JPWO2020100980A1 - Method for producing anion-modified cellulose nanofibers - Google Patents

Abstract

Provided is a method for producing anion-modified cellulose nanofibers with low power consumption. Anionic-modified cellulose is defibrated using a cavitation jet to produce anionic-modified cellulose nanofibers. In the cavitation jet device, the upstream pressure of the liquid jet injected through the nozzle or orifice is 0.01 MPa or more and 30.00 MPa or less, the downstream pressure / upstream pressure ratio is 0.001 to 0.500, and the nozzle. Alternatively, the maximum width of the cavitation jet generated by the liquid jet injected through the orifice is 50% or more and 130% or less of the inner diameter of the pipe immediately after the nozzle or the orifice.

Description

The present invention relates to a method for producing anion-modified cellulose nanofibers.

It is known that cellulose nanofibers having a nanoscale fiber diameter can be produced by chemically modifying cellulose as a raw material to introduce a carboxyl group to obtain oxidized cellulose and then mechanically treating (defibrating) it. Has been done. As a means for mechanically defibrating cellulose oxide, a method of treating with an operating pressure of 10 MPa to 400 MPa using a high-pressure disperser such as an ultra-high pressure homogenizer has been reported (Patent Document 1).

On the other hand, a method of treating cellulose oxide by applying an impact force to the cellulose oxide when cavitation bubbles generated by a liquid jet injected through a nozzle or an orifice pipe collapses has also been reported (Patent Document 2).

Japanese Patent No. 5108587 Patent No. 5248158

The method using a high-pressure disperser as described in Patent Document 1 is excellent in that high energy can be easily applied to the object to be treated, but since a very high pressure is used, cellulose is nano-ordered. A high amount of electric power is required to defibrate to the average fiber diameter of. On the other hand, the treatment with cavitation bubbles generated by the liquid jet as described in Patent Document 2 (treatment by the cavitation jet device) can be performed at a lower pressure than the treatment by the high pressure type disperser described in Patent Document 1. .. However, there have been no reports so far that cellulose was defibrated to a nano-order average fiber diameter using a cavitation jet device.

An object of the present invention is to provide a method capable of producing anion-modified cellulose nanofibers by defibrating anion-modified cellulose to a nano-order average fiber diameter with low power consumption.

The present inventors have diligently studied the above-mentioned problems. Specifically, we focused on a cavitation jet device that can be used with less power consumption than a high-pressure homogenizer. However, since anion-modified cellulose nanofibers are gel-like substances with extremely high viscosity, they tend to stay in the piping even if they are manufactured using a cavitation jet device, which has a lower pressure than a high-pressure homogenizer, and the treatment proceeds. There wasn't. As a result of further studies on this point, by adjusting the maximum width of the cavitation jet by the cavitation jet device and the inner diameter of the pipe immediately after the nozzle or orifice pipe of the cavitation jet device to be about the same, the above It was found that anion-modified cellulose (nanofiber of anion-modified cellulose) having a nano-order average fiber diameter can be efficiently obtained by suppressing the retention in the pipe of the pipe and using less power consumption than the high-pressure homogenizer. .. The present invention includes, but is not limited to, the following.
(1) Step 1 of preparing anion-modified cellulose, and step 2 of defibrating anion-modified cellulose using a cavitation jet device to produce anion-modified cellulose nanofibers.
A method for producing anion-modified cellulose nanofibers, which comprises.
The cavitation injection device gives an impact force to the anion-modified cellulose when the cavitation bubbles generated by the liquid injection injected through the nozzle or orifice collapse, and the upstream pressure of the liquid injection injected through the nozzle or orifice is 0.01 MPa. It is 30.00 MPa or less, and the ratio of downstream pressure / upstream pressure is 0.001 to 0.500.
The above-mentioned manufacturing method, wherein the maximum width of the cavitation jet generated by the liquid jet injected through the nozzle or orifice of the cavitation jet device is 50% or more and 130% or less of the inner diameter of the pipe immediately after the nozzle or orifice.
(2) The maximum width of the cavitation jet generated by the liquid jet injected through the nozzle or orifice of the cavitation jet device is 70% or more and 130% or less of the inner diameter of the pipe immediately after the nozzle or orifice. The method described.
(3) The method according to (1) or (2), wherein the anion-modified cellulose is a cellulose having a carboxyl group.
(4) The method according to (3), wherein the amount of carboxyl groups in the anion-modified cellulose is 0.4 mmol / g to 3.0 mmol / g with respect to the absolute dry mass of the anion-modified cellulose.
(5) The method according to (1) or (2), wherein the anion-modified cellulose is a cellulose having a carboxymethyl group.
(6) The method according to (5), wherein the degree of carboxymethyl substitution in the anion-modified cellulose is 0.01 or more and less than 0.40.

According to the present invention, anion-modified cellulose nanofibers having a nano-order average fiber diameter can be obtained with less power consumption than when a high-pressure homogenizer is used.

The present invention relates to a method for producing anion-modified cellulose nanofibers.

(1) Step 1
In step 1, an anion-modified cellulose is prepared. Anionic-modified cellulose is one in which an anionic group is introduced into the molecular chain of cellulose. Specifically, an anionic group is introduced into the pyranose ring of cellulose by an oxidation or substitution reaction.

(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., based on the origin, manufacturing 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, purified linters; cellulose produced by microorganisms such as acetic acid bacteria. The raw material of bleached pulp or unbleached pulp is not particularly limited, and examples thereof include wood, cotton, straw, bamboo, hemp, jute, and kenaf. Further, the method for producing bleached pulp or unbleached pulp is not particularly limited, and a mechanical method, a chemical method, or a method in which the two are combined may be used. The bleached pulp or unbleached pulp classified according to the production method includes, for example, mechanical pulp (thermomechanical pulp (TMP), crushed wood pulp), chemical pulp (conifer unbleached sulphite pulp (NUSP), conifer bleached sulphite pulp (NBSP). ) And the like, unbleached coniferous kraft pulp (NUKP), bleached coniferous kraft pulp (NBKP), unbleached broadleaf kraft pulp (LUKP), kraft pulp such as broadleaf bleached kraft pulp (LBKP)) and the like. Further, dissolved pulp may be used in addition to the pulp for papermaking. Dissolving pulp is chemically refined pulp, which is mainly dissolved in chemicals and used as a main raw material for artificial fibers, cellophane, and the like.

Examples of the regenerated cellulose include those obtained by dissolving cellulose in a solvent such as a cuprammonium solution, a cellulose zantate solution, or a morpholine derivative, and spinning it again.

The fine cellulose is obtained by subjecting a cellulosic material such as the above-mentioned natural cellulose or regenerated cellulose to a depolymerization treatment (for example, acid hydrolysis, alkali hydrolysis, enzymatic decomposition, blasting treatment, vibration ball mill treatment, etc.). Examples thereof include those obtained by mechanically processing the cellulosic material.

(1-2) Anion Degeneration Anion denaturation refers to the introduction of an anionic group into cellulose, specifically, the introduction of an anionic group into the pyranose ring of cellulose by an oxidation or substitution reaction. In the present invention, the oxidation reaction refers to a reaction in which the hydroxyl group of the pyranose ring is directly oxidized to a carboxyl group. Further, in the present invention, the substitution reaction means a reaction for 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 a carboxyl group into cellulose, also referred to as "oxidation") can be mentioned. In the present specification, the carboxyl group means -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-mentioned cellulose raw material by a known method. Although not particularly limited, the amount of carboxyl groups is preferably 0.4 mmol / g to 3.0 mmol / g, preferably 0.6 mmol / g to 2.0 mmol / g, based on the absolute dry mass of the anion-modified cellulose or the anion-modified cellulose nanofibers. / G is further preferable, 1.0 mmol / g to 2.0 mmol / g is further preferable, and 1.1 mmol / g to 2.0 mmol / g is further preferable.

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

As an example of the carboxylation (oxidation) method, a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide, and a mixture thereof. There are ways to do this. 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 is 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. For example, 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivative (for example, 4-hydroxy TEMPO) can be mentioned. 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 further preferable with respect to 1 g of cellulose that has been completely dried. Further, it is preferably about 0.1 mmol / L to 4 mmol / L with respect to the reaction system.

The bromide is a compound containing bromine, and examples thereof include alkali metals bromide that can be dissociated and ionized in water. Further, the iodide is a compound containing iodine, and an example thereof includes an alkali metal iodide. The amount of bromide or iodide used can be selected within a range in which the oxidation reaction can be promoted. The total amount of bromide and iodide is, for example, preferably 0.1 mmol to 100 mmol, more preferably 0.1 mmol to 10 mmol, still more preferably 0.5 mmol to 5 mmol with respect to 1 g of dry cellulose. The modification is a modification due to an oxidation reaction.

As the oxidizing agent, known ones can be used, and for example, halogen, hypohalogenic acid, subhalogenic acid, perhalogen acid or salts thereof, halogen oxide, peroxide and the like can be used. Of these, sodium hypochlorite, which is inexpensive and has a low environmental impact, is preferable. The appropriate amount of the oxidizing agent to be used is, for example, 0.5 mmol to 500 mmol, more preferably 0.5 mmol to 50 mmol, still more preferably 1 mmol to 25 mmol, and most preferably 3 mmol to 10 mmol with respect to 1 g of cellulose that has been completely dried. .. 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. As the reaction progresses, carboxyl groups are generated in the cellulose, so that the pH of the reaction solution is lowered. In order to allow the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at 8 to 12, preferably about 10 to 11. Water is preferable as the reaction medium because it is easy to handle and side reactions are unlikely to occur. The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of oxidation, and is usually about 0.5 hour to 6 hours, for example, about 0.5 hour to 4 hours.

Further, the oxidation reaction may be carried out in two steps. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the first-stage reaction again under the same or different reaction conditions, the efficiency is not affected by the reaction inhibition by the salt produced as a by-product in the first-stage reaction. It can be oxidized well.

Another example of the carboxylation (oxidation) method is a method of oxidizing by contacting a gas containing ozone with a cellulose raw material. By this oxidation reaction, the hydroxyl groups at at least the 2nd and 6th positions 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 part 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 ozone treatment conditions are within these ranges, it is possible to prevent the cellulose from being excessively oxidized and decomposed, and the yield of the oxidized cellulose becomes good. After the ozone treatment, the additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the additional oxidation treatment is not particularly limited, and examples thereof include chlorine-based compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfate, and peracetic acid. For example, the additional oxidation treatment can be performed by dissolving these oxidizing agents in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and immersing the cellulose raw material in the solution.

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

(1-2-2) Carboxalkylation As an example of anion modification, introduction of a carboxyalkyl group such as a carboxymethyl group can be mentioned. As used herein, the carboxyalkyl group refers to -RCOH (acid type) and -RCOOM (metal salt type). Here, R is an alkylene group such as a methylene group and an ethylene group, and M is a metal ion.

The carboxyalkylated cellulose may be obtained by a known method, or a commercially available product may be used. The degree of carboxyalkyl substitution of cellulose per anhydrous glucose unit is preferably less than 0.40. Further, when the anionic group is a carboxymethyl group, the degree of carboxymethyl substitution is preferably less than 0.40. When the degree of substitution is 0.40 or more, the crystallinity of cellulose is lowered. The lower limit of the carboxyalkyl substitution degree is preferably 0.01 or more. Considering operability, the degree of substitution is particularly preferably 0.02 or more and 0.35 or less, further preferably 0.10 or more and 0.35 or less, and 0.15 or more and 0.35 or less. Is more preferable, and 0.15 or more and 0.30 or less is further preferable. The anhydrous glucose unit means individual anhydrous glucose (glucose residue) constituting cellulose, and the carboxyalkyl substitution degree is carboxyalkyl among the hydroxyl groups (-OH) in the glucose residue constituting cellulose. The percentage of those substituted with ether groups (-ORCOOH or -ORCOOM) (number of carboxyalkyl ether groups per glucose residue) is shown.

As an example of the method for producing carboxyalkylated cellulose, a method including the following steps can be mentioned. The modification is a modification by a substitution reaction. Carboxymethylated cellulose will be described as an example.
i) The bottoming material, the solvent, and the mercerizing agent are mixed, and the reaction temperature is 0 ° C. to 70 ° C., preferably 10 ° C. to 60 ° C., and the reaction time is 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Process to process,
ii) Next, a carboxymethylating agent was added in an amount of 0.05 to 10.0 times per glucose residue, and the reaction temperature was 30 ° C. to 90 ° C., preferably 40 ° C. to 80 ° C., and the reaction time was 30 minutes to 10 hours. A step of carrying out the etherification reaction, preferably for 1 to 4 hours.

The above-mentioned cellulose raw material can be used as the bottoming raw material. 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 A mixed medium of seeds or more can be used. When the lower alcohol is mixed, the mixing ratio is preferably 60% by mass to 95% by mass. As the mercerizing agent, it is preferable to use 0.5 to 20 times the mole of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, per anhydrous glucose residue of the bottoming 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 a carboxymethyl substituent into the cellulose, the celluloses electrically repel each other. Therefore, the cellulose into which the carboxymethyl substituent has been introduced can be nano-defibrated. If the carboxymethyl substituent per glucose unit is less than 0.01, nanodefibration may not be sufficient. The degree of carboxymethyl substitution is more preferably 0.10 or more and less than 0.40, still more preferably 0.15 or more and less than 0.40, and further preferably 0.20 or more and less than 0.40. The degree of carboxyalkyl substitution in carboxyalkylated cellulose is usually the same as the degree of carboxyalkyl substitution when the same carboxyalkylated cellulose is used as a nanofiber.

The degree of carboxymethyl substitution per glucose unit can be measured by the following method:
Weigh approximately 2.0 g of carboxymethylated cellulose (absolutely dry) and place 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 the mixture is shaken for 3 hours to convert the carboxymethylated cellulose salt (CM-modified cellulose) into hydrogen-type CM-modified cellulose. Weigh 1.5 g to 2.0 g of hydrogen-type CM-formed cellulose (absolutely dry) and place it in an Erlenmeyer flask with a 300 mL stopper. Wet hydrogen-type CM-formed cellulose with 15 mL of 80 mass% methanol, add 100 mL of 0.1 N NaOH, and shake at room temperature for 3 hours. Excess NaOH was back titrated with 0.1 N H ₂ SO ₄ using phenolphthalein as an indicator. The carboxymethyl substitution degree (DS) is calculated by the following formula:
A = [(100 x F'-(0.1 N H ₂ SO ₄ ) (mL) x F) x 0.1] / (absolute dry mass (g) of hydrogen-type CM-formed cellulose)
DS = 0.162 × A / (1-0.058 × A)
A: 1N NaOH amount (mL) required to neutralize 1 g of hydrogen-type CM-formed cellulose
F: 0.1N H ₂ SO ₄ factor F': 0.1N NaOH factor.

The degree of substitution of the carboxyalkyl group other than the carboxymethyl group can also 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 a powder or an aqueous solution of a phosphoric acid compound with a cellulose raw material, a method of adding an aqueous solution of a phosphoric acid compound to a slurry of a cellulose raw material, and the like. Examples of the phosphoric acid-based compound include phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. Among the above, a compound having a phosphoric acid group is preferable because it is low in cost, easy to handle, and a phosphoric acid group can be introduced into the cellulose of pulp fibers to improve the defibration efficiency. Compounds 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 phosphoric acid group can be introduced into cellulose by using one or more of these. Of these, phosphoric acid, sodium phosphate of phosphoric acid, potassium salt of phosphoric acid, and phosphoric acid from the viewpoints of high efficiency of introducing phosphoric acid groups, easy defibration in the following defibration steps, and easy industrial application. Ammonium salt is preferred. In particular, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferable. In addition, it is desirable to use the phosphoric acid-based compound as an aqueous solution because the reaction can proceed uniformly and the efficiency of introducing a phosphoric acid group is high. The pH of the aqueous solution of the phosphoric acid-based compound is preferably 7 or less because the efficiency of introducing the phosphoric acid group is high, but is preferably 3 to 7 from the viewpoint of suppressing the hydrolysis of pulp fibers.

The following methods can be mentioned as examples of the method for producing phosphoric acid esterified cellulose. A phosphoric acid-based compound is added to a suspension of a cellulosic raw material having a solid content concentration of 0.1% by mass to 10% by mass with stirring to introduce a phosphoric acid group into the cellulose. When the cellulose raw material is 100 parts by mass, the amount of the phosphoric acid compound added is preferably 0.2 parts by mass to 500 parts by mass and preferably 1 part by mass to 400 parts by mass as the amount of phosphorus element. More preferred. When the ratio of the phosphoric acid-based compound is at least the above 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 a plateau, 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 nitrogen-containing compound exhibiting basicity is preferable. "Basic" here is defined as the aqueous solution turning pink to red in the presence of a phenolphthalein indicator, or the pH of the aqueous solution being 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. For example, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like can be mentioned. Of these, urea, which is low in cost and easy to handle, is preferable. The amount of the other compound added is preferably 2 parts by mass to 1000 parts by mass, more preferably 100 parts by mass to 700 parts by mass, based on 100 parts by mass of the solid content of the cellulose raw material. The reaction temperature is preferably 0 ° C. to 95 ° C., more preferably 30 ° C. to 90 ° C. The reaction time is not particularly limited, but is about 1 minute to 600 minutes, more preferably 30 minutes to 480 minutes. When the conditions of the esterification reaction are within these ranges, it is possible to prevent the cellulose from being excessively esterified and easily dissolved, and the yield of the phosphate esterified cellulose becomes good. After dehydrating the obtained phosphoric acid esterified cellulose suspension, it is preferable to heat-treat it at 100 ° C. 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 contained in the heat treatment, remove the water, and then heat-treat at 100 ° C. to 170 ° C.

The degree of phosphoric acid group substitution per glucose unit of the phosphoric acid esterified cellulose is preferably 0.001 or more and less than 0.40. By introducing a phosphate group substituent into the cellulose, the celluloses electrically repel each other. Therefore, the cellulose into which a phosphate group has been introduced can be easily nano-defibrated. If the degree of phosphate substitution per glucose unit is less than 0.001, nano-defibration cannot be sufficiently performed. On the other hand, if the degree of phosphate substitution per glucose unit is greater than 0.40, it swells or dissolves and may not be obtained as nanofibers. In order to efficiently perform defibration, it is preferable that the phosphoric acid esterified cellulose raw material obtained above is boiled and then washed with cold water. These esterification modifications are substitution reaction modifications. The degree of substitution in esterified cellulose and the degree of substitution when the esterified cellulose is used as nanofibers are usually the same.

The degree of phosphate substitution per glucose unit can be measured by the following method:
A slurry of phosphoric acid esterified cellulose having a solid content of 0.2% by mass is prepared. A strong acid ion exchange resin (Amberjet 1024; manufactured by Organo, conditioned) with a volume of 1/10 is added to the slurry, shaken for 1 hour, and then poured onto a mesh with an opening of 90 μm. And the slurry are separated to convert the phosphate esterified cellulose into hydrogen-type phosphate esterified cellulose. Next, 50 μL of a 0.1 N sodium hydroxide aqueous solution is added to the slurry treated with the ion exchange resin once every 30 seconds, and the change in the value of electrical conductivity indicated by the slurry is measured. Of the measurement results, the amount of alkali (mmol) required in the region where the electrical conductivity drops sharply is divided by the solid content (g) in the slurry to be titrated, so that 1 g of hydrogen-type phosphate esterified cellulose is used. The amount of phosphate groups (mmol / g) is calculated. In addition, the degree of phosphate substitution (DS) per glucose unit of phosphate esterified cellulose is calculated by the following equation:
DS = 0.162 × A / (1-0.079 × A)
A: Amount of phosphate groups per gram of hydrogen-type phosphoric acid esterified cellulose (mmol / g)

(1-3) Anion-modified cellulose An anion-modified cellulose can be obtained by performing anion modification as illustrated above on cellulose as a raw material. Moreover, you may use the commercially available one. As the type of anion-modified cellulose, cellulose having a carboxyl group or cellulose having a carboxylalkyl group is preferable. In particular, the carboxylated cellulose obtained by oxidizing cellulose with an N-oxyl compound and an oxidizing agent has a uniformly introduced carboxyl group, is easily defibrated uniformly, and has high transparency. Is preferable in that

As the anion-modified cellulose, those in which at least a part of the fibrous shape is maintained even when dispersed in water or a water-soluble organic solvent are used. Nanofibers cannot be obtained if fibrous shapes are not maintained (ie, those that dissolve). The fact 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 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 for crystal 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 have been refined by defibration. The crystallinity of cellulose can be controlled by the degree of 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 diffraction measuring device (LabX XRD-6000, manufactured by Shimadzu Corporation). The crystallinity is calculated by using a method such as Segal, and the diffraction intensity of the 002 surface of 2θ = 22.6 ° and 2θ = are based on the diffraction intensity of 2θ = 10 ° to 30 ° in the X-ray diffraction diagram. It is calculated by the following formula from the diffraction intensity of the amorphous portion of 18.5 °.
Xc = (I002c-Ia) / I002c × 100
Xc: Type I crystallinity (%) of cellulose
I002c: 2θ = 22.6 °, diffraction intensity of 002 surface Ia: 2θ = 18.5 °, diffraction intensity of amorphous part.

The ratio of cellulose type I crystals of anion-modified cellulose and the ratio of cellulose type I crystals when the same anion-modified cellulose is used as nanofibers are usually the same.

(2) Step 2
In step 2, anion-modified cellulose nanofibers are produced by treating (defibrating) anionic-modified cellulose using a cavitation jet device.

(2-1) Anion-modified cellulose dispersion A dispersion of anion-modified cellulose is prepared for defibration. As the dispersion medium, water, an organic solvent, or a mixture thereof can be appropriately selected. The type of organic solvent is not limited, but for example, a polar solvent having a high affinity for a hydroxyl group in cellulose is preferable, and methanol, ethanol, isopropanol, isobutanol, sec-butanol, tert-butanol, methyl cellosolve, ethyl cellosolve, and ethylene glycol are preferable. , Glycerin, ethylene glycol dimethyl ether, 1,4-dioxane, tetrahydrofuran, acetone, methyl ethyl ketone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide and the like. The dispersion medium 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 a dispersion medium (that is, 100% water) from the viewpoint of ease of 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.

The solid content concentration of the anion-modified cellulose dispersion to be used in the cavitation jet device is preferably 10.0% by mass or less, more preferably 7.0% by mass or less, still more preferably 0.1 to 5.0% by mass. Treatment within the range is preferable from the viewpoint of bubble generation efficiency.

The pH of the anion-modified cellulose dispersion is preferably pH 6 to 13, more preferably pH 6 to 12, and even more preferably pH 6 to 10. When the pH is 6 or more, the defibration of the anion-modified cellulose is likely to proceed. On the other hand, if the pH exceeds 13, alkaline burning of the pulp fibers occurs and the whiteness decreases, which is not preferable.

(2-2) Cavitation jet device The cavitation jet device compresses the jet liquid and injects it from the tip of the nozzle or the orifice toward the liquid to be jetted at high speed, resulting in extremely high shearing force near the nozzle or orifice and rapid operation. It is a device that shreds solid lumps in the jet liquid and the liquid to be jetted by the decay energy of cavitation bubbles generated by the expansion of the liquid due to the depressurization. Since there is no physical contact with the fiber such as a blade, it is unlikely to cause the fiber to be shortened.

As the jet liquid, the dispersion medium used for the above-mentioned anion-modified cellulose dispersion or the anion-modified cellulose dispersion itself can be used. The above-mentioned anion-modified cellulose dispersion is used as the liquid to be injected. The jet liquid is jetted toward the anion-modified cellulose dispersion which is the liquid to be jetted to generate a jet, so that cavitation is generated in the liquid to be jetted, and the decay energy of the cavitation bubbles causes the anion-modified cellulose in the liquid to be jetted. Can be defibrated. It is preferable to use an anion-modified cellulose dispersion as the jet liquid from the viewpoint of efficient defibration. When an anion-modified cellulose dispersion is used as the jet liquid, in addition to the action and effect of cavitation generated around the jet, the hydrodynamic shear force when jetting from the nozzle or orifice at high pressure can be obtained, so defibration can be performed efficiently. be able to.

Since cavitation occurs when the liquid is accelerated and the local pressure becomes lower than the vapor pressure of the liquid, the flow velocity and pressure are important to control the occurrence of cavitation. The basic dimensionless number representing the cavitation state, the cavitation number σ, is defined as the following mathematical formula 1 (edited by Yoji Kato, new edition of cavitation basics and recent progress, Maki Shoten, 1999).

A large number of cavitations indicates that the flow field is in a state where cavitation is unlikely to occur. When cavitation is generated through a nozzle or orifice such as a cavitation jet, the cavitation number σ is derived from the upstream pressure p _{1 of} the nozzle or orifice, the downstream pressure p ₂ of the nozzle or orifice, and the saturated vapor pressure p _v of the sample water. It can be rewritten as the following formula 2, and in the cavitation jet, the pressure difference between p ₁ , p ₂ , and p _v is large, and p ₁ >> p ₂ >> p _v , so the cavitation number σ Can be further approximated to p ₂ / p ₁ (H. Soyama, J. Soc. Mat. Sci. Japan, 47 (4), 381 1998).

In the present invention, the cavitation condition is that the cavitation number σ (that is, downstream pressure / upstream pressure) that can be approximated to p ₂ / p ₁ described above is 0.001 or more and 0.500 or less, and 0.003. It is preferably 0.200 or more, and particularly preferably 0.010 or more and 0.100 or less. When the cavitation number σ is less than 0.001, the defibration effect is small because the pressure difference from the surroundings when the cavitation bubbles collapse is small, and when it is larger than 0.500, the flow pressure difference is low. Cavitation is less likely to occur.

When injecting the jet liquid through a nozzle or orifice to generate cavitation, the pressure of the jet liquid (upstream pressure) is preferably 0.01 MPa or more and 30.00 MPa or less, and 0.70 MPa or more and 20.00 MPa or less. It is preferably 2.00 MPa or more and 10.00 MPa or less. If the upstream pressure is less than 0.01 MPa, it is difficult to generate a pressure difference with the downstream pressure, and the effect is small. Further, if it is higher than 30.00 MPa, the energy consumption becomes large, which is disadvantageous in terms of cost. On the other hand, the pressure inside the container (downstream pressure) is preferably 0.05 MPa or more and 0.50 MPa or less in static pressure.

The injection speed of the injection liquid is preferably in the range of 1 m / sec or more and 200 m / sec or less, and preferably in the range of 20 m / sec or more and 100 m / sec or less. When the injection speed is less than 1 m / sec, the pressure drop is low and cavitation is unlikely to occur, so that the effect is weak. On the other hand, if it is larger than 200 m / sec, high pressure is required and a special device is required, which is disadvantageous in terms of cost.

The cavitation jet device has a pipe or container of a certain size immediately after the nozzle or orifice for injecting the liquid, which is the place where cavitation occurs. Anion-modified cellulose if the inner diameter of the pipe immediately after this nozzle or orifice (inner diameter not including the wall thickness of the pipe or vessel) is comparable to the maximum width of the cavitation jet produced by the liquid jet jetted through the nozzle or orifice. The defibration will proceed efficiently. Therefore, in the present invention, the maximum width of the cavitation jet generated by the liquid jet injected through the nozzle or the orifice is adjusted to be 50% or more of the inner diameter of the pipe immediately after the nozzle or the orifice. In the above range, 55% or more is more preferable, 60% or more is more preferable, 65% or more is more preferable, 70% or more is further preferable, 80% or more is further preferable, and 85% or more is further preferable. Also, adjust the length so that it is 130% or less. The above range is more preferably 110% or less, and more preferably less than 100%. Here, the nozzle refers to a pipe-shaped part for injecting a liquid in a certain direction, and generally, the liquid is speeded up by reducing the area of the circular cross section of the pipe (or reducing the inner diameter of the pipe). Refers to the parts that are ejected with. An orifice is a hole made in the wall to inject a liquid. When a liquid is injected from a nozzle or orifice, a group of cavitation bubbles generated by the liquid jet is seen in a conical shape with the outlet of the nozzle or orifice as the apex. This group of cavitation bubbles is called a cavitation jet. The maximum width of the cavitation jet means the maximum width (diameter) perpendicular to the injection direction of the cavitation jet. The maximum width of the cavitation jet varies depending on conditions such as the nozzle or orifice used, the jet liquid, the liquid to be jetted, the jet velocity, the downstream pressure / upstream pressure ratio, and the temperature. When measuring the maximum width of the cavitation jet, if the width of the cavitation jet is large and it touches the inner wall of the pipe immediately after the nozzle or orifice, use a larger pipe so that the cavitation jet does not touch the inner wall under the same conditions. The injection is performed and the maximum width of the cavitation jet is obtained. Further, a plurality of nozzles or orifices may be connected to the pipe immediately after the nozzle or orifice, and a liquid may be injected into the pipe from each nozzle or orifice to generate a plurality of cavitation jets. The maximum width of the cavitation jet is the maximum width when the cavitation jet generated from each nozzle or orifice is regarded as one cavitation jet. That is, when a plurality of cavitation jets merge at the end, it is the maximum width of the merged cavitation jets, while at least a part of the plurality of cavitation jets do not merge and are independent of each other. Is the maximum width obtained by connecting the outermost positions of a plurality of observed cavitation jets (the side away from the center of the plane perpendicular to the jet direction of each jet to the inner wall side of the pipe). ..

Further, the pipe immediately after the nozzle or orifice means an arbitrary container or pipe to which the nozzle or orifice is connected and where a cavitation jet is formed. The shape of the pipe may be any of a cylindrical shape, a square tubular shape, a conical shape, a pyramidal shape, and the like, but in order to prevent the retention of fibers after defibration, the pipe shape is preferably cylindrical. The pipe diameter immediately after the nozzle or orifice means the width (inner diameter of the pipe) perpendicular to the injection direction of the cavitation jet of the pipe. When the pipe has a tubular shape other than a cylindrical shape, such as a square cylinder, it means the smallest width among the widths perpendicular to the injection direction of the cavitation jet. Further, when the pipe is conical or pyramidal, it means the inner diameter of the pipe having the maximum width of the cavitation jet (in the case of pyramid, the minimum width of the same cross section).

If the maximum width of the cavitation jet caused by the liquid jet jetted through the nozzle or orifice is less than 50% of the inner diameter of the pipe immediately after the nozzle or orifice, the pipe (or vessel) immediately after the nozzle or orifice becomes the cavitation jet. On the other hand, since it is too large, the anion-modified cellulose and the anion-modified cellulose nanofibers stay in the pipe (or container), and the defibration does not proceed easily. On the other hand, if the length exceeds 130%, many parts of the cavitation jet may come into direct contact with the pipe immediately after the nozzle or orifice, causing erosion of the pipe. If the maximum width of the cavitation jet is 100% or more and 130% or less of the inner diameter of the pipe immediately after the nozzle or orifice, a part (end) of the cavitation jet will come into contact with the nozzle or the pipe immediately after the orifice. , The contact is partial, and the impact at the end of the cavitation jet (the part far from the nozzle or orifice) is rather weak and can be used because it has little effect on the piping. When the maximum width of the cavitation jet is less than 100% of the inner diameter of the pipe immediately after the nozzle or orifice, corrosion of the pipe immediately after the nozzle or orifice does not occur, which is preferable.

The ratio of the maximum width of the cavitation jet to the diameter of the pipe immediately after the nozzle or orifice adjusts the inner diameter of the pipe immediately after the nozzle or orifice, adjusts the above-mentioned downstream pressure / upstream pressure ratio, or injects. It can be adjusted by changing the maximum width of the cavitation jet, such as by adjusting the injection speed of the liquid.

The injection of the liquid to generate cavitation may be carried out in an open container such as a pulper, but is preferably carried out in a pressure vessel to control cavitation.

Cavitation is affected by the amount of gas in the liquid, and if there is too much gas, the impact force is weakened because collision and coalescence of bubbles occur and a cushioning effect is generated in which the decay impact force is absorbed by other bubbles. Since the amount of gas in the liquid is affected by the dissolved gas and vapor pressure, it is preferable to adjust the impact force of cavitation by controlling the processing temperature within a certain range. The treatment temperature is preferably 0 ° C. or higher and 70 ° C. or lower, and more preferably 10 ° C. or higher and 60 ° C. or lower, although it depends on the type of the dispersion medium. Generally, it is considered that the impact force is maximized at the midpoint between the melting point and the boiling point. Therefore, when water is used as the dispersion medium, about 50 ° C. is preferable, but other temperatures are within the above range. If there is, a sufficient defibration effect can be obtained.

Surfactants may be added to the jet liquid and / or the liquid to be jetted to reduce the energy required to generate cavitation. The surfactant to be used is not particularly limited, and for example, a nonionic surfactant such as a fatty acid salt, a higher alkyl sulfate, an alkylbenzene sulfonate, a higher alcohol, an alkylphenol, an alkylene oxide adduct such as a fatty acid, and anionic surfactant. Agents, cationic surfactants, amphoteric surfactants and the like can be mentioned. These may be used alone or in combination of two or more. When a surfactant is added, the amount added may be any amount necessary to reduce the surface tension of the jet liquid and / or the liquid to be jetted.

The treatment by the cavitation jet device may be repeated a plurality of times until the desired degree of defibration is obtained. When processing a plurality of times, it may be circulated in one device as many times as necessary, or may be processed by using a plurality of devices in parallel or by sequentially flowing them to a plurality of devices.

(2-3) Anion-modified cellulose nanofibers By defibrating with the above-mentioned cavitation jet device, anion-modified cellulose can be defibrated to an average fiber diameter of nano-order to obtain nanofibers. The nano-order average fiber diameter means an average fiber diameter of less than 1 μm. In the present invention, the anion-modified cellulose nanofibers preferably have an average fiber diameter of about 3 nm to 500 nm, more preferably about 3 nm to 150 nm, and even more preferably about 3 nm to 20 nm. The aspect ratio is 30 or more, preferably 50 or more, and more preferably 100 or more. The upper limit of the aspect ratio is not limited, but is about 500 or less.

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

The anion-modified cellulose nanofibers preferably have high transparency when made into a dispersion. According to the method of the present invention, anion-modified cellulose nanofibers showing high transparency when made into a dispersion can be obtained. Transparency is measured, for example, by the following methods:
A cellulose nanofiber dispersion having a predetermined concentration was prepared, and a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation) was used, and a square cell having an optical path length of 10 mm was used to transmit 660 nm light (%). ) Is measured and used as transparency.

In the present invention, for example, the transparency of an anion-modified cellulose nanofiber dispersion having a solid content of 1.0% by mass using water as a dispersion medium is preferably 70% or more, more preferably 80% or more. It is more preferably 90% or more. High transparency means that there are few undefibrated fibers and the defibration has proceeded uniformly. The upper limit of transparency is not particularly limited, but is, for example, 99%.

The viscosity of the anion-modified cellulose nanofibers is not particularly limited, but in the present invention, it is possible to produce a dispersion having a relatively high viscosity. Viscosity is measured, for example, by the following methods:
A cellulose nanofiber dispersion having a predetermined concentration was prepared, and according to the method of JIS-Z-8803, using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.), the rotation speed was 60 rpm or 6 rpm at 25 ° C. 3 Measure the value after minutes.

For example, for an anion-modified cellulose nanofiber dispersion having a solid content of 1.0% by mass using water as a dispersion medium, the B-type viscosity at 6 rpm measured by the above method is 5000 mPa · s or more, or 7000 mPa · s or more, or A dispersion having a value of 10000 mPa · s or more, 15000 mPa · s or more, or 17000 mPa · s or more can be formed, and the B-type viscosity at 60 rpm is 1000 mPa · s or more, 2000 mPa · s or more, or 3000 mPa · s. It is possible to form a dispersion having s or more, or 4000 mPa · s or more. High viscosity means less damage to the fibers during defibration. Since the cavitation jet device has a lower processing pressure than the ultra-high pressure homogenizer, it is considered that the fiber damage during defibration is reduced. The upper limit of the viscosity is not particularly limited. On the other hand, depending on the application, a low-viscosity dispersion may be desired. In that case, a lower-viscosity anion may be obtained by changing the type of cellulose raw material used or increasing the number of treatments by a cavitation jet. A modified cellulose nanofiber dispersion may be produced.

The obtained dispersion of anion-modified cellulose nanofibers may be dried or mixed with other compounds, depending on the intended use. The drying method is not particularly limited, and examples thereof include spray drying, pressing, air drying, hot air drying, and vacuum drying. Examples of the drying device include a continuous tunnel drying device, a band drying device, a vertical drying device, a vertical turbo drying device, a multi-stage disk drying device, an aeration drying device, a rotary drying device, an air flow drying device, and a spray dryer drying device. , Spray drying device, Cylindrical drying device, Drum drying device, Screw conveyor drying device, Rotating drying device with heating tube, Vibration transport drying device, etc., batch type box drying device, aeration drying device, vacuum box drying device, or Examples include a stirring and drying device. These drying devices may be used alone or in combination of two or more. The drum drying device is preferable because it can uniformly supply heat energy directly to the object to be dried, so that it has high energy efficiency and can immediately recover the dried object without applying heat more than necessary.

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>
5.00 g (absolutely dry) of bleached unbeaten kraft pulp (whiteness 85%) derived from softwood, 39 mg (0.05 mmol per 1 g of absolute dry cellulose) of TEMPO (manufactured by Sigma Aldrich) and 514 mg of sodium bromide (absolutely dry). It was added to 500 mL of an aqueous solution prepared by dissolving 1.0 mmol) in 1 g of absolute dry cellulose, and stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that the sodium hypochlorite content was 5.5 mmol / g, and the oxidation reaction was started at room temperature. Although the pH in the system decreased during the reaction, a 3M aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system did not change. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield at this time was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.4 mmol / g. Water is added to the reaction mixture to adjust the concentration to 1.0% by mass, and cavitation treatment is performed at an upstream pressure of 9 MPa and a downstream pressure of 0.40 MPa using a cavitation jet device (the diameter inside the pipe immediately after the nozzle is 5.0 cm). Was repeated for 1 to 24 passes to obtain a carboxylated cellulose nanofiber dispersion. The number of passes in the cavitation process was calculated using the following formula:
Number of passes = Nozzle flow rate x Processing time / Sample amount The cavitation jet generated during this processing had a shape close to a cone with the nozzle outlet at the apex, and the maximum width of the jet was about 4.5 cm.

The amount of power consumed by the cavitation jet device when defibrating from carboxylated cellulose to carboxylated cellulose nanofibers, and a dispersion using the obtained carboxylated cellulose nanofibers as a dispersion medium (solid content concentration 1. Table 1 shows the viscosity when 0% by mass) and the transparency of the dispersion. The method for measuring viscosity and transparency is as follows.

<Measurement of viscosity>
In a glass beaker, 300 g of an aqueous dispersion is prepared so that the solid content concentration of the carboxylated cellulose nanofibers is 1.0% by mass. The aqueous dispersion was set to 25 ° C., and the viscosity after 3 minutes was measured at a rotation speed of 60 rpm or 6 rpm using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) according to the method of JIS-Z-8803.

<Measurement of transparency>
After preparing a carboxylated cellulose nanofiber aqueous dispersion so that the solid content concentration is 1.0% by mass, a square type with an optical path length of 10 mm is used using a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation). Using a cell, the transmittance (%) of 660 nm light was measured and used as the transparency.

<Example 2>
Oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Example 1 except that sodium hypochlorite was added so as to be 6.0 mmol / g and the oxidation reaction was started. The pulp yield at this time was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol / g. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and the upstream pressure was 9 MPa and the downstream pressure was 0 using a cavitation jet device (the diameter inside the pipe immediately after the nozzle was 2.3 cm) in which the hole shape of the nozzle was adjusted. A cavitation treatment was carried out at .45 MPa for 24 passes to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the diameter inside the pipe immediately after the nozzle was 70%. Table 1 shows the power consumption, the viscosity of the dispersion (solid content concentration 1.0% by mass), and the transparency of the dispersion measured in the same manner as in Example 1.

<Example 3>
Sodium hypochlorite using 500 mL of an aqueous solution of 80 mg of TEMPO (manufactured by Sigma Aldrich) (0.1 mmol per 1 g of absolute dry cellulose) and 800 mg of sodium bromide (1.47 mmol per 1 g of absolute dry cellulose). Oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Example 1 except that the oxidation reaction was started by adding the amount to 8.6 mmol / g. The pulp yield at this time was 86%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.9 mmol / g. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and using a cavitation jet device (the diameter inside the pipe immediately after the nozzle was 2.3 cm) equipped with the same nozzle as in Example 2, the upstream pressure was 9 MPa and the downstream A cavitation treatment was carried out for 16 passes at a pressure of 0.45 MPa to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the diameter inside the pipe immediately after the nozzle was 59%. Table 1 shows the power consumption, the viscosity of the dispersion (solid content concentration 1.0% by mass), and the transparency of the dispersion measured in the same manner as in Example 1.

<Example 4>
Examples except that 20 mg of TEMPO (manufactured by Sigma-Aldrich) (0.025 mmol with respect to 1 g of absolute dry cellulose) was added so that sodium hypochlorite was added at 2.2 mmol / g to start the oxidation reaction. Oxidized pulp (carboxylated cellulose) was obtained in the same manner as in 1. The pulp yield at this time was 93%, the time required for the oxidation reaction was 60 minutes, and the amount of carboxyl groups was 0.7 mmol / g. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and using a cavitation jet device (the diameter inside the pipe immediately after the nozzle was 2.3 cm) equipped with the same nozzle as in Example 2, the upstream pressure was 9 MPa and the downstream A cavitation treatment was carried out for 70 passes at a pressure of 0.40 MPa to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the diameter inside the pipe immediately after the nozzle was 61%. Table 1 shows the power consumption, the viscosity of the dispersion (solid content concentration 1.0% by mass), and the transparency of the dispersion measured in the same manner as in Example 1.

<Example 5>
Oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Example 2. Water was added to the reaction mixture to adjust the concentration to 2.5% by mass, and using a cavitation jet device (the diameter inside the pipe immediately after the nozzle was 2.3 cm) equipped with the same nozzle as in Example 2, the upstream pressure was 9 MPa and the downstream A cavitation treatment was carried out for 63 passes at a pressure of 0.40 MPa to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the diameter inside the pipe immediately after the nozzle was 62%. Table 1 shows the power consumption, the viscosity of the dispersion (solid content concentration 1.0% by mass), and the transparency of the dispersion measured in the same manner as in Example 1.

<Example 6>
Oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Example 2. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and using a cavitation jet device (the diameter inside the pipe immediately after the nozzle was 2.9 cm) equipped with the same nozzle as in Example 2, the upstream pressure was 9 MPa and the downstream A cavitation treatment was carried out at a pressure of 0.04 MPa for 30 passes to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the diameter inside the pipe immediately after the nozzle was 51%. Table 1 shows the power consumption, the viscosity of the dispersion (solid content concentration 1.0% by mass), and the transparency of the dispersion measured in the same manner as in Example 1.

<Example 7>
Oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Example 2. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and using a cavitation jet device (the diameter inside the pipe immediately after the nozzle was 2.9 cm) equipped with the same nozzle as in Example 2, the upstream pressure was 9 MPa and the downstream A cavitation treatment was carried out at a pressure of 0.27 MPa for 30 passes to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the diameter inside the pipe immediately after the nozzle was 50%. Table 1 shows the power consumption, the viscosity of the dispersion (solid content concentration 1.0% by mass), and the transparency of the dispersion measured in the same manner as in Example 1.

<Example 8>
A carboxylated cellulose nanofiber dispersion was obtained in the same manner as in Example 6 except that the upstream pressure was 9 MPa, the downstream pressure was 0.45 MPa, and the diameter inside the pipe immediately after the nozzle was 2.3 cm. The ratio of the maximum width of the jet to the diameter inside the pipe immediately after the nozzle was 65%. Table 1 shows the power consumption, the viscosity of the dispersion (solid content concentration 1.0% by mass), and the transparency of the dispersion measured in the same manner as in Example 1.

<Example 9>
A carboxylated cellulose nanofiber dispersion was obtained in the same manner as in Example 8 except that the upstream pressure was 9 MPa and the downstream pressure was 0.63 MPa. The ratio of the maximum width of the jet to the diameter inside the pipe immediately after the nozzle was 66%. Table 1 shows the power consumption, the viscosity of the dispersion (solid content concentration 1.0% by mass), and the transparency of the dispersion measured in the same manner as in Example 1.

<Example 10>
Oxidized pulp (carboxylated cellulose) was obtained in the same manner as in Example 1. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and using a cavitation jet device (the diameter inside the pipe immediately after the nozzle was 2.3 cm) equipped with the same nozzle as in Example 2, the upstream pressure was 9 MPa and the downstream A cavitation treatment was carried out at a pressure of 0.54 MPa for 30 passes to obtain a carboxylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the diameter inside the pipe immediately after the nozzle was 60%. Table 1 shows the power consumption, the viscosity of the dispersion (solid content concentration 1.0% by mass), and the transparency of the dispersion measured in the same manner as in Example 1.

<Example 11>
To a biaxial kneader whose rotation speed was adjusted to 100 rpm, 130 parts by mass of water and 20 parts by mass of sodium hydroxide dissolved in 100 parts by mass of water were added to add broadleaf pulp (LBKP manufactured by Nippon Paper Industries, Ltd.). 100 parts by mass was charged by the dry mass when dried at 100 ° C. for 60 minutes. Mercerized cellulose was prepared by stirring and mixing at 30 ° C. for 90 minutes. Further, 230 parts by mass of isopropanol (IPA) and 60 parts by mass of sodium monochloroacetate were added with stirring, and after stirring for 30 minutes, the temperature was raised to 70 ° C. and a carboxymethylation reaction was carried out for 90 minutes. After completion of the reaction, the reaction was neutralized, deliquesed, dried and pulverized to obtain a sodium salt of carboxymethylated cellulose having a degree of carboxymethyl substitution of 0.31 and a degree of crystallinity of cellulose type I of 67%. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and a cavitation jet device (the diameter inside the pipe immediately after the nozzle was 2.3 cm) equipped with the same nozzle as in Example 2 was used to increase the upstream pressure to 9 MPa and downstream. Cavitation treatment was carried out for 40 passes at a pressure of 0.40 MPa to obtain a carboxymethylated cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the diameter inside the pipe immediately after the nozzle was 63%. Table 1 shows the power consumption, the viscosity of the dispersion (solid content concentration 1.0% by mass), and the transparency of the dispersion measured in the same manner as in Example 1.

<Example 12>
6.75 g of sodium dihydrogen phosphate dihydrate and 4.83 g of disodium hydrogen phosphate are dissolved in 19.62 g of water to obtain an aqueous solution of a phosphoric acid compound (hereinafter referred to as "phosphorylation reagent"). It was. Water was added to unbleached softwood kraft pulp (NUKP, water content 80%, Canadian standard drainage (CSF) 580 ml as measured according to JIS P8121) to a concentration of 4% by mass. Then, using a double disc refiner, the mixture was beaten until the irregular CSF (plain weave 80 mesh, conforming to JIS P8121 except that the pulp sampling amount was 0.3 g) was 200 ml and the average length fiber length was 0.66 mm. The cellulose suspension thus obtained was diluted to 0.3%, and a pulp sheet (thickness 200 μm) having a water content of 90% and a solid content (absolute dry mass) of 3 g was obtained by a papermaking method. This pulp sheet is immersed in 31.2 g of the phosphorylation reagent (80 parts by mass as the amount of phosphorus element with respect to 100 parts by mass of dried pulp) and heated in a blower dryer (Yamato Scientific Co., Ltd. DKM400) at 105 ° C. for 1 hour. Further, heat treatment was performed at 150 ° C. for 1 hour to introduce a phosphoric acid group into the cellulose fibers. Next, 500 ml of ion-exchanged water was added to a pulp sheet in which a phosphoric acid group was introduced into cellulose fibers, and the pulp sheet was stirred and washed, and then dehydrated. The dehydrated sheet was diluted with 300 ml of ion-exchanged water, and 5 ml of a 1N aqueous sodium hydroxide solution was added little by little with stirring to obtain a cellulose suspension having a pH of 12 to 13. Then, this cellulose suspension was dehydrated, and 500 ml of ion-exchanged water was added for washing. This dehydration washing was repeated twice more. The degree of phosphoric acid group substitution at this time was 0.34. Water was added to the reaction mixture to adjust the concentration to 1.0% by mass, and using a cavitation jet device (the diameter inside the pipe immediately after the nozzle was 2.3 cm) equipped with the same nozzle as in Example 2, the upstream pressure was 9 MPa and the downstream A cavitation treatment was carried out at a pressure of 0.40 MPa for 30 passes to obtain a phosphate esterified cellulose nanofiber dispersion. The ratio of the maximum width of the jet to the diameter inside the pipe immediately after the nozzle was 61%. Table 1 shows the power consumption, the viscosity of the dispersion (solid content concentration 1.0% by mass), and the transparency of the dispersion measured in the same manner as in Example 1.

<Comparative example 1>
Water was added to the reaction mixture (carboxylated cellulose) obtained in the same manner as in Example 1 to adjust the concentration to 1.0% by mass, and treated with an ultra-high pressure homogenizer (20 ° C., 150 MPa) for 1 to 3 passes. , Carboxylated cellulose nanofiber dispersion was obtained.

Table 1 shows the amount of electric energy consumed by the ultra-high pressure homogenizer when defibrating from carboxylated cellulose to carboxylated cellulose nanofibers. Table 1 shows the viscosities and transparency of the carboxylated cellulose nanofiber aqueous dispersion (solid content concentration 1.0% by mass) measured in the same manner as in Example 1.

<Comparative example 2>
The treatment was carried out in the same manner as in Example 1 except that a cavitation jet device having a diameter of 3.0 cm in the pipe immediately after the nozzle was used. The cavitation jet has a shape close to a cone with the nozzle outlet at the apex, but the end (the part far from the nozzle) contacts the pipe. The maximum width of the jet in Comparative Example 2 is understood to be 4.5 cm as in Example 1 because the jet was injected under the same conditions as in Example 1. In Comparative Example 2, the pipe was eroded due to the influence of the cavitation jet, and could not be treated.

<Comparative example 3>
The treatment was carried out in the same manner as in Example 1 except that a cavitation jet device having a diameter of 30 cm in the pipe immediately after the nozzle was used. The cavitation jet generated during this process had a shape close to a cone with the nozzle outlet as the apex, and the maximum width of the jet was about 4.5 cm, as in Example 1.
Similar to Example 1, the amount of power consumed by the cavitation jet device when defibrating from carboxylated cellulose to carboxylated cellulose nanofibers, carboxylated cellulose nanofiber aqueous dispersion (solid content concentration 1.0 mass) %) Viscosity and transparency of the dispersion are shown in Table 1.

<Comparative example 4>
Water was added to the reaction mixture (carboxylated cellulose) obtained in the same manner as in Example 4 to adjust the concentration to 1.0% by mass, and the reaction mixture was treated with an ultra-high pressure homogenizer (20 ° C., 150 Mpa) for 5 passes to obtain carboxyl. A cellulose nanofiber dispersion was obtained. Table 1 shows the amount of electric energy consumed by the ultra-high pressure homogenizer when defibrating from carboxylated cellulose to carboxylated cellulose nanofibers. Table 1 shows the viscosities and transparency of the carboxylated cellulose nanofiber aqueous dispersion (solid content concentration 1.0% by mass) measured in the same manner as in Example 1.

From the results in Table 1, the method using the cavitation jet device during the production of the carboxylated cellulose nanofibers of Examples 1 to 5 to 10 consumes less power than the method using the ultra-high pressure homogenizer of Comparative Example 1. It can be seen that carboxylated cellulose nanofibers with high transparency can be produced. Further, in the method using the cavitation jet device at the time of producing the carboxylated cellulose nanofibers of Example 4, compared with the method using the ultra-high pressure homogenizer of Comparative Example 4, the carboxylated cellulose nanofibers having high transparency can be produced with less power consumption. It turns out that it can be manufactured. Further, the carboxymethylated cellulose nanofibers of Example 11 and the phosphate esterified cellulose nanofibers of Example 12 can also be produced into highly transparent cellulose nanofibers with low power consumption by using a cavitation jet device. I know I can do it.

On the other hand, in Comparative Example 2 using a cavitation jet device having a small inner diameter of the pipe immediately after the nozzle, erosion occurred and the treatment could not be performed. Further, in Comparative Example 3 in which the inner diameter of the pipe immediately after the nozzle is larger than the maximum width of the cavitation jet (the maximum width of the jet is 15% of the diameter inside the pipe immediately after the nozzle), defibration is difficult to proceed and the defibration treatment is performed. It was difficult to increase the transparency even if the number of passes was increased. The carboxylated cellulose nanofiber is a gel-like substance having a very high viscosity, and in Comparative Example 3 in which the pipe diameter immediately after the nozzle is too large compared to the width of the cavitation jet, it stays in the pipe and defibration does not proceed. It is thought that it was.

Further, it can be seen that in the methods of Examples 1 and 4, a nanofiber dispersion having a high viscosity while having the same high transparency as that of Comparative Examples 1 and 4 using an ultra-high pressure homogenizer can be obtained. .. It is presumed that in the defibration treatment with the ultra-high pressure homogenizer of Comparative Examples 1 and 4, the fibers were easily cut and the fiber length was shortened, so that the viscosity was lowered.

Claims (6)

Step 1 of preparing anion-modified cellulose and step 2 of producing anion-modified cellulose nanofibers by defibrating anion-modified cellulose using a cavitation jet device.
A method for producing anion-modified cellulose nanofibers, which comprises.
The cavitation injection device gives an impact force to the anion-modified cellulose when the cavitation bubbles generated by the liquid injection injected through the nozzle or orifice collapse, and the upstream pressure of the liquid injection injected through the nozzle or orifice is 0.01 MPa. It is 30.00 MPa or less, and the ratio of downstream pressure / upstream pressure is 0.001 to 0.500.
The above-mentioned manufacturing method, wherein the maximum width of the cavitation jet generated by the liquid jet injected through the nozzle or orifice of the cavitation jet device is 50% or more and 130% or less of the inner diameter of the pipe immediately after the nozzle or orifice. The method according to claim 1, wherein the maximum width of the cavitation jet generated by the liquid jet injected through the nozzle or orifice of the cavitation jet device is 70% or more and 130% or less of the inner diameter of the pipe immediately after the nozzle or orifice. .. The method according to claim 1 or 2, wherein the anion-modified cellulose is a cellulose having a carboxyl group. The method according to claim 3, wherein the amount of carboxyl groups in the anion-modified cellulose is 0.4 mmol / g to 3.0 mmol / g with respect to the absolute dry mass of the anion-modified cellulose. The method according to claim 1 or 2, wherein the anion-modified cellulose is a cellulose having a carboxymethyl group. The method according to claim 5, wherein the degree of carboxymethyl substitution in the anion-modified cellulose is 0.01 or more and less than 0.40.