JP2020059815A - Method for producing anion modified-cellulose nanofiber - Google Patents

Abstract

To provide a method for efficiently producing an acid type anion modified-cellulose nanofiber capable of forming a dispersion having high transparency.SOLUTION: A mixture of a metal salt type anion modified-cellulose and an amphipathic polymer compound is mechanically treated to form a metal salt type anion modified-cellulose nanofiber dispersion, an acid and a water-soluble organic solvent are added to the dispersion, and the metal salt type is converted into an acid type.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing anion-modified cellulose nanofibers. More specifically, the present invention relates to a method for efficiently producing an acid-type anion-modified cellulose nanofiber from a metal salt-type anion-modified cellulose nanofiber, and using this acid-type anion-modified cellulose nanofiber, an anion having high transparency is obtained. It relates to a method for producing a modified cellulose nanofiber dispersion.

  It is known that by introducing an anionic group such as carboxyl group or carboxymethyl group into the cellulose molecular chain and mechanically treating (defibrating) it can be converted into cellulose nanofibers having a nanoscale fiber diameter. There is. Cellulose nanofibers are light and have high strength, have biodegradability, and have high transparency when formed into a film. Therefore, application to various fields is being investigated.

  Usually, the anion-modified cellulose nanofibers have a high hydrophilicity because the introduced anionic group forms a salt such as sodium salt, and therefore has a high hydrophobicity such as polyethylene terephthalate (PET) or polylactic acid (PLA). It has low compatibility with rigid polymers. Further, the dispersibility in a low-polar organic solvent is low. As a method for solving this problem, by acidifying a metal salt type anionic group (for example, -COONa), it is converted to an acid type (for example, -COOH), and the hydrophilicity of the anion-modified cellulose nanofibers is increased. A method of lowering it is possible. As a method of converting to an acid form, the present applicant has 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).

International Publication No. 2010/116795 JP, 2018-100383, A

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

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

As a result of intensive studies, the present inventors prepared a metal salt-type anion-modified cellulose, added an amphiphilic polymer compound thereto, and then defibrated it to obtain a metal salt-type cellulose nanofiber, which was obtained. It was found that acid-type anion-modified cellulose nanofibers capable of forming a highly transparent dispersion can be efficiently produced by adding an acid to the nanofibers and converting the nanofibers into an acid form. The present 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, and a dispersion containing the metal salt-type anion-modified cellulose nanofibers. Step 2 of forming a body, and an acid and a water-soluble organic solvent are added to the dispersion containing the metal salt-type anion-modified cellulose nanofibers obtained in Step 2 to obtain a metal salt-type anion-modified cellulose nanofiber. , Step 3 of converting to the acid form,
A method for producing an acid-type anion-modified cellulose nanofiber, comprising:
(2) After the step 3, the method further includes a step 4 of performing filtration to remove the amphiphilic polymer compound together with the water-soluble organic solvent to produce an aggregate of acid-type anion-modified cellulose nanofibers. The method described in.
(3) A step 5 of adding an organic solvent to the aggregate 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 the mixture containing the hydrophobizing agent obtained in Step 6 is mechanically treated to produce an anion-modified cellulose nanoparticle containing the organic solvent as a dispersion medium. Step 7 of forming a dispersion of fibers
The method according to (1) or (2), further comprising:
(4) The method according to any one of (1) to (3), wherein the anion-modified cellulose nanofiber is a cellulose nanofiber having a carboxyalkyl group or a cellulose nanofiber having a carboxyl group.

  According to the present invention, acid-type anion-modified cellulose nanofibers capable of forming a highly transparent dispersion can be efficiently produced. The amphiphilic polymer compound is contained in the obtained metal salt type anion-modified cellulose nanofibers by adding an amphiphilic polymer compound to the metal salt-type anion-modified cellulose and then defibrating the cellulose. Will be done. By the presence of this amphiphilic polymer compound when adding an acid, the aggregation of the cellulose nanofibers is suppressed, from the acid type anion-modified cellulose nanofibers, an anion-modified cellulose nanofiber dispersion having high transparency You will be able to get it. Since the amphipathic 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 being dispersed in a low-polarity dispersion medium. it can. In the present invention, it is possible to produce an acid-type anion-modified cellulose nanofiber capable of forming a highly transparent dispersion from a relatively high concentration of a metal salt-type anion-modified cellulose cellulose nanofiber, which is highly efficient. It can be manufactured. In addition, according to the present invention, acid-type anion-modified cellulose nanofibers capable of forming a dispersion having high viscosity can be produced.

  The present invention relates to a method for producing anion-modified cellulose nanofibers. More specifically, it relates to a method for producing an acid-type anion-modified cellulose nanofiber from a metal salt-type anion-modified cellulose nanofiber. Specifically, a mixture containing a metal salt-type anion-modified cellulose and an amphipathic polymer compound is prepared (step 1), and the mixture of step 1 is mechanically treated to obtain a metal salt-type mixture in the mixture. The anion-modified cellulose is defibrated and converted into metal salt-type anion-modified cellulose nanofibers to form a dispersion containing the metal salt-type anion-modified cellulose nanofibers (step 2), and the dispersion obtained in step 2 is obtained. It includes 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 acid-type anion-modified cellulose nanofiber aggregate obtained in step 4 is added to an organic solvent (step 5), a hydrophobizing agent is further added (step 6), and the mixture containing the hydrophobizing agent is added to the organic solvent. It may be mechanically treated (defibration) in to form an anion-modified cellulose nanofiber dispersion dispersed in an organic solvent (step 7).

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

(1-1) Anion-modified cellulose Anion-modified cellulose refers to a cellulose having an anionic group introduced into its molecular chain. Among these, those in which the counterion of the introduced anionic group is a metal ion such as sodium or potassium is referred to as a metal salt type anion-modified cellulose. The metal salt type anion-modified cellulose can be obtained, for example, by the following method. Moreover, you may use a commercially available thing. The type of anion-modified cellulose is preferably cellulose having a carboxyl group or cellulose having a carboxyalkyl group. Particularly, carboxylated cellulose obtained by oxidizing cellulose with an N-oxyl compound and an oxidizing agent, or carboxyalkylated cellulose has an anionic group uniformly introduced, and is easily disentangled uniformly. It is preferable in that a highly transparent cellulose nanofiber can be obtained.

  As the anion-modified cellulose, one that maintains at least a part of the fibrous shape even when dispersed in water or a water-soluble organic solvent is used. Nanofibers cannot be obtained by using a material that does not maintain a fibrous shape (that is, a material that dissolves). The fact that at least part of the fibrous shape is maintained when dispersed means that a fibrous substance can be observed by observing the dispersion of anion-modified cellulose with an electron microscope. Further, anion-modified cellulose capable of observing the peak of the cellulose type I crystal when measured by X-ray diffraction is preferable.

The crystallinity of cellulose in the anion-modified cellulose is preferably 50% or more, and more preferably 60% or more in the crystal type I. 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 defibration. The crystallinity of cellulose can be controlled by the crystallinity of cellulose as a raw material and the degree of anion 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 measurement device (LabX XRD-6000, manufactured by Shimadzu Corporation). The degree of crystallinity was calculated by using a method such as Segal, and the diffraction intensity at 2θ = 22.6 ° and the 2θ = 2θ = 22.6 ° were used as a baseline with the diffraction intensity at 2θ = 10 ° to 30 ° in the X-ray diffraction diagram as a baseline. It is calculated from the diffraction intensity of the amorphous portion at 18.5 ° by the following formula.
Xc = (I002c-Ia) / I002c × 100
Xc: Type I crystallinity of cellulose (%)
I002c: 2θ = 22.6 °, diffraction intensity Ia: 2θ = 18.5 °, amorphous region diffraction intensity.

The ratio of the cellulose type I crystals of the anion-modified cellulose and the ratio of the 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 that is a raw material of the anion-modified cellulose is not particularly limited. Cellulose is generally classified into natural cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose excluding non-crystalline regions, and the like according to the origin, production method and the like. 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, refined linters; cellulose produced by microorganisms such as acetic acid bacteria. The raw material of bleached pulp or unbleached pulp is not particularly limited, and examples thereof include wood, cotton, straw, bamboo, hemp, jute, kenaf, and the like. The method for producing bleached pulp or unbleached pulp is not particularly limited, and may be a mechanical method, a chemical method, or a method in which the two are combined in between. Examples of the bleached pulp or unbleached pulp classified by the production method include mechanical pulp (thermo-mechanical pulp (TMP), groundwood pulp), chemical pulp (unbleached softwood sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP). ) And the like, sulfite unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP) and the like) and the like. Furthermore, dissolving pulp may be used in addition to the pulp for papermaking. Dissolving pulp is chemically refined pulp, which is mainly used by dissolving it in chemicals and is a main raw material for artificial fibers, cellophane, and the like.

Examples of the regenerated cellulose include those prepared by dissolving cellulose in a solvent such as a copper ammonia solution, a cellulose xanthate solution, and a morpholine derivative and spinning the solution again.
The fine cellulose can be obtained by depolymerizing a cellulosic material such as the above natural cellulose or regenerated cellulose (for example, acid hydrolysis, alkali hydrolysis, enzymatic decomposition, explosion treatment, vibration ball mill treatment, etc.). Examples thereof include those obtained by mechanically treating the cellulose-based material.

(1-1-2) Anion modification Anion modification means introducing an anionic group into cellulose, and specifically, introducing 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. In the present invention, the substitution reaction means a reaction of introducing an anionic group into the pyranose ring by a substitution reaction other than the oxidation.

(1-1-2-1) Carboxyalkylation As an example of anion modification, introduction of a carboxyalkyl group such as a carboxymethyl group can be mentioned. In the present 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 may be obtained by a known method, or a commercially available product may be used. The degree of carboxyalkyl substitution of anhydrous glucose unit of cellulose is preferably less than 0.40. Further, when the anionic group is a carboxymethyl group, the carboxymethyl substitution degree is preferably less than 0.40. If the degree of substitution is 0.40 or more, the dispersibility of the cellulose nanofiber will be reduced. The lower limit of the carboxyalkyl substitution degree is preferably 0.01 or more. Considering operability, the substitution degree is particularly preferably 0.02 to 0.35, and further preferably 0.10 to 0.30. The anhydroglucose unit means individual anhydrous glucose (glucose residue) that constitutes cellulose, and the degree of carboxyalkyl substitution means carboxyalkyl among hydroxyl groups (-OH) in the glucose residue that constitutes cellulose. The ratio (number of carboxyalkyl ether groups per glucose residue) substituted with an ether group (-ORCOOH or -ORCOOM) 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. Description will be made by taking carboxymethyl cellulose as an example.

i) A bottoming raw material, a solvent, and a mercerizing agent are mixed, and a reaction temperature is 0 ° C to 70 ° C, preferably 10 ° C to 60 ° C, and a reaction time is 15 minutes to 8 hours, preferably 30 minutes to 7 hours, and mercerization is performed. Process,
ii) Then, a carboxymethylating agent is added 0.05 to 10.0 times mol per glucose residue, and 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 performing the etherification reaction for preferably 1 to 4 hours.

  As the bottoming raw material, the above-mentioned cellulose raw material can be used. As the solvent, 3 to 20 times by mass of water or lower alcohol, specifically, water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol or the like alone, or 2 One or more mixed media can be used. When the 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 0.5 to 20 times mol of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, per anhydrous glucose residue of the bottoming raw material.

  As described above, the degree of carboxymethyl substitution per glucose unit of cellulose is less than 0.40, and preferably 0.01 or more and less than 0.40. By introducing a carboxymethyl substituent into cellulose, the cellulose electrically repels each other. Therefore, the cellulose having the carboxymethyl substituent introduced therein can be nanofibrillated. If the carboxymethyl substituent per glucose unit is less than 0.02, nano-defibration may not be performed sufficiently. The degree of carboxyalkyl substitution in carboxyalkylated cellulose and the degree of carboxyalkyl substitution when the same carboxyalkylated cellulose is used as nanofibers are usually the same.

The degree of carboxymethyl substitution per glucose unit can be measured by the following method:
About 2.0 g of carboxymethyl cellulose (extra dry) is precisely weighed and put in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution prepared by adding 100 mL of special grade concentrated nitric acid to 900 mL of methanol is added, and shaken for 3 hours to convert the carboxymethyl cellulose salt (CM cellulose) into hydrogen CM cellulose. 1.5 g to 2.0 g of hydrogenated CM cellulose (absolutely dried) is precisely weighed and placed in a 300 mL Erlenmeyer flask with a ground stopper. The hydrogenated CM cellulose is wetted with 15 mL of 80 mass% methanol, 100 mL of 0.1 N NaOH is added, and the mixture is 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 ′ − (0.1 N H ₂ SO ₄ ) (mL) × F) × 0.1] / (absolute dry mass (g) of hydrogenated CM cellulose)
DS = 0.162 × A / (1-0.058 × A)
A: 1N NaOH amount (mL) required to neutralize 1 g of hydrogenated CM cellulose
F: Factor of 0.1 N H ₂ SO ₄ F ′: Factor of 0.1 N NaOH.

The degree of substitution of a carboxyalkyl group other than the carboxymethyl group can be measured by the same method as above.
(1-1-2-2) Carboxylation (oxidation)
As an example of anion modification, carboxylation (introduction of carboxyl group into cellulose, also referred to as “oxidation”) can be mentioned. In the present specification, the carboxyl group refers to -COOH (acid type) and -COOM (metal salt type) (in the formula, 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 the carboxyl group is preferably 0.6 mmol / g to 3.0 mmol / g, and 1.0 mmol / g to 2.0 mmol based on the absolute dry mass of the anion-modified cellulose or anion-modified cellulose nanofibers. / G is more preferable.

The amount of carboxyl groups of anion-modified cellulose or anion-modified cellulose nanofibers can be measured by the following method:
60 ml of 0.5 mass% slurry of carboxylated cellulose (aqueous dispersion) was prepared and adjusted to pH 2.5 by adding 0.1 M hydrochloric acid aqueous solution, and then 0.05 N sodium hydroxide aqueous solution was added dropwise to adjust the pH to 11 The electrical conductivity is measured until it becomes, and it is calculated from the amount (a) of sodium hydroxide consumed in the neutralization step of the weak acid with a gradual change in electrical conductivity using the following formula:
Amount of carboxyl group [mmol / g carboxylated cellulose] = a [ml] × 0.05 / mass of carboxylated cellulose [g].

As an example of a carboxylation (oxidation) method, a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide, and a mixture thereof. Can be mentioned. This oxidation reaction, C6-position primary hydroxyl groups of the glucopyranose ring of the cellulose surface is selectively oxidized, and an aldehyde group on the surface, a carboxyl group (-COOH) or carboxylate groups (-COO ^-) and cellulosic fibers having a Can be obtained. The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less.

  The 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 is a compound that 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 used is not particularly limited as long as it is a catalytic amount capable of oxidizing cellulose as a raw material. For example, 0.01 mmol to 10 mmol is preferable, 0.01 mmol to 1 mmol is more preferable, and 0.05 mmol to 0.5 mmol is still more preferable for 1 g of absolutely dried cellulose. Moreover, about 0.1 mmol / L to 4 mmol / L is preferable for the reaction system.

  Bromides are compounds containing bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. Further, iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used can be selected within a range that can accelerate 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, still more preferably 0.5 mmol to 5 mmol, per 1 g of absolutely dried cellulose. The modification is modification by an oxidation reaction.

  As the oxidizing agent, known ones can be used, and for example, halogen, hypohalous acid, halogenous acid, perhalogenic acid or salts thereof, halogen oxides, peroxides and the like can be used. Of these, sodium hypochlorite, which is inexpensive and has a low environmental load, is preferable. The appropriate amount of the oxidizing agent used is preferably 0.5 mmol to 500 mmol, more preferably 0.5 mmol to 50 mmol, still more preferably 1 mmol to 25 mmol, most preferably 3 mmol to 10 mmol, for 1 g of absolutely dry cellulose. . Further, for example, 1 mol to 40 mol is preferable with respect to 1 mol of the N-oxyl compound.

  In the cellulose oxidation step, 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. Since a carboxyl group is generated in the cellulose as the reaction progresses, the pH of the reaction solution is lowered. 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 8 to 12, preferably about 10 to 11. Water is preferable as the reaction medium because it is easy to handle and side reactions are unlikely to occur. The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of oxidation, and is usually 0.5 hours to 6 hours, for example, 0.5 hours to 4 hours.

  The oxidation reaction may be carried out in two stages. For example, by oxidizing the oxidized cellulose obtained by filtering after the completion of the reaction in the first step again under the same or different reaction conditions, the reaction efficiency by the salt produced as a by-product in the reaction in the first step is not increased, and the efficiency is improved. Can be well oxidized.

As another example of the carboxylation (oxidation) method, there can be mentioned a method in which a gas containing ozone and a cellulose raw material are brought into contact with each other to be oxidized. By this oxidation reaction, at least the 2- and 6-position hydroxyl groups of the glucopyranose ring are oxidized, and the cellulose chain is decomposed. Ozone concentration in the ozone containing gas ^is preferably ^{50g / m 3 ~250g / m 3} , more preferably ^{50g / m 3 ~220g / m 3} . The amount of ozone added to the cellulose raw material is preferably 0.1 parts by mass to 30 parts by mass, and 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. Although the ozone treatment time is not particularly limited, it is about 1 minute to 360 minutes, preferably about 30 minutes to 360 minutes. When the conditions of the ozone treatment are within these ranges, it is possible to prevent the cellulose from being excessively oxidized and decomposed, and the yield of the oxidized cellulose becomes good. After performing the ozone treatment, an additional oxidizing 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, and oxygen, hydrogen peroxide, persulfuric acid, peracetic acid and the like. For example, an additional oxidization 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 oxidized cellulose can be adjusted by controlling the reaction conditions such as the addition amount of the oxidizing agent and the reaction time. The amount of carboxyl groups in oxidized cellulose and the amount of carboxyl groups when the same oxidized cellulose is used as nanofibers are usually the same.

(1-1-2-3) Esterification Esterification can be mentioned as an example of anion modification. Examples of the esterification method include a method of mixing a powder of a phosphoric acid compound or an aqueous solution with a cellulose raw material, a method of adding an aqueous solution of a phosphoric acid compound to a slurry of a cellulose raw material, and the like. Examples of the phosphoric acid compound 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 in cost, easy to handle, and a phosphate group can be introduced into the cellulose of the pulp fiber to improve the defibration efficiency. Examples of the compound having a phosphoric acid group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite and 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. Phosphoric acid groups can be introduced into cellulose by using one type or a combination of two or more types. Among these, phosphoric acid, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, phosphoric acid, from the viewpoint of high efficiency of phosphate group introduction, easy to defibrate in the following defibration step, and easy to apply industrially The ammonium salt of is preferred. Particularly, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferable. Further, it is preferable to use the phosphoric acid compound as an aqueous solution because the reaction can be uniformly proceeded and the efficiency of introducing the phosphoric acid group can be increased. The pH of the aqueous solution of a phosphoric acid compound is preferably 7 or less because the efficiency of introducing a phosphoric acid group is high, but a pH of 3 to 7 is preferable from the viewpoint of suppressing hydrolysis of pulp fibers.

  The following method may be mentioned as an example of the method for producing phosphoric acid esterified cellulose. A phosphoric acid compound is added to a suspension of a cellulosic material having a solid content concentration of 0.1% by mass to 10% by mass while stirring to introduce a phosphoric acid group into the cellulose. When the amount of 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 amount of phosphorus element. Is more preferable. When the ratio of the phosphoric acid compound is at least the above lower limit, the yield of fine fibrous cellulose can be further improved. However, when the content exceeds the upper limit, the effect of improving the yield reaches the ceiling, and it is not preferable in terms of cost.

  In addition to the phosphoric acid compound, powders or aqueous solutions of other compounds may be mixed. The compound other than the phosphoric acid compound is not particularly limited, but a nitrogen-containing compound having basicity is preferable. Here, "basic" is defined as an aqueous solution exhibiting a pink to red color in the presence of a phenolphthalein indicator, or a pH of the aqueous solution of greater than 7. The basic nitrogen-containing compound used in the present invention is not particularly limited as long as the effects of the present invention are exhibited, but a compound having an amino group is preferable. Examples thereof include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine and hexamethylenediamine. Of these, urea is preferable because it is inexpensive and easy to handle. The addition amount of the other compound is preferably 2 parts by mass to 1000 parts by mass, and more preferably 100 parts by mass to 700 parts by mass with respect to 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. The reaction time is not particularly limited, but is about 1 minute to 600 minutes, more preferably 30 minutes to 480 minutes. When the conditions of the esterification reaction are within these ranges, it is possible to prevent the cellulose from being excessively esterified and easily dissolved, and the yield of the phosphorylated esterified cellulose becomes good. After dehydrating the obtained phosphoric acid esterified cellulose suspension, it is preferable to heat-treat at 100 ° C. to 170 ° C. from the viewpoint of suppressing hydrolysis of cellulose. Furthermore, it is preferable to heat at 130 ° C. or lower, preferably 110 ° C. or lower while water is included in the heat treatment, remove water, and then perform heat treatment at 100 ° C. to 170 ° C.

  It is preferable that the phosphate group-substituted cellulose has a phosphate group substitution degree of 0.001 or more and less than 0.40 per glucose unit. By introducing a phosphate group substituent into cellulose, the cellulose electrically repels each other. Therefore, the cellulose having the phosphate group introduced therein can be easily nano-disentangled. When the phosphate group substitution degree per glucose unit is less than 0.001, nanofibrillation cannot be sufficiently carried out. On the other hand, if the phosphate group substitution degree per glucose unit is greater than 0.40, it may swell or dissolve, and it may not be possible to obtain nanofibers. In order to efficiently perform defibration, it is preferable that the phosphoric acid esterified cellulose-based raw material obtained above is boiled and then washed with cold water. Modification by esterification of these is modification by substitution reaction. The degree of substitution in esterified cellulose and the degree of substitution when the same esterified cellulose is used as nanofibers are usually the same.

(1-2) Amphiphilic polymer compound In step 1, the amphiphilic polymer compound is added to the above-mentioned metal salt type anion-modified cellulose to form a mixture. The 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, a compound soluble in both water and the following water-soluble organic solvent is preferable. Specifically, cellulose derivatives (hydroxypropyl methyl cellulose, cellulose acetate, ethyl cellulose, methyl cellulose, ethyl methyl cellulose, nitrocellulose), various polymers (vinyl chloride resin, vinylidene chloride, polyvinyl chloride, polyvinyl alcohol, polystyrene, ABS resin, polyisobutylene) , PMMA resin, polycarbonate, urea resin, epoxy resin, unsaturated polyester), polyethylene glycol and its derivatives, nonionic surfactants, and the like, but are not limited thereto. 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 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 preventing aggregation when converting the anion-modified cellulose into nanofibers and adding an acid becomes small. On the other hand, if the amount is too large, the above effect is not enhanced, so that an appropriate amount is preferable from the viewpoint of cost.

(2) Step 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 to obtain the metal salt-type anion-modified cellulose. 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 (defibration)
For mechanical treatment (defibration of anion-modified cellulose), a device capable of applying a strong shearing force such as, but not limited to, a high-speed rotation type, a colloid mill type, a high pressure type, a roll mill type, and an ultrasonic type is used. For efficient defibration, it is preferable to use a wet high-pressure or ultra-high-pressure homogenizer that can apply a pressure of 50 MPa or more and a strong shearing force. The pressure is more preferably 100 MPa or more, further preferably 140 MPa or more. A high-pressure or ultra-high-pressure homogenizer pressurizes a fluid with a pump to make it high pressure and ejects it from a very delicate gap provided in the flow path to emulsify by total energy such as collision between particles and shearing force due to pressure difference. It is a device for performing dispersion, crushing, crushing, and ultra-fine processing. Prior to defibration and dispersion treatment with a high-pressure homogenizer, it is possible to carry out a preliminary treatment, if necessary, using a known mixing, stirring, emulsifying and dispersing device such as a high speed shear mixer.

  Upon 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. As the dispersion medium at the time of defibration, water, an organic solvent, or a mixture thereof can be appropriately selected. The type of the organic solvent is not limited, but for example, a polar solvent having a high affinity with a hydroxyl group in cellulose is preferable, and 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 above dispersion media may be used alone or in combination of two or more. For example, a form in which two or more kinds of organic solvents are mixed, a form containing water and an organic solvent, a form containing only water, and the like can be appropriately selected. It is preferable to use only water as the dispersion medium (that is, 100% water) from the viewpoint of easy handling. The mixing ratio when water and the organic solvent are mixed is not particularly limited, and the mixing ratio may be appropriately adjusted according to the type of the organic solvent used.

(1-2) Anion-Modified Cellulose Nanofibers The above-mentioned mechanical treatment (defibration) converts the metal salt-type anion-modified cellulose into metal salt-type anion-modified cellulose nanofibers.

  The 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, and more preferably about 3 nm to 20 nm. The aspect ratio is 30 or more, preferably 50 or more, 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 the average fiber length of the anion-modified cellulose nanofibers are determined by 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. The measurement can be performed by analyzing 200 randomly selected fibers and calculating an average. Also, the aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length / average fiber diameter.

The metal salt-type anion-modified cellulose nanofiber is a cellulose nanofiber having a metal (for example, sodium, potassium, etc.) derived from a drug used in the reaction of anion modification as a counterion of an anionic group. For example, in the metal salt type carboxylated cellulose nanofiber, the carboxyl group is -COO ^- M ⁺ , and in the metal salt type carboxyalkylated cellulose nanofiber, the carboxylalkyl group is -RCOO ^- M ^+. (In the formula, M is a metal such as sodium and potassium, and R is an alkylene group such as a methylene group and an ethylene group.).

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

(3) Step 3
In step 3, an acid form in which the metal in the metal salt form is replaced with hydrogen by adding an acid and a water-soluble organic solvent to the dispersion containing the metal salt form anion-modified cellulose nanofibers (for example, -COOH, -RCOOH, etc.).

(3-1) Acid An acid is added to convert the metal salt type anion-modified cellulose nanofibers to the acid type. The type of acid used is not particularly limited and may be an inorganic acid or an organic acid. Examples of the inorganic acid include sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, nitrous acid, phosphoric acid and the like. Examples of the organic acid 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. Preferred is hydrochloric acid or sulfuric acid which is versatile and easily available. The pH during the acid treatment is preferably in the range of 1-6, more preferably 2-5. The amount of the acid added is not particularly limited as long as it can convert the metal salt-type anion-modified cellulose nanofibers to the acid type, and for example, in the case of a strong acid, it is preferably 1 equivalent or more with respect to the anionic group. If it is a weak acid, it is preferably 10 equivalents or more.

(3-2) Water-soluble organic solvent A water-soluble organic solvent is added to the anion-modified cellulose nanofibers at the same time as the acid is added in step 3 or before the acid is added. The water-soluble organic solvent refers to an organic solvent that can be arbitrarily mixed without being separated from water. 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 can be mentioned, and these may be used alone or in combination.

  The addition amount of the water-soluble organic solvent is not particularly limited, as long as it can be removed from the anion-modified cellulose nanofiber dispersion in the subsequent step, the solid content concentration in the dispersion of the anion-modified cellulose nanofiber is The amount is preferably about 0.5 to 2.0% by mass.

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

  The method of filtration is not particularly limited, and may be performed by a usual method such as using a filter, but since the cellulose nanofiber dispersion swells by absorbing a solvent such as water, it takes time in natural filtration. It is preferable to use a method of promoting filtration with 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 an aggregate.

  After performing the first filtration, the water-soluble organic solvent may be added again, and the filtration may be performed again to wash the acid-type anion-modified cellulose nanofibers. The number of times of washing with the 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 amphipathic polymer compound remaining in the aggregate of the acid type anion-modified cellulose nanofibers can be promoted.

  The anion-modified cellulose nanofiber aggregate obtained in step 4 is in an acid form, and usually has a form containing a small amount of a water-soluble organic solvent (swollen with a small amount of a water-soluble organic solvent). Most of the amphipathic polymer compounds are removed together with the water-soluble organic solvent by filtration, but it is also possible that some of them remain due to physical adsorption on the cellulose nanofibers. The residual amount of the amphipathic polymer compound in the anion-modified cellulose nanofiber aggregate obtained in step 4 is preferably 30% by mass or less based on the anion-modified cellulose nanofiber, and more preferably 10% by mass. % Or less.

  Since the obtained aggregate of acid-type anion-modified cellulose nanofibers has lower hydrophilicity than metal salt-type anion-modified cellulose nanofibers, it should be used for complexing with hydrophobic compounds. You can Further, in order to further increase the hydrophobicity, it may be reacted with a known hydrophobizing agent.

In addition, as described below, it may be dispersed again in an organic solvent (including both a water-soluble organic solvent and a less polar organic solvent).
(5) Step 5
An organic solvent is added to the aggregate of acid-type anion-modified cellulose nanofibers obtained in step 4 to form a mixture (step 5), which is reacted with a hydrophobizing agent (step 6) and mechanically treated again. By (step 7), a dispersion of anion-modified cellulose nanofibers containing an organic solvent as a dispersion medium may be produced.

  In step 5, an organic solvent having a polarity lower than that of the above-mentioned water-soluble organic solvent (which separates when mixed with water) is used. Since the anion-modified cellulose nanofiber is in the acid form, it has a high affinity for a low-polarity organic solvent.

  Examples of the low-polarity organic solvent 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 can be mentioned. These 1 type (s) or 2 or more types can be appropriately selected and used according to the use of the final anion-modified cellulose nanofiber.

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

  When the organic solvent is added to form the mixture, addition of the organic solvent and filtration are repeated several times (about 2 to 10 times). This replaces the original water-soluble organic solvent with a 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. It is preferable to add it in an amount such that it is about 1 to 10.0 mass%.

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

  As the hydrophobizing agent, methylamine, ethylamine, oleylamine, propylamine, dodecylamine, stearylamine, tetradecylamine, 1-hexenylamine, 1-dodecenylamine, 9,12-octadecadienylamine (linolamine), 9 , 12,15-Octadecatrienylamine, linoleylamine and other primary amines, dimethylamine, diethylamine and other secondary amines, trimethylamine, triethylamine and other tertiary amines, benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride , Quaternary ammonium such as cetylpyridinium chloride, cetrimonium chloride, dofanium chloride, tetraethylammonium bromide and didecyldimethylammonium chloride, aromatic amines such as aniline, pyridine and benzylamine, Diamines such as diamine, hexamethylenediamine, polyether amines such as JEFFAMINE (registered trademark) M600, JEFFAMINE (registered trademark) M1000, JEFFAMINE (registered trademark) M2005, JEFFAMINE (registered trademark) M2070 manufactured by HUNTSMAN, triphenylphosphine , And phosphine such as trimethylphosphine, but are not limited thereto. Of these, primary amine, secondary amine, tertiary amine, quaternary ammonium, phosphine and polyether amine are preferably used from the viewpoint of dispersibility in a solvent, and tertiary amine, quaternary ammonium and phosphine are preferable. More preferably, polyether amine is used.

  The addition amount of the hydrophobizing agent may be appropriately determined depending on the type of the hydrophobizing agent used, the degree of anion modification in the anion-modified cellulose nanofibers, and the like. For example, it may be added in an amount of about 50 to 150%, preferably 70 to 130%, and more preferably 80 to 120% with respect to the amount (mol number) of the anionic group. Can be added to.

(7) Step 7
After adding the hydrophobizing agent in step 6 and thoroughly mixing by stirring or the like, in step 7, the same apparatus as that used for defibration of the anion-modified cellulose described above is used, and a machine is used in an organic solvent. Treatment is performed to form a dispersion of anion-modified cellulose nanofibers 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. Clarity is measured, for example, by the following method:
A cellulose nanofiber dispersion having a predetermined concentration was prepared, and a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation) was used to measure the transmittance of 660 nm light using a rectangular cell having an optical path length of 10 mm. To do.

  In the present invention, for example, an acid type anion-modified cellulose nanofiber dispersion in which the dispersion medium is toluene and the solid content of the cellulose nanofibers (excluding the hydrophobizing agent) is 1.0% by mass is measured by the above method. It is possible to produce a dispersion having a transparency of 80.0% or more.

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

  In the present invention, for example, an acid type anion-modified cellulose nanofiber dispersion in which the dispersion medium is toluene and the solid content of the cellulose nanofibers (excluding the hydrophobizing agent) is 1.0% by mass is measured by the above method. A dispersion having a B-type viscosity at 60 rpm of 100 mPa · s or more, preferably 300 mPa · s or more can be formed, and a B-type viscosity at 6 rpm of 500 mPa · s or more, preferably 1500 mPa · s or more. Can be formed.

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

  The carboxymethylated pulp obtained in the above step was adjusted to 3.2% by mass with water. To this sodium salt type carboxymethylated pulp, polyethylene glycol (molecular weight: 600) having a mass twice that of the carboxymethylated pulp was added and mixed using a homogenizer. The obtained mixture was adjusted with water so that the solid content of carboxymethylated pulp was 3.0% by mass, and defibration treatment was performed 3 times with an ultrahigh pressure homogenizer (20 ° C., 150 MPa) to obtain a solid content of 3. A dispersion containing sodium salt type carboxymethylated cellulose nanofibers (hereinafter, cellulose nanofibers are also referred to as “CNF”) having 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% were added, and sodium salt type carboxymethylated CNF (-CH ₂ COONa) was added to the acid type. It was converted to the _(-CH 2 COOH).

  The obtained mixture of acid-type carboxymethylated CNF aggregates, acetone, polyethylene glycol, and hydrochloric acid was suction-filtered using a glass filter (Shibata Scientific Co., Ltd., 15G3) (Diaphragm vacuum pump by ULVAC Kiko, DCT-). 40) was carried out, and aggregates of carboxymethylated CNF were separated by filtration. The same amount of acetone as described above was added again to the mixture, and after mixing, suction filtration was performed again. This addition of acetone and suction filtration were repeated 3 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 obtained acid-type carboxymethylated CNF. Table 1 shows yields (ratio of the mass of the obtained acid-type CNF to the mass of the used metal salt-type CNF excluding Na ion).

  Toluene was added to and mixed with the obtained acetone mixture of acid-type carboxymethylated CNF aggregates, 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 obtained mixed solution of acid-type carboxymethylated CNF in toluene so as to be 1 equivalent to the carboxymethyl group of CNF, and a homogenizer was added. After mixing and stirring at 8000 rpm for 10 minutes, carboxymethylated CNF using toluene as a dispersion medium is treated by using an ultrahigh pressure homogenizer once at 20 ° C. at a pressure of 80 MPa and three times at 150 MPa (defibration). A dispersion of The solid content of the obtained dispersion was adjusted to 3.7% by mass with toluene (the solid content of carboxymethylated CNF containing no hydrophobizing agent was 1.0% by mass), and UV-VIS spectrophotometer UV was used. -1800 (manufactured by Shimadzu Corp.) was used to measure the transmittance of 660 nm light (referred to as "transparency") using a prismatic cell having an optical path length of 10 mm. The results are shown in Table 2.

  Regarding the viscosity of the obtained dispersion (dispersion medium: toluene, solid content: 3.7% by mass) at 25 ° C, a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) was used according to the method of JIS-Z-8803. ) Was used at a rotation speed of 60 rpm or 6 rpm. The results are shown in Table 2. The viscosity value is the value after 3 minutes.

<Example 2>
An acetone mixed solution 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 amount 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. The results are shown in Table 1. Table 1 shows yields (ratio of the mass of the obtained acid-type CNF to the mass of the used metal salt-type CNF excluding Na ion).

  Then, in the same manner as in Example 1, a carboxymethylated CNF dispersion using toluene having a solid content of 3.7% by mass (the solid content of carboxymethylated CNF containing no hydrophobizing agent is 1.0% by mass) as a dispersion medium. The body was manufactured and the transparency and viscosity were measured. The results are shown in Table 2.

<Comparative Example 1>
A sodium salt type carboxymethylated CNF dispersion (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 Corporation) was added thereto, and the mixture was stirred and contacted at 20 ° C. for 0.3 hours, and sodium salt-type carboxymethylated CNF (—CH ₂ COONa) was added to the acid. was converted to the type _(-CH 2 COOH).

  The obtained mixture of acid-type carboxymethylated CNF and a cation exchange resin was subjected to suction filtration (a diaphragm vacuum pump, DCT-40 manufactured by ULVAC Kiko, Inc.) using a metal mesh filter having openings of 30 μm. After 400 g of acetone was added to 320 g of the filtrate and mixed, centrifugation (3,000 rpm, 10 minutes, apparatus: 7800 manufactured by Kubota Seisakusho) was performed. Then, 640 g of acetone was added to the precipitate and mixed, and then the mixture was centrifuged 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 were repeated 3 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 obtained acid-type carboxymethylated CNF. Table 1 shows yields (ratio of the mass of the obtained acid-type CNF to the mass of the used metal salt-type CNF excluding Na ion).

  Also, using the obtained acetone-mixed solution of acid-type carboxymethylated CNF aggregates, a toluene mixed solution of acid-type carboxymethylated CNF aggregates was prepared in the same manner as in Example 1. A hydrophobizing agent was added and stirred and defibrated in the same manner as in 1, and the solid content was 3.7% by mass (the solid content of carboxymethylated CNF containing no hydrophobizing agent was 1.0% by mass) (dispersion medium: A toluene carboxymethylated CNF dispersion was obtained. The transparency and the viscosity of this dispersion were measured in the same manner as in Example 1. The results are shown in Table 2.

<Comparative example 2>
An acetone mixed solution 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. The results are shown in Table 1. Table 1 shows yields (ratio of the mass of the obtained acid-type CNF to the mass of the used metal salt-type CNF excluding Na ion).

  Also, in the same manner as in Example 1, a carboxymethylated CNF dispersion using 3.7% by mass of solid content (the solid content of carboxymethylated CNF containing no hydrophobizing agent is 1.0% by mass) as a dispersion medium. The body was manufactured and the transparency and viscosity were measured. The results are shown in Table 2.

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 of Table 1, in Examples 1 and 2 in which polyethylene glycol was added to the metal salt-type anion-modified cellulose and then defibration was performed, compared with Comparative Example 1 using a cation exchange resin, acetone of CNF 1 g It can be seen that the usage amount can be saved and the operation time can be shortened. Further, it can be seen that the yields of Examples 1 and 2 are higher than those of Comparative Example 1.

  In Examples 1 and 2, a metal salt type CNF dispersion having a solid content of 3.0% by mass was used first, whereas in Comparative Example 1, a metal salt type CNF dispersion having 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 has a high concentration and a high viscosity (gel state), it is difficult to bring the CNF dispersion into sufficient contact with the cation exchange resin, and the CNF dispersion is filtered with the cation exchange resin. Since it was difficult to distinguish, a lower concentration than that in Example 1 was adopted. In addition, in Comparative Example 1, the operation of adding acetone and the centrifugation was repeated twice before repeating the addition of acetone and the suction filtration three times. This is because even if acetone was added to an acid type CNF dispersion having a solid content of 1.0% by mass, the acetone concentration in the mixed solvent was low, CNF did not easily aggregate to a level capable of removing water, and suction filtration was performed. Since it takes a very long time to perform, the centrifugation was performed first. In Comparative Example 1, when centrifugal separation is not performed, it is considered that suction filtration requires 2-3 times longer time.

  In Comparative Example 1, the addition of acetone and centrifugation, and the addition of acetone and suction filtration were necessary, so that the acid form of CNF was lost to some extent together with the cation exchange resin, which was lower than those of Examples 1 and 2. It is considered that the yield was reached.

  As described above, from Table 1, in the method of the present invention (Example 1), compared with Comparative Examples 1 and 2, a higher concentration of the metal salt-type CNF dispersion was used to produce acid-type CNF in a higher yield. I know that I can do it.

  In addition, from the results of Table 2, carboxy having a dispersion medium of toluene (low-polarity organic solvent) obtained in Examples 1 and 2 in which polyethylene glycol was added to metal salt-type anion-modified cellulose and then defibration was performed. It can be seen that the methylated CNF dispersion has the same transparency as that of Comparative Example 1 using the cation exchange resin, and has significantly higher transparency than that of Comparative Example 2 not using polyethylene glycol.

Further, it can be seen that the carboxymethylated CNF dispersions of Examples 1 and 2 using toluene as a dispersion medium have a significantly higher viscosity 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, an ultrahigh pressure homogenizer was used. It is presumed that CNF was likely to be broken during the defibration treatment and the CNF fiber length was shortened, and thus the viscosity was lowered. Further, in Comparative Example 2 using the hydrochloric acid method, polyethylene glycol was used during conversion to the acid form. The presence of the PEG-hydrochloric acid method results in stronger aggregation of CNF when converted to the acid form than in Examples 1 and 2 using the PEG-hydrochloric acid method, and is less likely to be defibrated when mechanically treated in an organic solvent (toluene). It is assumed that the viscosity became low.

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, and a dispersion containing the metal salt-type anion-modified cellulose nanofibers. Step 2 of forming a body, and an acid and a water-soluble organic solvent are added to the dispersion containing the metal salt-type anion-modified cellulose nanofibers obtained in Step 2 to obtain a metal salt-type anion-modified cellulose nanofiber. , Step 3 of converting to the acid form,
A method for producing an acid-type anion-modified cellulose nanofiber, comprising:   The method according to claim 1, further comprising, after Step 3, Step 4 of performing filtration to remove an amphipathic polymer compound together with a water-soluble organic solvent to produce an aggregate of acid-type anion-modified cellulose nanofibers. Method. Step 5 of adding an organic solvent to the aggregate 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 and using the organic solvent as a dispersion medium Step 7 of forming a dispersion of fibers
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 nanofiber is a cellulose nanofiber having a carboxyalkyl group or a cellulose nanofiber having a carboxyl group.