Process for the production of oxidized cellulose and nanocellulose

Abstract

The present application has an object to stably and efficiently provide oxidized cellulose having excellent defibratability. The above object can be achieved by a production method of oxidized cellulose containing an oxide of a cellulose-based raw material based on hypochlorous acid or a salt thereof, substantially free of N-oxyl compounds, and having a degree of polymerization of 600 or less, the production method including a step of oxidizing the cellulose-based raw material by using hypochlorous acid or a salt thereof to obtain the oxidized cellulose, the viscosity of a slurry of the above cellulose-based raw material at the same concentration as that at the time of the above oxidation being in a range of 1000 Pa·s or less at 30°C or 40°C.

Description

Technical Field

[0001] This invention relates to methods for manufacturing oxidized cellulose and nanocellulose. Background Technology

[0002] Various techniques for manufacturing nanocellulose materials such as cellulose nanofibers (hereinafter also referred to as "CNF") by oxidizing various cellulose-based raw materials with oxidants and micronizing the resulting oxidized cellulose are proposed (see, for example, Patent Document 1 and Patent Document 2).

[0003] Patent Document 1 discloses a method for oxidizing cellulose fibers by using hypochlorous acid or its salt as an oxidant and oxidizing cellulose-based raw materials under high concentration conditions of 14-43% by mass in the reaction system. Patent Document 2 discloses a method for oxidizing cellulose fibers by using hypochlorous acid or its salt as an oxidant and setting the effective chlorine concentration in the reaction system to 6-14% by mass while adjusting the pH to 5.0-14.0. In these techniques, the oxidation process is performed without using N-oxygen radical compounds such as 2,2,6,6-tetramethyl-1-piperidine-N-oxygen radical (TEMPO) as a catalyst. Therefore, N-oxygen radical compounds do not remain in the cellulose fibers, thus reducing environmental impact and enabling the production of nanocellulose materials.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2018 / 230354

[0007] Patent Document 2: International Publication No. 2020 / 027307 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] <The Problem to be Solved by the First Invention (First Topic)>

[0010] Patent Documents 1 and 2 disclose examples of manufacturing nanocellulose materials by micronizing oxidized cellulose, illustrating a process of obtaining nanocellulose materials through a defiberization step achieved by mechanical treatment using an ultrasonic homogenizer. However, there is room for further improvement in the energy required for defiberization in the aforementioned process. From the perspective of production cost, there is a need to find oxidized cellulose with easy defiberization properties, even under mild processing conditions, in the manufacture of nanocellulose materials. Furthermore, in order to stably manufacture micronized cellulose fibers or to obtain nanocellulose materials with low light scattering and high transparency in the dispersion medium, it is desirable to have good defiberization properties of the nanocellulose material before defiberization, i.e., oxidized cellulose.

[0011] Patent documents 1 and 2 specifically describe a method of using several hundred milligrams of cellulose-based raw materials to react with hypochlorous acid or its salt, where the effective chlorine concentration in the reaction system is 6–43% by mass, to obtain oxidized cellulose and nanocellulose materials. However, in this method, the amount of the target oxidized cellulose and nanocellulose materials is limited, and a method is sought that can stably and effectively supply oxidized cellulose fibers with excellent defibrillation properties.

[0012] The present invention was made in view of the above circumstances, and its main objective is to provide oxidized cellulose that provides stable and efficient defibrillation properties.

[0013] <The Problem to be Solved by the Second Invention (Second Topic)>

[0014] Patent Documents 1 and 2 disclose, as specific examples of obtaining oxidized cellulose by oxidizing cellulose-based raw materials with hypochlorous acid or its salts, an example of obtaining oxidized cellulose by solid-liquid separation of cellulose oxides obtained by oxidizing cellulose-based raw materials with hypochlorous acid or its salts through filtration. However, in the method for manufacturing oxidized cellulose, there is still room for further improvement in the yield of the obtained oxidized cellulose through the above-described solid-liquid separation process.

[0015] The present invention was made in view of the above circumstances, and its main objective is to provide a method for manufacturing oxidized cellulose in high yield.

[0016] Solution for solving the problem

[0017] <Solution for solving the first problem>

[0018] Through in-depth research, the inventors discovered that by using hypochlorous acid or its salts, the viscosity of the slurry containing cellulose-based raw materials of the same concentration as those used during oxidation can be controlled to below 1000 Pa·s, and the cellulose-based raw materials can be oxidized, thereby stably and effectively producing oxidized cellulose with excellent defibrillation properties, thus completing this invention.

[0019] <Solution for solving the second problem>

[0020] Through in-depth research, the inventors discovered that by a process including solid-liquid separation of an oxide dispersion containing cellulose oxides and a dispersion medium to obtain oxidized cellulose, wherein the pH of the oxide dispersion is below 4.0 and the oxide dispersion substantially does not contain N-oxygen free radical compounds, or by a process including oxidizing the cellulose raw material with a specified amount of hypochlorous acid or its salt to obtain the aforementioned cellulose oxide, wherein the pH of the oxide dispersion is below 4.0, oxidized cellulose can be obtained in high yield, thus completing the present invention.

[0021] Specifically, the present invention is as follows.

[0022] [1] A method for manufacturing oxidized cellulose, wherein the oxidized cellulose comprises an oxide of a cellulose-based raw material based on hypochlorous acid or its salt, substantially free of N-oxygen free radical compounds, and the degree of polymerization of the oxidized cellulose is 600 or less.

[0023] The manufacturing method includes the step of oxidizing cellulose raw materials by using hypochlorous acid or its salts to obtain oxidized cellulose.

[0024] The viscosity of the slurry of the aforementioned cellulose-based raw material, which is at the same concentration as that used in the aforementioned oxidation, is in the range of 1000 Pa·s or less when measured using a viscometer equipped with an SPP rotor at a rotation speed of 100 rpm and at a temperature of 30°C or 40°C.

[0025] [2] According to the manufacturing method described in [1], the concentration of the cellulose-based raw material is less than 35% by mass relative to the total amount of the reaction mixture.

[0026] [3] According to the manufacturing method described in [1] or [2], the concentration of the cellulose-based raw material exceeds 6.5% by mass relative to the total amount of the reaction mixture.

[0027] [4] The manufacturing method according to any one of [1] to [3], wherein the effective chlorine concentration of the aforementioned hypochlorous acid or its salt in the reaction system is 6% by mass or more and 43% by mass or less.

[0028] [5] The manufacturing method according to any one of [1] to [3], wherein the effective chlorine concentration of the aforementioned hypochlorous acid or its salt in the reaction system is less than 14% by mass.

[0029] [6] The manufacturing method according to any one of [1] to [5], wherein the reaction temperature of the aforementioned oxidation is 30°C or higher.

[0030] [7] The manufacturing method according to any one of [1] to [6], wherein the reaction time of the aforementioned oxidation is 2 hours or more.

[0031] [8] The manufacturing method according to any one of [1] to [7], wherein the pH of the reaction system is less than 11.

[0032] [9] The manufacturing method according to any one of [1] to [8], wherein the aforementioned viscosity is in the range of 30 Pa·s or less.

[0033]

[10] A method for manufacturing nanocellulose, comprising: after an oxidation step in any one of the manufacturing methods of [1] to [9], a step of obtaining nanocellulose by defibrillation.

[0034]

[11] A method for manufacturing oxidized cellulose, comprising:

[0035] The process of separating the oxide dispersion containing cellulose-based oxides and a dispersion medium into solid and liquid components to obtain oxidized cellulose.

[0036] The aforementioned oxide dispersion has a pH below 4.0 and does not substantially contain N-oxygen free radical compounds.

[0037]

[12] The manufacturing method according to

[11] further includes:

[0038] The process of oxidizing cellulose-based raw materials using hypochlorous acid or its salts to obtain the aforementioned cellulose-based oxides.

[0039]

[13] A method for manufacturing oxidized cellulose, comprising:

[0040] A process of oxidizing a cellulose-based raw material with hypochlorous acid or a salt thereof at a mass ratio of 0.2 or more relative to the cellulose raw material to obtain a cellulose-based oxide; and

[0041] The process of separating the oxide dispersion containing the aforementioned cellulose-based oxides and dispersion medium into solid and liquid components to obtain oxidized cellulose.

[0042] The pH of the aforementioned oxide dispersion is below 4.0.

[0043]

[14] The manufacturing method according to

[12] or

[13] further includes:

[0044] The process of treating the aforementioned hypochlorous acid or its salt in the aforementioned oxide dispersion.

[0045]

[15] The manufacturing method according to any one of

[11] to

[14] further includes:

[0046] The step of adding acid and / or cation exchange resin to prepare the aforementioned oxide dispersion with a pH of less than 4.0.

[0047]

[16] The manufacturing method according to any one of

[11] to

[15] further includes:

[0048] The process of adding alkali to adjust the pH of the oxidized cellulose dispersion containing the aforementioned oxidized cellulose and dispersion medium to a value greater than 4.0.

[0049]

[17] The manufacturing method according to any one of

[11] to

[16] , wherein the pH of the aforementioned oxide dispersion is 2.5 or less.

[0050]

[18] The manufacturing method according to any one of

[11] to

[17] , wherein the aforementioned process of obtaining oxidized cellulose is a process of solid-liquid separation by filtering the aforementioned oxide dispersion.

[0051]

[19] The manufacturing method according to any one of

[11] to

[18] further includes:

[0052] The process of cleaning the aforementioned oxide dispersion or the aforementioned oxidized cellulose with an acidic cleaning solution.

[0053]

[20] The manufacturing method according to any one of

[11] to

[19] , wherein the degree of polymerization of the aforementioned oxidized cellulose is 600 or less.

[0054]

[21] An oxidized cellulose obtained by any one of the manufacturing methods described in

[11] to

[20] .

[0055]

[22] A method for manufacturing nanocellulose, comprising:

[0056] The process of defibrilating the oxidized cellulose obtained by any one of the manufacturing methods in

[11] to

[20] to obtain nanocellulose.

[0057]

[23] A nanocellulose obtained by the manufacturing method described in

[22] .

[0058] The effects of the invention

[0059] <Effects of the First Invention>

[0060] According to the manufacturing method of the present invention, oxidized cellulose with excellent defibrillation properties can be obtained stably and effectively. In particular, the oxidized cellulose of the present invention can be uniformly micronized even when defibrillated under mild conditions, exhibiting excellent defibrillation properties.

[0061] <Effects of the Second Invention>

[0062] The method for producing oxidized cellulose according to the present invention can obtain oxidized cellulose in high yield. In particular, the method of the present invention can suppress mesh clogging during solid-liquid separation by filtration, thus resulting in excellent manufacturing efficiency. Attached Figure Description

[0063] Figure 1 This is a flowchart illustrating an example of a manufacturing method of the second invention. Detailed Implementation

[0064] The first invention primarily focuses on oxidizing a cellulose-based raw material to obtain oxidized cellulose. The second invention primarily focuses on post-processing the oxidized cellulose obtained by oxidizing the cellulose-based raw material. Hereinafter, the first and second inventions will be described separately, but reference can be made to the specific embodiments of the first invention within the second invention, and vice versa. Furthermore, the first and second inventions can be combined to form a method comprising the steps of: oxidizing a cellulose-based raw material to obtain oxidized cellulose; and post-processing the aforementioned oxidized cellulose.

[0065] <<First Specific Implementation Method>>

[0066] <Methods for manufacturing oxidized cellulose>

[0067] The manufacturing method of the present invention is a method for manufacturing oxidized cellulose, wherein the oxidized cellulose comprises an oxide of a cellulose-based raw material based on hypochlorous acid or a salt thereof, substantially free of N-oxygen free radical compounds, and the degree of polymerization of the oxidized cellulose is 600 or less. The manufacturing method of the present invention includes a step of obtaining oxidized cellulose by oxidizing a cellulose-based raw material using hypochlorous acid or a salt thereof. Furthermore, the viscosity of the slurry of the aforementioned cellulose-based raw material at the same concentration as during the aforementioned oxidation is in the range of 1000 Pa·s or less using a viscometer equipped with an SPP rotor and under measurement conditions (hereinafter also referred to as "Measurement Condition A") at a rotation speed of 100 rpm and a temperature of 30°C or 40°C.

[0068] The manufacturing method of the present invention can also be described in another way as follows.

[0069] A method for manufacturing oxidized cellulose, wherein the oxidized cellulose comprises an oxide of a cellulose-based raw material based on hypochlorous acid or its salt, substantially free of N-oxygen free radical compounds, and the degree of polymerization of the oxidized cellulose is below 600.

[0070] The manufacturing method includes a step of obtaining oxidized cellulose by oxidizing the aforementioned cellulose-based raw material in a reaction system containing hypochlorous acid or its salt and a cellulose-based raw material.

[0071] The aforementioned reaction system contains the aforementioned cellulose raw material at a specified concentration.

[0072] The aforementioned specified concentration refers to a concentration of 1000 Pa·s or less when the viscosity of a slurry composed solely of the aforementioned cellulose-based raw materials and water, and containing the aforementioned cellulose-based raw materials at the aforementioned specified concentration, is measured using measurement conditions A.

[0073] The manufacturing method of the present invention can also be further described as follows. It should be noted that the "initial viscosity of the reaction system" mentioned below refers to the viscosity of the reaction system at the beginning of the reaction.

[0074] A method for manufacturing oxidized cellulose, comprising an oxide of a cellulose-based raw material based on hypochlorous acid or its salt, substantially free of N-oxygen free radical compounds, wherein the degree of polymerization of the oxidized cellulose is below 600.

[0075] The manufacturing method includes a step of obtaining oxidized cellulose by oxidizing the aforementioned cellulose-based raw material in a reaction system containing hypochlorous acid or its salt and a cellulose-based raw material.

[0076] The initial viscosity of the aforementioned reaction system was below 1000 Pa·s under measurement condition A.

[0077] The above-mentioned reaction start time refers to the time from the end of the input of the components constituting the reaction system into the system, preferably within 10 minutes, more preferably within 5 minutes, and even more preferably within 1 minute. As one specific method, the above-mentioned reaction start time refers to the time from the end of the input of the cellulose-based raw material into the system containing hypochlorous acid or its salt, preferably within 10 minutes, more preferably within 5 minutes, and even more preferably within 1 minute.

[0078] In conventional methods for manufacturing oxidized cellulose, the following problem exists: the amount of cellulose supplied for the oxidation reaction is small, resulting in a limited amount of oxidized cellulose and hindering the improvement of the desired oxidized cellulose yield. One method to improve the yield of oxidized cellulose is to increase the reaction scale and the concentration of cellulose-based raw materials in the reaction system. According to the research results of the present inventors, it has been clarified that in order to obtain oxidized cellulose with excellent defibrillation properties, it is desirable to adequately supply hypochlorous acid or its salt to the surface of the cellulose raw material. However, if the amount of cellulose raw material is increased, hypochlorous acid or its salt cannot adequately act on a portion of the cellulose raw material, resulting in unsatisfactory oxidized cellulose yield. The inventors discovered that by controlling the viscosity of the reaction system, specifically by preparing a slurry consisting only of the aforementioned cellulose-based raw material and water with the same concentration as during oxidation (i.e., the concentration of the cellulose-based raw material at the time of feeding during the oxidation reaction), and measuring its viscosity (hereinafter also referred to as slurry viscosity), and by oxidizing at a concentration of cellulose-based raw material that is 1000 Pa·s or less at 30°C or 40°C, hypochlorous acid or its salt becomes sufficiently homogeneous within the reaction system, thereby stably and effectively producing oxidized cellulose with excellent defibrillation properties, thus completing the present invention. Furthermore, by setting the reaction system to a concentration of cellulose-based raw material with a viscosity of 1000 Pa·s or less, the reaction system can be homogenized using a mixer or kneader described later.

[0079] The reaction system in this invention refers to a mixture of the components (including the dispersion medium) that make up the oxidation reaction (hereinafter also referred to as the reaction mixture).

[0080] From the viewpoint of facilitating stirring and mixing operations, the viscosity of the slurry or the initial viscosity of the reaction system in this invention is preferably 30 Pa·s or less, more preferably 20 Pa·s or less, further preferably 10 Pa·s or less, and even more preferably 5 Pa·s or less.

[0081] From the viewpoint of making the reaction system uniform, the lower the lower limit of the viscosity of the slurry or the initial viscosity of the reaction system, the better. There is no particular limitation on the lower limit value. It can be greater than 0 Pa·s, greater than 0.01 Pa·s, greater than 0.1 Pa·s, or greater than 0.3 Pa·s.

[0082] The range of slurry viscosity or initial viscosity of the reaction system can be set, for example, to be greater than 0 Pa·s and less than 30 Pa·s, greater than 0.01 Pa·s and less than 20 Pa·s, greater than 0.1 Pa·s and less than 10 Pa·s, or greater than 0.3 Pa·s and less than 5 Pa·s.

[0083] Methods for controlling the viscosity of the slurry or the initial viscosity of the reaction system include, for example, adjusting the concentration of the cellulose-based raw material and the temperature. Specifically, control is achieved in a way that increasing the concentration of the cellulose-based raw material increases the viscosity of the slurry or the initial viscosity of the reaction system. Alternatively, control is achieved in a way that increasing the oxidation temperature increases the viscosity of the slurry or the initial viscosity of the reaction system.

[0084] The viscosity of the slurry was measured using a slurry made from cellulose-based raw materials. The viscosity measured from the slurry reproduces the initial viscosity of the reaction system (the mixture of components during the oxidation reaction). The viscosity of the slurry was measured as follows: a slurry of cellulose-based raw materials was prepared at the same concentration as during oxidation, at 30°C or 40°C, and the mixture was stirred at 100 rpm using a viscometer equipped with an SPP rotor. Specifically, the initial viscosity of the reaction system can be measured using the method described in the examples.

[0085] As cellulose-based raw materials oxidize to form cellulose oxide, there is a tendency for the viscosity of the reaction system to decrease. There is also a tendency for the viscosity of the reaction system to be highest at the beginning of the reaction. It can be said that the viscosity of the slurry mentioned above is equal to the viscosity of the reaction system at the beginning of the reaction (i.e., the initial viscosity of the reaction system).

[0086] The cellulose-based raw materials used in this invention are not particularly limited to materials with cellulose as the main component, and examples include pulp, natural cellulose, regenerated cellulose, and fine cellulose obtained by mechanically depolymerizing cellulose. Commercially available products such as crystalline cellulose derived from pulp can be used directly as cellulose-based raw materials. Alternatively, unused biomass containing large amounts of cellulose, such as tofu residue and soybean hulls, can also be used as raw materials. Cotton and sea squirts can also be used as raw materials.

[0087] There are no particular limitations on the types of pulp. Examples include coniferous wood, as well as broadleaf wood, bamboo, rice straw, bagasse, hemp, and hibiscus. One type of pulp can be used alone, or two or more can be used in combination. To facilitate the impregnation of the oxidizing agent into the raw pulp, the cellulose-based raw materials can be pretreated with an appropriate concentration of alkali.

[0088] In addition, as pulp, mechanical pulp, chemimechanical pulp, semi-chemical pulp, and chemical pulp (kraft pulp, sulfite pulp, alkali pulp) can be used.

[0089] In the manufacturing method of the present invention, fine cellulose obtained by mechanical or chemical treatment of cellulose can be used as the cellulose-based raw material. Powdered pulp is a suitable example of fine cellulose. By using powdered pulp, further micronization is achieved, and nanocellulose can be effectively obtained. Furthermore, the particle size of the powdered pulp is typically in the range of 1 to 1000 μm, preferably in the range of 1 to 500 μm, and more preferably in the range of 1 to 100 μm. The particle size mentioned here refers to the average particle size, meaning the value when the volumetric distribution is 50% when the particle size distribution is expressed as a volumetric distribution using laser scattering as the measurement principle.

[0090] The crystallinity of cellulose-based raw materials is not limited as long as it allows for the production of nanocellulose, and is typically in the range of 10% to 90%. Preferably, the crystallinity is in the range of 20% to 80%, and more preferably in the range of 30% to 70%.

[0091] Regarding the crystallinity mentioned above, solid crystallinity testing can be performed on cellulose-based raw materials. 13 The crystallinity is determined by C-NMR and calculated based on the ratio of crystalline to amorphous regions. Specifically, the crystallinity can be calculated using the method described in the examples.

[0092] Examples of hypochlorous acid or its salts used in the oxidation of cellulose-based raw materials include hypochlorous acid solution, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and ammonium hypochlorite. Among these, sodium hypochlorite is preferred from the viewpoint of ease of processing.

[0093] One method for producing oxidized cellulose by oxidizing cellulose-based raw materials is to mix the cellulose-based raw materials with a reaction solution containing hypochlorous acid or a salt thereof. From the viewpoint of ease of handling and minimizing side reactions, water is preferably the solvent contained in the reaction solution.

[0094] In the oxidation process, the amount of hypochlorous acid or its salt is not particularly limited, but it is preferable to use hypochlorous acid or its salt with an effective chlorine concentration of 6% by mass or more and 43% by mass or less. By using hypochlorous acid or its salt with an effective chlorine concentration of 6% by mass or more and 43% by mass or less, the amount of carboxyl groups in the oxidized cellulose can be sufficiently increased, and the cellulose can be sufficiently micronized, thus eliminating the need for mechanical defiberization after the oxidation reaction.

[0095] In addition, the effective chlorine concentration of hypochlorous acid or its salt in the reaction solution (reaction system) is preferably in the range of 6 to 43% by mass.

[0096] From the viewpoint of facilitating the micronization of oxidized cellulose, the lower limit of the effective chlorine concentration is more preferably 7% by mass or more, further preferably 8% by mass or more, even more preferably 8.5% by mass or more, and even more preferably 9% by mass or more. Furthermore, from the viewpoint of suppressing excessive cellulose decomposition, 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 with the above-mentioned lower and upper limits. The range of the effective chlorine concentration is more preferably 7 to 43% by mass, and even more preferably 8 to 43% by mass.

[0097] From the viewpoint of reducing the manufacturing cost of oxidized cellulose and improving the ease of obtaining or processing hypochlorous acid or its salts, it is preferable to keep the effective chlorine concentration low. From this viewpoint, the upper limit of the effective chlorine concentration is preferably less than 14% by mass, more preferably less than 13% by mass, further preferably less than 12% by mass, and even more preferably less than 11% by mass. From the viewpoint of facilitating the micronization of oxidized cellulose and improving productivity, the range of the effective chlorine concentration is preferably 6% by mass or more and less than 14% by mass, more preferably 7% by mass or more and less than 14% by mass, further preferably 7% by mass or more and less than 13% by mass, and even more preferably 8% by mass or more and less than 13% by mass.

[0098] It should be noted that the effective chlorine concentration of hypochlorous acid or its salts is defined as follows. Hypochlorous acid is a weak acid existing in aqueous solution, and hypochlorite is a compound in which the hydrogen atoms of hypochlorous acid are replaced by other cations. For example, since sodium hypochlorite exists as a hypochlorite in the solvent (preferably in aqueous solution), the concentration is determined not by measuring the concentration of sodium hypochlorite, but by measuring the amount of effective chlorine in the solution. Here, for the effective chlorine of sodium hypochlorite, the oxidizing power of the divalent oxygen atom generated by the decomposition of sodium hypochlorite is equivalent to two atomic equivalents of monovalent chlorine. Therefore, the bonded chlorine atom of sodium hypochlorite (NaClO) has the same oxidizing power as the two-atom unbonded chlorine (Cl2), resulting in effective chlorine = 2 × (chlorine in NaClO). As a specific procedure for determination, the sample is first accurately weighed, water, potassium iodide, and acetic acid are added and allowed to stand. For free iodine, an aqueous starch solution is used as an indicator, and the effective chlorine concentration is determined by titration with sodium thiosulfate solution.

[0099] The presence or absence of pH adjustment and the pH range in the manufacturing method of the present invention are arbitrary, and the process can be carried out while adjusting the pH to a range of 5.0 or higher. Within this range, the oxidation reaction of the cellulose-based raw materials can be sufficiently carried out, resulting in a significant increase in the amount of carboxyl groups in the oxidized cellulose and a tendency to be easily micronized by stirring. The pH of the reaction system is more preferably 7.0 or higher, further preferably 8.0 or higher, even more preferably 8.5 or higher, even more preferably 9.0 or higher, and still more preferably 9.5 or higher. There is no particular limitation on the upper limit of the pH of the reaction system, but it is preferably 14.5 or lower, more preferably 14.0 or lower, further preferably 13.0 or lower, even more preferably 12.5 or lower, even more preferably 12.0 or lower, and still more preferably 11.5 or lower. Furthermore, the pH range of the reaction system is more preferably 7.0 to 14.0, more preferably 8.0 to 13.5, and even more preferably 8.5 to 13.0.

[0100] Increasing the reaction scale and the concentration of cellulose-based raw materials can lead to an increase in the viscosity of the reaction system and make it difficult to adequately supply hypochlorous acid or its salts to the surface of the cellulose raw materials. Furthermore, as mentioned above, from the viewpoint of reducing the manufacturing cost of oxidized cellulose and improving the ease of obtaining or processing hypochlorous acid or its salts, it is preferable to keep the effective chlorine concentration low. On the other hand, by keeping the effective chlorine concentration low, for example, setting it to less than 14% by mass, the oxidation reaction may sometimes become insufficient, resulting in a decrease in the defibrillability of the oxidized cellulose. From the viewpoint of both suppressing the effective chlorine concentration and increasing the oxidation effect of hypochlorous acid or its salts at the surface of the cellulose raw materials, the pH of the reaction system is preferably less than 11, more preferably less than 10.7, and even more preferably less than 10.5. In this case, the lower limit of the pH of the reaction system is not particularly limited, but is generally 5.0 or higher, preferably 6.0 or higher, more preferably 7.0 or higher, even more preferably 8.0 or higher, even more preferably 9.0 or higher, and even more preferably greater than 9.0. The pH range of the reaction system can be any combination of the above-mentioned upper and lower limits. The pH of the reaction system is preferably 5.0 or higher and less than 11, more preferably 6.0 or higher and less than 11, even more preferably 7.0 or higher and less than 11, even more preferably 8.0 or higher and less than 11, even more preferably 8.0 or higher and less than 10.7, even more preferably 9.0 or higher and less than 10.7, even more preferably 9.0 or higher and less than 10.5, and even more preferably greater than 9.0 and less than 10.5.

[0101] In the reaction, as carboxyl groups are generated from the cellulose-based raw material through oxidation, the pH of the reaction system decreases. Therefore, from the viewpoint of efficiently carrying out the oxidation reaction, it is preferable to add an alkaline agent (e.g., sodium hydroxide) or an acid (e.g., hydrochloric acid) to the reaction system to adjust the pH of the reaction system while carrying out the oxidation reaction.

[0102] The following example, using sodium hypochlorite as hypochlorous acid or its salt, will be used to further explain the method for manufacturing oxidized cellulose.

[0103] When using sodium hypochlorite to oxidize cellulose-based raw materials, the reaction solution is preferably an aqueous sodium hypochlorite solution. Methods for adjusting the effective chlorine concentration of the aqueous sodium hypochlorite solution to a target concentration (e.g., a target concentration in the range of 6% to 43% by mass) include: concentrating the aqueous sodium hypochlorite solution with an effective chlorine concentration lower than the target concentration; diluting the aqueous sodium hypochlorite solution with an effective chlorine concentration higher than the target concentration; and dissolving sodium hypochlorite crystals (e.g., sodium hypochlorite pentahydrate) in a solvent. Among these, adjusting the effective chlorine concentration as an oxidant by diluting the aqueous sodium hypochlorite solution or dissolving sodium hypochlorite crystals in a solvent results in less self-decomposition (i.e., less decrease in effective chlorine concentration) and facilitates adjustment of the effective chlorine concentration, and is therefore preferred.

[0104] There are no particular limitations on the method of mixing cellulose-based raw materials with sodium hypochlorite aqueous solution. From the viewpoint of ease of operation, it is preferable to add cellulose-based raw materials to sodium hypochlorite aqueous solution and mix them.

[0105] To efficiently carry out the oxidation reaction of cellulose-based raw materials, it is preferable to conduct the oxidation reaction while stirring the mixture of cellulose-based raw materials and sodium hypochlorite aqueous solution. Examples of stirring methods include, for instance, a mixer with stirring blades, a homogenizing mixer, a distribution mixer, a homogenizer, and an external circulation mixer. Among these, from the viewpoint of smoothly carrying out the oxidation reaction of cellulose-based raw materials and easily adjusting the degree of polymerization of oxidized cellulose to below a specified value, it is preferable to use one or more of the following methods: a shear mixer such as a homogenizing mixer or homogenizer, a mixer with stirring blades, and a distribution mixer; the method of using a mixer with stirring blades is particularly preferred. When using a mixer with stirring blades, a device equipped with known stirring blades such as helical blades, paddle blades, turbine blades, swept blades, anchor blades, rectifying blades, MAXBLEND blades, FULLZONE blades, ribbon blades, and screw blades (with guide tubes, etc.) can be used. Furthermore, when using a mixer with stirring blades, it is preferable to stir at a rotational speed of 50 to 1000 rpm. Alternatively, multi-screw mixers such as single-screw mixers and twin-screw mixers can also be used.

[0106] The reaction temperature in oxidation reactions is generally sufficient to be in the range of 15°C to 100°C. From the viewpoint of further improving the oxidation reaction, the reaction temperature is preferably 30°C or higher, more preferably above 30°C, further preferably 31°C or higher, and even more preferably 35°C or higher. There is a tendency that as the reaction temperature increases, the viscosity becomes higher and the homogeneity of the reaction system decreases. From the viewpoint of improving the homogeneity of the reaction system and increasing productivity, the reaction temperature is preferably 60°C or lower, more preferably 55°C or lower, and even more preferably 40°C or lower. The reaction temperature mentioned here refers to the temperature measured by temperature measurement of the reaction mixture.

[0107] The reaction time of the oxidation reaction can be set according to the degree of oxidation, and is usually from 15 minutes to about 50 hours. From the viewpoint of further improving the oxidation reaction, the reaction time is preferably 2 hours or more, more preferably more than 2 hours, and even more preferably 3 hours or more. There is no particular upper limit to the reaction time, but it is preferably 20 hours or less, more preferably 15 hours or less, and even more preferably 12 hours or less.

[0108] From the viewpoint of improving workability by setting the viscosity of the slurry or the initial viscosity of the reaction system to a range of 1000 Pa·s or less, and facilitating stirring during the oxidation reaction, the concentration of the cellulose-based raw material relative to the total amount of the reaction mixture (i.e., the total amount of the reaction system) at the start of the oxidation reaction is preferably 35% by mass or less, more preferably 20% by mass or less, further preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0109] The lower limit of the concentration of cellulose-based raw materials is generally only 0.1% by mass or more. From the point of view of improving productivity, it is preferred to be more than 6.5% by mass, more preferably more than 6.6% by mass, further preferably more than 6.8% by mass, and even more preferably more than 7% by mass.

[0110] The concentration of the cellulose-based raw material is preferably in the range of more than 6.5% by mass and less than 35% by mass, more preferably in the range of more than 6.5% by mass and less than 20% by mass, even more preferably in the range of more than 6.5% by mass and less than 15% by mass, and even more preferably in the range of more than 6.5% by mass and less than 10% by mass.

[0111] The concentration of the cellulose-based raw material mentioned here during the oxidation reaction is the concentration of the cellulose-based raw material at the time of feeding.

[0112] There is no particular limitation on the pressure during the reaction, but it is usually in the range of above atmospheric pressure and below 1.0 MPaG (gauge pressure, the same below). Here, atmospheric pressure refers to the pressure equal to atmospheric pressure.

[0113] Oxidation under pressure tends to suppress the amount of hypochlorous acid or its salts used and to produce oxidized cellulose more efficiently. From an efficiency point of view, the pressure is preferably 0.1 MPaG or more and 1.0 MPaG or less. At this pressure, the effective chlorine concentration of hypochlorous acid or its salts only needs to be more than 0% by mass and less than 43% by mass. From the point of view of improving efficiency, it is preferably 0.1% by mass or more and 20% by mass or less, more preferably 1.0% by mass or more and 15% by mass or less, and even more preferably 1.0% by mass or more and 10% by mass or less.

[0114] In the manufacture of oxidized cellulose, after the cellulose-based raw material is oxidized, a treatment to terminate the oxidation reaction can be performed. That is, it may also include a step of treating hypochlorous acid or its salts used in the oxidation process (hereinafter also referred to as the "treatment step"). The method of treating hypochlorous acid or its salts is not particularly limited; treatment can be carried out by ultraviolet irradiation, self-decomposition under high temperature conditions, etc. Suitable methods for reducing hypochlorous acid or its salts can be listed. Specifically, methods such as adding reducing agents such as sulfites, aminosulfonic acids or their salts, thiosulfates, hydrogen peroxide, oxalic acid or its salts, formic acid or its salts, hypophosphite, etc., and adding decomposition catalysts such as nickel oxide can be listed.

[0115] Examples of the aforementioned sulfites include sulfites, bisulfites, metabisulfites, and dithionites, which can be hydrates. Specifically, examples of the aforementioned sulfites include sodium bisulfite, potassium bisulfite, ammonium bisulfite, calcium bisulfite, sodium sulfite, potassium sulfite, ammonium sulfite, zinc sulfite, ammonium sulfite, sodium dithionite, potassium dithionite, calcium dithionite, sodium metabisulfite, potassium metabisulfite, magnesium metabisulfite, calcium metabisulfite, and ammonium metabisulfite, among which sodium sulfite is preferred.

[0116] Among the above-mentioned aminosulfonic acids or their salts, aminosulfonates are preferred. Specifically, examples of aminosulfonates include sodium aminosulfonate, potassium aminosulfonate, calcium aminosulfonate, and nickel aminosulfonate.

[0117] Specifically, examples of the aforementioned thiosulfates include sodium thiosulfate, potassium thiosulfate, and ammonium thiosulfate.

[0118] Specifically, examples of the aforementioned oxalates include sodium oxalate and potassium oxalate.

[0119] Specifically, examples of formates mentioned above include sodium formate and potassium formate.

[0120] As hypophosphites, examples include sodium hypophosphite.

[0121] These reducing agents can be used alone or in combination of two or more.

[0122] The amount of reducing agent added can be adjusted appropriately based on the amount of hypochlorous acid or its salt (effective chlorine concentration). In addition to treating hypochlorous acid or its salt, methods can also be used in combination with adding acids and metal catalysts to stop the oxidation reaction of cellulosic raw materials.

[0123] Using the cellulose oxide-containing solution obtained through the above reaction, known separation processes such as centrifugation and filtration are performed, followed by further purification as needed. This allows cellulose oxide to be obtained as an oxide of a cellulose-based raw material based on hypochlorous acid or its salt. Alternatively, the cellulose oxide-containing solution obtained through the above reaction can be directly supplied to subsequent processes.

[0124] [Oxidized cellulose]

[0125] In the manufacturing method of the present invention, cellulose-based raw materials are oxidized using hypochlorous acid or its salts to obtain oxidized cellulose. The oxidized cellulose is preferably in slurry form. The slurry referred to herein is a suspension containing oxidized cellulose. The slurry may contain a solvent used during oxidation. Alternatively, a dispersion medium may be appropriately added to prepare a slurry form. By making the oxidized cellulose a slurry, it tends to be easy to process and easy to micronize.

[0126] When the oxidized cellulose in this invention is a slurry, and the total amount of the slurry is set to 100% by mass, the amount of oxidized cellulose is usually in the range of 0.1% by mass or more and 95% by mass or less, preferably 1% by mass or more and 50% by mass or less, and more preferably 1% by mass or more and 30% by mass or less.

[0127] The oxidized cellulose of this invention comprises fibrous cellulose obtained by oxidizing cellulose-based raw materials using hypochlorous acid or its salts. The oxidized cellulose of this invention is also referred to as oxidized cellulose fiber. That is, the oxidized cellulose of this invention comprises oxides of cellulose-based raw materials based on hypochlorous acid or its salts. It should be noted that the main component of plants is cellulose, and the substance obtained by bundling cellulose molecules is called cellulose microfibrils. Cellulose in cellulose-based raw materials is also contained in the form of cellulose microfibrils.

[0128] (Degree of Aggregation)

[0129] The degree of polymerization of the oxidized cellulose in this invention is 600 or less. If the degree of polymerization of the oxidized cellulose exceeds 600, there is a tendency for defibrillation to require a large amount of energy, and there is a tendency for it to not exhibit sufficient defibrillability. By keeping the degree of polymerization of the oxidized cellulose to 600 or less, it can be micronized under mild conditions, and micronization can be achieved through ordinary stirring and mixing, with a tendency to effectively obtain nanocellulose. From the viewpoint of defibrillability, the lower limit of the degree of polymerization of the oxidized cellulose is not particularly limited. However, if the degree of polymerization of the oxidized cellulose is less than 30, the proportion of particulate cellulose increases compared to fibrous cellulose, the quality of the slurry containing the oxidized cellulose becomes uneven, and the viscosity becomes unstable. From the above viewpoint, the degree of polymerization of the oxidized cellulose is preferably 30 to 600.

[0130] The degree of polymerization is more preferably 580 or less, further preferably 560 or less, even more preferably 550 or less, even more preferably 500 or less, even more preferably 450 or less, and still more preferably 400 or less. Regarding the lower limit of the degree of polymerization, from the viewpoint of improving the viscosity stability of the slurry, it is more preferably 50 or more, further preferably 60 or more, even more preferably 80 or more, even more preferably 90 or more, even more preferably 100 or more, and particularly preferably 110 or more. The preferred range of the degree of polymerization can be defined by appropriately combining the above-mentioned upper and lower limits. The degree of polymerization of oxidized cellulose is more preferably 50 to 600, more preferably 60 to 600, even more preferably 80 to 600, even more preferably 80 to 550, even more preferably 80 to 500, still more preferably 80 to 450, and particularly preferably 80 to 400.

[0131] By setting the slurry viscosity or the initial viscosity of the reaction system to below 1000 Pa·s, the hypochlorous acid or its salt can be made sufficiently homogeneous within the reaction system, thereby enabling the degree of polymerization of oxidized cellulose to be set to below 600.

[0132] Furthermore, the degree of polymerization of oxidized cellulose can be adjusted, for example, by changing the reaction time, reaction temperature, pH, and the effective chlorine concentration of hypochlorous acid or its salts during the oxidation reaction. Specifically, increasing the degree of oxidation tends to decrease the degree of polymerization; therefore, methods such as increasing the oxidation reaction time and / or reaction temperature can be used to reduce the degree of polymerization.

[0133] Furthermore, the degree of polymerization of oxidized cellulose can be adjusted by the stirring conditions of the reaction system during the oxidation reaction. For example, if the reaction system is sufficiently homogenized using stirring blades or similar methods, the oxidation reaction tends to proceed smoothly and the degree of polymerization decreases. On the other hand, under conditions where the stirring of the reaction system, such as stirring with a stirrer, is insufficient, the reaction tends to become uneven, making it difficult to sufficiently reduce the degree of polymerization of oxidized cellulose. In addition, the degree of polymerization of oxidized cellulose tends to vary depending on the choice of cellulose as the raw material. Therefore, the degree of polymerization of oxidized cellulose can also be adjusted by selecting the cellulose-based raw material. It should be noted that 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. Specifically, the degree of polymerization of oxidized cellulose can be determined by the method described in the examples.

[0134] (Carboxyl group content)

[0135] The carboxyl content of oxidized cellulose is preferably 0.30 to 2.0 mmol / g. If the carboxyl content is 0.30 mmol / g or more, the oxidized cellulose can be endowed with sufficient decellulose-degradability. Therefore, it tends to be micronized under mild conditions and through normal stirring or mixing. On the other hand, if the carboxyl content is 2.0 mmol / g or less, excessive decomposition can be suppressed when oxidized cellulose is blended with other components, resulting in nanocellulose with a low proportion of particulate cellulose and uniform quality. From this viewpoint, the carboxyl content of oxidized cellulose is more preferably 0.35 mmol / g or more, further 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. Regarding the upper limit of the carboxyl content, it is more preferably below 1.5 mmol / g, further preferably below 1.2 mmol / g, even more preferably below 1.0 mmol / g, and even more preferably 0.9 mmol / g. The preferred range of carboxyl content can be determined by appropriately combining the above-mentioned upper and lower limits. The carboxyl content of oxidized cellulose is more preferably 0.35 to 2.0 mmol / g, further 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 above 0.50 and below 1.2 mmol / g, and even more preferably 0.55 to 1.0 mmol / g.

[0136] It should be noted that the carboxyl content (mmol / g) in oxidized cellulose refers to the following value: 0.1 mol / L hydrochloric acid was added to an aqueous solution containing oxidized cellulose and water to adjust the pH to 2.5, followed by the dropwise addition of 0.05 N sodium hydroxide solution. The conductivity was measured until the pH reached 11.0. The value was calculated using the following formula based on the amount of sodium hydroxide (a) consumed during the neutralization phase of the weak acid with a moderate change in conductivity. The carboxyl content of oxidized cellulose can be adjusted by changing the reaction time, reaction temperature, and pH of the reaction solution.

[0137] Carboxyl group content = a (ml) × 0.05 / mass of oxidized cellulose (g)

[0138] Specifically, the amount of carboxyl groups can be determined by following these steps.

[0139] Add 0.1M hydrochloric acid aqueous solution to 60 ml of an oxidized cellulose aqueous dispersion with the concentration adjusted to 0.5% by mass. After adjusting the pH to 2.5, add 0.05N sodium hydroxide aqueous solution dropwise. Measure the conductivity until the pH reaches 11.0. Calculate the amount of carboxyl group (mmol / g) based on the amount of sodium hydroxide consumed (a) during the mildly varying conductivity neutralization phase of the weak acid and using the above formula.

[0140] (Light transmittance)

[0141] Regarding the oxidized cellulose in this invention, the transmittance of the nanocellulose aqueous dispersion obtained by defibraging a 0.1% by mass aqueous dispersion of the oxidized cellulose using a rotary mixer at a rotational speed of 2000 rpm and a rotational speed of 800 rpm for 10 minutes preferably exhibits a value of 60% or more. More preferably, the transmittance of this nanocellulose aqueous dispersion is 70% or more, further preferably 75% or more, and even more preferably 80% or more. It should be noted that the transmittance is a value measured at a wavelength of 660 nm using a spectrophotometer.

[0142] It should be noted that the reasons for the excellent defibrillation properties (especially ease of defibrillation) of the oxidized cellulose in this invention and the provision of high-quality pulp are not yet certain, but can be considered to be roughly as follows: Defibrillation occurs through the breaking of hydrogen bonds between cellulose microfibrils. In oxidation treatment using hypochlorous acid or its salts, the degree of polymerization of microfibrils decreases as oxidation proceeds (i.e., the cellulose molecular chains are shortened). It can be considered that, in this embodiment, through oxidation treatment, the number of hydrogen bonds that should be broken by defibrillation in each microfibril is small, and therefore, as oxidation proceeds, the amount of carboxyl groups increases, thereby increasing the repulsive force between microfibrils and improving the defibrillation properties of oxidized cellulose.

[0143] The oxidized cellulose of this invention is obtained by oxidation using hypochlorous acid or its salt. The resulting oxidized cellulose preferably has at least two oxidized hydroxyl groups in the pyranose ring constituting cellulose. More specifically, the hydroxyl groups at the second and third positions of the pyranose ring are oxidized to introduce a carboxyl group. Furthermore, it is preferable that the hydroxyl group at the sixth position of the pyranose ring in the aforementioned nanocellulose or oxidized cellulose remains unoxidized and is still a hydroxyl group. It should be noted that the position of the carboxyl group in the pyranose ring can be determined by comparing the solution NMR spectrum using oxidized rayon as a model molecule with the solid NMR spectrum of oxidized cellulose. 13 The analysis was performed by comparing C-NMR spectra.

[0144] Rayon has the same chemical structure as cellulose, and its oxide (oxidized rayon) is water-soluble. This is achieved by dissolving oxidized rayon in heavy water and performing a one-dimensional solution treatment. 13 C-NMR measurements revealed a peak at 165–185 ppm at which the carbon atom attributed to the carboxyl group was observed. In one method used in this invention, oxidized cellulose or nanocellulose obtained by oxidizing raw cellulose with hypochlorous acid or its salt, two signals appeared within this chemical shift range. Furthermore, solution-based two-dimensional NMR measurements confirmed that the carboxyl group was introduced at both the 2- and 3-positions.

[0145] Solid cellulose oxide or nanocellulose is obtained by oxidizing raw cellulose with hypochlorous acid or its salt. 13 In C-NMR, with a high amount of carboxyl group introduction, two signals appear at 165–185 ppm; with a low amount of carboxyl group introduction, a very broad signal may appear. Based on the results of oxidized rayon, the signals of carboxyl carbons introduced at the 2 and 3 positions are adjacent, which appears in low-resolution solid-state NMR. 13 In C-NMR, the two signals were not sufficiently separated. Therefore, even with low carboxyl group introduction, a broad signal was observed. In other words, in solid-state... 13 In the C-NMR spectrum, the broadening of the peaks appearing at 165–185 ppm confirmed the introduction of carboxyl groups at the 2 and 3 positions.

[0146] That is, for solids 13 By drawing a baseline from the peaks in the 165ppm to 185ppm range in the C-NMR spectrum and calculating the overall area value, the area value is vertically divided at the peak apex. The ratio of the area values ​​of the two peaks obtained is calculated (large area value / small area value). If the ratio of the peak area value is greater than 1.2, it can be said to be a broad peak.

[0147] Furthermore, the presence or absence of the aforementioned broad peak can be determined by the ratio of the length L of the baseline in the range of 165ppm to 185ppm to the length L' of the vertical line from the peak to the baseline. That is, if the ratio L' / L is 0.1 or higher, a broad peak can be identified. The aforementioned ratio L' / L can be 0.2 or higher, 0.3 or higher, 0.4 or higher, or 0.5 or higher. There is no particular upper limit to the ratio L' / L; generally, it is acceptable as long as it is below 3.0, below 2.0, or below 1.0.

[0148] In addition, the structure of the above-mentioned pyranose ring can also be determined by analysis according to the method described in Sustainable Chem. Eng. 2020, 8, 48, 17800-17806.

[0149] The oxidized cellulose of this invention does not require the use of N-oxygen free radical compounds such as TEMPO for preparation. Therefore, the oxidized cellulose and nanocellulose of this invention are substantially free of N-oxygen free radical compounds. Here, in the first invention, "substantially free of N-oxygen free radical compounds" means that the oxidized cellulose or nanocellulose is completely free of N-oxygen free radical compounds, or that the content of N-oxygen free radical compounds relative to the total amount of oxidized cellulose or nanocellulose is 2.0 ppm by mass or less, preferably 1.0 ppm by mass or less. Furthermore, when the content of N-oxygen free radical compounds is preferably 2.0 ppm by mass or less, more preferably 1.0 ppm by mass or less, as an increase compared to the cellulose-based raw material, it also means "substantially free of N-oxygen free radical compounds".

[0150] By essentially eliminating N-oxygen free radical compounds, it is possible to suppress the presence of N-oxygen free radical compounds, which may have concerns about their environmental and human health impacts, within oxidized cellulose or nanocellulose. The content of N-oxygen free radical compounds can be determined using known methods. One known method is the use of a trace total nitrogen analyzer. Specifically, the nitrogen content derived from N-oxygen free radical compounds in oxidized cellulose or nanocellulose can be determined as a nitrogen content using a trace total nitrogen analyzer (e.g., Mitsubishi Chemical Analytech, device name: TN-2100H, etc.).

[0151] [Nanocellulose]

[0152] The oxidized cellulose of this invention can be micronized to produce nanocellulose. One aspect of this invention is a method for manufacturing nanocellulose, comprising: a step of defibrating the oxidized cellulose obtained using the manufacturing method of this invention to obtain nanocellulose. Specifically, the method for manufacturing nanocellulose of this invention includes: a step of oxidizing a cellulose-based raw material using hypochlorous acid or a salt thereof to obtain oxidized cellulose; and a step of defibrating the aforementioned oxidized cellulose to obtain nanocellulose, wherein the oxidized cellulose comprises an oxide of a cellulose-based raw material based on hypochlorous acid or a salt thereof, substantially does not contain N-oxygen free radical compounds, the degree of polymerization of the oxidized cellulose is 600 or less, and the slurry viscosity or the initial viscosity of the reaction system is in the range of 1000 Pa·s or less.

[0153] Furthermore, the oxidized cellulose of this invention can be used by blending with other components. That is, even without micronization, by blending with other components and stirring the oxidized cellulose appropriately, a composition containing nanocellulose and at least one other component can be obtained. Moreover, the user of the oxidized cellulose of this invention can also micronize it themselves to produce nanocellulose during use.

[0154] In this invention, nanocellulose refers to a substance derived from oxidized cellulose obtained using the manufacturing method of this invention, which is then decellulosed and micronized. Nanocellulose comprises fine cellulose fibers.

[0155] The average fiber length of the nanocellulose in this invention is preferably 50 nm or more and 800 nm or less. By making the average fiber length 50 nm or more, there is a tendency for the quality of the nanocellulose to become more uniform. From the viewpoint of achieving more uniform quality, the lower limit of the average fiber length is more preferably 100 nm or more, and even more preferably 150 nm or more. By making the average fiber length 800 nm or less, there is a tendency to suppress the proportion of coarse cellulose fibers and suppress the precipitation of nanocellulose. From the viewpoint of further suppressing precipitation, the upper limit of the average fiber length is more preferably 700 nm or less, and even more preferably 600 nm or less.

[0156] From the viewpoint of further improving the quality of nanocellulose, the average fiber length is more preferably 50 nm or more and 700 nm or less, more preferably 100 nm or more and 700 nm or less, and even more preferably 100 nm or more and 600 nm or less.

[0157] The average fiber width of the nanocellulose in this invention is preferably 1 nm or more and 100 nm or less. By making the average fiber width 1 nm or more, there is a tendency for the quality of the nanocellulose to become more uniform. From the viewpoint of achieving more uniform quality, the lower limit of the average fiber width is more preferably 2 nm or more, and even more preferably 3 nm or more. By making the average fiber width 100 nm or less, there is a tendency to suppress the proportion of coarse nanocellulose and suppress the precipitation of nanocellulose. From the viewpoint of further suppressing precipitation, the average fiber width is more preferably 50 nm or less, and even more preferably 30 nm or less.

[0158] From the viewpoint of further improving the quality of nanocellulose, the average fiber width is more preferably 2nm or more and 50nm or less, and even more preferably 3nm or more and 30nm or less.

[0159] In the nanocellulose of the present invention, the aspect ratio (average fiber length / average fiber width), expressed as the ratio of average fiber width to average fiber length, is preferably 20 or more and 200 or less.

[0160] By setting the aspect ratio to 200 or less, there is a tendency for the nanocellulose to be uniformly dispersed, thereby improving its quality. From this perspective, an aspect ratio of 190 or less is more preferred, and 180 or less is even more preferred.

[0161] On the other hand, when the aspect ratio is too low, i.e., when the shape of the nanocellulose is coarse rod-like compared to its slender fibrous form, there is a tendency for aggregation due to uneven distribution, leading to a decrease in the quality of the nanocellulose. Therefore, an aspect ratio of 20 or more is preferred, more preferably 30 or more, and even more preferably 40 or more.

[0162] It should be noted that the average fiber width and average fiber length are as follows: With a nanocellulose concentration of approximately 1–10 ppm, nanocellulose is mixed with water and thoroughly diluted. The resulting cellulose aqueous dispersion is then allowed to air dry on a mica substrate. The shape of the nanocellulose is observed using a scanning probe microscope. An arbitrary number of fibers are randomly selected from the obtained image. The cross-sectional height of the shape image is set to the fiber width, and the perimeter ÷ 2 is set to the fiber length. The values ​​are calculated accordingly. Image processing software can be used in this calculation of average fiber width and average fiber length. The image processing conditions are arbitrary, and even for the same image, the calculated values ​​may differ depending on the conditions. For the average fiber length, the range of differences caused by conditions is preferably within ±100 nm. For the average fiber width, the range of differences caused by conditions is preferably within ±10 nm. More detailed measurement methods are based on the methods described in the examples below.

[0163] When determining the various physical properties of nanocellulose in this invention, nanocellulose can be used as the test sample, or a composition containing nanocellulose can be used as the test sample, or nanocellulose in a composition containing nanocellulose can be separated from other components (mixtures) and used as the test sample.

[0164] Regarding the nanocellulose in this invention, as one approach, it can be characterized by average fiber width, average fiber length, or aspect ratio as described above; as another approach, it can also have a specified ZETA potential and transmittance.

[0165] (ZETA potential)

[0166] In one embodiment of this application, the ZETA potential of the nanocellulose in this invention is preferably -30 mV or lower. If the ZETA potential is -30 mV or lower (i.e., an absolute value of 30 mV or higher), sufficient repulsion between microfibrils is achieved, easily generating nanocellulose with a high surface charge density. This improves the dispersion stability of the nanocellulose, resulting in excellent viscosity stability and workability when preparing a slurry. 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 higher (i.e., an absolute value of 100 mV or lower), there is a tendency for oxidative breakage in the fiber direction associated with oxidation to be suppressed; therefore, there is a tendency to obtain nanocellulose with uniform size.

[0167] The ZETA potential tends to increase by setting one or more of the oxidation reaction time, reaction temperature, and stirring conditions (e.g., extending the reaction time) to a point where oxidation is further advanced (i.e., the degree of oxidation is increased). Additionally, the ZETA potential can be appropriately controlled by using hypochlorous acid or its salts for oxidation.

[0168] Based on the above viewpoints, the ZETA potential of the nanocellulose in this invention is more preferably below -35mV, further preferably below -40mV, and even more preferably below -50mV. Furthermore, regarding the lower limit of the ZETA potential, it is preferably above -90mV, more preferably above -85mV, further preferably above -80mV, and even more preferably above -77mV. The range of the ZETA potential can be appropriately combined with the above-mentioned lower and upper limits.

[0169] The ZETA potential is preferably -90mV or higher and -35mV or lower, more preferably -85mV or higher and -40mV or lower, and even more preferably -80mV or higher and -50mV or lower. It should be noted that, in this specification, the ZETA potential refers to the following value: a cellulose aqueous dispersion prepared by mixing the nanocellulose of the present invention with water to achieve a nanocellulose concentration of 0.1% by mass, measured under conditions of pH 8.0 and 20°C.

[0170] The ZETA potential can be measured using the following method.

[0171] Dilute the nanocellulose with pure water to a concentration of approximately 0.1%. Add a 0.05 mol / L sodium hydroxide aqueous solution to the diluted nanocellulose aqueous dispersion to adjust the pH to approximately 8.0. Measure the Zeta potential at 20°C using, for example, a Zeta potentiometer (ELSZ-1000) manufactured by Otsuka Electronics Co., Ltd.

[0172] (Light transmittance)

[0173] The nanocellulose dispersion obtained by dispersing the nanocellulose of the present invention in a dispersion medium exhibits high light transmittance due to low light scattering from the cellulose fibers. Specifically, in a suitable embodiment, the transmittance of the mixture of the nanocellulose of the present invention and water, with a solid component concentration of 0.1% by mass, is 95% or higher. More preferably, this transmittance is 96% or higher, even more preferably 97% or higher, and still more preferably 99% or higher. It should be noted that the transmittance is a value measured at a wavelength of 660 nm using a spectrophotometer.

[0174] Transmittance can be measured, for example, by adding an aqueous dispersion of nanocellulose into a 10 mm thick quartz dish and using a spectrophotometer (JASCO V-550).

[0175] The nanocellulose in this invention is an aggregate of a single unit fiber. When a carboxyl group is introduced into the nanocellulose of this invention, it is sufficient to include at least one carboxylated nanocellulose fiber (also denoted as carboxylated CNF), and the main component is preferably carboxylated nanocellulose. Here, "main component is carboxylated CNF" means that the proportion of carboxylated CNF in the total amount of microcellulose is more than 50% by mass, preferably more than 70% by mass, and more preferably more than 80% by mass. The upper limit of the above proportion is 100% by mass, but it can be 98% by mass or 95% by mass.

[0176] As a method for defibrillating oxidized cellulose, there are no particular limitations as long as the operation can disperse nanocellulose. Here, nanocellulose refers to the general term for substances obtained by miniaturizing cellulose, including cellulose nanofibers, cellulose nanocrystals, etc.

[0177] Fiber disintegration can be achieved using, for example, velocity fields and velocity variations of arbitrary intensity; impacts on inclusions and obstacles; ultrasonic waves; pressure loads, etc. This dispersion process can be appropriately performed using a liquid disperser.

[0178] There are no particular limitations on the type of liquid disperser, and examples include homogenizing mixers, magnetic stirrers, stirring rods, mixers with stirring blades, distribution mixers, homogenizers, external circulation mixers, rotary mixers, vibratory mixers, and ultrasonic dispersers. In addition to the above-mentioned devices, other liquid dispersers include rotary shear mixers, colloid mills, roller mills, pressure homogenizers, container-driven mills, and media mixing mills. Furthermore, kneaders can also be used as liquid dispersers.

[0179] A rotary shear mixer is a device that disperses materials by allowing them to pass through the gap between the rotating blades and the outer cylinder. Dispersion is achieved through shear flow and velocity variations in intensity within the gap.

[0180] A colloid mill is a device that disperses substances through shear flow in the gap between a rotating and a stationary disc. A roller mill disperses substances by utilizing the shear and compressive forces achieved through the gaps between multiple rotating rollers.

[0181] Pressure homogenizers are used as dispersers that eject slurries from fine orifices under high pressure; they are also called pressure jet dispersers. High-pressure homogenizers are preferred among these pressure homogenizers. A high-pressure homogenizer refers to a homogenizer capable of ejecting slurries at pressures of 10 MPa or higher, preferably 100 MPa or higher. Examples of high-pressure homogenizers include, for instance, microfluidizers and wet jet mills, which are counter-impact type high-pressure homogenizers.

[0182] Container-driven mills are devices that disperse materials through the impact and friction of media such as balls within a container. Specifically, they include rotary mills, vibratory mills, and planetary mills. Media-stirred mills are devices that use media such as balls and beads and utilize the impact and shear forces of these media for dispersion. Specifically, they include grinding mills and bead mills (sand mills).

[0183] A kneader is a device used to perform the operation of wetting powders with liquid (also known as kneading or mixing). Specifically, there are double-wrist kneaders (devices that disperse powders using biaxial mixing blades in two semi-cylindrical containers); Banbury mixers (devices that disperse powders under pressure in a closed system); and extrusion kneaders such as screw extruders, Co-Kneaders, and extruders.

[0184] Methods for defiberization include, for example, those based on screw agitators, paddle agitators, distribution agitators, turbine agitators, high-speed rotating homogenizers, high-pressure homogenizers, ultra-high-pressure homogenizers, double-cylinder homogenizers, ultrasonic homogenizers, water flow impact dispersers, pulpers, disc homogenizers, cone homogenizers, double-disc homogenizers, grinding machines, single-screw or multi-screw mixers, self-rotating and revolution-rotating mixers, vibrating mixers, and other mixing and stirring devices.

[0185] The devices used in fiber unwinding can be used individually or in combination of two or more types.

[0186] From the viewpoint of being able to manufacture nanocellulose that can be further defibriled, the defibrilation of oxidized cellulose can be performed, for example, using a method based on an ultra-high pressure homogenizer. When using an ultra-high pressure homogenizer for defibrilation, the pressure during the defibrilation process is preferably 100 MPa or more, more preferably 120 MPa or more, and even more preferably 150 MPa or more. The number of defibrilation processes is not particularly limited, but from the viewpoint of ensuring sufficient defibrilation, it is preferably two or more times, more preferably three or more times.

[0187] Oxidized cellulose has excellent defibrillation properties. Therefore, as a defibrillation method, it can be fully defibriled even when using gentle stirring, such as a self-rotating mixer or a vibrating mixer, to obtain homogenized nanocellulose.

[0188] A rotary-revolutionary mixer is a device that mixes materials in a container by causing the container to rotate and revolve. According to this mixer, mixing can be performed without the use of mixing blades, thus achieving gentler mixing. The rotational and revolutionary speeds during mixing can be appropriately set; for example, the revolutionary speed can be set to 400–3000 rpm, and the revolutionary speed to 200–1500 rpm. In the case of a rotary-revolutionary mixer, from the viewpoint of achieving gentle mixing and ensuring uniform quality, it is preferable to perform defiberization treatment by mixing at a revolutionary speed of 1200–2500 rpm and a revolutionary speed of 600–1000 rpm for 3–15 minutes. A revolutionary speed of 1500–2300 rpm and a revolutionary speed of 700–950 rpm are more preferred. When defibrillating the oxidized cellulose fibers using a rotary mixer, the concentration of the oxidized cellulose aqueous dispersion as the material is, for example, 0.01 to 1.0% by mass, preferably 0.1 to 0.5% by mass.

[0189] Examples of vibratory mixers include vortex mixers (contact mixers). In a vortex mixer, stirring is achieved by creating a vortex within the liquid material in the container. Vibratory mixers such as vortex mixers allow for stirring without the use of blades, thus enabling gentler stirring. Furthermore, vibratory mixers such as vortex mixers allow for gentle stirring using simple equipment, making them preferable from the viewpoint of production equipment and production costs. The rotational speed of the vortex mixer is, for example, 600 to 3000 rpm, and the defiberization process is preferably performed under conditions of stirring for 3 to 15 minutes. When defiberizing the oxidized cellulose fibers using a vortex mixer, the concentration of the oxidized cellulose aqueous dispersion as the material is, for example, 0.01 to 1.0% by mass, preferably 0.1 to 0.5% by mass.

[0190] The defibrillation process is preferably carried out while the oxidized cellulose is mixed with a dispersion medium. There are no particular limitations 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 solvents can be used alone, or two or more can be used in combination.

[0191] Among the aforementioned dispersion media, examples of alcohols include methanol, ethanol, isopropanol, isobutanol, sec-butanol, tert-butanol, methyl cellosolve, ethylene glycol, and glycerol. Examples of ethers include ethylene glycol dimethyl ether, 1,4-dioxane, and tetrahydrofuran. Examples of ketones include acetone and methyl ethyl ketone.

[0192] During the defibrillation process, oxidized cellulose and the resulting nanocellulose obtained by defibrillation are easily separated by using an organic solvent as a dispersion medium. Furthermore, since nanocellulose can be dispersed in an organic solvent, it is easily mixed with resins, resin raw material monomers, etc., dissolved in the organic solvent. To mix with various components such as resins, rubbers, and solid particles, a nanocellulose dispersion obtained by dispersing the defibrillated nanocellulose in water and / or an organic solvent can be used.

[0193] The oxidized cellulose and nanocellulose obtained by the manufacturing method of the present invention can be applied to a variety of uses. Specifically, they can be used as, for example, various materials (e.g., resins, fibers, rubber, etc.) and in various applications (e.g., food, cosmetics, medical products, coatings, inks, etc.). Furthermore, the compositions containing nanocellulose can be formed into films for use as various sheets or films. The application fields of the compositions containing nanocellulose are not particularly limited, and they can be used in the manufacture of products in various fields such as automotive components, mechanical parts, electrochemical products, electronic devices, cosmetics, medical products, building materials, daily necessities, and stationery.

[0194] <<Second Specific Implementation Method>>

[0195] <Methods for manufacturing oxidized cellulose>

[0196] The method for manufacturing oxidized cellulose of the present invention includes a step of performing solid-liquid separation on an oxide dispersion comprising a cellulose-based oxide and a dispersion medium to obtain oxidized cellulose (hereinafter also referred to as the "separation step"). Furthermore, the pH of the oxide dispersion is 4.0 or below. Moreover, the oxide dispersion substantially does not contain N-oxygen free radical compounds, or may further include a step of oxidizing the cellulose-based raw material using a predetermined amount of hypochlorous acid or its salt to obtain the aforementioned cellulose-based oxide.

[0197] Here, in the second invention, the meaning of "substantially free of N-oxygen free radical compounds" is as explained in the relevant section of the aforementioned <<First Specific Embodiment>> (wherein, "oxidized cellulose or nanocellulose" is replaced with "oxide dispersion").

[0198] According to the method for manufacturing oxidized cellulose of the present invention, oxidized cellulose can be obtained in high yield. The reasons for this can be inferred as follows (but are not limited to this). In conventional manufacturing methods, when cellulose oxides obtained by oxidizing cellulose-based raw materials using hypochlorous acid or its salts are dispersed in a dispersion medium and then subjected to solid-liquid separation, the cellulose oxides undergo micronization in the dispersion medium, with some transferring from the solid phase to the liquid phase, resulting in a lower yield of the obtained oxidized cellulose. Especially when solid-liquid separation is performed by filtration, the filter cloth sometimes becomes clogged, making solid-liquid separation itself difficult. On the other hand, according to the method for manufacturing oxidized cellulose of the present invention, by maintaining the pH of the oxide dispersion at 4.0 or below, micronization of the cellulose oxides in the dispersion medium is suppressed, thereby increasing the yield of oxidized cellulose recovered by solid-liquid separation. Especially when solid-liquid separation is performed by filtration, the filter cloth does not become clogged, improving the operability of solid-liquid separation; furthermore, it is easier to clean the oxidized cellulose from the filter cloth afterwards.

[0199] The following is in accordance with Figure 1 Each step of the process shown in the flowchart is described in detail for the manufacturing method of the present invention, but the present invention is not limited thereto and various modifications can be made without departing from its spirit.

[0200] [Oxidation Process]

[0201] In the manufacturing method of the present invention, in order to prepare the cellulose oxide for use in the separation process, a step of oxidizing the cellulose raw material to obtain the cellulose oxide may be included (hereinafter referred to as the "oxidation step"). In the oxidation step, an oxidizing agent may be used to oxidize the cellulose raw material, and hypochlorous acid or its salt is particularly preferred.

[0202] Cellulose oxides can be obtained by using hypochlorous acid or its salts for oxidation, thus avoiding the use of N-oxygen radical compounds such as 2,2,6,6-tetramethyl-1-piperidine-N-oxygen radical (TEMPO) as oxidants.

[0203] Specific examples of hypochlorous acid or its salts are described in the relevant sections of the aforementioned <<First Specific Embodiment>>.

[0204] Specific examples of cellulose-based raw materials are described in the relevant sections of the aforementioned <<First Specific Embodiment>>.

[0205] Regarding the second invention, cellulose oxides refer to materials whose main component is cellulose containing carboxyl groups. In the separation process described later, cellulose oxides obtained through an oxidation process are preferably used, but there are no particular limitations.

[0206] Regarding the second invention, the oxide dispersion refers to a substance containing cellulose oxides and a dispersion medium, wherein the pH is below 4.0.

[0207] Regarding the second invention, oxidized cellulose refers to a component in a material primarily composed of cellulose containing carboxyl groups, which can be contained in the solid phase within a dispersion. For example, it refers to a component in the polymerized components of cellulose that, due to a degree of polymerization exceeding a specified value or a water solubility below a specified value, is not dissolved in the dispersion medium but is extracted in the form of a solid phase.

[0208] It should be noted that the pH values ​​mentioned in this manual can be measured using a pH meter equipped with a pH electrode. Alternatively, a pH controller with a pH electrode can be used to control the pH range.

[0209] One method for obtaining cellulose oxides by oxidizing cellulose-based raw materials is to mix the cellulose-based raw materials with a reaction solution containing hypochlorous acid or a salt thereof. From the viewpoint of ease of handling and minimizing side reactions, water is preferably the solvent contained in the reaction solution.

[0210] In the oxidation process, hypochlorous acid or its salt is not particularly limited, but its mass ratio relative to the cellulose-based raw material is preferably 0.2 or more, more preferably 0.5 or more, and even more preferably 1.0 or more. Within this range, the amount of carboxyl groups in the resulting cellulose-based oxide and oxidized cellulose can be sufficiently increased, tending to achieve sufficient micronization during the subsequent defiberization process. There is no particular limitation on the upper limit of the above mass ratio, but it is preferably 20 or less, more preferably 10 or less, and even more preferably 5.0 or less. The range of the above mass ratio can be any appropriate combination of the upper and lower limits; for example, it can be set to 0.2 or more and 20 or less, 0.5 or more and 10 or less, or 1.0 or more and 5.0 or less.

[0211] Oxidized cellulose can be obtained, for example, by oxidizing a cellulose-based raw material under the conditions set in the above mass ratio and then performing a separation process described later. Alternatively, it can be manufactured by appropriately controlling the above mass ratio, the pH during the reaction, the reaction temperature, and other reaction conditions. The structure (oxidation state of the hydroxyl groups) of the oxidized cellulose obtained in this manner is as described in the relevant section of the aforementioned <<First Specific Embodiment>>.

[0212] In the oxidation process, the presence or absence of pH adjustment and the range of pH are arbitrary. Preferred pH values ​​and pH adjustment methods are as described in the relevant sections of the aforementioned <<First Specific Embodiment>>.

[0213] [Processing Procedure]

[0214] The manufacturing method of the present invention may further include a step of treating the hypochlorous acid or a salt thereof used in the oxidation step (hereinafter also referred to as the "treatment step"). By including the treatment step, it is possible to stop the reaction of oxidizing the cellulosic raw material. Specific details of the treatment step are as described in the relevant section of the aforementioned <<First Specific Embodiment>>.

[0215] [Protonization process]

[0216] In the manufacturing method of the present invention, in order to prepare an oxide dispersion for use in the separation step, it may further include a step of adding acid to prepare an oxide dispersion with a pH of 4.0 or lower (hereinafter also referred to as the "protonation step"). Here, the cellulose-based oxide contained in the oxide dispersion contains a carboxyl group, and the protonation step is a step for converting at least a portion of the carboxyl group from the salt form (-COO-X+: X+ refers to a cation such as sodium) to the proton form (-COO-H+).

[0217] The acid used in the protonation process is not particularly limited as long as it can prepare an oxide dispersion with a pH of 4.0 or lower; inorganic acids and organic acids are examples. Among these, inorganic acids are preferred from the viewpoint of ease of processing, and hydrochloric acid is particularly preferred. Furthermore, cation exchange resins can be used in the protonation process.

[0218] As a cation exchange resin, any counter ion that is H+ can be used; both strongly acidic and weakly acidic ion exchange resins can be employed, with strongly acidic ion exchange resins being preferred. Examples of strongly acidic and weakly acidic ion exchange resins include resins containing sulfonic acid or carboxyl groups introduced into styrene-based or acrylic resins. The shape of the cation exchange resin is not particularly limited; various shapes such as fine particles, membranes, and fibers can be used. From the viewpoint of efficiently desalting carboxylated cellulose nanofiber salts and easily separating them after desalination, granular form is preferred. Commercially available products can be used as such cation exchange resins. Commercially available products include, for example, Amberjet 1020, 1024, 1060, and 1220 (all manufactured by organic companies); Amberlite IR-200C and IR-120B (all manufactured by Tokyo Organic Chemical Company); LEWATIT SP112 and S100 (all manufactured by Bayer); GELCK08P (manufactured by Mitsubishi Chemical Company); and Dowex 50W-X8 (manufactured by The Dow Chemical Company).

[0219] After protonation using cation exchange resin, the cation exchange resin can simply be filtered out using a metal screen or similar material.

[0220] There are no particular limitations on the dispersion medium used in the protonation process; it is preferable to use the solvent contained in the aforementioned acid directly. Alternatively, depending on the purpose, dispersion media not present in the acid may be used in combination, replacing the solvent contained in the acid with other dispersion media. Specific examples of dispersion media include those described as the dispersion liquid used in the defibrillation process described in the aforementioned <<First Embodiment>>.

[0221] The pH of the oxide dispersion is preferably 4.0 or lower, more preferably 3.0 or lower, and even more preferably 2.5 or lower. In this case, the lower limit of the pH of the oxide dispersion is not particularly limited, and is generally 1.0 or higher, preferably 1.5 or higher, and more preferably 2.0 or higher. The pH range of the oxide dispersion can be any appropriate combination of the above-mentioned upper and lower limits; for example, it can be set to 1.0 or higher and 4.0 or lower, 1.5 or higher and 3.0 or lower, or 2.0 or higher and 2.5 or lower.

[0222] In cases where a protonation step is included, the protonation step can be performed before the separation step, preferably after the oxidation step, but it can also be performed simultaneously with a part of the oxidation step.

[0223] Cellulose oxides can be used in separation processes by further refining them before, during, or after the protonation process, as needed. Alternatively, a solution containing cellulose oxides obtained from the oxidation process can be directly supplied to the separation process.

[0224] [Separation Process]

[0225] The method for manufacturing oxidized cellulose according to the present invention includes a step (separation step) of performing solid-liquid separation on an oxide dispersion containing a cellulose-based oxide and a dispersion medium to obtain oxidized cellulose. Furthermore, the pH of the oxide dispersion is 4.0 or lower.

[0226] There are no particular limitations on the method for solid-liquid separation of oxide dispersions, but examples include methods that utilize known separation processes such as centrifugation and filtration to remove the liquid phase and obtain the oxidized cellulose contained in the solid phase. From an operational point of view, solid-liquid separation of oxide dispersions by filtration is preferred.

[0227] The pH of the oxide dispersion in the separation process is the same as that of the oxide dispersion prepared by the protonation process, as described above.

[0228] The dispersion medium used in the separation process is the same as that used in the protonation process, and it is preferable to use the dispersion medium used here directly. Specific examples of the dispersion medium are also the same as those used in the protonation process.

[0229] [Cleaning Process]

[0230] The method for manufacturing oxidized cellulose of the present invention may further include a step of cleaning the oxide dispersion or oxidized cellulose with an acidic cleaning solution (hereinafter also referred to as the "cleaning step").

[0231] As an acidic cleaning solution used in the cleaning process, a solution containing the acid and dispersion medium used in the protonation process can be used, but there are no particular limitations.

[0232] The pH of the acidic cleaning solution is the same as that of the oxide dispersion described above, with the specific values ​​as stated above.

[0233] In cases where a cleaning step is included, the cleaning step can be performed before, after, or simultaneously with the separation step. Alternatively, as described later in the embodiments, the separation step and the cleaning step can be performed repeatedly.

[0234] [Salt Formation Process]

[0235] The manufacturing method of the present invention may further include: adding an alkali to adjust the pH of the oxidized cellulose dispersion containing oxidized cellulose and a dispersion medium obtained by the separation process to a value greater than 4.0 (hereinafter also referred to as the "salting process"). The salting process is also referred to as the "neutralization process"). Here, the oxidized cellulose contained in the oxidized cellulose dispersion contains carboxyl groups, and the salting process is a process for converting at least a portion of the carboxyl groups from the proton form (-COO-H+) to the salt form (-COO-X+: X+ refers to cations such as sodium and lithium).

[0236] As for the alkali used in the salt formation process, there are no particular limitations as long as it can adjust the pH of the oxidized cellulose dispersion to a level greater than 4.0; inorganic and organic alkalis can be used. Among these, from the viewpoint of ease of processing, inorganic alkalis are preferred, and sodium hydroxide is particularly preferred.

[0237] Alternatively, amines can also be used as bases. These amines can be primary, secondary, tertiary, or quaternary amines.

[0238] The pH of the oxidized cellulose dispersion is preferably 5.0 or higher, more preferably 6.0 or higher, and even more preferably 7.0 or higher. The upper limit of the pH is not particularly limited, but is preferably 14.5 or lower, more preferably 14.0 or lower, even more preferably 12.0 or lower, even more preferably 10.0 or lower, even more preferably 9.0 or lower, and particularly preferably 8.0 or lower. The pH range can be any appropriate combination of the above upper and lower limits, for example, it can be set to 5.0 or higher and 14.5 or lower, 5.0 or higher and 14.0 or lower, 6.0 or higher and 12.0 or lower, 6.0 or higher and 10.0 or lower, 7.0 or higher and 9.0 or lower, or 7.0 or higher and 8.0 or lower.

[0239] There are no particular limitations on the dispersion medium used in the salt formation process, but it is preferable to use the solvent contained in the alkali directly. Alternatively, depending on the purpose, dispersion media not present in the alkali may be used in combination, or the solvent contained in the alkali may be replaced with other dispersion media. Specific examples of dispersion media are the same as those used in the protonation process. In order to facilitate the separation of nanocellulose in the subsequent defibrillation process, water and / or organic solvents are preferred.

[0240] In cases involving a salt-forming process, the salt-forming process can be performed after the separation process, either before, after, or simultaneously with the washing process.

[0241] <Oxidized Cellulose>

[0242] The oxidized cellulose of the present invention is obtained by the manufacturing method of the present invention. Specifically, the oxidized cellulose is a component derived from the oxide dispersion used in the separation process and extracted in solid phase form through a solid-liquid separation operation.

[0243] Oxidized cellulose is preferably in slurry form. The slurry referred to herein is a suspension containing oxidized cellulose. This slurry can be contained in a dispersion medium used in the separation process. Alternatively, a dispersion medium can be appropriately added to prepare a slurry form. By making oxidized cellulose a slurry, it tends to be easier to handle and easier to micronize.

[0244] Oxidized cellulose includes fibrous cellulose obtained by oxidizing cellulose-based raw materials using hypochlorous acid or its salts. The oxidized cellulose in this invention is also referred to as oxidized cellulose fiber. That is, the oxidized cellulose in this invention comprises oxides of cellulose-based raw materials based on hypochlorous acid or its salts.

[0245] The preferred degree of polymerization of oxidized cellulose, its adjustment method, and its determination method are as described in the relevant section of the aforementioned <<First Specific Embodiment>>.

[0246] The preferred transmittance of the nanocellulose aqueous dispersion obtained by defibrillating an oxidized cellulose aqueous dispersion with a concentration of 0.1% by mass using a rotary mixer at a rotational speed of 2000 rpm and a rotational speed of 800 rpm for 10 minutes is as described in the relevant section of the aforementioned <<First Specific Embodiment>>.

[0247] Furthermore, the oxidized cellulose of the present invention can be used by blending with other components. That is, even without micronization, by blending with other components and stirring the oxidized cellulose appropriately, a composition containing nanocellulose and at least one other component can be obtained. Moreover, the user of the oxidized cellulose of the present invention can also micronize it to produce nanocellulose during use.

[0248] <Methods for manufacturing nanocellulose>

[0249] The method for manufacturing nanocellulose of the present invention includes the step of defibrating oxidized cellulose obtained by the method for manufacturing oxidized cellulose of the present invention to obtain nanocellulose.

[0250] The defiberization method is not particularly limited as long as it is a method for micronizing oxidized cellulose, but it is preferable to perform the defiberization while the oxidized cellulose is mixed with a dispersion medium. Specific defiberization methods are as described in the relevant sections of the aforementioned <<First Specific Embodiment>>.

[0251] The dispersion medium used in the defibrillation process is the same as that used in the salt formation process, and it is preferable to use the dispersion medium used here directly. Specific examples of the dispersion medium are the same as those used in the protonation process. Water and / or an organic solvent are preferred for easy separation of the nanocellulose. Furthermore, since nanocellulose dispersed in an organic solvent can be obtained, it is easy to mix with resins, resin raw material monomers, etc., dissolved in the organic solvent. For mixing with various components such as resins, rubbers, and solid particles, a nanocellulose dispersion obtained by dispersing the defibrillated nanocellulose in water and / or an organic solvent can be used.

[0252] Nanocellulose

[0253] The nanocellulose of the present invention is obtained by the manufacturing method of the present invention. It refers to a substance derived from the oxidized cellulose of the present invention, obtained by defibrillation and micronization of the oxidized cellulose. In this specification, nanocellulose refers to a general term for substances obtained by micronizing cellulose, including microcellulose fibers, cellulose nanocrystals, etc. Microcellulose fibers are also called cellulose nanofibers (CNFs).

[0254] The average fiber length, average fiber width, their measurement methods, and aspect ratio (average fiber length / average fiber width) of nanocellulose are as described in the relevant section of the aforementioned <<First Specific Embodiment>>.

[0255] The transmittance of the aqueous dispersion of nanocellulose preferably exhibits a value of 60% or higher. More preferably, the transmittance of this aqueous dispersion is 70% or higher, even more preferably 75% or higher, and still more preferably 80% or higher. Specific methods for measuring transmittance are described in the examples described later.

[0256] The uses of oxidized cellulose and nanocellulose obtained by the manufacturing method of the present invention are as described in the relevant section of the foregoing <<First Specific Embodiment>>.

[0257] <<Combination of the First Invention and the Second Invention>>

[0258] The first invention and the second invention can be combined to form a method comprising the following steps: a step of oxidizing a cellulose-based raw material to obtain oxidized cellulose; and a step of post-processing the aforementioned oxidized cellulose. As an example, the following methods can be listed, but are not limited thereto; the specific methods of the first invention and the specific methods of the second invention can be appropriately combined.

[0259] [An example of a combination]

[0260] A method for manufacturing oxidized cellulose, wherein the oxidized cellulose is substantially free of N-oxygen free radical compounds, and the degree of polymerization of the oxidized cellulose is below 600; the manufacturing method includes:

[0261] The process of obtaining first oxidized cellulose by oxidizing a cellulose-based raw material using hypochlorous acid or its salt (here, the viscosity of the slurry of the aforementioned cellulose-based raw material at the same concentration as the aforementioned oxidation is in the range of 1000 Pa·s or less using a viscometer equipped with an SPP rotor and under the measurement conditions of a rotation speed of 100 rpm and a temperature of 30°C or 40°C) [part of the first invention]; and

[0262] The process of performing solid-liquid separation on the oxide dispersion containing the aforementioned first oxidized cellulose and the dispersion medium to obtain the second oxidized cellulose (here, the pH of the aforementioned oxide dispersion is 4.0 or less) [part of the second invention].

[0263] It should be noted that "first cellulose oxide" and "second cellulose oxide" in the aforementioned [second invention section] correspond to "cellulose oxide" and "cellulose oxide" in the aforementioned <<second specific embodiment>>, respectively.

[0264] Example

[0265] The present invention will be specifically described below through embodiments, but the present invention is not limited to these embodiments. It should be noted that, unless otherwise specified, "parts" refers to "parts by mass" and "%" refers to "% by mass".

[0266] The determination of various physical properties is carried out as follows.

[0267] [Determination of the viscosity-uniform polymerization degree of oxidized cellulose]

[0268] Oxidized cellulose was added to an aqueous solution of sodium borohydride adjusted to pH 10 and subjected to reduction treatment at 25°C for 5 hours. The amount of sodium borohydride was set to 0.1 g relative to 1 g of oxidized cellulose fiber. After reduction treatment, solid-liquid separation was performed by vacuum filtration, followed by washing with water, and the resulting oxidized cellulose fiber was freeze-dried. 0.04 g of dried oxidized cellulose fiber was added to 10 ml of pure water and stirred for 2 minutes, followed by the addition of 10 ml of 1 mol / L copper ethylenediamine solution and dissolution. 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. Based on the flow time of the blank solution (t0), the flow time of the cellulose solution (t), and the concentration of oxidized cellulose fiber (c [g / ml]), the relative viscosity (ηr), specific viscosity (ηsp), and intrinsic viscosity ([η]) were calculated sequentially as shown in the following formula, and the degree of polymerization (DP) of the oxidized cellulose fiber was calculated according to the viscosity measurement formula.

[0269] ηr=η / η0=t / t0

[0270] ηsp=ηr-1

[0271] [η]=ηsp / (100×c(1+0.28ηsp))

[0272] DP = 175 × [η]

[0273] [Determination of average fiber width and average fiber length]

[0274] Pure water was added to the aqueous dispersion of nanocellulose to adjust the concentration of oxidized CNF in the CNF aqueous dispersion to 5 ppm. The CNF aqueous dispersion with adjusted concentration was allowed to air dry on a mica substrate, and the shape of the oxidized CNF was observed using an Oxfordasylum scanning probe microscope "MFP-3D Infinity" in AC mode.

[0275] To analyze the average fiber length, the obtained image was binarized using the image processing software "ImageJ". For fibers with more than 100 fibers, the average fiber length was calculated as fiber length = "circumference" ÷ 2.

[0276] For the average fiber width, the software included with "MFP-3D infinity" is used to calculate the number-average fiber width [nm] for fibers with more than 50 fibers, with the cross-sectional height of the shape image equal to the fiber width.

[0277] [Viscosity determination of the reaction system]

[0278] First, pulps consisting solely of cellulose-based raw materials and water were prepared. Specifically, using the powdered pulp (VP-1) used in the Examples / Comparative Examples, pulps with the same concentrations of cellulose-based raw materials as in the reaction systems of the Examples / Comparative Examples (7%, 15%, and 20%, respectively) were prepared. The viscosity of these pulps was measured at 30°C or 40°C.

[0279] In the viscosity determination of the slurry, a viscometer (Toki Sangyo Co., Ltd., RE-85U) equipped with an SPP (Scrolled Parallel Plate) rotor was used, and the slurry was stirred and measured at a speed of 100 rpm (equivalent to 200 s⁻¹ shear rate). It should be noted that the SPP rotor used is a parallel disc rotor system with vortex grooves manufactured by Toki Sangyo Co., Ltd., with a rotor diameter of φ19.4.

[0280] It should be noted that the viscosity measurement should be performed after the cellulose-based raw materials and water have been mixed.

[0281] The viscosities of 7%, 15%, and 20% slurries at 30°C were below 1.00 Pa·s, 1.91 Pa·s, and 9.11 Pa·s, respectively.

[0282] The viscosities of 7%, 15%, and 20% slurries at 40°C were below 1.00 Pa·s, 2.32 Pa·s, and 11.91 Pa·s, respectively.

[0283] [Light transmittance of nanocellulose]

[0284] Aqueous dispersions with a CNF concentration of 0.1% by mass were prepared by adding pure water to nanocellulose. The aqueous dispersions were placed in 10 mm thick quartz cuvettes and measured using a spectrophotometer (JASCO V-550). The transmittance value at a wavelength of 660 nm obtained was set as the transmittance.

[0285] [Crystallinity of cellulose-based raw materials]

[0286] Regarding crystallinity, solid-state testing was conducted on freeze-dried cellulose-based raw materials. 13 C-NMR measurements were performed using the peak at the fourth carbon atom of cellulose (hereinafter also referred to as C4). The C4 peak appears in the range of approximately 80–95 ppm, with overlapping peaks in the crystalline portion (high ppm side, approximately 85–95 ppm) and the amorphous portion (low ppm side). The peak area was divided into crystalline portion (SC) and amorphous portion (SA) using a vertical segmentation method. Crystallinity was determined using the following formula.

[0287] Crystallinity = SC / (SC+SA)×100

[0288] solid 13 C-NMR measurements are performed under the following conditions.

[0289] Device: JNM-ECA, JEOL

[0290] Frequency: 15kHz

[0291] Determination method: CP / MAS method

[0292] Standby time: 5 seconds

[0293] Total number of times: 10,000

[0294] <Embodiments and Comparative Examples of the First Invention>

[0295] [Example 1A]

[0296] 780g of sodium hypochlorite pentahydrate crystals with an effective chlorine concentration of 42% by mass were added to a 2L glass container with a jacket and baffle. Pure water was added and stirred to set the effective chlorine concentration to 21% by mass. 35% by mass hydrochloric acid was added and stirred to obtain an aqueous solution of sodium hypochlorite with a pH of 11.

[0297] Using a mixer (THREE-ONE MOTOR, BL600) manufactured by Shin-Dong Science & Technology Co., Ltd., with three swept blades, the above sodium hypochlorite aqueous solution was stirred at 300 rpm while water at 30°C was circulated in the jacket. After heating to 30°C, 118 g of powdered pulp (VP-1, crystallinity: 40%) from TDI Co., Ltd. was added as a cellulose-based raw material.

[0298] After supplying the cellulose-based raw material, the mixture was kept at 30°C while 25% by mass of sodium hydroxide was added, and the pH of the reaction was adjusted to 11. The mixture was then stirred for 2 hours under the same conditions. No problems were observed during the stirring of the reaction system. It should be noted that the initial concentration of the cellulose-based raw material in the slurry during the reaction was 7% by mass. Therefore, based on the viscosity measured according to the above [Viscosity Measurement of the Reaction System], the viscosity of the reaction system was set to be below 1.00 Pa·s.

[0299] After the reaction was completed, repeated centrifugation (1000G, 10 minutes) and decantation were performed, and an amount of pure water equivalent to the amount of liquid removed was added to recover the oxidized cellulose. Water was added to adjust the oxidized cellulose concentration to 1%, and the mixture was then defibrinated using a homogenizer at 10,000 rpm for 10 minutes to obtain an aqueous dispersion of nanocellulose. Analysis of the aqueous dispersion revealed that it contained nanocellulose with an average fiber length of 165 nm and an average fiber width of 3.2 nm.

[0300] In addition, the degree of polymerization of oxidized cellulose is 96.

[0301] It should be noted that the effective chlorine concentration in sodium hypochlorite aqueous solution is determined using the following method.

[0302] (Determination of available chlorine concentration in sodium hypochlorite aqueous solution)

[0303] Accurately weigh 0.582 g of an aqueous solution obtained by adding sodium hypochlorite pentahydrate crystals to pure water. Add 50 ml of pure water, 2 g of potassium iodide, and 10 ml of acetic acid. Immediately seal the container and let it stand in the dark for 15 minutes. After 15 minutes, titrate the released iodine with 0.1 mol / L sodium thiosulfate solution. The titration volume (indicator: starch solution) was 34.55 ml. A blank test was performed for correction. Since 1 ml of 0.1 mol / L sodium thiosulfate solution is equivalent to 3.545 mg of Cl, the effective chlorine concentration in the sodium hypochlorite aqueous solution is 21% by mass.

[0304] After freeze-drying the oxidized cellulose obtained in each manufacturing example, the sample was placed at 23°C and 50% RH for at least 24 hours to obtain a solid sample. 13 C-NMR measurements confirm that the hydroxyl groups at positions 2 and 3 of the pyranose ring have been oxidized to form carboxyl groups. The following shows the solid structure. 13 C-NMR measurement conditions.

[0305] (1) Test tube: Zirconia tube (4mm diameter)

[0306] (2) Magnetic field strength: 9.4T (1H resonance frequency: 400MHz)

[0307] (3) MAS speed: 15kHz

[0308] (4) Pulse sequence: CPMAS method

[0309] (5) Contact time: 3ms

[0310] (6) Standby time: 5 seconds

[0311] (7) Cumulative number of times: 10,000 to 15,000

[0312] (8) Measuring apparatus: JNM ECA-400 (manufactured by Nippon Electronics Corporation)

[0313] [Example 2A]

[0314] The amount of powdered pulp was changed to 275g, but otherwise the conditions were the same as in Example 1A. It should be noted that the initial concentration of the cellulose-based raw material in the pulp during the reaction was 15% by mass; therefore, based on the viscosity measured according to the above [Viscosity Measurement of the Reaction System], the viscosity of the reaction system was set to 1.91 Pa·s. No problems were observed during the stirring of the reaction system. The analysis results of the aqueous dispersion of nanocellulose obtained by defibrillation under the same conditions showed that it was nanocellulose with an average fiber length of 168 nm and an average fiber width of 3.4 nm.

[0315] In addition, the degree of polymerization of oxidized cellulose is 105.

[0316] [Example 3A]

[0317] 780g of sodium hypochlorite pentahydrate crystals with an effective chlorine concentration of 42% by mass were added to a 4L glass container with a jacket and baffle. Pure water was added and stirred to set the effective chlorine concentration to 13% by mass. 35% by mass hydrochloric acid was added and stirred to obtain an aqueous sodium hypochlorite solution with pH 10.

[0318] Using a mixer (THREE-ONE MOTOR, BL600) manufactured by Shin-Dong Science & Technology Co., Ltd., with three swept blades, the above sodium hypochlorite aqueous solution was stirred at 300 rpm while 40°C water was circulated in the jacket. After heating to 40°C, 190g of powdered pulp (VP-1, crystallinity: 40%) from TDI Co., Ltd. was added as a cellulose-based raw material.

[0319] After supplying the cellulose-based raw material, the mixture was kept at 40°C while 25% by mass of sodium hydroxide was added, and the pH of the reaction was adjusted to 10. The mixture was then stirred for 4 hours under the same conditions. No problems were observed during the stirring of the reaction system. It should be noted that the initial concentration of the cellulose-based raw material in the slurry during the reaction was 7% by mass. Therefore, based on the viscosity measured according to the above-described [Viscosity Measurement of the Reaction System], the viscosity of the reaction system was set to be below 1.00 Pa·s.

[0320] After the reaction was completed, repeated centrifugation (1000G, 10 minutes) and decantation were performed, and an amount of pure water equivalent to the amount of liquid removed was added to recover the oxidized cellulose. Water was added to adjust the concentration of the oxidized cellulose to 1%, and the mixture was then defibrinated using a homogenizer at 10,000 rpm for 10 minutes to obtain an aqueous dispersion of nanocellulose. Analysis of the aqueous dispersion revealed that it contained nanocellulose with an average fiber length of 174 nm and an average fiber width of 4.2 nm.

[0321] In addition, the degree of polymerization of oxidized cellulose is 101.

[0322] [Example 4A]

[0323] The amount of powdered pulp was changed to 445g, but otherwise the conditions were the same as in Example 3A. It should be noted that the initial concentration of cellulose-based raw materials in the pulp during the reaction was 15% by mass. Therefore, based on the viscosity measured according to the above [Viscosity Measurement of the Reaction System], the viscosity of the reaction system was set to 2.32 Pa·s.

[0324] No problems were observed during the stirring of the reaction system. The analysis results of the aqueous dispersion of nanocellulose obtained by defibrillation under the same conditions as in Example 3A showed that it was nanocellulose with an average fiber length of 181 nm and an average fiber width of 4.5 nm.

[0325] In addition, the degree of polymerization of oxidized cellulose is 114.

[0326] [Example 5A]

[0327] The concentration of the cellulose-based raw material in the aforementioned reaction system was set to 20% by mass relative to the total amount of the reaction system, otherwise, the process was the same as in Example 1A. According to the viscosity measured as described above (viscosity measurement of the reaction system), the viscosity of the reaction system was 9.11 Pa·s. Because the viscosity decreased slowly, although the oxidation reaction could be confirmed, the reaction system was difficult to stir.

[0328] [Example 6A]

[0329] The concentration of the cellulose-based raw material in the aforementioned reaction system was set to 20% by mass relative to the total amount of the reaction system, otherwise, the process was the same as in Example 3A. According to the viscosity measured as described above (viscosity measurement of the reaction system), the viscosity of the reaction system was 11.91 Pa·s. Because the viscosity decreased slowly, although the oxidation reaction could be confirmed, the reaction system was difficult to stir.

[0330] [Comparative Example 1A]

[0331] When the viscosity exceeds 1000 Pa·s, even using a mixer, it is impossible to stir and carry out the oxidation reaction.

[0332] <Embodiments and Comparative Examples of the Second Invention>

[0333] [Example 1B]

[0334] (Oxidation process)

[0335] Add 350g of sodium hypochlorite pentahydrate crystals with an effective chlorine concentration of 42% by mass to a beaker, add pure water and stir to set the effective chlorine concentration to 21% by mass. Add 35% by mass hydrochloric acid and stir to obtain a sodium hypochlorite aqueous solution with pH 11.

[0336] Using a THREE-ONE MOTOR BL600 (manufactured by Shin-Tung Science & Technology Co., Ltd.), the sodium hypochlorite aqueous solution was stirred at 200 rpm with a propeller-type agitator while being heated to 30°C in a constant-temperature water bath. Then, 50 g of powdered pulp (VP-1, crystallinity: 40%) from TDI Co., Ltd. was added as the cellulose-based raw material. After supplying the cellulose-based raw material, the mixture was kept at 30°C in the same constant-temperature water bath, and the pH of the reaction system was adjusted to 11 while adding 48% sodium hydroxide. The mixture was stirred for 2 hours. Subsequently, pure water was added and diluted 2 times, and sodium hydroxide was added to bring the pH to 13, thereby slowing down the oxidation reaction and obtaining cellulose oxides dispersed in water.

[0337] (Processing steps)

[0338] The resulting cellulose oxide dispersed in water was reduced by adding an aqueous sodium sulfite solution to reduce the remaining sodium hypochlorite.

[0339] (Protonization process)

[0340] Subsequently, hydrochloric acid was added to convert the carboxyl groups of the cellulose oxide from the salt form (-COO-Na+) to the proton form (-COO-H+), resulting in an aqueous dispersion with a pH of 2.5.

[0341] It should be noted that the pH control in this embodiment is performed using a pH controller (Tokyo Glass Equipment Co., Ltd., FD-02).

[0342] (Separation process, cleaning process)

[0343] The resulting aqueous dispersion at pH 2.5 was subjected to solid-liquid separation and washing. Specifically, the supernatant was removed by centrifugation (1000g, 10 minutes) and decantation. A volume of pure water equivalent to the amount removed was added, and the mixture was thoroughly stirred with a spatula. This process was repeated six times. Finally, the centrifugation and decantation were performed to obtain oxidized cellulose. The yield of oxidized cellulose (oxidized cellulose amount / raw cellulose amount × 100) was 63%.

[0344] (Salt production process)

[0345] Subsequently, sodium hydroxide, in approximately the same molar amount as the introduced carboxyl groups, was added to restore the carboxylic acid group from the protonated form (-COO-H+) to the salt form (-COO-Na+), yielding an aqueous dispersion with a pH of 7.5. The concentration of oxidized cellulose in this aqueous dispersion was 12% by mass. The degree of polymerization of oxidized cellulose was 90.

[0346] (Fiber unwinding process)

[0347] After adjusting the concentration of oxidized cellulose to 1% by mass by adding pure water to an aqueous dispersion at pH 7.5, the cellulose was decellulosed using a homogenizer (10,000 rpm, 10 minutes) to obtain nanocellulose with an average fiber length of 200 nm and an average fiber width of 3 nm. When pure water was added to the obtained CNF to prepare an aqueous dispersion with a solid content of 0.1% by mass, its transmittance (660 nm) was 97%. A higher transmittance value indicates better decellulose decelluloseing properties.

[0348] Compared to Comparative Example 1B described later, CNF has a higher transmittance value, which can be presumably because the protonation process removes the components that hinder the defibrillation of oxidized cellulose during the defibrillation process.

[0349] [Example 2B]

[0350] In the protonation process, instead of preparing an aqueous dispersion with a pH of 2.5, hydrochloric acid is added to prepare an aqueous dispersion with a pH of 3.5. In the salt formation process, instead of obtaining an aqueous dispersion with a pH of 7.5, sodium hydroxide is added in an amount approximately equal to the amount of carboxyl groups introduced to obtain an aqueous dispersion with a pH of 7.3. Otherwise, the same procedure as in Example 1B is followed to obtain oxidized cellulose and nanocellulose.

[0351] The yield of the obtained oxidized cellulose was 46%. The concentration of oxidized cellulose after the salt formation process was 11% by mass, and the degree of polymerization of oxidized cellulose was 95%.

[0352] The obtained nanocellulose has an average fiber length of 210 nm, an average fiber width of 3 nm, and a light transmittance of 95% for an aqueous dispersion with a solid content concentration of 0.1% by mass.

[0353] [Example 3B]

[0354] Instead of repeatedly centrifuging (1000g, 10 minutes) and decanting six times to remove the supernatant, and adding an amount of pure water equivalent to the amount removed, and stirring thoroughly with a spatula, solid-liquid separation was performed by pressure filtration (0.2MPa, filter cloth aeration rate of 0.3cc / cm2 / sec) to remove the filtrate as the liquid phase. The separated solid phase was washed with pure water at pH 6.8. In the salt formation process, instead of obtaining an aqueous dispersion with pH 7.5, an aqueous dispersion with pH 7.4 was obtained by adding sodium hydroxide in an amount approximately equal to the amount of carboxyl groups introduced. Otherwise, the same procedure as in Example 1B was followed to obtain oxidized cellulose and nanocellulose.

[0355] During pressure filtration, the filter cloth did not become clogged, allowing for continued use and washing with pure water at pH 6.8. A slight turbidity was observed in the filtrate during washing with pure water. It can be inferred that the turbidity is a partial result of the carboxylic acid groups dissociating from the protonated form (-COO-H+) to the salt form (-COO-Na+) during washing with pure water at pH 6.8. This causes a portion of the cellulose oxide to redisperse from the separated solid phase into the liquid phase, resulting in the turbidity in the filtrate.

[0356] The yield of the obtained oxidized cellulose was 67%. The concentration of oxidized cellulose after the salt formation process was 12% by mass, and the degree of polymerization of oxidized cellulose was 92.

[0357] The obtained nanocellulose has an average fiber length of 190 nm, an average fiber width of 3 nm, and a light transmittance of 95% for an aqueous dispersion with a solid content concentration of 0.1% by mass.

[0358] [Example 4B]

[0359] Instead of washing the separated solid phase with pure water at pH 6.8, the separated solid phase was washed with water whose pH was adjusted to 2.5 by adding hydrochloric acid to the pure water. Otherwise, the same procedure as in Example 3B was followed to obtain oxidized cellulose and nanocellulose.

[0360] Similar to the results of Example 3B, the filter cloth did not become clogged during pressure filtration, and it could continue to be used and washed with pure water. However, no turbidity was observed in the filtrate during washing.

[0361] The yield of the obtained oxidized cellulose was 69%. The concentration of oxidized cellulose after the salt formation process was 12% by mass, and the degree of polymerization of oxidized cellulose was 91.

[0362] The obtained nanocellulose has an average fiber length of 185 nm, an average fiber width of 3 nm, and a light transmittance of 95% for an aqueous dispersion with a solid content concentration of 0.1% by mass.

[0363] Compared to Example 3B, the oxidized cellulose yield was higher. This is presumably because washing the separated solid phase with water adjusted to pH 2.5 prevented the carboxylic acid groups from dissociating from the protonated form (-COO-H+) to the salt form (-COO-Na+), thus inhibiting the redispersion of some of the cellulose oxides from the separated solid phase into the liquid phase. It should be noted that, from the viewpoint of treating the filtrate, the absence of turbidity in the filtrate is also preferable.

[0364] [Example 5B]

[0365] 500g of a sodium hypochlorite aqueous solution with a pH of 12.6 and an effective chlorine concentration of 12% by mass was added to a jacketed glass container. Using a three-bladed swept blade mixer (THREE-ONE MOTOR, BL600) manufactured by Shin-Tokyo Science & Technology Co., Ltd., the mixture was stirred at 300 rpm while heated to 30°C. Then, 40g of powdered pulp (KC FLOCK W-100GK, crystallinity: 38%) from Nippon Paper Corporation was added as the cellulose-based raw material. After supplying the cellulose-based raw material, the mixture was kept at 30°C while stirring until the pH dropped to 10.3. Subsequently, a 25% by mass sodium hydroxide aqueous solution was added to adjust the pH to 10.3. The reaction was carried out under the same conditions for a total of 7 hours after the addition of the cellulose-based raw material. After the reaction was completed, the redox potential was checked, and hydrogen peroxide aqueous solution was added to the remaining sodium hypochlorite to deactivate it. Furthermore, hydrochloric acid was added to convert the carboxyl groups of oxidized cellulose from the salt form (-COO-Na+) to the proton form (-COO-H+), yielding an aqueous dispersion with pH 2.5. Solid-liquid separation was performed by pressure filtration at 0.2 MPa, followed by washing with hydrochloric acid water at pH 2.5. Sodium hydroxide was added to the obtained proton-form oxidized cellulose to restore the carboxyl groups from the proton form (-COO-H+) to the salt form (-COO-Na+), yielding an aqueous dispersion of salt-form oxidized cellulose with pH 6.8. The carboxyl group content was determined to be 0.73 mmol / g, with a degree of polymerization of 100.

[0366] [Example 6B]

[0367] As the cellulose-based raw material, ashless filter paper made of cotton (ADVANTEC TOYO, crystallinity 59%) was used. Otherwise, the same procedure as in Example 1B was followed to obtain oxidized cellulose and nanocellulose.

[0368] The yield of the obtained oxidized cellulose was 65%. The concentration of oxidized cellulose after the salt formation process was 10% by mass, and the degree of polymerization of oxidized cellulose was 90.

[0369] The obtained nanocellulose has an average fiber length of 160 nm, an average fiber width of 10 nm, and a light transmittance of 90% for an aqueous dispersion with a solid content concentration of 0.1% by mass.

[0370] [Example 7B]

[0371] Example 7B was implemented with reference to Japanese Patent Application Publication No. 2017-218470. Additionally, referring to Japanese Patent Application Publication No. 2008-231258, which describes using sea squirt sacs as a raw material for cellulose materials, oxidized cellulose and nanocellulose were manufactured using sea squirt sacs as a cellulose-based raw material.

[0372] The sea squirt sacs were immersed in 0.2% NaOH at room temperature and then micronized using a stirrer. After immersion overnight in 5% NaOH at room temperature, they were washed with water and then subjected to a 0.3% sodium chlorite aqueous solution at 60°C for 2 hours. This treatment was repeated three times to remove non-cellulose components. The treated material was then thoroughly washed with water and freeze-dried to obtain sea squirt sac cellulose.

[0373] As a cellulose-based raw material, the above-mentioned sea squirt cellulose was used, and except that, the same procedure as in Example 1B was followed to obtain oxidized cellulose and nanocellulose.

[0374] The yield of the obtained oxidized cellulose was 70%. The concentration of oxidized cellulose after the salt formation process was 8% by mass, and the degree of polymerization of oxidized cellulose was 110.

[0375] The obtained nanocellulose has an average fiber length of 230 nm, an average fiber width of 12 nm, and a light transmittance of 85% for an aqueous dispersion with a solid content concentration of 0.1% by mass.

[0376] [Comparative Example 1B]

[0377] Without performing a protonation process, the separation process was carried out directly after the hypochlorous acid treatment process. In the salt formation process, instead of obtaining an aqueous dispersion with a pH of 7.5, an equimolar amount of sodium hydroxide exceeding the amount of carboxyl groups introduced was added to obtain an aqueous dispersion with a pH of 7.4. Otherwise, the same procedure as in Example 1B was followed to obtain oxidized cellulose and nanocellulose.

[0378] The yield of the obtained oxidized cellulose was 18%. The concentration of oxidized cellulose after the salt formation process was 11% by mass, and the degree of polymerization of oxidized cellulose was 98%.

[0379] The obtained nanocellulose has an average fiber length of 210 nm, an average fiber width of 3 nm, and a light transmittance of 91% for an aqueous dispersion with a solid content of 0.1% by mass.

[0380] Compared with Example 1B, the mass yield of oxidized cellulose was significantly lower. It can be inferred that this is because, during the separation process, when stirring with a spatula, a portion of the cellulose oxide undergoes defibrination and becomes nanocellulose, transferring to the supernatant side to be removed.

[0381] [Refer to Example 1B]

[0382] Without performing a protonation process, the separation process was carried out directly after the hypochlorous acid treatment process. Otherwise, the operation was the same as in Example 3B to obtain oxidized cellulose and nanocellulose.

[0383] Unlike the results of Example 3B, during pressure filtration, the filter cloth became clogged, thus reducing the discharge rate of the filtrate to such an extent that the filter cloth could not be used further and could not be cleaned with pure water.

[0384] Industrial availability

[0385] The manufacturing method of the present invention can provide nanocellulose for use in various materials (e.g., resins, fibers, rubber, etc.) and for various applications (e.g., food, cosmetics, medical products, coatings, inks, etc.), and is industrially available in a wide range of fields such as automotive components, mechanical parts, electrochemical products, electronic devices, cosmetics, medical products, building materials, daily necessities, stationery, etc.

Claims

1. A method for manufacturing oxidized cellulose, wherein, The oxidized cellulose comprises an oxide of a cellulose-based raw material based on hypochlorous acid or its salt, substantially free of N-oxygen free radical compounds, and the degree of polymerization of the oxidized cellulose is 60 or higher and 600 or lower. The manufacturing method includes the step of oxidizing cellulose raw materials by using hypochlorous acid or its salts to obtain oxidized cellulose. The viscosity of the slurry of the cellulose-based raw material at the same concentration as during the oxidation process is in the range of 30 Pa·s or less, measured using a viscometer equipped with an SPP rotor at a rotation speed of 100 rpm and at a temperature of 30°C or 40°C. The manufacturing method further includes a protonation step: adding acid to prepare an oxide dispersion with a pH below 4.0, wherein the cellulose oxide contained in the oxide dispersion contains a carboxyl group.

2. The manufacturing method according to claim 1, wherein, The concentration of the cellulose-based raw material is less than 35% by mass relative to the total amount of the reaction mixture.

3. The manufacturing method according to claim 1 or 2, wherein, The concentration of the cellulose-based feedstock relative to the total mass of the reaction mixture exceeds 6.5% by mass.

4. The manufacturing method according to claim 1 or 2, wherein, The effective chlorine concentration of the hypochlorous acid or its salt in the reaction system is above 6% by mass and below 43% by mass.

5. The manufacturing method according to claim 1 or 2, wherein, The effective chlorine concentration of the hypochlorous acid or its salt in the reaction system is less than 14% by mass.

6. The manufacturing method according to claim 1 or 2, wherein, The oxidation reaction temperature is above 30°C.

7. The manufacturing method according to claim 1 or 2, wherein, The oxidation reaction time is more than 2 hours.

8. The manufacturing method according to claim 1 or 2, wherein, The pH of the reaction system is less than 11.

9. A method for manufacturing nanocellulose, comprising: The step of obtaining nanocellulose by defibrillation following the oxidation step in the manufacturing method according to any one of claims 1 to 8.

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