Oxidized cellulose, nanocellulose, and dispersions thereof

Abstract

To provide oxidized cellulose excellent in defibration.SOLUTION: The oxidized cellulose is oxidized cellulose which is an oxide of a cellulose-based raw material by a hypochlorous acid or a salt thereof, and substantially contains no N-oxyl compound, wherein the degree of polymerization is 600 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to oxidized cellulose, nanocellulose, and dispersions thereof. More specifically, it relates to oxidized cellulose obtained by oxidizing a cellulosic raw material with an oxidizing agent, and a dispersion of oxidized cellulose containing the same, as well as nanocellulose obtained by defibrating the oxidized cellulose, and a dispersion of nanocellulose 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 obtaining oxidized cellulose by oxidizing a cellulosic raw material under high-concentration conditions where the effective chlorine concentration in the reaction system is 14 to 43% by mass, using hypochlorous acid or a salt thereof as an oxidizing agent. Patent Document 2 discloses obtaining oxidized cellulose by oxidizing a cellulosic raw material while adjusting the pH to 5.0 to 14.0, with the effective chlorine concentration in the reaction system being 6 to 14% by mass, using hypochlorous acid or a salt thereof as an oxidizing agent. 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] Patent documents 1 and 2 disclose a specific example of producing nanocellulose material by micronizing oxidized cellulose, in which nanocellulose material is obtained through a defibration process using an ultrasonic homogenizer. However, the above process has room for further improvement in terms of the energy required for defibration. In the production of nanocellulose material, from the viewpoint of production cost, there is a need for oxidized cellulose that is easily defibrated and can be defibrated even under mild processing conditions. Furthermore, in order to stably produce finely milled cellulose fibers, or to obtain a highly transparent nanocellulose material with low light scattering in the dispersion medium, it is necessary that the oxidized cellulose, which is the state before defibration of the nanocellulose material, has good defibration properties.

[0006] This invention has been made in view of the above circumstances, and its main objective is to provide oxidized cellulose with excellent defibrillation properties. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides the following means. [1] Oxidized cellulose, which is an oxide of a cellulosic raw material made of hypochlorous acid or a salt thereof, substantially free of N-oxyl compounds and having a degree of polymerization of 600 or less.

[0008] [2] Oxidized cellulose of [1], having a carboxyl group content of 0.30 to 2.0 mmol / g. [3] The oxidized cellulose according to [1] or [2], wherein the light transmittance of the nanocellulose aqueous dispersion obtained by defibrating the 0.1% by mass aqueous dispersion of oxidized cellulose in a rotating agitator at a rotational speed of 2000 rpm and a rotational speed of 800 rpm for 10 minutes is 60% or more. 〔4〕Cellulose oxide which is cellulose oxide as a raw material, and the light transmittance of the nano-cellulose aqueous dispersion obtained by defibrating the 0.1 mass% aqueous dispersion of the cellulose oxide under the conditions of a revolution speed of 2000 rpm and a rotation speed of 800 rpm for 10 minutes using a planetary stirrer is 60% or more, cellulose oxide. 〔5〕The cellulose oxide according to 〔4〕, wherein the cellulose oxide is an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof. 〔6〕A cellulose oxide dispersion in which the cellulose oxide according to any one of 〔1〕 to 〔5〕 is dispersed in a dispersion medium.

[0009] 〔7〕Nano-cellulose obtained by defibrating the cellulose oxide according to any one of 〔1〕 to 〔6〕, and having an average fiber width of 1 to 200 nm. 〔8〕Nano-cellulose obtained by defibrating the cellulose oxide according to any one of 〔1〕 to 〔6〕 under the conditions of a revolution speed of 1200 to 2500 rpm and a rotation speed of 600 to 1000 rpm for 3 to 15 minutes using a planetary stirrer. 〔9〕A nano-cellulose dispersion in which the nano-cellulose according to 〔7〕 or 〔8〕 is dispersed in a dispersion medium.

Advantages of the Invention

[0010] According to the present invention, cellulose oxide excellent in defibratability can be obtained. In particular, the cellulose oxide of the present invention can be uniformly refined even when defibrated under mild conditions, and is excellent in easy defibratability.

Modes for Carrying Out the Invention

[0011] 《Cellulose Oxide》 The oxidized cellulose of the present disclosure (hereinafter also referred to as "the present oxidized cellulose") is fibrous cellulose obtained by oxidizing a cellulose-based raw material with hypochlorous acid or a salt thereof, and is the material before the fibrillation treatment. The present oxidized cellulose can also be referred to as an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof. The main component of plants is cellulose, and what is formed by bundling cellulose molecules is called cellulose microfibril. Cellulose in the cellulose-based raw material is also contained in the form of cellulose microfibrils. In addition, since "oxidized cellulose" is fibrous cellulose oxidized as described above, it is also referred to as "oxidized cellulose fiber".

[0012] Since the oxidized cellulose 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 the present specification, "substantially does not contain an N-oxyl compound" means that the oxidized cellulose does not contain any N-oxyl compound at all, or the content of the N-oxyl compound is 2.0 mass ppm or less with respect to the total amount of the oxidized cellulose, preferably 1.0 mass ppm or less. Also, 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". By substantially not containing an N-oxyl compound, it is possible to suppress the residue of the N-oxyl compound, which is a concern for the environment and the human body, in the oxidized cellulose. The content of the N-oxyl compound can be measured by known means. Examples of known means include a method using a micro total nitrogen analyzer. Specifically, the nitrogen component derived from the N-oxyl compound in the oxidized cellulose can be measured as the amount of nitrogen using a micro total nitrogen analyzer (for example, manufactured by Mitsubishi Chemical Analytech Co., Ltd., apparatus name: TN-2100H, etc.). Hereinafter, the present oxidized cellulose will be described in detail.

[0013] [Degree of polymerization] In one preferred embodiment of this disclosure, the degree of polymerization of the oxidized cellulose is 600 or less. When the degree of polymerization of the oxidized cellulose exceeds 600, it tends to require a large amount of energy for defibration, and it tends not to exhibit sufficient defibration properties. Furthermore, when the degree of polymerization of the oxidized cellulose exceeds 600, there is a large amount of oxidized cellulose that has not been sufficiently defibrated, and when this is dispersed as finely ground nanocellulose in a dispersion medium, light scattering increases, which can reduce transparency. In addition, there tends to be variation in the size of the resulting nanocellulose, resulting in non-uniform quality. As a result, the viscosity of the slurry containing nanocellulose together with solid particles (hereinafter also referred to as "nanocellulose-containing slurry") becomes unstable, and the handling and coating properties of the slurry may decrease. From the viewpoint of easy defibration, no lower limit is particularly set for the degree of polymerization of the oxidized cellulose. However, when the degree of polymerization of the oxidized cellulose is less than 50, the proportion of particulate cellulose rather than fibrous cellulose increases, resulting in non-uniform slurry quality and unstable viscosity, as well as difficulty in obtaining thixotropy, one of the characteristics of nanocellulose. From the above viewpoint, the degree of polymerization of this oxidized cellulose is preferably 50 to 600.

[0014] The degree of polymerization of this oxidized cellulose is more preferably 580 or less, even more preferably 560 or less, even more preferably 550 or less, even more preferably 500 or less, even more preferably 450 or less, and even more preferably 400 or less. Regarding the lower limit of the degree of polymerization, from the viewpoint of improving the viscosity stability and coating properties of the slurry, it is more preferably 60 or more, even more preferably 70 or more, even more preferably 80 or more, even more preferably 90 or more, even more preferably 100 or more, even more preferably 110 or more, and particularly preferably 120 or more. The preferred range for the degree of polymerization can be determined by appropriately combining the upper and lower limits described above. The degree of polymerization of this oxidized cellulose is more preferably 60 to 600, even more preferably 70 to 600, even more preferably 80 to 600, even more preferably 80 to 550, even more preferably 80 to 500, even more preferably 80 to 450, and particularly preferably 80 to 400.

[0015] The degree of polymerization of oxidized cellulose can be adjusted by changing the reaction time, reaction temperature, pH, and the effective chlorine concentration of hypochlorous acid or its salt during the oxidation reaction. Specifically, since increasing the degree of oxidation tends to decrease the degree of polymerization, methods to reduce the degree of polymerization include, for example, increasing the oxidation reaction time and / or reaction temperature. Alternatively, the degree of polymerization of oxidized cellulose can be adjusted by the stirring conditions of the reaction system during the oxidation reaction. For example, under conditions where the reaction system is sufficiently homogenized using a stirring blade or the like, the oxidation reaction proceeds smoothly and the degree of polymerization tends to decrease. On the other hand, under conditions where stirring of the reaction system is likely to be insufficient, such as stirring with a stirrer, the reaction tends to become non-uniform, making it difficult to sufficiently reduce the degree of polymerization of the cellulose fibers. Furthermore, the degree of polymerization of oxidized cellulose also tends to vary depending on the selection of the raw material cellulose. For this reason, the degree of polymerization of oxidized cellulose can also be adjusted by selecting the cellulosic raw material. In this specification, the degree of polymerization of oxidized cellulose is the average degree of polymerization (viscosity-average degree of polymerization) measured by the viscosity method. Details are described in the examples below.

[0016] [Carboxylate group amount] The amount of carboxyl groups in the oxidized cellulose is preferably 0.30 to 2.0 mmol / g. When the amount of carboxyl groups is 0.30 mmol / g or more, sufficient defibrillability can be imparted to the oxidized cellulose. As a result, even when defibrillation is performed under mild conditions, a nanocellulose-containing slurry with uniform quality can be obtained, improving 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 defibrillation 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 is more preferably 1.5 mmol / g or less, even more preferably 1.2 mmol / g, even more preferably 1.0 mmol / g or less, and even more preferably 0.9 mmol / g. 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.

[0017] The amount of carboxyl groups (mmol / g) in oxidized cellulose was calculated using the following formula from the amount of sodium hydroxide consumed during the neutralization stage of a weak acid, where the change in electrical conductivity was gradual. This was done by adding a 0.1 M hydrochloric acid solution to an aqueous solution of oxidized cellulose mixed with water to adjust the pH to 2.5, then adding a 0.05 N sodium hydroxide solution dropwise until the pH reached 11.0. Further details are provided in the examples described later. The amount of carboxyl groups in oxidized cellulose can be adjusted by changing the reaction time, reaction temperature, pH of the reaction solution, etc. Carboxylate group amount = a (ml) × 0.05 / Oxidized cellulose mass (g)

[0018] This oxidized cellulose can be obtained, for example, by oxidizing a cellulosic raw material under conditions where the effective chlorine concentration of hypochlorous acid or its salt in the reaction system is relatively high (e.g., 14% to 43% by mass).

[0019] Preferably, this oxidized cellulose has a structure in which at least two of the hydroxyl groups of the glucopyranose ring constituting the cellulose are oxidized, and more specifically, has 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 oxidized cellulose remains unoxidized and as a hydroxyl group. Note that the position of the carboxyl group on the glucopyranose ring of the oxidized cellulose is solid. 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.

[0020] 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.

[0021] The oxidized cellulose described herein exhibits excellent defibrillation properties. In particular, this oxidized cellulose can be uniformly pulverized even when defibrillated under mild conditions, demonstrating excellent ease of defibrillation. Furthermore, when the pulverized oxidized cellulose is mixed with inorganic particles such as pigments to form a slurry, the slurry viscosity remains stable over time, and it exhibits excellent handling and coating properties. In addition, because it does not contain N-oxyl compounds, it can reduce its impact on the environment.

[0022] [Method for producing oxidized cellulose] Next, the method for producing this oxidized cellulose will be described. This oxidized cellulose can be produced by a method that includes a step of oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof.

[0023] 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.

[0024] 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.

[0025] One method for producing oxidized cellulose by oxidation of a cellulosic raw material is to mix the cellulosic raw material with a reaction solution containing hypochlorous acid or a salt thereof. The reaction solution preferably contains water as a solvent 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The method for producing this oxidized cellulose will be further explained below, using sodium hypochlorite as the hypochlorous acid or its salt as an example.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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 formed in the cellulosic raw material due to 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 and carry out the oxidation reaction while adjusting the pH of the reaction system. 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.

[0034] Using the solution containing oxidized cellulose obtained by the above reaction, performing known isolation treatments such as filtration, and further purifying as necessary, 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 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 carboxyl 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, since the proton form has a peak around 1720 cm -1 and the salt form has a peak around 1600 cm -1 , they can be distinguished from each other. The solution containing oxidized cellulose obtained by the above reaction may be directly subjected to fibrillation treatment.

[0035] 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 set the pH to 6.0 or more, and at least a part of the carboxyl 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, under alkaline conditions with a pH of 10 or more, at least a part of the carboxyl groups can be in the salt form (-COO - X + :X + refers to cations such as sodium and lithium).

[0036] The present 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, this oxidized cellulose encompasses salt-type, proton-type, and modified forms with modifying groups. Furthermore, the nanocellulose obtained from this oxidized cellulose also encompasses salt-type, proton-type, and modified forms with modifying groups.

[0037] This oxidized cellulose may also be in the form of a mixture with a dispersion medium. That is, one aspect of the present invention is an oxidized cellulose dispersion in which this oxidized cellulose is dispersed in a dispersion medium. Examples of the dispersion medium include those similar to the dispersion medium described later.

[0038] Nanocellulose The nanocellulose of this disclosure (hereinafter also referred to as "this nanocellulose") can be obtained by defibrating oxidized cellulose, which is obtained by oxidizing a cellulosic raw material with an oxidizing agent, and then nano-forming it. That is, this nanocellulose can be produced by a method that includes the steps of oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof, and defibrating the oxidized cellulose obtained in the said step. The oxidation step is as described above. Furthermore, since "nanocellulose" is fibrous cellulose made by finely processing oxidized fibrous cellulose, it is also called "fine cellulose fiber."

[0039] Methods for defibrating oxidized cellulose include, for example, mechanical defibration. Here, nanocellulose (hereinafter also referred to as nanocellulose) is a general term for cellulose that has been nano-sized, 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] The defibration of this oxidized cellulose may be carried out using, for example, a method using an ultra-high pressure homogenizer, as this method allows for the efficient production of nanocellulose with more advanced defibration. When defibration is carried out using an ultra-high pressure homogenizer, the pressure during the defibration process 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 the defibration, it is preferably 2 or more times, more preferably 3 or more times.

[0042] This oxidized cellulose is excellent in its ease of defibrillation, and is therefore suitable because it can be sufficiently defibrillated even when mild stirring is applied as a defibrillation method, such as using a rotational agitator or a vibrating agitator, thereby obtaining homogenized nanocellulose.

[0043] A rotating-orbit agitator is a device that mixes materials in a container by rotating and orbiting the container into which the materials are introduced. With a rotating-orbit agitator, stirring is performed without using agitator blades, thus enabling gentler stirring. The orbital speed and rotational speed during stirring with a rotating-orbit agitator can be set as appropriate, but for example, the orbital speed can be set to 400 to 3000 rpm and the rotational speed to 200 to 1500 rpm. When using a rotating-orbit agitator, from the viewpoint of ensuring uniformity of quality while achieving gentle stirring, it is preferable to perform the defibration treatment by stirring for 3 to 15 minutes at an orbital speed of 1200 to 2500 rpm and a rotational speed of 600 to 1000 rpm. The orbital speed is more preferably 1500 to 2300 rpm, and the rotational speed is more preferably 700 to 950 rpm. When defibrating oxidized cellulose using a rotating and revolving agitator, the concentration of the aqueous dispersion of oxidized cellulose used as the material can be adjusted as appropriate, but is, for example, 0.01 to 1.0% by mass, and preferably 0.1 to 0.5% by mass.

[0044] Examples of vibrating agitators include vortex mixers (touch mixers). In a vortex mixer, agitation is achieved by forming a vortex in the liquid material inside the container. With vibrating agitators such as vortex mixers, agitation is achieved without using agitator blades, thus enabling gentler agitation. Furthermore, vibrating agitators such as vortex mixers are superior in terms of production equipment and production costs because gentle agitation can be achieved with simple equipment. The rotation speed of the vortex mixer is preferably 600 to 3000 rpm, and the defibration treatment is performed under conditions of agitation for 3 to 15 minutes. When defibrating oxidized cellulose using a vortex mixer, the concentration of the oxidized cellulose aqueous dispersion used as the material can be adjusted as appropriate, but is preferably 0.01 to 1.0 mass%, and more preferably 0.1 to 0.5 mass%.

[0045] The defibration treatment is preferably carried out with the 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.

[0046] 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.

[0047] 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 the organic solvent 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.

[0048] [Average fiber width] The average fiber width of this nanocellulose is preferably 1 to 200 nm. In particular, this oxidized cellulose is favored because, through defibration treatment, it is possible to obtain nanocellulose with an average fiber width of 1 to 20 nm, preferably 1 to 10 nm, and more preferably 1 to 5 nm, which is sufficiently nano-sized. Furthermore, when the average fiber width of this nanocellulose is sufficiently small, at 1 to 5 nm, the slurry containing this nanocellulose has stable viscosity and good handling and coating properties. The average fiber width of this nanocellulose is more preferably 4.8 nm or less, even more preferably 4.5 nm or less, and even more preferably 4.2 nm or less. From the viewpoint of easy defibration, no lower limit is particularly set for the average fiber width. However, if the average fiber width is less than 1 nm, it approaches the form of a single cellulose molecule, and the quality as nanocellulose tends to be uneven. For this reason, the average fiber width is preferably 1 nm or more, and more preferably 1.5 nm or more.

[0049] [Average fiber length] The average fiber length of this nanocellulose is preferably 100 to 2000 nm. More preferably, the average fiber length is 100 to 1000 nm, even more preferably 100 to 500 nm, and even more preferably 100 to 400 nm.

[0050] [Aspect Ratio] In this nanocellulose, the aspect ratio (average fiber length / average fiber width), which is expressed as the ratio of the average fiber width to the average fiber length, is preferably 20 to 200. More preferably, the aspect ratio is 30 or more, and even more preferably 40 or more. Furthermore, the aspect ratio is more preferably 180 or less, and even more preferably 150 or less.

[0051] 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, differences in the calculated values ​​may occur 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.

[0052] [Light transmittance] This oxidized cellulose allows for sufficient defibration even under mild defibration conditions, resulting in nanocellulose with sufficiently small fiber widths. Furthermore, because the resulting nanocellulose has sufficiently small fiber widths, when dispersed in a dispersion medium, it exhibits high light transmittance due to less light scattering from cellulose fibers. Therefore, this nanocellulose can be effectively used in applications where transparency is required.

[0053] Specifically, it is preferable that the light transmittance of the nanocellulose aqueous dispersion obtained by defibrating a 0.1% by mass aqueous dispersion of the oxidized cellulose in a rotary-orbiting agitator at an orbital speed of 2000 rpm and a rotational speed of 800 rpm for 10 minutes is 60% or higher. More preferably, the light transmittance of this nanocellulose aqueous dispersion is 70% or higher, even more preferably 75% or higher, and even more preferably 80% or higher. The light transmittance is the value at a wavelength of 660 nm measured by a spectrophotometer.

[0054] Furthermore, it is preferable that the light transmittance of the nanocellulose aqueous dispersion obtained by defibrating a 0.1% by mass aqueous dispersion of the oxidized cellulose in a vortex mixer at a rotation speed of 3000 rpm for 10 minutes is 60% or higher. More preferably, the light transmittance of this nanocellulose aqueous dispersion is 70% or higher, even more preferably 75% or higher, and even more preferably 80% or higher.

[0055] Although the reason why the oxidized cellulose in this disclosure exhibits excellent defibrillability (particularly easy defibrillability) and yields a high-quality slurry is not entirely clear, the following is generally considered to be the cause. Defibrillation proceeds by the cleavage of hydrogen bonds between cellulose microfibrils. In oxidation treatment using hypochlorous acid or its salts, the degree of polymerization of the microfibrils decreases (i.e., the cellulose molecular chains become shorter) as oxidation progresses. This decrease in the degree of polymerization is more pronounced with increasing oxidation when oxidized with relatively high concentrations of hypochlorous acid or its salts compared to, for example, the TEMPO oxidation method. Therefore, in this embodiment, it is thought that the number of hydrogen bonds to be cleaved by defibrillation in each microfibril is reduced by the oxidation treatment, and furthermore, the amount of carboxyl groups increases as oxidation progresses, strengthening the repulsive force between microfibrils and improving the defibrillability of the oxidized cellulose. In addition, it is thought that the improved defibrillability of the oxidized cellulose made it possible to obtain nanocellulose that can improve the viscosity stability, handling properties, and coating properties of the slurry.

[0056] (Other embodiments) In another preferred embodiment of the present disclosure, oxidized cellulose is provided, obtained by oxidizing a cellulosic raw material with an oxidizing agent. This oxidized cellulose can also be called oxidized cellulose, which is an oxide of the cellulosic raw material. The oxidized cellulose of this embodiment has a light transmittance of 60% or more in a nanocellulose aqueous dispersion obtained by defibrating a 0.1% by mass aqueous dispersion of the oxidized cellulose in a rotating and revolving agitator at a rotational speed of 2000 rpm and a rotational speed of 800 rpm for 10 minutes.

[0057] Furthermore, in another preferred embodiment of the present disclosure, the oxidized cellulose is obtained by defibrating a 0.1% by mass aqueous dispersion of the oxidized cellulose in a vortex mixer at a rotation speed of 3000 rpm for 10 minutes, and the light transmittance of the nanocellulose aqueous dispersion is 60% or more.

[0058] In other words, with these other forms of oxidized cellulose, defibration proceeds sufficiently even under mild defibration conditions, and nanocellulose with a fiber width of approximately 1 to 5 nm can be obtained. Because the obtained nanocellulose has a sufficiently small fiber width, when dispersed in a dispersion medium, there is less light scattering from cellulose fibers, resulting in high light transmittance. Therefore, it can be effectively used in applications where transparency is required. Furthermore, nanocellulose obtained by defibrating the above-mentioned other forms of oxidized cellulose, even when the defibration treatment is carried out under mild conditions, can stabilize the viscosity of the slurry when used as a nanocellulose-containing slurry, and the handling and coating properties of the slurry can be improved.

[0059] Examples of the oxidizing agents mentioned above include halogens, hypochlorous acid or its salts, and peroxides. Of these, hypochlorous acid or its salts are preferred because they allow for the production of homogenized nanocellulose, have a low environmental impact, and are inexpensive. Hypochlorous acid or its salts are as previously described.

[0060] 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. [Examples]

[0061] 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".

[0062] (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 at 200 rpm for 30 minutes using the above-mentioned stirrer with a propeller-type stirring blade to perform the oxidation reaction. 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 to obtain oxidized cellulose A. The obtained oxidized cellulose A was washed with pure water, and the amount of carboxyl groups in the filtered product (oxidized cellulose A) after washing was measured to be 0.45 mmol / g. Next, pure water was added to oxidized cellulose A to prepare a 0.1% dispersion. Using a rotational and rotational mixer "Awatori Rentaro ARE-310" manufactured by Thinky Co., Ltd., the dispersion was processed for 10 minutes in mix mode under conditions of a rotational speed of 2000 rpm and a rotational speed of 800 rpm to obtain CNF aqueous dispersion A as a nanocellulose dispersion. Furthermore, the nitrogen content derived from N-oxyl compounds in oxidized cellulose A 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.

[0063] 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.

[0064] 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)

[0065] [Manufacturing Example 2] Oxidized cellulose B and CNF aqueous dispersion B were 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 3] Oxidized cellulose C and CNF aqueous dispersion C were 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 and the cellulosic raw material was changed to powdered cellulose (VP-1) manufactured by TDI Corporation. [Manufacturing Example 4] Oxidized cellulose D and CNF aqueous dispersion D were obtained by processing under the same conditions as in Production Example 1, except that the oxidation reaction time was set to 120 minutes and the cellulosic raw material was changed to powdered cellulose (KC Floc W-100GK) manufactured by Nippon Paper Industries Co., Ltd.

[0066] [Manufacturing Example 5] Oxidized cellulose E and CNF aqueous dispersion E were obtained by processing under the same conditions as in Production Example 1, except that the oxidation reaction time was set to 240 minutes. [Manufacturing Example 6] Oxidized cellulose F and CNF aqueous dispersion F were obtained by processing under the same conditions as in Production Example 1, except that the oxidation reaction time was set to 360 minutes. [Manufacturing Example 7] Oxidized cellulose G and CNF aqueous dispersion G were obtained by processing under the same conditions as in Production Example 1, except that the oxidation reaction temperature was set to 50°C. [Manufacturing Example 8] Oxidized cellulose H and CNF aqueous dispersion H were obtained by processing under the same conditions as in Production Example 1, except that the oxidation reaction time was set to 480 minutes.

[0067] 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 cellulose13 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.

[0068] [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 to obtain oxidized cellulose P. After washing the obtained filtered product (oxidized cellulose P) with pure water, the amount of carboxyl groups was measured to be 0.42 mmol / g, and the amount of filtered product was 0.31 g. The obtained oxidized cellulose P was dispersed in pure water to prepare a 0.1% dispersion. Using a rotational and rotational mixer "Awatori Rentaro ARE-310" manufactured by Thinky Co., Ltd., the dispersion was subjected to defibration treatment for 10 minutes in mix mode under conditions of a rotational speed of 2000 rpm and a rotational speed of 800 rpm to obtain a CNF aqueous dispersion P.

[0069] [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 reduce the effective chlorine concentration to 14% by mass. Then, 35% by mass hydrochloric acid was added and stirred to make 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 to obtain oxidized cellulose Q. 0.12 g of the filtered product was washed with pure water. The amount of carboxyl groups in the filtered product (oxidized cellulose Q) after washing was measured to be 1.12 mmol / g. Next, a 0.1% dispersion was prepared by adding pure water to oxidized cellulose Q, and a defibrillation treatment was performed under the same conditions as in Comparative Production Example 1 to obtain a CNF aqueous dispersion Q.

[0070] [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. 360 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 (oxidized cellulose R) was taken out and washed with pure water by suction filtration using a PTFE mesh filter with a mesh opening of 0.1 μm. Pure water was added to the obtained oxidized cellulose R 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 opening of 0.1 μm. Pure water was added to the oxidized cellulose R to prepare a 0.1% dispersion, and it was subjected to defibration treatment under the same conditions as in Comparative Production Example 1 to obtain CNF aqueous dispersion R.

[0071] [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 cellulosic raw materials, the mixture was stirred under the same conditions for 3 hours in the same constant-temperature water bath while maintaining a temperature of 55°C. 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 to obtain oxidized cellulose S, which was 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. A 0.1% dispersion was prepared by adding pure water to the obtained oxidized cellulose S, and the dispersion was treated to defibrillate under the same conditions as in Comparative Production Example 1 to obtain CNF aqueous dispersion S.

[0072] [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 by suction filtration using a PTFE membrane filter with a mesh size of 0.1 μm to obtain oxidized cellulose T. The obtained filtered product (oxidized cellulose T) was washed with pure water, and the amount of carboxyl groups was measured. The amount of carboxyl groups was 1.55 mmol / g, and the amount of filtered product was approximately 1.0 g. A 0.1% dispersion was prepared by adding pure water to the obtained oxidized cellulose T, and the dispersion was subjected to defibration treatment under the same conditions as in comparative production example 1 to obtain CNF aqueous dispersion T. The nitrogen component derived from the N-oxyl compound in oxidized cellulose T 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.

[0073] (2) Rating 1 [Examples 1-1 to 1-8, Comparative Examples 1-1 to 1-5] The following evaluations were performed using the oxidized cellulose and CNF aqueous dispersions obtained in each of the production examples 1-8 and comparative production examples 1-5. The evaluation results are shown in Table 1.

[0074] [Measurement of viscosity-average degree of polymerization] Oxidized cellulose was added to an aqueous sodium borohydride solution adjusted to pH 10, and a reduction treatment was carried out at 25°C for 5 hours. The amount of sodium borohydride was 0.1 g per 1 g of oxidized cellulose. After the reduction treatment, solid-liquid separation was performed by suction filtration, and the obtained oxidized cellulose was washed with water and freeze-dried. 0.04 g of dried oxidized cellulose was added to 10 ml of pure water and stirred for 2 minutes, then 10 ml of 1 M copper ethylenediamine solution was added to dissolve it. Subsequently, the flow time of the blank solution and the flow time of the cellulose solution were measured at 25°C using a capillary viscometer. From the flow time of the blank solution (t0), the flow time of the cellulose solution (t), and the concentration of oxidized cellulose (c [g / ml]), the relative viscosity (η) was calculated using the following formula. r ), specific viscosity (η sp The intrinsic viscosity ([η]) was determined sequentially, and the degree of polymerization (DP) of oxidized cellulose was calculated from the viscosity measurement formula. η r =η / η0=t / t0 η sp =η r -1 [η]=η sp / (100 × c(1 + 0.28η) sp )) DP = 175 × [η]

[0075] [Measurement of average fiber width] Pure water was added to each of the CNF aqueous dispersions A-H 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.

[0076] [Easy defibration] ○Fibre removal method A Each of the CNF aqueous dispersions A-H 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). The solid content concentration of each CNF aqueous dispersion was 0.1% by mass. A higher light transmittance indicates that the dispersion can be easily defibrated into sufficiently fine fibers even under mild conditions, and that the defibration properties are good. The evaluation criteria are as follows (the same applies to defibration method B). ◎: Light transmittance of 80% or more ○: Light transmittance is 70% or more but less than 80% △: Light transmittance is 60% or more but less than 70% ×: Light transmittance is less than 60%

[0077] ○Defibration method B Each of the oxidized celluloses A-H and P-T obtained above was mixed with water to prepare an aqueous dispersion of oxidized cellulose with a solid content concentration of 0.1%. This aqueous dispersion of oxidized cellulose was placed in a 13.5 ml glass container and processed for 10 minutes using a vortex mixer (VTX-3000L) manufactured by LMS to obtain an aqueous dispersion of CNF. The solid content concentration of each aqueous dispersion of CNF was 0.1% by mass. Each aqueous dispersion of CNF 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). Each measurement value was evaluated on a four-point scale, similar to the defibration method A.

[0078] [Slurry viscosity stability] Aqueous slurries (50g) containing 30% by mass of titanium dioxide (Ishihara Sangyo Co., Ltd., R-820) and each CNF aqueous dispersion A-H, P-T were prepared by varying the amount of nanocellulose added so that the initial viscosity (viscosity immediately after slurry preparation) was the same in each example (300mPa·s). For mixing to prepare the aqueous slurries, a Thinky mixer "Awatori Rentaro ARE-310" (mix mode, revolution: 2000rpm, rotation: 800rpm, 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 evaluation 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.

[0079] [Slurry handling performance] Each of the CNF aqueous dispersions A-H and P-T was mixed and stirred with aluminum silicate powder and water to a concentration of 5% by mass and 0.5% by mass of nanocellulose, respectively, 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.

[0080] [Surface condition after slurry coating (coating properties)] To each of the CNF aqueous dispersions A-H and P-T, aluminum silicate powder and water were added and mixed and stirred to a composition of 5% by mass of aluminum silicate powder and 0.5% by mass of nanocellulose to prepare the 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.

[0081] [Table 1]

[0082] 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 Table 2).

[0083] The oxidized cellulose in Examples 1-1 to 1-8 exhibited high light transmittance when prepared as a CNF aqueous dispersion, as the cellulose microfibrils were easily disintegrated even with gentle stirring using a rotational mixer or a vortex mixer. Furthermore, fine cellulose fibers with an average fiber width of 5 nm or less could be obtained by defibration treatment using a rotational mixer. In addition, the slurries in Examples 1-1 to 1-8 showed a good balance of viscosity stability, handling properties, and coating properties. In particular, Examples 1-1 to 1-7, which had a degree of polymerization on the order of three orders of magnitude, received "◎" or "○" in all evaluations for viscosity stability, handling properties, and coating properties, demonstrating excellent slurry characteristics.

[0084] In contrast, Comparative Examples 1-1 and 1-2, with polymerization degrees of 730 and 650 respectively, showed difficulty in separating cellulose microfibrils with gentle stirring using a rotational mixer or a vortex mixer, resulting in a "×" rating for ease of fibrillation. Furthermore, all slurry properties were rated "△," which was inferior to Examples 1-1 to 1-8. Comparative Examples 1-3 to 1-5, which used different oxidation methods, also showed inferior ratings for ease of fibrillation and slurry properties compared to the examples.

[0085] (3) Rating 2 [Examples 2-1 to 2-11, Comparative Examples 2-1 to 2-5] [Easy defibration] Using the oxidized cellulose A-H, P-T obtained in each of the production examples 1-8 and comparative production examples 1-5, aqueous dispersions of oxidized cellulose with concentrations of 0.1% (Examples 2-1, 2-2, 2-4, 2-6, 2-8-2-11, Comparative Examples 2-1-2-5) or 0.5% (Examples 2-3, 2-5, 2-7) were prepared. These aqueous dispersions of oxidized cellulose were treated with a stirrer, and the resulting CNF aqueous dispersion was placed in a 10 mm thick quartz cell. The light transmittance at a wavelength of 660 nm was measured using a spectrophotometer (JASCO V-550). For the CNF aqueous dispersion obtained by defibration of the 0.5% oxidized cellulose aqueous dispersion, the CNF aqueous dispersion was diluted to 0.1% with pure water, and the light transmittance was measured. A 310-310 rotating / revolving mixer manufactured by Thinky Co., Ltd. was used as the agitator, and the mixture was processed for 10 minutes in mix mode at a rotation speed of 2000 rpm and a rotation speed of 800 rpm. The evaluation criteria are as follows. ◎: Light transmittance of 80% or more ○: Light transmittance is 70% or more but less than 80% △: Light transmittance is 60% or more but less than 70% ×: Light transmittance is less than 60%

[0086] In the above evaluation of ease of fibrillation, the average fiber width, slurry viscosity stability, slurry handling properties, and surface condition after slurry coating were measured and evaluated using each CNF aqueous dispersion obtained by the fibrillation treatment. The evaluation results, along with the amount of carboxyl groups of the oxidized cellulose used in the fibrillation treatment, are shown in Table 2. The measurement and evaluation of the average fiber width, slurry viscosity stability, slurry handling properties, and surface condition after slurry coating were performed in the same manner as in (2) above.

[0087] [Table 2]

[0088] The oxidized cellulose in Examples 2-1 to 2-11 readily disintegrated even with gentle stirring using a rotary-orbit mixer, and exhibited high light transmittance when used as a CNF aqueous dispersion. Furthermore, even when the oxidized cellulose concentration during the defibrillation process was increased from 0.1% to 0.5%, the light transmittance of the CNF aqueous dispersion remained sufficiently high, and the viscosity stability, handling properties, and coating properties of the aqueous slurry were also well-balanced.

[0089] In contrast, in Comparative Examples 2-1 to 2-5, when defibration was performed by gentle stirring with a rotating / revolving mixer, the light transmittance of the CNF aqueous dispersion was low, in the 50% range. Furthermore, Comparative Examples 2-1 to 2-5 also exhibited inferior slurry characteristics compared to Examples 2-1 to 2-11.

Claims

1. A paint comprising nanocellulose or a nanocellulose dispersion, The nanocellulose is formed by defibrating oxidized cellulose, and has an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. The nanocellulose dispersion is a nanocellulose dispersion in which the nanocellulose is dispersed in a dispersion medium. paint.

2. A rubber containing nanocellulose, The nanocellulose is formed by defibrating oxidized cellulose, and has an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. Rubber.

3. A resin containing nanocellulose, The aforementioned nanocellulose is a nanocellulose obtained by defibrating oxidized cellulose, having an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. resin.

4. A film comprising nanocellulose, The aforementioned nanocellulose is a nanocellulose obtained by defibrating oxidized cellulose, having an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. film.

5. A dispersant comprising nanocellulose or a nanocellulose dispersion, The aforementioned nanocellulose is a nanocellulose obtained by defibrating oxidized cellulose, having an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. The nanocellulose dispersion is a nanocellulose dispersion in which the nanocellulose is dispersed in a dispersion medium. Dispersant.

6. A cosmetic product comprising the dispersant described in claim 5.

7. Nanocellulose or nanocellulose dispersion, and inorganic particles A slurry containing, The aforementioned nanocellulose is a nanocellulose obtained by defibrating oxidized cellulose, having an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. The nanocellulose dispersion is a nanocellulose dispersion in which the nanocellulose is dispersed in a dispersion medium. slurry.

8. The inorganic particles include titanium dioxide, The slurry according to claim 7.

9. Nanocellulose or nanocellulose dispersion, and pigment A slurry containing, The aforementioned nanocellulose is a nanocellulose obtained by defibrating oxidized cellulose, having an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. The nanocellulose dispersion is a nanocellulose dispersion in which the nanocellulose is dispersed in a dispersion medium. slurry.

10. An additive comprising nanocellulose or a nanocellulose dispersion, An additive used in slurries containing inorganic particles, The aforementioned nanocellulose is a nanocellulose obtained by defibrating oxidized cellulose, having an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. The nanocellulose dispersion is a nanocellulose dispersion in which the nanocellulose is dispersed in a dispersion medium. Additives.

11. The inorganic particles include titanium dioxide, The additive according to claim 10.

12. An additive comprising nanocellulose or a nanocellulose dispersion, An additive used in a slurry containing pigments, The aforementioned nanocellulose is a nanocellulose obtained by defibrating oxidized cellulose, having an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. The nanocellulose dispersion is a nanocellulose dispersion in which the nanocellulose is dispersed in a dispersion medium. Additives.

13. A mechanical part comprising nanocellulose, The aforementioned nanocellulose is a nanocellulose obtained by defibrating oxidized cellulose, having an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. Machine parts.

14. An electrical appliance containing nanocellulose, The aforementioned nanocellulose is a nanocellulose obtained by defibrating oxidized cellulose, having an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. electric appliances.

15. An electronic device comprising nanocellulose, The aforementioned nanocellulose is a nanocellulose obtained by defibrating oxidized cellulose, having an average fiber width of 1 to 200 nm. The oxidized cellulose is, Oxidized cellulose (excluding oxidized regenerated cellulose) containing 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 degree of polymerization is 600 or less. The oxidized cellulose is such that the amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more. electronic equipment.

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