JP7199230B2 - Method for producing hydrophobized anion-modified cellulose nanofiber dispersion and dry solid of hydrophobized anion-modified cellulose - Google Patents

Description

The present invention relates to a method for producing a dispersion of hydrophobized anionically modified cellulose nanofibers and a dry solid of hydrophobized anionically modified cellulose.

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 high-molecular-weight 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.

In Patent Document 1, when dispersing cellulose nanofibers in a medium containing an organic solvent, as a "second production method", an acid is added to an aqueous cellulose nanofiber dispersion to obtain a carboxylate-type group of cellulose nanofibers. a step of substituting a portion of with a carboxylic acid type group, a step of adding an organic solvent to a cellulose nanofiber gel in which a portion of the group has been substituted with a carboxylic acid type, and cellulose nanofiber water to which the organic solvent has been added A method is described that includes removing the aqueous solvent from the dispersion.

In addition, Patent Document 2 discloses, as a “first production method”, a step of subjecting an aqueous dispersion of cellulose nanofibers substituted with a carboxylic acid type to an amine treatment, and recovering the amine-treated cellulose nanofibers and dispersing them in a dispersion medium. and redispersing at to prepare a cellulose nanofiber dispersion.

WO2010/134357 Japanese Unexamined Patent Application Publication No. 2012-21081

In the method described in Patent Document 1, the organic solvent that can be used as the final dispersion medium is limited to three types of dimethylsulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide. is a water-soluble organic solvent that is arbitrarily miscible with water. The method described in Patent Document 1 does not describe the use of an organic solvent such as toluene, which has low polarity and is almost insoluble in water, as the dispersion medium for the cellulose nanofiber dispersion. Also, Patent Document 2 does not describe the use of a low-polarity, sparingly water-soluble organic solvent as a dispersion medium.

After producing a cellulose nanofiber dispersion using a water-soluble organic solvent as a dispersion medium using the methods described in Patent Documents 1 and 2, the water-soluble organic solvent is replaced with a low-polarity water-insoluble organic solvent. It is conceivable to produce a cellulose nanofiber dispersion using an organic solvent that is poorly soluble in water as a dispersion medium, but when replacing the solvent, it is necessary to repeat addition of the solvent and removal by suction filtration or the like many times. However, there is a problem that it takes a lot of cost and time, and the yield of cellulose nanofibers is also lowered. In addition, in the methods described in Patent Documents 1 and 2, defibration is performed when the cellulose nanofiber aqueous dispersion is first obtained, fibrillation is performed after adding an organic solvent (and, in some cases, acid-type cellulose nanofibers The defibration process (mechanical treatment with a mixer, homogenizer, etc.) is required at least twice, and as the number of fibrillation increases, the cellulose fibers are damaged. There is a problem of receiving

An object of the present invention is to provide a method capable of more efficiently producing a dispersion of anion-modified cellulose nanofibers using an organic solvent as a dispersion medium.

As a result of extensive studies, the present inventors made the anion-modified cellulose hydrophobic by adding a hydrophobizing agent and a water-soluble organic solvent to the anion-modified cellulose before fibrillating the anion-modified cellulose into nanofibers. The dispersion medium is removed from the obtained dispersion of the hydrophobized anion-modified cellulose to obtain a dry solid of the hydrophobized anion-modified cellulose (the solid content concentration is higher than 90% by mass), and the dry solid is dissolved in an organic solvent. The present inventors have found that dispersion of anion-modified cellulose nanofibers using an organic solvent as a dispersion medium can be efficiently produced by dispersing the nanofibers while fiberizing. The invention includes, but is not limited to:
(1) Step 1 of preparing an anion-modified cellulose dispersion,
Step 2 of adding a hydrophobizing agent and a water-soluble organic solvent to a dispersion of anion-modified cellulose to produce a dispersion of hydrophobized anion-modified cellulose;
Step 3 of removing the water-soluble organic solvent and the dispersion medium from the dispersion of the hydrophobized anion-modified cellulose to produce a dry solid of the hydrophobized anion-modified cellulose, and Step 4 of mixing with an organic solvent and defibrating the hydrophobized anion-modified cellulose in the organic solvent to produce a dispersion of hydrophobized anion-modified cellulose nanofibers using the organic solvent as a dispersion medium;
including
A method for producing a dispersion of hydrophobized anion-modified cellulose nanofibers, wherein the dry solids of the hydrophobized anion-modified cellulose have a solid content concentration higher than 90% by mass.
(2) The method according to (1), wherein the water-soluble organic solvent has a surface tension of 35 N/m or less at 20°C.
(3) The method according to (1) or (2), wherein the water-soluble organic solvent has a boiling point of less than 100°C at 1 atmosphere.
(4) The method according to any one of (1) to (3), wherein the anion-modified cellulose is a cellulose having a carboxyl group or a cellulose having a carboxyalkyl group.
(5) Dry solids of hydrophobized anionically modified cellulose comprising anionically modified cellulose bound with a hydrophobizing agent and having a solids concentration of greater than 90% by weight.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to efficiently produce a dispersion of anion-modified cellulose nanofibers using an organic solvent as a dispersion medium. In the method of the present invention, there is no need to perform a solvent replacement step that repeats centrifugation, suction filtration, etc. for replacing water or a highly polar water-soluble organic solvent with a less polar organic solvent. Since the anion-modified cellulose nanofibers can be dispersed in the medium, cost and time can be saved. In addition, conventionally, after fibrillation into cellulose nanofibers, a hydrophobizing agent is added, followed by fibrillation again in an organic solvent to produce a dispersion using an organic solvent as a dispersion medium. In , the number of times of defibration can be reduced by manufacturing hydrophobized cellulose and then fibrillating it in an organic solvent, which is advantageous in that the cellulose fibers are less damaged. In addition, cellulose nanofiber is a material that swells in an aqueous medium and exhibits high viscosity. However, in the present invention, the anion-modified cellulose, which is not very viscous before being fibrillated into cellulose nanofibers, is hydrophobized, so the concentration is higher. of cellulose (for example, 2 to 10% by mass) can be used for hydrophobization treatment, and the efficiency of hydrophobization is high.

TECHNICAL FIELD The present invention relates to a method for producing a dispersion of hydrophobized anion-modified cellulose nanofibers using an organic solvent as a dispersion medium. Hereinafter, cellulose nanofiber may be referred to as "CNF". Specifically, in the method of the present invention, an anion-modified cellulose dispersion is prepared (step 1), a hydrophobizing agent and a water-soluble organic solvent are added to the anion-modified cellulose dispersion, and a hydrophobized anion-modified A dispersion of cellulose is produced (step 2), and the water-soluble organic solvent and dispersion medium are removed from the dispersion of hydrophobized anion-modified cellulose to produce a dry solid of hydrophobized anion-modified cellulose (step 3). , A dry solid of hydrophobized anion-modified cellulose is mixed with an organic solvent, and the hydrophobized anion-modified cellulose is defibrated in the organic solvent to produce a dispersion of hydrophobized anion-modified CNF using the organic solvent as a dispersion medium. (step 4). At this time, in step 3, drying (removing the dispersion medium) is performed until the solid content concentration of the dried solid becomes higher than 90% by mass.

(1) Process 1
In step 1, a dispersion of anion-modified cellulose is prepared. Anion-modified cellulose is cellulose in which an anionic group is introduced into the molecular chain, as described in more detail below.

(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.

(1-2) 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.

(1-2-1) 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 0.60 mmol/g to 3.00 mmol/g, more preferably 1.00 mmol/g to 2.00 mmol/g, relative to the absolute dry weight of the carboxylated cellulose.

The carboxyl group content of carboxylated cellulose 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 carboxylated 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 carboxylated cellulose and the amount of carboxyl groups when the same carboxylated cellulose is used as nanofibers are usually the same.

(1-2-2) Carboxyalkylation An example of anion modification is the introduction of a carboxyalkyl group such as a carboxymethyl group into cellulose. 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 CNF 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) Mix the raw material, solvent and mercerizing agent, and mercerize at a reaction temperature of 0 to 70° C., preferably 10 to 60° C., for a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. process,
ii) Then, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times mol per glucose residue, the reaction temperature is 30 to 90° C., preferably 40 to 80° C., and the reaction time is 30 minutes to 10 hours, preferably A step of performing an etherification reaction for 1 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 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 0.01, 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 is back-titrated with 0.1 N H ₂ SO ₄ 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.
(1-2-3) 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 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 to 500 parts by mass, more preferably 1 to 400 parts by mass, in terms of elemental phosphorus. 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 to 1000 parts by mass, more preferably 100 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 to 95°C, more preferably 30 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 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.

(1-3) Anion-Modified Cellulose Anion-modified cellulose can be obtained by anion-modifying the raw material cellulose as exemplified above. 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 with an N-oxyl compound and an oxidizing agent is preferable in that anionic groups are uniformly introduced and it is easily fibrillated uniformly.

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.
In the anion-modified cellulose obtained by the above method, the introduced anionic group is usually in the form of a metal salt (for example, -COO ^- M ⁺ or -RCOO ^- M ⁺ (M is a metal such as sodium or potassium). and R is an alkylene group such as a methylene group or an ethylene group)). It is preferable to convert the metal salt-type anionic groups in the anion-modified cellulose to acid-type (eg, —COOH, —RCOOH, etc.) in order to facilitate the subsequent reaction with the hydrophobizing agent.

The method for converting to the acid form is not particularly limited, and examples thereof include a method of adding acid to anion-modified cellulose and a method of contacting anion-modified cellulose with a cation exchange resin. When an acid is added, the type of acid used is not particularly limited, and examples include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, nitrous acid, and phosphoric acid, acetic acid, lactic acid, oxalic acid, citric acid, formic acid, and adipic acid. , sebacic acid, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid, gluconic acid and the like. Hydrochloric acid or sulfuric acid, which are common and readily available, are preferred. The pH at which the acid is added 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 into an acid form. If so, it is preferably 10 equivalents or more. When contacting with an acidic ion exchange resin, examples of acidic ion exchange resins include strongly acidic cation exchange resins and weakly acidic cation exchange resins.

(1-4) Dispersion of Anion-Modified Cellulose As the dispersion medium for the dispersion of anion-modified cellulose prepared in step 1, water, an organic solvent, or a mixture thereof can be appropriately selected. Although the type of organic solvent does not matter, for example, a polar solvent that has a high affinity for hydroxyl groups in cellulose, and a water-soluble organic solvent that can be mixed with water in any proportion 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 can be mentioned. 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.

In the subsequent step 2, a water-soluble organic solvent is added to the anion-modified cellulose dispersion together with a hydrophobizing agent. At that time, the concentration of anion-modified cellulose in the anion-modified cellulose dispersion is diluted. Therefore, in step 1, the concentration of anion-modified cellulose in the anion-modified cellulose dispersion may be high, for example, preferably 10 to 30% by mass, more preferably 20 to 30% by mass.

(2) Process 2
In step 2, a hydrophobizing agent and a water-soluble organic solvent are added to the anion-modified cellulose dispersion to hydrophobize the anion-modified cellulose to produce a hydrophobized anion-modified cellulose dispersion. Hydrophobization refers to a treatment for imparting hydrophobic groups to anion-modified cellulose to improve the hydrophobicity of the anion-modified cellulose.

The hydrophobizing agent is preferably a compound having an amine or phosphine that can interact with the anionic group of the anion-modified cellulose to form an onium salt. Any of ammonium, aromatic amines, diamines, polyetheramines and phosphines may be used. For example, methylamine, ethylamine, oleylamine, propylamine, dodecylamine, stearylamine, tetradecylamine, 1-hexenylamine, 1-dodecenylamine, 9,12-octadecadienylamine (linoleamine), 9,12,15 - primary amines such as octadecatrienylamine and linoleylamine, secondary amines such as dimethylamine and diethylamine, tertiary amines such as trimethylamine and triethylamine, benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetylpyridinium chloride , cetrimonium, dophanium chloride, tetraethylammonium bromide, quaternary ammonium such as didecyldimethylammonium chloride, aromatic amines such as aniline, pyridine and benzylamine, diamines such as ethylenediamine and hexamethylenediamine, JEFFAMINE manufactured by HUNTSMAN ( JEFFAMINE (Registered Trademark) M600, JEFFAMINE (Registered Trademark) M1000, JEFFAMINE (Registered Trademark) M2005, JEFFAMINE (Registered Trademark) M2070, polyether amines, triphenylphosphine, trimethylphosphine, etc., phosphines, etc., but are not limited thereto. . 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.

A water-soluble organic solvent is an organic solvent that can be mixed with water in any proportion, and examples thereof include methanol, ethanol, isopropanol, isobutanol, sec-butanol, tert-butanol, methyl cellosolve, ethyl cellosolve, ethylene glycol, and glycerin. , ethylene glycol dimethyl ether, 1,4-dioxane, tetrahydrofuran, acetone, methyl ethyl ketone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide and the like.

In step 2, a hydrophobizing agent and a water-soluble organic solvent are added to the anion-modified cellulose dispersion obtained in step 1. In this case, the water-soluble organic solvent may be added after adding the hydrophobizing agent to the anion-modified cellulose dispersion. It is preferable to add the hydrophobizing agent after adding the water-soluble organic solvent to the cellulose dispersion, and more preferably to add the hydrophobizing agent to the anion-modified cellulose dispersion after dissolving the hydrophobizing agent in the water-soluble organic solvent.

In step 3 after step 2, the water-soluble organic solvent and dispersion medium are removed from the hydrophobized anionically modified cellulose dispersion to produce a dry solid. Normally, when the dispersion medium is removed from the cellulose dispersion, the cellulose fibers are strongly aggregated due to hydrogen bonding, making it extremely difficult to defibrate into nanofibers in the subsequent step 4. In the present invention, by adding a hydrophobizing agent and a water-soluble organic solvent in step 2, the aggregation of cellulose fibers during drying in step 3 is weakened, and disentanglement into nanofibers in subsequent step 4 is facilitated. can be promoted. Specifically, it is thought that the hydroxyl groups of the anion-modified cellulose are protected by the hydrophobizing agent, and the hydrogen bonding between the cellulose fibers during drying (when the dispersion medium is removed) is inhibited. It is believed that by entering between fibers, aggregation of cellulose fibers is inhibited. In addition, if a water-soluble organic solvent with a lower surface tension and a lower boiling point than water is used, the force that attracts the cellulose fibers to each other during drying in step 3 will be weakened, and aggregation will be alleviated. It is thought that the shortened length shortens the time for the cellulose fibers to attract each other, allowing them to dry before causing strong agglomeration.

Generally, a hydrophobizing agent with a high molecular weight has a strong effect of weakening the cohesion of cellulose fibers during drying in step 3. On the other hand, if the hydrophobizing agent has a high molecular weight, the Since the proportion of anion-modified cellulose in the resulting dry solid and the proportion of CNF in the hydrophobized anion-modified CNF dispersion obtained in step 4 are reduced, the properties of anion-modified cellulose or CNF (e.g., development of viscosity, etc.) is sometimes difficult to obtain. In the present invention, by adding a water-soluble organic solvent in addition to a hydrophobizing agent, even when a low molecular weight hydrophobizing agent is used, aggregation of cellulose fibers during drying in step 3 can be weakened. can be performed, and defibration can be advanced in the subsequent step 4 to obtain a nanofiber dispersion. Thus, but not limited to, relatively low molecular weight hydrophobizing agents can be used, for example, hydrophobizing agents with a molecular weight of 3000 or less can be used, and hydrophobizing agents with a molecular weight of 2500 or less can be used. can be used, and a hydrophobizing agent with a molecular weight of 2000 or less can be used. The lower limit of the molecular weight of the hydrophobizing agent is not limited, but if the molecular weight is too small, the effect of weakening the aggregation of cellulose fibers becomes small, so the molecular weight is preferably 100 or more, more preferably 200 or more, and even more preferably 500 or more. In addition, in this specification, a molecular weight may be a weight average molecular weight.

Generally, when the molecular weight of the hydrophobizing agent is as low as 600 or less, it may be difficult to sufficiently weaken the cohesion of the cellulose fibers during drying in step 3 only by adding the hydrophobizing agent. However, in the present invention, the water-soluble organic solvent added together with the hydrophobizing agent reinforces the effect of the hydrophobizing agent on weakening the cohesion of the cellulose fibers. will be able to As the water-soluble organic solvent capable of reinforcing the above action of the hydrophobizing agent, one having a low surface tension and a low boiling point is preferred. Solvents with low surface tension have a weak force to attract fibers together during drying (when removing the solvent), leading to relaxation of aggregation. Solvents with low boiling points attract fibers together because drying time is short. The time is shortened, which leads to relaxation of aggregation. The surface tension of the water-soluble organic solvent is preferably lower than the surface tension of water (73 N/m at 20°C), more preferably 35 N/m or less at 20°C, more preferably 30 N/m or less, and 26 N/m. m or less is more preferable. The surface tension can be measured by a commonly used method such as plate method, ring method and hanging drop method. The boiling point of the water-soluble organic solvent at 1 atm is preferably lower than the boiling point of water (100°C), more preferably 90°C or lower, and even more preferably 80°C or lower.

The amount of the 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, 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

The amount of the water-soluble organic solvent added is not particularly limited, but for example, when the concentration of the anion-modified cellulose in the dispersion is 0.01 to 15% by mass, preferably 1 to 10% by mass, more preferably 2 to 6% by mass. It may be added in such an amount that

A dispersion of hydrophobized anion-modified cellulose can be produced by adding a hydrophobizing agent and a water-soluble organic solvent to an anion-modified cellulose dispersion and mixing for a certain period of time with stirring.

(3) Process 3
In step 3, the dispersion medium and water-soluble organic solvent are removed from the dispersion of hydrophobized anion-modified cellulose obtained in step 2 to produce a dry solid of hydrophobized anion-modified cellulose. At this time, it is necessary to sufficiently remove the dispersion medium so that the solid content concentration in the dry solid is higher than 90% by mass. The solid content concentration in the dry solids is preferably higher than 95% by mass, more preferably 97% by mass or more, and still more preferably 98% by mass or more. Cellulose tends to swell by absorbing water or a water-soluble organic solvent, but in Step 3, it is necessary to sufficiently remove the water or water-soluble organic solvent absorbed by the cellulose. By sufficiently removing the dispersion medium containing water and the water-soluble organic solvent in step 3, the solvent replacement step can be omitted, and dispersion in the low-polar organic solvent can be carried out in the subsequent step 4. . On the other hand, if the solid after drying contains 5% by mass or more of a dispersion medium (water and/or water-soluble organic solvent), defibrate and disperse in a low-polar organic solvent such as toluene in step 4. In this case, it becomes impossible to sufficiently mix with a low-polarity solvent, causing problems such as the occurrence of precipitation and a decrease in the transparency of the resulting dispersion.

Solids concentration in dry solids can be measured by the following procedure:
The dry solid is dried in an oven at 105° C. for 12 hours, and the solid content concentration of the dry solid is calculated from the masses before and after drying.

Solid concentration of dry solids (mass%) = mass after drying / mass before drying x 100
The means for removing the dispersion medium and the water-soluble organic solvent is not particularly limited, and for example, drying may be performed by placing at a temperature of 60 to 130° C. for 3 to 24 hours.

(4) Step 4
In step 4, the dry solid of hydrophobized anion-modified cellulose is mixed with an organic solvent, the hydrophobized anion-modified cellulose is fibrillated in the organic solvent, and a dispersion of hydrophobized anion-modified CNF using the organic solvent as a dispersion medium is obtained. to manufacture.

The type of organic solvent to be used is not particularly limited, and it may be a water-soluble organic solvent as described above. ) Even if an organic solvent is used as a dispersion medium, a uniformly dispersed CNF dispersion can be produced. The type of organic solvent may be selected according to the use of the CNF dispersion.

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 depending on the final application of the anion-modified CNF.

The mixing ratio of the organic solvent to the dry solid of the hydrophobized anion-modified cellulose is not particularly limited. The organic solvent is preferably added in an amount of 01 to 5% by mass, more preferably 0.5 to 3.0% by mass.

After mixing the dry solid of hydrophobized anion-modified cellulose with an organic solvent, the cellulose is defibrated by mechanical treatment in the organic solvent, and a dispersion of hydrophobized anion-modified CNF using the organic solvent as a dispersion medium is obtained. Form.

Although the device used for fibrillation is not limited, it is preferable to use a device capable of applying a strong shearing force to the dispersion, such as a high-speed rotation type, colloid mill type, high pressure type, roll mill type, and ultrasonic type. For efficient fibrillation, it is preferable to use a wet high-pressure or ultrahigh-pressure homogenizer capable of applying a pressure of 50 MPa or more to the dispersion 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.

Nanofibers of hydrophobized anion-modified cellulose can be obtained by the above defibration. CNF (cellulose nanofiber) is a fiber having an average fiber diameter of about 3 to 500 nm, preferably about 3 to 150 nm, more preferably about 3 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 hydrophobized anion-modified CNF are atomic force microscope (AFM) when the diameter is less than 20 nm, and 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.

INDUSTRIAL APPLICABILITY According to the present invention, a dispersion of hydrophobized anion-modified CNF using an organic solvent as a dispersion medium can be efficiently produced. The dispersion obtained in the present invention is characterized by uniform dispersion and high transparency even when a low-polarity organic solvent such as toluene is used as the dispersion medium. Transparency is measured, for example, in the following way:
A CNF 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, Make it transparent.

In the present invention, for example, for a hydrophobized anion-modified CNF dispersion in which the dispersion medium is toluene and the solid content (in terms of CNF (not including the hydrophobizing agent)) is 1.0% by mass, the transparency measured by the above method Dispersions can be prepared in which the is 70% or more, more preferably 75% or more, and even more preferably 80% or more.

(5) Dry Solid of Hydrophobized Anion-Modified Cellulose The dry solid of the hydrophobized anion-modified cellulose obtained in step 3 has the hydrophilicity of the anion-modified cellulose reduced by the hydrophobization treatment, and is water or water-soluble. Since it contains almost no aqueous dispersion medium such as an organic solvent, it can be used by being well mixed with various organic solvents and hydrophobic polymers. The dry solids of hydrophobized anionically modified cellulose comprise anionically modified cellulose with attached hydrophobizing agents. The hydrophobizing agent is as described above and preferably has a molecular weight of less than 1000, more preferably 600 or less. The dispersion medium is sufficiently removed so that the solid content concentration in the dry solid is higher than 90% by mass, and the solid content concentration is more preferably higher than 95% by mass, more preferably 97% by mass or more. Yes, more preferably 98% by mass or more.

In the present invention, when the hydrophobized anion-modified cellulose is dried, aggregation of the cellulose fibers can be suppressed, resulting in an increase in bulk. Therefore, the dry solid of the obtained hydrophobized anion-modified cellulose becomes a cellulose fiber that is easily dispersed in an organic solvent and has good handling performance.

The dry solid of the hydrophobized anion-modified cellulose is mainly composed of the hydrophobized anion-modified cellulose, and optionally conventional additives ( antibacterial agents, coloring agents, resin base materials, resin antistatic agents, antifogging agents, light stabilizers, UV absorbers, pigments, inorganic fillers, antifungal agents, preservatives, foaming agents, flame retardants, etc.) It may contain small amounts of the above additives by drying. When the dry solid of the hydrophobized anion-modified cellulose contains additives other than the hydrophobized anion-modified cellulose, the proportion of the hydrophobized anion-modified cellulose in the dry solid is preferably 80% by mass or more, and more preferably 90% by mass or more. Preferably, 95% by mass or more is more preferable. The dry solids may be free of additives and consist solely of hydrophobized anionically modified cellulose (with a small amount of residual carrier medium).

The form of the dried solid of the hydrophobized anion-modified cellulose is not particularly limited. can be selected.

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>
500 g (absolutely dry) of bleached unbeaten kraft pulp (85% whiteness) derived from softwood is added to 500 ml of an aqueous solution of 780 mg of TEMPO (Sigma Aldrich) and 75.5 g of sodium bromide, until the pulp is uniformly dispersed. Stirred. An aqueous sodium hypochlorite solution was added to the reaction system so as to have a concentration of 6.0 mmol/g to initiate an oxidation reaction. The pH in the system decreased during the reaction, but was adjusted to pH 10 by successively adding 3M sodium hydroxide aqueous solution. The reaction was terminated when the sodium hypochlorite was consumed and the pH in the system stopped changing. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was sufficiently washed with water to obtain a pulp (carboxylated cellulose) into which carboxyl groups were introduced. The carboxyl group content of this carboxylated cellulose was 1.42 mmol/g.

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

A hydrophobizing agent (JEFFAMINE (registered trademark) M-600 (manufactured by HUNTSMAN, molecular weight 600)) dissolved in methanol was added to the resulting acid-type carboxylated cellulose dispersion, and the carboxymethylated cellulose in the dispersion was added. was adjusted to 4% by mass. The amount of the hydrophobizing agent added was an amount equivalent to 1 equivalent to the amount of carboxyl groups. Mixed with a homogenizer (1500 rpm, 10 minutes) to produce a dispersion of carboxylated cellulose with a hydrophobizing agent (hydrophobicized carboxylated cellulose). The dispersion of hydrophobized carboxylated cellulose was allowed to stand at a temperature of 70° C. for 2 hours to produce a dry solid of hydrophobized carboxylated cellulose (solid content concentration 98% by mass).

Toluene was added to the obtained dry solid so that the solid content was 1% by mass in terms of carboxylated cellulose (not including hydrophobizing agent), and the mixture was mixed at 3000 rpm for 10 minutes. Subsequently, using an ultrahigh-pressure homogenizer, the material was treated (fibrillated) once at 20° C. at 80 MPa and further at 150 MPa three times to obtain a dispersion of hydrophobized carboxylated CNF using toluene as a dispersion medium. The yield (ie the ratio of the mass of carboxylated CNF in the finally obtained hydrophobized carboxylated CNF to the mass of carboxylated cellulose used) was 100%.

The transparency of the obtained hydrophobized carboxylated CNF dispersion (dispersion medium: toluene, solid content (in terms of carboxylated CNF): 1% by mass) was measured by the method described above. Table 1 shows the results.

<Example 2>
A dispersion of hydrophobized carboxylated CNF using toluene as a dispersion medium was produced in the same manner as in Example 1 except that the treatment with an ultrahigh pressure homogenizer was performed once at 80 MPa and 5 times at 150 MPa. The transparency of the obtained hydrophobized carboxylated CNF dispersion (dispersion medium: toluene, solid content (in terms of carboxylated CNF): 1% by mass) was measured in the same manner as in Example 1. Table 1 shows the results.

<Example 3>
A dispersion of hydrophobized carboxylated CNF using toluene as a dispersion medium was produced in the same manner as in Example 2, except that acetone was used instead of methanol. The transparency of the obtained hydrophobized carboxylated CNF dispersion (dispersion medium: toluene, solid content (in terms of carboxylated CNF): 1% by mass) was measured in the same manner as in Example 1. Table 1 shows the results.

<Example 4>
A dispersion of hydrophobized carboxylated CNF using toluene as a dispersion medium was produced in the same manner as in Example 2, except that tetrahydrofuran was used instead of methanol. The transparency of the obtained hydrophobized carboxylated CNF dispersion (dispersion medium: toluene, solid content (in terms of carboxylated CNF): 1% by mass) was measured in the same manner as in Example 1. Table 1 shows the results.

<Comparative Example 1>
A dispersion of hydrophobized carboxylated CNF using toluene as a dispersion medium was produced in the same manner as in Example 2, except that water was used instead of methanol. The transparency of the obtained hydrophobized carboxylated CNF dispersion (dispersion medium: toluene, solid content (in terms of carboxylated CNF): 1% by mass) was measured in the same manner as in Example 1. Table 1 shows the results.

<Comparative Example 2>
Carboxylated cellulose having a carboxyl group content of 1.42 mmol/g was produced in the same manner as in Example 1. The carboxylated cellulose was adjusted to a solid content concentration of 1% by mass with water, and treated (defibrated) at 20° C. at 80 MPa once and then at 150 MPa three times using an ultrahigh-pressure homogenizer (fibrillation). An aqueous dispersion of CNF was obtained.

A cation exchange resin was added to the aqueous dispersion of carboxylated CNF, and the sodium salt type carboxyl group (-COONa) in the carboxylated CNF was converted to an acid form (-COOH). After that, it was separated from the cation exchange resin by suction filtration using a metal mesh, and the filtrate was recovered. After adding acetone to the obtained acid-form carboxylated CNF, centrifugation (3000 rpm, 10 minutes, device: 7800 manufactured by Kubota Seisakusho Co., Ltd.) was performed. After acetone was added to the obtained precipitate and mixed, centrifugation was performed again under the same conditions. Next, after adding acetone to the precipitate, suction filtration (diaphragm type vacuum pump, DCT-40, manufactured by ULVAC KIKO CO., LTD.) was performed using a glass filter (15G3, manufactured by Shibata Scientific Co., Ltd.). This addition of acetone and suction filtration was repeated three times. Further, toluene was used in place of acetone, and the addition of toluene and suction filtration were repeated three times to replace the dispersion medium of the carboxylated CNF with toluene.

To the obtained mixture of carboxylated CNF and toluene (solid content concentration 1% by mass), JEFFAMINE (registered trademark) M-600 (manufactured by HUNTSMAN, molecular weight 600) as a hydrophobizing agent is added to 1 equivalent with respect to the amount of carboxyl groups. After mixing and stirring with a homogenizer at 8000 rpm for 10 minutes, the toluene is dispersed by treating (defibrating) with an ultrahigh pressure homogenizer at 20 ° C. once at 80 MPa and twice at 150 MPa. A dispersion of hydrophobized carboxylated CNF as a vehicle was obtained. The yield (ie the ratio of the mass of carboxylated CNF in the finally obtained hydrophobized carboxylated CNF to the mass of carboxylated cellulose used) was 85%. The transparency and viscosity of the obtained hydrophobized carboxylated CNF dispersion (dispersion medium: toluene, solid content (in terms of carboxylated CNF): 1% by mass) were measured in the same manner as in Example 1. Table 1 shows the results.

In Examples 1 to 4 and Comparative Example 1, a hydrophobizing agent was added before defibration into CNF, and the hydrophobized carboxylated cellulose was fibrillated in an organic solvent, thereby making the organic solvent a dispersion medium. A dispersion of carboxylated CNF was produced. On the other hand, in Comparative Example 2, after the carboxylated CNF was produced, the solvent was replaced and then hydrophobized. In the methods of Examples 1 to 4 and Comparative Example 1, the operation is simpler than the conventional method using solvent replacement, and the hydrophobized carboxylated CNF dispersion can be produced with a high yield. I understand that.

Furthermore, in Examples 1 to 4, in which a water-soluble organic solvent was added together with a hydrophobizing agent, dispersions with higher transparency were produced than in Comparative Example 1, in which no water-soluble organic solvent was added. A high degree of transparency indicates that defibration proceeds well and that fibrillation is uniform.

The methods of Examples 1 to 4 do not require conventional solvent replacement in which solvent addition and centrifugation or suction filtration are repeated, so compared to the method using conventional solvent replacement (Comparative Example 2), the cost and time-saving dispersions of hydrophobized anion-modified CNFs with high transparency can be produced.

In addition, when adding the hydrophobizing agent, the viscosity of the CNF dispersion is high in the method of Comparative Example 2, so the solid content of the CNF dispersion is 1% by mass to achieve sufficient mixing with the hydrophobizing agent. Although it was necessary to adjust, in Examples 1 to 4, it is sufficient to add a hydrophobizing agent to the carboxylated cellulose before making it into CNF, and the solid content mass of the carboxylated cellulose after adding the hydrophobizing agent is 4% by mass. Therefore, there is an advantage that hydrophobization is efficient.

As described above, in the method of the present invention (Examples 1 to 4), compared to Comparative Examples 1 and 2, a dispersion of hydrophobized anion-modified CNF using a low-polarity organic solvent such as toluene as a dispersion medium, It turns out that it can be manufactured efficiently.

<Example 5>
A dispersion of hydrophobized carboxylated CNF using toluene as a dispersion medium was produced in the same manner as in Example 1 except that oleylamine (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 267) was used as a hydrophobizing agent. The transparency and viscosity of the obtained hydrophobized carboxylated CNF dispersion (dispersion medium: toluene, solid content (in terms of carboxylated CNF): 1% by mass) were measured in the same manner as in Example 1. Table 2 shows the results.

<Comparative Example 3>
An attempt was made to produce a hydrophobized carboxylated CNF dispersion using toluene as a dispersion medium in the same manner as in Comparative Example 1, except that oleylamine (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 267) was used as a hydrophobizing agent. Defibrillation did not proceed, and a CNF dispersion was not obtained.

Example 5 and Comparative Example 3 are examples using a hydrophobizing agent having a small molecular weight. When a hydrophobizing agent with a small molecular weight is used, it is difficult to sufficiently weaken the cohesion of cellulose fibers during drying, and defibration did not proceed in Comparative Example 3. In Example 5, it was possible to defibrate.

Claims (2)

Step 1 of preparing a dispersion of anion-modified cellulose,
Step 2 of adding a hydrophobizing agent and a water-soluble organic solvent to a dispersion of anion-modified cellulose to produce a dispersion of hydrophobized anion-modified cellulose;
Step 3 of removing the water-soluble organic solvent and the dispersion medium from the dispersion of the hydrophobized anion-modified cellulose to produce a dry solid of the hydrophobized anion-modified cellulose, and Step 4 of mixing with an organic solvent and defibrating the hydrophobized anion-modified cellulose in the organic solvent to produce a dispersion of hydrophobized anion-modified cellulose nanofibers using the organic solvent as a dispersion medium;
including
The dry solids of the hydrophobized anion-modified cellulose have a solid content concentration of higher than 90% by mass,
The water-soluble organic solvent has a surface tension of 35 N/m or less at 20°C and a boiling point of less than 100°C at 1 atm ,
Organic solvents mixed in step 4 include benzene, toluene, xylene, n-hexane, n-octane, cyclohexane, methylcyclohexane, dichloromethane, dichloroethane, chloroform, carbon tetrachloride, fluorotrichloromethane, trichlorotrifluoromethane, and hexafluorobenzene. , or one or more low-polarity organic solvents selected from cyclopentyl methyl ether,
A method for producing a dispersion of hydrophobized anionically modified cellulose nanofibers. The method according to claim 1 , wherein the anion-modified cellulose is a cellulose having a carboxyl group or a cellulose having a carboxyalkyl group.