JP2020111665A - Manufacturing method of hydrophobing anion modified cellulose nanofiber dispersion and dry solid product of hydrophobing anion modified cellulose - Google Patents

Abstract

To provide a method capable of efficiently manufacturing a dispersion of anion modified cellulose nanofiber having an organic solvent as a dispersant.SOLUTION: A hydrophobing agent and a water-soluble organic solvent are added to a dispersion of anion modified cellulose to obtain hydrophobing anion modified cellulose, thereafter the dispersant is removed to obtain a dry solid product with a solid content concentration of higher than 90 mass%, which is then mixed with an organic solvent to fibrillate the hydrophobing anion modified cellulose in the organic solvent, and a dispersion of hydrophobing anion modified cellulose nanofiber having an organic solvent as a dispersant is manufactured.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a dispersion of hydrophobized anion-modified cellulose nanofibers, and a dried solid product of hydrophobized anion-modified cellulose.

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, are biodegradable, and have high transparency when formed into a film, and thus application to various fields is being studied.

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

In Patent Document 1, when dispersing cellulose nanofibers in a medium containing an organic solvent, as a “second manufacturing method”, an acid is added to an aqueous dispersion of cellulose nanofibers to form a carboxylate group of cellulose nanofibers. Of substituting a part of the carboxylic acid type group, a step of adding an organic solvent to the gel of cellulose nanofiber partially substituted with a carboxylic acid type, and cellulose nanofiber water to which the organic solvent is added A method is described which comprises removing the aqueous solvent from the dispersion.

Further, in Patent Document 2, as a “first production method”, a step of treating a carboxylic acid type cellulose nanofiber aqueous dispersion with an amine, and collecting the amine-treated cellulose nanofibers in a dispersion medium. The method is described in which the step of re-dispersing the cellulose nanofiber dispersion is prepared.

International Publication No. 2010/134357 JP2012-21081A

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 dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide. Is a water-soluble organic solvent that is optionally miscible with water. The method described in Patent Document 1 does not describe the use of an organic solvent such as toluene, which has a low polarity and is hardly soluble in water, as a dispersion medium of the cellulose nanofiber dispersion liquid. Further, Patent Document 2 also does not describe the use of a low-polarity, poorly water-soluble organic solvent as a dispersion medium.

By producing a cellulose nanofiber dispersion using a water-soluble organic solvent as a dispersion medium by using the methods described in Patent Documents 1 and 2, by substituting the water-soluble organic solvent with a poorly water-soluble organic solvent having a low polarity. Although it is possible to produce a cellulose nanofiber dispersion using an organic solvent that is poorly soluble in water as a dispersion medium, it is necessary to repeat the addition of the solvent and the removal by suction filtration and the like many times during the solvent replacement. However, there is a problem that the cost and time are required, and the yield of the cellulose nanofiber is reduced. In addition, in the methods described in Patent Documents 1 and 2, defibration performed when first obtaining an aqueous dispersion of cellulose nanofibers and defibration performed after addition of an organic solvent (also, in some cases, acid-type cellulose nanofibers). Requires at least two defibration steps (mechanical treatment with a mixer, homogenizer, etc.) when re-dispersing the gel in water in water, and cellulose fibers are damaged as the number of defibration increases. 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 intensive investigations by the present inventors, before defibrating anion-modified cellulose into nanofibers, a hydrophobicizing agent and a water-soluble organic solvent are added to the anion-modified cellulose to hydrophobize the anion-modified cellulose, 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 (solid content concentration is higher than 90% by mass), and the dry solid is dissolved in an organic solvent. It has been found that an anion-modified cellulose nanofiber dispersion using an organic solvent as a dispersion medium can be efficiently produced by dispersing while finely dispersing. The present invention includes, but is not limited to:
(1) Step 1 of preparing a dispersion of anion-modified cellulose,
A step 2 of producing a dispersion of hydrophobized anion-modified cellulose by adding a hydrophobizing agent and a water-soluble organic solvent to the dispersion of anion-modified cellulose;
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 a dry solid of the hydrophobized anion-modified cellulose. A step 4 of mixing with an organic solvent to defibrate 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 method for producing a dispersion of hydrophobized anion-modified cellulose nanofibers, wherein the dry solid of hydrophobized anion-modified cellulose has a solid content concentration of higher than 90% by mass.
(2) The method according to (1), wherein the water-soluble organic solvent has a surface tension at 20° C. of 35 N/m or less.
(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 atm.
(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) A dry solid of a hydrophobicized anion-modified cellulose, which contains anion-modified cellulose having a hydrophobizing agent bound thereto and has a solid content concentration of higher than 90% by mass.

According to the present invention, a dispersion of anion-modified cellulose nanofibers containing an organic solvent as a dispersion medium can be efficiently produced. The method of the present invention does not require a solvent substitution step of repeating centrifugal separation for replacing water or a highly polar water-soluble organic solvent with a low-polarity organic solvent, suction filtration, and the like in a low-polarity organic solvent. Since the anion-modified cellulose nanofibers can be dispersed in, the cost and time can be saved. Further, conventionally, a cellulose nanofiber was defibrated, then a hydrophobizing agent was added, and defibration was performed again in an organic solvent to produce a dispersion having an organic solvent as a dispersion medium. Then, by manufacturing the hydrophobized cellulose and then defibrating it in an organic solvent, it is possible to reduce the number of times of defibration, and it is possible to obtain the advantage that the damage to the cellulose fibers is reduced. Cellulose nanofibers are materials that swell in an aqueous medium and exhibit high viscosity, and conventionally, when a hydrophobizing agent is added, the cellulose nanofibers are sufficiently mixed with the hydrophobizing agent. It was necessary to make the concentration of about 1% by mass, but in the present invention, since a hydrophobic treatment is applied to the anion-modified cellulose which is not so high in viscosity before being defibrated into cellulose nanofibers, a higher concentration Hydrophobic treatment can be performed using the cellulose (for example, 2 to 10% by mass), and the efficiency of hydrophobization is high.

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, the cellulose nanofiber may be referred to as “CNF”. Specifically, the method of the present invention prepares a dispersion of anion-modified cellulose (step 1) and adds a hydrophobizing agent and a water-soluble organic solvent to the dispersion of anion-modified cellulose to modify the hydrophobically-modified anion. A dispersion of cellulose is produced (step 2), the water-soluble organic solvent and the 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 to defibrate the hydrophobized anion-modified cellulose in an organic solvent to produce a dispersion of hydrophobized anion-modified CNF using the organic solvent as a dispersion medium. (Step 4) is included. At this time, in step 3, drying (removal of the dispersion medium) is performed until the solid content concentration of the dried solid becomes higher than 90% by mass.

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

(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, and microcrystalline cellulose excluding the non-crystalline region 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 the bleached pulp or the non-bleached 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 manufacturing method include mechanical pulp (thermo-mechanical pulp (TMP), groundwood pulp), chemical pulp (softwood unbleached 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. Further, dissolving pulp may be used in addition to the papermaking pulp. 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 cellulosic material.

(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 the hydroxyl group of the pyranose ring to a carboxyl group. Further, 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.

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

The amount of carboxyl groups of carboxylated cellulose can be measured by the following method:
60 ml of a 0.5% by mass slurry of carboxylated cellulose (aqueous dispersion) was prepared and adjusted to pH 2.5 by adding a 0.1 M hydrochloric acid aqueous solution, and then a 0.05 N sodium hydroxide aqueous solution was added dropwise to adjust the pH to 11 The electric conductivity is measured until it becomes, and it is calculated from the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid whose electric conductivity changes slowly 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 with 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, and further preferably 0.5 mmol to 5 mmol with respect to 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, for example, 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, relative to 1 g of absolutely dried 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 solution of sodium hydroxide 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 due to 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 may 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. 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 conditions of the ozone treatment are within these ranges, the cellulose can be prevented from being excessively oxidized and decomposed, and the yield of the oxidized cellulose will be 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, 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 to perform the additional oxidation treatment.

The amount of carboxyl groups of carboxylated cellulose can be adjusted by controlling the reaction conditions such as the addition amount of the above-mentioned oxidizing agent 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 made into nanofibers are usually the same.

(1-2-2) Carboxyalkylation As an example of anion modification, introduction of a carboxyalkyl group such as a carboxymethyl group into cellulose 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 per anhydroglucose unit of cellulose is preferably less than 0.40. Furthermore, 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 CNF is lowered. 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. In addition, the anhydrous glucose unit means an individual anhydrous glucose (glucose residue) that constitutes cellulose, and the carboxyalkyl substitution degree is a carboxyalkyl group among the hydroxyl groups (—OH) in the glucose residue that constitutes cellulose. The ratio (number of carboxyalkyl ether groups per glucose residue) of those substituted with ether groups (-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 mercerization treatment is carried out at a reaction temperature of 0 to 70° C., preferably 10 to 60° C., and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Process,
ii) Next, 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.

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, etc. alone or 2 One or more mixed media can be used. When the lower alcohol is mixed, the mixing ratio is preferably 60 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 nano-defibrated. If the carboxymethyl substituent is less than 0.01 per glucose unit, 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 placed 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 carboxymethylated cellulose salt (CMized cellulose) into hydrogenated CM-modified cellulose. 1.5 g to 2.0 g of hydrogenated CM cellulose (absolutely dry) 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. Back titration of excess NaOH 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 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 described above.
(1-2-3) Esterification Esterification can be mentioned as an example of anion modification. Examples of the esterification method include a method of mixing powders and aqueous solutions of a phosphoric acid compound with a cellulose raw material, a method of adding an aqueous solution of a phosphoric acid compound to a slurry of a cellulose raw material, and the like. Examples of 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 phosphoric acid group is preferable because it is low in cost, easy to handle, and can introduce a phosphoric acid group 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. A phosphate group can be introduced into cellulose by using one kind or a combination of two or more kinds. 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 Ammonium salts are preferred. Particularly, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferable. In addition, it is desirable to use the phosphoric acid compound as an aqueous solution because the reaction can be proceeded uniformly and the efficiency of introducing a phosphoric acid group is high. 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 to 10 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 to 500 parts by mass, and more preferably 1 to 400 parts by mass, as the amount of elemental phosphorus. When the ratio of the phosphoric acid compound is at least the lower limit value, the yield of fine fibrous cellulose can be further improved. However, if the upper limit is exceeded, the effect of improving the yield will reach the ceiling, which 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. The term "basic" as used herein is defined as that the aqueous solution exhibits a pink to red color in the presence of the phenolphthalein indicator, or that the pH of the aqueous solution is 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 to 1000 parts by mass, more preferably 100 to 700 parts by mass, relative to 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 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 to 170° C. from the viewpoint of suppressing hydrolysis of cellulose. Further, 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.

The degree of substitution of phosphate groups per glucose unit of the phosphate-esterified cellulose is preferably 0.001 or more and less than 0.40. By introducing a phosphate group substituent into the 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 degree of substitution of phosphate groups per glucose unit is greater than 0.40, swelling or dissolution may result in failure to obtain nanofibers. In order to efficiently perform defibration, it is preferable that the phosphoric acid esterified cellulosic material obtained above is boiled and then washed with cold water. The modification by esterification is a modification by a 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.

(1-3) Anion-Modified Cellulose Anion-modified cellulose can be obtained by subjecting the cellulose as a raw material to anion modification as exemplified above. Moreover, you may use a commercially available thing. As the type of anion-modified cellulose, cellulose having a carboxyl group or cellulose having a carboxyalkyl group is preferable. Particularly, carboxylated cellulose obtained by oxidizing cellulose with an N-oxyl compound and an oxidizing agent is preferable because anionic groups are uniformly introduced and uniform fibrillation is easy.

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 using a material that does not maintain a fibrous shape (that is, a material that dissolves). That at least a 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 crystalline 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 the raw material cellulose 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 diffractometer (LabX XRD-6000, manufactured by Shimadzu Corporation). The degree of crystallinity was calculated by using a method such as Segal, and the diffraction intensity of 2θ=22.6° on the 002 plane and 2θ=2θ=22.6° were used as the baseline with the diffraction intensity of 2θ=10° to 30° of the X-ray diffraction diagram as the baseline. It is calculated by the following formula from the diffraction intensity of the amorphous portion at 18.5°.
Xc=(I002c-Ia)/I002c×100
Xc: Type I crystallinity of cellulose (%)
I002c: 2θ=22.6°, 002 plane diffraction intensity Ia: 2θ=18.5°, amorphous part diffraction intensity.

The ratio of cellulose I-type crystals of anion-modified cellulose and the ratio of cellulose I-type 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 a metal salt type (for example, -COO ^- M ⁺ , or -RCOO ^- M ⁺ (M is a metal such as sodium or potassium). And R is an alkylene group such as a methylene group or an ethylene group)). In order to accelerate the subsequent reaction with the hydrophobizing agent, it is preferable to convert the metal salt type anionic group in the anion-modified cellulose into an acid type (for example, —COOH, —RCOOH, etc.).

The method of converting to an acid form is not particularly limited, and examples thereof include a method of adding an 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 thereof include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, nitrous acid and phosphoric acid, and acetic acid, lactic acid, oxalic acid, citric acid, formic acid, adipic acid. , Sebacic acid, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid, gluconic acid and the like. General-purpose and easily available hydrochloric acid or sulfuric acid is preferable. The pH when adding the acid is preferably in the range of 1 to 6, more preferably 2 to 5. The addition amount of the acid is not particularly limited as long as it can convert the metal salt type anion-modified cellulose into the acid type, and for example, in the case of a strong acid, 1 equivalent or more relative to the anionic group is preferable, and a weak acid is used. If so, 10 equivalents or more are preferable. When brought into contact with an acidic ion exchange resin, examples of the acidic ion exchange resin include strong acidic cation exchange resin and weak acidic cation exchange resin.

(1-4) Dispersion of anion-modified cellulose The dispersion medium in the dispersion of anion-modified cellulose prepared in step 1 can be appropriately selected from water, an organic solvent, or a mixture thereof. The type of the organic solvent is not limited, for example, a polar solvent having a high affinity with a hydroxyl group in cellulose, and a water-soluble organic solvent that can be mixed with water at an arbitrary ratio 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. Examples thereof include sulfoxide. 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.

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

(2) Step 2
In step 2, a hydrophobicizing 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 a hydrophobic group 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 capable of interacting with an anionic group of anion-modified cellulose to form an onium salt, and a primary amine, a secondary amine, a tertiary amine, or a quaternary amine. Any of ammonium, aromatic amine, diamine, polyetheramine and phosphine may be used. For example, methylamine, ethylamine, oleylamine, propylamine, dodecylamine, stearylamine, tetradecylamine, 1-hexenylamine, 1-dodecenylamine, 9,12-octadecadienylamine (linolamine), 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 , Quaternary ammonium such as cetrimonium, dofanium chloride, tetraethylammonium bromide and didecyldimethylammonium chloride, aromatic amines such as aniline, pyridine and benzylamine, diamines such as ethylenediamine and hexamethylenediamine, JEFFAMINE manufactured by HUNTSMAN ( (Registered trademark) M600, JEFFAMINE (registered trademark) M1000, JEFFAMINE (registered trademark) M2005, JEFFAMINE (registered trademark) M2070, and other polyether amines, phosphines such as triphenylphosphine, trimethylphosphine, and the like, but are not limited thereto. .. Among 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 water-soluble organic solvent is an organic solvent that can be mixed with water at an arbitrary ratio, 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, dimethyl sulfoxide and the like.

In step 2, the hydrophobizing agent and the water-soluble organic solvent are added to the anion-modified cellulose dispersion obtained in step 1. At this time, the water-soluble organic solvent may be added after adding the hydrophobizing agent to the anion-modified cellulose dispersion, but from the viewpoint that the hydrophobizing agent is easily mixed uniformly with the anion-modified cellulose dispersion, It is preferable to add the water-soluble organic solvent to the cellulose dispersion before adding the hydrophobizing agent, and it is more preferable to dissolve the hydrophobizing agent in the water-soluble organic solvent and then add to the anion-modified cellulose dispersion.

In step 3 after step 2, the water-soluble organic solvent and the dispersion medium are removed from the hydrophobized anion-modified cellulose dispersion to produce a dry solid. Usually, when the dispersion medium is removed from the cellulose dispersion, the cellulose fibers are strongly aggregated by hydrogen bonds, and it becomes very difficult to disintegrate into nanofibers in the subsequent Step 4. In the present invention, by adding the hydrophobizing agent and the water-soluble organic solvent in step 2, the aggregation of the cellulose fibers during drying in step 3 is weakened, and the fibrillation into nanofibers in step 4 is performed later. Can be promoted. Specifically, it is considered that the hydroxyl groups of anion-modified cellulose are protected by a hydrophobizing agent, and hydrogen bonds between cellulose fibers during drying (when the dispersion medium is removed) are hindered. It is considered that the interpenetration between the fibers inhibits the aggregation of the cellulose fibers. When a water-soluble organic solvent having a lower surface tension and a lower boiling point than that of water is used, the force of attracting the cellulose fibers to each other at the time of drying in Step 3 can be weakened to reduce aggregation, and the drying time can be reduced. It is considered that the shorter time shortens the time for attracting the cellulose fibers to each other, and it becomes possible to dry the cellulose fibers before causing strong aggregation.

As the hydrophobizing agent, one having a higher molecular weight usually has a stronger effect of weakening the aggregation of the cellulose fibers during drying in the step 3, but on the other hand, if the molecular weight of the hydrophobizing agent is higher, the step 3 Since the ratio of anion-modified cellulose in the obtained dry solid and the ratio of CNF in the hydrophobized anion-modified CNF dispersion obtained in step 4 are small, the properties as anion-modified cellulose or CNF (for example, development of viscosity) However, it may be difficult to obtain. In the present invention, by adding a water-soluble organic solvent in addition to the hydrophobizing agent, even when a low molecular weight hydrophobizing agent is used, the aggregation of the cellulose fibers during the drying step 3 is weakened. As a result, it becomes possible to proceed with defibration in the subsequent step 4 to obtain a nanofiber dispersion. Therefore, although not limited thereto, a hydrophobizing agent having a relatively low molecular weight can be used, for example, a hydrophobizing agent having a molecular weight of 3000 or less can be used, and a hydrophobizing agent having a molecular weight of 2500 or less can be used. Can be used, and a hydrophobizing agent having a molecular weight of 2000 or less can be used. The lower limit of the molecular weight of the hydrophobizing agent is not limited. However, if the molecular weight is too small, the action of weakening the aggregation of the cellulose fibers is reduced, so the molecular weight is preferably 100 or more, more preferably 200 or more, and further preferably 500 or more. In addition, in this specification, a molecular weight may be a weight average molecular weight.

Usually, when the molecular weight of the hydrophobizing agent is as low as 600 or less, it may be difficult to sufficiently weaken the aggregation of the cellulose fibers at the time of 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 action of weakening the aggregation of the cellulose fibers by the hydrophobizing agent, so that the hydrophobizing agent having a relatively low molecular weight as described above is used. Will be able to. As the water-soluble organic solvent capable of reinforcing the above action of the hydrophobizing agent, those having a low surface tension are preferable, and those having a low boiling point are preferable. Solvents with low surface tension have a weaker force to attract fibers to each other during drying (solvent removal), which leads to relaxation of aggregation, and solvents with a low boiling point attract fibers to each other because the drying time is short. It shortens the time and reduces 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, more preferably 30 N/m or less, and 26 N/m at 20°C. It is more preferably m or less. The surface tension can be measured by a conventional method such as a plate method, a ring method or a 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 further preferably 80° C. or lower.

The addition amount of the hydrophobizing agent may be appropriately determined depending on the kind of the 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%, and more preferably 80 to 120% with respect to the amount (mol number) of the anionic group. It may be added to.

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

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

(3) Step 3
In step 3, the dispersion medium and the water-soluble organic solvent are removed from the dispersion of the 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 dried solid substance is higher than 90% by mass. The solid content concentration in the dried solid material is preferably higher than 95% by mass, more preferably 97% by mass or more, and further preferably 98% by mass or more. Although cellulose easily absorbs water or a water-soluble organic solvent and swells, 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 can be performed in a low-polarity organic solvent in step 4 later. .. On the other hand, when the solid matter after drying contains 5% by mass or more of the dispersion medium (water and/or water-soluble organic solvent), in step 4, defibrate and disperse it in a low-polarity organic solvent such as toluene. In such a case, the solvent cannot be sufficiently mixed with the low-polarity solvent, which causes problems such as precipitation and deterioration of transparency of the obtained dispersion.

The 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 mass before and after the drying.

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

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

The type of organic solvent used is not particularly limited and may be a water-soluble organic solvent as described above, but in the present invention, it has a lower polarity than the water-soluble organic solvent (such as when separated when mixed with water). ) Even if an organic solvent is used as a dispersion medium, it is possible to produce a CNF dispersion that is uniformly dispersed. The type of organic solvent may be selected according to the application of the CNF dispersion.

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. Examples thereof include methane, trichlorotrifluoromethane, hexafluorobenzene, tetrahydrofuran, 1,2-dimethoxyethane, cyclopentyl methyl ether, methyl tertiary butyl ether and the like. These 1 type(s) or 2 or more types can be appropriately selected and used according to the use of the final anion-modified CNF.

The mixing ratio of the organic solvent to the dry solid matter of the hydrophobized anion-modified cellulose is not particularly limited, but considering the efficiency of defibration, the solid content concentration (excluding the hydrophobizing agent portion) of the anion-modified cellulose is 0. It is preferable to add the organic solvent so as to be from 0 to 5% by mass, more preferably from 0.5 to 3.0% by mass.

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

The device used for defibration is not limited, but it is preferable to use a device capable of applying a strong shearing force to the dispersion, such as a high-speed rotation type, a colloid mill type, a high pressure type, a roll mill type, or an ultrasonic type. For efficient defibration, it is preferable to use a wet high-pressure or ultra-high-pressure homogenizer capable of applying a pressure of 50 MPa or more to the dispersion and applying 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 ultrafine pulverization. Prior to the 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.

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

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 in that the dispersion is uniform and the transparency of the dispersion is high even when a low-polarity organic solvent such as toluene is used as the dispersion medium. Clarity is measured, for example, by the following method:
A CNF 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, Be transparent.

In the present invention, for example, the transparency measured by the above method for a hydrophobic anion-modified CNF dispersion in which the dispersion medium is toluene and the solid content (CNF conversion (excluding hydrophobizing agent)) is 1.0% by mass. Of 70% or more, more preferably 75% or more, even more preferably 80% or more can be produced.

(5) Dry Solid of Hydrophobized Anion-Modified Cellulose The dry solid of hydrophobized anion-modified cellulose obtained in Step 3 has the hydrophilicity of the anion-modified cellulose reduced by the hydrophobization treatment, and is also water or water-soluble. Since it hardly contains an aqueous dispersion medium such as an organic solvent, it can be used by being mixed well with various organic solvents and hydrophobic polymers. The dry solid of hydrophobized anion-modified cellulose contains anion-modified cellulose to which a hydrophobizing agent is bound. 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, further preferably 97% by mass or more. And 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 and the bulkiness becomes high. Therefore, the obtained dry solid of the hydrophobized anion-modified cellulose is easily dispersed in an organic solvent and becomes a cellulose fiber having good handling performance.

The dry solid of the hydrophobized anion-modified cellulose is mainly composed of the hydrophobized anion-modified cellulose. However, an additive conventionally used (depending on the application, such as before removing the dispersion medium from the dispersion of the hydrophobized anion-modified cellulose ( Antibacterial agent, colorant, resin base material, resin antistatic agent, antifogging agent, light stabilizer, UV absorber, pigment, inorganic filler, antifungal agent, preservative, foaming agent, flame retardant, etc.) are mixed. A small amount of the above-mentioned additives may be contained by drying after drying. When the dry solid of the hydrophobized anion-modified cellulose contains an additive 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. It is preferably 95% by mass or more and more preferably. The dry solids may be free of additives and may consist solely of hydrophobized anion-modified cellulose (with a small amount of residual dispersion medium).

The form of the dry solid of the hydrophobized anion-modified cellulose is not particularly limited, and may be in the form of a bulk (lump) after removing the dispersion medium, or may be appropriately pulverized into a powder, depending on the application. And select it.

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>
Bleached unbeaten kraft pulp from softwood (whiteness 85%) 500 g (absolute dryness) was added to 780 mg of TEMPO (Sigma Aldrich) and 500 ml of an aqueous solution in which sodium bromide 75.5 g was dissolved, until the pulp was uniformly dispersed. It was stirred. An aqueous sodium hypochlorite solution was added to the reaction system at 6.0 mmol/g to start the oxidation reaction. Although the pH in the system was lowered during the reaction, the pH was adjusted to 10 by sequentially adding a 3M sodium hydroxide aqueous solution. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system stopped changing. The mixture after the reaction was filtered with a glass filter to separate the pulp, and the pulp was sufficiently washed with water to obtain a pulp having carboxyl groups introduced (carboxylated cellulose). The carboxyl group content of the 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 the acid type (-COOH. ). Then, it was dehydrated by suction filtration using a glass filter. Again, the solid content concentration of the carboxylated cellulose was adjusted to 5% by mass with water and then dehydrated. This step was repeated 3 times to obtain acid-type carboxylated cellulose having a solid content concentration of 25% by mass.

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

Toluene was added to the obtained dried solid matter so that the solid content would be 1% by mass in terms of carboxylated cellulose (without a hydrophobizing agent), and the mixture was mixed at 3000 rpm for 10 minutes. Subsequently, a dispersion of hydrophobized carboxylated CNF using toluene as a dispersion medium was obtained by processing (defibration) once at 80 MPa at 20° C. and further at 150 MPa three times using an ultrahigh pressure homogenizer. The yield (that is, the ratio of the weight of carboxylated CNF in the finally obtained hydrophobic carboxylated CNF to the weight of carboxylated cellulose used) was 100%.

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

<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 the ultrahigh pressure homogenizer was performed once at 80 MPa and five times at 150 MPa. The transparency of the obtained dispersion of hydrophobic carboxylated CNF (dispersion medium: toluene, solid content (carboxylated CNF conversion): 1% by mass) was measured in the same manner as in Example 1. The results are shown in Table 1.

<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 dispersion of hydrophobic carboxylated CNF (dispersion medium: toluene, solid content (carboxylated CNF conversion): 1% by mass) was measured in the same manner as in Example 1. The results are shown in Table 1.

<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 dispersion of hydrophobic carboxylated CNF (dispersion medium: toluene, solid content (carboxylated CNF conversion): 1% by mass) was measured in the same manner as in Example 1. The results are shown in Table 1.

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

<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 with water to a solid content concentration of 1% by mass and treated with an ultrahigh pressure homogenizer at 20° C. once at 80 MPa and further at 150 MPa three times (fibrillation) to carry out carboxylation. An aqueous dispersion of CNF was obtained.

A cation exchange resin was added to the carboxylated CNF aqueous dispersion to convert the sodium salt type carboxyl group (-COONa) in the carboxylated CNF to the acid type (-COOH). Then, filtration with a cation exchange resin was performed by suction filtration using a metal mesh, and the filtrate was collected. After acetone was added to the obtained acid-type carboxylated CNF, centrifugation (3000 rpm, 10 minutes, apparatus: 7800 manufactured by Kubota Seisakusho) was performed. Acetone was added to the obtained precipitate and mixed, and then again centrifuged under the same conditions. Then, after adding acetone to the precipitate, suction filtration (a diaphragm vacuum pump, DCT-40, manufactured by ULVAC Kiko, Inc.) was performed using a glass filter (15G3, manufactured by Shibata Scientific Co., Ltd.). This addition of acetone and suction filtration were repeated 3 times. Further, toluene was used instead of acetone, and the dispersion medium of carboxylated CNF was replaced with toluene by repeating the addition of toluene and suction filtration three times.

JEFFAMINE (registered trademark) M-600 (manufactured by HUNTSMAN, molecular weight 600) as a hydrophobizing agent was added to the obtained mixture of carboxylated CNF and toluene (solid content concentration 1% by mass) in an amount of 1 equivalent to the amount of the carboxyl group. The mixture was added as described above, mixed and stirred using a homogenizer at 8000 rpm for 10 minutes, and then treated with an ultrahigh pressure homogenizer at 20° C. once at a pressure of 80 MPa and twice at 150 MPa (fibrillation) to disperse toluene. A dispersion of hydrophobized carboxylated CNFs as medium was obtained. The yield (that is, the ratio of the weight of carboxylated CNF in the finally obtained hydrophobic carboxylated CNF to the weight of carboxylated cellulose used) was 85%. The transparency and viscosity of the obtained dispersion of hydrophobic carboxylated CNF (dispersion medium: toluene, solid content (converted to carboxylated CNF): 1% by mass) were measured in the same manner as in Example 1. The results are shown in Table 1.

In Examples 1 to 4 and Comparative Example 1, a hydrophobizing agent was added before defibration into CNFs, and defibration of the hydrophobized carboxylated cellulose in an organic solvent was performed to obtain a hydrophobic solvent containing an organic solvent as a dispersion medium. A dispersion of decarboxylated CNF is produced. On the other hand, in Comparative Example 2, after producing carboxylated CNF, solvent replacement was performed and then hydrophobization was performed. In the methods of Examples 1 to 4 and Comparative Example 1, the operation is simpler than that in the conventional method using solvent substitution, and a hydrophobic carboxylated CNF dispersion can be produced in a high yield. I understand that

Furthermore, in Examples 1 to 4 in which the water-soluble organic solvent was added together with the hydrophobizing agent, it can be seen that a dispersion having high transparency could be produced as compared with Comparative Example 1 in which the water-soluble organic solvent was not added. A high degree of transparency indicates that the defibration proceeds satisfactorily and the defibration is uniform.

Since the methods of Examples 1 to 4 do not require conventional solvent replacement in which solvent addition and centrifugation or suction filtration are repeated, the cost is higher than that of the method using conventional solvent replacement (Comparative Example 2). It is possible to produce dispersions of hydrophobized anion-modified CNF with high transparency while saving time and time.

Further, when the hydrophobizing agent is added, since the viscosity of the CNF dispersion is high in the method of Comparative Example 2, the solid content mass of the CNF dispersion is set to 1% by mass in order to achieve sufficient mixing with the hydrophobizing agent. It was necessary to adjust, but in Examples 1 to 4, it is sufficient to add a hydrophobizing agent to the carboxylated cellulose before being made 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 the efficiency of hydrophobization is high.

As described above, in the method of the present invention (Examples 1 to 4), as compared with Comparative Examples 1 and 2, a dispersion of a hydrophobized anion-modified CNF using a low-polar organic solvent such as toluene as a dispersion medium, It turns out that it can manufacture 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 (produced by Tokyo Chemical Industry Co., Ltd., molecular weight 267) was used as the hydrophobizing agent. The transparency and viscosity of the obtained dispersion of hydrophobic carboxylated CNF (dispersion medium: toluene, solid content (converted to carboxylated CNF): 1% by mass) were measured in the same manner as in Example 1. The results are shown in Table 2.

<Comparative example 3>
An attempt was made to produce a dispersion of hydrophobically carboxylated CNF 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 the hydrophobizing agent. Disentanglement did not proceed, and a CNF dispersion could not be obtained.

Example 5 and Comparative Example 3 are examples using a hydrophobizing agent having a small molecular weight. When a hydrophobizing agent having a small molecular weight is used, it is difficult to sufficiently weaken the aggregation of the cellulose fibers during drying, and defibration did not proceed in Comparative Example 3, but a water-soluble organic solvent was added together with the hydrophobizing agent. In Example 5 which was performed, it was possible to defibrate.

Claims (5)

Step 1 of preparing a dispersion of anion-modified cellulose,
A step 2 of producing a dispersion of hydrophobized anion-modified cellulose by adding a hydrophobizing agent and a water-soluble organic solvent to the dispersion of anion-modified cellulose;
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 a dry solid of the hydrophobized anion-modified cellulose. A step 4 of mixing with an organic solvent to defibrate 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 method for producing a dispersion of hydrophobized anion-modified cellulose nanofibers, wherein the dry solid of hydrophobized anion-modified cellulose has a solid content concentration of higher than 90% by mass. The method according to claim 1, wherein the water-soluble organic solvent has a surface tension at 20° C. of 35 N/m or less. The method according to claim 1 or 2, wherein the water-soluble organic solvent has a boiling point of less than 100°C at 1 atm. The method according to any one of claims 1 to 3, wherein the anion-modified cellulose is a cellulose having a carboxyl group or a cellulose having a carboxyalkyl group. A dry solid of a hydrophobized anion-modified cellulose, comprising anion-modified cellulose having a hydrophobizing agent bound thereto and having a solid content concentration of higher than 90% by mass.