JP7432390B2 - Hydrophobized anion-modified cellulose nanofiber dispersion and method for producing the same, and dry solid of hydrophobized anion-modified cellulose and method for producing the same - Google Patents

Description

The present invention relates to a dispersion of hydrophobized anion-modified cellulose nanofibers and a method for producing the same, as well as a dry solid of hydrophobized anion-modified cellulose and a method for producing the same.

It is known that by introducing anionic groups such as carboxyl groups and carboxymethyl groups into cellulose molecular chains and mechanically treating (fibrillating) them, it is possible to convert them into cellulose nanofibers with nanoscale fiber diameters. There is. Cellulose nanofibers are light, strong, and biodegradable, so their applications in various fields are being considered.

Normally, anion-modified cellulose nanofibers have a highly hydrophilic state in which the introduced anionic groups form salts such as sodium salts, and therefore hydrophobic materials such as polyethylene terephthalate (PET) and polylactic acid (PLA) It has low compatibility with other polymers. Furthermore, the dispersibility in low polarity organic solvents is low. A method to solve this problem is to make the metal salt type anionic group (e.g. -COONa) acidic, convert it to the acid form (e.g. -COOH), and improve the hydrophilicity of the anion-modified cellulose nanofibers. There are ways to lower it.

Patent Document 1 describes a "second production method" in which cellulose nanofibers are dispersed in a medium containing an organic solvent, in which an acid is added to an aqueous dispersion of cellulose nanofibers to form a carboxylate group of cellulose nanofibers. a step of substituting a part of the group with a carboxylic acid type group, a step of adding an organic solvent to the cellulose nanofiber gel in which some of the groups have been replaced with a carboxylic acid type group, and a step of adding an organic solvent to the cellulose nanofiber water to which the organic solvent has been added. A method is described that includes removing the aqueous solvent from the dispersion.

Furthermore, Patent Document 2 describes, as a "first production method," a step of treating an aqueous dispersion of cellulose nanofibers substituted with a carboxylic acid type with an amine, recovering the amine-treated cellulose nanofibers, and dispersing the cellulose nanofibers in a dispersion medium. A method is described that includes the step of preparing a cellulose nanofiber dispersion by redispersing the cellulose nanofibers in the cellulose nanofibers.

International Publication No. 2010/134357 Japanese Patent Application Publication No. 2012-21081

In the method described in Patent Document 1, the organic solvents that can be used as the final dispersion medium are limited to three types: dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide. is a water-soluble organic solvent that is miscible with water. The method described in Patent Document 1 does not describe the use of an organic solvent, such as toluene, which has low polarity and is hardly soluble in water, as a dispersion medium for the cellulose nanofiber dispersion. Further, Patent Document 2 also does not describe the use of a low polarity and poorly soluble organic solvent in water as a dispersion medium.

After producing a cellulose nanofiber dispersion using a water-soluble organic solvent as a dispersion medium using the method described in Patent Documents 1 and 2, by replacing the water-soluble organic solvent with a low polar poorly water-soluble organic solvent. It is conceivable to produce a cellulose nanofiber dispersion using an organic solvent that is sparingly soluble in water as a dispersion medium, but when replacing the solvent, it is necessary to repeat the addition of the solvent and removal by suction filtration, etc. many times. However, there is a problem in that it is costly and time consuming, and cellulose nanofibers are lost during repeated solvent replacement operations, resulting in a decrease in yield. In addition, in the methods described in Patent Documents 1 and 2, at least two defibration steps (mixer or However, as the number of defibration increases, the cellulose fibers are damaged.

In order to solve the above-mentioned problems, the present applicant added a specific amount or more of a hydrophobizing agent to a dispersion of anion-modified cellulose to produce a dispersion of hydrophobized anion-modified cellulose, and then prepared a dispersion of hydrophobized anion-modified cellulose. A dry solid of hydrophobized anion-modified cellulose is produced by removing the dispersion medium, and then the dry solid of hydrophobized anion-modified cellulose is defibrated in an organic solvent to produce a hydrophobized anion using the organic solvent as a dispersion medium. We proposed a method for producing a dispersion of modified cellulose nanofibers (Japanese Patent Application No. 2019-003113). By this method, it has become possible to produce dispersions of hydrophobized anion-modified cellulose nanofibers using various organic solvents as dispersion media, including low polar organic solvents that are sparingly soluble in water, at high yields.
An object of the present invention is to provide a method for producing a dispersion of anion-modified cellulose nanofibers using an organic solvent with improved viscosity as a dispersion medium by applying the above-described method.

As a result of intensive studies, the present inventors added a hydrophobizing agent to a dispersion of anion-modified cellulose to produce a dispersion of hydrophobized anion-modified cellulose, and from the obtained dispersion of hydrophobized anion-modified cellulose, A method for obtaining a dispersion of hydrophobized anion-modified cellulose nanofibers by removing a dispersion medium to obtain a dry solid of hydrophobized anion-modified cellulose and defibrating this dry solid in an organic solvent, in which a specific hydrophobizing agent is used. We have found that the viscosity of a dispersion of hydrophobized anion-modified cellulose nanofibers using an organic solvent as a dispersion medium is improved when using this method. The present invention includes, but is not limited to, the following:
[1] Step 1 of producing a hydrophobized anion-modified cellulose dispersion by adding a hydrophobizing agent to the anion-modified cellulose dispersion;
Step 2 of removing the dispersion medium from the dispersion of the hydrophobized anion-modified cellulose to produce a dry solid of the hydrophobized anion-modified cellulose, and mixing the dry solid of the hydrophobized anion-modified cellulose with an organic solvent, step 3 of defibrating the hydrophobized anion-modified cellulose in the organic solvent to produce a dispersion of hydrophobized anion-modified cellulose nanofibers using the organic solvent as a dispersion medium;
including;
The hydrophobizing agent is a polyether amine having a polyalkylene glycol group and a hydrocarbon group having 2 or more carbon atoms,
A method for producing a dispersion of hydrophobized anion-modified cellulose nanofibers in which the dry solid of hydrophobized anion-modified cellulose has a solid content concentration higher than 90% by mass.
[2] Step 1 of adding a hydrophobizing agent to a dispersion of anion-modified cellulose to produce a dispersion of hydrophobized anion-modified cellulose, and removing the dispersion medium from the dispersion of hydrophobized anion-modified cellulose to obtain a hydrophobizing agent. Step 2 of producing a dry solid of anion-modified cellulose;
including;
The hydrophobizing agent is a polyether amine having a polyalkylene glycol group and a hydrocarbon group having 2 or more carbon atoms,
The dry solid of the hydrophobized anion-modified cellulose has a solid content concentration higher than 90% by mass,
A method for producing a dry solid of hydrophobized anion-modified cellulose.
[3] The method according to [1] or [2], wherein the anion-modified cellulose is cellulose having a carboxyl group or cellulose having a carboxyalkyl group.
[4] Contains anion-modified cellulose bound to a hydrophobizing agent, the solid content concentration is higher than 90% by mass, and the hydrophobizing agent is a polyetheramine having a polyalkylene glycol group and a hydrocarbon group having 2 or more carbon atoms. , a dry solid of hydrophobized anion-modified cellulose.
[5] Contains anion-modified cellulose nanofibers bound to a hydrophobizing agent, an organic solvent is used as a dispersion medium, and the hydrophobizing agent is a polyether amine having a polyalkylene glycol group and a hydrocarbon group having 2 or more carbon atoms. Dispersion of hydrophobized anion-modified cellulose nanofibers.

According to the present invention, a dispersion of hydrophobized anion-modified cellulose nanofibers with improved viscosity can be obtained in a method for efficiently producing a dispersion of hydrophobized anion-modified cellulose nanofibers using an organic solvent as a dispersion medium. It is considered that a dispersion of hydrophobized anion-modified cellulose nanofibers having high viscosity can be suitably used as an additive in fields where hydrophobicity and shape retention are required. The present invention also provides a dry solid of hydrophobized anion-modified cellulose that can be suitably used to produce a dispersion of hydrophobized anion-modified cellulose nanofibers with improved viscosity, and a method for producing the same. The dry solid of hydrophobized anion-modified cellulose of the present invention is easily compatible with various organic solvents including low polarity organic solvents, and a dispersion of hydrophobized anion-modified cellulose nanofibers can be produced using an organic solvent as a dispersion medium. It can be suitably used as a material for. Additionally, dry solids have the advantage of being easy to store and transport.

The present invention relates to a method for producing a dispersion of hydrophobized anion-modified cellulose nanofibers using an organic solvent as a dispersion medium. Hereinafter, cellulose nanofibers may be referred to as "CNF". Specifically, in the method of the present invention, a hydrophobizing agent is added to a dispersion of anion-modified cellulose to produce a dispersion of hydrophobized anion-modified cellulose (Step 1). The dispersion medium is removed to produce a dry solid of hydrophobized anion-modified cellulose (Step 2), and the dry solid of hydrophobized anion-modified cellulose is mixed with an organic solvent to form a hydrophobized anion-modified cellulose in the organic solvent. (step 3) to produce a dispersion of hydrophobized anion-modified CNF using an organic solvent as a dispersion medium. At this time, the hydrophobizing agent added in step 1 is a polyether amine having a polyalkylene glycol group and a hydrocarbon group having 2 or more carbon atoms, and in step 2, the solid content concentration of the dry solid is 90 Drying (removal of dispersion medium) is performed until the amount becomes higher than % by mass. The dry solid of hydrophobized anion-modified cellulose produced in step 2 can be suitably used as a material for producing a dispersion of hydrophobized anion-modified CNF using an organic solvent as a dispersion medium.

(1) Process 1
In step 1, a hydrophobizing agent is added to the anion-modified cellulose dispersion. Anion-modified cellulose is cellulose in which an anionic group is introduced into the molecular chain, as explained in more detail below.

(1-1) Cellulose raw material The type of cellulose that is the raw material for anion-modified cellulose is not particularly limited. Cellulose is generally classified into natural cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose excluding non-crystalline regions, etc. based on its origin, manufacturing method, etc. In the present invention, any of these celluloses can be used as a raw material.

Examples of natural cellulose include bleached pulp or unbleached pulp (bleached wood pulp or unbleached wood pulp); linters, purified linters; and cellulose produced by microorganisms such as acetic acid bacteria. The raw material for bleached pulp or unbleached pulp is not particularly limited, and examples thereof include wood, cotton, straw, bamboo, hemp, jute, kenaf, and the like. Furthermore, the method for producing bleached pulp or unbleached pulp is not particularly limited, and may be a mechanical method, a chemical method, or a combination of the two in between. Examples of bleached pulp or unbleached pulp classified by production method include mechanical pulp (thermomechanical pulp (TMP), groundwood pulp), and chemical pulp (softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp ( Examples include sulfite pulp such as NBSP); kraft pulp such as softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), and hardwood bleached kraft pulp (LBKP). Furthermore, dissolving pulp may be used in addition to papermaking pulp. Dissolving pulp is a chemically refined pulp that is mainly used after being dissolved in chemicals, and is the main raw material for artificial fibers, cellophane, etc.

Examples of regenerated cellulose include those obtained by dissolving cellulose in a solvent such as a cupric ammonia solution, a cellulose xanthate solution, or a morpholine derivative, and respinning the resulting solution. Fine cellulose is obtained by depolymerizing cellulose materials such as the above-mentioned natural cellulose and regenerated cellulose (for example, acid hydrolysis, alkaline hydrolysis, enzymatic decomposition, blasting treatment, vibrating ball mill treatment, etc.) Examples include those obtained by mechanically processing the above-mentioned cellulose-based materials.

(1-2) Anion modification The anion modification in "anion modified cellulose" refers to the introduction of an anionic group into cellulose, and specifically, the introduction of an anionic group into the pyranose ring of cellulose through oxidation or substitution reaction. Say something. In the present invention, the oxidation reaction refers to a reaction in which the hydroxyl group of the pyranose ring is directly oxidized to a carboxyl group. Furthermore, in the present invention, the substitution reaction refers to a reaction in which an anionic group is introduced into a pyranose ring by a substitution reaction other than the oxidation.

(1-2-1) Carboxylation (oxidation)
As an example of anionic modification, carboxylation (introduction of carboxyl groups into cellulose, also referred to as "oxidation") can be mentioned. Anion-modified cellulose obtained by carboxylating cellulose raw materials is called carboxylated cellulose (or oxidized cellulose). In this specification, the carboxyl group refers to -COOH (acid type) and -COOM (metal salt type) (wherein M is a metal ion). Carboxylation (oxidation) of the cellulose raw material can be obtained, for example, by the method described below, but is not limited thereto. Additionally, commercially available carboxylated cellulose may be used in step 1. The amount of carboxyl groups in carboxylated cellulose is preferably 0.6 mmol/g to 3.0 mmol/g, more preferably 1.0 mmol/g to 2.0 mmol/g, based on the absolute dry mass of carboxylated cellulose. Not limited to these.

The amount of carboxyl groups in carboxylated cellulose can be measured by the following method:
Prepare 60 ml of 0.5% by mass slurry (aqueous dispersion) of carboxylated cellulose, add 0.1M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then dropwise add 0.05N sodium hydroxide aqueous solution to adjust the pH to 11. The electrical conductivity is measured until the electrical conductivity changes, and the amount of sodium hydroxide (a) consumed during the neutralization stage of the weak acid, where the electrical conductivity changes slowly, is calculated using the following formula:
Amount of carboxyl groups [mmol/g carboxylated cellulose] = a [ml] x 0.05/mass of carboxylated cellulose [g].

As an example of a carboxylation (oxidation) method, a cellulose feedstock is oxidized in water with an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides, and mixtures thereof. Here are some ways to do it. Through this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized, resulting in cellulose fibers having an aldehyde group and a carboxyl group (-COOH) or a carboxylate group (-COO ^- ) on the surface. (carboxylated cellulose). The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less.

The N-oxyl compound refers to a compound capable of generating nitroxy radicals. As the N-oxyl compound, any compound can be used as long as it promotes the desired oxidation reaction. Examples include 2,2,6,6-tetramethylpiperidine-1-oxyradical (TEMPO) and its derivatives (eg, 4-hydroxyTEMPO). The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount that can oxidize cellulose as a raw material. For example, 0.01 mmol to 10 mmol is preferable, more preferably 0.01 mmol to 1 mmol, and even more preferably 0.05 mmol to 0.5 mmol, per 1 g of bone dry cellulose. Further, it is preferably about 0.1 mmol/L to 4 mmol/L to the reaction system.

Bromide is a compound containing bromine, examples of which include alkali metal bromides that can be dissociated and ionized in water. Moreover, iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide to be used can be selected within a range that can promote the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 mmol to 100 mmol, more preferably 0.1 mmol to 10 mmol, and even more preferably 0.5 mmol to 5 mmol, per 1 g of bone dry cellulose. The modification is a modification due to an oxidation reaction.

As the oxidizing agent, known ones can be used, such as halogen, hypohalous acid, halous acid, perhalogenic acid, salts thereof, halogen oxides, peroxides, and the like. Among these, sodium hypochlorite is preferred because it is inexpensive and has a low environmental impact. The appropriate amount of the oxidizing agent to be used is, for example, preferably 0.5 mmol to 500 mmol, more preferably 0.5 mmol to 50 mmol, even more preferably 1 mmol to 25 mmol, and most preferably 3 mmol to 10 mmol, per 1 g of bone dry cellulose. . Further, for example, it is preferably 1 mol to 40 mol per 1 mol of the N-oxyl compound.

In the cellulose oxidation process, the reaction can proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4°C to 40°C, and may be room temperature of about 15°C to 30°C. As the reaction progresses, carboxyl groups are generated in the cellulose, so a decrease in the pH of the reaction solution is observed. In order for 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 at about 8 to 12, preferably about 10 to 11. Water is preferred as the reaction medium 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 degree of progress of oxidation, and is usually about 0.5 to 6 hours, for example about 0.5 to 4 hours.

Further, the oxidation reaction may be carried out in two stages. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the first-stage reaction again under the same or different reaction conditions, the efficiency can be improved without being inhibited by the salt produced as a by-product in the first-stage reaction. Can be oxidized well.

Another example of the carboxylation (oxidation) method is a method of oxidizing a cellulose raw material by bringing it into contact with a gas containing ozone. This oxidation reaction oxidizes the hydroxyl groups at at least the 2- and 6-positions of the glucopyranose ring and causes decomposition of the cellulose chain. The ozone concentration in the ozone-containing gas is preferably 50 g/m ³ to 250 g/m ³ , more preferably 50 g/m ³ to 220 g/m ³ . The amount of ozone added to the cellulose raw material is preferably 0.1 parts by mass to 30 parts by mass, more preferably 5 parts by mass to 30 parts by mass, when the solid content of the cellulose raw material is 100 parts by mass. . The ozone treatment temperature is preferably 0°C to 50°C, more preferably 20°C to 50°C. The ozone treatment time is not particularly limited, but is about 1 minute to 360 minutes, preferably about 30 minutes to 360 minutes. When the ozone treatment conditions are within these ranges, excessive oxidation and decomposition of cellulose can be prevented, resulting in a good yield of oxidized cellulose. After the ozone treatment, additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the additional oxidation treatment is not particularly limited, but examples thereof include chlorine-based compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, the additional oxidation treatment can be performed by dissolving these oxidizing agents in water or a polar organic solvent such as alcohol to prepare an oxidizing agent solution, and immersing the cellulose raw material in the solution.

The amount of carboxyl groups in the carboxylated cellulose can be adjusted by controlling reaction conditions such as the amount of the oxidizing agent added and the reaction time. The amount of carboxyl groups in carboxylated cellulose and the amount of carboxyl groups when the same carboxylated cellulose is made into nanofibers are usually the same.

(1-2-2) Carboxyalkylation An example of anionic modification is the introduction of a carboxyalkyl group such as a carboxymethyl group into cellulose. Anion-modified cellulose obtained by carboxyalkylation of cellulose raw materials is called carboxyalkylated cellulose. In this specification, the carboxyalkyl group refers to -RCOOH (acid type) and -RCOOM (metal salt type). Here, R is an alkylene group such as a methylene group or an ethylene group, and M is a metal ion.

The carboxyalkylated cellulose used in Step 1 may be obtained by a known method, or a commercially available product may be used. The degree of carboxyalkyl substitution per anhydroglucose unit of cellulose is preferably less than 0.40. Further, when the carboxyalkyl group is a carboxymethyl group, the degree of carboxymethyl substitution is preferably less than 0.40. When the degree of substitution is less than 0.40, the dispersibility of CNF can be maintained to a certain degree. Further, the lower limit of the degree of carboxyalkyl substitution is preferably 0.01 or more. In consideration of operability, the degree of substitution is particularly preferably from 0.02 to 0.35, and even more preferably from 0.10 to 0.30. Note that anhydroglucose units mean individual anhydroglucoses (glucose residues) that constitute cellulose, and carboxyalkyl substitution degree refers to carboxyalkyl substitution among hydroxyl groups (-OH) in glucose residues that constitute cellulose. The proportion of those substituted with ether groups (-ORCOOH or -ORCOOM) (number of carboxyalkyl ether groups per glucose residue) is shown.

An example of a method for producing carboxyalkylated cellulose is a method including the following steps. The modification is modification by substitution reaction. This will be explained using carboxymethylated cellulose as an example.

i) A step of mixing the cellulose raw material, a solvent, and a mercerizing agent and mercerizing the mixture at a reaction temperature of 0 to 70°C, preferably 10 to 60°C, and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. ,
ii) Next, 0.05 to 10.0 times the mole of carboxymethylating agent per glucose residue is added, the reaction temperature is 30 to 90°C, preferably 40 to 80°C, and the reaction time is 30 minutes to 10 hours, preferably A step of carrying out an etherification reaction for 1 to 4 hours.

As the raw material, the above-mentioned cellulose raw material can be used. As a solvent, 3 to 20 times the mass of water or a lower alcohol, specifically water, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, isobutanol, tertiary butanol, etc. alone, or two More than one species of mixed media can be used. When lower alcohol is mixed, the mixing ratio is preferably 60 to 95% by mass. As the mercerizing agent, it is preferable to use alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, in an amount of 0.5 to 20 times the mole per anhydroglucose residue in the bottom starting material.

As described above, the degree of carboxymethyl substitution per glucose unit of cellulose is less than 0.40, preferably 0.01 or more and less than 0.40. By introducing carboxymethyl substituents into cellulose, the cellulose cells become electrically repulsive to each other. Therefore, cellulose into which carboxymethyl substituents have been introduced can be nano-fibrillated. Note that if the carboxymethyl substituent per glucose unit is less than 0.01, nanofibrillation may not be sufficient. The degree of carboxyalkyl substitution in carboxyalkylated cellulose and the degree of carboxyalkyl substitution when the same carboxyalkylated cellulose is made into nanofibers are usually the same.

The degree of carboxymethyl substitution per glucose unit can be measured by the following method:
Accurately weigh about 2.0 g of carboxymethylated cellulose (absolutely dried) and place it in a 300 mL Erlenmeyer flask with a stopper. Add 100 mL of a solution prepared by adding 100 mL of special grade concentrated nitric acid to 900 mL of methanol, and shake for 3 hours to convert the carboxymethylated cellulose salt (CM-modified cellulose) into hydrogen-type CM-modified cellulose. Accurately weigh 1.5 g to 2.0 g of hydrogenated CM cellulose (absolutely dry) and place it in a 300 mL Erlenmeyer flask with a stopper. Wet the hydrogenated CM cellulose with 15 mL of 80% by mass methanol, add 100 mL of 0.1N NaOH, and shake at room temperature for 3 hours. Excess NaOH is back-titrated with 0.1N H ₂ SO ₄ using phenolphthalein as indicator. The degree of carboxymethyl substitution (DS) is calculated by the following formula:
A = [(100 x F' - (0.1N H ₂ SO ₄ ) (mL) x F) x 0.1]/(absolute dry mass (g) of hydrogenated CM cellulose)
DS=0.162×A/(1-0.058×A)
A: Amount of 1N NaOH required to neutralize 1g of hydrogenated CM cellulose (mL)
F: Factor of 0.1N H ₂ SO ₄ F': Factor of 0.1N NaOH.

Furthermore, the amount (mmol/g) of carboxymethyl groups (anionic groups) can be calculated from the degree of carboxymethyl substitution (DS) using the following formula:
Amount of carboxymethyl group (mmol/g)=(DS/(DS×58+162))×1000.
The degree of substitution of carboxyalkyl groups other than carboxymethyl groups can also be obtained by the same method as above, and the amount of carboxyalkyl groups can be calculated from the following formula using the degree of carboxyalkyl substitution (DS). can:
Amount of carboxyalkyl group (mmol/g)=[DS/{DS×(molecular weight of carboxyalkyl group−1)+162}]×1000.
(1-2-3) Esterification Esterification can be cited as an example of anionic modification. Anion-modified cellulose obtained by esterifying a cellulose raw material is called esterified cellulose, and especially esterified cellulose obtained using a phosphoric acid compound described below is called phosphoric acid esterified cellulose. In step 1, for example, esterified cellulose produced by the method described below may be used, but the method is not limited thereto. Alternatively, commercially available esterified cellulose may be used in step 1.
Examples of the method for esterifying the cellulose raw material include a method of mixing a powder or aqueous solution of a phosphoric acid compound with a cellulose raw material, a method of adding an aqueous solution of a phosphoric acid compound to a slurry of the cellulose raw material, and the like. Examples of the phosphoric acid compounds include phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. Among the above, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, Potassium phosphite, sodium hypophosphite, potassium hypophosphite, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, Preferred are ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate, and the like. These can be used alone or in combination of two or more. Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, phosphoric acid More preferred are ammonium salts. Particularly preferred are sodium dihydrogen phosphate and disodium hydrogen phosphate. Furthermore, it is desirable to use the phosphoric acid compound in the form of an aqueous solution because the reaction can proceed uniformly and the efficiency of introducing phosphoric acid groups can be increased. The pH of the aqueous solution of the phosphoric acid compound is preferably 7 or less since this increases the efficiency of introducing phosphoric acid groups, but the pH is preferably 3 to 7 from the viewpoint of suppressing hydrolysis of pulp fibers.

Examples of methods for producing phosphoric acid esterified cellulose include the following methods. A phosphoric acid compound is added to a suspension of cellulose raw material having a solid content concentration of 0.1 to 10% by mass while stirring to introduce phosphoric acid groups into cellulose. When the cellulose-based raw material is 100 parts by mass, the amount of the phosphoric acid compound added is preferably 0.2 to 500 parts by mass, more preferably 1 to 400 parts by mass as the amount of phosphorus element. If the proportion of the phosphoric acid compound is at least the above lower limit, the yield of fine fibrous cellulose can be further improved. The yield improvement effect reaches a ceiling near the upper limit value.

In addition to the phosphoric acid compound, powders or aqueous solutions of other compounds may be mixed. Other compounds that can be mixed in addition to the phosphoric acid compound are not particularly limited, but nitrogen-containing compounds that exhibit basicity are preferred. "Basic" herein is defined as a pink to red color of the aqueous solution in the presence of the phenolphthalein indicator, or a pH of the aqueous solution greater than 7. The basic nitrogen-containing compound used in the present invention is not particularly limited as long as it exhibits the effects of the present invention, but compounds having an amino group are preferred. Examples include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, and the like. Among them, urea is preferred because it is low cost and easy to handle. The amount of other compounds added is preferably 2 to 1000 parts by weight, more preferably 100 to 700 parts by weight, based on 100 parts by weight of the solid content of the cellulose raw material. The reaction temperature is preferably 0 to 95°C, more preferably 30 to 90°C. The reaction time is not particularly limited, but is approximately 1 minute to 600 minutes, more preferably 30 minutes to 480 minutes. When the conditions for the esterification reaction are within these ranges, cellulose can be prevented from being excessively esterified and easily dissolved, and the yield of phosphoric acid esterified cellulose can be improved. After dehydrating the obtained phosphoric acid esterified cellulose suspension, it is preferably heat-treated at 100 to 170° C. from the viewpoint of suppressing hydrolysis of cellulose. Further, during heat treatment, it is preferable to heat at 130° C. or lower, preferably 110° C. or lower while water is contained, and after removing water, heat treatment at 100° C. to 170° C.

The degree of phosphoric acid group substitution per glucose unit of the phosphoric acid esterified cellulose is preferably 0.001 or more and less than 0.40. By introducing phosphate substituents into cellulose, the cellulose cells become electrically repulsive to each other. Therefore, cellulose into which phosphate groups have been introduced can be easily nano-fibrillated. If the degree of phosphate group substitution per glucose unit is less than 0.001, sufficient nanofibrillation cannot be achieved. On the other hand, if the degree of phosphate group substitution per glucose unit is greater than 0.40, the nanofibers may not be obtained due to swelling or dissolution. In order to efficiently defibrate, it is preferable to obtain phosphoric acid esterified cellulose by the above method, then boil it and wash it with cold water. These modifications by esterification are modifications by substitution reactions. The degree of substitution in esterified cellulose and the degree of substitution when the same esterified cellulose is made into nanofibers are usually the same. In addition, the amount (mmol/g) of phosphoric acid groups (anionic groups) can be calculated from the degree of phosphoric acid group substitution (DS) using the following formula:
Amount of phosphate groups (mmol/g)=(DS/(DS×64+162))×1000.
(1-2-4) Xantation An example of anionic modification is xantation. Xanthating refers to treating a cellulose raw material with an aqueous alkali metal hydroxide solution to produce alkali cellulose, and then reacting the alkali cellulose with carbon disulfide (CS ₂ ) to convert the alkali cellulose into metal alkoxide (-O ^- M ⁺ ) ( M is alkali metal) is converted into xanthate (-OCSS ^- M ⁺ ) to produce cellulose xanthate. In this specification, anion-modified cellulose obtained by xantating a cellulose raw material is referred to as xanthated cellulose.
The xanthated cellulose used in step 1 may be obtained by a known method, or a commercially available product may be used. The degree of xanthate substitution per anhydroglucose unit of the xanthated cellulose is preferably 0.33 or more and 1.20 or less. If it is 0.33 or more, it will lead to promotion of fibrillation in the subsequent step 3, and if it is 1.20 or less, a decrease in the yield of xanthated cellulose can be suppressed. The degree of xanthate substitution can be adjusted by adjusting the amount of carbon disulfide supplied and the contact time of carbon disulfide and alkali cellulose.
As an example of a method for producing xanthated cellulose, the following method can be mentioned. The modification is modification by substitution reaction.
First, a cellulose raw material is treated with an aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide to obtain alkali cellulose. At this time, the concentration of the aqueous alkali metal hydroxide solution is preferably 4 to 9% by mass. When the content is 4% by mass or more, mercerization of cellulose can proceed, and when the content is 9% by mass or less, the cellulose type I crystal structure in the resulting alkali cellulose can be maintained to a certain extent. The above treatment time is preferably 30 minutes or more and 6 hours or less, more preferably 1 hour or more and 5 hours or less. The treatment temperature is preferably around room temperature. Note that if the treatment temperature is low, such as under refrigerated conditions, the alkali metal hydroxide aqueous solution will more easily penetrate into the crystalline region of cellulose. The concentration is preferably 4% by mass or more and 7% by mass or less, and when the temperature is 10° C. or higher, the concentration of the aqueous alkali metal hydroxide solution is preferably 4% by mass or more and 9% by mass or less.
It is preferable to subject the alkali cellulose obtained by the above treatment to solid-liquid separation to remove as much moisture as possible. Thereby, the reaction in the next xanthate treatment can be promoted. As a method for solid-liquid separation, for example, general dehydration methods such as centrifugation and filtration can be used. The concentration of alkali metal hydroxide contained in the alkali cellulose after solid-liquid separation is preferably about 3 to 8% by mass.
Next, a xanthate treatment is performed in which the alkali cellulose is reacted with carbon disulfide to convert the alkali metal alkoxide in the alkali cellulose into an alkali metal salt of xanthogenic acid. Carbon disulfide is preferably supplied in an amount of 10% by mass or more based on the mass of cellulose. Further, the contact time between carbon disulfide and alkali cellulose is preferably 30 minutes or more, more preferably 1 hour or more. The upper limit of the contact time is not particularly limited, but it is preferably 6 hours or less because the reaction is considered to be sufficiently completed in about 6 hours.
In this xanthate treatment, it is preferable to bring the dehydrated alkali cellulose into contact with gaseous carbon disulfide at a temperature of 46° C. or lower. When the temperature is 46° C. or lower, a decrease in the degree of polymerization due to decomposition of alkali cellulose can be suppressed.
It is preferable to wash the obtained xanthated cellulose to remove impurities, alkalis, carbon disulfide, etc., because the load during defibration in the subsequent step 3 can be reduced. It is preferable to use water for washing because it can reduce the pH caused by alkali and there is almost no risk of damaging the fibers. The pH of the xanthated cellulose slurry after washing is preferably 10.5 or less, more preferably 9.5 or less.

(1-3) Anion-modified cellulose The anion-modified cellulose used in step 1 can be obtained by subjecting the raw material cellulose to anion modification as exemplified above. Furthermore, commercially available anion-modified cellulose may be used in step 1. As the type of anion-modified cellulose, cellulose having a carboxyl group or cellulose having a carboxyalkyl group is preferable. In particular, carboxylated cellulose obtained by oxidizing cellulose using an N-oxyl compound and an oxidizing agent is preferable because it has anionic groups uniformly introduced therein and is easily defibrated uniformly.

The anion-modified cellulose used is one that maintains at least a portion of its fibrous shape even when dispersed in water or a water-soluble organic solvent. If a material that does not maintain its fibrous shape (that is, a material that dissolves) is used, nanofibers cannot be obtained. At least a portion of the fibrous shape is maintained when dispersed, which means that when a dispersion of anion-modified cellulose is observed with an electron microscope, a fibrous substance can be observed. Further, anion-modified cellulose is preferred, since it allows the peak of cellulose type I crystals to be observed when measured by X-ray diffraction.

The degree of crystallinity of cellulose in the anion-modified cellulose is preferably 50% or more, and more preferably 60% or more in type I crystal. By adjusting the crystallinity within the above range, it is possible to sufficiently obtain crystalline cellulose fibers that do not dissolve even after the fibers are made fine by fibrillation. The crystallinity of cellulose can be controlled by the crystallinity of cellulose as a raw material and the degree of anionic modification. The method for measuring the crystallinity of anion-modified cellulose is as follows:
The sample is placed on a glass cell and measured using an X-ray diffraction measuring device (LabX XRD-6000, manufactured by Shimadzu Corporation). The crystallinity was calculated using the method of Segal et al., using the diffraction intensity of 2θ = 10° to 30° in the X-ray diffraction diagram as the baseline, and the diffraction intensity of the 002 plane at 2θ = 22.6° and 2θ = It is calculated from the diffraction intensity of the amorphous portion at 18.5° using the following formula.
Xc=(I002c-Ia)/I002c×100
Xc: Crystallinity of type I cellulose (%)
I002c: 2θ=22.6°, diffraction intensity of 002 plane Ia: 2θ=18.5°, diffraction intensity of amorphous portion.

The proportion of cellulose type I crystals in anion-modified cellulose and the proportion of cellulose type I crystals when the same anion-modified cellulose is made into nanofibers are usually the same.
The anion-modified cellulose obtained by the above method usually has an anionic group introduced in the form of a metal salt (for example, -COO ^- M ⁺ or -RCOO ^- M ⁺ (M is a metal such as sodium or potassium). and R is an alkylene group such as a methylene group or an ethylene group)). In order to promote the subsequent reaction with a hydrophobizing agent, it is preferable to convert the metal salt type anionic group in the anion-modified cellulose to an acid type (eg, -COOH, -RCOOH, etc.).

The method of converting into the acid form is not particularly limited, and examples thereof include a method of adding an acid to anion-modified cellulose, a method of bringing anion-modified cellulose into contact with a cation exchange resin, and the like. When adding an acid, the type of acid used is not particularly limited, and examples include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, nitrous acid, and phosphoric acid, as well as acetic acid, lactic acid, oxalic acid, citric acid, formic acid, and adipic acid. , sebacic acid, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid, gluconic acid and the like. Hydrochloric acid or sulfuric acid is preferred because it is versatile and easily available. The pH when adding the acid is preferably in the range of 1 to 6, more preferably 2 to 5. The amount of acid added is not particularly limited as long as it can convert the metal salt type anion-modified cellulose into the acid type, but for example, if it is a strong acid, it is preferably 1 equivalent or more with respect to the anionic group, and if it is a weak acid If so, the amount is preferably 10 equivalents or more. When contacting with an acidic ion exchange resin, examples of the acidic ion exchange resin include strongly acidic cation exchange resins and weakly acidic cation exchange resins.

(1-4) Dispersion of anion-modified cellulose The dispersion of anion-modified cellulose used in step 1 is one in which the above-mentioned anion-modified cellulose is dispersed or suspended in a dispersion medium. The dispersion medium in the dispersion can be appropriately selected from water, an organic solvent, or a mixture thereof. The type of organic solvent does not matter, but for example, polar solvents that have a high affinity with the hydroxyl groups in cellulose, and water-soluble organic solvents that can be mixed with water at a certain ratio are preferred, such as methanol, ethanol, isopropanol, isobutanol, sec-butanol, tert-butanol, methyl cellosolve, ethyl cellosolve, ethylene glycol, glycerin, ethylene glycol dimethyl ether, 1,4-dioxane, tetrahydrofuran, acetone, methyl ethyl ketone, methyl propyl ketone, N,N-dimethylformamide, N,N- Dimethylacetamide, dimethylsulfoxide and the like can be mentioned. The above-mentioned dispersion medium may be used alone or in combination of two or more types. For example, a form in which two or more types of organic solvents are mixed, a form in which water and an organic solvent are contained, a form in which only water is used, etc. can be appropriately selected. It is preferable to use only water as a dispersion medium (ie, 100% water) from the viewpoint of ease of handling. The mixing ratio when mixing water and an organic solvent is not particularly limited, and may be adjusted as appropriate depending on the type of organic solvent used.

The concentration of anion-modified cellulose in the dispersion is preferably 0.01 to 15% by mass, and in consideration of the efficiency when mixing with the subsequent hydrophobizing agent, it is preferably 1 to 10% by mass, and 2 to 6% by mass. is even more preferable.

(1-5) Hydrophobizing agent In step 1, a hydrophobizing agent is added to the anion-modified cellulose dispersion to hydrophobize the anion-modified cellulose to produce a hydrophobized anion-modified cellulose dispersion. Hydrophobization refers to a treatment in which a hydrophobizing agent is bonded to anion-modified cellulose to improve the hydrophobicity of the anion-modified cellulose.

In the present invention, a polyether amine having a polyalkylene glycol group and a hydrocarbon group having 2 or more carbon atoms is used as the hydrophobizing agent. Hydrophobized anion-modified cellulose is formed by bonding the amine in the polyether amine with the anionic group of the anion-modified cellulose. The amine in the polyether amine may be any of primary amine, secondary amine, tertiary amine, quaternary ammonium, aromatic amine, and diamine.
The hydrophobizing agent (polyether amine) used in the present invention has a polyalkylene glycol group in addition to the amine. The polyalkylene glycol group forms the polyether moiety in the polyether amine, and is a group obtained by polymerization or copolymerization of alkylene oxides such as ethylene oxide, propylene oxide, and tetrahydrofuran. Among these, polyalkylene glycol groups obtained by polymerization of propylene oxide are preferred because they have appropriate hydrophobicity. The number of repeating ethylene oxide units and propylene oxide units in the polyalkylene glycol group is not particularly limited, and may be appropriately selected depending on the solubility in organic solvents and the degree of hydrophobicity imparted to the anion-modified cellulose. Generally, ethylene oxide units contribute to improving hydrophilicity, and propylene oxide units contribute to improving hydrophobicity. For example, although not limited thereto, polyether amines having about 5 to 25 propylene oxide units are preferred because they have appropriate hydrophobicity.
The hydrophobizing agent used in the present invention has a hydrocarbon group having two or more carbon atoms in addition to an amine and a polyalkylene glycol group. The type of hydrocarbon group is not particularly limited, and examples include linear or branched alkyl groups, aryl groups, vinyl groups, and alkylaryl groups. Among these, a hydrocarbon group containing a straight-chain alkyl group is preferred because it can impart high hydrophobicity to anion-modified cellulose. The number of carbon atoms in the hydrocarbon group is 2 or more, more preferably 3 or more and 20 or less, and still more preferably 6 or more and 17 or less. Generally, as the number of carbon atoms in the hydrocarbon group in the hydrophobizing agent increases, the hydrophobicity of the hydrophobizing agent improves.

Examples of the hydrophobizing agent having the above structure include, but are not limited to, polypropylene glycol monoamine adducts of alkylphenols. For example, the polypropylene glycol monoamine adduct of nonylalkylphenol is JEFFAMINE (registered trademark) -ω-(nonylphenoxy)poly[oxy(methylethylene)] (branched type)). Also, α-[2-amino(methyl)ethyl]-ω-(methylphenoxy)poly[oxy(methylethylene)], α-[2-amino(methyl)ethyl]-ω-(ethylphenoxy)poly[oxy (methylethylene)], α-[2-amino(methyl)ethyl]-ω-(propylphenoxy)poly[oxy(methylethylene)], α-[2-amino(methyl)ethyl]-ω-(butylphenoxy) ) Poly[oxy(methylethylene)], α-[2-amino(methyl)ethyl]-ω-(pentylphenoxy)poly[oxy(methylethylene)], α-[2-amino(methyl)ethyl]-ω -(hexylphenoxy)poly[oxy(methylethylene)], α-[2-amino(methyl)ethyl]-ω-(heptylphenoxy)poly[oxy(methylethylene)], α-[2-amino(methyl)ethyl] )ethyl]-ω-(octylphenoxy)poly[oxy(methylethylene)], α-[2-amino(methyl)ethyl]-ω-(decylphenoxy)poly[oxy(methylethylene)], etc. can also be used. Yes, but not limited to this.

The hydrophobizing agent is preferably added to the anion-modified cellulose in an amount of 0.40 g or more per 1 g of the hydrophobizing agent. More preferably, the amount of the hydrophobizing agent bound is 0.50 g or more, and even more preferably 1.00 g or more. A method for calculating the amount of the hydrophobizing agent bound will be described later. The hydrophobizing agent binds to the anionic groups of the anionically modified cellulose. When a sufficient amount of hydrophobizing agent is added according to the amount of anionic groups in the anion-modified cellulose, aggregation due to hydrogen bonding between cellulose fibers during drying in Step 2 of producing a dry solid product is inhibited. , the defibration and nanofiber formation in the subsequent step 3 are promoted. There is no particular upper limit to the amount of the hydrophobizing agent bound to 1 g of anion-modified cellulose, but if the amount of the hydrophobizing agent bound to the anion-modified cellulose is too high, the proportion of anion-modified cellulose in the hydrophobized anion-modified cellulose will decrease. The amount of the hydrophobizing agent bound to 1 g of modified cellulose is preferably 10.00 g or less, more preferably 5.00 g or less.

The hydrophobizing agent binds to the anionic groups of the anion-modified cellulose. Due to the reaction mode, the added hydrophobizing agent reacts entirely with anionic groups. The present inventors used infrared spectroscopy to find that when 1 molar equivalent or more of a hydrophobizing agent was added, all of the anion-modified cellulose that was in the acid form (-COOH) changed to -COO ^- . I've confirmed it. This indicates that the amine as a hydrophobizing agent was ionically bonded to all of the anionic groups of the anionically modified cellulose. Therefore, the amount of the hydrophobizing agent bound to 1 g of anion-modified cellulose can be calculated according to the amount of the hydrophobizing agent added using the following formula:
i) When the hydrophobizing agent is added in an amount equal to or more (number of moles) to the amount (number of moles) of the anionic group Amount of hydrophobizing agent bound to 1 g of anion-modified cellulose [g] = Anionicity of the anion-modified cellulose Amount of group [mmol/g] × Molecular weight of hydrophobizing agent × 0.001 × Valency of anionic group ii) The amount (number of moles) of the hydrophobizing agent added is less than the amount (number of moles) of anionic group Case Amount of hydrophobizing agent bound to 1 g of anion-modified cellulose [g] = Amount of anionic groups in anion-modified cellulose [mmol/g] x Molecular weight of hydrophobizing agent x 0.001 x Number of moles of added hydrophobizing agent [ mmol]/Number of moles of anionic group [mmol]
In i), the valence of the anionic group is 1 when the anionic group is a carboxyl group or a carboxyalkyl group, and when the anionic group is a phosphate group (for example, H ₂ PO ₄ -) It is 2. In ii), the number of moles (mmol) of anionic groups can be determined from the amount of anionic groups (mmol/g) and the absolute dry mass (g) of the anion-modified cellulose.

The hydrophobizing agent may be added in an amount of 50 to 150%, preferably 70 to 130%, more preferably 80 to 120%, based on the amount (number of moles) of anionic groups in the anion-modified cellulose. More preferably, it may be added in an amount of 100 to 120%.

The hydrophobizing agent may be added to the anion-modified cellulose dispersion as it is or mixed with water or a water-soluble organic solvent. The concentration of anion-modified cellulose in the anion-modified cellulose dispersion when adding the hydrophobizing agent is preferably 0.01 to 50% by mass, preferably 1 to 45% by mass, and more preferably 2 to 40% by mass. . A dispersion of hydrophobized anion-modified cellulose can be produced by mixing the hydrophobizing agent and anion-modified cellulose for a certain period of time while stirring.

(2) Process 2
In step 2, the dispersion medium is removed from the dispersion of hydrophobized anion-modified cellulose obtained in step 1 to produce a dry solid of hydrophobized anion-modified cellulose. At this time, it is necessary to sufficiently remove the dispersion medium so that the solid content concentration in the dry solid becomes higher than 90% by mass. The solid content concentration in the dry solid is preferably higher than 95% by mass, more preferably 97% by mass or higher, and even more preferably 98% by mass or higher. Cellulose easily absorbs water or water-soluble organic solvents and swells, but in step 2, the water or water-soluble organic solvents absorbed by cellulose are also sufficiently removed so as to satisfy the solid content concentration described above. It is necessary. By sufficiently removing the dispersion medium, which is water or a water-soluble organic solvent, in step 2, the solvent replacement step can be omitted and dispersion can be performed in a low polar organic solvent in the subsequent step 3. . On the other hand, if the solid after drying contains 10% by mass or more of a dispersion medium (water and/or a water-soluble organic solvent), it may be defibrated and dispersed in a low polar organic solvent such as toluene in step 3. In this case, it becomes impossible to mix sufficiently with a low polarity solvent, which may cause problems such as precipitation.

Solids concentration in dry solids can be measured by the following procedure:
The dried solid is dried in an oven at 105° C. for 12 hours, and the solid content concentration of the dried solid is calculated from the mass before and after drying.
Solid content concentration (mass%) of dry solid matter = mass after drying/mass before drying x 100.

The means for removing the dispersion medium is not particularly limited, and for example, the dispersion medium may be removed by placing it at a temperature of 60 to 130° C. for 3 to 24 hours.
The obtained dry solid of hydrophobized anion-modified cellulose can be easily converted into hydrophobized anion-modified CNF by defibrating it in an organic solvent as in step 3 described below. The dry solid of hydrophobized anion-modified cellulose can be suitably used as a raw material for producing hydrophobized anion-modified CNF.
(3) Process 3
In step 3, the dry solid of hydrophobized anion-modified cellulose is mixed with an organic solvent, and the hydrophobized anion-modified cellulose is defibrated in the organic solvent to form a dispersion of hydrophobized anion-modified CNF using the organic solvent as a dispersion medium. Manufacture.

The type of organic solvent used is not particularly limited, and may be a water-soluble organic solvent as described above, but in the present invention, it is less polar than a water-soluble organic solvent (i.e., a solvent that separates when mixed with water). ) Organic solvents can also be used as dispersion media for CNF dispersions. The type of organic solvent may be selected depending on the use of the CNF dispersion.

Examples of low polar organic solvents include, but are not limited to, benzene, toluene, xylene, n-hexane, n-octane, cyclohexane, methylcyclohexane, dichloromethane, dichloroethane, chloroform, methylene chloride, carbon tetrachloride, fluorotrichloro. Examples include methane, trichlorotrifluoromethane, hexafluorobenzene, ethylbenzene, xylene, cyclopentyl methyl ether, and methyl tert-butyl ether. One or more of these can be appropriately selected and used depending on the final use of the anion-modified CNF.
Among organic solvents, toluene, methylpropyl ketone, ethylbenzene, xylene, ethyl acetate, and tetrahydrofuran are preferred because they have high compatibility with the hydrophobizing agent used in the present invention and increase the dispersibility of the hydrophobized anion-modified CNF dispersion. .

The mixing ratio of the organic solvent to the dry solid of the hydrophobized anion-modified cellulose is not particularly limited, but considering the efficiency of defibration, the solid content concentration of the anion-modified cellulose (not including the hydrophobizing agent portion) is 0. The organic solvent is preferably added in an amount of 0.01 to 5% by weight, more preferably 0.5 to 3.0% by weight.

After mixing an organic solvent with a dry solid of hydrophobized anion-modified cellulose, the cellulose is defibrated in the organic solvent to form a dispersion of hydrophobized anion-modified CNF using the organic solvent as a dispersion medium.

The device used for fibrillation is not limited, but it is preferable to use a device that can apply a strong shearing force to the dispersion, such as a high-speed rotation type, a colloid mill type, a high pressure type, a roll mill type, or an ultrasonic type. For efficient fibrillation, it is preferable to use a wet high pressure or ultra-high pressure homogenizer that can apply a pressure of 50 MPa or more to the dispersion and a strong shearing force. The pressure is more preferably 100 MPa or more, and still more preferably 140 MPa or more. A high-pressure or ultra-high-pressure homogenizer uses a pump to pressurize the fluid to a high pressure, which is then ejected through very delicate gaps in the flow path, resulting in emulsification using the combined energy of collisions between particles and shearing forces caused by pressure differences. This is a device that performs dispersion, disintegration, pulverization, and ultra-fine refining. Before the defibration and dispersion treatment with a high-pressure homogenizer, if necessary, a pretreatment can be performed using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer.

By the above defibration, nanofibers of hydrophobized anion-modified cellulose can be obtained. CNF (cellulose nanofiber) is a fiber with an average fiber diameter of about 2 to 500 nm, preferably about 2 to 150 nm, and more preferably about 2 to 20 nm. The aspect ratio is 30 or more, preferably 50 or more, and more preferably 100 or more. The upper limit of the aspect ratio is not limited, but is about 500 or less.

The average fiber diameter and average fiber length of the hydrophobized anion-modified CNFs were determined using an atomic force microscope (AFM) if the diameter was less than 20 nm, and a field emission scanning electron microscope (FE-SEM) if the diameter was 20 nm or more. It can be measured by analyzing 200 randomly selected fibers and calculating the average. Additionally, the aspect ratio can be calculated using the following formula:
Aspect ratio = average fiber length/average fiber diameter.

According to the present invention, a CNF dispersion using an organic solvent having a relatively high viscosity as a dispersion medium can be produced. In the method of the present invention, since the number of defibrations is smaller than in the conventional method of performing defibration two or more times, damage to cellulose fibers is reduced and a CNF dispersion with high viscosity can be produced. Moreover, the viscosity of the hydrophobized anion-modified CNF dispersion can be improved by the specific hydrophobizing agent used in the present invention. The viscosity of the CNF dispersion is measured, for example, by the following method:
Prepare a CNF dispersion with a predetermined concentration, and use a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) according to the method of JIS-Z-8803 at 25°C and a rotation speed of 60 rpm or 6 rpm for 3 minutes. Measure the value after.

In the present invention, for example, a hydrophobizing anion-modified CNF dispersion using toluene as a dispersion medium and having a solid content concentration (in terms of CNF (not including a hydrophobizing agent)) of 1.0% by mass was measured by the above method. A dispersion having a Type B viscosity at 60 rpm of 1000 mPa·s or more, preferably 1500 mPa·s or more, and more preferably 1800 mPa·s or more can be formed.

Furthermore, in the present invention, when a low polar organic solvent such as toluene is used as a dispersion medium, a dispersion with good dispersibility can be obtained. The dispersibility of hydrophobized anion-modified CNF can be evaluated by measuring transparency. Transparency is measured, for example, in the following way:
A CNF dispersion with a predetermined concentration was prepared, and the transmittance of 660 nm light was measured using a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation) using a square cell with an optical path length of 10 mm. Transparency.

In the present invention, for example, a hydrophobizing anion-modified CNF dispersion using toluene as a dispersion medium and having a solid content concentration (in terms of CNF (not including a hydrophobizing agent)) of 1.0% by mass was measured by the above method. It is possible to produce a dispersion having a transparency of 75% or more, more preferably 80% or more, still more preferably 85% or more, still more preferably 90% or more.

(4) Dry solid of hydrophobized anion-modified cellulose The dry solid of hydrophobized anion-modified cellulose obtained in step 2 has the hydrophilicity of the anion-modified cellulose lowered by the hydrophobization treatment, and is not soluble in water or water-soluble. Since it contains almost no aqueous dispersion medium such as an organic solvent, it can be mixed well with various organic solvents and hydrophobic polymers. The dry solid of hydrophobized anion-modified cellulose includes anion-modified cellulose bound to a hydrophobizing agent. The hydrophobizing agent is as described above, and it is preferable that the amount of the hydrophobizing agent bound to 1 g of the above-mentioned anion-modified cellulose is 0.40 g or more. The dry solid has the dispersion medium sufficiently removed so that the solid content concentration is higher than 90% by mass, more preferably the solid content concentration is higher than 95% by mass, and more preferably 97% by mass or more. , more preferably 98% by mass or more.

In the present invention, agglomeration of cellulose fibers during drying of a hydrophobized anion-modified cellulose dispersion is suppressed, and a dry solid with high bulk can be obtained. Therefore, the dry solid material of the present invention becomes a cellulose fiber material that is easily dispersed in an organic solvent and has good handling performance.

The dry solid material of hydrophobized anion-modified cellulose mainly consists of hydrophobized anion-modified cellulose, but prior to removing the dispersion medium from the dispersion of hydrophobized anion-modified cellulose, known additives (antibacterial agent, colorant, resin base material, resin antistatic agent, antifog agent, light stabilizer, ultraviolet absorber, pigment, inorganic filler, mold inhibitor, preservative, foaming agent, flame retardant, etc.). The above additives may be included by drying the product. When the dry solid of the hydrophobized anion-modified cellulose contains additives other than the hydrophobized anion-modified cellulose, the proportion of the hydrophobized anion-modified cellulose in the dry solid is preferably 80% by mass or more, and further 90% by mass or more. It is preferably 95% by mass or more, and more preferably 95% by mass or more. The dry solid may be free of additives and may consist only of hydrophobized anion-modified cellulose (with a small amount of residual dispersion medium).

The form of the dry solid of the hydrophobized anion-modified cellulose is not particularly limited, and may be in the form of a bulk (lump) after removing the dispersion medium, or may be pulverized as appropriate to form a powder, depending on the use. You can select it.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples.
<Example 1>
Add 500 g (absolutely dry) of bleached unbeaten kraft pulp (85% whiteness) derived from coniferous trees to 500 ml of an aqueous solution containing 780 mg of TEMPO (Sigma Aldrich) and 75.5 g of sodium bromide, and stir until the pulp is uniformly dispersed. Stirred. An aqueous sodium hypochlorite solution was added to the reaction system at a concentration of 6.0 mmol/g to start the oxidation reaction. During the reaction, the pH in the system decreased, but the pH was adjusted to 10 by successively adding a 3M aqueous sodium hydroxide solution. The reaction was terminated when the sodium hypochlorite was consumed and the pH within the system stopped changing. After the reaction, the mixture was filtered through a glass filter to separate the pulp, and the pulp was sufficiently washed with water to obtain pulp into which carboxyl groups were introduced (carboxylated cellulose). The amount of carboxyl groups in this carboxylated cellulose was 1.42 mmol/g.

The solid content concentration of carboxylated cellulose was adjusted to 5% by mass with water, and hydrochloric acid with a concentration of 10% was added to convert the sodium salt type carboxyl group (-COONa) in the carboxylated cellulose to the acid type (-COOH). ). Thereafter, the mixture was dehydrated by suction filtration using a glass filter. Once again, the solid content concentration of carboxylated cellulose was adjusted to 5% by mass with water, and then dehydrated. This process was repeated three times to obtain acid type carboxylated cellulose with a solid content concentration of 25% by mass.

The obtained dispersion of acid type carboxylated cellulose was diluted with water to a solid content concentration of 4% by mass, and JEFFAMINE (registered trademark) XJT-436 (manufactured by HUNTSMAN, molecular weight 1004) was added as a hydrophobizing agent. It was added in an amount of 1 equivalent based on the amount of carboxyl groups. When the amount of the hydrophobizing agent bound is calculated according to the above formula, it is 1.43 g. The mixture was mixed with a homogenizer (1500 rpm, 10 minutes) to produce a dispersion of carboxylated cellulose bound with a hydrophobizing agent (hydrophobized carboxylated cellulose). The dispersion of hydrophobized carboxylated cellulose was allowed to stand at a temperature of 70° C. for 15 hours to produce a dry solid of hydrophobized carboxylated cellulose (solid content concentration 98% by mass).
Toluene was added to the obtained dry solid so that the solid content was 1% by mass in terms of carboxylated cellulose (not including a hydrophobizing agent), and the mixture was stirred at 8000 rpm for 10 minutes. Subsequently, a dispersion of hydrophobized carboxylated CNF using toluene as a dispersion medium was obtained by processing (defibration) at 20° C. once at 80 MPa and then twice at 150 MPa using an ultra-high pressure homogenizer. The yield (ie, the ratio of the mass of carboxylated CNF in the finally obtained hydrophobized carboxylated CNF to the mass of the carboxylated cellulose used) was 100%.

The transparency and viscosity of the obtained dispersion of hydrophobized carboxylated CNF (dispersion medium: toluene, solid content concentration (in terms of carboxylated CNF): 1.0% by mass) were measured by the above-mentioned method. The results are shown in Table 1.

<Example 2>
A dispersion of hydrophobized carboxylated CNF using methanol as a dispersion was obtained in the same manner as in Example 1 except that methanol was used instead of toluene. The transparency and viscosity of the obtained dispersion of hydrophobized carboxylated CNF (dispersion medium: methanol, solid content concentration (in terms of carboxylated CNF): 1.0% by mass) were measured in the same manner as in Example 1. The results are shown in Table 1.
<Comparative example 1>
A dispersion of hydrophobized carboxylated CNF using toluene as a dispersion medium was produced in the same manner as in Example 1 except that JEFFAMINE (registered trademark) M-1000 (manufactured by HUNTSMAN, molecular weight 1000) was used as a hydrophobizing agent. . The amount of hydrophobizing agent bound is 1.42 g. The transparency and viscosity of the obtained dispersion of hydrophobized carboxylated CNF (dispersion medium: toluene, solid content concentration (calculated as carboxylated CNF): 1% by mass) were measured in the same manner as in Example 1. The results are shown in Table 1.
<Comparative example 2>
A dispersion of hydrophobized carboxylated CNF using methanol as a dispersion was obtained in the same manner as in Comparative Example 1 except that methanol was used instead of toluene. The transparency and viscosity of the obtained dispersion of hydrophobized carboxylated CNF (dispersion medium: methanol, solid content concentration (in terms of carboxylated CNF): 1.0% by mass) were measured in the same manner as in Example 1. The results are shown in Table 1.

また、比較例に用いたＪＥＦＦＡＭＩＮＥ（登録商標）Ｍ－１０００の化学式は、以下の通りである：

The chemical formula of JEFFAMINE (registered trademark) XJT-436 used in the examples is as follows:

In addition, the chemical formula of JEFFAMINE (registered trademark) M-1000 used in the comparative example is as follows:

From the results in Table 1, by using a polyether amine having a polyalkylene glycol group and a hydrocarbon group having 2 or more carbon atoms as a hydrophobizing agent (Examples 1 and 2), the dispersions of Comparative Examples 1 and 2 were improved. In comparison, it can be seen that a dispersion with improved viscosity can be obtained. In particular, when toluene was used as the dispersion medium, it was found that the transparency was high and the dispersibility was good. The reason for this is that the used hydrophobizing agent having a polyalkylene glycol group and a hydrocarbon group having 2 or more carbon atoms is highly compatible with toluene, which improves the dispersibility. are doing. However, it is not limited to this theory. For reference, Table 2 shows the SP values of each hydrophobizing agent, each organic solvent, and cellulose used in Examples and Comparative Examples. It can be said that the closer the SP values are, the higher the compatibility is. Note that the SP values in Table 2 are values calculated by the Fedors method, and the column for polyalkylene glycol group of Example 1 in Table 2 is the SP value of -(OCH ₂ CHCH ₃ ) _13.5 NH ₂ calculated. The alkyl group column is the calculated SP value of nonylbenzene, and the polyalkylene glycol group column of Comparative Example 1 is CH ₃ (OCH ₂ CH ₂ ) ₃ (OCH ₂ CHCH ₃ ). The SP value of ₁₉ NH ₂ is calculated.

Claims (5)

Step 1 of producing a hydrophobized anion-modified cellulose dispersion by adding a hydrophobizing agent to the anion-modified cellulose dispersion;
Step 2 of removing the dispersion medium from the dispersion of the hydrophobized anion-modified cellulose to produce a dry solid of the hydrophobized anion-modified cellulose, and mixing the dry solid of the hydrophobized anion-modified cellulose with an organic solvent, step 3 of defibrating the hydrophobized anion-modified cellulose in the organic solvent to produce a dispersion of hydrophobized anion-modified cellulose nanofibers using the organic solvent as a dispersion medium;
including;
The hydrophobizing agent is a polyether monoamine , and the polyether monoamine has a hydrocarbon group having 6 or more carbon atoms in addition to an amine and a polyalkylene glycol group, and the polyalkylene glycol group has 5 to 25 carbon atoms. having propylene oxide units,
The dry solid of the hydrophobized anion-modified cellulose has a solid content concentration higher than 90% by mass,
A method for producing a dispersion of hydrophobized anion-modified cellulose nanofibers. Step 1 of adding a hydrophobizing agent to a dispersion of anion-modified cellulose to produce a dispersion of hydrophobized anion-modified cellulose; and removing the dispersion medium from the dispersion of hydrophobized anion-modified cellulose to produce a hydrophobized anion-modified cellulose dispersion. Step 2 of producing a dry solid of cellulose;
including;
The hydrophobizing agent is a polyether monoamine , and the polyether monoamine has a hydrocarbon group having 6 or more carbon atoms in addition to an amine and a polyalkylene glycol group, and the polyalkylene glycol group has 5 to 25 carbon atoms. having propylene oxide units,
The dry solid of the hydrophobized anion-modified cellulose has a solid content concentration higher than 90% by mass,
A method for producing a dry solid of hydrophobized anion-modified cellulose. The method according to claim 1 or 2, wherein the anion-modified cellulose is cellulose having a carboxyl group or cellulose having a carboxyalkyl group. It contains anion-modified cellulose bound to a hydrophobizing agent, the solid content concentration is higher than 90% by mass, the hydrophobizing agent is a polyether monoamine , and the polyether monoamine contains, in addition to an amine and a polyalkylene glycol group, A dry solid of hydrophobized anion-modified cellulose having a hydrocarbon group having 6 or more carbon atoms, and a polyalkylene glycol group having 5 to 25 propylene oxide units . It contains anion-modified cellulose nanofibers bound to a hydrophobizing agent, an organic solvent is used as a dispersion medium, the hydrophobizing agent is a polyether monoamine , and the polyether monoamine is composed of an amine and 5 to 25 propylene oxide units. A dispersion of hydrophobized anion-modified cellulose nanofibers having a hydrocarbon group having 6 or more carbon atoms in addition to a polyalkylene glycol group .