomes 11, and measuring the electrical conductivity. The amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity is gradual, is then calculated from the amount of sodium hydroxide consumed (a). Amount of carboxy group = a (ml) × 0.05 / mass of oxidized cellulose (g)

[0036] Using the solution containing oxidized cellulose obtained by the above reaction, known isolation treatments such as filtration are carried out, and further purification is performed as necessary to obtain oxidized cellulose as an oxide of a cellulose-based raw material with hypochlorous acid or its salt. Also, before the isolation treatment such as filtration, from the viewpoint of improving the filtration property and yield of the isolation treatment, an acid is added to the solution containing oxidized cellulose, for example, the pH is set to 4.0 or less, and at least a part of the carboxy groups generated by oxidation is in the salt form (-COO - X + :X + refers to cations such as sodium and lithium) can be converted to the proton form (-COO - H + ). In the infrared absorption spectrum, the proton form has a peak around 1720 cm -1 and the salt form has a peak around 1600 cm -1 , so they can be distinguished. The solution containing oxidized cellulose obtained by the above reaction may be directly subjected to fibrillation treatment.

[0037] In the solution containing oxidized cellulose, when the pH is set to 4.0 or less for the isolation treatment, in order to improve the handling property when used for the subsequent fibrillation treatment, for example, a base is added to make the pH 6.0 or more, and at least a part of the carboxy groups is in the salt form (-COO - X + :X + refers to cations such as sodium and lithium). Also, the solution containing oxidized cellulose may be made into a composition containing oxidized cellulose by replacing its solvent or the like. In the composition containing oxidized cellulose, for example, the pH is set to an alkaline condition of 10 or more, and at least a part of the carboxy groups is in the salt form (-COO - X + :X + refers to cations such as sodium and lithium).

[0038] A method for producing oxidized cellulose may further include a step of mixing the obtained oxidized cellulose with a compound having a modifying group in order to control the physical properties of the oxidized cellulose. The compound having a modifying group is not particularly limited as long as it has a modifying group that can form an ionic or covalent bond with the carboxyl groups and hydroxyl groups of the oxidized cellulose. Examples of compounds having a modifying group that can form an ionic bond include primary amines, secondary amines, tertiary amines, quaternary ammonium compounds, and phosphonium compounds. Examples of compounds having a modifying group that can form a covalent bond include alcohols, isocyanate compounds, and epoxy compounds. As described above, oxidized cellulose encompasses salt-type, proton-type, and modified forms with modifying groups. Furthermore, nanocellulose obtained from this oxidized cellulose also encompasses salt-type, proton-type, and modified forms with modifying groups.

[0039] (Process B: Fiber removal treatment) This nanocellulose can be obtained by defibrating and nano-reducing the oxidized cellulose obtained above. Methods for defibrating oxidized cellulose include methods using weak stirring with a magnetic stirrer, etc., and mechanical defibration. Mechanical defibration is preferred for oxidized cellulose because it allows for sufficient defibration of the oxidized cellulose and shortens the defibration time. Here, nanocellulose (also called nanocellulose) is a general term for cellulose that has been nano-reduced, and includes cellulose nanofibers and cellulose nanocrystals.

[0040] Examples of mechanical defibration methods include methods using various mixing and stirring devices such as screw mixers, paddle mixers, disperser mixers, turbine mixers, homomixers under high-speed rotation, high-pressure homogenizers, ultra-high-pressure homogenizers, double-cylinder homogenizers, ultrasonic homogenizers, water flow opposing impact type dispersers, beaters, disc type refiners, conical type refiners, double-disc type refiners, grinders, single-screw or multi-screw kneaders, rotational and revolving stirrers, and vibrating stirrers. By using these devices individually or in combination of two or more types, and preferably treating oxidized cellulose in a dispersion medium, oxidized cellulose can be nano-sized to produce nanocellulose.

[0041] For defibration of oxidized cellulose, a method using an ultra-high pressure homogenizer is preferable because it allows for the efficient production of nanocellulose with more advanced defibration. When applying defibration treatment with an ultra-high pressure homogenizer, the pressure during defibration treatment is preferably 100 MPa or higher, more preferably 120 MPa or higher, and even more preferably 150 MPa or higher. The number of defibration treatments is not particularly limited, but from the viewpoint of sufficiently advancing defibration, it is preferably two or more times, more preferably three or more times. Furthermore, the above-mentioned oxidized cellulose can also be sufficiently defibrated by mild stirring using a rotational agitator or a vibrating agitator. An example of a vibrating agitator is a vortex mixer (touch mixer). In other words, with the above-mentioned oxidized cellulose, homogenized nanocellulose can be obtained even when defibration treatment is performed under mild defibration conditions.

[0042] The defibration treatment is preferably carried out with oxidized cellulose mixed with a dispersion medium. There are no particular restrictions on the dispersion medium, and it can be appropriately selected depending on the purpose. Specific examples of dispersion media include water, alcohols, ethers, ketones, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. One of these may be used alone as the solvent, or two or more may be used in combination.

[0043] Examples of alcohols among the above dispersion media include methanol, ethanol, isopropanol, isobutanol, sec-butyl alcohol, tert-butyl alcohol, methyl cellosolve, ethylene glycol, and glycerin. Examples of ethers include ethylene glycol dimethyl ether, 1,4-dioxane, and tetrahydrofuran. Examples of ketones include acetone and methyl ethyl ketone.

[0044] By using an organic solvent as a dispersion medium during the defibration process, the isolation of oxidized cellulose and the nanocellulose obtained by defibration becomes easier. Furthermore, since nanocellulose is obtained dispersed in an organic solvent, it becomes easier to mix it with resins that dissolve in organic solvents and their raw material monomers. The nanocellulose dispersion obtained by dispersing the defibrated nanocellulose in water and / or an organic solvent dispersion medium can be used for mixing with various components such as resins, rubbers, and solid particles.

[0045] The nanocellulose and nanocellulose dispersions containing the same described above can be applied to a variety of uses. Specifically, for example, they may be used as reinforcing materials mixed with various materials (e.g., resins, fibers, rubber, etc.), or as thickeners or dispersants in various applications (e.g., food, cosmetics, pharmaceuticals, paints, inks, etc.). Furthermore, the nanocellulose dispersion can be formed into a film and used as various sheets or films. The fields in which this nanocellulose and nanocellulose dispersion can be applied are not particularly limited, and they can be used in the manufacture of products in various fields such as automotive components, machine parts, electrical appliances, electronic equipment, cosmetics, pharmaceuticals, building materials, daily necessities, stationery, etc. In addition, for example, when nanocellulose and nanocellulose dispersions containing the same are used as additives to slurries containing inorganic particles such as pigments, they are preferable because they can improve the viscosity stability, handling properties, and coating performance of the slurry.

[0046] • Second embodiment In one preferred embodiment of the present disclosure, the nanocellulose is nanocellulose obtained by oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof (also referred to as nanocellulose which is an oxide of the cellulosic raw material by hypochlorous acid or a salt thereof), does not contain an N-oxyl compound, and has an average fiber width of 1 nm or more and 5 nm or less. When the average fiber width of the nanocellulose is 1 to 5 nm, the zeta potential of the nanocellulose is preferably -25 mV or less, and more preferably -30 mV or less, in that it improves the dispersion stability of the nanocellulose and improves the handling properties when it is made into a slurry. Details of the method for producing the nanocellulose can be found by referring to the description of the first embodiment above.

[0047] • Third embodiment In one preferred embodiment of the present disclosure, the nanocellulose is nanocellulose obtained by oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof (also referred to as nanocellulose which is an oxide of the cellulosic raw material by hypochlorous acid or a salt thereof), does not contain N-oxyl compounds, and has an aspect ratio of 20 to 150. When the aspect ratio of the nanocellulose is 20 to 150, the zeta potential of the nanocellulose is preferably -25mV or less, and more preferably -30mV or less, in that it improves the dispersion stability of the nanocellulose and improves the handling properties when it is made into a slurry. Details of the method for producing the nanocellulose can be found by referring to the description of the first embodiment above. [Examples]

[0048] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the following, unless otherwise specified, "parts" means "parts by mass" and "%" means "percent mass".

[0049] (1) Production of oxidized cellulose and nanocellulose [Manufacturing Example 1] As a cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5mm squares with scissors and processed at 25,000 rpm for 1 minute using an Osaka Chemical Co., Ltd. "Wonder Blender WB-1" to mechanically defibrate it into a cotton-like material. 350 g of sodium hypochlorite pentahydrate crystals with an effective chlorine concentration of 42% by mass was placed in a beaker, and pure water was added and stirred to obtain a sodium hypochlorite aqueous solution with an effective chlorine concentration of 21% by mass. 35% by mass hydrochloric acid was then added and stirred to obtain an aqueous solution with a pH of 11.0. This sodium hypochlorite aqueous solution was heated to 30°C in a constant temperature water bath while being stirred at 200 rpm using a propeller-type stirring blade in a stirrer (Three One Motor, BL600) manufactured by Shinto Kagaku Co., Ltd. Then, 50 g of the mechanically defibrated coniferous kraft pulp (carboxyl group content: 0.05 mmol / g) was added. After supplying the cellulosic raw materials, the reaction was carried out by adjusting the pH to 11.0 while maintaining the temperature at 30°C in the same constant-temperature water bath, and adding 48% by mass sodium hydroxide. The mixture was then stirred for 20 minutes at 200 rpm using a propeller-type stirring blade in the aforementioned stirrer. After the reaction was complete, the product was separated into solid and liquid by suction filtration using a PTFE membrane filter with a mesh size of 0.1 μm, and the obtained oxidized cellulose was washed with pure water. The amount of carboxyl groups in the filtered product (oxidized cellulose) after washing was measured to be 0.37 mmol / g. Next, a 5% dispersion was prepared by adding pure water to oxidized cellulose, and this was processed at 200 MPa for 10 passes using a Sugino Machine Co., Ltd. ultra-high pressure homogenizer "Starburst Lab HJP-25005" to obtain CNF aqueous dispersion A as a nanocellulose dispersion. In the ultra-high pressure homogenizer, the oxidized cellulose aqueous dispersion is circulated through the ultra-high pressure defibration section built into the homogenizer to promote defibration. One pass is defined as one cycle of passing the dispersion through this ultra-high pressure defibration section. Furthermore, the nitrogen content derived from N-oxyl compounds in oxidized cellulose was measured using a trace total nitrogen analyzer (Mitsubishi Chemical Analytec Co., Ltd., instrument name: TN-2100H), and the increase from the raw pulp was calculated to be less than 1 ppm.

[0050] The effective chlorine concentration in the sodium hypochlorite aqueous solution was measured by the following method. (Measurement of available chlorine concentration in sodium hypochlorite aqueous solution) 0.582 g of an aqueous solution of sodium hypochlorite pentahydrate crystals added to pure water was precisely weighed, 50 ml of pure water was added, 2 g of potassium iodide and 10 ml of acetic acid were added, and the container was immediately sealed and left in the dark for 15 minutes. After 15 minutes, the liberated iodine was titrated with a 0.1 mol / L sodium thiosulfate solution (indicator: starch solution), and the titration volume was 34.55 ml. A blank test was performed separately and corrected, and since 1 ml of 0.1 mol / L sodium thiosulfate solution corresponds to 3.545 mg Cl, the effective chlorine concentration in the sodium hypochlorite aqueous solution is 21% by mass.

[0051] The amount of carboxyl groups in oxidized cellulose was measured by the following method. (Measurement of carboxyl group content) To 60 ml of an aqueous dispersion of oxidized cellulose, adjusted to a concentration of 0.5% by mass, a 0.1 M hydrochloric acid solution was added to bring the pH to 2.5. Then, a 0.05 N sodium hydroxide solution was added dropwise, and the electrical conductivity was measured until the pH reached 11.0. The amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity was gradual (a), was used to calculate the amount of carboxyl groups (mmol / g) using the following formula. Amount of carboxyl groups = a (ml) × 0.05 / Mass of oxidized cellulose (g)

[0052] [Manufacturing Example 2] CNF aqueous dispersion B was obtained by processing under the same conditions as in Production Example 1, except that the reaction time in the oxidation reaction was set to 30 minutes. [Manufacturing Example 3] A CNF aqueous dispersion C was obtained by processing under the same conditions as in Production Example 1, except that the reaction time in the oxidation reaction was set to 120 minutes. [Manufacturing Example 4] CNF aqueous dispersion D was obtained by processing under the same conditions as in Production Example 1, except that the reaction time in the oxidation reaction was set to 360 minutes. [Manufacturing Example 5] A CNF aqueous dispersion E was obtained by processing under the same conditions as in Production Example 1, except that the reaction time in the oxidation reaction was set to 480 minutes. [Manufacturing Example 6] A CNF aqueous dispersion F was obtained by processing under the same conditions as in Production Example 1, except that the reaction temperature in the oxidation reaction was changed from 30°C to 40°C and the reaction time was set to 120 minutes. [Manufacturing Example 7] CNF aqueous dispersion G was obtained by processing under the same conditions as in Production Example 1, except that the reaction temperature in the oxidation reaction was changed from 30°C to 50°C and the reaction time was set to 120 minutes. [Manufacturing Example 8] CNF aqueous dispersion H was obtained by processing under the same conditions as in Production Example 1, except that the reaction temperature in the oxidation reaction was changed from 30°C to 40°C and the reaction time was set to 480 minutes. [Manufacturing Example 9] CNF aqueous dispersion I was obtained by processing under the same conditions as in Production Example 1, except that the reaction temperature in the oxidation reaction was changed from 30°C to 20°C and the reaction time was set to 120 minutes. [Manufacturing Example 10] CNF aqueous dispersion J was obtained by processing under the same conditions as in Production Example 1, except that the reaction time in the oxidation reaction was set to 15 minutes. [Manufacturing Example 11] CNF aqueous dispersion K was obtained by processing under the same conditions as in Production Example 1, except that the reaction temperature in the oxidation reaction was changed from 30°C to 15°C and the reaction time was set to 120 minutes.

[0053] The oxidized cellulose obtained in each manufacturing example was freeze-dried, and the solid sample was left at 23°C and 50% RH for at least 24 hours. 13 ¹ 13 The measurement conditions for C-NMR are shown below. (1) Sample tube: Zirconia tube (4 mm diameter) (2) Magnetic field strength: 9.4T (1H resonance frequency: 400MHz) (3) MAS rotation speed: 15kHz (4) Pulse sequence: CPMAS method (5) Contact time: 3ms (6) Waiting time: 5 seconds (7) Cumulative number of times: 10,000 to 15,000 times (8) Measuring device: JNM ECA-400 (manufactured by JEOL Ltd.) Furthermore, it was confirmed from two-dimensional NMR measurements using a model molecule of the oxidized cellulose that the oxidized cellulose obtained in each production example has a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized and carboxyl groups are introduced. Also, regarding the sixth-ranked item, solid cellulose-based raw materials 13 1C-NMR and solid oxidized cellulose 13 Since no change was observed in the spectral data compared with C-NMR, it was determined that the hydroxyl group at position 6 was not oxidized and remained as a hydroxyl group in the oxidized cellulose.

[0054] [Comparative Manufacturing Example 1] As a cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5mm squares with scissors and processed at 25,000 rpm for 1 minute using an Osaka Chemical Co., Ltd. "Wonder Blender WB-1" to mechanically defibrate it into a cotton-like material. 30.0 g of sodium hypochlorite pentahydrate crystals with an effective chlorine concentration of 43% by mass was placed in a 100 ml beaker, and pure water and 35% by mass hydrochloric acid were added and stirred to prepare an aqueous solution with an effective chlorine concentration of 21% by mass and a pH of 11.0. This sodium hypochlorite aqueous solution was heated to 30°C in a constant temperature water bath while being stirred with a stirrer, and then 0.35 g of the mechanically defibrated coniferous kraft pulp described above was added. After supplying the cellulosic raw material, the mixture was kept warm at 30°C in the same constant-temperature water bath, and 48% by mass of sodium hydroxide was added to maintain a pH of 11.0. The mixture was then stirred with a stirrer for 30 minutes. Next, the product was separated into solid and liquid components by suction filtration using a PTFE membrane filter with a mesh size of 0.1 μm, and the resulting filtered product was washed with pure water. The amount of carboxyl groups in the filtered product (oxidized cellulose) after washing was measured to be 0.42 mmol / g. The obtained oxidized cellulose was dispersed in pure water to prepare a 5% dispersion, which was then subjected to defibrillation treatment for 10 minutes using a Hielscher UP-400S ultrasonic homogenizer under the conditions of CYCLE=0.5 and AMPLYUDE=50 to obtain a CNF aqueous dispersion P. In the ultrasonic homogenizer, the ultrasonic oscillator was immersed in the oxidized cellulose aqueous dispersion in a container, and defibrillation was promoted by the ultrasonic waves emitted from the oscillator.

[0055] [Comparative Manufacturing Example 2] As a cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5mm squares with scissors and processed at 25,000 rpm for 1 minute using an Osaka Chemical Co., Ltd. "Wonder Blender WB-1" to mechanically defibrate it into a cotton-like material. 30.3 g of sodium hypochlorite pentahydrate crystals with an effective chlorine concentration of 42% by mass was placed in a beaker, and pure water was added and stirred to adjust the effective chlorine concentration to 14% by mass. Then, 35% by mass hydrochloric acid was added and stirred to prepare an aqueous solution with a pH of 9.0. This sodium hypochlorite aqueous solution was heated to 30°C in a constant temperature water bath while being stirred with a stirrer, and then 0.35 g of the mechanically defibrated coniferous kraft pulp described above was added. After supplying the cellulosic raw materials, the reaction was carried out by adjusting the pH to 9.0 while maintaining the temperature at 30°C in the same constant-temperature water bath, and stirring with a stirrer for 30 minutes. After the reaction was complete, the product was separated into solid and liquid by suction filtration using a PTFE mesh filter with a mesh size of 0.1 μm, and the resulting filtered product was washed with pure water. The amount of carboxyl groups in the filtered product (oxidized cellulose) after washing was measured to be 1.12 mmol / g. Next, a 5% dispersion was prepared by adding pure water to oxidized cellulose, and the dispersion was subjected to defibration treatment using an ultrasonic homogenizer under the same conditions as in Comparative Production Example 1 to obtain CNF aqueous dispersion Q.

[0056] [Comparative Manufacturing Example 3] As a cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5mm squares with scissors and mechanically defibrated into a cotton-like material by processing it at 25,000 rpm for 1 minute using an Osaka Chemical "Wonder Blender WB-1". The cellulose fibers after mechanical defibration were dispersed in sufficient water and wet powder was obtained by suction filtration using a PTFE mesh filter with a mesh opening of 0.1 μm. The above wet powder (80% moisture by mass, equivalent to 20g of dry powder) is placed in a container, and then an ozone concentration of 200g / m³ is added. 3 60 L of ozone-oxygen mixed gas was added and shaken at 25°C for 2 minutes. After standing for 6 hours, the ozone and other substances in the container were removed, and the oxidized cellulose was taken out and washed with pure water by suction filtration using a PTFE mesh filter with a mesh size of 0.1 μm. Pure water was added to the obtained oxidized cellulose to prepare a 2% by mass dispersion, and sodium hydroxide was added to make a 0.3% by mass sodium hydroxide solution. After stirring for 5 minutes, it was left to stand at 25°C for 30 minutes. Subsequently, it was washed with pure water by suction filtration using a PTFE mesh filter with a mesh size of 0.1 μm. The amount of carboxyl groups in the oxidized cellulose after washing was measured to be 0.43 mmol / g. A 5% dispersion was prepared by adding pure water to the oxidized cellulose, and this was processed using a Sugino Machine Co., Ltd. ultra-high pressure homogenizer "Starburst Lab HJP-25005" under conditions of 200 MPa and 10 passes to obtain CNF aqueous dispersion R.

[0057] [Comparative Manufacturing Example 4] As a cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5mm squares with scissors and processed at 25,000 rpm for 1 minute using an Osaka Chemical Co., Ltd. "Wonder Blender WB-1" to mechanically defibrate it into a cotton-like material. 4.92 g of sodium periodate was placed in a beaker, and pure water was added to make an aqueous solution (total volume 600 ml). This sodium periodate aqueous solution was heated to 55°C in a constant temperature water bath while being stirred at 200 rpm using a propeller-type stirring blade with a stirrer manufactured by Shinto Kagaku Co., Ltd. (Three One Motor, BL600), and then 6 g of the mechanically defibrated softwood kraft pulp described above was added. After supplying the cellulose-based raw materials, the mixture was stirred under the same conditions for 3 hours using a stirrer while maintaining the temperature at 55°C in the same constant-temperature water bath. After the reaction was complete, the product was separated into solid and liquid components by suction filtration using a PTFE membrane filter with a mesh size of 0.1 μm, and then washed with pure water. Next, the product obtained above was added to a 1M aqueous acetic acid solution containing sodium chlorite, and the mixture was stirred at 25°C for 48 hours under the same stirring conditions as above. After the reaction was complete, the product was separated into solid and liquid components by suction filtration using a PTFE membrane filter with a mesh size of 0.1 μm, and washed with pure water. The amount of carboxyl groups in the oxidized cellulose after washing was measured to be 1.72 mmol / g. A 5% dispersion was prepared by adding pure water to the obtained oxidized cellulose, adjusting the pH to 7.5 by adding an aqueous sodium hydroxide solution, and then washing with water. The obtained dispersion was treated with a Sugino Machine Co., Ltd. ultra-high pressure homogenizer "Starburst Lab HJP-25005" under conditions of 200 MPa and 10 passes to obtain CNF aqueous dispersion S.

[0058] [Comparative Manufacturing Example 5] As a cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5mm squares with scissors and processed at 25,000 rpm for 1 minute using an Osaka Chemical Co., Ltd. "Wonder Blender WB-1" to mechanically defibrate it into a cotton-like material. 0.016 g of TEMPO and 0.1 g of sodium bromide were placed in a beaker, pure water was added and stirred to make an aqueous solution, and 1.0 g of the mechanically defibrated softwood kraft pulp was added. The above aqueous solution was heated to 25°C in a constant temperature water bath while being stirred with a stirrer. Then, 0.1M sodium hydroxide was added and stirred to obtain an aqueous solution with a pH of 10.0. To this, 2.58g of sodium hypochlorite aqueous solution with an effective chlorine concentration of 13.2% by mass was added, and while maintaining the temperature at 25°C in the same constant temperature water bath, the pH during the reaction was adjusted to 10.0 by adding 0.1M sodium hydroxide, and the mixture was stirred with a stirrer for 120 minutes. After the reaction was complete, the product was separated into solid and liquid components by suction filtration using a PTFE membrane filter with a mesh size of 0.1 μm, and the resulting filtered product was washed with pure water. The amount of carboxyl groups in the filtered product (oxidized cellulose) after washing was measured to be 1.55 mmol / g. A 5% dispersion was prepared by adding pure water to the obtained filtered product, adjusting the pH to 7.5 with sodium hydroxide aqueous solution, and washing with water. The resulting dispersion was treated with a Sugino Machine Co., Ltd. ultra-high pressure homogenizer "Starburst Lab HJP-25005" at 200 MPa and 10 passes to obtain CNF aqueous dispersion T. The nitrogen component derived from the N-oxyl compound in the oxidized cellulose was measured as nitrogen content under the same conditions as in Production Example 1, and the increase from the raw material pulp was calculated to be 5 ppm.

[0059] [First Embodiment] [Examples 1-1 to 1-9, Comparative Examples 1-1 to 1-5]: Investigation of Zeta Potential The following evaluations were performed using the CNF aqueous dispersions obtained in Production Examples 1-9 and Comparative Production Examples 1-5 to investigate the relationship between the zeta potential and dispersion stability of nanocellulose. The evaluation results are shown in Table 1.

[0060] [Zeta potential measurement] Each of the CNF aqueous dispersions A-I and P-T obtained above was diluted with pure water to a nanocellulose concentration of 0.1%. After dilution, a 0.05 mol / L sodium hydroxide aqueous solution was added to the CNF aqueous dispersion to adjust the pH to 8.0, and the zeta potential was measured at 20°C using an Otsuka Electronics zeta potential meter (ELSZ-1000). [Measurement of average fiber width] Pure water was added to each of the CNF aqueous dispersions A-I and P-T obtained above, and the concentration of nanocellulose in the CNF aqueous dispersion was adjusted to 5 ppm. The CNF aqueous dispersions after concentration adjustment were air-dried on a mica substrate, and the shape of the nanocellulose was observed in AC mode using an Oxford Asylum scanning probe microscope "MFP-3D infinity". For the average fiber width, the number-average fiber width [nm] was calculated for 50 or more fibers using the software included with the "MFP-3D infinity", with the cross-sectional height of the shape image equaling the fiber width.

[0061] [Light transmittance measurement] Each of the CNF aqueous dispersions A-I and P-T obtained above was placed in a 10 mm thick quartz cell, and the light transmittance at a wavelength of 660 nm was measured using a spectrophotometer (JASCO V-550). [Stability of CNF aqueous dispersions] Each CNF aqueous dispersion A-I and P-T was diluted with pure water to a nanocellulose concentration of 0.1% by mass, and then stored at 25°C for 4 weeks. The solid content concentration in the supernatant was measured immediately after dilution and after 4 weeks of storage, and the dispersion rate was calculated using the following formula. The dispersion stability was also determined according to the following criteria. The solid content concentration was calculated from the change in mass before and after drying at 105°C. Dispersion rate (%) = (Solid content concentration after 4 weeks / Solid content concentration immediately after dilution) × 100 ◎: Variance is less than 95% ○: Variance is between 90% and 95% △: Variance rate is between 85% and 90% ×: Variance is less than 85%

[0062] [Slurry viscosity stability] For aqueous slurries (50g) containing 5% by mass of titanium dioxide (Ishihara Sangyo Co., Ltd., R-820) and each CNF aqueous dispersion A-I, P-T, the amount of nanocellulose added was varied so that the initial viscosity (viscosity immediately after slurry preparation) was the same in each example (300 mPa·s). For mixing to prepare the aqueous slurries, a Thinky mixer "Awatori Rentaro ARE-310" (mix mode, revolution: 2000 rpm, rotation: 800 rpm, 20 minutes) was used. The viscosity was measured immediately after preparation (initial viscosity) and after standing for one week. The viscosity change rate was calculated using the following formula, and the viscosity stability of the aqueous slurry was determined according to the following criteria. Viscosity change rate (%) = (N2 / N1) × 100 (In the formula, N1 is the initial viscosity of the slurry, and N2 is the viscosity of the slurry after standing for one week after sample preparation.) ◎: Viscosity change rate is less than 105% ○: Viscosity change rate is 105% or more and less than 110% △: Viscosity change rate is 110% or more but less than 115% ×: Viscosity change rate is 115% or higher The samples were left standing at room temperature (23±2℃). The initial viscosity of the slurry and the viscosity after standing for one week were determined by stirring with a spatula at a speed that did not introduce bubbles, and then measuring with a Toki Sangyo E-type viscometer (TV-22) at 25°C and 100 rpm (shear speed 200 s). -1 The measurements were taken under the following conditions.

[0063] [Slurry handling performance] Each CNF aqueous dispersion A-I, P-T was mixed and stirred with water to a concentration of 5% by mass of aluminum silicate powder and 0.5% by mass of nanocellulose to prepare a processing solution. After lightly stirring this processing solution with a spatula, it was scooped up, and the dripping when the spatula was tilted was visually observed to evaluate the slurry handling properties according to the following criteria. ◎: Dripping occurred immediately after tilting. ○: Dripping occurred after tilting for 5 seconds or more. △: Dripping occurred after tilting for 10 seconds or more. ×: No dripping occurred even after 15 seconds.

[0064] [Surface condition after slurry coating (coating properties)] To each of the CNF aqueous dispersions A-I and P-T, water was added and mixed with 5% by mass of aluminum silicate powder and 0.5% by mass of nanocellulose to prepare a processing solution. The processing amount of aluminum silicate powder was 5 g / m². 2 The processing solution was applied to woven fabric (100% polyester, 100mm x 100mm) and dried. Ten of the coated woven fabrics were visually inspected for uneven coating (processing irregularities) and evaluated according to the following criteria. ◎: No processing inconsistencies were visible in any of the 10 pieces. ○: No processing inconsistencies were visible in 8-9 photos. △: No processing inconsistencies were visible in 4-7 sheets. ×: Either no processing inconsistencies were visible in 1-3 sheets, or processing inconsistencies were visible in all 10 sheets.

[0065] [Table 1]

[0066] In Table 1, cases where N-oxyl compounds were not used during the oxidation treatment of cellulosic raw materials (i.e., the CNF dispersion substantially does not contain N-oxyl compounds) are indicated with "×", and cases where N-oxyl compounds were used (i.e., the CNF dispersion contains N-oxyl compounds) are indicated with "○" (the same applies to Tables 2 and 3 below).

[0067] As shown in Table 1, when comparing Examples 1-1 to 1-9, in which nanocellulose was produced by oxidation treatment with hypochlorite, with Comparative Examples 1-1 and 1-2, Examples 1-1 to 1-9, with a zeta potential of -30mV or less, showed superior slurry characteristics compared to Comparative Examples 1-1 and 1-2, with zeta potentials of -17.9mV and -21.7mV, respectively. Specifically, the CNF aqueous dispersions of Examples 1-1 to 1-9 exhibited high dispersion stability of nanocellulose. Furthermore, the slurries obtained in Examples 1-1 to 1-9 showed a good balance of viscosity stability, handling properties, and coating properties. In particular, Examples 1-1 to 1-7 received an "◎" or "○" rating for viscosity stability, handling properties, and coating properties, demonstrating excellent slurry characteristics. Moreover, from the results of Examples 1-1, 1-2, and 1-9, which have similar zeta potentials, it was found that Examples 1-1 and 1-2, with an average fiber width of 5 nm or less, exhibited superior slurry characteristics compared to Example 1-9, which had an average fiber width of 5.3 nm. In contrast, Comparative Examples 1-1 to 1-4 received a "×" rating for dispersion stability, and their slurry characteristics were also inferior to those of Examples 1-1 to 1-9. Comparative Example 1-5 showed good dispersion stability, but all of its slurry characteristics received a "×" rating.

[0068] [Second Example] [Examples 2-1 to 2-9, Comparative Examples 2-1 to 2-5]: Study on average fiber width The CNF aqueous dispersions A-H, J, P-T obtained in Production Examples 1-8, 10, and Comparative Production Examples 1-5 were evaluated in the same manner as in the first example above, and the relationship between the average fiber width of nanocellulose and dispersion stability was investigated. The evaluation results are shown in Table 2.

[0069] [Table 2]

[0070] According to Table 2, when comparing Examples 2-1 to 2-9, in which nanocellulose was produced by oxidation treatment with hypochlorite, with Comparative Examples 2-1 and 2-2, Examples 2-1 to 2-9, with an average fiber diameter of 5.0 nm or less, showed superior slurry properties compared to Comparative Examples 2-1 and 2-2, with average fiber diameters of 5.3 nm and 5.2 nm, respectively. Furthermore, from the results of Examples 2-1 and 2-9, which have similar average fiber widths, it was found that Example 2-1, with a zeta potential of -30mV or less, exhibits superior slurry characteristics compared to Example 2-9, where the zeta potential of nanocellulose is -28.5mV.

[0071] [Third Embodiment] [Examples 3-1 to 3-9, Comparative Examples 3-1 to 3-5]: Examination of Aspect Ratio Using the CNF aqueous dispersions A-H, K, P-T obtained in Production Examples 1-8, 11 and Comparative Production Examples 1-5, the average fiber length and average fiber width of nanocellulose were measured, and the aspect ratio was calculated. The same evaluation as in the first example was performed to investigate the relationship between the aspect ratio and dispersion stability of nanocellulose. The average fiber length and average fiber width were measured using the following procedure. [Measurement of average fiber length and average fiber width] Pure water was added to each of the CNF aqueous dispersions A-H, K, and P-T obtained above, and the concentration of nanocellulose in the CNF aqueous dispersion was adjusted to 5 ppm. The adjusted CNF aqueous dispersions were air-dried on a mica substrate, and the shape of the nanocellulose was observed in AC mode using an Oxford Asylum scanning probe microscope "MFP-3D infinity". For the average fiber length, the obtained images were binarized and analyzed using the image processing software "Image J". For 100 fibers, the number-average fiber length was calculated as fiber length = circumference ÷ 2. For the average fiber width, the number-average fiber width [nm] was calculated for 50 or more fibers using the software included with "MFP-3D infinity", with the cross-sectional height of the shape image = fiber width. The aspect ratio was also calculated from (average fiber length / average fiber width). The evaluation results are shown in Table 3.

[0072] [Table 3]

[0073] According to Table 3, when comparing Examples 3-1 to 3-9, in which nanocellulose was produced by oxidation treatment with hypochlorite, with Comparative Examples 3-1 and 3-2, Examples 3-1 to 3-9, with aspect ratios of 150 or less, showed superior slurry properties compared to Comparative Examples 3-1 and 3-2, which had aspect ratios of 183 and 165, respectively. Furthermore, from the results of Examples 3-2 and 3-9, which have similar aspect ratios, it was found that Example 3-2, with a zeta potential of -30mV or less, exhibits superior slurry characteristics compared to Example 3-9, where the zeta potential of nanocellulose is -28.6mV.

Claims

1. Nanocellulose having a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized and carboxyl groups are introduced, The average fiber width is between 1 nm and 5 nm. The zeta potential is -30 mV or less. The aspect ratio is between 20 and 150. The carboxyl group content is 0.30 mmol / g or more. Nanocellulose.

2. The nanocellulose according to claim 1, wherein the light transmittance of the mixed solution obtained by mixing with water to a solid content concentration of 0.1% by mass is 95% or more.

3. Nanocellulose having a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized and carboxyl groups are introduced, The average fiber width is between 1 nm and 5 nm. The aspect ratio is between 20 and 150. The carboxyl group content is 0.30 mmol / g or more. Nanocellulose.

4. Nanocellulose having a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized and carboxyl groups are introduced, The average fiber width is between 1 nm and 5 nm. The light transmittance of the mixed solution, which is obtained by mixing with water to a solid content concentration of 0.1% by mass, is 95% or higher. The aspect ratio is between 20 and 150. The carboxyl group content is 0.30 mmol / g or more. Nanocellulose.

5. A nanocellulose dispersion in which nanocellulose according to any one of claims 1 to 4 is dispersed in a dispersion medium.

6. A cosmetic product comprising nanocellulose according to any one of claims 1 to 4 or a nanocellulose dispersion according to claim 5.

7. A paint comprising nanocellulose according to any one of claims 1 to 4 or a nanocellulose dispersion according to claim 5.

8. Rubber containing nanocellulose according to any one of claims 1 to 4.

9. A resin containing nanocellulose according to any one of claims 1 to 4.

10. A film containing nanocellulose according to any one of claims 1 to 4.

11. Nanocellulose according to any one of claims 1 to 4 or nanocellulose dispersion according to claim 5, and inorganic particles A slurry containing [something].

12. The inorganic particles include titanium oxide, The slurry according to claim 11.

13. Nanocellulose according to any one of claims 1 to 4 or nanocellulose dispersion according to claim 5, and pigment A slurry containing [something].

14. comprising nanocellulose according to any one of claims 1 to 4 or a nanocellulose dispersion according to claim 5, An additive used in slurries containing inorganic particles.

15. The inorganic particles include titanium dioxide, The additive according to claim 14.

16. comprising nanocellulose according to any one of claims 1 to 4 or a nanocellulose dispersion according to claim 5, An additive used in slurries containing pigments.

17. A mechanical part containing nanocellulose according to any one of claims 1 to 4.

18. An electrical appliance containing nanocellulose according to any one of claims 1 to 4.

19. An electronic device comprising nanocellulose according to any one of claims 1 to 4.

20. A pharmaceutical product comprising nanocellulose according to any one of claims 1 to 4.

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