JP2020019859A - Method for producing cellulose nanofiber - Google Patents

Abstract

To provide a low-cost method capable of producing a cellulose nanofiber with low energy.SOLUTION: Energy consumption during fibrillation is reduced by adding a modifier which is one or more compounds selected from the group consisting of a primary amine compound, a secondary amine compound, a tertiary amine compound, a primary phosphine compound, a secondary phosphine compound, a tertiary phosphine compound and a quaternary onium compound when fibrillating anion-modified cellulose into nanofibers. Further, the modifier is made into a reusable state by bringing the obtained nanofiber dispersion into contact with an acid to desorb the modifier and bringing the recovered liquid into contact with an anion exchange resin.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a cellulose nanofiber. Specifically, after producing cellulose nanofibers with low energy by using a modifying agent, a method for producing a cellulose nanofiber, comprising a step of collecting the modifying agent and a step of reusing the collected modifying agent About.

  When cellulose as a raw material is treated in the presence of 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as TEMPO) and sodium chlorite as an oxidizing agent, cellulose is obtained. Can efficiently introduce a carboxyl group to the surface of the microfibrils. It is known that, when cellulose having a carboxyl group introduced therein is mechanically treated in water with a mixer or the like, it can be converted into cellulose nanofibers having a nanoscale fiber diameter (Patent Document 1). It is preferable to reduce energy consumption such as power consumption in the mechanical treatment performed to convert cellulose into nanofibers, since this leads to reduction in production cost of cellulose nanofibers.

  As a method of reducing energy in such a mechanical treatment (forming nanofibers), a chemical treatment comprising an oxidation treatment, a hydrolysis treatment, or a combination thereof is applied to the pulp fiber before the mechanical treatment. A method has been reported in which pulp fibers are coarsely defibrated by a refiner (Patent Document 2). Further, in the micronization step (mechanical processing), after performing the first micronization processing using a pressure-type disperser, a rotor provided with stirring blades and a screen arranged outside the stirring blades are provided. A method of suppressing energy consumption required for miniaturization by performing a second miniaturization process for miniaturization using a high-speed rotary disperser has been reported (Patent Document 3).

JP 2008-001728 A JP 2018-3216 A JP 2014-125690 A

  However, in the method described in Patent Document 2, pulp (cellulose) as a raw material is significantly reduced in fiber length, which may not be preferable depending on the use of cellulose nanofiber. For example, when cellulose nanofibers are used for imparting shape retention, a shorter fiber is not preferable because a longer fiber has a higher effect than a shorter fiber. Further, the method described in Patent Document 3 requires two types of dispersers, a pressure type disperser and a high-speed rotary type disperser, which complicates the manufacturing process and increases the cost. There is a need for a low-cost method that can produce cellulose nanofibers with low energy.

  The present inventors have conducted intensive studies and found that, in the mechanical treatment of cellulose (anion-modified cellulose) into which an anionic group such as a carboxyl group has been introduced, a primary amine compound, a secondary amine compound, a tertiary amine compound, A phosphine compound, a secondary phosphine compound, a tertiary phosphine compound, and a modifier, which is one or more compounds selected from the group consisting of a quaternary onium compound, are added to the anion-modified cellulose with low energy, It has been found that the fibrillation of anion-modified cellulose can be performed. Furthermore, by contacting the anion-modified cellulose nanofiber obtained by defibration with an acid, the modifier can be removed from the anion-modified cellulose nanofiber and recovered, and the recovered modifier can be used as an anion exchange resin. It has been found that the modifier can be regenerated and reused by being brought into contact with.

The present invention includes, but is not limited to, the following.
(1) One or more compounds selected from the group consisting of primary amine compounds, secondary amine compounds, tertiary amine compounds, primary phosphine compounds, secondary phosphine compounds, tertiary phosphine compounds, and quaternary onium compounds Mixing the modifying agent with the anion-modified cellulose,
A step 2, in which the anion-modified cellulose mixed with the modifier obtained in the step 1 is defibrated to obtain an anion-modified cellulose nanofiber;
A step of contacting an anion-modified cellulose nanofiber obtained in step 2 with an acid to remove the modifier from the anion-modified cellulose nanofiber, filtering the filtrate, and collecting a filtrate containing the modifier; and Step 4 of bringing the filtrate collected in Step 3 into contact with an anion exchange resin
A method for producing an anion-modified cellulose nanofiber, comprising:
(2) The liquid containing the modifier obtained by contacting the anion exchange resin in step 4 is further contacted with a cation exchange resin to adsorb the modifier in the liquid to the cation exchange resin. Step 5,
The modifier is desorbed from the cation exchange resin by contacting the cation exchange resin adsorbed with the modifier obtained in step 5 with a smaller amount of acid than the liquid obtained in step 4. Step 6 of recovering in an acid solution, and Step 7 of bringing the acid solution containing the modifier obtained in Step 6 into contact with the anion exchange resin
The method according to (1), further comprising:
(3) mixing a liquid containing a modifier obtained by contacting with an anion exchange resin in step 4 or step 7 with an anion-modified cellulose prepared separately from the anion-modified cellulose in step 1, The method according to (1) or (2), further comprising a step 8 of defibrating to obtain an anion-modified cellulose nanofiber.
(4) any of (1) to (3), further including a step 9 of regenerating the anion exchange resin by bringing the basic solution into contact with the anion exchange resin used in the step 4 and / or the step 7; The method according to one.
(5) The method according to any one of (1) to (4), wherein the anion-modified cellulose has a carboxyl group.
(6) The anion-modified cellulose according to any one of (1) to (5), wherein the anion-modified cellulose is a cellulose having a carboxyl group obtained by oxidizing cellulose using an N-oxyl compound and an oxidizing agent. Production method.
(7) The method according to (5) or (6), comprising, before step 1, converting a carboxyl group in the anion-modified cellulose to an acid form (COOH).
(8) The method according to any one of (1) to (7), wherein the modifier has a hydroxyl group or is a compound having a hydroxide ion as a counter ion.
(9) The method according to any one of (1) to (8), wherein the modifier is a quaternary onium compound selected from a quaternary ammonium compound or a quaternary phosphonium compound.

  According to the method of the present invention, anion-modified cellulose can be defibrated with low energy. For example, when fibrillating anion-modified cellulose using an ultrahigh-pressure homogenizer, a nanofiber dispersion having high transparency can be obtained with a small number of passes. Further, according to the method of the present invention, the modifier used in the defibration is removed from the nanofibers, collected, and brought into contact with an anion exchange resin to be regenerated, whereby the modifier can be reused. Possible, and costs are reduced.

  The present invention reduces the energy consumption required for fibrillation by adding a modifying agent when fibrillating cellulose (anion-modified cellulose) into which an anionic group such as a carboxyl group has been introduced into an nanofiber. Then, the used modifier is desorbed from the nanofibers using an acid and collected, and regenerated with an anion exchange resin, so that the modifier can be reused, and the cost of using the modifier is reduced. It is an invention for reducing the amount of light.

1. Mixing step 1 of modifier and anion-modified cellulose
<Modifier>
In the present invention, a modifier is mixed before fibrillating the anion-modified cellulose. The anion-modified cellulose will be described later. By adding the modifier, it becomes possible to reduce the energy consumption during the fibrillation of anion-modified cellulose.

  The modifier used in the present invention is selected from the group consisting of primary amine compounds, secondary amine compounds, tertiary amine compounds, primary phosphine compounds, secondary phosphine compounds, tertiary phosphine compounds, and quaternary onium compounds. One or a combination of two or more compounds. As the quaternary onium compound, a quaternary ammonium compound or a quaternary phosphonium compound is preferable.

  The substituent in the modifier is a hydrocarbon group or a hydrocarbon group containing a hetero atom, and the total number of carbon atoms in all the substituents is preferably about 4 to 120. The substituents may be linked to each other to form a ring. Examples where the substituent is a hydrocarbon group include, but are not limited to, alkyl groups, aralkyl groups, and aromatic groups. As the alkyl group, an alkyl group having 1 to 18 carbon atoms is preferable, for example, methyl, ethyl, n-propyl, n-butyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, Examples include, but are not limited to, n-heptadecyl and n-octadecyl. The aralkyl group is preferably an aralkyl group having 7 to 20 carbon atoms, for example, a benzyl group, an o-toluylmethyl group, a m-toluylmethyl group, a p-toluylmethyl group, a 2-phenylethyl group, a 1-naphthylmethyl group. , 2-naphthylmethyl group and the like, but are not limited thereto. The aromatic group is preferably an aromatic group having 6 to 20 carbon atoms, and examples thereof include a phenyl group, a biphenyl group, a naphthyl group, and a tosyl group, but are not limited thereto.

  Examples of the case where the substituent is a hydrocarbon group containing a hetero atom include, but are not limited to, a hydroxy-substituted hydrocarbon group having 1 to 30 carbon atoms, an alkoxy-substituted hydrocarbon group, and a phenoxy-substituted hydrocarbon group. Not done.

  Examples of the case where the substituents form a ring include pyridine, methylpyridine, ethylpyridine, dimethylpyridine, hydroxypyridine, pyridine derivatives such as dimethylaminopyridine, imidazole, methylimidazole, dimethylimidazole, ethylimidazole, benzimidazole and the like. And pyrazole derivatives such as pyrazole, methylpyrazole, dimethylpyrazole, ethylpyrazole and benzpyrazole, but are not limited thereto.

  When fibrillating the anion-modified cellulose in the next step, water or an organic solvent or a combination thereof can be appropriately selected as a dispersion medium. When water or a highly polar organic solvent is selected as the dispersion medium, for example, among those described above, those having a linear or branched alkyl group having about 1 to 6 carbon atoms as a substituent may be used as a modifier. preferable. Further, those having a straight-chain or branched alkyl group having about 3 to 4 carbon atoms are more preferable because they have a high effect of reducing energy consumption during fibrillation. When a low-polarity organic solvent is selected as the dispersion medium, a modifier having a substituent having more carbon atoms than those described above can be appropriately selected.

  Specific examples of the modifier include, but are not limited to, amine compounds such as monofunctionalized amines such as propylamine, 3-ethoxypropylamine, triisopropanolamine, hexylamine, heptylamine, and the like. Octylamine, nonylamine, decylamine, undecylamine, dodecylamine, octadecylamine, 2-ethylhexylamine, dihexylamine, dioctylamine, didodecylamine, trioctylamine, tridecylamine, tridodecylamine, triethylamine, triethanolamine, Dimethylbutylamine, dimethyloctylamine, dimethylbenzylamine, dimethyloctadecylamine, diethylamine, butylamine, dibutylamine, tributylamine, stearylamine, Stearylamine, oleylamine, alkylpolyalkylene glycolamine (for example, methyltriethylene glycolamine, bis (methyltriethylene glycol) amine, butyltriethylene glycolamine, lauryl polypropylene glycolamine, methyltripropylene glycolamine, phenol polypropylene glycolamine, Isotridecyl polypropylene glycol amine, bis (methyl tripropylene glycol) amine, N-methyl methyl polypropylene glycol amine, methyl polypropylene glycol amine, bis (methyl polypropylene glycol) amine, tris (methyl diglycol) amine, ethylene glycol and propylene glycol Has random or block distribution of units Methylpolyalkylene glycol amines); difunctional amines such as triethylene glycol diamine, tripropylene glycol diamine, polyethylene glycol diamine, polypropylene glycol diamine, poly with random or block distribution of ethylene glycol and propylene glycol units. Alkylene glycol diamine, butane diol polyalkylene glycol diamine, resorcinol polyalkylene glycol diamine; trifunctional amines such as glycerol polyalkylene glycol triamine having a random or block distribution of ethylene glycol and propylene glycol units, bis (tri Ethylene glycol amine) amine, bis (polyalkylene glycol amine) Min; tetrafunctional amines such as pentaerythritol polyalkylene glycol tetraamine having random or block distribution of ethylene glycol and propylene glycol units, N, N'-bis (polypropylene glycol amine) polyalkylene glycol diamine, and the like. No. Examples of the phosphine compound include tris (hydroxypropyl) phosphine, tris (hydroxyethyl) phosphine, tris (hydroxymethyl) phosphine, tris (hydroxybutyl) phosphine, tris (hydroxyoctyl) phosphine, tricyclohexylphosphine, triphenylphosphine, Examples include methyldiphenylphosphine, ethyldiphenylphosphine, allyldiphenylphosphine, dicyclohexylphenylphosphine, and tris (dimethylphenyl) phosphine. As the quaternary onium compound, any of an inorganic salt and a hydroxide ion can be used as a counter ion. However, when the counter ion is a hydroxide ion, the fibrillation property is good and preferable. For example, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, dodecyltrimethylammonium hydroxide, tetradecyltrimethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, octadecyltrimethylammonium hydroxide, oleyltrimethylammonium hydroxide, didodecyldimethylammonium Hydroxide, ditetradecyldimethylammonium hydroxide, dihexadecyldimethylammonium hydroxide, dioctadecyldimethylammonium hydroxide, dioleyldimethylammonium hydroxide, dodecyldimethylbenzylammonium hydroxide, tetradecyldimethylbenzylammonium hydroxide, hexa Decyl dimethi Quaternary ammonium compounds such as benzylammonium hydroxide, octadecyldimethylbenzylammonium hydroxide, oleyldimethylbenzylhydroxide, tetramethylammonium hydroxide, tetrapropylammonium hydroxide, benzyltrimethylammonium hydroxide and benzyltriethylammonium hydroxide; Butylphosphonium hydroxide, tetraethylphosphonium hydroxide, triethylbenzylphosphonium hydroxide, tetraoctylphosphonium hydroxide, trimethyldecylphosphonium hydroxide, trimethyldodecylphosphonium hydroxide, trimethylhexadecylphosphonium hydroxide, trimethyloctadecylphosphonium hydroxide, Libutyl methyl phosphonium hydroxide, tributyl dodecyl phosphonium hydroxide, tributyl octadecyl phosphonium hydroxide, trioctyl ethyl phosphonium hydroxide, tributyl hexadecyl phosphonium hydroxide, methyl triphenyl phosphonium hydroxide, ethyl triphenyl phosphonium hydroxide, diphenyl dioctyl phosphonium Quaternary such as hydroxide, triphenyloctadecylphosphonium hydroxide, tetraphenylphosphonium hydroxide, tributylallylphosphonium hydroxide, tetramethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, benzyltrimethylphosphonium hydroxide, butyltriphenylphosphonium hydroxide E Suphonium compounds can be mentioned. Among them, triisopropanolamine, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, tris (3-hydroxypropyl) phosphine, tetrabutylphosphonium hydroxide, polyethylene glycolamine and polypropylene glycolamine are particularly preferable.

  Although it is not clear why the above-described modifier can reduce the energy consumption during fibrillation, the modifier is bonded to the anionic group of the anion-modified cellulose and between the cellulose fibers. It is presumed that they may play a role of entering and separating the cellulose fibers from each other.

<Anion-modified cellulose>
(1) Cellulose In the present invention, cellulose means a polysaccharide having a structure in which D-glucopyranose (also simply referred to as "glucose residue" or "anhydroglucose") is connected by β-1,4 bonds. Cellulose is generally classified into natural cellulose, regenerated cellulose, microcellulose, microcrystalline cellulose excluding the non-crystalline region, and the like according to its origin, production method, and the like. In the present invention, any of these celluloses can be used as a raw material for anion-modified cellulose.

  Examples of the natural cellulose include bleached pulp or unbleached pulp (bleached wood pulp or unbleached wood pulp); linters, refined linters; cellulose produced by microorganisms such as acetic acid bacteria; The raw material of bleached pulp or unbleached pulp is not particularly limited, and examples thereof include wood, cotton, straw, bamboo, hemp, jute, kenaf, and the like. The method for producing bleached pulp or unbleached pulp is not particularly limited, and may be a mechanical method, a chemical method, or a method combining the two in the middle. Examples of bleached pulp or unbleached pulp classified according to the production method include mechanical pulp (thermomechanical pulp (TMP), groundwood pulp), chemical pulp (softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP) ), Softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), kraft pulp such as hardwood bleached kraft pulp (LBKP), and the like.

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

(2) Anion modification Anion modification is to introduce an anionic group into cellulose, specifically, to introduce an anionic group (anionic group) into a pyranose ring by an oxidation or substitution reaction. In the present invention, the oxidation reaction refers to a reaction in which a hydroxyl group of a pyranose ring is directly oxidized to a carboxyl group. In the present invention, the substitution reaction refers to a reaction for introducing an anionic group into a pyranose ring by a substitution reaction other than the oxidation.

(3) Carboxylated Carboxylated (oxidized) cellulose can be used as the anion-modified cellulose. The carboxyl group in the present invention refers to -COOH (acid type) or -COOM (salt type) (where 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 the carboxyl group is preferably 0.6 mmol / g to 3.0 mmol / g, more preferably 1.0 mmol / g to 2.0 mmol, based on the absolute dry mass of the anion-modified cellulose or the anion-modified cellulose nanofiber. / G is more preferred.

The amount of carboxyl groups of anion-modified cellulose or anion-modified cellulose nanofiber can be measured by the following method:
60 ml of a 0.5% by mass slurry of carboxylated cellulose (aqueous dispersion) was prepared, and a 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. The electrical conductivity is measured until the value reaches 0.0, and the amount of sodium hydroxide consumed in the neutralization stage of the weak acid having a gradual change in electrical conductivity is calculated using the following equation:
Carboxyl group content [mmol / g carboxylated cellulose] = a [ml] × 0.05 / mass of carboxylated cellulose [g].

As one 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. Can be mentioned. By this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized, and the cellulose fiber having an aldehyde group and a carboxyl group (—COOH) or a carboxylate group (—COO ⁻ ) on the surface. Can be obtained. The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less.

  An N-oxyl compound refers to a compound that can generate a nitroxy radical. As the N-oxyl compound, any compound can be used as long as the compound promotes a target 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, the amount is preferably 0.01 mmol to 10 mmol, more preferably 0.01 mmol to 1 mmol, and still more preferably 0.05 mmol to 0.5 mmol, based on 1 g of absolutely dried cellulose. Further, the amount is preferably about 0.1 mmol / L to 4 mmol / L with respect to the reaction system.

  Bromides are compounds containing bromine, examples of which include alkali metal bromides that can 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 promote the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 mmol to 100 mmol, more preferably 0.1 mmol to 10 mmol, still more preferably 0.5 mmol to 5 mmol, based on 1 g of absolutely dried cellulose. The modification is a modification by an oxidation reaction.

  As the oxidizing agent, known agents can be used. For example, halogen, hypohalous acid, halogenous acid, perhalic acid or salts thereof, halogen oxide, peroxide and the like can be used. Among them, sodium hypochlorite which is inexpensive and has a low environmental load is preferable. An appropriate amount of the oxidizing agent 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, and most preferably 3 mmol to 10 mmol, based on 1 g of absolutely dried cellulose. . In addition, for example, 1 mol to 40 mol is preferable for 1 mol of the N-oxyl compound.

  In the step of oxidizing cellulose, 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 proceeds, a decrease in the pH of the reaction solution is observed. To promote the oxidation reaction efficiently, an alkaline solution such as an aqueous sodium hydroxide solution is added to maintain the pH of the reaction solution at 8.0 to 12.0, preferably about 10.0 to 11.0. Is preferred. Water is preferred as the reaction medium because of its easy handling and little side reaction. The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of the oxidation, and is usually about 0.5 to 6 hours, for example, about 0.5 to 4 hours.

  Further, the oxidation reaction may be performed in two stages. 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 of the oxidized cellulose can be reduced without being inhibited by the salt produced as a by-product in the first-stage reaction. Can be well oxidized.

As another example of the carboxylation (oxidation) method, there can be mentioned a method of oxidizing by contacting a gas containing ozone with a cellulose raw material. By this oxidation reaction, at least the hydroxyl groups at the 2- and 6-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 to 30 parts by mass, more preferably 5 to 30 parts by mass, when the solid content of the cellulose raw material is 100 parts by mass. . The ozone treatment temperature is preferably from 0C to 50C, more preferably from 20C to 50C. 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 oxidized cellulose is improved. After the ozone treatment, an 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 compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, these oxidizing agents can be dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and the additional oxidation treatment can be performed by immersing the cellulose raw material in the solution.

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

(4) Carboxyalkylation As anion-modified cellulose, cellulose into which a carboxyalkyl group such as a carboxymethyl group has been introduced can be used. The carboxyalkyl group in the present invention refers to -RCOOH (acid type) or -RCOOM (salt type). Here, R is an alkylene group such as a methylene group or an ethylene group, and M is a metal ion. Since the carboxyalkyl group contains a carboxyl group portion (-COOH or -COOM portion), the term "cellulose having a carboxyl group" in the present invention refers to the above-mentioned carboxylation (oxidation). 3.) Not only cellulose but also carboxyalkylated cellulose.

  The carboxyalkylated cellulose may be obtained by a known method, or a commercially available product may be used. Preferably, the cellulose has a degree of carboxyalkyl substitution per anhydroglucose unit of 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 dispersibility of the cellulose nanofiber decreases. The lower limit of the degree of carboxyalkyl substitution is preferably 0.01 or more. In consideration of the operability, the degree of substitution is particularly preferably from 0.02 to 0.35, and more preferably from 0.10 to 0.30. In addition, the anhydrous glucose unit means the individual anhydrous glucose (glucose residue) constituting cellulose, and the carboxyalkyl substitution degree means the carboxyalkyl group among the hydroxyl groups (-OH) in the glucose residue constituting cellulose. The ratio of those substituted with an ether group (-ORCOOH or -ORCOOM) (the number of carboxyalkyl ether groups per glucose residue) is shown.

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

i) The starting material, a solvent and a 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. Processing,
ii) Next, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times per mol of glucose residue, and the reaction temperature is 30 ° C to 90 ° C, preferably 40 ° C to 80 ° C, and the reaction time is 30 minutes to 10 hours. A step of conducting an etherification reaction for preferably 1 hour to 4 hours.

  As the starting material, the above-mentioned cellulose material can be used. As the solvent, 3 to 20 times by mass of water or a lower alcohol, specifically, water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol or the like alone or 2 More than one mixed medium can be used. When lower alcohols are mixed, the mixing ratio is preferably from 60% by mass to 95% by mass. As the mercerizing agent, it is preferable to use 0.5 to 20 moles of an alkali metal hydroxide, specifically, sodium hydroxide and potassium hydroxide, per anhydroglucose residue in the starting 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 the cellulose, the celluloses repel each other. For this reason, the cellulose into which the carboxymethyl substituent is introduced can be nano-defibrated. When the carboxymethyl substituent per glucose unit is smaller than 0.02, nanofibrillation may not be sufficiently performed. The degree of carboxyalkyl substitution in the anion-modified cellulose is usually the same as the degree of carboxyalkyl substitution when the anion-modified cellulose is used as a nanofiber.

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

The degree of carboxyalkyl group substitution other than the carboxymethyl group can be measured in the same manner as described above.
(5) Esterification Esterified cellulose may be used as the anion-modified cellulose. Examples of the esterification method include a method of mixing a phosphoric acid compound powder or an aqueous solution with the cellulose raw material, and a method of adding an aqueous solution of the phosphoric acid compound to a slurry of the cellulose raw material. Examples of the phosphoric acid compound include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. Among them, compounds having a phosphate group are preferable because they are low-cost, easy to handle, and can improve the defibration efficiency by introducing a phosphate group into cellulose of the pulp fiber. Compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, phosphorus Tripotassium acid, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate and the like can be mentioned. Phosphoric acid groups can be introduced into cellulose by using one or more of these. Among them, 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 defibration in the following defibration step, and easy industrial application. Are preferred. Particularly, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferable. In addition, the phosphoric acid-based compound is preferably used as an aqueous solution because the reaction can proceed uniformly and the efficiency of introducing a phosphate group is increased. The pH of the aqueous solution of the phosphoric acid compound is preferably 7 or less from the viewpoint of increasing the efficiency of the introduction of the phosphoric acid group, but is preferably from 3.0 to 7.0 from the viewpoint of suppressing hydrolysis of the pulp fiber.

  The following method can be mentioned as an example of the method for producing the phosphorylated cellulose. A phosphoric acid-based compound is added to a suspension of a cellulose-based material having a solid concentration of 0.1 to 10% by mass while stirring to introduce a phosphate group into cellulose. When the cellulose-based material is 100 parts by mass, the amount of the phosphoric acid-based compound is preferably 0.2 to 500 parts by mass, preferably 1 to 400 parts by mass, as the amount of phosphorus element. Is more preferred. When the proportion of the phosphoric acid compound is at least the lower limit, the yield of fine fibrous cellulose can be further improved. However, if the ratio exceeds the upper limit, the effect of improving the yield will level off, which is not preferable in terms of cost.

  In addition to the phosphoric acid compound, a powder or an aqueous solution of another compound may be mixed. The compound other than the phosphoric acid compound is not particularly limited, but is preferably a basic nitrogen-containing compound. As used herein, "basic" is defined as the aqueous solution exhibiting a pink to red color in the presence of the phenolphthalein indicator, or the pH of the aqueous solution being greater than 7.0. The nitrogen-containing compound exhibiting basicity 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 include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, and the like. Among them, urea which is easy to handle at low cost is preferable. The amount of the other compound to be added is preferably 2 parts by mass to 1,000 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 from 0C to 95C, more preferably from 30C to 90C. The reaction time is not particularly limited, but is about 1 minute to 600 minutes, and 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 from being easily dissolved, thereby improving the yield of the phosphorylated cellulose. After dehydrating the obtained phosphated cellulose suspension, it is preferable to perform a heat treatment 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.

  It is preferable that the phosphoric acid-substituted cellulose has a phosphate group substitution degree per glucose unit of 0.001 or more and less than 0.40. By introducing a phosphate group substituent into cellulose, the celluloses repel each other electrically. For this reason, the cellulose into which the phosphate group has been introduced can be easily nanofibrillated. If the degree of substitution of the phosphate group per glucose unit is less than 0.001, nanofibrillation cannot be sufficiently performed. On the other hand, if the degree of substitution of the phosphate group per glucose unit is more than 0.40, it may swell or dissolve, and thus may not be obtained as nanofiber. In order to carry out the defibration efficiently, it is preferable that the phosphoric esterified cellulose-based material obtained above is boiled and then washed with cold water. These modifications by esterification are modifications by a substitution reaction. The degree of substitution in the anion-modified cellulose and the degree of substitution when the anion-modified cellulose is used as a nanofiber are usually the same.

(6) Anion-modified cellulose Anion-modified cellulose can be obtained by subjecting cellulose as a raw material to anion modification as exemplified above. The type of anion-modified cellulose is preferably anion-modified cellulose having a carboxyl group, such as carboxylated cellulose or carboxyalkylated cellulose, in consideration of the ease of binding with a modifier. In particular, in carboxylated cellulose obtained by oxidizing cellulose using an N-oxyl compound and an oxidizing agent, a carboxyl group is uniformly introduced, and a modifying agent is bonded to the carboxyl group to modify the carboxyl group. It is preferable that the agent is uniformly distributed in the anion-modified cellulose, so that the effect of lowering energy during fibrillation can be obtained more effectively.

  In the present invention, as the anion-modified cellulose, one that maintains at least a part of the fibrous shape even when dispersed in water or a highly polar organic solvent is used. If a material that does not maintain a fibrous shape (that is, a material that dissolves) is used, nanofibers cannot be obtained. The phrase "at least a part of the fibrous shape is maintained when dispersed" means that a fibrous substance can be observed when an anion-modified cellulose dispersion is observed with an electron microscope. Further, an 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 for crystalline Form I, and more preferably 60% or more. When the crystallinity is adjusted to the above range, crystalline cellulose fibers that do not dissolve even after the fibers have been refined by defibration can be efficiently obtained. The crystallinity of cellulose can be controlled by the degree of crystallization of cellulose as a raw material and the degree of anion modification. The method for measuring the crystallinity of the 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 is calculated by using a method such as Segal or the like, and the diffraction intensity of the 002 plane of 2θ = 22.6 ° and 2θ = 22.6 = 22.6 ° based on the diffraction intensity of 2θ = 10 ° to 30 ° in the X-ray diffraction diagram as a base line. It is calculated from the diffraction intensity of the amorphous portion of 18.5 ° by the following formula:
Xc = (I002c-Ia) / I002c × 100
Xc: Crystallinity of cellulose I type (%)
I002c: 2θ = 22.6 °, diffraction intensity of 002 plane Ia: 2θ = 18.5 °, diffraction intensity of amorphous portion.

The ratio of the cellulose I-type crystals of the anion-modified cellulose and the ratio of the cellulose I-type crystals when the anion-modified cellulose is made into nanofibers are usually the same.
The anion-modified cellulose is preferably in the form of a dispersion in order to be subjected to the subsequent fibrillation step. As the dispersion medium, water, an organic solvent, or a mixture thereof can be appropriately selected. Although the type of the organic solvent is not limited, 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, dimethyl sulfoxide and the like. The above-mentioned dispersion medium may be used alone or as a mixture 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) because 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.

The concentration of the anion-modified cellulose in the dispersion is preferably 0.01% by mass to 10% by mass in consideration of the operability during fibrillation.
When the anion-modified cellulose is a cellulose having a carboxyl group, the carboxyl group may be converted to an acid form (COOH) before adding the modifier. By converting the carboxyl group to the acid form before the addition of the modifier, the binding property between the modifier and the carboxyl group is increased, so that the effect of reducing energy consumption during fibrillation can be more enhanced. become. The method for converting to the acid form is not particularly limited, and examples thereof include a method of adding an acid and a method of contacting an acidic ion exchange resin with an anion-modified cellulose. When adding an acid, the kind of the acid to be used is not particularly limited, and a mineral acid such as hydrochloric acid or sulfuric acid, which is generally and easily available, may be used. Examples of the acidic ion exchange resin include a strongly acidic cation exchange resin and a weakly acidic cation exchange resin. The conversion step to the acid form is usually carried out before adding the modifier to the anion-modified cellulose, thereby increasing the binding property between the modifier and the anion-modified cellulose to reduce the energy during fibrillation. However, this does not preclude the application of fine fibers obtained by defibration. For example, if you want to finally obtain an anion-modified cellulose nanofiber using an organic solvent that is not easily defibrated as a dispersion medium, the state of the fine fibers obtained by defibration in an easily defibrated dispersion medium such as water By converting the anion-modified cellulose into an acid form, modifying it with a hydrophobizing agent or the like, and defibrating again in an organic solvent, good fibrillation in an organic solvent can be obtained. However, the present invention is not limited to this. The conversion step to the acid form may be performed even when only water is used as the dispersion medium, and the conversion step to the acid form may be performed by changing the type of the dispersion medium or the state of the anion-modified cellulose. Irrespective of this, it may or may not be performed.

<Mixing of modifier and anion-modified cellulose>
The amount of the modifier to be added to the anion-modified cellulose dispersion can be appropriately determined according to the type of the modifier used, the degree of anion modification of the anion-modified cellulose, and the like. For example, it may be added in an amount of about 10% to 150% with respect to the amount (molar number) of the anionic group to which the modifier can bind, preferably 30% to 120%, more preferably 50%. % To 100%.

  The pH of the anion-modified cellulose dispersion subjected to the fibrillation step after the addition of the modifier is changed by adding the modifier to the acidic anion-modified cellulose. Specifically, when the phosphine compound is added in an amount of 100% based on the amount (mole number) of the anionic group, the pH of the dispersion is in a neutral to weakly alkaline range (6. 0 to 9.0). When the addition amount is smaller than this range, a range of neutral to weak alkalinity (pH 6.0 to 9.0, preferably pH 7.0 to 7.0) using a general-purpose alkali chemical such as sodium hydroxide or an organic alkali is used. It is preferable to adjust the pH to 8.5). For example, when the anion-modified cellulose having a carboxyl group is converted to an acid form by adding an acid and the pH of the dispersion is acidic, the pH of the dispersion is made neutral by adding a modifier having a hydroxyl group. It may be adjusted to a range of weak alkalinity.

2. Fibrillation process 2 of anion-modified cellulose
<Defibration>
After adding a modifier to the dispersion of anion-modified cellulose, the anion-modified cellulose is defibrated by mechanical treatment. The device used for defibration is not limited, but it is preferable to use a device capable of applying a strong shear force to the dispersion liquid, such as a high-speed rotation type, a colloid mill type, a high pressure type, a roll mill type, and 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 at least 100 MPa, even more preferably at least 140 MPa. A high-pressure or ultra-high-pressure homogenizer is a device that pressurizes a fluid with a pump and ejects it from a very delicate gap provided in the flow channel, thereby emulsifying, dispersing, It is a device that performs defibration, pulverization, and ultra-miniaturization. Prior to the defibration and dispersion treatment with a high-pressure homogenizer, if necessary, a pretreatment can be performed using a known mixing, stirring, emulsifying, or dispersing device such as a high-speed shear mixer.

  As described above, the dispersion to be defibrated can be appropriately selected from water or an organic solvent, or a combination thereof. Further, the concentration of the anion-modified cellulose is preferably 0.01% by mass to 10% by mass. The dispersion to be defibrated contains a modifier as described above. By containing the modifying agent, it is possible to defibrate with a small energy consumption. For example, when using a high-pressure or ultra-high-pressure homogenizer, a nanofiber dispersion having high transparency can be obtained with a small number of passes. The degree of transparency indicates the degree of defibration into nanofibers.

<Cellulose nanofiber>
By the above defibration, nanofibers of anion-modified cellulose can be obtained. The nanofiber of anion-modified cellulose is a fiber having an average fiber diameter of about 3 nm to 500 nm, preferably about 3 nm to 150 nm, and more preferably about 3 nm to 20 nm. The aspect ratio is 30 or more, preferably 50 or more, 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 nanofibers of anion-modified cellulose are measured using an atomic force microscope (AFM) when the diameter is less than 20 nm, and using a field emission scanning electron microscope (FE-SEM) when the diameter is 20 nm or more. It can be measured by analyzing 200 randomly selected fibers and calculating the average. Also, the aspect ratio can be calculated by the following equation:
Aspect ratio = average fiber length / average fiber diameter.

According to the production method of the present invention, it is possible to produce an anion-modified cellulose nanofiber that forms a highly transparent dispersion with low energy consumption during fibrillation. The high degree of transparency indicates that the conversion into nanofibers was successfully performed by defibration. For example, nanofibers of anion-modified cellulose obtained by the production method of the present invention include, but are not limited to, passing a dispersion of anion-modified cellulose having a solid content of 1% by mass once through an ultrahigh-pressure homogenizer of 100 MPa to 150 MPa. By this, it can be converted into a nanofiber dispersion having a transmittance of 660 nm light (optical path length 10 mm) (referred to as transparency) of 80.0% to 99.9%. In addition, a nanofiber dispersion having a transparency of 90.0% to 99.9% can be obtained by passing twice. The transparency after two passes is preferably 96.0 to 99.9%. Such a cellulose nanofiber can be optimally used for applications requiring transparency. The method for measuring the transparency of cellulose nanofibers is as follows:
A cellulose nanofiber dispersion (solid content 1% by mass) was prepared, and a 660 nm light was transmitted using a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation) using a square cell having an optical path length of 10 mm. Measure the rate.

3. Step 3 of contacting anion-modified cellulose nanofiber with acid to recover modifier
The modifier is bonded to the anion-modified cellulose nanofiber obtained in step 2. In step 3, the modifier is detached from the nanofiber by contacting the anion-modified cellulose nanofiber to which the modifier is bonded with an acid, and is collected. The acid to be contacted is preferably a strong acid, but is not limited thereto. For example, hydrochloric acid or sulfuric acid is preferable. Further, a strongly acidic ion exchange resin may be brought into contact. However, when a strongly acidic ion exchange resin is used, when the modifier is to be reused later, it takes time to remove the modifier from the strongly acidic ion exchange resin. Most preferably, a strong acid is used. The amount of the acid is not particularly limited as long as it can remove a part or all of the modifier bound to the nanofiber. Use of an unnecessarily large amount of acid is not preferable because it leads to an increase in cost and a decrease in the concentration of the recovered modifier. The acid may be added, for example, until the pH of the dispersion becomes about 2.0 to 4.0.

  After contacting with an acid, the cellulose nanofibers are filtered by a commonly used method, and when a strongly acidic ion exchange resin is used, the strongly acidic liquid is contacted after filtering the ion exchange resin. By removing the modifier from the ion-exchange resin into the filtrate, the filtrate containing the modifier is recovered. The filtration method is not particularly limited, and for example, a dehydration apparatus such as a centrifugal dehydration type, a vacuum dehydration type, and a pressure dehydration type can be used, and a plurality of these can be used in combination. The filtrate containing the obtained modifier is subjected to contact with the anion exchange resin in the next step. It is considered that the obtained cellulose nanofiber does not contain a modifier or contains only a trace amount. The cellulose nanofiber may be appropriately subjected to operations such as washing, concentration, drying, redispersion, and solvent replacement by a known method according to a desired use.

4. Step 4 of bringing the filtrate containing the modifier into contact with the anion exchange resin
The filtrate containing the modifier recovered in Step 3 is brought into contact with an anion exchange resin. The filtrate recovered in step 3 is considered to be present in the form containing a salt of an acid due to the contact with the acid in step 3. The present inventors have found that when a salt-containing modifier is used, the effect of reducing energy consumption during fibrillation is small. It has also been found that when a modifier containing a salt is brought into contact with an anion exchange resin, the effect of reducing energy consumption during fibrillation is enhanced. Therefore, in the present invention, the liquid obtained by adding the acid in Step 3 (including the modifier in the form of an acid salt) is brought into contact with the anion exchange resin.

  The anion exchange resin is not particularly limited as long as it can remove a portion of the salt derived from the acid added in step 3, and is not limited thereto. For example, a strongly basic anion exchange resin of a hydroxyl group type having a quaternary ammonium group Resins are preferred.

  The method of contacting the liquid obtained in step 3 with the anion exchange resin is not particularly limited, and the liquid and the anion exchange resin are placed in a container such as a beaker and stirred, and then the resin is removed. An ordinary method may be used, such as passing the liquid through a column filled with.

  The liquid obtained by passing through the anion exchange resin (the liquid obtained in step 4) contains a modifier, and is added at the time of fibrillation (step 1) as described in step 8 below. It can be used again as a modifier. According to the present invention, a reusable modifier can be recovered by performing the above-described steps, and thereby, the cost of the modifier can be reduced.

5. Step 5 of contacting the liquid obtained in Step 4 with a cation exchange resin
In the present invention, the following steps 5 to 7 can be optionally performed. As described above, the liquid obtained in step 4 can be reused as a modifier added during fibrillation. However, when a large amount of acid is added in step 3 or a large amount of solvent is required for washing, May have a low modifier concentration. In that case, by performing the following steps 5 to 7, the concentration of the modifier can be increased. Although described later in Step 8, the concentration of the modifying agent may be increased by a method other than the following Steps 5 to 7, and Steps 5 to 7 are not essential to the present invention, and the concentration of the modifying agent may be increased. Is one way to increase

  In step 5, the liquid containing the modifier obtained in step 4 is brought into contact with the cation exchange resin to adsorb the modifier to the cation exchange resin. The cation exchange resin is not particularly limited as long as it is capable of adsorbing the modifier, but in consideration of the ease of recovery of the modifier in the next step 6, a weakly acidic cation having a carboxyl group is considered. Ion exchange resins are preferred.

  The method of contacting the liquid obtained in step 4 with the cation exchange resin is not particularly limited, and the liquid and the cation exchange resin are placed in a container such as a beaker, stirred and then the resin is removed, or the cation exchange resin is removed. An ordinary method may be used, such as passing the liquid through a column filled with.

6. Step 6 of contacting the cation exchange resin with an acid in Step 5 to recover the modifier
After adsorbing the modifier to the cation exchange resin in step 5, the cation exchange resin is brought into contact with an acid, so that the modifier is desorbed from the cation exchange resin and eluted into the acid solution. . At this time, by making the amount of the acid added to the cation exchange resin smaller than the amount obtained in step 4, the concentration of the modifier in the liquid obtained in step 4 is improved. The concentration of the bulking agent can be increased. The amount of the acid added in the step 6 may be smaller than the amount of the acid obtained in the step 4, and is not particularly limited. For example, it is preferable to add the acid until the pH of the acid reaches about 2.0 to 4.0.

  The type of acid used is not particularly limited, but a strong acid such as hydrochloric acid or sulfuric acid can be preferably used. The method of contacting the cation exchange resin with the acid is not particularly limited, and the acid may be passed through a column filled with the cation exchange resin, or the cation exchange resin may be taken out of the column into another container and the resin may be immersed. An acid may be added as described above.

After contact with the cation exchange resin, if necessary, the cation exchange resin is removed by a known method, and the liquid containing the modifier is recovered.
7. Step 7 of contacting the liquid obtained in Step 6 with an anion exchange resin
The solution of the acid containing the modifier obtained in Step 6 is brought into contact with the anion exchange resin. The modifier in the liquid obtained in step 6 is considered to exist in a form containing an acid salt by contact with an acid, similarly to the modifier in the liquid obtained in step 3. As described above in step 4, by bringing the salt-containing modifier into contact with the anion exchange resin, the effect of reducing the energy consumption during fibrillation by the modifier can be increased. The anion exchange resin may be any resin as long as it can remove the portion of the salt derived from the acid added in step 6, as in step 4. For example, although not limited thereto, a hydroxyl group type strongly basic anion exchange resin having a quaternary ammonium group is preferable.

  The method of contacting the liquid obtained in step 6 with the anion exchange resin is not particularly limited, and the liquid and the anion exchange resin are placed in a container such as a beaker, stirred, and then the resin is removed, or the anion exchange resin is removed. An ordinary method may be used, such as passing the liquid through a column filled with.

8. Step 8 of reusing the liquid contacted with the anion exchange resin as a modifier
The liquid obtained by contacting with the anion exchange resin in step 4 and the liquid obtained by contacting with the anion exchange resin in step 7 each contain a modifier, and are used when fibrillating the anion-modified cellulose. Can be used again. These modifiers have an increased effect of reducing energy consumption during fibrillation due to contact with the anion exchange resin, and can be reused favorably. Further, the liquid obtained in step 7 has a higher concentration of the modifier through steps 5 to 7, and is particularly preferably reused (for example, by directly adding it to a dispersion of anion-modified cellulose). be able to. The liquid obtained in step 4 can also be used as a modifier as it is. However, since the concentration of the modifier in the liquid may be low due to the addition of an acid in step 3, the concentration may be reduced by some means. Is preferably used. Means for increasing the concentration of the modifier in the liquid obtained in step 4 are not limited to these, but include performing steps 5 to 7 and volatilizing the solvent appropriately. Since thermal energy is required to volatilize the solvent, it is preferable to perform Steps 5 to 7 from the viewpoint of cost.

9. Step 9 of regenerating anion exchange resin
The anion exchange resin used in Steps 4 and 7 can be regenerated using a known method. For example, when a strongly basic anion exchange resin of a hydroxyl group type is used as the anion exchange resin in the step 4 and / or the step 7, the anion exchange resin is again brought into contact with the hydroxyl group by contacting a strongly basic solution. Can be returned to the mold. The regenerated anion exchange resin can be used again in step 4 and / or step 7.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Unless otherwise specified, parts and% indicate parts by mass and% by mass, respectively.

(Reference Example 1)
A bleached softwood pulp (manufactured by Nippon Paper Industries Co., Ltd.) is prepared as a raw material for cellulose, TEMPO is used as an N-oxyl compound, sodium hypochlorite and sodium bromide are used as oxidizing agents, and the amount of carboxyl groups is 1.5 mmol / g. (Dispersion medium: water) was produced. Hydrochloric acid was added to the aqueous dispersion of carboxylated cellulose until the pH reached 2.4, to convert the carboxyl groups to the acid form (COOH). Thereafter, it was dehydrated and washed with ion-exchanged water to obtain 500 ml of an aqueous dispersion of an acid-type anion-modified cellulose having a solid content of 1% by mass. The pH of the obtained dispersion was 4.9. To this dispersion, tetrabutylammonium hydroxide was added until the pH of the dispersion was 7.0. The obtained dispersion was passed once through a 150 MPa ultrahigh pressure homogenizer (one pass), and the transparency was measured. Similarly, the transparency after two passes was measured (two passes). The methods for measuring the amount of carboxyl groups and the transparency are as described above. Table 1 shows the results.

(Reference Examples 2 to 8)
Instead of tetrabutylammonium hydroxide, tetrabutylphosphonium hydroxide (Reference Example 2), tris (3-hydroxypropyl) phosphine (Reference Example 3), tetraethylammonium hydroxide (Reference Example 4), and triisopropanolamine (Reference Example) 5) A cellulose nanofiber dispersion was prepared in the same manner as in Reference Example 1 except that 3-ethoxypropylamine (Reference Example 6), sodium hydroxide (Reference Example 7), and ammonia (Reference Example 8) were used. And the transparency was measured. Also, the transparency was measured in the same manner as in Reference Example 1 (Reference Example 9) except that tetrabutylammonium hydroxide was not added. Table 1 shows the results.

  From the results in Table 1, compounds selected from the group consisting of primary amine compounds, secondary amine compounds, tertiary amine compounds, primary phosphine compounds, secondary phosphine compounds, tertiary phosphine compounds, and quaternary onium compounds It can be seen that, in Reference Examples 1 to 6 using a certain modifier, higher transparency can be achieved with a smaller number of passes to the ultrahigh pressure homogenizer than in Reference Examples 7 and 8. The high degree of transparency indicates the degree of defibration into nanofibers, and by using the above-described modifier, the number of passes is small, that is, the defibration into nanofibers is performed with low energy consumption. It turns out that you can do it.

(Example 1)
Hydrochloric acid was added to the anion-modified cellulose nanofiber obtained by passing once through the ultrahigh pressure homogenizer in Reference Example 1 until the pH reached 2.4. This was filtered using a glass filter to obtain a 350 ml filtrate. The obtained filtrate was put into a beaker, an anion exchange resin (Amberjet 4400OH type, manufactured by Organo Corporation) was added thereto, and the mixture was stirred with a stirrer to bring the filtrate into contact with the anion exchange resin. Thereafter, the anion exchange resin was removed using a mesh. Next, the liquid after contact with the anion exchange resin was similarly contacted with a cation exchange resin (Amberlite IRC76, manufactured by Organo Corporation). The cation exchange resin after the contact was recovered and immersed in 50 ml of 1M hydrochloric acid. This was filtered using a nylon mesh having a pore size of 250 μm to obtain a filtrate. The obtained filtrate was again brought into contact with an anion exchange resin (Amberjet 4400OH type, manufactured by Organo Co., Ltd.) in the same manner to obtain a liquid containing a modifier (tetrabutylammonium hydroxide).

  The obtained liquid was added to an aqueous dispersion of an acid-type anion-modified cellulose prepared according to the method described in Reference Example 1 until the pH reached 7.0. Thereafter, the solid content concentration was adjusted to 1% by mass with ion-exchanged water. The obtained dispersion was passed once through a 150 MPa ultra-high pressure homogenizer, and the transparency was measured. The method of measuring the transparency is as described above. Table 2 shows the results.

(Example 2)
Instead of the anion-modified cellulose nanofiber of Reference Example 1, anion-modified cellulose nanofiber was obtained in the same manner as in Example 1 except that the anion-modified cellulose nanofiber obtained by passing once through an ultrahigh pressure homogenizer in Reference Example 3 was used. Nanofibers were prepared and the transparency was measured. Table 2 shows the results.

(Comparative Example 1)
Hydrochloric acid was added to the anion-modified cellulose nanofiber obtained by passing once through the ultrahigh pressure homogenizer in Reference Example 1 until the pH reached 2.4. This was filtered using a glass filter to obtain a 350 ml filtrate. The obtained filtrate was added to an aqueous dispersion of an acid-type anion-modified cellulose prepared according to the method described in Reference Example 1, and the solid content concentration was adjusted to 1% by mass. Thereafter, the pH was adjusted to 7.0 by adding sodium hydroxide. The obtained dispersion was passed once through a 150 MPa ultra-high pressure homogenizer, and the transparency was measured. The method of measuring the transparency is as described above. Table 2 shows the results.

(Comparative Example 2)
Instead of the anion-modified cellulose nanofiber of Reference Example 1, anion-modified cellulose was prepared in the same manner as in Comparative Example 1 except that the anion-modified cellulose nanofiber obtained by passing once through an ultrahigh pressure homogenizer in Reference Example 3 was used. Nanofibers were prepared and the transparency was measured. Table 2 shows the results.

    From the results in Table 2, it can be seen that after once using the modifier for fibrillation, it can be removed from the anion-modified cellulose nanofiber by the addition of an acid and recovered. It can be seen that the function (energy consumption reduction effect) of the modifier can be recovered by contacting with the.

Claims (9)

It is at least one compound selected from the group consisting of primary amine compounds, secondary amine compounds, tertiary amine compounds, primary phosphine compounds, secondary phosphine compounds, tertiary phosphine compounds, and quaternary onium compounds. Mixing the filler with the anion-modified cellulose, step 1,
A step 2, in which the anion-modified cellulose mixed with the modifier obtained in the step 1 is defibrated to obtain an anion-modified cellulose nanofiber;
A step of contacting an anion-modified cellulose nanofiber obtained in step 2 with an acid to remove the modifier from the anion-modified cellulose nanofiber, filtering the filtrate, and collecting a filtrate containing the modifier; and Step 4 of bringing the filtrate collected in Step 3 into contact with an anion exchange resin
A method for producing an anion-modified cellulose nanofiber, comprising: A step of contacting the liquid containing the modifier obtained by contacting the anion exchange resin in step 4 with a cation exchange resin to adsorb the modifier in the liquid to the cation exchange resin;
The modifier is desorbed from the cation exchange resin by contacting the cation exchange resin adsorbed with the modifier obtained in step 5 with a smaller amount of acid than the liquid obtained in step 4. Step 6 of recovering in an acid solution, and Step 7 of bringing the acid solution containing the modifier obtained in Step 6 into contact with the anion exchange resin
The method of claim 1, further comprising:   The solution containing the modifier obtained by contacting the anion-exchange resin in step 4 or step 7 is mixed with an anion-modified cellulose prepared separately from the anion-modified cellulose in step 1, and defibration of the anion-modified cellulose is performed. The method according to claim 1, further comprising performing step 8 to obtain anion-modified cellulose nanofiber.   The method according to any one of claims 1 to 3, further comprising a step 9 of regenerating the anion exchange resin by bringing a basic solution into contact with the anion exchange resin used in the step 4 and / or the step 7. Method.   The method according to any one of claims 1 to 4, wherein the anion-modified cellulose has a carboxyl group.   The method according to any one of claims 1 to 5, wherein the anion-modified cellulose is a cellulose having a carboxyl group obtained by oxidizing cellulose using an N-oxyl compound and an oxidizing agent.   The method according to claim 5 or 6, comprising, before step 1, converting a carboxyl group in the anion-modified cellulose to an acid form (COOH).   The method according to any one of claims 1 to 7, wherein the modifier has a hydroxyl group or is a compound having a hydroxide ion as a counter ion. The method according to any one of claims 1 to 8, wherein the modifier is a quaternary onium compound selected from a quaternary ammonium compound or a quaternary phosphonium compound.