JP7239294B2 - Method for producing anion-modified cellulose nanofiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing anion-modified cellulose nanofibers. More specifically, it relates to a method for efficiently producing acid-type anion-modified cellulose nanofibers from metal salt-type anion-modified cellulose nanofibers. It relates to a method for producing a modified cellulose nanofiber dispersion.

It is known that by introducing anionic groups such as carboxyl groups and carboxymethyl groups into the cellulose molecular chain and mechanically processing (fibrillating) it can be converted into cellulose nanofibers with nanoscale fiber diameters. there is Cellulose nanofibers are lightweight, have high strength, are biodegradable, and have high transparency when formed into films.

Usually, anion-modified cellulose nanofibers are highly hydrophilic because the introduced anionic groups form salts such as sodium salts. It has low compatibility with other rigid polymers. In addition, the dispersibility in low-polarity organic solvents is low. As a method to solve this problem, by acidifying the metal salt type anionic group (eg, —COONa), it is converted to the acid type (eg, —COOH), and the hydrophilicity of the anion-modified cellulose nanofiber is increased. There are ways to lower it. As a method for converting to an acid form, the present applicant disclosed a method of adding an acid such as a mineral acid (Patent Document 1) and a method of desalting using a cation exchange resin (Patent Document 2).

WO2010/116795 JP 2018-100383 A

In order to reduce the hydrophilicity and increase the affinity with hydrophobic polymers and organic solvents, when converting the metal salt form to the acid form, in the method of Patent Document 1, when an acid is added, anion-modified cellulose Aggregation of nanofibers occurs. A dispersion can be obtained by mechanically pulverizing the aggregated cellulose nanofibers again, but the resulting dispersion has poor transparency. On the other hand, in the method of Patent Document 2, when the cellulose nanofibers are highly concentrated and gel-like, they are sufficiently mixed and brought into contact with the cation exchange resin, or the resin and cellulose nanofibers are separated by filtration after contact. difficult and difficult to manufacture efficiently.

An object of the present invention is to provide a method capable of efficiently producing acid-type anion-modified cellulose nanofibers capable of forming a highly transparent dispersion.

As a result of intensive studies, the present inventors prepared metal salt-type anion-modified cellulose, added an amphipathic polymer compound to it, defibrated it, and obtained metal salt-type cellulose nanofibers. It was found that by adding an acid to the nanofibers to convert them into an acid form, it is possible to efficiently produce acid-type anion-modified cellulose nanofibers capable of forming a highly transparent dispersion. The invention includes, but is not limited to:
(1) Step 1 of preparing a mixture containing a metal salt-type anion-modified cellulose and an amphipathic polymer compound;
The mixture obtained in step 1 is mechanically treated to convert the metal salt-type anion-modified cellulose into metal salt-type anion-modified cellulose nanofibers, thereby producing a dispersion containing metal salt-type anion-modified cellulose nanofibers. An acid and a water-soluble organic solvent are added to the dispersion containing the metal salt-type anion-modified cellulose nanofibers obtained in the step 2 of forming the body, and the metal salt-type anion-modified cellulose nanofibers. , step 3 of converting to the acid form,
A method for producing acid-form anion-modified cellulose nanofibers.
(2) After step 3, further comprising step 4 of performing filtration to remove the amphipathic polymer compound together with the water-soluble organic solvent to produce aggregates of acid-type anion-modified cellulose nanofibers, (1) The method described in .
(3) Step 5 of adding an organic solvent to the aggregates of acid-type anion-modified cellulose nanofibers obtained in Step 4 to form a mixture;
Step 6 of adding a hydrophobizing agent to the mixture obtained in Step 5, and Mechanically treating the mixture containing the hydrophobizing agent obtained in Step 6 to obtain an anion-modified cellulose nano Step 7 of forming a dispersion of fibers
The method of (1) or (2), further comprising
(4) The method according to any one of (1) to (3), wherein the anion-modified cellulose nanofibers are cellulose nanofibers having carboxyalkyl groups or cellulose nanofibers having carboxyl groups.

INDUSTRIAL APPLICABILITY According to the present invention, acid-type anion-modified cellulose nanofibers capable of forming highly transparent dispersions can be efficiently produced. By adding an amphipathic polymer compound to a metal salt-type anion-modified cellulose and then defibrating the cellulose, the resulting metal salt-type anion-modified cellulose nanofiber contains an amphiphilic polymer compound. will be The presence of this amphiphilic polymer compound when the acid is added suppresses the aggregation of the cellulose nanofibers, and an anion-modified cellulose nanofiber dispersion having high transparency is obtained from the acid-type anion-modified cellulose nanofibers. be able to obtain Since the amphiphilic polymer compound dissolves in a water-soluble organic solvent, it can be removed from the cellulose nanofibers by repeating washing operations such as solvent addition and suction filtration before dispersing in a low-polarity dispersion medium. can. In the present invention, it is possible to produce acid-type anion-modified cellulose nanofibers capable of forming a highly transparent dispersion from relatively high-concentration metal salt-type anion-modified cellulose nanofibers, which is efficient. Manufacturing is possible. Moreover, in the present invention, acid-type anion-modified cellulose nanofibers capable of forming a highly viscous dispersion can be produced.

TECHNICAL FIELD The present invention relates to a method for producing anion-modified cellulose nanofibers. More particularly, it relates to a method for producing acid-type anion-modified cellulose nanofibers from metal salt-type anion-modified cellulose nanofibers. Specifically, a mixture containing a metal salt-type anion-modified cellulose and an amphiphilic polymer compound is prepared (step 1), and the mixture in step 1 is mechanically treated to remove the metal salt-type in the mixture. Anion-modified cellulose is fibrillated and converted into metal salt-type anion-modified cellulose nanofibers to form a dispersion containing metal salt-type anion-modified cellulose nanofibers (step 2), and the dispersion obtained in step 2 adding an acid and a water-soluble organic solvent to the body to convert the metal salt form to the acid form (Step 3). After step 3, the amphiphilic polymer compound may be removed together with the water-soluble organic solvent by filtration (step 4). The aggregate of acid-form anion-modified cellulose nanofibers obtained in step 4 is added to an organic solvent (step 5), a hydrophobizing agent is added (step 6), and the mixture containing the hydrophobizing agent is added to the organic solvent. It may be mechanically treated (defibrated) in an organic solvent to form an anion-modified cellulose nanofiber dispersion (Step 7).

(1) Process 1
In step 1, a mixture containing metal salt-type anion-modified cellulose and an amphipathic polymer compound is prepared.

(1-1) Anion-Modified Cellulose Anion-modified cellulose refers to cellulose in which an anionic group is introduced into the molecular chain. Among these, those in which the counter ion of the introduced anionic group is a metal ion such as sodium or potassium are referred to as metal salt-type anion-modified cellulose. Metal salt-type anion-modified cellulose can be obtained, for example, by the following method. Moreover, you may use a commercial thing. 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, or carboxyalkylated cellulose, has anionic groups uniformly introduced therein, and is easily fibrillated uniformly. , is preferable in that cellulose nanofibers with high transparency can be obtained.

As the anion-modified cellulose, one that maintains at least a part of its fibrous shape even when dispersed in water or a water-soluble organic solvent is used. Nanofibers cannot be obtained by using materials that do not maintain their fibrous shape (that is, materials that dissolve). The expression that at least a part of the fibrous shape is maintained when dispersed means that a fibrous substance can be observed when an anion-modified cellulose dispersion is observed with an electron microscope. In addition, anion-modified cellulose is preferable, since a peak of cellulose type I crystals can be observed when measured by X-ray diffraction.

The degree of crystallinity of cellulose in the anion-modified cellulose is preferably 50% or more, more preferably 60% or more for crystalline type I. By adjusting the crystallinity to the above range, it is possible to sufficiently obtain crystalline cellulose fibers that do not dissolve even after the fibers are refined by fibrillation. The crystallinity of cellulose can be controlled by the crystallinity of the raw material cellulose and the degree of anion modification. The method for measuring the crystallinity of anion-modified cellulose is as follows:
A sample is placed in a glass cell and measured using an X-ray diffraction measurement device (LabX XRD-6000, manufactured by Shimadzu Corporation). The degree of crystallinity is calculated using the method of Segal et al. Using the diffraction intensity at 2θ = 10° to 30° in the X-ray diffraction diagram as a baseline, the diffraction intensity at 2θ = 22.6° at the 002 plane and 2θ = It is calculated from the diffraction intensity of the amorphous portion at 18.5° by the following equation.
Xc=(I002c−Ia)/I002c×100
Xc: Crystallinity of type I of 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 the anion-modified cellulose and the proportion of cellulose type I crystals when the anion-modified cellulose is used as nanofibers are usually the same.
(1-1-1) Cellulose The type of cellulose used as a 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., according to its origin, production method, and the like. Any of these celluloses can be used as a raw material in the present invention.

Examples of natural cellulose include bleached or unbleached pulp (bleached wood pulp or unbleached wood pulp); linters, purified linters; cellulose produced by microorganisms such as acetic acid bacteria. Raw materials for bleached or unbleached pulp are not particularly limited, and examples thereof include wood, cotton, straw, bamboo, hemp, jute, and kenaf. Also, the method for producing the bleached pulp or the unbleached pulp is not particularly limited, and may be a mechanical method, a chemical method, or a combination of the two. Examples of bleached pulp or unbleached pulp classified by manufacturing method include mechanical pulp (thermomechanical pulp (TMP), groundwood pulp), chemical pulp (softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP) ), softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP) and other kraft pulps). Further, dissolving pulp may be used in addition to paper pulp. Dissolving pulp is pulp that has been chemically refined, and is mainly used by dissolving it in chemicals, and serves as a main raw material for artificial fibers, cellophane, and the like.

Examples of regenerated cellulose include those obtained by dissolving cellulose in some solvent such as cuprammonium solution, cellulose xanthate solution, morpholine derivative, and spinning again.
The fine cellulose is obtained by subjecting cellulosic materials such as the natural cellulose and regenerated cellulose to depolymerization (for example, acid hydrolysis, alkaline hydrolysis, enzymatic decomposition, explosion treatment, vibration ball mill treatment, etc.). and those obtained by mechanically processing the above cellulosic materials.

(1-1-2) Anion Modification Anion modification refers to the introduction of an anionic group into cellulose, specifically the introduction of an anionic group into the pyranose ring of cellulose by oxidation or substitution reaction. In the present invention, the oxidation reaction means a reaction of directly oxidizing a hydroxyl group of a pyranose ring to a carboxyl group. Further, in the present invention, a substitution reaction means a reaction for introducing an anionic group into a pyranose ring by a substitution reaction other than the oxidation.

(1-1-2-1) Carboxyalkylation An example of anion modification is the introduction of a carboxyalkyl group such as a carboxymethyl group. As used herein, a carboxyalkyl group refers to -RCOOH (acid form) and -RCOOM (metal salt form). Here, R is an alkylene group such as a methylene group or ethylene group, and M is a metal ion.

Carboxyalkylated cellulose may be obtained by a known method, or a commercially available product may be used. Preferably, the degree of carboxyalkyl substitution per anhydroglucose unit of the cellulose is less than 0.40. Furthermore, when the anionic group is a carboxymethyl group, the degree of carboxymethyl substitution is preferably less than 0.40. If the degree of substitution is 0.40 or more, the dispersibility of the cellulose nanofibers is lowered. Also, the lower limit of the degree of carboxyalkyl substitution is preferably 0.01 or more. Considering workability, the degree of substitution is particularly preferably 0.02 to 0.35, more preferably 0.10 to 0.30. The anhydroglucose unit means an individual anhydroglucose (glucose residue) constituting cellulose, and the degree of carboxyalkyl substitution refers to the hydroxyl group (—OH) in the glucose residue constituting cellulose. The percentage of those substituted with ether groups (-ORCOOH or -ORCOOM) (the number of carboxyalkyl ether groups per glucose residue) is shown.

An example of a method for producing carboxyalkylated cellulose includes the following steps. The modification is modification by a substitution reaction. Carboxymethylated cellulose will be described as an example.

i) Mixing the raw material with the solvent and the mercerizing agent, and mercerizing at a reaction temperature of 0° C. to 70° C., preferably 10° C. to 60° C., and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. the process of processing,
ii) then, 0.05 to 10.0 times mol of a carboxymethylating agent per glucose residue is added, the reaction temperature is 30° C. to 90° C., preferably 40° C. to 80° C., and the reaction time is 30 minutes to 10 hours; A step of conducting the etherification reaction preferably for 1 hour to 4 hours.

The above-mentioned cellulose raw material can be used as the bottom raw material. As the solvent, 3 to 20 times by weight of water or a lower alcohol, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, etc. alone, or two Mixed media of more than one species can be used. When a lower alcohol is mixed, the mixing ratio is preferably 60% by mass to 95% by mass. As the mercerizing agent, it is preferable to use an alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, in an amount of 0.5 to 20 times the moles of the anhydroglucose residue of the 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 celluloses electrically repel each other. Therefore, cellulose into which carboxymethyl substituents have been introduced can be nano-fibrillated. If the number of carboxymethyl substituents per glucose unit is less than 0.02, nano-fibrillation may not be sufficient. The degree of carboxyalkyl substitution in the carboxyalkylated cellulose is generally the same as the degree of carboxyalkyl substitution when the carboxyalkylated cellulose is made into nanofibers.

The degree of carboxymethyl substitution per glucose unit can be measured by the following method:
About 2.0 g of carboxymethylated cellulose (absolute dry) is precisely weighed and placed in a 300 mL conical flask with a common stopper. 100 mL of a solution obtained by adding 100 mL of special grade concentrated nitric acid to 900 mL of methanol is added and shaken for 3 hours to convert carboxymethylated cellulose salt (CM cellulose) into hydrogenated CM cellulose. 1.5 g to 2.0 g of hydrogenated CM cellulose (absolutely dried) is accurately weighed and placed in a 300 mL Erlenmeyer flask equipped with a common stopper. Hydrogenated CM-cellulose is wetted with 15 mL of 80% by mass methanol, 100 mL of 0.1 N NaOH is added, and shaken at room temperature for 3 hours. Excess NaOH was back-titrated with 0.1 N H2SO4 using phenolphthalein as an indicator. The degree of carboxymethyl substitution (DS) is calculated by the formula:
A=[(100×F′−(0.1N H ₂ SO ₄ ) (mL)×F)×0.1]/(absolute dry weight of hydrogen-type CM cellulose (g))
DS = 0.162 x A/(1 - 0.058 x A)
A: Amount of 1N NaOH (mL) required to neutralize 1 g of hydrogenated CM-cellulose
F: factor of 0.1N _H2SO4 F': factor of 0.1N _NaOH .

The degree of substitution with carboxyalkyl groups other than carboxymethyl groups can also be measured in the same manner as described above.
(1-1-2-2) carboxylation (oxidation)
An example of anionic modification is carboxylation (introduction of carboxyl groups to cellulose, also called "oxidation"). As used herein, a carboxyl group refers to -COOH (acid form) and -COOM (metal salt form) (wherein M is a metal ion). Carboxylated cellulose (also referred to as “oxidized cellulose”) can be obtained by carboxylating (oxidizing) the above cellulose raw material by a known method. Although not particularly limited, the amount of carboxyl groups is preferably 0.6 mmol/g to 3.0 mmol/g, more preferably 1.0 mmol/g to 2.0 mmol, relative to the absolute dry mass of anion-modified cellulose or anion-modified cellulose nanofibers. /g is more preferred.

The carboxyl group content of anion-modified cellulose or anion-modified cellulose nanofibers can be measured by the following method:
60 ml of a 0.5% by mass slurry (aqueous dispersion) of carboxylated cellulose was prepared, and 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. and 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 carboxylated cellulose]=a [ml]×0.05/carboxylated cellulose mass [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. You can mention how to do it. This oxidation reaction selectively oxidizes the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface, resulting in a cellulose fiber having an aldehyde group and a carboxyl group (-COOH) or carboxylate group ( ^-COO- ) on the surface. can be obtained. Although the concentration of cellulose during the reaction is not particularly limited, it is preferably 5% by mass or less.

An N-oxyl compound means a compound capable of generating a nitroxy radical. 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-oxy radical (TEMPO) and its derivatives (eg 4-hydroxy TEMPO). The amount of the N-oxyl compound to be used is not particularly limited as long as it is a catalytic amount that can oxidize the raw material cellulose. For example, it is preferably 0.01 mmol to 10 mmol, more preferably 0.01 mmol to 1 mmol, even more preferably 0.05 mmol to 0.5 mmol, relative to 1 g of absolute dry cellulose. Further, it is preferable that the concentration is about 0.1 mmol/L to 4 mmol/L with respect to the reaction system.

Bromides are compounds containing bromine, examples of which include alkali metal bromides that can be dissociated and ionized in water. Also, iodides are compounds containing iodine, examples of which 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, 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, relative to 1 g of absolute dry cellulose. The modification is modification by an oxidation reaction.

Known oxidizing agents can be used, for example, halogens, hypohalous acids, halogenous acids, perhalogenates or salts thereof, halogen oxides, peroxides and the like can be used. Among them, sodium hypochlorite is preferable because it is inexpensive and has less environmental load. An 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, relative to 1 g of absolute dry cellulose. . Further, for example, 1 mol to 40 mol is preferable with respect to 1 mol of the N-oxyl compound.

The oxidation process of cellulose allows the reaction to 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. Since carboxyl groups are generated in the cellulose as the reaction progresses, the pH of the reaction solution decreases. 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 at about 8-12, preferably about 10-11. Water is preferable as the reaction medium because it is easy to handle and less likely to cause side reactions. The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of the oxidation, and is usually 0.5 hours to 6 hours, for example, about 0.5 hours to 4 hours.

Moreover, 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 reaction in the first step, again under the same or different reaction conditions, the reaction can be efficiently It can be oxidized well.

Another example of the carboxylation (oxidation) method is a method of oxidizing by contacting a cellulose raw material with an ozone-containing gas. This oxidation reaction oxidizes at least the hydroxyl groups at the 2- and 6-positions of the glucopyranose ring and causes degradation of the cellulose chain. The ozone concentration in the gas containing ozone 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 to 30 parts by mass, more preferably 5 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, cellulose can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved. 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 include chlorine-based compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, these oxidizing agents can be dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and the cellulose raw material can be immersed in the solution for additional oxidation treatment.

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

(1-1-2-3) Esterification One example of anion modification is esterification. Examples of the esterification method include a method of mixing a cellulose raw material with powder or an aqueous solution of a phosphoric acid compound, a method of adding an aqueous solution of a phosphoric acid compound to a slurry of a cellulose raw material, and the like. 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, a compound having a phosphate group is preferable because it is low cost, easy to handle, and can introduce a phosphate group into the cellulose of the pulp fiber to improve defibration efficiency. Compounds having a phosphate group include 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, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate , ammonium pyrophosphate, ammonium metaphosphate and the like. Phosphate groups can be introduced into cellulose by using one or more of these in combination. Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, phosphoric acid, from the viewpoint of high efficiency of introduction of phosphate group, easy fibrillation in the fibrillation process described below, and easy industrial application is preferred. Sodium dihydrogen phosphate and disodium hydrogen phosphate are particularly preferred. Further, it is desirable to use the phosphoric acid-based compound in the form of an aqueous solution, since the reaction can proceed uniformly and the efficiency of introduction of the phosphoric acid group is increased. The pH of the aqueous solution of the phosphoric acid-based compound is preferably 7 or less because the efficiency of introducing phosphoric acid groups is increased, but from the viewpoint of suppressing hydrolysis of pulp fibers, pH 3 to 7 is preferable.

Examples of the method for producing the phosphorylated cellulose include the following method. A phosphoric acid compound is added to a suspension of a cellulosic raw material having a solid concentration of 0.1% by mass to 10% by mass while stirring to introduce a phosphoric acid group into the cellulose. When the cellulosic raw material is 100 parts by mass, the amount of the phosphoric acid compound added is preferably 0.2 parts by mass to 500 parts by mass, and 1 part by mass to 400 parts by mass, as the elemental amount of phosphorus. is more preferred. If the proportion of the phosphoric acid-based compound is at least the lower limit, the yield of fine fibrous cellulose can be further improved. However, if the above upper limit is exceeded, the effect of improving the yield reaches a ceiling, which is not preferable from the viewpoint of cost.

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

The degree of phosphate group substitution per glucose unit of the phosphated cellulose is preferably 0.001 or more and less than 0.40. By introducing a phosphate group substituent into cellulose, the celluloses electrically repel each other. Therefore, cellulose into which a phosphate group has 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 defibrate efficiently, it is preferable to wash the cellulose-based raw material obtained above with cold water after boiling it. Modification by these esterifications is modification by a substitution reaction. The degree of substitution in the esterified cellulose and the degree of substitution when the same esterified cellulose is made into nanofibers are usually the same.

(1-2) Amphiphilic Polymer Compound In step 1, an amphiphilic polymer compound is added to the metal salt-type anion-modified cellulose to form a mixture. An amphipathic polymer compound means a compound having both a hydrophilic group and a hydrophobic group in one molecule and having a molecular weight of about 200 to 20,000. As the amphipathic polymer compound, those soluble in both water and the following water-soluble organic solvents are preferred. Specifically, cellulose derivatives (hydroxypropylmethylcellulose, cellulose acetate, ethylcellulose, methylcellulose, ethylmethylcellulose, nitrocellulose), various polymers (vinyl chloride resin, vinylidene chloride, polyvinyl chloride, polyvinyl alcohol, polystyrene, ABS resin, polyisobutylene , PMMA resins, polycarbonates, urea resins, epoxy resins, unsaturated polyesters), polyethylene glycol and its derivatives, nonionic surfactants, and the like. Among these, polyethylene glycol having a molecular weight of about 200 to 4000 is preferable from the viewpoint of good dispersibility.

The amount of the amphipathic polymer compound to be added is preferably about 1.0 to 15.0 times, more preferably about 1.5 to 12.5 times the mass of the anion-modified cellulose. If the amount added is too small, the effect of converting the anion-modified cellulose into nanofibers and preventing aggregation when an acid is added is reduced. On the other hand, even if the amount is too large, the above effects are not enhanced, so a moderate amount is preferable from the viewpoint of cost.

(2) Process 2
In step 2, the mixture of the metal salt-type anion-modified cellulose obtained in step 1 and the amphipathic polymer compound is mechanically treated to defibrate the metal salt-type anion-modified cellulose, and the metal salt-type anion-modified cellulose is fibrillated. Anion-modified cellulose is converted to metal salt-type anion-modified cellulose nanofibers to form a dispersion containing metal salt-type anion-modified cellulose nanofibers.

(2-1) Mechanical treatment (fibrillation)
For the mechanical treatment (fibrillation of anion-modified cellulose), an apparatus capable of applying a strong shearing force such as, but not limited to, high-speed rotation type, colloid mill type, high pressure type, roll mill type, and ultrasonic type is used. For efficient defibration, it is preferable to use a wet high-pressure or ultrahigh-pressure homogenizer capable of applying a pressure of 50 MPa or more and a strong shearing force. The pressure is more preferably 100 MPa or higher, still more preferably 140 MPa or higher. A high-pressure or ultra-high-pressure homogenizer pressurizes a fluid with a pump to make it high pressure, and by jetting it out from very fine gaps provided in the flow path, it emulsifies with total energy such as shear force due to collision between particles and pressure difference. , dispersing, disintegrating, pulverizing, and ultra-fine. Prior to fibrillation and dispersion treatment with a high-pressure homogenizer, pretreatment can be performed using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer, if necessary.

At the time of defibration, it is preferable to adjust the solid content concentration of the anion-modified cellulose to 0.01% by mass to 10% by mass from the viewpoint of defibration efficiency. Water, an organic solvent, or a mixture thereof can be appropriately selected as a dispersion medium for fibrillation. Although the type of organic solvent is not limited, polar solvents having a high affinity for hydroxyl groups in cellulose 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, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and the like. The dispersion medium may be used alone, or two or more of them may be mixed and used. For example, a form in which two or more kinds of organic solvents are mixed, a form in which water and an organic solvent are contained, a form in which only water is used, or the like can be appropriately selected. Using only water as the dispersion medium (ie, 100% water) is preferred for ease of handling. When water and an organic solvent are mixed, the mixing ratio is not particularly limited, and the mixing ratio may be appropriately adjusted according to the type of organic solvent used.

(1-2) Anion-Modified Cellulose Nanofibers By the mechanical treatment (fibrillation) described above, the metal salt-type anion-modified cellulose is converted into metal salt-type anion-modified cellulose nanofibers.

Anion-modified cellulose nanofibers are fibers having an average fiber diameter of about 3 nm to 500 nm, preferably about 3 nm to 150 nm, more preferably about 3 nm to 20 nm. The aspect ratio is 30 or more, preferably 50 or more, more preferably 100 or more. Although the upper limit of the aspect ratio is not limited, it is about 500 or less.

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

Metal salt-type anion-modified cellulose nanofibers are cellulose nanofibers having metals (eg, sodium, potassium, etc.) derived from chemicals used in the anion-modification reaction as counter ions for anionic groups. For example, in metal salt-type carboxylated cellulose nanofibers, the carboxyl group is -COO ^- M ⁺ , and in metal salt-type carboxyalkylated cellulose nanofibers, the carboxyl alkyl group is -RCOO ^- M ⁺ . (wherein M is a metal such as sodium or potassium, and R is an alkylene group such as a methylene group or an ethylene group).

The metal salt-type anion-modified cellulose nanofibers obtained by the above method are in the form of a dispersion using water and/or a polar solvent as a dispersion medium. The concentration in the metal salt-type anion-modified cellulose nanofiber dispersion is not particularly limited as long as it can be mixed with the acid in the subsequent step 3, but is 0.5 to 10.0% by mass. is preferred. In the present invention, for example, even high-concentration anion-modified cellulose nanofiber dispersions of 1.5% by mass or more, or even 2.5% by mass or more can be handled. The use of a high-concentration anion-modified cellulose nanofiber dispersion increases the amount of cellulose nanofibers that can be treated at one time, thereby enabling efficient treatment.

(3) Process 3
In step 3, by adding an acid and a water-soluble organic solvent to the dispersion containing the metal salt-type anion-modified cellulose nanofibers, an acid form (for example, —COOH, —RCOOH, etc.).

(3-1) Acid An acid is added to convert the metal salt-type anion-modified cellulose nanofibers into an acid-type. The type of acid used is not particularly limited, and may be an inorganic acid or an organic acid. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, nitrous acid, phosphoric acid, and the like. Examples of organic acids include acetic acid, lactic acid, oxalic acid, citric acid, formic acid, adipic acid, sebacic acid, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid, and gluconic acid. Hydrochloric acid or sulfuric acid, which are commonly available and readily available, are preferred. The pH during acid treatment is preferably in the range of 1-6, more preferably 2-5. The amount of acid to be added is not particularly limited as long as it is an amount that can convert the metal salt-type anion-modified cellulose nanofibers into the acid form. 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, it is preferably 10 equivalents or more.

(3-2) Water-Soluble Organic Solvent Simultaneously with or before adding the acid in step 3, a water-soluble organic solvent is added to the anion-modified cellulose nanofibers. A water-soluble organic solvent refers to an organic solvent that can be optionally mixed with water without separating. Examples of water-soluble organic solvents include, but are not limited to, 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 the like, which may be used alone or in combination.

The amount of the water-soluble organic solvent to be added is not particularly limited as long as it is an amount that can be removed from the anion-modified cellulose nanofiber dispersion in a later step. An amount of about 0.5 to 2.0% by mass is preferred.

(4) Step 4
After converting the anion-modified cellulose nanofibers from the metal salt form to the acid form in step 3, optionally in step 4, filtration may be performed to remove the amphipathic polymer compound together with the acid and the water-soluble organic solvent. . Since the amphipathic polymer compound dissolves in both water and a water-soluble organic solvent, the acid, the solvent, and the amphiphilic polymer compound are separated by filtering the cellulose nanofiber dispersion to which the acid has been added. It can be filtered out from cellulose nanofibers.

The method of filtration is not particularly limited, and filtration may be performed by a conventional method such as using a filter. However, since the cellulose nanofiber dispersion absorbs solvents such as water and swells, natural filtration takes time. It is preferable to use a method of promoting filtration by pressure such as suction filtration. The filter used for filtration is not particularly limited, and for example, by using a filter cloth, a glass filter, a metal mesh, a filter paper, or the like, the acid-type anion-modified cellulose nanofibers can be filtered out in the form of aggregates.

After the first filtration, the acid-form anion-modified cellulose nanofibers may be washed by adding a water-soluble organic solvent and filtering again. The number of times of washing with a water-soluble organic solvent and filtration is not particularly limited, and may be, for example, 1 to 5 times, preferably 2 to 3 times. By repeating this washing, the removal of the amphiphilic polymer compound remaining in the aggregates of the acid-type anion-modified cellulose nanofibers can be promoted.

The aggregate of anion-modified cellulose nanofibers obtained in step 4 is in an acid form, and usually in a form containing a small amount of water-soluble organic solvent (swollen with a small amount of water-soluble organic solvent). Most of the amphiphilic polymer compound is removed by filtration together with the water-soluble organic solvent, but it is conceivable that some of it may remain due to physical adsorption to cellulose nanofibers or the like. The residual amount of the amphipathic polymer compound in the aggregate of the anion-modified cellulose nanofibers obtained in step 4 is preferably 30% by mass or less, more preferably 10% by mass, relative to the anion-modified cellulose nanofibers. % or less.

The resulting aggregates of acid-type anion-modified cellulose nanofibers have lower hydrophilicity than metal salt-type anion-modified cellulose nanofibers, so they can be used for compositing with hydrophobic compounds. can be done. Moreover, in order to further increase hydrophobicity, it may be reacted with a known hydrophobizing agent.

It may also be redispersed in organic solvents, including both water-soluble organic solvents and less polar organic solvents, as described below.
(5) Step 5
An organic solvent is added to the aggregates of acid-form anion-modified cellulose nanofibers obtained in step 4 to form a mixture (step 5), reacted with a hydrophobizing agent (step 6), and mechanically treated again. (Step 7), a dispersion of anion-modified cellulose nanofibers using an organic solvent as a dispersion medium may be produced.

In step 5, an organic solvent that is less polar (separates when mixed with water) than the above water-soluble organic solvents is used. Since the anion-modified cellulose nanofibers are in an acid form, they have a high affinity for low-polarity organic solvents.

Low polarity 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. methane, trichlorotrifluoromethane, hexafluorobenzene, tetrahydrofuran, 1,2-dimethoxyethane, cyclopentyl methyl ether, methyl tertiary butyl ether and the like. One or more of these can be appropriately selected and used according to the final application of the anion-modified cellulose nanofibers.

The device used when adding the organic solvent to form the mixture is not particularly limited, and known stirring means or the same device as used for defibrating the above-described anion-modified cellulose can be used.

When adding the organic solvent to form a mixture, the addition of the organic solvent and filtration are repeated several times (about 2 to 10 times). As a result, the original water-soluble organic solvent is replaced with the desired organic solvent.

The final content of the organic solvent in the mixture obtained in step 5 is not particularly limited, but from the viewpoint of enhancing the reactivity in the next step 6, the solid content of the anion-modified cellulose nanofibers in the mixture is 0.5. It is preferable to add it in such an amount that it becomes about 1 to 10.0% by mass.

(6) Step 6
A hydrophobizing agent is added to the mixture obtained in step 5 to bind the anion-modified cellulose nanofibers with the hydrophobizing agent.

Hydrophobizing agents include methylamine, ethylamine, oleylamine, propylamine, dodecylamine, stearylamine, tetradecylamine, 1-hexenylamine, 1-dodecenylamine, 9,12-octadecadienylamine (linoleamine), 9 , 12,15-octadecatrienylamine, primary amines such as linoleylamine, secondary amines such as dimethylamine and diethylamine, tertiary amines such as trimethylamine and triethylamine, benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride , cetylpyridinium chloride, cetrimonium chloride, dophanium chloride, tetraethylammonium bromide, didecyldimethylammonium chloride and other quaternary ammoniums; aniline, pyridine, aromatic amines such as benzylamine; diamines such as ethylenediamine and hexamethylenediamine; JEFFAMINE (registered trademark) M600, JEFFAMINE (registered trademark) M1000, JEFFAMINE (registered trademark) M2005, JEFFAMINE (registered trademark) M2070 and other polyether amines, and phosphines such as triphenylphosphine and trimethylphosphine. It is not limited to these. Among these, primary amines, secondary amines, tertiary amines, quaternary ammoniums, phosphines, and polyether amines are preferably used from the viewpoint of dispersibility in solvents, and tertiary amines, quaternary ammoniums, and phosphines. , more preferably polyetheramine.

The amount of hydrophobizing agent to be added may be appropriately determined according to the type of hydrophobizing agent used, the degree of anion modification in the anion-modified cellulose nanofiber, and the like. For example, it may be added in an amount of about 50 to 150%, preferably 70 to 130%, more preferably 80 to 120%, relative to the amount (number of moles) of the anionic group. should be added to

(7) Step 7
In step 6, a hydrophobizing agent is added and thoroughly mixed by stirring, etc., and then in step 7, using the same equipment as used for defibrating the anion-modified cellulose described above, mechanically in an organic solvent. A dispersion of anion-modified cellulose nanofibers is formed using an organic solvent as a dispersion medium.

According to the present invention, anion-modified cellulose nanofibers having high transparency even when dispersed in an organic solvent can be obtained. Transparency is measured, for example, in the following way:
A cellulose nanofiber dispersion with a predetermined concentration is prepared, and a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation) is used to measure the transmittance of 660 nm light using a prismatic cell with an optical path length of 10 mm. do.

In the present invention, for example, an acid-type anion-modified cellulose nanofiber dispersion in which toluene is used as a dispersion medium and the solid content of cellulose nanofibers (not including a hydrophobizing agent) is 1.0% by mass is measured by the above method. Dispersions can be produced with a transparency of 80.0% or higher.

Moreover, according to the present invention, anion-modified cellulose nanofibers having high viscosity when dispersed in an organic solvent can be obtained. Viscosity is measured, for example, by the following method:
A cellulose nanofiber dispersion with a predetermined concentration is prepared, and a Brookfield viscometer (manufactured by Toki Sangyo Co., Ltd.) is used according to the method of JIS-Z-8803, and the value after 3 minutes at a rotation speed of 60 rpm or 6 rpm. to measure.

In the present invention, for example, an acid-type anion-modified cellulose nanofiber dispersion in which toluene is used as a dispersion medium and the solid content of cellulose nanofibers (not including a hydrophobizing agent) is 1.0% by mass is measured by the above method. It is possible to form a dispersion having a B-type viscosity of 100 mPa s or more, preferably 300 mPa s or more at 60 rpm, and a B-type viscosity of 500 mPa s or more, preferably 1500 mPa s or more at 6 rpm. It is possible to form a dispersion of

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.
<Example 1>
200 g of pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) in dry weight and 440 g of sodium hydroxide in dry weight are added to a stirrer capable of mixing pulp, and water is added so that the pulp solid concentration becomes 15% by weight. rice field. Then, after stirring at 30°C for 30 minutes, the temperature was raised to 70°C, and 585 g (converted to active ingredient) of sodium monochloroacetate was added. After reacting for 1 hour, the reactant was taken out, neutralized and washed to obtain a carboxymethylated pulp having a degree of carboxymethyl substitution of 0.24 per glucose unit.

The carboxymethylated pulp obtained in the above step was adjusted to 3.2% by mass with water. Polyethylene glycol (molecular weight: 600) having twice the mass of the carboxymethylated pulp was added to the sodium salt type carboxymethylated pulp and mixed using a homogenizer. The resulting mixture was adjusted with water so that the solid content of the carboxymethylated pulp was 3.0% by mass, and defibrated three times with an ultrahigh-pressure homogenizer (20° C., 150 MPa) to reduce the solid content to 3.0% by mass. A dispersion containing sodium salt-type carboxymethylated cellulose nanofibers (hereinafter, cellulose nanofibers are also referred to as “CNF”) using 0% by mass of water as a dispersion medium and polyethylene glycol was prepared.

To 300 g of this carboxymethylated CNF (sodium salt type) dispersion, 300 g of acetone and 9.5 g of hydrochloric acid having a concentration of 10% are added, and the sodium salt type carboxymethylated CNF (—CH ₂ COONa) is converted into an acid form. (-CH ₂ COOH).

A mixture of the resulting acid-type carboxymethylated CNF aggregates, acetone, polyethylene glycol and hydrochloric acid was filtered using a glass filter (manufactured by Shibata Kagaku Co., Ltd., 15G3) (diaphragm type vacuum pump manufactured by ULVAC KIKO Co., Ltd., DCT- 40) was performed, and aggregates of carboxymethylated CNF were separated by filtration. After adding the same amount of acetone as the above and mixing again, suction filtration was performed again. This addition of acetone and suction filtration was repeated three times. The amount of acetone used so far was recorded. Also, the time from the first addition of acetone to the end of the final suction filtration was recorded. Table 1 shows the amount of acetone and the time for 1 g of the acid-form carboxymethylated CNF obtained. In addition, Table 1 shows the yield (ratio of the mass of the obtained acid-type CNF to the mass of the used metal salt-type CNF excluding Na ions).

Toluene was added to the acetone mixed solution of the obtained acid-type carboxymethylated CNF aggregates and mixed, and toluene addition and suction filtration were repeated three times in the same manner as above. JEFFAMINE (registered trademark) M2005 (manufactured by HUNTSMAN) as a hydrophobizing agent was added to the toluene mixed solution of the obtained acid-type carboxymethylated CNF so that it would be 1 equivalent with respect to the carboxymethyl group of CNF, and a homogenizer was used. After mixing and stirring at 8000 rpm for 10 minutes using an ultra-high pressure homogenizer, treatment (fibrillation) is performed once at 20 ° C. at a pressure of 80 MPa and 3 times at 150 MPa to obtain carboxymethylated CNF with toluene as a dispersion medium. was obtained. The solid content of the resulting dispersion was adjusted to 3.7% by mass using toluene (the solid content of carboxymethylated CNF containing no hydrophobizing agent was 1.0% by mass), and the UV-VIS spectrophotometer UV -1800 (manufactured by Shimadzu Corporation) was used to measure the transmittance of 660 nm light (referred to as "transparency") using a rectangular cell with an optical path length of 10 mm. Table 2 shows the results.

In addition, the viscosity at 25 ° C. of the obtained dispersion (dispersion medium: toluene, solid content: 3.7% by mass) was measured according to the method of JIS-Z-8803 using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd. ) at a rotation speed of 60 rpm or 6 rpm. Table 2 shows the results. Viscosity values are those after 3 minutes.

<Example 2>
An acetone mixture of acid-type carboxymethylated CNF aggregates was obtained in the same manner as in Example 1, except that the amount of polyethylene glycol added was 10 times the mass of CNF. As in Example 1, the amount of acetone used and the time from the first addition of acetone to the end of the final suction filtration were recorded. Table 1 shows the results. In addition, Table 1 shows the yield (ratio of the mass of the obtained acid-type CNF to the mass of the used metal salt-type CNF excluding Na ions).

Next, in the same manner as in Example 1, carboxymethylated CNF dispersion with toluene having a solid content of 3.7% by mass (the solid content of carboxymethylated CNF not containing a hydrophobizing agent is 1.0% by mass) as a dispersion medium. Bodies were prepared and measured for clarity and viscosity. Table 2 shows the results.

<Comparative Example 1>
A dispersion of sodium salt-type carboxymethylated CNF (dispersion medium: water) was prepared in the same manner as in Example 1, except that the solid content was 1.0% by mass and polyethylene glycol was not added. A cation exchange resin (“Amberjet 1024” manufactured by Organo Co., Ltd.) is added thereto and brought into contact with the sodium salt type carboxymethylated CNF (—CH ₂ COONa) by stirring at 20° C. for 0.3 hours. converted to the form (-CH ₂ COOH).

The resulting mixture of acid-type carboxymethylated CNF and cation exchange resin was subjected to suction filtration (diaphragm vacuum pump, DCT-40 manufactured by Ulvac Kiko) using a metal mesh filter with an opening of 30 μm. After adding 400 g of acetone to 320 g of the filtrate and mixing, centrifugation (3000 rpm, 10 minutes, device: 7800 manufactured by Kubota Seisakusho Co., Ltd.) was performed. Then, after adding 640 g of acetone to the precipitate and mixing, centrifugation was performed again under the same conditions. Next, 300 g of acetone was added again, and suction filtration was performed under the same conditions as in Example 1. This addition of acetone and suction filtration was repeated three times. The amount of acetone used so far was recorded. Also, the time from the first addition of acetone to the end of the final suction filtration was recorded. Table 1 shows the amount of acetone and the time for 1 g of the acid-form carboxymethylated CNF obtained. In addition, Table 1 shows the yield (ratio of the mass of the obtained acid-type CNF to the mass of the used metal salt-type CNF excluding Na ions).

Further, using the obtained acetone mixed solution of the acid-form carboxymethylated CNF aggregates, in the same manner as in Example 1, to prepare a toluene mixed solution of the acid-form carboxymethylated CNF aggregates, and then, In the same manner as in 1, a hydrophobizing agent is added, stirred, defibrated, and the solid content is 3.7% by mass (the solid content of carboxymethylated CNF that does not contain a hydrophobizing agent is 1.0% by mass) (dispersion medium: toluene) to give a carboxymethylated CNF dispersion. The transparency and viscosity of this dispersion were measured in the same manner as in Example 1. Table 2 shows the results.

<Comparative Example 2>
An acetone mixture of acid-type carboxymethylated CNF aggregates was obtained in the same manner as in Example 1, except that polyethylene glycol was not added. As in Example 1, the amount of acetone used and the time from the first addition of acetone to the end of the final suction filtration were recorded. Table 1 shows the results. In addition, Table 1 shows the yield (ratio of the mass of the obtained acid-type CNF to the mass of the used metal salt-type CNF excluding Na ions).

In addition, in the same manner as in Example 1, carboxymethylated CNF dispersion with toluene having a solid content of 3.7% by mass (the solid content of carboxymethylated CNF not containing a hydrophobizing agent is 1.0% by mass) as a dispersion medium Bodies were prepared and measured for clarity and viscosity. Table 2 shows the results.

表１の結果より、金属塩型のアニオン変性セルロースにポリエチレングリコールを加えてから解繊を行った実施例１及び２では、陽イオン交換樹脂を用いた比較例１に比べて、ＣＮＦ１ｇに対するアセトンの使用量を節約でき、また、操作にかかる時間も短期化することができることがわかる。また、実施例１及び２では、比較例１に比べて、収率も高いことがわかる。

From the results in Table 1, in Examples 1 and 2 in which polyethylene glycol was added to metal salt-type anion-modified cellulose before defibration, compared to Comparative Example 1 using a cation exchange resin, the amount of acetone per 1 g of CNF It can be seen that the amount of usage can be saved and the time required for operation can be shortened. Moreover, in Examples 1 and 2, compared with Comparative Example 1, it can be seen that the yield is also higher.

In Examples 1 and 2, a metal salt-type CNF dispersion with a solid content of 3.0% by mass was first used, whereas in Comparative Example 1, a metal salt-type CNF dispersion with a solid content of 1.0% by mass was used. Using. This is because, in the method of Comparative Example 1, when the CNF dispersion is highly concentrated and highly viscous (gel-like), it is difficult to bring it into sufficient contact with the cation exchange resin. A concentration lower than that of Example 1 was adopted because it was difficult to distinguish between them. Further, in Comparative Example 1, the addition of acetone and centrifugation were repeated twice before the addition of acetone and suction filtration were repeated three times. This is because even if acetone is added to an acid-type CNF dispersion with a solid content of 1.0% by mass, the acetone concentration in the mixed solvent is low, and the CNF does not easily aggregate to a level where moisture can be removed, and suction filtration Centrifugation was performed first, because it takes a very long time to perform the separation. If centrifugation is not performed in Comparative Example 1, it is considered that suction filtration takes 2 to 3 times longer.

In Comparative Example 1, addition of acetone and centrifugal separation, and addition of acetone and suction filtration were required, so the acid-form CNF was somewhat lost together with the cation exchange resin, and was lower than in Examples 1 and 2. It is thought that it became a yield.

As described above, from Table 1, in the method of the present invention (Example 1), compared to Comparative Examples 1 and 2, acid-type CNF is produced at a high yield using a high concentration metal salt-type CNF dispersion. I know you can.

In addition, from the results in Table 2, it was found that the carboxyl cellulose obtained in Examples 1 and 2, in which polyethylene glycol was added to the metal salt-type anion-modified cellulose before fibrillation was performed, and toluene (low-polarity organic solvent) was used as a dispersion medium. It can be seen that the methylated CNF dispersion has a transparency equivalent to that of Comparative Example 1 using a cation exchange resin, and a significantly higher transparency than Comparative Example 2 using no polyethylene glycol.

Moreover, it can be seen that the carboxymethylated CNF dispersions of Examples 1 and 2 using toluene as a dispersion medium have significantly higher viscosities than the dispersions of Comparative Examples 1 and 2. It is not clear why the dispersions of Examples 1 and 2 exhibit significantly higher viscosities than the dispersions of Comparative Examples 1 and 2, but in Comparative Example 1 using the cation exchange resin method, It is presumed that the CNF is likely to be cut during the fibrillation treatment, and the fiber length of the CNF is shortened, resulting in a lower viscosity. Since there is no It is presumed that the viscosity decreased.

Claims (4)

Step 1 of preparing a mixture containing a metal salt-type anion-modified cellulose and an amphipathic polymer compound;
The mixture obtained in step 1 is mechanically treated to convert the metal salt-type anion-modified cellulose into metal salt-type anion-modified cellulose nanofibers, thereby producing a dispersion containing metal salt-type anion-modified cellulose nanofibers. An acid and a water-soluble organic solvent are added to the dispersion containing the metal salt-type anion-modified cellulose nanofibers obtained in the step 2 of forming the body, and the metal salt-type anion-modified cellulose nanofibers. , step 3 of converting to the acid form,
including
The metal salt-type anion-modified cellulose is a cellulose in which an anionic group is introduced into the molecular chain of cellulose and has a metal ion as a counterion for the anionic group,
The acid form is a form in which the metal ion counter ion of the anionic group in the metal salt type anion-modified cellulose is substituted with hydrogen,
The amphipathic polymer compound includes hydroxypropylmethylcellulose, cellulose acetate, ethylcellulose, methylcellulose, ethylmethylcellulose, nitrocellulose, vinyl chloride resin, vinylidene chloride, polyvinyl alcohol, polystyrene, ABS resin, polyisobutylene, PMMA resin, polycarbonate, urea. one or more selected from resins, epoxy resins, unsaturated polyesters, polyethylene glycol and derivatives thereof, and nonionic surfactants ;
A method for producing an acid-type anion-modified cellulose nanofiber. 2. The method according to claim 1, further comprising a step 4 of performing filtration after step 3 to remove the amphipathic polymer compound together with the water-soluble organic solvent to produce aggregates of acid-form anion-modified cellulose nanofibers. Method. step 5 of adding an organic solvent to the aggregates of the acid-type anion-modified cellulose nanofibers obtained in step 4 to form a mixture;
Step 6 of adding a hydrophobizing agent to the mixture obtained in Step 5, and Mechanically treating the mixture containing the hydrophobizing agent obtained in Step 6 to obtain an anion-modified cellulose nano Step 7 of forming a dispersion of fibers
3. The method of claim 1 or 2, further comprising: The method according to any one of claims 1 to 3, wherein the anion-modified cellulose nanofibers are cellulose nanofibers having a carboxyalkyl group or cellulose nanofibers having a carboxyl group.