JP2023013727A - Oxycellulose, nanocellulose and dispersion liquid thereof - Google Patents

Abstract

To provide an oxycellulose that gives a nanocellulose having excellent fibrillation properties and capable of retaining its flowability.SOLUTION: An oxycellulose comprises an oxide of cellulose-based material with hypochlorous acid or a salt thereof and is substantially free of an N-oxyl compound, where at least some carboxy groups of the oxycellulose form a salt with a potassium ion.SELECTED DRAWING: None

Description

The present invention relates to oxidized cellulose, nanocellulose and dispersions thereof.

Various techniques have been proposed for producing nanocellulose materials such as cellulose nanofibers (hereinafter also referred to as "CNF") by oxidizing various cellulosic raw materials with an oxidizing agent and pulverizing the obtained oxidized cellulose. (For example, see Patent Document 1 and Patent Document 2).

In Patent Document 1, hypochlorous acid or a salt thereof is used as an oxidizing agent, and oxidized cellulose can be obtained by oxidizing a cellulosic raw material under high-concentration conditions such that the effective chlorine concentration in the reaction system is 14 to 43% by mass. disclosed. In Patent Document 2, hypochlorous acid or a salt thereof is used as an oxidizing agent, the effective chlorine concentration in the reaction system is 6 to 14% by mass, and the pH is adjusted to 5.0 to 14.0. to obtain oxidized cellulose. In these techniques, since the oxidation treatment is performed without using an N-oxyl compound such as 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (TEMPO) as a catalyst, the N-oxyl compound is It does not remain in the cellulose fibers, so it is possible to produce the nanocellulose material while reducing the impact on the environment.
Non-Patent Document 1 discloses obtaining oxidized cellulose by oxidizing a cellulosic raw material using hypochlorous acid or a salt thereof as an oxidizing agent.

In Patent Document 3, a fine fibrous cellulose having a fiber width of 1,000 nm or less and an oxoacid containing chlorine or a salt thereof are contained, and an oxoacid containing chlorine or a salt thereof is added to 100 parts by mass of the fine fibrous cellulose. A fine fibrous cellulose-containing composition is disclosed having a content of 0.0001 parts by weight or more and 10 parts by weight or less. Here, it is described that the oxoacid or salt thereof includes at least one selected from the group consisting of sodium hypochlorite, potassium hypochlorite and calcium hypochlorite.

Non-Patent Document 2 discloses the effect of carboxy counter ions on the biodegradability of TEMPO oxidized cellulose fibers and nanofibers. Non-Patent Document 2 discloses that -COOH type, -COOH type, -COOH type, -COOH type, It is described that oxidized cellulose of -COOCaCl type, _-COONH4 type, -COOK type, COOCs type and -COOCuCl type was obtained.

WO2018/230354 WO2020/027307 Japanese Patent Application Laid-Open No. 2020-033398

Sustainable Chem. Eng. 2020, 8, 48, 17800-17806 Cellulose (2013) 20: 2505-2515

Patent Documents 1 and 2 describe mechanical treatment using an ultrasonic homogenizer as a specific example of producing a nanocellulose material by refining oxidized cellulose obtained by oxidation with sodium hypochlorite. discloses an example of obtaining a nanocellulose material through a fibrillation process by. In addition, Non-Patent Document 1 also discloses oxidized cellulose similarly obtained by oxidation with sodium hypochlorite. In the production of nanocellulose materials, from the viewpoint of production costs, oxidized cellulose that can be easily defibrated even under mild treatment conditions is desired. In addition, in order to stably produce finely divided nanocellulose, it is required that the oxidized cellulose, which is in a state before defibration of the nanocellulose material, has good fibrillation properties.

In Patent Document 3, for the purpose of reducing the viscosity of fine fibrous cellulose, specifically, sodium hypochlorite or potassium hypochlorite is added to 0.01 parts by mass per 100 parts by mass of fine fibrous cellulose. Although it is disclosed to be added in an extremely small amount, it is not described to use potassium ions as counter cations for the carboxyl groups of the fine fibrous cellulose.

Non-Patent Document 2 discloses TEMPO oxidized cellulose fibers and nanofibers, but oxidized cellulose obtained by the action of hypochlorous acid or a salt thereof without using an N-oxyl compound such as TEMPO. Not listed.

In addition, nanocellulose can be used in combination with other materials, but for example, when used with an organic solvent, the viscosity of the mixture containing nanocellulose and the organic solvent increases and fluidity may be lost. From the viewpoint of ease of handling, there is a demand for nanocellulose that can maintain fluidity when combined with other materials such as organic solvents.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide oxidized cellulose from which nanocellulose can be obtained which is excellent in fibrillating properties and can maintain fluidity.

As a result of intensive studies to solve the above problems, the present inventors have found that the oxidized cellulose obtained by hypochlorous acid or a salt thereof has a potassium-type carboxyl group, thereby making the oxidized cellulose excellent in fibrillation properties. I found out. Moreover, the nanocellulose obtained from the oxidized cellulose can maintain its fluidity when mixed with an organic solvent or the like to form a slurry. As described above, the present invention has been completed.

According to the present invention, specifically, the following means are provided.
[1]
Oxidized cellulose containing an oxide of a cellulosic raw material by hypochlorous acid or a salt thereof and substantially free of an N-oxyl compound,
The oxidized cellulose has a potassium salt-type carboxy group,
oxidized cellulose.
[2]
The light transmittance of the 0.1% by mass aqueous dispersion of oxidized cellulose is 80% or more.
The oxidized cellulose according to [1].
[3]
The light transmittance measured by the following <conditions> is 90% or more,
The oxidized cellulose according to [1] or [2]:
<Condition>
An aqueous dispersion of oxidized cellulose having a concentration of 5% by mass is treated with an ultrasonic homogenizer for 10 seconds to obtain a fibrillation treatment liquid;
The light transmittance of an aqueous dispersion adjusted to have a solid content concentration of 0.1% by mass is measured from the fibrillation treatment liquid.
[4]
The carboxy group amount is 0.30 to 2.0 mmol / g,
The oxidized cellulose according to any one of [1] to [3].
[5]
An oxidized cellulose dispersion in which the oxidized cellulose according to any one of [1] to [4] is dispersed in a dispersion medium.
[6]
Nanocellulose obtained by defibrating the oxidized cellulose according to any one of [1] to [4].
[7]
Nanocellulose obtained by defibrating oxidized cellulose containing oxides of cellulosic raw materials,
The average fiber length of the nanocellulose is 50 to 2000 nm,
The nanocellulose has a potassium salt-type carboxy group,
nanocellulose.
[8]
A nanocellulose dispersion in which the nanocellulose according to [6] or [7] is dispersed in a dispersion medium.

According to the present invention, oxidized cellulose having excellent fibrillation properties can be obtained. In particular, the oxidized cellulose of the present invention can be uniformly pulverized even when the defibration treatment is performed under mild conditions, and is excellent in easy fibrillation. Moreover, the nanocellulose obtained from the oxidized cellulose of the present invention can maintain its fluidity when it is combined with other materials such as an organic solvent to form a slurry.

《Oxidized cellulose》
The oxidized cellulose of the present invention (hereinafter also referred to as "this oxidized cellulose") contains an oxide of a cellulosic raw material with hypochlorous acid or a salt thereof. Also, the oxidized cellulose is substantially free of N-oxyl compounds. The oxidized cellulose has potassium salt-type carboxyl groups.
The oxidized cellulose of the present invention has carboxy groups. The carboxy group in the present specification may contain a group represented by -COO, and includes all possible forms of -COOH such as proton form (-COOH) and salt form (-COO ^- X ⁺ ). contain. The “potassium salt type carboxy group” in the present invention refers to a group represented by —COO ⁻ K ⁺ .

A carboxy group contained in oxidized cellulose can form a salt form (-COO ^- X ⁺ ) with a metal such as sodium or an amine, or a proton form (-COOH). As a result of studies by the present inventors, it was found that the carboxyl group in oxidized cellulose containing an oxide of a cellulosic raw material by hypochlorous acid or a salt thereof and substantially free of an N-oxyl compound is converted into a potassium type (—COO ^- K ⁺ ), it was found that the fibrillation property was more excellent. Although the reason for this is not clear, it is believed that potassium ions have a larger ionic radius, and a certain distance is likely to occur between the oxidized cellulose fibers, making them easier to unravel. In addition, fibrillation proceeds by breaking hydrogen bonds between cellulose microfibrils. In the oxidation treatment using hypochlorous acid or a salt thereof, the degree of polymerization of microfibrils is lowered (that is, the cellulose molecular chain is shortened) as the oxidation progresses. This decrease in the degree of polymerization is thought to proceed more easily than in the case of, for example, the TEMPO oxidation method. It is considered that the force increased and the defibration property of oxidized cellulose improved. The reason why the oxidized cellulose of the present invention is excellent in defibration property is not limited to this.
Moreover, the nanocellulose obtained from the oxidized cellulose of the present invention maintains its fluidity when it is mixed with other materials such as an organic solvent to form a slurry because it contains a potassium-type carboxyl group. This is probably because the potassium type (hereinafter also referred to as the K type) is more hydrophilic than the sodium type (-COO ^- Na ⁺ , hereinafter also referred to as the Na type). The reason why the oxidized cellulose of the present invention maintains fluidity is not limited to this.

The present oxidized cellulose is fibrous cellulose obtained by oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof. Such oxidized cellulose can also be referred to as an oxide of a cellulosic raw material by hypochlorous acid or a salt thereof. The main component of plants is cellulose, and bundles of cellulose molecules are called cellulose microfibrils. Cellulose in cellulosic raw materials is also contained in the form of cellulose microfibrils.

The oxidized cellulose is substantially free of N-oxyl compounds. Here, in this specification, "substantially free of N-oxyl compounds" means that the oxidized cellulose does not contain any N-oxyl compounds, or the content of the N-oxyl compounds is equal to the total amount of the oxidized cellulose. is 2.0 mass ppm or less, preferably 1.0 mass ppm or less. Also, when the content of the N-oxyl compound is preferably 2.0 ppm by mass or less, more preferably 1.0 ppm by mass or less as an increase from the cellulosic raw material, "the N-oxyl compound is substantially means “not including”.
Furthermore, by oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof to obtain oxidized cellulose without using an N-oxyl compound, it becomes "substantially free of N-oxyl compounds." .
By substantially not containing an N-oxyl compound, it is possible to prevent the N-oxyl compound from remaining in the oxidized cellulose, which may affect the environment and the human body. The content of the N-oxyl compound can be measured by known means. Known means include a method using a trace total nitrogen analyzer. Specifically, the nitrogen component derived from the N-oxyl compound in the oxidized cellulose is measured as nitrogen content using a trace total nitrogen analyzer (for example, manufactured by Mitsubishi Chemical Analytech, device name: TN-2100H, etc.). be able to.

[Carboxy group amount]
The carboxy group content of the oxidized cellulose is preferably 0.30 to 2.0 mmol/g. The amount of carboxy groups used in this specification is the amount of groups containing —COO in oxidized cellulose, and refers to the total amount of proton-type (—COOH), salt-type (—COO ⁻ X ⁺ ), and the like.
When the amount of carboxyl groups is 0.30 mmol/g or more, the oxidized cellulose can be imparted with sufficient easy defibration properties. As a result, even when the fibrillation treatment is performed under mild conditions, a nanocellulose-containing slurry with uniform quality can be obtained. On the other hand, when the amount of carboxyl groups is 2.0 mmol/g or less, excessive decomposition of cellulose can be suppressed during fibrillation treatment, and nanocellulose having a low proportion of particulate cellulose and uniform quality can be obtained. . From such a viewpoint, the carboxyl group content of the present oxidized cellulose is more preferably 0.35 mmol/g or more, still more preferably 0.40 mmol/g or more, still more preferably 0.42 mmol/g or more, It is even more preferably 0.50 mmol/g or more, still more preferably over 0.50 mmol/g, and even more preferably 0.55 mmol/g or more. The upper limit of the amount of carboxy groups is more preferably 1.5 mmol/g or less, still more preferably 1.2 mmol/g, even more preferably 1.0 mmol/g or less, still more preferably 0.5 mmol/g or less. 9 mmol/g. A preferable range of the amount of carboxyl groups can be determined by appropriately combining the above-mentioned upper limit and lower limit. The amount of carboxyl groups in the present oxidized cellulose is more preferably 0.35 to 2.0 mmol/g, still more preferably 0.35 to 1.5 mmol/g, still more preferably 0.40 to 1.5 mmol. /g, still more preferably 0.50 to 1.2 mmol/g, still more preferably greater than 0.50 to 1.2 mmol/g, even more preferably 0.55 to 1.0 mmol/g is.

The amount of carboxyl groups (mmol/g) in oxidized cellulose was determined by adding 0.1 M hydrochloric acid aqueous solution to an aqueous solution of oxidized cellulose and water to adjust the pH to 2.5, and then adding 0.05 N sodium hydroxide aqueous solution dropwise. Then, the electrical conductivity was measured until the pH reached 11.0, and the amount of sodium hydroxide (a) consumed in the neutralization stage of the weak acid in which the change in electrical conductivity was moderate was calculated using the following formula. value. The details follow the method described in the examples below. The amount of carboxyl groups in the oxidized cellulose can be adjusted by changing the reaction time of the oxidation reaction, the reaction temperature, the pH of the reaction solution, and the like.
Carboxy group weight = a (ml) x 0.05/oxidized cellulose mass (g)

The present oxidized cellulose preferably has a structure in which at least two of the hydroxyl groups of the glucopyranose rings constituting the cellulose are oxidized. It has a structure in which a hydroxyl group is oxidized and a carboxy group is introduced. Moreover, it is preferable that the hydroxyl group at the 6th position of the glucopyranose ring in the present oxidized cellulose is not oxidized and remains as the hydroxyl group. The position of the carboxy group in the glucopyranose ring of oxidized cellulose can be analyzed by solid-state ¹³ C-NMR spectrum.
From the observation of peaks corresponding to the carboxyl groups at the 2nd and 3rd positions of the glucopyranose ring in the solid-state ¹³ C-NMR spectrum, it can be judged to have an oxidized structure. At this time, the peaks corresponding to the 2nd and 3rd carboxyl groups can be observed as broad peaks in the range of 165 ppm to 185 ppm. The broad peak referred to here can be determined by the area ratio of the peak.
That is, after drawing a baseline for the peaks in the range of 165 ppm to 185 ppm in the NMR spectrum and obtaining the overall area value, the ratio of the two peak area values obtained by vertically dividing the area value at the peak top (large area value/small area value), and if the ratio of the peak area value is 1.2 or more, it can be said that the peak is broad.
Further, the presence or absence of the broad peak can be determined by the ratio of the length L of the baseline in the range of 165 ppm to 185 ppm to the length L' of the perpendicular line from the top of the peak to the baseline. That is, if the ratio L'/L is 0.1 or more, it can be determined that a broad peak exists. The ratio L'/L may be 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more. Although the upper limit of the ratio L'/L is not particularly limited, it is usually 3.0 or less, may be 2.0 or less, or may be 1.0 or less.

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

[Degree of polymerization]
In one preferred embodiment of the present disclosure, the degree of polymerization of the present oxidized cellulose is 600 or less. If the polymerization degree of the present oxidized cellulose exceeds 600, it tends to require a large amount of energy for defibration, and tends to fail to exhibit sufficient fibrillability. Further, when the degree of polymerization of the present oxidized cellulose exceeds 600, the amount of oxidized cellulose that is insufficiently fibrillated increases, so that light scattering increases when nanocellulose obtained by miniaturizing this is dispersed in a dispersion medium. , the transparency may decrease. Furthermore, the size of the obtained nanocellulose tends to vary, resulting in non-uniform quality. From the viewpoint of easy fibrillation, the lower limit of the degree of polymerization of the present oxidized cellulose is not particularly set. However, if the degree of polymerization of the present oxidized cellulose is less than 50, the proportion of particulate cellulose rather than fibrous cellulose will increase, resulting in uneven slurry quality and unstable viscosity. It becomes difficult to obtain thixotropy, which is one of From the above point of view, the degree of polymerization of the present oxidized cellulose is preferably 50-600.

The degree of polymerization of the present oxidized cellulose is more preferably 580 or less, still more preferably 560 or less, still more preferably 550 or less, still more preferably 500 or less, still more preferably 450 or less, and still more preferably 450 or less. Preferably it is 400 or less. The lower limit of the degree of polymerization is more preferably 60 or more, still more preferably 70 or more, still more preferably 80 or more, and still more preferably from the viewpoint of improving viscosity stability and coatability of the slurry. is 90 or greater, even more preferably 100 or greater, even more preferably 110 or greater, and most preferably 120 or greater. A preferred range of the degree of polymerization can be determined by appropriately combining the above-mentioned upper limit and lower limit. The degree of polymerization of the present oxidized cellulose is more preferably 60 to 600, still more preferably 70 to 600, even more preferably 80 to 600, still more preferably 80 to 550, still more preferably 80 500, more preferably 80-450, and particularly preferably 80-400.

The degree of polymerization of oxidized cellulose can be adjusted by changing the reaction time, reaction temperature, pH, effective chlorine concentration of hypochlorous acid or its salt, and the like during the oxidation reaction. Specifically, since the degree of polymerization tends to decrease when the degree of oxidation is increased, methods of reducing the degree of polymerization include, for example, increasing the reaction time and/or reaction temperature for oxidation. As another method, the degree of polymerization of oxidized cellulose can be adjusted by the stirring conditions of the reaction system during the oxidation reaction. For example, under conditions in which the reaction system is sufficiently homogenized using a stirring blade or the like, the oxidation reaction tends to proceed smoothly and the degree of polymerization tends to decrease. On the other hand, under conditions where the reaction system tends to be insufficiently stirred, such as by stirring with a stirrer, the reaction tends to be uneven, making it difficult to sufficiently reduce the degree of polymerization of the cellulose fibers. In addition, the degree of polymerization of oxidized cellulose tends to vary depending on the selection of raw material cellulose. Therefore, the degree of polymerization of oxidized cellulose can be adjusted by selecting a cellulosic raw material. In this specification, the degree of polymerization of oxidized cellulose is the average degree of polymerization (viscosity average degree of polymerization) measured by the viscosity method. The degree of polymerization can be measured, for example, according to the following [measurement of viscosity-average degree of polymerization].
[Measurement of viscosity average degree of polymerization]
Oxidized cellulose is added to an aqueous solution of sodium borohydride adjusted to pH 10, and reduction treatment is performed at 25° C. for 5 hours. The amount of sodium borohydride is 0.1 g per 1 g of oxidized cellulose. After the reduction treatment, solid-liquid separation is performed by suction filtration, washing with water is performed, and the obtained oxidized cellulose is freeze-dried. After adding 0.04 g of dried oxidized cellulose to 10 ml of pure water and stirring for 2 minutes, 10 ml of 1M copper ethylenediamine solution is added and dissolved. After that, the flow-down time of the blank solution and the flow-down time of the cellulose solution are measured at 25° C. using a capillary type viscometer. Relative viscosity (η _r ), specific viscosity (η _sp ), The intrinsic viscosity ([η]) is determined sequentially, and the degree of polymerization (DP) of the oxidized cellulose is calculated from the viscometry formula.
η _r = η/η ₀ = t/t0
η _sp =η _r −1
[η]= _ηsp /(100×c(1+ _0.28ηsp ))
DP = 175 x [η]

The oxidized cellulose has potassium salt-type carboxyl groups. At least part of the carboxy groups of the present oxidized cellulose may be potassium salt-type carboxy groups. Here, "at least a portion" is usually 30% or more, 40% or more, 50% or more, or more than 50% of the total amount of carboxyl groups in oxidized cellulose. may be 60% or more, may be 70% or more, may be 80% or more, may be 90% or more, may be 95% or more , 98% or more. From the viewpoint of making the oxidized cellulose more excellent in fibrillating property and further maintaining the fluidity of the nanocellulose, it is preferable that more than 50% of the carboxyl groups in the oxidized cellulose form a salt with potassium ions. , more preferably 90% or more, still more preferably 95% or more, even more preferably 98% or more, and particularly preferably 100%.
The method for converting at least a part of the carboxy groups into potassium salt-type carboxy groups is described in detail in [Method for Producing Oxidized Cellulose] described later. and a method of treating the oxidized cellulose or nanocellulose obtained by the reaction with a potassium salt. Moreover, in the production of the present oxidized cellulose, it is preferable to use a potassium salt in an excess amount relative to the amount of carboxyl groups in the reaction system or post-reaction treatment. In addition, in the reaction system or post-reaction treatment, the amount of potassium salt-type carboxyl groups tends to increase as the pH increases. For example, by adjusting the pH to 7 or higher, more than 50% of the carboxyl groups in the oxidized cellulose are in the potassium salt form.

According to the present oxidized cellulose, defibration can be sufficiently advanced even under mild defibration conditions, and nanocellulose having a sufficiently small fiber width can be obtained. In addition, since the obtained nanocellulose has a sufficiently small fiber width, the cellulose fibers show little light scattering and the like when dispersed in a dispersion medium, and exhibit high light transmittance. The present oxidized cellulose is excellent in defibration property and tends to have a high light transmittance before the fibrillation treatment.
The light transmittance of the 0.1% by mass aqueous dispersion of the oxidized cellulose is preferably 80% or more, more preferably 85% or more, and still more preferably 88% or more.

An aqueous dispersion of the oxidized cellulose having a concentration of 5% by mass is treated with an ultrasonic homogenizer for 10 seconds to obtain a fibrillation treatment liquid. The light transmittance of the aqueous dispersion obtained by adjusting the solid content concentration to 0.1% by mass from the fibrillation treatment liquid is preferably 90% or more, more preferably 95% or more, and still more preferably 98% or more. is.
The nanocellulose or nanocellulose aqueous dispersion of the present invention obtained from the present oxidized cellulose also has a light transmittance of preferably 90% or more, more preferably 95% or more at a nanocellulose concentration of 0.1% by mass. , more preferably 98% or more.

The light transmittance is a value measured with a spectrophotometer at a wavelength of 660 nm. The temperature at which the light transmittance is measured is not particularly limited, but it is usually preferable to carry out the measurement at a temperature of 15 to 30°C. The measurement of the light transmittance specifically follows the measurement method described in the Examples.

[Method for producing oxidized cellulose]
The present oxidized cellulose can be produced by a method including a step of oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof.

The cellulosic raw material is not particularly limited as long as it is mainly composed of cellulose, and examples thereof include pulp, natural cellulose, regenerated cellulose, and fine cellulose depolymerized by mechanically treating cellulose. As the cellulosic raw material, commercially available products such as crystalline cellulose made from pulp can be used as they are. In addition, unused biomass containing a large amount of cellulose components, such as bean curd refuse and soybean hulls, may be used as a raw material. In addition, the cellulosic raw material may be preliminarily treated with an alkali of an appropriate concentration for the purpose of facilitating penetration of the oxidizing agent to be used into the raw pulp.

As a method for producing the present oxidized cellulose, in order to make the carboxy group a potassium type, production method I: a method using a reagent containing potassium as an oxidizing agent and a pH adjuster, production method II: hypochlorous acid or A method of treating an oxide obtained by oxidation with the salt with a potassium salt and the like can be mentioned.
Manufacturing method I and manufacturing method II are described below.

(Manufacturing method I)
Potassium hypochlorite is used as the hypochlorous acid or its salt used for oxidizing the cellulosic raw material.
A method for producing the present oxidized cellulose by oxidation of a cellulosic raw material includes a method of mixing a cellulosic raw material and a reaction solution containing potassium hypochlorite. The reaction solution preferably contains water as a solvent in terms of ease of handling and resistance to side reactions. The effective chlorine concentration of potassium hypochlorite in the reaction solution is preferably 1 to 30% by mass, more preferably 3 to 25% by mass, even more preferably 3 to 20% by mass. ~20 wt% is even more preferred, 5 to 18 wt% is even more preferred, and 6 to 18 wt% is even more preferred. When the effective chlorine concentration of the reaction solution is within the above range, the amount of carboxyl groups in the oxidized cellulose can be sufficiently increased, and the oxidized cellulose can be easily defibrated when obtaining nanocellulose.

The oxidation reaction of the cellulosic raw material with potassium hypochlorite is preferably carried out while adjusting the pH in the range of 5.0 to 14.0. Moreover, it is preferable to use potassium hydroxide for pH adjustment. Within this range, the oxidation reaction of the cellulosic raw material can be sufficiently advanced, and the amount of carboxyl groups in the oxidized cellulose can be sufficiently increased. This makes it possible to easily defibrate the oxidized cellulose. The pH of the reaction system is more preferably 6.0 or higher, still more preferably 7.0 or higher, and even more preferably 8.0 or higher. The upper limit of the pH of the reaction system is more preferably 13.5 or less, still more preferably 13.0 or less. The pH range of the reaction system is more preferably 7.0 to 14.0, still more preferably 8.0 to 13.5.

Using the solution containing oxidized cellulose obtained by the above reaction, a known isolation treatment such as filtration is performed, and if necessary, purification is performed to obtain an oxide of the cellulosic raw material with hypochlorous acid or a salt thereof. The oxidized cellulose may be obtained as such, the dispersion containing the oxidized cellulose obtained by the above reaction may be directly subjected to defibration treatment, or the above dispersion may be used as it is.

In addition, before the isolation treatment such as filtration, from the viewpoint of improving the filterability and yield of the isolation treatment, an acid is added to the solution containing oxidized cellulose, for example, the pH is adjusted to 4.0 or less, and the acid is generated by oxidation. At least part of the carboxyl groups may be in the proton type (--COOH).
In the infrared absorption spectrum, the proton form has a peak around 1720 cm ^-1 and the salt form has a peak around 1600 cm ^-1 , so they can be distinguished from each other.

In the solution containing oxidized cellulose, when the pH is set to 4.0 or less for the isolation treatment, for example, potassium hydroxide or the like is added in order to improve the handleability when used for the subsequent fibrillation treatment. A base containing potassium is added to adjust the pH to 6.0 or higher, and at least some of the carboxy groups are converted to the potassium form (-COO ^- K ⁺ ). A base containing potassium such as potassium hydroxide is preferably used in an excess amount relative to the amount of carboxyl groups in the oxidized cellulose.
Also, the solution containing oxidized cellulose may be made into a composition containing oxidized cellulose by, for example, replacing the solvent thereof.

(Manufacturing method II)
Hypochlorous acid or salts thereof used for oxidizing cellulosic raw materials include hypochlorous acid water, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and ammonium hypochlorite. is mentioned. Among these, sodium hypochlorite is preferable from the viewpoint of ease of handling.

A method for producing the present oxidized cellulose by oxidation of a cellulosic raw material includes a method of mixing a cellulosic raw material and a reaction solution containing hypochlorous acid or a salt thereof. The reaction solution preferably contains water as a solvent in terms of ease of handling and resistance to side reactions. The effective chlorine concentration of hypochlorous acid or a salt thereof in the reaction solution is preferably 6 to 43% by mass, more preferably 7 to 43% by mass, even more preferably 10 to 43% by mass. , 14 to 43% by mass. When the effective chlorine concentration of the reaction solution is within the above range, the amount of carboxyl groups in the oxidized cellulose can be sufficiently increased, and the oxidized cellulose can be easily defibrated when obtaining nanocellulose.

From the viewpoint of efficiently and sufficiently increasing the amount of carboxyl groups in oxidized cellulose, the effective chlorine concentration of the reaction solution is more preferably 15% by mass or more, still more preferably 18% by mass or more, and even more preferably 20% by mass. % by mass or more. In addition, from the viewpoint of suppressing excessive decomposition of cellulose during fibrillation, the effective chlorine concentration of the reaction solution is more preferably 40% by mass or less, and still more preferably 38% by mass or less. Regarding the range of effective chlorine concentration of the reaction liquid, the aforementioned lower limit and upper limit can be appropriately combined. The effective chlorine concentration range is more preferably 16 to 43% by mass, and still more preferably 18 to 40% by mass.

The aspect of the pH range in Production Method II is the same as the pH range in (Production Method I). The base used for pH adjustment is not particularly limited, and sodium hydroxide, potassium hydroxide and the like can be used, for example.

Hereinafter, the method for producing the present oxidized cellulose will be further described with reference to the case where sodium hypochlorite is used as hypochlorous acid or a salt thereof.
When the cellulosic raw material is oxidized using sodium hypochlorite, the reaction solution is preferably an aqueous sodium hypochlorite solution. As a method of adjusting the effective chlorine concentration of the sodium hypochlorite aqueous solution to the desired concentration (for example, the desired concentration: 6% by mass to 43% by mass), sodium hypochlorite with a lower effective chlorine concentration than the desired concentration A method of concentrating an aqueous solution, a method of diluting a sodium hypochlorite aqueous solution with a higher effective chlorine concentration than the target concentration, and sodium hypochlorite crystals (e.g., sodium hypochlorite pentahydrate) as a solvent The method of dissolving, etc. are mentioned. Among these, adjusting the effective chlorine concentration as an oxidizing agent by a method of diluting a sodium hypochlorite aqueous solution or a method of dissolving sodium hypochlorite crystals in a solvent is less self-decomposing (i.e., It is preferable because the decrease in the available chlorine concentration is small) and the adjustment of the available chlorine concentration is simple.
The method of mixing the cellulose-based raw material and the aqueous sodium hypochlorite solution is not particularly limited, but from the viewpoint of ease of operation, it is preferable to add the cellulose-based raw material to the aqueous sodium hypochlorite solution and mix.

Using the solution containing oxidized cellulose obtained by the above reaction, a known isolation treatment such as filtration is performed, and if necessary, purification is performed to obtain an oxide of the cellulosic raw material with hypochlorous acid or a salt thereof. Oxidized cellulose can be obtained as In addition, before the isolation treatment such as filtration, from the viewpoint of improving the filterability and yield of the isolation treatment, an acid is added to the solution containing oxidized cellulose, for example, the pH is adjusted to 4.0 or less, and the acid is generated by oxidation. At least a part of the carboxyl group can be converted from a salt form (-COO ^- X ⁺ : X ⁺ indicates a cation such as sodium) to a proton form (-COOH).

Especially when sodium hypochlorite is used in production method II, a base containing potassium such as potassium hydroxide is added to the obtained oxidized cellulose or the proton-type oxidized cellulose to adjust the pH to 6.0 or higher, and carboxyl At least part of the group is in the salt form (-COO ^- X ⁺ : X ⁺ indicates a cation such as sodium, lithium, etc.). Also, the solution containing oxidized cellulose may be made into a composition containing oxidized cellulose by, for example, replacing the solvent thereof. A base containing potassium such as potassium hydroxide is preferably used in an excess amount relative to the amount of carboxyl groups in the oxidized cellulose.

As used herein, the available chlorine concentration of hypochlorous acid or a salt thereof is defined as follows. Hypochlorous acid is a weak acid that exists as an aqueous solution, and hypochlorites are compounds in which hydrogen in hypochlorous acid is replaced with other cations.
For example, since sodium hypochlorite, which is hypochlorite, exists in a solvent (preferably in an aqueous solution), the concentration is measured as the amount of available chlorine in the solution, not the concentration of sodium hypochlorite. . Here, regarding the effective chlorine of sodium hypochlorite, the oxidizing power of the divalent oxygen atom generated by the decomposition of sodium hypochlorite is equivalent to 2 atomic equivalents of monovalent chlorine, so sodium hypochlorite A bound chlorine atom of (NaClO) has the same oxidizing power as two atoms of unbound chlorine (Cl ₂ ), so available chlorine=2×(chlorine in NaClO). As a specific measurement procedure, first, the sample is accurately weighed, water, potassium iodide and acetic acid are added and left to stand, and the released iodine is titrated with a sodium thiosulfate solution using an aqueous starch solution as an indicator to measure the effective chlorine concentration. do. Potassium hypochlorite can also be measured by the same method as above.

The following reaction conditions are aspects common to Production Method I and Production Method II.
In order to efficiently proceed with the oxidation reaction of the cellulosic raw material, it is preferable to stir the mixture of the cellulosic raw material and the sodium hypochlorite aqueous solution during the oxidation reaction. Examples of stirring methods include magnetic stirrers, stirring rods, stirrers with stirring blades (three-one motor), homomixers, disper-type mixers, homogenizers, and external circulation stirring. Among these, shear type stirrers such as homomixers and homogenizers, stirrer with stirring blades, and A method using one or more of disper-type mixers is preferred, and a method using a stirrer with stirring blades is particularly preferred. When a stirrer with stirring blades is used, a device equipped with known stirring blades such as propeller blades, paddle blades, and turbine blades can be used as the stirrer. When using a stirrer with stirring blades, it is preferable to stir at a rotational speed of 50 to 300 rpm.
The reaction temperature in the oxidation reaction is preferably 15°C to 100°C, more preferably 20°C to 90°C. During the reaction, the pH of the reaction system decreases as carboxyl groups are generated in the cellulosic raw material by the oxidation reaction. Therefore, from the viewpoint of allowing the oxidation reaction to proceed efficiently, an alkaline agent (such as sodium hydroxide or potassium hydroxide) or an acid (such as hydrochloric acid) is added to the reaction system to adjust the pH of the reaction system. It is preferable to carry out the oxidation reaction while The reaction time of the oxidation reaction can be set according to the degree of progress of the oxidation, but is preferably about 15 minutes to 50 hours. When the pH of the reaction system is set to 10 or higher, it is preferable to set the reaction temperature to 30° C. or higher and/or the reaction time to 30 minutes or longer.

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

《Nanocellulose》
The nanocellulose of the present disclosure (hereinafter also referred to as "the present nanocellulose") can be obtained by fibrillating oxidized cellulose obtained by oxidizing a cellulosic raw material with an oxidizing agent, if necessary, to nanoize it. That is, the present nanocellulose can be produced by a method including a step of oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof, and a step of defibrating the oxidized cellulose obtained by the step. The oxidation step is as described above.
In addition, the present oxidized cellulose can be nanoized into nanocellulose by defibrating and stirring appropriately in the presence of other components. A composition containing nanocellulose and other components can thereby be obtained.
In the present specification, the process of nanoizing oxidized cellulose to obtain nanocellulose is referred to as defibration process.

Examples of the method for defibrating oxidized cellulose include a method using mechanical fibrillation. Here, nanocellulose is a general term for nano-ized cellulose, and includes fine cellulose fibers (also referred to as cellulose nanofibers and CNF), cellulose nanocrystals, and the like.

The defibration treatment can be performed by applying a shearing force to the oxidized cellulose by stirring or the like, and any operation that disperses the nanocellulose can be performed. As defibration treatment, for example, a velocity field and velocity fluctuation of arbitrary strength; collision with inclusions and obstacles; ultrasonic waves; pressure load; and the like can be used. A submerged disperser can be suitably used for such a dispersing operation.
The submerged disperser is not particularly limited, and examples thereof include a homomixer, a magnetic stirrer, a stirring rod, a stirrer with stirring blades, a disper-type mixer, a homogenizer, an external circulation stirrer, a rotation-revolution stirrer, a vibrating stirrer, A method using an ultrasonic disperser or the like can be mentioned. Examples of the submerged disperser include, in addition to the devices described above, rotary shear type stirrers, colloid mills, roll mills, pressure homogenizers, container-driven mills, medium stirring mills, and the like. Furthermore, a kneader can be used as the submerged disperser.

A rotary shear type agitator is a device that disperses a material to be agitated by passing it through a gap between a rotor blade and an outer cylinder.
A colloid mill is a device that disperses by shear flow in the gap between rotating and stationary discs. Roll mills distribute shear and compression forces through the gaps between multiple rotating rolls.
A pressure homogenizer is used as a disperser that discharges slurry or the like from pores at high pressure, and is also called a pressure injection disperser. A high pressure homogenizer is preferable as the pressure homogenizer. A high-pressure homogenizer is, for example, a homogenizer capable of discharging slurry at a pressure of 10 MPa or higher, preferably 100 MPa or higher. Examples of high-pressure homogenizers include counter-collision-type high-pressure homogenizers such as microfluidizers and wet jet mills.
A container-driven mill is a device in which media such as balls in a container are dispersed by collision and friction. A medium agitation mill is a device that uses media such as balls and beads to disperse by the impact force and shear force of the media.
A kneader is a device that performs an operation (also called kneading or kneading) to wet powder with a liquid. a Banbury mixer (closed system, a device for dispersing under pressure); a screw extruder, a co-kneader, an extruder, and other extrusion type kneaders;
These devices may be used singly or in combination of two or more.

The defibration treatment is preferably carried out while the present oxidized cellulose is mixed with a dispersion medium. The dispersion medium is not particularly limited and 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 dimethylsulfoxide. As the solvent, one of these may be used alone, or two or more thereof may be used in combination.

Among the above dispersion media, alcohols include methanol, ethanol, isopropanol, isobutanol, sec-butyl alcohol, tert-butyl alcohol, methyl cellosolve, ethylene glycol and glycerin. Ethers include ethylene glycol dimethyl ether, 1,4-dioxane and tetrahydrofuran. Ketones include acetone and methyl ethyl ketone.

By using an organic solvent as a dispersion medium in the defibration treatment, it becomes easy to isolate oxidized cellulose and nanocellulose obtained by defibrating it. Moreover, since the nanocellulose dispersed in the organic solvent is obtained, it becomes easy to mix with the resin soluble in the organic solvent, the resin raw material monomer, and the like. A nanocellulose dispersion obtained by dispersing nanocellulose obtained by fibrillation in a dispersion medium such as water and/or an organic solvent can be used for mixing with various components such as resins, rubbers, and solid particles. .

[Average fiber width]
The average fiber width of the present nanocellulose is preferably 1 to 200 nm. In particular, the present oxidized cellulose is suitable in that it is possible to obtain sufficiently nano-sized nanocellulose with an average fiber width of 1 to 20 nm, preferably 1 to 10 nm, and more preferably 1 to 5 nm by fibrillation. is. Moreover, when the average fiber width of the present nanocellulose is sufficiently small as 1 to 5 nm, the slurry containing this nanocellulose has a stabilized viscosity and good handleability and coatability. The average fiber width of the present nanocellulose is more preferably 4.8 nm or less, still more preferably 4.5 nm or less, and still more preferably 4.2 nm or less. From the standpoint of easy fibrillation, the lower limit of the average fiber width is not particularly set. However, if the average fiber width is less than 1 nm, the nanocellulose tends to have a non-uniform quality because it is close to a cellulose monomolecular form. Therefore, the average fiber width is preferably 1 nm or more, more preferably 1.5 nm or more.

[Average fiber length]
The average fiber length of the present nanocellulose is preferably 50 to 2000 nm. The average fiber length is more preferably 50 to 1000 nm, still more preferably 80 to 500 nm, still more preferably 80 to 250 nm, still more preferably 80 to 200 nm, still more preferably 100 to 200 nm. be.

[aspect ratio]
In the present nanocellulose, the aspect ratio (average fiber length/average fiber width) represented by the ratio of the average fiber width to the average fiber length is preferably 20-200. The aspect ratio is more preferably 30 or more, still more preferably 40 or more. Also, the aspect ratio is more preferably 180 or less, and even more preferably 150 or less.

The average fiber width and average fiber length are obtained by mixing nanocellulose and water so that the concentration of nanocellulose is approximately 1 to 10 ppm, and naturally drying the sufficiently diluted cellulose aqueous dispersion on a mica base material. Observe the shape of nanocellulose using a scanning probe microscope, randomly select an arbitrary number of fibers from the obtained image, set the cross-sectional height of the shape image = fiber width, and the perimeter ÷ 2 = fiber length It is a value calculated by Image processing software can be used to calculate such average fiber width and average fiber length. At this time, the image processing conditions are arbitrary, but there are cases where the values calculated for the same image differ depending on the image processing conditions. The range of the difference in values depending on the image processing conditions is preferably within the range of ±100 nm for the average fiber length. The range of difference in values depending on conditions is preferably within the range of ±10 nm for the average fiber width. A more detailed measurement method follows, for example, the following measurement method.
[Measurement of average fiber width and average fiber length]
Add pure water to the nanocellulose aqueous dispersion, dilute it 1000 to 1000000 times, dry it naturally on a mica substrate, and use a scanning probe microscope "MFP-3D infinity" manufactured by Oxford Asylum, AC mode. Then, we observe the shape of nanocellulose. The fiber length was analyzed by binarizing the obtained image using image processing software "ImageJ". For 100 or more fibers, the average fiber length is obtained by dividing the fiber length by 2. As for the fiber width, the software attached to "MFP-3D infinity" is used to find the average fiber width for 50 or more fibers by setting the cross-sectional height of the shape image=fiber width.

One aspect of the present invention is nanocellulose obtained by defibrating oxidized cellulose containing oxides of cellulosic raw materials, wherein the nanocellulose has an average fiber length of 50 to 2000 nm, and the nanocellulose is Nanocellulose having a potassium salt-type carboxyl group. Although this nanocellulose has an average fiber length within the above range, it is possible to suppress an increase in the viscosity of the nanocellulose, and to maintain fluidity when it is combined with other materials such as an organic solvent to form a slurry.
The average fiber length of nanocellulose is preferably 50 to 1000 nm, more preferably 80 to 500 nm, even more preferably 80 to 250 nm, still more preferably 80 to 200 nm, still more preferably 100 to 250 nm. 200 nm.
The nanocellulose is derived from oxidized cellulose containing oxides of cellulosic raw materials, but the oxidation method is not particularly limited as long as the oxidized cellulose has a carboxy group.
The detailed aspects and preferred aspects of the nanocellulose can be exemplified in the same manner as the <<oxidized cellulose>> and <<nanocellulose>> described above.

The nanocellulose described above and the nanocellulose dispersion containing the same can be applied to various uses. Specifically, for example, it may be used as a reinforcing material by being mixed with various materials (e.g., resin, fiber, rubber, etc.), and various uses (e.g., food, cosmetics, etc.) as a thickener or dispersant. medical products, paints, inks, etc.). Also, the nanocellulose dispersion can be formed into a film and used as various sheets or films. The fields to which the present nanocellulose and nanocellulose dispersions containing the same are applied are not particularly limited, and various fields such as automobile members, machine parts, electric appliances, electronic devices, cosmetics, medical products, building materials, daily necessities, stationery, etc. can be used in the manufacture of products of Further, for example, the nanocellulose of the present invention suppresses an increase in viscosity and maintains fluidity, and is therefore preferable from the aspect of ejection stability when used as an ink for water-based inkjet recording.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. In the following description, "parts" means "parts by mass" and "%" means "% by mass" unless otherwise specified.

[Example 1: Method using potassium hypochlorite]
300 g of an aqueous potassium hypochlorite solution having an available chlorine concentration of 5.6% by mass was placed in a glass container, and 35% by mass hydrochloric acid was added thereto and stirred to adjust the pH to 11.
The sodium hypochlorite aqueous solution is stirred at 200 rpm using a four-paddle blade with a stirrer (three-one motor, BL600) manufactured by Sintokagaku Co., Ltd., and heated to 50 ° C. in a water bath. As a system raw material, 3 g of pulp powder (VP-1) manufactured by TDI Co., Ltd. was added.
After supplying the cellulosic raw material, while maintaining the temperature at 50° C., the pH during the reaction was adjusted to 11 while adding 2 mol/L of potassium hydroxide, and the mixture was stirred for 3 hours under the same conditions using a stirrer. . The pH was controlled using a pH controller (Tokyo Glass Instruments Co., Ltd., FD-02). After completion of the reaction, solid-liquid separation and washing were performed by suction filtration to recover oxidized cellulose. The weight yield was calculated from the collected amount, and the amount of carboxy groups was measured by titration. The weight yield was 65% and the amount of carboxy groups was 0.5 g/mol. Since the pH of the reaction system was 11, the carboxyl group of the obtained oxidized cellulose was K-type.
Water was added so that the concentration of oxidized cellulose was 5% by mass to prepare 10 g, and fibrillated under the conditions of CYCLE 0.5 and AMPLITUDE 50 with Hielscher's "UP-400S" ultrasonic homogenizer to form a nanocellulose aqueous dispersion. got Samples are taken at predetermined time intervals, pure water is added to adjust the concentration of oxidized cellulose to 0.1% by mass, placed in a quartz cell with a thickness of 10 mm, and the light transmittance at a wavelength of 660 nm is measured using a spectrophotometer (JASCO V-550). It was measured. Light transmittance was measured at room temperature (in the range of about 20-26°C). In addition, 0 second in Table 1 is a value measured without fibrillation treatment. The average fiber length of the obtained nanocellulose was 130 nm. The average fiber length was measured in accordance with [Measurement of Average Fiber Width and Average Fiber Length] described above.
A 5% nanocellulose aqueous dispersion was placed in a glass container, 0.4, 0.8 and 1.0 mL of ethanol were added thereto and stirred for 10 seconds with a touch mixer. After allowing to stand still for 5 minutes, the container was turned upside down and it was visually confirmed whether or not the contents flowed down within 5 seconds. In addition, the viscosity of the 5% nanocellulose aqueous dispersion was measured using an "MCR301" rheometer manufactured by Anton Paar.

The effective chlorine concentration in the potassium hypochlorite aqueous solution was measured by the following method.
(Measurement of effective chlorine concentration in potassium hypochlorite aqueous solution)
1.00 g of an aqueous potassium hypochlorite solution was precisely weighed, 50 ml of pure water was added, 2 g of potassium iodide and 10 ml of acetic acid were added, immediately sealed and left in a dark place for 15 minutes. After standing for 15 minutes, the liberated iodine was titrated with a 0.1 mol/L sodium thiosulfate solution (indicator, starch test solution), and the titration amount was 15.80 ml. A blank test was performed separately and corrected. Since 1 ml of 0.1 mol/L sodium thiosulfate solution corresponds to 3.545 mg Cl, the effective chlorine concentration in the potassium hypochlorite aqueous solution is 5.6% by mass.

The amount of carboxyl groups in oxidized cellulose was measured by the following method.
(Measurement of carboxy group content)
0.1 M hydrochloric acid aqueous solution was added to 60 ml of the oxidized cellulose aqueous dispersion in which the concentration of oxidized cellulose was adjusted to 0.5% by mass to adjust the pH to 2.5. was measured until the electrical conductivity reached 11.0, and from the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid in which the change in electrical conductivity was moderate, the amount of carboxyl groups (mmol /g) was calculated.
Carboxy group amount = a (ml) x 0.05/mass of oxidized cellulose (g)

[Comparative Example 1]
The procedure of Example 1 was repeated except that sodium hypochlorite was used instead of potassium hypochlorite and sodium hydroxide was used instead of potassium hydroxide to obtain Na-type oxidized cellulose. The weight yield was 65% and the amount of carboxy groups was 0.5 g/mol. The average fiber length of the obtained nanocellulose was 120 nm.

After freeze-drying the oxidized cellulose obtained in the example, solid-state ¹³ C-NMR of a sample left at 23° C. and 50% RH for 24 hours or more was measured. It was confirmed to have a structure in which the hydroxyl group at the 3-position was oxidized and a carboxyl group was introduced. Measurement conditions for solid-state ¹³ C-NMR are shown below.
(1) Sample tube: Zirconia tube (4 mm diameter)
(2) Magnetic field strength: 9.4 T (1H resonance frequency: 400 MHz)
(3) MAS rotation speed: 15 kHz
(4) Pulse sequence: CPMAS method (5) Contact time: 3ms
(6) Waiting time: 5 seconds (7) Accumulation times: 10000 to 15000 times (8) Measuring device: JNM ECA-400 (manufactured by JEOL Ltd.)
Moreover, the fact that the oxidized cellulose obtained in each production example has a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized and a carboxyl group is introduced indicates that the model molecule of the oxidized cellulose is a sample. It was also confirmed from the results of two-dimensional NMR measurement.
In addition, since there was no change in spectral data between the solid ¹³ C-NMR of the cellulosic raw material and the solid ¹³ C-NMR of the oxidized cellulose, the hydroxyl group at the 6th position was not oxidized. , determined that hydroxyl groups remained in oxidized cellulose.

Table 1 shows the measurement results of the light transmittance in Example 1 and Comparative Example 1. It was found that the K-type oxidized cellulose had a higher light transmittance than the Na-type oxidized cellulose even for the same defibration time, and had better defibration properties.

Table 2 shows the results of fluidity evaluation of the gel when ethanol was added. The case where it ran down within 10 seconds was indicated by ◯, and the case where it did not flow down within 10 seconds was indicated by x. The fluidity of the gel formed when an organic solvent was added was found to be better with the K type.

Table 3 shows the viscosity measurement results. Viscosity was measured at a shear rate of 1 or 10 (1/s). The unit is Pa·s. The K type was found to have a lower viscosity.

[Example 2: Method for inducing potassium form after obtaining oxidized cellulose]
350 g of sodium hypochlorite pentahydrate crystals having an effective chlorine concentration of 42% by mass were placed in a glass container, and pure water was added and stirred to adjust the effective chlorine concentration to 21% by mass. 35% by mass hydrochloric acid was added thereto and stirred to obtain an aqueous sodium hypochlorite solution with a pH of 11.
The sodium hypochlorite aqueous solution is stirred at 200 rpm using a propeller-type stirring blade with a stirrer (three-one motor, BL600) manufactured by Sintokagaku Co., Ltd. After heating to 30 ° C. in a constant temperature water bath, cellulose As a system raw material, 50 g of pulp powder (VP-1) manufactured by TDI Co., Ltd. was added. After supplying the cellulosic raw material, the temperature was maintained at 30°C in the constant temperature water bath, and while maintaining the conditions in which the pH of the reaction system was adjusted to 11 while adding 48% by mass of sodium hydroxide, stirring was performed with a stirrer for 2 hours. went. After that, pure water was added to dilute the solution two-fold to suppress the progress of the oxidation reaction, thereby obtaining oxidized cellulose dispersed in water.
An aqueous solution of sodium sulfite was added to the obtained oxidized cellulose dispersed in water to reduce the residual excess sodium hypochlorite.
After that, hydrochloric acid was added to change the carboxy group of the cellulose oxide from the salt form (--COO ^- Na ⁺ ) to the proton form (--COOH), thereby obtaining an aqueous dispersion of pH 2.5. The pH was controlled using a pH controller (Tokyo Glass Instruments Co., Ltd., FD-02).
Solid-liquid separation and washing were performed on the obtained aqueous dispersion of pH 2.5. Specifically, the supernatant is removed by centrifugation (1000 G, 10 minutes) and decantation, and an operation of adding diluted hydrochloric acid of pH 2.5 equivalent to the removed amount and sufficiently stirring with a spoon to homogenize is repeated 8 times. The above centrifugation and decantation were repeated and finally the oxidized cellulose was obtained.
Then, 0.1 M potassium hydroxide was added to induce the carboxylic acid group from the proton form (--COOH) to the salt form (--COO ^- K ⁺ ) to obtain an aqueous dispersion with a pH of 10.8. Since the aqueous dispersion was adjusted to pH 10.8, the carboxyl group of the obtained oxidized cellulose is of K type.
Water was added so that the oxidized cellulose concentration was 4.5% by mass to prepare 10 g, and fibrillated under the conditions of CYCLE 0.5 and AMPLITUDE 50 with Hielscher's "UP-400S" ultrasonic homogenizer to make nanocellulose water. A dispersion was obtained. The average fiber length of the obtained nanocellulose was 170 nm. The average fiber length was measured in accordance with [Measurement of Average Fiber Width and Average Fiber Length] described above.
A 4.5% by mass nanocellulose aqueous dispersion was placed in a glass container, 0.4, 0.8, and 1.0 mL of ethanol were added thereto and stirred for 10 seconds with a touch mixer. After allowing to stand still for 5 minutes, the container was turned upside down and it was visually confirmed whether or not the liquid flowed down within 5 seconds. In addition, the viscosity of the 4.5% nanocellulose aqueous dispersion was measured using an "MCR301" rheometer manufactured by Anton Paar.

In addition, the effective chlorine concentration in the sodium hypochlorite aqueous solution was measured in accordance with the above-described (measurement of the effective chlorine concentration in the potassium hypochlorite aqueous solution), and the sodium hypochlorite pentahydrate used in Example 2. The same procedure was carried out using an aqueous solution of hydrated crystals.

[Comparative Example 2]
The procedure was the same as in Example 2, except that 0.1M sodium hydroxide was used instead of 0.1M potassium hydroxide to obtain Na-type oxidized cellulose. The average fiber length of the obtained nanocellulose was 170 nm.

Table 4 shows the results of fluidity evaluation of the gel when ethanol was added. The case where it ran down within 10 seconds was indicated by ◯, and the case where it did not flow down within 10 seconds was indicated by x. The fluidity of the gel formed when an organic solvent was added was found to be better with the K type.

Table 5 shows the viscosity measurement results. Viscosity was measured at a shear rate of 1 or 10 (1/s). The unit is Pa·s. The K type was found to have a lower viscosity.

Claims (8)

Oxidized cellulose containing an oxide of a cellulosic raw material by hypochlorous acid or a salt thereof and substantially free of an N-oxyl compound,
The oxidized cellulose has a potassium salt-type carboxy group,
oxidized cellulose. The light transmittance of the 0.1% by mass aqueous dispersion of oxidized cellulose is 80% or more.
The oxidized cellulose of claim 1. The light transmittance measured by the following <conditions> is 90% or more,
Oxidized cellulose according to claim 1 or 2:
<Condition>
An aqueous dispersion of oxidized cellulose having a concentration of 5% by mass is treated with an ultrasonic homogenizer for 10 seconds to obtain a fibrillation treatment liquid;
The light transmittance of an aqueous dispersion adjusted to have a solid content concentration of 0.1% by mass is measured from the fibrillation treatment liquid. The carboxy group amount is 0.30 to 2.0 mmol / g,
Oxidized cellulose according to any one of claims 1-3. An oxidized cellulose dispersion in which the oxidized cellulose according to any one of claims 1 to 4 is dispersed in a dispersion medium. Nanocellulose obtained by defibrating the oxidized cellulose according to any one of claims 1 to 4. Nanocellulose obtained by defibrating oxidized cellulose containing oxides of cellulosic raw materials,
The average fiber length of the nanocellulose is 50 to 2000 nm,
The nanocellulose has a potassium salt-type carboxy group,
nanocellulose. A nanocellulose dispersion in which the nanocellulose according to claim 6 or 7 is dispersed in a dispersion medium.