Nanocellulose and its dispersion

Abstract

The present invention provides nanocellulose that has an average fiber width of 1-200 nm and is an oxide of a cellulosic raw material, which does not contain an N-oxyl compound in a cellulose fiber, has excellent dispersion stability in a dispersion medium, and uses hypochlorous acid or a salt thereof, the nanocellulose not substantially containing an N-oxyl compound and having a zeta potential of at most -30 mV.

Description

Technical Field

[0001] The present invention relates to nanocellulose and its dispersion. Specifically, it relates to nanocellulose obtained by defibrating oxidized cellulose obtained by oxidizing a cellulose-based raw material with an oxidizing agent, and a nanocellulose dispersion containing the same.

Background Art

[0002] Techniques for producing nanocellulose materials such as cellulose nanofibers (hereinafter also referred to as CNF) have been variously proposed by oxidizing various cellulose-based raw materials with an oxidizing agent and then refining the obtained oxidized cellulose (see, for example, Patent Document 1 and Patent Document 2).

[0003] Patent Document 1 discloses that hypochlorous acid or its salt is used as an oxidizing agent, and the oxidized cellulose obtained by oxidizing a cellulose-based raw material under high-concentration conditions where the available chlorine concentration in the reaction system is 14 to 43% by mass is defibrated and nanosized. Patent Document 2 discloses that hypochlorous acid or its salt is used as an oxidizing agent, the available chlorine concentration in the reaction system is 6 to 14% by mass, and the oxidized cellulose obtained by oxidizing a cellulose-based raw material while adjusting the pH to 5.0 to 14.0 is defibrated and nanosized. In these techniques, since the oxidation treatment is performed without using an N-oxyl compound such as 2,2,6,6-tetramethyl-1-piperidine-N-oxyl radical (TEMPO) as a catalyst, the N-oxyl compound does not remain in the cellulose fiber, and thus it is possible to produce a nanocellulose material while reducing the impact on the environment and the like.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

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

[0006] The present invention has been made in view of the above circumstances, and the main object thereof is to provide nanocellulose that does not contain an N-oxyl compound in the cellulose fiber and has excellent dispersion stability in a dispersion medium.

Means for Solving the Problems

[0007] In order to solve the above problems, according to the present invention, the following means are provided. 〔1〕Nanocellulose which is an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof, has an average fiber width of 1 nm or more and 200 nm or less, substantially does not contain an N-oxyl compound, and has a zeta potential of -30 mV or less. 〔2〕The nanocellulose according to 〔1〕, having an average fiber width of 1 nm or more and 5 nm or less. 〔3〕The nanocellulose according to 〔1〕 or 〔2〕, having an aspect ratio of 20 or more and 150 or less. 〔4〕The nanocellulose according to any one of 〔1〕 to 〔3〕, 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 mass%. 〔5〕Nanocellulose which is an oxide of a cellulose-based 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. A nanocellulose which is an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof, has an average fiber width of 1 nm or more and 200 nm or less, does not contain an N-oxyl compound, and has an aspect ratio of 20 or more and 150 or less. A nanocellulose which is an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof, has an average fiber width of 1 nm or more and 200 nm or less, does not contain an N-oxyl compound, and has a light transmittance of 95% or more in a mixed solution mixed with water to a solid content concentration of 0.1 mass%. A nanocellulose dispersion in which the nanocellulose according to any one of [1] to [7] is dispersed in a dispersion medium.

Advantages of the Invention

[0008] According to the present invention, it is possible to obtain nanocellulose having excellent dispersion stability in a dispersion medium. Further, since it does not contain an N-oxyl compound, the influence on the environment and the like can be reduced.

Embodiments for Carrying Out the Invention

[0009] 《Nanocellulose》 The nanocellulose of the present disclosure (hereinafter also referred to as "the present nanocellulose") is a fibrous nanocellulose obtained by defibrating oxidized cellulose obtained by oxidizing a cellulose-based raw material with hypochlorous acid or a salt thereof. Further, the above oxidized cellulose can also be referred to as an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof. Hereinafter, the present nanocellulose will be described in detail. Since "nanocellulose" is fibrous cellulose obtained by refining oxidized fibrous cellulose, it is also referred to as "fine cellulose fiber".

[0010] Since the nanocellulose is obtained by oxidizing a cellulose-based raw material with hypochlorous acid or a salt thereof, it substantially does not contain an N-oxyl compound. Here, in this specification, "substantially does not contain an N-oxyl compound" means that the nanocellulose contains no N-oxyl compound at all, or the content of the N-oxyl compound is 2.0 mass ppm or less, preferably 1.0 mass ppm or less, based on the total amount of the nanocellulose. Further, when the content of the N-oxyl compound is preferably 2.0 mass ppm or less, more preferably 1.0 mass ppm or less, as an increase from the cellulose-based raw material, it also means "substantially does not contain an N-oxyl compound". Since it substantially does not contain an N-oxyl compound, it is possible to suppress the residue of the N-oxyl compound, which raises concerns about the impact on the environment and the human body, in the nanocellulose. The content of the N-oxyl compound can be measured by known means. Examples of the known means include a method using a trace total nitrogen analyzer. Specifically, the nitrogen component derived from the N-oxyl compound in the nanocellulose can be measured as the amount of nitrogen using a trace total nitrogen analyzer (for example, manufactured by Mitsubishi Chemical Analytech Co., Ltd., device 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 a decrease in quality. In addition, 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 the handleability and coatability tend to decrease. From such 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 approaches the state of a single cellulose molecule, and the quality as nanocellulose tends to become non-uniform, and when made into a slurry, the viscosity stability, handleability, and coatability tend to decrease. 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, handleability, and coatability of the slurry can be improved, 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, so the dispersion stability can be improved. 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, aggregation of the solid particles can be suppressed, and the dispersion stability can be improved. Furthermore, aggregation between the solid particles and the nanocellulose, or aggregation between the nanocelluloses can be suppressed, the handleability of the slurry can be improved, and uneven processing can be suppressed. 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 handleability 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 are calculated as follows: Nano-cellulose and water are mixed so that the concentration of nano-cellulose is approximately 1 to 10 ppm, and the sufficiently diluted nano-cellulose aqueous dispersion is naturally dried on a mica substrate. The shape of the nano-cellulose is observed using a scanning probe microscope. An arbitrary number of fibers are randomly selected from the obtained image, and the value is calculated by setting the cross-sectional height of the shape image = fiber width and the perimeter length ÷ 2 = fiber length. For calculating such average fiber width and average fiber length, image processing software can be used. At this time, the conditions for image processing are arbitrary, but even for the same image, there may be a difference in the calculated values depending on the conditions for image processing. The range of the difference in values due to the conditions for image processing is preferably within ±100 nm for the average fiber length. The range of the difference in values due to the conditions for image processing is preferably within ±10 nm for the average fiber width. A more detailed measurement method follows the method described in the examples below.

[0016] This nano-cellulose preferably has a structure in which at least two of the hydroxyl groups of the glucopyranose ring constituting cellulose are oxidized. More specifically, it has a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized to introduce carboxyl groups. Further, it is preferable that the hydroxyl group at the 6th position of the glucopyranose ring in this nano-cellulose is not oxidized and remains as a hydroxyl group. The position of the carboxyl group in the glucopyranose ring of the nano-cellulose can be analyzed by a solid 13 C-NMR spectrum. In the above solid 13 C-NMR spectrum, when peaks corresponding to the carboxyl groups at the 2nd and 3rd positions of the glucopyranose ring are observed, it can be determined that it has an oxidized structure. At this time, the peaks corresponding to the carboxyl groups at the 2nd and 3rd positions can be observed as broad peaks in the range of 165 ppm to 185 ppm. The broad peak mentioned here can be determined by the area ratio of the peaks. That is, a baseline was drawn for the peak in the range of 165 ppm to 185 ppm in the NMR spectrum to obtain the total area value. Then, the ratio of the two peak area values (the larger area value / the smaller area value) obtained by vertically dividing the area value at the peak top was determined. If the ratio of the peak area values is 1.2 or more, it can be said that it is a broad peak. In addition, the presence or absence of the above-mentioned broad peak can be determined by the ratio of the length L of the baseline in the range of 165 ppm to 185 ppm and the length L' of the perpendicular line from the peak top to the baseline. That is, if the ratio L' / L is 0.1 or more, it can be determined that a broad peak exists. The ratio L' / L may be 0.2 or more, may be 0.3 or more, may be 0.4 or more, or may be 0.5 or more. The upper limit value of the ratio L' / L is not particularly limited, but usually may be 3.0 or less, may be 2.0 or less, or may be 1.0 or less.

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

[0018] [Zeta potential] In a preferred embodiment of the present disclosure, this nanocellulose has a zeta potential of -30 mV or less. When the zeta potential is -30 mV or less (that is, the absolute value is 30 mV or more), sufficient repulsion between microfibrils is obtained, and nanocellulose with a high surface charge density is likely to be generated during mechanical fibrillation. Thereby, the dispersion stability of the nanocellulose can be improved, and the viscosity stability, handling property, and coating property when made into a slurry can be made excellent. From the viewpoint of dispersion stability, the lower limit of the zeta potential is not particularly limited. However, when the zeta potential is -100 mV or more (that is, the absolute value is 100 mV or less), since oxidative cleavage in the fiber direction due to the progress of oxidation tends to be suppressed, nanocellulose with a uniform size can be obtained, and excellent coating properties can be exhibited.

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

[0020] [Light transmittance] The nanocellulose dispersion in which the present nanocellulose is dispersed in a dispersion medium has less light scattering of cellulose fibers and can exhibit a high light transmittance. Specifically, in a preferred embodiment, the light transmittance of the present nanocellulose in a mixed solution obtained by mixing with water to a solid content concentration of 0.1% by mass is 95% or more. Therefore, the present nanocellulose and the nanocellulose dispersion liquid containing the same can be widely applied to uses requiring transparency and are useful. The light transmittance is more preferably 96% or more, still more preferably 97% or more, and even more preferably 99% or more. The light transmittance is a value at a wavelength of 660 nm measured by 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 including step A of oxidizing a cellulose-based raw material with hypochlorous acid or its salt to obtain oxidized cellulose, and step B of defibrating the oxidized cellulose. Since "oxidized cellulose" is oxidized fibrous cellulose, it is also referred to as "oxidized cellulose fiber".

[0022] (Step A: Production of Oxidized Cellulose) The cellulose-based raw material is not particularly limited as long as it is a material mainly composed of cellulose. For example, it includes pulp, natural cellulose, regenerated cellulose, and fine cellulose obtained by depolymerizing cellulose by mechanical treatment. As the cellulose-based raw material, commercially available products such as crystalline cellulose using pulp as a raw material can be used as they are. In addition, unused biomass containing a large amount of cellulose components, such as okara and soybean hulls, may be used as a raw material. Also, for the purpose of facilitating the penetration of the oxidizing agent used into the raw material pulp, the cellulose-based raw material may be treated with an alkali of an appropriate concentration in advance.

[0023] Examples of hypochlorous acid or its salt used for oxidizing the cellulose-based raw material include aqueous hypochlorous acid, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and ammonium hypochlorite. Among these, sodium hypochlorite is preferred in terms of ease of handling.

[0024] As a method for producing oxidized cellulose by oxidizing a cellulose-based raw material, a method of mixing a cellulose-based raw material and a reaction solution containing hypochlorous acid or a salt thereof can be mentioned. As the solvent contained in the reaction solution, water is preferable in terms of ease of handling and difficulty in causing side reactions. The effective chlorine concentration of hypochlorous acid or its salt in the reaction solution is preferably 6 to 43% by mass, more preferably 7 to 43% by mass, still more preferably 10 to 43% by mass, and even more preferably 14 to 43% by mass. When the effective chlorine concentration of the reaction solution is within the above range, the amount of carboxy groups in the oxidized cellulose can be made sufficiently large, and fibrillation of the oxidized cellulose can be easily performed when obtaining nanocellulose.

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

[0026] Incidentally, the available 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 hypochlorite is a compound in which the hydrogen of hypochlorous acid is replaced by other cations. For example, since sodium hypochlorite, which is a hypochlorite, exists in a solvent (preferably in an aqueous solution), the concentration is measured not as the concentration of sodium hypochlorite but as the amount of available chlorine in the solution. Here, regarding the available chlorine of sodium hypochlorite, since the oxidizing power of the divalent oxygen atoms generated by the decomposition of sodium hypochlorite corresponds to two atomic equivalents of monovalent chlorine, the bound chlorine atoms of sodium hypochlorite (NaClO) have the same oxidizing power as two atoms of unbound chlorine (Cl2), and available chlorine = 2×(chlorine in NaClO). As a specific procedure for measurement, first, the sample is precisely weighed, water, potassium iodide, and acetic acid are added and left to stand, and the free iodine is titrated with a sodium thiosulfate solution using an aqueous starch solution as an indicator to measure the available chlorine concentration.

[0027] The oxidation reaction of the cellulosic raw material with hypochlorous acid or its salts is preferably carried out while adjusting the pH to the range of 5.0 to 14.0. Within this range, the oxidation reaction of the cellulosic raw material can proceed sufficiently, and the amount of carboxyl groups in the oxidized cellulose can be made sufficiently large. Thereby, fibrillation of the oxidized cellulose can be easily carried out. The pH of the reaction system is more preferably 6.0 or higher, still more preferably 7.0 or higher, and even more preferably 8.0 or higher. Regarding the upper limit of the pH of the reaction system, it is more preferably 13.5 or lower, still more preferably 13.0 or lower. Also, the pH range of the reaction system is more preferably 7.0 to 14.0, and still more preferably 8.0 to 13.5.

[0028] Hereinafter, the method for producing oxidized cellulose will be further described by taking the case of using sodium hypochlorite as hypochlorous acid or its salt as an example.

[0029] When oxidizing a cellulose-based raw material using sodium hypochlorite, the reaction solution is preferably an aqueous sodium hypochlorite solution. As a method for adjusting the available chlorine concentration of the aqueous sodium hypochlorite solution to the target concentration (for example, target concentration: 6 mass% to 43 mass%), methods include concentrating an aqueous sodium hypochlorite solution with a lower available chlorine concentration than the target concentration, diluting an aqueous sodium hypochlorite solution with a higher available chlorine concentration than the target concentration, and dissolving crystals of sodium hypochlorite (for example, sodium hypochlorite pentahydrate) in a solvent. Among these, adjusting the available chlorine concentration as an oxidizing agent by diluting an aqueous sodium hypochlorite solution or dissolving crystals of sodium hypochlorite in a solvent is preferred because there is less self-decomposition (that is, less decrease in the available chlorine concentration) and the adjustment of the available chlorine concentration is simple.

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

[0031] In order to efficiently proceed with the oxidation reaction of the cellulose-based raw material, during the oxidation reaction, it is preferable to stir the mixture of the cellulose-based raw material and the aqueous sodium hypochlorite solution. Examples of the stirring method include a magnetic stirrer, a stirring rod, a stirrer with a stirring blade (three-one motor), a homomixer, a disperser-type mixer, a homogenizer, external circulation stirring, etc. Among these, from the point that the oxidation reaction of the cellulose-based raw material proceeds smoothly and it is easy to adjust the degree of polymerization of the oxidized cellulose to a predetermined value or less, a method using one or more of shear-type stirrers such as a homomixer and a homogenizer, a stirrer with a stirring blade, and a disperser-type mixer is preferred, and a method using a stirrer with a stirring blade is particularly preferred. When using a stirrer with a stirring blade, a device equipped with a known stirring blade such as a propeller blade, a paddle blade, or a turbine blade can be used as the stirrer. Also, when using a stirrer with a stirring blade, 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, as carboxyl groups are generated in the cellulose-based raw material by the oxidation reaction, the pH of the reaction system decreases. Therefore, from the viewpoint of efficiently advancing the oxidation reaction, it is preferable to add an alkali agent (e.g., sodium hydroxide, etc.) or an acid (e.g., hydrochloric acid, etc.) to the reaction system to adjust the pH of the reaction system to the above-mentioned preferable range. The reaction time of the oxidation reaction can be set according to the degree of progress of the oxidation, but it is preferably about 15 minutes to 50 hours. When the pH of the reaction system is 10 or more, it is preferable to set the reaction temperature to 30°C or more and / or the reaction time to 30 minutes or more.

[0033] In addition, by adjusting the reaction time, reaction temperature, stirring conditions, etc. of the oxidation reaction, the fiber width and zeta potential of the nanocellulose can be adjusted to desired values. Specifically, as the reaction time is lengthened and / or the reaction temperature is increased, the oxidation on the surface of the cellulose microfibrils in the cellulose-based raw material progresses, and the repulsion between the fibrils strengthens due to electrostatic repulsion and osmotic pressure, resulting in a tendency for the average fiber width to become smaller. Also, by setting one or more of the reaction time, reaction temperature, and stirring conditions of the oxidation on the side where the oxidation progresses more (i.e., the side where the degree of oxidation is increased) (for example, lengthening the reaction time), the zeta potential tends to increase.

[0034] The carboxyl group content of the oxidized cellulose obtained by the above oxidation reaction is preferably 0.30 to 2.0 mmol / g. When the carboxyl group content of the oxidized cellulose is 0.30 mmol / g or more, the fibrillability of the oxidized cellulose can be sufficiently increased, and nanofibrils with a uniform fiber width can be obtained. Thereby, the quality of the nanofibril-containing slurry can be made uniform, and the viscosity stability, handleability, and coatability of the slurry can be improved. On the other hand, when the carboxyl group content is 2.0 mmol / g or less, it is possible to suppress excessive decomposition of cellulose during the fibrillation treatment, and nanofibrils with a small ratio of particulate cellulose and uniform quality can be obtained. From these viewpoints, the carboxyl group content of the oxidized cellulose is more preferably 0.35 mmol / g or more, still more preferably 0.40 mmol / g or more, even more preferably 0.42 mmol / g or more, still 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 preferable range of the carboxyl group content can be determined by appropriately combining the above-mentioned upper and lower limits. The carboxyl group content of this oxidized cellulose is more preferably 0.35 to 2.0 mmol / g, still more preferably 0.35 to 1.5 mmol / g, even more preferably 0.40 to 1.5 mmol / g, still 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] Note that the carboxyl group content (mmol / g) in the oxidized cellulose can be calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of a weak acid with a gentle change in electrical conductivity, after adding 0.1 M hydrochloric acid aqueous solution to an aqueous solution containing oxidized cellulose to adjust the pH to 2.5 and then dropping 0.05 N sodium hydroxide aqueous solution until the pH reaches 11. Amount of carboxy group = a (ml) × 0.05 / mass of oxidized cellulose (g)

[0036] Using the solution containing the oxidized cellulose obtained by the above reaction, known isolation treatments such as filtration are performed, and further purification is carried out as necessary, whereby oxidized cellulose can be obtained 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 filterability and yield of the isolation treatment, an acid is added to the solution containing the 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) 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 the oxidized cellulose obtained by the above reaction may be directly subjected to fibrillation treatment.

[0037] In the solution containing the oxidized cellulose, when the pH is set to 4.0 or less for the isolation treatment, in order to improve the handleability when used for the subsequent fibrillation treatment, for example, a base is added to set the pH to 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 the oxidized cellulose may be made into a composition containing the oxidized cellulose by replacing its solvent or the like. Also in the composition containing the 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] The 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 can form an ionic bond or a covalent bond with a carboxy group or a hydroxy group possessed by the oxidized cellulose. Examples of the compound having a modifying group capable of forming an ionic bond include primary amines, secondary amines, tertiary amines, quaternary ammonium compounds, and phosphonium compounds. Examples of the compound having a modifying group capable of forming a covalent bond include alcohols, isocyanate compounds, and epoxy compounds. As described above, oxidized cellulose includes salt-type, proton-type, and modified-type modes by a modifying group. Also, the nanocellulose obtained from the present oxidized cellulose also includes salt-type, proton-type, and modified-type modes by a modifying group.

[0039] (Step B: fibrillation treatment) This nanocellulose can be obtained by defibrating the oxidized cellulose obtained above to nanoscale. Examples of the method for defibrating oxidized cellulose include a method by weak stirring using a magnetic stirrer or the like, and a method by mechanical defibrillation. In terms of being able to sufficiently perform the defibrillation of oxidized cellulose and shortening the defibrillation time, it is preferable that the defibrillation of oxidized cellulose is by mechanical defibrillation. Here, nanocellulose (also referred to as nanocellulose) represents a general term for those obtained by nanosizing cellulose, and includes cellulose nanofibers, cellulose nanocrystals, and the like.

[0040] Examples of mechanical fibrillation 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 counter-collision type dispersers, beaters, disk refiners, conical refiners, double-disk refiners, grinders, single-axis or multi-axis kneaders, rotating and revolving stirrers, vibration type stirrers, etc. By using these devices alone or in combination of two or more types, preferably by treating oxidized cellulose in a dispersion medium, the oxidized cellulose can be nanofibrillated to produce nanocellulose.

[0041] In terms of efficiently producing more fibrillated nanocellulose, the method using an ultra-high-pressure homogenizer can preferably be used for the fibrillation of oxidized cellulose. When applying the fibrillation treatment by an ultra-high-pressure homogenizer, the pressure during the fibrillation treatment is preferably 100 MPa or more, more preferably 120 MPa or more, and even more preferably 150 MPa or more. The number of fibrillation treatment times is not particularly limited, but from the perspective of sufficiently advancing fibrillation, it is preferably 2 times or more, more preferably 3 times or more. Also, the above-mentioned oxidized cellulose can be sufficiently fibrillated by gentle stirring using a rotating and revolving stirrer, a vibration type stirrer, etc. Examples of the vibration type stirrer include a vortex mixer (touch mixer). That is, according to the above-mentioned oxidized cellulose, even when the fibrillation treatment is performed under mild fibrillation conditions, uniform nanocellulose can be obtained.

[0042] The fibrillation treatment is preferably carried out in a state where the oxidized cellulose is mixed with a dispersion medium. There is no particular limitation on the dispersion medium, and it can be appropriately selected according to the purpose. Specific examples of the dispersion medium include water, alcohols, ethers, ketones, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide, etc. As the solvent, one of these can be used alone, or two or more types can be used in combination.

[0043] Among the above dispersion media, examples of alcohols 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 the dispersion medium during the fibrillation treatment, it becomes easy to isolate oxidized cellulose and the nanocellulose obtained by fibrillation of the oxidized cellulose. In addition, since nanocellulose dispersed in the organic solvent can be obtained, it becomes easy to mix with resins, resin raw material monomers, etc. that dissolve in the organic solvent. The nanocellulose dispersion liquid in which the nanocellulose obtained by fibrillation is dispersed in a dispersion medium of water and / or an organic solvent can be used for mixing with various components such as resins, rubbers, and solid particles.

[0045] The nanocellulose and the nanocellulose dispersion liquid containing the same described above can be applied to various uses. Specifically, for example, it may be used by being mixed with various materials (such as resins, fibers, rubbers, etc.) as a reinforcing material, or may be used in various applications (such as foods, cosmetics, medical products, paints, inks, etc.) as a thickening agent or a dispersing agent. Further, the nanocellulose dispersion liquid can be formed into a film and used as various sheets or films. The fields to which this nanocellulose and the nanocellulose dispersion liquid containing the same are applied are not particularly limited, and it can be used, for example, in the manufacture of products in various fields such as automotive parts, machine parts, household appliances, electronic devices, cosmetics, medical products, building materials, daily necessities, and stationery. Also, for example, when nanocellulose and the nanocellulose dispersion liquid containing the same are used as an additive to a slurry containing inorganic particles such as pigments, it is suitable in that it can improve the viscosity stability, handleability, and coating performance of the slurry.

[0046] ·Second Embodiment In a preferred embodiment of the present disclosure, the present nanocellulose is nanocellulose obtained by oxidizing a cellulose-based raw material with hypochlorous acid or a salt thereof (also referred to as nanocellulose which is an oxide of a cellulose-based 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 present nanocellulose is 1 to 5 nm, the zeta potential of the present nanocellulose is preferably -25 mV or less, more preferably -30 mV or less, in that the dispersion stability of the nanocellulose is improved and the handleability when made into a slurry can be improved. Regarding details such as the production method of the present nanocellulose, the description of the first embodiment above can be incorporated.

[0047] · Third Embodiment In a preferred embodiment of the present disclosure, the present nanocellulose is nanocellulose obtained by oxidizing a cellulose-based raw material with hypochlorous acid or a salt thereof (also referred to as nanocellulose which is an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof), does not contain an N-oxyl compound, and has an aspect ratio of 20 or more and 150 or less. When the aspect ratio of the present nanocellulose is 20 or more and 150 or less, the zeta potential of the present nanocellulose is preferably -25 mV or less, more preferably -30 mV or less, in that the dispersion stability of the nanocellulose is improved and the handleability when made into a slurry can be improved. Regarding details such as the production method of the present nanocellulose, the description of the first embodiment above can be incorporated.

Examples

[0048] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. In the following, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0049] (1) Production of oxidized cellulose and nanocellulose 〔Production Example 1〕 As a cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5 mm squares with scissors and mechanically defibrated into a cotton-like form by treating it with a "WONDER BLENDER WB-1" manufactured by Osaka Chemical Co., Ltd. at 25,000 rpm for 1 minute. 350 g of sodium hypochlorite pentahydrate crystals with an available chlorine concentration of 42% by mass were placed in a beaker, pure water was added and stirred to obtain an aqueous sodium hypochlorite solution with an available chlorine concentration of 21% by mass. 35% hydrochloric acid was added thereto and stirred to obtain an aqueous solution with a pH of 11.0. This aqueous sodium hypochlorite solution was heated to 30 °C in a constant temperature water bath while stirring at 200 rpm using a stirrer (Three One Motor, BL600) manufactured by Shinto Kagaku Co., Ltd. with a propeller type stirring blade, and then 50 g of the above mechanically defibrated softwood kraft pulp (carboxy group content: 0.05 mmol / g) was added. After supplying the cellulose-based raw material, while maintaining the temperature at 30 °C in the same constant temperature water bath, 48% by mass sodium hydroxide was added while adjusting the pH during the reaction to 11.0, and the mixture was stirred at 200 rpm for 20 minutes using the above stirrer with a propeller type stirring blade to carry out an oxidation reaction. After the reaction was completed, the product was separated into solid and liquid by suction filtration using a PTFE membrane filter with a pore size of 0.1 μm, and the obtained oxidized cellulose was washed with pure water. When the carboxy group content of the filtered residue (oxidized cellulose) after washing was measured, it was 0.37 mmol / g. Subsequently, pure water was added to the oxidized cellulose to prepare a 5% dispersion, which was treated at 200 MPa for 10 passes using an ultra-high pressure homogenizer "STARBURST LAB HJP-25005" manufactured by Sugino Machine, Ltd. to obtain a 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 defibrating section built into the ultra-high pressure homogenizer to promote defibrillation. One pass of the liquid through the ultra-high pressure defibrating section is called one pass. Also, the nitrogen component derived from the N-oxyl compound in the oxidized cellulose was measured as the nitrogen amount using a trace total nitrogen analyzer (manufactured by Mitsubishi Chemical Analytech Co., Ltd., model name: TN-2100H), and as a result of calculating the increase from the raw material pulp, it was 1 ppm or less.

[0050] The available chlorine concentration in the aqueous sodium hypochlorite solution was measured by the following method. (Measurement of available chlorine concentration in aqueous sodium hypochlorite solution) 0.582 g of an aqueous solution obtained by adding sodium hypochlorite pentahydrate crystals 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 immediately sealed and left in the dark for 15 minutes. After standing for 15 minutes, the liberated iodine was titrated with a 0.1 mol / L sodium thiosulfate solution (indicator: starch test solution). As a result, the titration volume was 34.55 ml. Separately, a blank test was conducted for correction. Since 1 ml of the 0.1 mol / L sodium thiosulfate solution corresponds to 3.545 mg of Cl, the available chlorine concentration in the aqueous sodium hypochlorite solution is 21% by mass.

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

[0052] [Production Example 2] A CNF aqueous dispersion B was obtained by treating under the same conditions as in Production Example 1 except that the reaction time in the oxidation reaction was 30 minutes. [Production Example 3] A CNF aqueous dispersion C was obtained by treating under the same conditions as in Production Example 1 except that the reaction time in the oxidation reaction was 120 minutes. [Production Example 4] A CNF aqueous dispersion D was obtained by treating under the same conditions as in Production Example 1 except that the reaction time in the oxidation reaction was 360 minutes. [Production Example 5] A CNF aqueous dispersion E was obtained by treating under the same conditions as in Production Example 1 except that the reaction time in the oxidation reaction was 480 minutes. [Production Example 6] A CNF aqueous dispersion F was obtained by treating 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 120 minutes. [Production Example 7] A CNF aqueous dispersion G was obtained by treating 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 120 minutes. [Production Example 8] A CNF aqueous dispersion H was obtained by treating 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 480 minutes. [Production Example 9] A CNF aqueous dispersion I was obtained by treating 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 120 minutes. [Production Example 10] A CNF aqueous dispersion J was obtained by treating under the same conditions as in Production Example 1 except that the reaction time in the oxidation reaction was 15 minutes. [Production Example 11] A CNF aqueous dispersion K was obtained by treating 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 120 minutes.

[0053] After freeze-drying the oxidized cellulose obtained in each production example, the solid of the sample left at 23 °C and 50% RH for 24 hours or more 13 As a result of measuring solid-state 13C-NMR, it was confirmed that all had a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring were oxidized and carboxyl groups were introduced. Solid 13 The measurement conditions for solid-state 13C-NMR are shown below. (1) Sample tube: Zirconia tube (4 mm diameter) (2) Magnetic field strength: 9.4 T (1H resonance frequency: 400 MHz) (3) MAS rotation speed: 15 kHz (4) Pulse sequence: CPMAS method (5) Contact time: 3 ms (6) Waiting time: 5 seconds (7) Number of integrations: 10,000 - 15,000 times (8) Measuring device: JNM ECA - 400 (manufactured by JEOL Ltd.) In addition, it was also confirmed from the results of measuring two - dimensional NMR using a model molecule of the oxidized cellulose as a sample 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. In addition, regarding the 6th position, the solid of the cellulose - based raw material 13 C - NMR and the solid of the oxidized cellulose 13 Since no change in the spectral data was observed between the C - NMRs, it was determined that the hydroxyl group at the 6th position was not oxidized and remained as a hydroxyl group in the oxidized cellulose.

[0054] 〔Comparative Production Example 1〕 As the cellulose - based raw material, softwood pulp (SIGMA - ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5 - mm squares with scissors and mechanically defibrated into a cottony state by treating it at 25,000 rpm for 1 minute using "WONDER BLENDER WB - 1" manufactured by Osaka Chemical Co., Ltd. 30.0 g of sodium hypochlorite pentahydrate crystals with an available chlorine concentration of 43 mass% were placed in a 100 - ml beaker, and pure water and 35 mass% hydrochloric acid were added and stirred to obtain an aqueous solution with an available chlorine concentration of 21 mass% and a pH of 11.0. After warming this sodium hypochlorite aqueous solution to 30 °C in a constant - temperature water bath while stirring with a stirrer, 0.35 g of the mechanically defibrated softwood kraft pulp was added. After supplying the cellulose-based raw material, while maintaining the temperature at 30 °C in the same constant-temperature water bath, 48% by mass of sodium hydroxide was added to maintain a pH of 11.0, and the mixture was stirred with a stirrer for 30 minutes. Next, a PTFE membrane filter with a pore size of 0.1 μm was used to perform solid-liquid separation of the product by suction filtration, and the obtained residue on the filter was washed with pure water. When the amount of carboxyl groups in the residue on the filter (oxidized cellulose) after washing was measured, it was 0.42 mmol / g. The obtained oxidized cellulose was dispersed in pure water to prepare a 5% dispersion, and defibrillation treatment was performed for 10 minutes under the conditions of CYCLE = 0.5 and AMPLIYUDE = 50 using an ultrasonic homogenizer "UP-400S" manufactured by Hielscher to obtain a CNF aqueous dispersion P. In the ultrasonic homogenizer, the ultrasonic oscillation part was immersed in the oxidized cellulose aqueous dispersion placed in the container, and defibrillation was advanced by the ultrasonic waves oscillated from the ultrasonic oscillation part.

[0055] [Comparative Production Example 2] As the cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5 mm squares with scissors and mechanically defibrillated into a cottony state by treating it at 25,000 rpm for 1 minute using a "Wander Blender WB-1" manufactured by Osaka Chemical Co., Ltd. 30.3 g of sodium hypochlorite pentahydrate crystals with an available chlorine concentration of 42% by mass were placed in a beaker, pure water was added and stirred to adjust the available chlorine concentration to 14% by mass. Then, 35% hydrochloric acid was added and stirred to obtain an aqueous solution with a pH of 9.0. After heating this sodium hypochlorite aqueous solution to 30 °C in a constant-temperature water bath while stirring with a stirrer, 0.35 g of the above mechanically defibrillated softwood kraft pulp was added. After supplying the cellulose-based raw material, while maintaining the temperature at 30 °C in the same constant temperature water bath, the pH during the reaction was adjusted to 9.0 while adding 48 mass% sodium hydroxide, and the oxidation reaction was carried out by stirring with a stirrer for 30 minutes. After the reaction, the product was separated into solid and liquid by suction filtration using a PTFE mesh filter with an opening size of 0.1 μm, and the obtained filtrate residue was washed with pure water. When the amount of carboxyl groups in the washed filtrate residue (oxidized cellulose) was measured, it was 1.12 mmol / g. Subsequently, pure water was added to the oxidized cellulose to prepare a 5% dispersion, and defibrillation treatment was performed under the same conditions as in Comparative Production Example 1 using an ultrasonic homogenizer to obtain a CNF aqueous dispersion Q.

[0056] 〔Comparative Production Example 3〕 As the cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5 mm squares with scissors and mechanically defibrillated into a cotton-like shape by treating it at 25,000 rpm for 1 minute using "WONDER BLENDER WB-1" manufactured by Osaka Chemical Co., Ltd. The cellulose fibers after mechanical defibrillation were dispersed in sufficient water, and wet powder was obtained by suction filtration using a PTFE mesh filter with an opening size of 0.1 μm. The above wet powder (80 mass% water, 20 g in terms of dry powder) was placed in a container, and subsequently, 60 L of an ozone-oxygen mixed gas with an ozone concentration of 200 g / m 3 was added, and the mixture was shaken at 25 °C for 2 minutes. After standing for 6 hours, ozone and the like in the container were removed, and then the oxidized cellulose was taken out and washed with pure water by suction filtration using a PTFE mesh filter with an opening size of 0.1 μm. Pure water was added to the obtained oxidized cellulose to prepare a 2 mass% dispersion, and sodium hydroxide was added to make a 0.3 mass% sodium hydroxide solution. After stirring for 5 minutes, it was left standing at 25 °C for 30 minutes. Subsequently, it was washed with pure water by suction filtration using a PTFE mesh filter with an opening size of 0.1 μm. When the amount of carboxyl groups in the washed oxidized cellulose was measured, it was 0.43 mmol / g. Pure water was added to the oxidized cellulose to prepare a 5% dispersion, which was then treated at 200 MPa for 10 passes using a high-pressure homogenizer "Starburst Lab HJP-25005" manufactured by Sugino Machine Limited to obtain CNF aqueous dispersion R.

[0057] [Comparative Production Example 4] As a cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5 mm squares with scissors and mechanically defibrated into a cotton-like form by treating it at 25,000 rpm for 1 minute using a "Wonder Blender WB-1" manufactured by Osaka Chemical Co., Ltd. 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 aqueous sodium periodate solution was heated to 55°C in a constant-temperature water bath while stirring at 200 rpm using a stirrer (Three One Motor, BL600) manufactured by Shinto Kagaku Co., Ltd. with a propeller-type stirring blade, and then 6 g of the above mechanically defibrated softwood kraft pulp was added. After supplying the cellulose-based raw material, stirring was carried out 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 completed, the product was separated by solid-liquid separation by suction filtration using a PTFE membrane filter with a pore size of 0.1 μm and washed with pure water. Next, the product obtained above was added to a 1 M acetic acid aqueous solution containing sodium chlorite, and stirring was carried out at 25°C for 48 hours under the same stirring conditions as above. After the reaction was completed, the product was separated by solid-liquid separation by suction filtration using a PTFE membrane filter with a pore size of 0.1 μm and washed with pure water. When the amount of carboxyl groups in the washed oxidized cellulose was measured, it was 1.72 mmol / g. Pure water was added to the obtained oxidized cellulose to prepare a 5% dispersion, and an aqueous sodium hydroxide solution was added to adjust the pH to 7.5, followed by washing with water. The obtained dispersion was treated at 200 MPa for 10 passes using a high-pressure homogenizer "Starburst Lab HJP-25005" manufactured by Sugino Machine Limited to obtain CNF aqueous dispersion S.

[0058] [Comparative Production Example 5] As a cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut into 5 mm squares with scissors and mechanically fibrillated into a cotton-like state by treating it at 25,000 rpm for 1 minute using a "Wander Blender WB-1" manufactured by Osaka Chemical Co., Ltd. 0.016 g of TEMPO and 0.1 g of sodium bromide were placed in a beaker, pure water was added and stirred to form an aqueous solution, and 1.0 g of the mechanically fibrillated softwood kraft pulp was added. While stirring the above aqueous solution with a stirrer, it was heated to 25 °C in a constant temperature water bath, then 0.1 M sodium hydroxide was added and stirred to make an aqueous solution with a pH of 10.0. To this, 2.58 g of an aqueous sodium hypochlorite solution with an available chlorine concentration of 13.2 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 0.1 M sodium hydroxide, and stirring was carried out with a stirrer for 120 minutes. After the reaction was completed, the product was separated into solid and liquid by suction filtration using a PTFE membrane filter with a pore size of 0.1 μm, and the obtained filtrate residue was washed with pure water. When the amount of carboxyl groups in the washed filtrate residue (oxidized cellulose) was measured, it was 1.55 mmol / g. Pure water was added to the obtained filtrate residue to prepare a 5% dispersion, and an aqueous sodium hydroxide solution was added to adjust the pH to 7.5, followed by washing with water. The obtained dispersion was treated at 200 MPa for 10 passes using a high-pressure homogenizer "Starburst Lab HJP-25005" manufactured by Sugino Machine, Ltd. to obtain a CNF aqueous dispersion T. The nitrogen component derived from the N-oxyl compound in the oxidized cellulose was measured as the nitrogen amount under the same conditions as in Production Example 1, and as a result of calculating the increase from the raw material pulp, it was 5 ppm.

[0059] [First Example] [Examples 1-1 to 1-9, Comparative Examples 1-1 to 1-5]: Examination of Zeta Potential Using the CNF aqueous dispersions obtained in each of Production Examples 1 to 9 and Comparative Production Examples 1 to 5, the following evaluations were carried out to examine the relationship between the zeta potential of nanocellulose and dispersion stability. The evaluation results are shown in Table 1.

[0060] 〔Zeta potential measurement〕 Pure water was added to each of the CNF aqueous dispersions A to I, P to T obtained above, and diluted so that the concentration of nanocellulose became 0.1%. To the diluted CNF aqueous dispersion, an aqueous sodium hydroxide solution of 0.05 mol / L was added to adjust the pH to 8.0, and the zeta potential was measured at 20 °C using a zeta potential meter (ELSZ-1000) manufactured by Otsuka Electronics Co., Ltd. 〔Measurement of average fiber width〕 Pure water was added to each of the CNF aqueous dispersions A to I, P to T obtained above, and adjusted so that the concentration of nanocellulose in the CNF aqueous dispersion became 5 ppm. The CNF aqueous dispersion after the concentration adjustment was naturally dried on a mica substrate, and the shape of the nanocellulose was observed in the AC mode using a scanning probe microscope “MFP-3D infinity” manufactured by Oxford Asylum. Regarding the average fiber width, the number average fiber width [nm] was determined for 50 or more fibers as the cross-sectional height of the shape image = fiber width using the software attached to “MFP-3D infinity”.

[0061] 〔Measurement of light transmittance〕 Each of the CNF aqueous dispersions A to I, P to T obtained above was placed in a quartz cell with a thickness of 10 mm, and the light transmittance at a wavelength of 660 nm was measured using a spectrophotometer (JASCO V-550). 〔Stability of CNF aqueous dispersion〕 Pure water was added to each of the CNF aqueous dispersions A to I, P to T, diluted so that the concentration of nanocellulose in the CNF aqueous dispersion became 0.1% by mass, and allowed to stand and 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 from the following formula, and the dispersion stability was determined according to the following criteria. The solid content concentration was calculated from the mass change before and after drying at 105 °C. Dispersion rate (%) = (solid content concentration after 4 weeks / solid content concentration immediately after dilution) × 100 ◎: Dispersion rate is less than 95% ○: Dispersion rate is 90% or more and less than 95% △: Dispersion rate is 85% or more and less than 90% ×: Dispersion rate is less than 85%

[0062] 〔Slurry Viscosity Stability〕 For an aqueous slurry (50 g) containing 5% by mass of titanium oxide (manufactured by Ishihara Sangyo Co., Ltd., R-820) and each of the CNF aqueous dispersions A to I, P to T, the amount of nanocellulose added was varied so that the initial viscosity, which is the viscosity immediately after the preparation of the slurry, was the same (300 mPa·s) in each example. For the mixing to prepare the aqueous slurry, a mixer "Awatori Ren-taro ARE-310" (mixing mode, revolution: 2000 rpm, rotation: 800 rpm, 20 minutes) manufactured by Shinchi Co., Ltd. was used. Then, the viscosity immediately after preparation (initial viscosity) and the viscosity after standing for 1 week were measured, the viscosity change rate was calculated from 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 1 week after the 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 and less than 115% ×: Viscosity change rate is 115% or more Note that the standing was carried out indoors (23 ± 2°C). The initial viscosity of the slurry and the viscosity after standing for 1 week were measured at 25°C and 100 rpm (shear rate 200 s -1 ) using an E-type viscometer (TV-22) manufactured by Toki Sangyo Co., Ltd. after stirring at a speed such that no bubbles entered with a spatula.

[0063] 〔Slurry Handleability〕 Water was added to each of the CNF aqueous dispersions A to I, P to T so that the amount of aluminum silicate powder was 5% by mass and the amount of nanocellulose was 0.5% by mass, and the mixture was blended and stirred to prepare a processing liquid. After gently stirring this processing liquid with a spatula and then scooping it up, the dripping of the liquid when the spatula was tilted was visually observed, and the slurry handleability was evaluated according to the following criteria. ◎: Dripping occurred immediately after tilting. ○: Dripping occurred 5 seconds or more after tilting. △: Dripping occurred 10 seconds or more after tilting. ×: Even after 15 seconds, no dripping occurred.

[0064] 〔Surface state (coating property) after slurry coating〕 Water was added to each of the CNF aqueous dispersions A - I, P - T so that the aluminum silicate powder was 5% by mass and the nanocellulose was 0.5% by mass, and they were blended and stirred to prepare a processing liquid. The processing liquid was applied to a woven fabric (100% polyester, 100 mm × 100 mm) so that the processed amount of the aluminum silicate powder was 5 g / m 2 and dried. For 10 pieces of the coated woven fabric, unevenly coated areas (processing unevenness) were visually observed and evaluated according to the following criteria. ◎: No processing unevenness was visible in all 10 pieces. ○: No processing unevenness was visible in 8 - 9 pieces. △: No processing unevenness was visible in 4 - 7 pieces. ×: No processing unevenness was visible in 1 - 3 pieces or processing unevenness was visible in all 10 pieces.

[0065]

Table 1

[0066] In Table 1, when an N - oxyl compound was not used during the oxidation treatment of the cellulose - based raw material (that is, when the CNF dispersion was substantially free of the N - oxyl compound), it was represented by "×", and when an N - oxyl compound was used (that is, when the CNF dispersion contained the N - oxyl compound), it was represented by "○" (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 hypochlorite oxidation treatment with Comparative Examples 1 - 1 and 1 - 2, Examples 1 - 1 to 1 - 9 with a zeta potential of - 30 mV or less showed better slurry properties compared to Comparative Examples 1 - 1 and 1 - 2 with zeta potentials of - 17.9 mV and - 21.7 mV, respectively. Specifically, in the CNF aqueous dispersions of Examples 1-1 to 1-9, the dispersion stability of nanocellulose was high. Also, the slurries obtained in Examples 1-1 to 1-9 had a balanced viscosity stability, handleability, and coatability. In particular, in Examples 1-1 to 1-7, all of the viscosity stability, handleability, and coatability of the slurry were evaluated as "◎" or "○", indicating excellent slurry properties. Also, from the results of Examples 1-1, 1-2, and 1-9 having similar zeta potentials, it was found that Examples 1-1 and 1-2 with an average fiber width of nanocellulose of 5 nm or less exhibited more excellent slurry properties compared to Example 1-9 with an average fiber width of 5.3 nm. In contrast, in Comparative Examples 1-1 to 1-4, the dispersion stability was evaluated as "×", and the slurry properties were also inferior to those of Examples 1-1 to 1-9. In Comparative Example 1-5, although the dispersion stability was good, all of the slurry properties were evaluated as "×".

[0068] [Second Example] [Examples 2-1 to 2-9, Comparative Examples 2-1 to 2-5]: Examination of average fiber width Using the CNF aqueous dispersions A to H, J, P to T obtained in each of Production Examples 1 to 8, 10 and Comparative Production Examples 1 to 5, the same evaluation as in the above First Example was performed, and the relationship between the average fiber width of nanocellulose and the dispersion stability was examined. 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 exhibited more excellent slurry properties compared to Comparative Examples 2-1 and 2-2 with average fiber diameters of 5.3 nm and 5.2 nm, respectively. Also, from the results of Examples 2-1 and 2-9 having the same average fiber width, it was found that Example 2-1 with a zeta potential of -30 mV or less exhibited better slurry properties compared to Example 2-9 with a zeta potential of -28.5 mV for nanocellulose.

[0071] [Third Example] [Examples 3-1 to 3-9, Comparative Examples 3-1 to 3-5]: Examination of aspect ratio Using the CNF aqueous dispersions A to H, K, P to T obtained in each of Production Examples 1 to 8, 11 and Comparative Production Examples 1 to 5, the average fiber length and average fiber width of the nanocellulose were measured to calculate the aspect ratio, and the same evaluation as in the above First Example was performed to examine the relationship between the aspect ratio and dispersion stability of the nanocellulose. The average fiber length and average fiber width were measured by the following procedure. [Measurement of average fiber length and average fiber width] Pure water was added to each of the CNF aqueous dispersions A to H, K, P to T obtained above, and adjusted so that the concentration of the nanocellulose in the CNF aqueous dispersion became 5 ppm. The CNF aqueous dispersion after concentration adjustment was naturally dried on a mica substrate, and the shape of the nanocellulose was observed in AC mode using a scanning probe microscope "MFP-3D infinity" manufactured by Oxford Asylum. Regarding the average fiber length, the obtained image was binarized and analyzed using image processing software "Image J". For 100 fibers, the number average fiber length was determined as fiber length = perimeter length ÷ 2. Regarding the average fiber width, using the software attached to "MFP-3D infinity", for 50 or more fibers, the number average fiber width [nm] was determined as the cross-sectional height of the shape image = fiber width. Also, the aspect ratio was 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 Examples 3-1 to 3-9 in which nanocellulose was produced by oxidation treatment with hypochlorite were compared with Comparative Examples 3-1 and 3-2, Examples 3-1 to 3-9 having an aspect ratio of 150 or less showed better slurry properties than Comparative Examples 3-1 and 3-2 having aspect ratios of 183 and 165, respectively. Further, from the results of Examples 3-2 and 3-9 having comparable aspect ratios, it was found that Example 3-2 having a zeta potential of -30 mV or less showed better slurry properties than Example 3-9 having a zeta potential of -28.6 mV for the nanocellulose.

Claims

1. Nanocellulose which is an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof, and has an average fiber width of 1 nm or more and 5 nm or less, substantially free of N-oxyl compounds, has a zeta potential of -30 mV or less, has an aspect ratio of 20 or more and 150 or less, and has a carboxy group content of 0.30 mmol / g or more. Nanocellulose.

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

3. Nanocellulose which is an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof, substantially free of N-oxyl compounds, has an average fiber width of 1 nm or more and 5 nm or less, has an aspect ratio of 20 or more and 150 or less, and has a carboxy group content of 0.30 mmol / g or more. Nanocellulose.

4. Nanocellulose which is an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof, and has an average fiber width of 1 nm or more and 5 nm or less, substantially free of N-oxyl compounds, has a light transmittance of 95% or more in a mixed solution mixed with water to a solid content concentration of 0.1% by mass, has an aspect ratio of 20 or more and 150 or less, and has a carboxy group content of 0.30 mmol / g or more. Nanocellulose.

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

6. A cosmetic containing the nanocellulose according to any one of claims 1 to 4 or the nanocellulose dispersion according to claim 5.

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

8. A rubber containing the nanocellulose according to any one of claims 1 to 4.

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

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

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