JP7316750B2 - Method for producing hydrophobized cellulose nanofiber dispersion - Google Patents

Description

TECHNICAL FIELD The present invention relates to hydrophobized cellulose nanofibers and methods for producing the same.

2,2,6,6-tetramethyl-1-piperidine-N-oxyl (hereinafter sometimes referred to as “TEMPO”) catalyst is used as a method for producing oxidized cellulose nanofibers using natural fiber materials such as cellulose as raw materials. A method of oxidizing in the presence of is known (Patent Document 1).
Since the oxidized cellulose nanofibers obtained by this production method are hydrophilic, they have low compatibility with hydrophobic synthetic polymers such as polyethylene terephthalate (PET) and polylactic acid (PLA). As a method of obtaining a composite material with these hydrophobic synthetic polymers, a method of binding a hydrophobizing agent to oxidized cellulose nanofibers is known (Patent Document 2). According to this production method, a hydrophobic cellulose nanofiber dispersion in which linear or branched molecules having a molecular weight of 300 or more are bound to cellulose molecules via carboxyl groups and amino groups is obtained, and has affinity with hydrophobic polymer materials. It is said that it has excellent properties and can easily form a composite with a polymer material.

Japanese Unexamined Patent Application Publication No. 2008-001728 WO2013/077354

In the method for producing a hydrophobized cellulose nanofiber dispersion disclosed in Patent Document 2, it is difficult to wash and dehydrate an aqueous dispersion of oxidized cellulose nanofibers after defibration. Washing and dehydration are carried out by replacing the solvent with an organic solvent before the addition step of the agent. In this solvent replacement step, solvent replacement is performed by performing dispersion and washing with an organic solvent multiple times. Therefore, there is a problem that the yield of the obtained hydrophobized cellulose nanofibers is reduced. Moreover, in order to remove the unreacted substances remaining after the reaction with the hydrophobizing agent, it is necessary to re-disperse with an organic solvent and wash several times, which complicates the process and reduces the yield. Furthermore, from the viewpoint of safety, an aqueous dispersion medium is desired, but in order to disperse in an aqueous system, it is necessary to replace the organic solvent with water, which complicates the process and further reduces the yield. The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a method for producing a hydrophobized cellulose nanofiber dispersion with improved yield.

The hydrophobized cellulose nanofiber dispersion of the present invention is provided by the following [1] to [6].
[1]: A method for producing a hydrophobized cellulose nanofiber dispersion having the following steps.
(Step 1): A step of treating a cellulose raw material in a reaction solution containing an N-oxyl compound and a co-oxidant to obtain a dispersion of oxidized cellulose fibers (Step 2): The oxidized cellulose fibers obtained in Step 1 Step of adding an acid to the dispersion to substitute at least part of the carboxylate groups in the oxidized cellulose fibers with carboxyl groups (step 3): the dispersion of oxidized cellulose fibers having carboxyl groups obtained in step 2. A step of adding a compound having an amino group (hydrophobizing agent) to obtain a dispersion of hydrophobized cellulose fibers (step 4): defibrating the hydrophobized cellulose fibers in the dispersion obtained in step 3 Step [2]: The method for producing a hydrophobized cellulose nanofiber dispersion according to Claim 1, wherein no washing step is included between the steps 2 and 3.
[3]: The method for producing a hydrophobized cellulose nanofiber dispersion liquid according to [1] or [2], wherein the compound having an amino group in the step 3 is a linear compound having an average molecular weight of 300 or more. .
[4]: The method for producing a hydrophobized cellulose nanofiber dispersion according to any one of [1] to [3], wherein the compound having an amino group is polyethylene glycol amine.
[5]: The method for producing a hydrophobized cellulose nanofiber dispersion according to any one of [1] to [4], wherein the dispersion medium of the hydrophobized cellulose nanofiber dispersion is water or an aqueous organic solvent. .
[6]: The method for producing a hydrophobized cellulose nanofiber dispersion according to any one of [1] to [4], wherein the dispersion medium of the hydrophobized cellulose nanofiber dispersion is an organic solvent.

According to the present invention, it is possible to provide a method for producing a hydrophobized cellulose nanofiber dispersion with improved yield.

The hydrophobized cellulose nanofiber dispersion of the present invention is provided by the following [1] to [6].
[1]: A method for producing a hydrophobized cellulose nanofiber dispersion having the following steps.
(Step 1): A step of treating a cellulose raw material in a reaction solution containing an N-oxyl compound and a co-oxidant to obtain a dispersion of oxidized cellulose fibers (Step 2): The oxidized cellulose fibers obtained in Step 1 Step of adding an acid to the dispersion to substitute at least part of the carboxylate groups in the oxidized cellulose fibers with carboxyl groups (step 3): the dispersion of oxidized cellulose fibers having carboxyl groups obtained in step 2. A step of adding a compound having an amino group (hydrophobizing agent) to obtain a dispersion of hydrophobized cellulose fibers (step 4): defibrating the hydrophobized cellulose fibers in the dispersion obtained in step 3 Step [2]: The method for producing a hydrophobized cellulose nanofiber dispersion according to Claim 1, wherein no washing step is included between the steps 2 and 3.
[3]: The method for producing a hydrophobized cellulose nanofiber dispersion liquid according to [1] or [2], wherein the compound having an amino group in the step 3 is a linear compound having an average molecular weight of 300 or more. .
[4]: The method for producing a hydrophobized cellulose nanofiber dispersion according to any one of [1] to [3], wherein the compound having an amino group is polyethylene glycol amine.
[5]: The method for producing a hydrophobized cellulose nanofiber dispersion according to any one of [1] to [4], wherein the dispersion medium of the hydrophobized cellulose nanofiber dispersion is water or an aqueous organic solvent. .
[6]: The method for producing a hydrophobized cellulose nanofiber dispersion according to any one of [1] to [4], wherein the dispersion medium of the hydrophobized cellulose nanofiber dispersion is an organic solvent.

<Step 1: Oxidation>
The oxidation step includes a method of oxidation in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides or mixtures thereof. According to this method, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized, and oxidized cellulose fibers having mainly carboxylate groups ( ^--COO.sup.- ) on the surface can be obtained. The concentration of the cellulosic raw material during the reaction is not particularly limited, but is preferably 5% by weight or less.

- Cellulose-based raw materials -
The origin of the cellulosic raw material is not particularly limited, but for example, plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (e.g., unbleached softwood kraft pulp (NUKP), bleached softwood kraft) Pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP) thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (e.g. sea squirts), algae, microorganisms (e.g. acetic acid bacteria (Acetobacter)), microbial products, etc. The cellulosic raw material used in the present invention may be any one of them. It may be a combination of two or more, preferably a plant- or microorganism-derived cellulosic raw material (eg, cellulose fiber), more preferably a plant-derived cellulosic raw material (eg, cellulose fiber).

The fiber diameter of the cellulose fiber raw material is not particularly limited, but the number average fiber diameter of softwood kraft pulp, which is a general pulp, is usually about 10 to 40 μm, and the number average fiber diameter of hardwood kraft pulp is usually about 10 to 30 μm. In the case of other pulps, those that have undergone general refining are about 50 μm. For example, in the case of refining a chip or the like having a size of several cm, it is preferable to perform a mechanical treatment with a disaggregator such as a refiner or a beater to reduce the size to about 50 μm.

-N-oxyl compound-
An N-oxyl compound means a compound capable of generating a nitroxy radical. Examples of N-oxyl compounds include 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). As the N-oxyl compound, any compound can be used as long as it promotes the desired oxidation reaction.

The amount of the N-oxyl compound to be used is not limited as long as it is a catalyst amount capable of oxidizing the raw material cellulose. For example, it is preferably 0.01 mmol or more, more preferably 0.05 mmol or more, relative to 1 g of absolutely dry cellulose. The upper limit is preferably 10 mmol or less, more preferably 1 mmol or less, and even more preferably 0.5 mmol or less. Therefore, the amount of the N-oxyl compound used is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and even more preferably 0.05 to 0.5 mmol, relative to 1 g of absolute dry cellulose.

-Bromide-
Bromide is a compound containing bromine, and examples thereof include alkali metal bromides such as sodium bromide that can be dissociated and ionized in water. Also, iodides are compounds containing iodine, and examples thereof include alkali metal iodides. The amount of bromide or iodide to be used can be selected within a range capable of promoting the oxidation reaction. The total amount of bromide and iodide is preferably 0.1 mmol or more, more preferably 0.5 mmol or more, relative to 1 g of absolute dry cellulose, for example. The upper limit is preferably 100 mmol or less, more preferably 10 mmol or less,
5 mmol or less is more preferable. Therefore, the total amount of bromide and iodide is preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, even more preferably 0.5 to 5 mmol, per 1 g of absolute dry cellulose.

-Oxidant-
Examples of the oxidizing agent include, but are not limited to, halogens, hypohalous acids, halogenous acids, perhalogenates, salts thereof, halogen oxides, and peroxides. Among them, hypohalous acid or a salt thereof is preferable, hypochlorous acid or a salt thereof is more preferable, and sodium hypochlorite is even more preferable, because it is inexpensive and has a low environmental load. The amount of the oxidizing agent used is preferably 0.5 mmol or more, more preferably 1 mmol or more, and even more preferably 3 mmol or more. The upper limit is preferably 500 mmol or less, more preferably 50 mmol or less, and even more preferably 25 mmol or less. Therefore, the amount of the oxidizing agent used is preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, per 1 g of absolute dry cellulose.
~25mmol is more preferred, and 3-10mmol is most preferred. When using an N-oxyl compound, the amount of oxidizing agent used is 1 mol per 1 mol of the N-oxyl compound.
The above is preferable. The upper limit is preferably 40 mol. Therefore, the amount of the oxidizing agent to be used is preferably 1-40 mol per 1 mol of the N-oxyl compound.

Conditions such as pH and temperature during the oxidation reaction are not particularly limited, and generally the reaction proceeds efficiently even under relatively mild conditions. The reaction temperature is preferably 4°C or higher, more preferably 15°C or higher. The upper limit is preferably 40°C or lower, more preferably 30°C or lower. Therefore, the reaction temperature is preferably 4 to 40°C, and may be about 15 to 30°C, that is, room temperature. The pH of the reaction solution is preferably 8 or higher, more preferably 10 or higher. The upper limit is preferably 12 or less, more preferably 11 or less. Therefore, the pH of the reaction solution is preferably about 8-12, more preferably about 10-11. Normally, carboxyl groups are generated in cellulose as the oxidation reaction progresses, so the pH of the reaction solution tends to decrease. Therefore, in order to allow the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution within the above range. The reaction medium for oxidation is preferably water because of its ease of handling and the fact that side reactions are less likely to occur.

The reaction time in the oxidation reaction can be appropriately set according to the progress of oxidation, and is usually 0.5 hours or longer. The upper limit is usually 6 hours or less, preferably 4 hours or less. Therefore, the reaction time for oxidation is usually 0.5 to 6 hours, for example, about 0.5 to 4 hours.

Oxidation may be carried out in two or more steps. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the reaction in the first step, again under the same or different reaction conditions, the reaction can be efficiently It can be oxidized well.

The amounts of carboxylate groups, carboxyl groups, and aldehyde groups mainly contained in the oxidized cellulose can be adjusted by controlling the amount of the oxidizing agent added and the reaction time.

An example of a method for measuring the amount of (carboxylate group+carboxyl group) is described below. Prepare 60 ml of 0.5% by weight slurry (aqueous dispersion) of oxidized cellulose, add 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.4, and then drop 0.05 N sodium hydroxide aqueous solution to adjust the pH to 11. It can be calculated from the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid, where the change in conductivity is gradual, using the following formula:
Carboxyl group amount [mmol/g oxidized cellulose or cellulose nanofiber] = a
[ml]×0.05/mass of oxidized cellulose [g].

The obtained oxidized cellulose fibers do not need to be particularly washed before being sent to the replacement step described later, but they can be washed with distilled water or the like.

<Step 2: Substitution>
A carboxylate group ( ^--COO.sup.- ) contained in the oxidized cellulose fiber is replaced with a carboxyl group (--COOH group). Oxidized cellulose fibers having carboxylate groups on their surfaces can well disperse cellulose nanofibers in water due to charge repulsion between carboxylate groups. However, since many organic solvents generally have a lower polarity than water, the degree of ionization described above may be low in organic solvents, and cellulose nanofibers tend to aggregate and gel.

Therefore, in the present invention, a hydrophobic polymer such as PET or PLA is obtained by exchanging the counterion of the carboxylate group with a linear molecule or branched molecule (branched molecule) that easily exhibits hydrophobicity. We decided to increase the affinity with the material.

In step 2, as a pretreatment for the treatment of exchanging with linear or branched molecules, the carboxylate groups (—COO ⁻ ) contained in the oxidized cellulose fibers are replaced with carboxyl groups (—COOH groups) to form linear chains. It is transformed into a structure that can be easily exchanged with a branched molecule.

In the case of the present embodiment, the carboxylate groups contained in the oxidized cellulose fibers are substituted with carboxyl groups. to manage.

The retention time is set according to the type of acid added, the pH of the acid solution, the content of oxidized cellulose fibers, and the like. If the pH of the acidic solution is constant, the substitution rate with carboxyl groups increases as the retention time increases, and changes monotonously with changes in retention time. . The ratio of carboxylate groups to carboxyl groups in the treated oxidized cellulose fibers can be measured using an analyzer such as FT-IR.

In step 2, the type of acid is not particularly limited as long as the aqueous dispersion of oxidized cellulose fibers can be maintained acidic. Any of organic acids such as malic acid, lactic acid, adipic acid, sebacic acid, sodium sebacate, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid and gluconic acid can be used. Hydrochloric acid is preferably used from the viewpoints of avoiding deterioration and damage of cellulose nanofibers due to acid and easiness of waste liquid treatment.

The carboxyl group-substituted oxidized cellulose fibers are collected by suction filtration using a Buchner funnel or the like. Although it is preferable not to wash the collected oxidized cellulose fibers in order to improve the yield, it is possible to wash them with distilled water or the like. In addition, since the oxidized cellulose fibers in this step are not defibrated, they are easy to collect.

<Step 3: Hydrophobicization>
Hydrophobization in this step is to improve compatibility with a hydrophobic polymer. Therefore, the hydrophobizing agent used in this step includes not only hydrophobic but also amphiphilic polymers that are compatible with both hydrophilic and hydrophobic solvents. In particular, the oxidized cellulose fiber dispersion having a carboxyl group obtained in the substitution step is mixed with a linear or branched molecule having an amino group at the terminal and an average molecular weight of 300 or more as a hydrophobizing agent. Preferably, the oxidized cellulose fibers are hydrophobized by bonding.

The hydrophobizing agent used in step 3 is, for example, a linear molecule with a large molecular weight, such as polyethylene glycol, to which an amino acid is added that can react with the carboxyl groups of the oxidized cellulose fibers to form a salt. groups are attached. The amount of the amine containing a linear or branched molecule to be added may be appropriately changed according to the type of amine. be.

Branched and linear cationic polyacrylamides, cationic polyacrylamide-polyethylene glycol copolymers, polypropylene-polyethylene glycol copolymers having terminal amino groups, and the like may be used as hydrophobizing agents used in step 3. good.

In the present embodiment, the hydrophobizing agent used has an average molecular weight (weight average molecular weight) of 300 or more, more preferably a linear or branched molecule with an average molecular weight of 500 or more, more preferably the above average The molecular weight is 1000 or more. By modifying the oxidized cellulose fiber with a linear molecule having a large molecular weight in this way, the surface of the oxidized cellulose fiber, which is originally hydrophilic, can be replaced with hydrophobic (or amphiphilic) linear or branched molecules. covered. As a result, when mixed with a hydrophobic polymeric material such as PET or PLA, the hydrophilic cellulose main chain portion is less likely to be exposed to the hydrophobic polymeric material, and aggregation of the oxidized cellulose fibers is prevented. be. Note that the larger the molecular weight of the linear or branched molecule, the longer the linear or branched molecule extending outward from the surface of the oxidized cellulose fiber, making it more difficult for the cellulose main chain portion to exhibit hydrophilicity. Dispersibility in hydrophobic polymers can be enhanced.

The hydrophobized cellulose fibers obtained in the hydrophobization step are desirably washed before being sent to the defibration step described later. Water is preferably used for washing. For example, it can be washed by suction filtration using a Buchner funnel or the like. The number of washings may be one or more. By the washing, unreacted oxidizing agents and various by-products can be easily removed.

<Step 4: defibration>
By defibrating the hydrophobized cellulose fibers, the oxidized cellulose fibers modified with a hydrophobizing agent bonded via a carboxylic acid group and an amino group are dispersed individually (cellulose nanofibers). A fine dispersion can be obtained. Unlike the defibration described in Patent Document 2, this process weakens the affinity between cellulose fibers by reacting carboxyl groups with a hydrophobizing agent before defibration, so defibration can be performed with a smaller shear force. be.

The device used for fibrillation is not particularly limited, but examples thereof include devices of types such as high-speed rotation type, colloid mill type, high pressure type, roll mill type, and ultrasonic type. Ultra high pressure homogenizers are more preferred. The apparatus is preferably capable of applying strong shear forces to the cellulosic raw material or modified cellulose (usually the dispersion). The pressure that can be applied by the device is preferably 50 MPa or higher, more preferably 100 MPa or higher, and still more preferably 140 MPa or higher. The apparatus is preferably a wet high-pressure or ultrahigh-pressure homogenizer capable of applying the above-described pressure to the cellulosic raw material or modified cellulose (usually a dispersion liquid) and applying a strong shearing force. Thereby, defibration can be performed efficiently. The number of times of treatment (pass) in the fibrillation device may be one or two or more, preferably two or more.

The solid content concentration of the modified cellulose in the dispersion is usually 0.1% by weight or more, preferably 0.2% by weight or more, and more preferably 0.3% by weight or more. As a result, the amount of liquid becomes appropriate with respect to the amount of cellulose fiber raw material, which is efficient. The upper limit is usually 10% by weight or less, preferably 6% by weight or less. Thereby, fluidity can be maintained. Prior to defibration treatment, a preliminary treatment may be performed as necessary. Pretreatment may be performed using a mixing, stirring, emulsifying, or dispersing device such as a high-speed shear mixer.

The average fiber diameter of the cellulose nanofibers obtained in the fibrillation step is 2 nm or more and 50
It is preferably 0 nm or less. The average fiber diameter and average fiber length of cellulose nanofibers are measured by, for example, preparing a 0.001% by weight aqueous dispersion of cellulose nanofibers, thinly spreading this diluted dispersion on a mica sample table, and heating at 50°C. A sample for observation is prepared by drying, and the cross-sectional height of the shape image observed with an atomic force microscope (AFM) is measured to calculate the number average fiber diameter or fiber length.

The average aspect ratio of the hydrophobized cellulose nanofibers obtained in the defibration step is usually 50 or more. Although the upper limit is not particularly limited, it is usually 1000 or less. Average aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length/average fiber diameter

The dispersion medium used in steps [1] to [4] can be water or an aqueous organic solvent that can be arbitrarily mixed with water, but it is preferable to use water. A dispersion is obtained.

<Step 5: Solvent replacement 1>
When water is used as the dispersion medium in step [4], the resulting hydrophobized cellulose nanofiber dispersion can be replaced with an aqueous organic solvent. The step of dispersing in an aqueous organic solvent and the step of collecting the dispersed hydrophobized cellulose nanofibers with a Buchner or the like are repeated several times (2 to 10 times) to replace the solvent.

Aqueous organic solvents are organic solvents that are optionally miscible with water. Examples include methanol, ethanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, Dimethylsulfoxide, acetonitrile, ethyl acetate, and combinations thereof. Among them, lower alcohols having 1 to 4 carbon atoms such as methanol, ethanol and 2-propanol are preferred, and ethanol is most preferred from the viewpoint of safety and availability.

<Step 6: Solvent replacement 2>
The hydrophobized cellulose nanofiber dispersion obtained in step [4] or step [5] can be solvent-substituted with a hydrocarbon-based or ether-based organic solvent. The step of dispersing in an organic solvent and the step of collecting the dispersed hydrophobized cellulose nanofibers with a Buchner or the like are repeated several times (2 to 10 times) to replace the solvent. The organic solvent to be substituted may be selected according to the application of the cellulose nanofiber dispersion to be produced. In addition, since the cellulose nanofibers are already hydrophobized in this step, solvent replacement with an organic solvent can be easily performed.

Hydrocarbon organic solvents include benzene, toluene, xylene, n-hexane, n-octane, cyclohexane, methylcyclohexane, dichloromethane, dichloroethane, chloroform, methylene chloride, carbon tetrachloride, fluorotrichloromethane, trichlorotrifluoromethane, hexa fluorobenzene and the like.

Ether-based organic solvents include tetrahydrofuran (THF), 1,2-dimethoxyethane (DME), cyclopentyl methyl ether (CPME), methyl tertiary butyl ether (MTBE), 1,4-dioxane, methyl cellosolve (2-methoxy ethanol).

The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples.

<Example 1>
500 g (absolutely dry) of bleached unbeaten kraft pulp (whiteness 85%) derived from softwood is TE
MPO (Sigma Aldrich) 1.95 g (0.95 g per 1 g of absolute dry cellulose)
025 mmol) and 51.4 g of sodium bromide (1 mmol per 1 g of absolute dry cellulose)
) was added to 500 ml of the aqueous solution and stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system so that sodium hypochlorite was 6.0 mmol/g to initiate an oxidation reaction. The pH in the system decreased during the reaction, but was adjusted to pH 10 by successively adding 3M sodium hydroxide aqueous solution. Consumes sodium hypochlorite, pH in the system
The reaction was terminated when no change occurred. The time required for the oxidation reaction was 90 minutes, and the total amount of carboxylate groups and carboxyl groups was 1.6 mmol/g. (Step [1])

Hydrochloric acid was added to the mixture after the reaction to adjust the pH to 1, and then stirring was continued for 60 minutes. (Step [2])

Next, distilled water was added to the obtained oxidized cellulose fibers to form an aqueous dispersion (concentration 0.1% (g/mL)), and then polyethylene glycol amine (molecular weight 2000) was added and reacted to obtain an aqueous dispersion of hydrophobized cellulose fibers (step [3]).

The resulting aqueous dispersion of hydrophobized cellulose fibers was subjected to suction filtration using a Buchner funnel, and then washed with water to remove by-produced salts, unreacted polyethylene glycol amine, and the like.

After dispersing the washed hydrophobized cellulose fibers in water (0.1% (g/mL)), the hydrophobized cellulose was fibrillated twice with a high-pressure homogenizer to defibrate the hydrophobized cellulose fibers of Example 1. A nanofiber dispersion was obtained (step [4]).

<Example 2>
The aqueous dispersion of the hydrophobized cellulose nanofibers obtained in Example 1 was subjected to suction filtration using a Buchner funnel, and then ethanol was added to the recovered hydrophobized cellulose nanofibers and stirred to obtain a dispersion (concentration of 0). .1% (g/mL)), and the step of performing suction filtration again using a Buchner funnel was repeated five times to replace the solvent of the cellulose nanofibers with ethanol (step [5]).

Next, ethanol is added to the hydrophobized cellulose nanofibers whose solvent has been replaced with ethanol and stirred to obtain a dispersion (concentration of 0.1% (g/mL)) to obtain a dispersion of the hydrophobized cellulose nanofibers of Example 2. rice field.

<Example 3>
The ethanol dispersion of the hydrophobized cellulose nanofibers obtained in Example 2 was subjected to suction filtration using a Buchner funnel, and then chloroform was added and stirred to obtain a dispersion (concentration 0.1% (g/mL)). Then, after suction filtration using a Buchner funnel, chloroform was added to the recovered hydrophobized cellulose nanofibers and stirred to make a dispersion (concentration 0.1% (g / mL)), and suction was performed using the Buchner funnel again. By repeating the filtering step five times, the cellulose nanofibers were solvent-substituted with chloroform (step [6]).

Next, chloroform is added to the hydrophobized cellulose nanofibers after solvent substitution with chloroform and stirred to obtain a dispersion (concentration 0.1% (g/mL)) to obtain a dispersion of the hydrophobized cellulose nanofibers of Example 3. rice field.

<Comparative example 1>
Step 1 was carried out in the same manner as in Example 1, and the subsequent steps were carried out as follows to obtain a hydrophobized cellulose nanofiber dispersion of Comparative Example 1.

The oxidized cellulose fibers obtained in step 1 were collected by suction filtration using a Buchner funnel. Water is added to the oxidized cellulose fibers to form an aqueous dispersion with a concentration of 0.1% (g/mL), and then the aqueous dispersion is fibrillated twice with a high-pressure homogenizer to defibrate the oxidized cellulose fibers. , to obtain oxidized cellulose nanofibers.

Next, 1M hydrochloric acid was added to 100 mL of oxidized cellulose nanofibers with a concentration of 0.1% (g/mL) to adjust the pH to 1, and 1 mL was added with stirring, and then stirring was continued for 60 minutes. Oxidation treatment was performed. After that, the oxidized cellulose nanofibers were recovered by suction filtration using a Buchner funnel. Through the above steps, 90% or more of the carboxylate groups on the surface of the cellulose were substituted with carboxyl groups.

Ethanol was added to the collected oxidized cellulose nanofibers to form a dispersion (concentration of 0.1% (g/mL)), and suction filtration was performed using a Buchner funnel, and then ethanol was added to the collected oxidized cellulose nanofibers and stirred. A dispersion liquid (concentration of 0.1% (g/mL)) was obtained by using a Buchner funnel, and the step of performing suction filtration again using a Buchner funnel was repeated five times to replace the solvent of the cellulose nanofibers with ethanol.

Next, chloroform is added to the cellulose nanofibers whose solvent has been replaced with ethanol to form a dispersion (concentration of 0.1% (g/mL)), suction filtration is performed using a Buchner funnel, and the process of collecting is repeated five times. , the cellulose nanofibers were solvent-exchanged with chloroform.

Next, to the recovered oxidized cellulose nanofibers chloroform dispersion (0.1% (g/mL)), polyethylene glycol amine (molecular weight: 2000) was added in an amount equimolar to the carboxyl groups of the cellulose nanofibers to carry out a reaction. rice field.

Next, after the reaction solution is subjected to suction filtration using a Buchner funnel, chloroform is added to obtain a dispersion (concentration of 0.1% (g/mL)), suction filtration is again performed using a Buchner funnel, and the step of recovery. was repeated 5 times to remove unreacted polyethylene glycol amine.

Next, chloroform was added to obtain a dispersion (concentration of 0.1% (g/mL)), and a hydrophobized cellulose nanofiber dispersion of Comparative Example 1 was prepared.

<Comparative Example 2>
Ethanol was added to the hydrophobized cellulose nanofiber dispersion of Comparative Example 1 to obtain a dispersion (concentration of 0.1% (g/mL)), and after suction filtration using a Buchner funnel, ethanol was added to the recovered oxidized cellulose nanofibers. was added and stirred to obtain a dispersion (concentration of 0.1% (g/mL)), and the step of performing suction filtration again using a Buchner funnel was repeated five times to replace the solvent of the cellulose nanofibers with ethanol.

Next, distilled water is added to the cellulose nanofibers whose solvent has been replaced with ethanol to form a dispersion (concentration of 0.1% (g/mL)), suction filtration is performed using a Buchner funnel, and the process of collecting is repeated five times. Thus, the hydrophobized cellulose nanofibers were solvent-substituted with water.

Next, water is added to the hydrophobized cellulose nanofibers whose solvent has been replaced with water and stirred to obtain a dispersion (concentration 0.1% (g/mL)) to obtain a hydrophobized cellulose nanofiber dispersion of Comparative Example 2. rice field.

In the examples of the present invention, the washing after the reaction with the hydrophobizing agent is before defibration, so it can be easily washed with water. After that, it is necessary to react with a hydrophobizing agent and wash the resulting hydrophobized nanofibers with a dispersion medium several times. Therefore, the present invention can provide a method for producing a hydrophobized cellulose nanofiber dispersion with greatly improved yield.

凡例 ◎：歩留りが非常に良好、○：歩留りが良好、
△：歩留りがやや不良、×：歩留りが不良 table

Legend ◎: Very good yield, ○: Good yield,
△: Slightly poor yield, ×: Poor yield

Claims (6)

Steps 1-4 below:
(Step 1) A cellulose raw material is treated in a reaction liquid containing an N-oxyl compound, a compound selected from the group consisting of bromides, iodides, or mixtures thereof, and an oxidizing agent to obtain a dispersion of oxidized cellulose fibers. the step of obtaining
(Step 2) a step of adding an acid to the oxidized cellulose fiber dispersion obtained in step 1 to substitute at least a portion of the carboxylate groups in the oxidized cellulose fibers with carboxyl groups;
(Step 3) adding polyethylene glycol amine to the dispersion of oxidized cellulose fibers having carboxyl groups obtained in Step 2 to obtain a dispersion of hydrophobized cellulose fibers; A method for producing a hydrophobized cellulose nanofiber dispersion having a step of defibrating the hydrophobized cellulose fibers in the dispersion, wherein the above manufacturing method does not include a washing step between the step 2 and the step 3. . 2. The method for producing a hydrophobized cellulose nanofiber dispersion according to claim 1, further comprising washing between said step 3 and said step 4. 3. The method for producing a hydrophobized cellulose nanofiber dispersion according to claim 1 or 2, wherein the polyethylene glycol amine in step 3 is a linear compound having an average molecular weight of 300 or more. The method for producing a hydrophobized cellulose nanofiber dispersion according to any one of claims 1 to 3 , wherein in the step 4, the hydrophobized cellulose fibers are defibrated using water as a dispersion medium. 5. The hydrophobized cellulose nanofiber dispersion according to claim 4, further comprising a step of replacing the dispersion medium of the hydrophobized cellulose nanofiber dispersion using water as the dispersion medium obtained in step 4 with an aqueous organic solvent. Production method. 5. Production of the hydrophobized cellulose nanofiber dispersion according to claim 4, further comprising the step of replacing the dispersion medium of the hydrophobized cellulose nanofiber dispersion using water as the dispersion medium obtained in step 4 with an organic solvent. Method.