WO2020235669A1 - Novel cellulose nanofibers, and production method of dried product thereof - Google Patents

Abstract

The present invention provides novel cellulose nanofibers which have excellent dispersibility in an organic solvent. More specifically, the present invention is of novel cellulose nanofibers obtained by introducing a carboxyl group and a quaternary organic onium ion as the counterion of said carboxyl group wherein, if the quaternary organic onium ion together with a bromide ion forms a salt, the melting point of said salt, measured in accordance with JIS-K7121, is less than or equal to 100°C, and the dispersion yield of the cellulose nanofibers is higher in the case that the dispersion medium is an organic solvent than in the case that the dispersion medium is water.

Description

New method for producing cellulose nanofibers and their dried products Reference of related application

This patent application is accompanied by a priority claim based on Japanese Patent Application No. 2019-96276 filed on May 22, 2019, and all the disclosures in the previous patent application are by citation. As part of this specification.

The present invention relates to a method for producing cellulose nanofibers and a dried product thereof.

In recent years, due to the depletion of resources and the increase in carbon dioxide concentration in the atmosphere, warming, environmental pollution, waste problems, etc., the amount of fossil resources used during production is small, and carbon dioxide can be processed with low energy at the time of disposal. Attention is being paid to the use of environmentally friendly materials that emit less. Under these circumstances, biodegradation represented by biomass resource-derived materials that do not use fossil resources as raw materials but part or all of them as raw materials such as natural plants, and polylactic acid that is decomposed in the environment into water and carbon dioxide. Active use of sex materials is expected.

Cellulose, which accounts for about half of the production of biomass materials, is expected to be effectively used due to its large production. Cellulose has high strength, high elastic modulus, and extremely low coefficient of thermal expansion, and when described in terms of heat resistance, it is known that it does not have a glass transition point and exhibits a high thermal decomposition temperature of 230 degrees.

However, it cannot be said that cellulose is often used as a material for its large production volume. One of the reasons is low solubility and dispersibility in aqueous and non-aqueous solvents. Cellulose is a homopolysaccharide in which D-glucopyranose, which is a 6-membered ring of glucose, is β- (1 → 4) glucoside-bonded, and has hydroxyl groups at the C2, C3, and C6 positions. Therefore, strong hydrogen bonds are formed in the molecule and between the molecules, and they are insoluble in water and general solvents.

One of the most common uses of cellulose is carboxymethylation. Carboxylic groups are randomly introduced into the hydroxyl groups at the C2, C3, and C6 positions, and depending on the degree of substitution, the carboxymethylated cellulose fibers are water-soluble at the degree of substitution and can be used as a thickener, and are insoluble at the degree of substitution. And various materials can be obtained. However, since a large amount of organic solvent is used in the carboxymethylation reaction of cellulose and toxic monochloroacetic acid is used, there are problems such as environmental pollution and waste liquid treatment. Moreover, since the introduced carboxyl group has no distinction in the position of the hydroxyl group, the product has a non-uniform chemical structure.

On the other hand, when cellulose is treated using an oxidation reaction catalyzed by an N-oxyl compound such as 2,2,6,6-tetramethyl-1-piperidinyloxy radical (TEMPO) to adjust the degree of treatment. It is known that a homogeneous cellulose nanofiber dispersion can be obtained by a light dispersion treatment in water. At this time, the cellulose nanofibers are defibrated to the microfibril level and exist as cellulose-derived fibers having a width of several nm to several hundred nm in the dispersion medium. Further, in this TEMPO oxidation reaction, only water is used as a reaction medium without using an organic solvent, and the reaction is completed in a short time under mild conditions of normal temperature and pressure, and the environmental adaptability of the reaction process is extremely high.

The mechanism by which the oxidized cellulose obtained by the TEMPO oxidation reaction is dispersed to the nano level by a light mechanical treatment is known as follows. By the oxidation reaction, the hydroxyl group at the C6 position on the surface of the microfibrils of cellulose is selectively oxidized, and the carboxyl group is introduced via the aldehyde group. Since this carboxyl group is ionized and exhibits an osmotic effect in the dispersion medium, nano-order microfibrils are easily isolated, and a homogeneous cellulose nanofiber dispersion can be obtained. Furthermore, by utilizing the electrostatic action of the carboxyl group introduced into the cellulose nanofibers to form various salts having a cationic property as counterions, cellulose modified products having different characteristics can be obtained. Since this treatment can retain the crystallinity of the raw material cellulose without destroying it, it has high physical properties.

In this way, cellulose nanofibers can be used as nanodispersions, liquid states, and modifiers, have a low environmental load, and have high physical properties. Therefore, the treatment and oxides by the TEMPO oxidation reaction are cellulose nanofibers. It is expected as a new form of use of fiber.

One example of active development for industrial use is compounding with resin. By mixing a dried product of cellulose nanofiber dispersion in the resin, the purpose is to improve the functionality of the resin by utilizing the light weight, high strength, high elastic modulus, low coefficient of linear thermal expansion, and high heat resistance of cellulose. Is. Dispersibility of cellulose nanofibers in the resin is mentioned as an important factor for improving the functionality at this time. It is known that when cellulose nanofibers are unevenly distributed or aggregated, the effect of mixing cellulose nanofibers is significantly reduced.

Therefore, in order to increase the affinity with the hydrophobic resin and improve the dispersibility, a method for hydrophobizing the hydrophilic cellulose nanofibers has been developed.

For example, in Patent Document 1, after the cellulose oxide obtained by the TEMPO oxidation reaction is dispersed to form cellulose nanofibers, an acid is added to aggregate the cellulose oxide and take it out as a gel. This is added to an organic solvent to replace the water in the gel with a solvent, then an alkali dissolved in the organic solvent is allowed to act, and further solvent substitution is repeated and then dispersion treatment is performed to carry out hydrophobic cellulose containing the organic solvent. A method for obtaining a nanofiber dispersion is shown.

Patent Document 2 discloses a method in which cellulose oxide obtained by a TEMPO oxidation reaction is pH-adjusted with an organic alkali and dispersed in water or an organic solvent. In this method, the dispersion medium is basically captured as water, and it is possible to use an organic solvent containing water. However, in the cellulose nanofiber dispersion liquid containing water, the drying efficiency is low, and it may be difficult to improve the productivity. Furthermore, in the drying process, the organic solvent is first evaporated and removed, and as a result, the cellulose nanofibers maintain their original hydrophilicity as the same characteristics as the aqueous dispersion, and organic alkali is used as the alkali. It may be difficult to fully exert the reforming effect.

In Patent Document 3, some of the present inventors have introduced organic onium as a counterion in a dispersion containing cellulose nanofibers into which a carboxyl group obtained by a TEMPO oxidation reaction has been introduced and a dispersion medium. A cellulose nanofiber dispersion containing ions and further containing no water in the dispersion medium is disclosed, and tetrabutylammonium ions and the like are described as organic onium ions used as counterions.

International Publication No. 2013/077354 International Publication No. 2011/1116112 Japanese Patent Application No. 2013-2448787

However, as a result of the studies by the present inventors, the conventional cellulose nanofiber dispersion obtained by hydrophobizing the cellulose into which the carboxyl group introduced by the TEMPO oxidation reaction is introduced has dispersibility in a wide range of organic solvents. Although it is shown, it also disperses in water, so that the water resistance of the dried product obtained from the cellulose nanofiber dispersion becomes low, which may make it difficult to manufacture and handle.

On the other hand, when a primary amine such as dodecylamine is used for hydrophobization of cellulose having a carboxyl group introduced by a TEMPO oxidation reaction, the obtained cellulose nanofiber dispersion does not disperse in water and contains alcohol or the like. It may be dispersed in an organic solvent having a relatively high dielectric constant. However, the cellulose nanofiber dispersion modified with a primary amine such as dodecylamine is subjected to a multi-step process in which the carboxyl group is once converted into a sodium salt, acid-washed, and then modified again with the primary amine. It has been clarified by the present inventors that it may be difficult to disperse it in an organic solvent and further to make it into a dried product.

Under such technical circumstances, as a result of further studies, the present inventors have made a combination of a specific organic onium ion and cellulose having a carboxyl group introduced by a TEMPO oxidation reaction, which is excellent for an organic solvent. It has been found that cellulose nanofibers having a high dispersibility can be obtained.

In addition, the present inventors efficiently dry a composition containing organic onium ions, cellulose having a carboxyl group introduced by a TEMPO oxidation reaction, and an organic solvent under specific conditions. We have found that nanofibers can be dried. The present invention is based on such findings.

Therefore, one object of the present invention is to obtain cellulose nanofibers having excellent dispersibility in an organic solvent.

Another object of the present invention is to provide a method capable of efficiently drying cellulose nanofibers.

[1] Cellulose nanofibers containing cellulose formed by introducing a carboxyl group and a quaternary organic onium ion as a counterion of the carboxyl group.
When the quaternary organic onium ion forms a salt together with the bromide ion, the melting point of the salt measured according to JIS-K7121 is 100 ° C. or lower.
The dispersion yield of the cellulose nanofiber dispersion measured by the following test method is higher when the dispersion medium is an organic solvent than when the dispersion medium is water.
Test method: At 25 ° C., cellulose nanofibers having a solid content concentration of 0.1% by weight in a dispersion medium were centrifuged at 12,000 g for 10 minutes to separate the precipitate from the supernatant, and the obtained precipitate was obtained. Based on the weight of the product and the supernatant, the dispersion yield is calculated according to the following formula.

[2] The cellulose nanofiber according to [1], wherein the quaternary organic onium ion is at least one selected from a quaternary ammonium ion and a quaternary phosphonium ion.
[3] The cellulose nanofiber according to any one of [1] and [2], wherein the quaternary organic onium ion is represented by the following formula (1).

[In the formula, M represents a nitrogen atom or a phosphorus ^atom, R ^1, R 2, ^{R 3} and ^{R 4} represents a hydrocarbon ^group, R ^1, R 2, hydrocarbon represented by ^{R 3} and ^{R 4} At least one of the groups has 6 or more carbon atoms. ]
[4] All the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ have 6 or more carbon atoms.
At least one of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ has 8 or more carbon atoms.
The cellulose nanofiber according to [3], wherein the total number of carbon atoms of all the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ is 30 or more.
[5] The cellulose nano according to [3] or [4], wherein three or more of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ are aliphatic hydrocarbon groups. Fiber.
[6] M excluding quaternary organic onium ion and ^R 1 is phosphorus ^atom, R 2, ^{R 3} and ^{R 4} are the same, the cellulose nanofiber according to any one of [3] to [5].
[7] The cellulose nanofiber according to any one of [1] to [6], which comprises an organic solvent as a dispersion medium.
[8] The cellulose nanofiber according to any one of [1] to [7], wherein the relative permittivity of the organic solvent is 75 or less.
[9] The cellulose nanofiber according to any one of [1] to [8], wherein the organic solvent is a water-soluble organic solvent.
[10] The organic solvents are methanol, ethanol, isopropyl alcohol, t-butyl alcohol, acetone, ethyl acetate, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone and The cellulose nanofiber according to any one of [1] to [9], which is at least one selected from the group consisting of N-methylacetamide.
[11] The cellulose nanofiber according to any one of [1] to [10], wherein the dispersion yield is 25% or more when the dispersion medium is an organic solvent.
[12] The cellulose nanofiber according to any one of [1] to [11], wherein the dispersion yield is 20% or less when the dispersion medium is water.
[13] The cellulose nanofiber according to any one of [1] to [12], wherein the content of the carboxyl group is 0.1 mm or more and 3.0 mm or less per dry weight of the cellulose nanofiber.
[14], The dried product of cellulose nanofibers according to any one of [1] to [13].
[15] A method for producing a dried product of cellulose nanofibers.
Including a step of contacting the cellulose nanofiber dispersion with an acid to obtain a gel-like composition and a step of drying the gel-like composition to obtain a dried cellulose nanofiber.
The cellulose nanofiber dispersion is
A method comprising a cellulose nanofiber in which an organic onium ion is introduced as a counterion of a carborvoxyl group and the carboxyl group, and an organic solvent as a dispersion medium.
[16] The method according to [15], wherein the drying is carried out by a supercritical drying method, a freeze drying method or an evaporation drying method.
[17] The method according to either [15] or [16], wherein the acid is brought into contact with the cellulose nanofiber dispersion in a substantially anhydrous state.
[18] The method according to any one of [15] to [17], wherein the dried product of the cellulose nanofibers is airgel, cryogel or xerogel.

According to the first aspect of the present invention, it is possible to provide cellulose nanofibers having excellent dispersibility in an organic solvent. In the first embodiment, since the cellulose nanofibers have high dispersibility in organic solvents as compared with dispersibility in water, they can be advantageously used in avoiding adsorption of water and the like.

Further, according to the second aspect of the present invention, the dried body of cellulose nanofibers can be efficiently dried. In the second embodiment, since the drying treatment can be carried out in a substantially anhydrous state without solvent substitution in the step of obtaining the dried product from the cellulose nanofiber dispersion, water adsorption or the like can be performed. It is possible to easily provide a dried product of cellulose nanofibers while avoiding the above.

As shown in FIG. 1A, it is a photograph of a cellulose nanofiber dispersion dispersed in each organic solvent (methanol, ethanol, isopropyl alcohol, acetone, t-butyl alcohol). FIG. 1B is a photograph showing the birefringence of the cellulose nanofiber dispersion dispersed in each organic solvent (methanol, ethanol, isopropyl alcohol, acetone, t-butyl alcohol). It is a photograph of a dried product (airgel) of cellulose nanofibers.

First Aspect According to the first embodiment of the present invention, it is a cellulose nanofiber containing cellulose obtained by introducing a carboxyl group and a quaternary organic onium ion as a counterion of the carboxyl group. hand,
When the quaternary organic onium ion forms a salt together with the bromide ion, the melting point of the salt measured according to JIS-K7121 is 100 ° C. or lower.
The dispersion yield of the cellulose nanofibers measured by the following test method is higher when the dispersion medium is an organic solvent than when the dispersion medium is water.

Test method: At 25 ° C., cellulose nanofibers having a solid content concentration of 0.1% by weight in a dispersion medium were centrifuged at 12,000 g for 10 minutes to separate the precipitate and the supernatant, and the obtained precipitate was obtained. Based on the weight of the product and the supernatant, the dispersion yield is calculated according to the following formula. Further details of the above test method can be carried out according to Example 1 described later. In the above test method, the dispersion treatment is carried out under the same conditions when the organic solvent is used and when water is used.

According to one embodiment of the present invention, the relative permittivity of the organic solvent is, for example, 75 or less, preferably 10 to 75, more preferably 10 to 40, still more preferably 10 to 35. is there.

The organic solvent is preferably a water-soluble organic solvent. More specifically, the organic solvent is preferably methanol (Methanol), ethanol (EtOH), isopropyl alcohol (i-PrOH), t-butyl alcohol (t-BuOH), acetone, ethyl acetate, N, N-dimethyl. At least one selected from the group consisting of formamide, N, N-dimethylacetamide, dimethylsulfoxide, N-methyl-2-pyrrolidone and N-methylacetamide, more preferably methanol, ethanol, isopropyl alcohol, t-. It is butyl alcohol or acetone, and even more preferably ethanol.

According to a preferred embodiment of the present invention, the dispersion yield of the cellulose nanofibers when the organic solvent is used as the dispersion medium is usually 25% or more, preferably 25 to 100%, and more preferably 40. It is ~ 100%, more preferably 50-100% or more, and even more preferably 90-100%.

According to one embodiment of the present invention, the dispersion yield of the cellulose nanofibers when water is used as the dispersion medium is usually 20% or less, preferably 0 to 10%, and more preferably 0 to 5. %, More preferably 0 to 1%, and even more preferably 0 to 0.1%.

According to a preferred embodiment of the present invention, the dispersion yield of the cellulose nanofibers when the organic solvent is used as the dispersion medium is preferably 25 to 100%, and the cellulose nanofibers when water is used as the dispersion medium. The dispersion yield of the above is 0 to 10%. According to a more preferable embodiment of the present invention, the dispersion yield of the cellulose nanofibers when the organic solvent is used as the dispersion medium is preferably 40 to 100%, and the cellulose nanofibers when water is used as the dispersion medium. The dispersion yield of the fiber is 0 to 5%. According to a more preferable embodiment of the present invention, the dispersion yield of the cellulose nanofibers when the organic solvent is used as the dispersion medium is preferably 90 to 100%, and the cellulose when water is used as the dispersion medium. The dispersion yield of the nanofibers is 0 to 0.1%. In any of the above preferred embodiments, the organic solvent is preferably methanol, ethanol, isopropyl alcohol, t-butyl alcohol or acetone, more preferably ethanol.

According to one embodiment of the present invention, it is preferable that the quaternary organic onium ion forms a room temperature molten salt together with the bromide ion. According to a preferred embodiment of the present invention, when the quaternary organic onium ion forms a salt together with the bromide ion, the melting point of the salt measured according to JIS-K7121 is usually 100 ° C. or lower, preferably 1 to 100. ° C., more preferably 10 to 100 ° C., even more preferably 15 to 99 ° C.

According to a preferred embodiment of the present invention, when the quaternary onium ion forms a salt together with the bromide ion or the hydroxide ion, the salt is preferably water-insoluble at 20 ° C. and is water-insoluble. Is more preferable. Here, the term "water-insoluble" means a substance that is hygroscopic at 20 ° C. and is water-insoluble. Here, the water-insoluble substance means a substance that belongs to "almost insoluble (the amount of solvent required to dissolve 1 g of solute is 10,000 mL or more)" according to the general rules of the 17th revised Japanese Pharmacopoeia.

Further, according to a preferred embodiment of the present invention, when the quaternary organic onium ion forms a salt together with the bromide ion or the hydroxide ion, the salt is preferably ethanol-soluble. Here, ethanol solubility means an ethanol-soluble component measured according to JIS K3362-2008.

Further, suitable quaternary organic onium ions include quaternary ammonium ions, quaternary phosphonium ions, or combinations thereof.

According to one embodiment of the present invention, the lower limit of the number of carbon atoms in the side chain of the quaternary organic onium ion is usually 4 or more, preferably 6 or more, and even more preferably 8 or more.

Further, according to one embodiment of the present invention, the number of carbon atoms in the side chain of the organic onium ion is not particularly limited, but is usually 20 or less, preferably 15 or less.

Further, according to one embodiment of the present invention, the quaternary organic onium ion is represented by the following formula (1).

[In the formula, M represents a nitrogen atom or a phosphorus ^atom, R ^1, R 2, ^{R 3} and ^{R 4} represents a hydrocarbon ^group, R ^1, R 2, hydrocarbon represented by ^{R 3} and ^{R 4} At least one of the groups has 6 or more carbon atoms. ]

In the formula ^(1), the number of carbon atoms in all of the hydrocarbon groups represented by R ^1, R 2, ^{R 3} and ^{R 4} are usually 6 or more, preferably from 6 to 30, even more preferably 6 It is ~ 20, and even more preferably 6 ~ 15.

Further, in the formula (1), at least one of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ has preferably 8 or more carbon atoms, more preferably 8 to 30 carbon atoms. , Even more preferably 8 to 20, and even more preferably 8 to 15.

Further, in the formula (1), the total number of carbon atoms of the hydrocarbons of R ¹ , R ² , R ³ and R ⁴ is usually 20 or more, preferably 25 or more, and more preferably 30 or more. According to another embodiment, the total number of carbon atoms of the hydrocarbons of R ¹ , R ² , R ³ and R ⁴ is usually 20 to 60, preferably 20 to 50, and more preferably 20. ~ 40.

Further, according to one embodiment, in the formula (1), three or more groups among the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ are aliphatic hydrocarbon groups. Further, according to a preferred embodiment, ^four of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ are aliphatic hydrocarbon groups.

Further, according to one embodiment, in the formula (1), three or more groups among the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ are aliphatic hydrocarbon groups. Moreover, according to another embodiment, all the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ are aliphatic hydrocarbon groups. According to any of the above embodiments, in formula (1), one or less of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ is an aralkyl group or an aromatic group. is there.

Examples of the aliphatic hydrocarbon group, preferably an aliphatic hydrocarbon group having 6 to 30 carbon atoms, examples of case R ^{1, R 2,} R ³ and R ⁴ is an aliphatic hydrocarbon group, an alkyl, alkenyl, Alkinyl, cycloalkyl, cycloalkenyl, cycloalkynyl and the like can be mentioned, but more preferably alkyl groups (eg, methyl, ethyl, n-propyl, n-butyl, n-dodecyl, n-tridecyl, n-tetradecyl, n- Pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, etc.).

As the aralkyl group, an aralkyl group having 7 to 20 carbon atoms is preferable, and examples thereof include a benzyl group, an o-toluylmethyl group, an m-toluylmethyl group, a p-toluylmethyl group, a 2-phenylethyl group and a 1-naphthylmethyl group. Examples include a group and a 2-naphthylmethyl group. Further, as the aromatic group, an aromatic group having 6 to 20 carbon atoms is preferable, and phenyl group, biphenyl group, benzyl group, tosyl group and the like can be exemplified. R ¹ , R ² , R ³ and R ⁴ may have substituents such as methyl, ethyl, fluorine, chlorine and the like that do not affect their thermal stability.

Further, according to one embodiment, in the formula (1), M is a phosphorus atom and R ¹ , R ² , R ³ and R ⁴ are the same.

According to a preferred embodiment of the present invention, it is a cellulose nanofiber into which a quaternary organic onium ion is introduced.
As the quaternary organic onium ion, cellulose nanofibers represented by the following formula (1) are provided.

[In the above formula, M represents a nitrogen atom or a phosphorus atom, and R ¹ , R ² , R ³ and R ⁴ represent a hydrocarbon group.
All hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ have 6 or more carbon atoms, and at least among the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ^4. One carbon number is 8 or more,
The total number of carbon atoms in the hydrocarbons of R ¹ , R ² , R ³ and R ⁴ is usually 20 or more, and 3 or more of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ The group is an aliphatic hydrocarbon group,
However, those in which M is a phosphorus atom and R ¹ , R ² , R ³ and R ⁴ are the same are excluded. ]

In any of the embodiments of the present invention, the quaternary organic onium ion is preferably water-insoluble at 20 ° C., more preferably water-insoluble, as a property of the bromide salt. According to a particularly preferred embodiment of the present invention, the quaternary organic onium ion is tetraoctylammonium ion, tetradodecylammonium ion, tributyldodecylphosphonium ion or trihexyltetradecylphosphonium ion.

According to one embodiment, the cellulose nanofibers of the present invention can be produced by combining cellulose into which a carborvoxyl group has been introduced and a quaternary organic onium ion as a counterion of a carboxyl group.
Hereinafter, an embodiment of the method for producing cellulose nanofibers and cellulose into which a carboxyl group has been introduced will be described. According to one embodiment of the present invention, the production method includes at least an oxidation step and a counterion substitution step. Further, a solvent replacement step and a dispersion step may be included.

As a material using cellulose as a starting material, natural cellulose or chemically modified cellulose can be used. Specifically, wood-based pulp such as bleached and unbleached kraft wood pulp, pre-hydrogenated kraft wood pulp, sulfite wood pulp, non-wood pulp such as cotton and bacterial cellulose, and mixtures thereof shall be used. Any of these physically and chemically treated substances may be used. Preferably, natural cellulose having a crystalline form I is preferable.

<Oxidation process>
The method for oxidizing cellulose is not particularly limited as long as it is a method for introducing a carboxyl group into cellulose as a raw material, and is appropriately selected depending on the intended purpose. For example, it can be appropriately selected from a generally known method of oxidizing a hydroxyl group to a carboxylic acid via an aldehyde. Among them, a method in which an N-oxyl compound is used as a catalyst and a hypohalite or a hypohalogenate is used as an copolymer is preferable. In particular, 2,2,6,6-tetramethyl-1-pipedinyloxy radical (TEMPO) is used as a catalyst, and an oxidizing agent such as sodium hypochlorite and a bromide such as sodium bromide are used while adjusting the pH. The TEMPO oxidation method treated with the above is suitable from the viewpoints that the reaction is completely in water without using an organic solvent as a reaction medium, the availability of reagents, the cost, and the stability of the reaction.

In the TEMPO oxidation method, only the surface of crystalline cellulose microfibrils is oxidized, and oxidation does not occur inside the crystal, so that the crystal structure can be maintained. Therefore, the product has the characteristics of high strength, high elastic modulus, low coefficient of linear thermal expansion, and high heat resistance inherent in cellulose.

The oxidation treatment by the above-mentioned TEMPO oxidation method is usually performed by the following procedure.
An N-oxyl compound and an oxidizing agent or a copolymer are added to the cellulose dispersed in water to oxidize the cellulose. Sodium hydroxide is added during the oxidation reaction to control the pH in the reaction system from 9 to 11. The reaction temperature is preferably 0 ° C. or higher and 40 ° C. or lower. At this time, the hydroxyl group at the C6 position on the surface of the cellulose fiber is oxidized to a carboxyl group. After completion of the reaction, it can be thoroughly washed with water and recovered, and used as a constituent material in the present invention.

As the oxidizing agent, hypochlorous acid or a salt thereof, hypochlorous acid or a salt thereof can be used, and sodium hypochlorite is preferable. Examples of the bromide include lithium bromide, potassium bromide, sodium bromide and the like, and sodium bromide is preferable from the viewpoint of ease of handling.

The content of the carboxyl group introduced into the cellulose can be adjusted by appropriately setting the reaction conditions. Since the cellulose into which the carboxyl group has been introduced is dispersed in the dispersion medium by the charge repulsion of the carboxyl group through the dispersion step described later, it is preferable to control the content of the carboxyl group within an appropriate range. The content of the carboxyl group introduced into the cellulose is preferably 0.1 mmoL or more and 3 mmoL or less, and more preferably 0.6 mmoL or more and 2.5 mmoL or less per dry weight. It is advantageous to set the content of the carboxyl group to 0.1 mmoL or more per dry weight in order to stably disperse the cellulose in the dispersion medium. Further, setting the content of the carboxyl group to 3 mmoL or less per dry weight is advantageous in avoiding a decrease in water resistance due to an excessive increase in affinity for the dispersion medium.

The amount of carboxyl groups contained in cellulose can be calculated by the following method. Take 0.2 g of the oxidized cellulose in terms of dry weight in a beaker and add 80 mL of ion-exchanged water. 5 mL of a 0.01 M sodium chloride aqueous solution is added thereto, and 0.1 M hydrochloric acid is added while stirring to adjust the pH to 2.0 as a whole. Using an automatic titrator (AUT-701 manufactured by DKK-TOA CORPORATION), a 0.1 M sodium hydroxide aqueous solution was injected at 0.05 mL / 30 seconds, and the conductivity and pH value were measured every 30 seconds to measure pH 11 The measurement was continued until. The titration amount of sodium hydroxide can be obtained from the obtained conductivity curve, and the carboxyl group content can be calculated.

After the oxidation step is completed by stopping the oxidation reaction, the product is recovered from the reaction solution by filtration. After completion of the reaction, the carboxyl group introduced into the cellulose forms a salt having a metal ion derived from a cation present in the reaction medium as a counter ion.
As a method for recovering cellulose after the oxidation treatment, (a) a method of filtering while the carboxyl group forms a salt, and (b) an acid is added to the reaction solution to adjust the inside of the system under acidic conditions to obtain a carboxylic acid. Examples thereof include a method of filtering and (c) a method of adding an organic solvent to aggregate and then filtering. Among them, (b) the method of recovering as a carboxylic acid is preferable from the viewpoint of handleability, recovery efficiency, and waste liquid treatment. Further, in the counterion substitution step described later, the method of recovering as a carboxylic acid is preferable because the formation of by-products can be suppressed and the substitution efficiency is excellent when the counterion does not contain a metal ion.

The metal ion content in cellulose after the oxidation reaction can usually be easily examined by elemental analysis by fluorescent X-ray analysis. When recovered by a method of filtering while forming a salt, the content of metal ions is usually 5 wt% or more, whereas when recovered by a method of filtering as a carboxylic acid, it is usually 1 wt% or less. Become. Further, the recovered cellulose can be purified by repeating washing, and the catalyst and by-products can be removed. At this time, the amount of residual metal ions and salts can be reduced by repeating the washing with a washing liquid prepared under acidic conditions of pH 3 or less using hydrochloric acid or the like and then repeating the washing with pure water.

<Counterion replacement process>
Next, the counterion substitution step can be carried out by adding an alkali to the suspension of cellulose having a carboxyl group introduced therein.

At this time, it is preferable to adjust the pH of the cellulose suspension to a range of pH 4 or more and pH 12 or less using an alkali. In particular, the pH may be set to be alkaline with a pH of 7 or more and a pH of 12 or less, and a carboxylate may be formed with the added alkali. As a result, the osmotic repulsive force associated with the ionization of the carboxyl group is likely to occur, so that the dispersibility is improved and the cellulose nanofiber dispersion is easily obtained.

A quaternary organic onium compound can be used as the alkali for adjusting the pH of the suspension. Examples of the counter ion of the quaternary organic onium forming the quaternary organic onium compound include halide ion (bromid ion, fluoride ion, iodo ion) or hydroxide ion, but when the mixing of metal ion has an adverse effect. Hydroxide ions are preferable in view of dispersibility in the dispersion medium and dispersion medium.

As described above, the cellulose-modified product (cellulose obtained by introducing a carboxyl group and an organic onium ion as a counterion of the carboxyl group) obtained by using a quaternary organic onium compound as an alkali is paired with a metal ion. The dispersion treatment can be performed with lower energy and in a shorter time than when an inorganic alkali as an ion is used, and the homogeneity of the dispersion finally reached is also high. It is considered that this is because the ionic radius of the counterion is larger when the organic onium compound is used, and therefore the effect of separating the fine cellulose fibers from each other in the dispersion medium is greater. Furthermore, if a water-insoluble quaternary organic onium compound is contained, the viscosity characteristics of the dispersion can be adjusted by the combination of the quaternary organic onium compound and the organic solvent, which can increase the industrial application range. it can. Therefore, the ion exchange treatment is preferably carried out in an organic solvent.

<Solvent replacement step>
When cellulose having a carboxyl group introduced in the oxidation treatment is used as a dispersion, the cellulose can be dispersed to a homogeneous dispersion by mixing the cellulose and the dispersion medium and performing the dispersion treatment using the method described later. It will be possible. As a pretreatment for mixing with the dispersion medium, the oxidized cellulose can be replaced with a solvent. Here, since the reaction medium is water in the cellulose oxidation step and the cleaning agent used for cleaning after the reaction is mainly water, the cellulose after the oxidation treatment is recovered as a wet state containing water. Therefore, when an organic solvent other than water is contained as the dispersion medium, the purpose is to remove water as an impurity in the dispersion medium, to make cellulose and the dispersion medium compatible in advance to improve dispersibility, or to use an insoluble component of the dispersion medium. It is preferable to perform solvent substitution for the purpose of removal.

In the present invention, as described above, it is preferable to perform ion exchange treatment using a water-insoluble quaternary onium salt in an organic solvent. When ion exchange is carried out using a water-insoluble quaternary onium salt, charge repulsion due to the carboxyl group can be maintained even after solvent substitution, so that aggregation of cellulose fibers can be suppressed. Further, by coordinating the water-insoluble quaternary organic onium ion, the affinity with the organic solvent is remarkably improved, water can be easily discharged, and the solvent can be replaced efficiently.

The organic solvent used for solvent substitution can be appropriately selected according to the purpose as long as the cellulose fibers do not aggregate or denature. Further, it may be the same as the dispersion medium used when preparing the cellulose nanofiber dispersion.

<Dispersion process>
By the dispersion step, cellulose having a carboxyl group introduced or a cellulose-modified product can be prepared into a cellulose nanofiber dispersion. In other words, in one embodiment of the present invention, a carboxyl group-introduced cellulose or a cellulose-modified product is described as a form of cellulose before the stage of preparation into the cellulose nanofiber dispersion of the present invention.

As a method of dispersion processing in the dispersion process, various already known dispersion treatments are possible. For example, homomixer processing, mixer processing with rotary blade, high pressure homogenizer processing, ultrahigh pressure homogenizer processing, ultrasonic homogenizer processing, nanogenizer processing, disc type refiner processing, conical type refiner processing, double disc type refiner processing, grinder processing, ball mill processing. , Kneading process by biaxial kneader, underwater facing process, etc. Among these, a mixer treatment with a rotary blade, a high-pressure homogenizer treatment, an ultra-high pressure homogenizer treatment, and an ultrasonic homogenizer treatment are preferable from the viewpoint of miniaturization efficiency. Of these processes, it is also possible to perform dispersion by combining two or more processing methods.

When a cellulose-modified product obtained by substituting a counterion as the organic onium ion of the carboxyl group introduced into cellulose in the dispersion treatment is used, it has a high affinity for an organic solvent. Therefore, even when an organic solvent such as alcohol is used as the dispersion medium, Cellulose nanofiber dispersions can be prepared.

According to one embodiment of the present invention, the above-mentioned organic solvent can be used as the organic solvent used as the dispersion medium in the dispersion treatment.

The principle that cellulose, which is originally highly hydrophilic, is dispersed as nanofibers in an organic solvent that does not contain water and maintains dispersibility by this method is considered as follows. First, the dissociability of organic onium ions used in the counterion exchange step is extremely high. Furthermore, the hydrocarbon group of the organic onium compound has a hydrophobic interaction with the organic solvent. It is considered that these effects dissociate the ions even in the organic solvent, and the osmotic effect associated with the ionization of the carboxyl group of the oxidized cellulose acts to enable dispersion in the organic solvent.

According to one embodiment of the present invention, the light transmittance of the cellulose nanofiber dispersion obtained by the dispersion step at an optical path length of 10 mm at 660 nm is the solid content concentration of the cellulose nanofibers contained in the cellulose nanofiber dispersion. At 0.2%, it is preferably 85% or more with the dispersion medium as a reference. Within the above range, it is shown that the dispersion has excellent homogeneity. That is, when the light transmittance is low in the visible light region of 660 nm, it is suggested that there are many aggregates of cellulose fibers that hinder the transmission of test light. By measuring the light transmittance, it can be easily used as an index showing the dispersibility of cellulose.

The light transmittance of the cellulose nanofiber dispersion is obtained by adjusting the solid content concentration of the cellulose nanofibers, filling the cellulose cells, and measuring the transmittance at a specified wavelength using a spectrophotometer. Further, according to one embodiment of the present invention, the fiber width of cellulose as a cellulose nanofiber dispersion is preferably 2 nm or more and 200 nm or less. That is, in order to maintain the fiber shape, it is preferably 2 nm or more, and if it is 200 nm or less, it has optical transparency and thus the degree of freedom in product design is improved. The fiber shape of cellulose can be confirmed by developing a cellulose nanofiber dispersion prepared to 0.0001 to 0.001 wt% on mica or the like having a smooth surface, drying it, and observing it by SEM.

The solid content concentration of the cellulose fibers with respect to the dispersion medium in the dispersion step can be appropriately adjusted within a range that does not hinder the dispersion treatment, and the concentration treatment may be performed after the dispersion treatment. The concentration method is not particularly limited, but a method such as centrifugation, decompression, or vacuum evaporation can be appropriately selected as long as the aggregation due to drying of the cellulose fibers and the deterioration of the characteristics due to the decomposition reaction do not become a problem.

In addition, water is added to the cellulose nanofiber dispersion after the dispersion step according to the function to be added for the purpose of adjusting the viscosity, adjusting the drying rate, improving the affinity with different materials, etc. within the range where aggregation and precipitation do not occur. Various organic solvents can be mixed. At this time, in order to alleviate the shock caused by mixing different solvents, the addition rate, pH adjustment, stirring method, temperature and the like can be appropriately selected.

Further, the obtained cellulose modified product or cellulose nanofiber dispersion may contain a metal or the like. Metals include platinum group elements such as gold, silver, platinum, palladium, ruthenium, iridium, rhodium, and osmium, as well as metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Alternatively, these alloys, oxides, compound oxides, carbides and the like can be used. As a method for supporting a metal, in addition to mixing fine particles such as metal or metal oxide, a cellulose nanofiber dispersion having a carboxyl group forms a complex of metal or metal oxide, and metal particles are added by adding a reducing agent. Can be precipitated as. When this method is used, the fine metal particles are uniformly immobilized on the surface of the cellulose fiber, so that the effect can be efficiently exerted by a small amount of metal.

In addition, various additives including water-soluble polysaccharides and various resins may be contained for the purpose of further increasing the charge repulsion between fibers and controlling the viscosity of the dispersion liquid as long as aggregation and precipitation are not generated. For example, chemically modified cellulose, carrageenan, xanthan gum, guar gum, gum arabic, sodium alginate, agar, solubilized starch, glycerin, sorbitol, antifoaming agent, water-soluble polymer, synthetic polymer and the like can be used. Alternatively, various solvents may be contained in order to impart functionality such as coatability and wettability. Alcohols, cellsolves, glycols, etc. can be used. Furthermore, various dyes, pigments, organic fillers, and inorganic fillers may be contained for the purpose of imparting design.

Further, various cross-linking agents may be contained in order to improve water resistance and electrolyte resistance. For example, oxazoline, divinyl sulfone, carbodiimide, dihydrazine, dihydrazide, epichlorohydrin, glioxal, organic titanium compound, organic zirconium compound and the like can be used. Further, the pH can be adjusted by adding an acid or an alkali for the purpose of improving the reactivity.

The cellulose nanofiber dispersion thus obtained can maintain the dispersed state in the state where water is excluded as described above. Furthermore, it has excellent affinity with organic solvents and can exist as homogeneous cellulose nanofibers in organic solvents.

Further, using a cellulose nanofiber dispersion, a resin composite for the purpose of improving strength and weight reduction is formed by mixing with a resin, or a functional layer containing cellulose nanofibers is applied by coating on a base material or the like. It is possible to use it as a constituent material of a molded product, such as forming.

This enables more homogeneous compounding with highly hydrophobic substances such as resins, greatly expanding the range of industrial use of cellulose.

Therefore, according to one embodiment of the present invention, the cellulose nanofibers can be provided as a dispersion together with an organic solvent as a dispersion medium. The shape of the cellulose nanofiber dispersion is preferably liquid or gel.

According to one embodiment of the present invention, the cellulose nanofiber dispersion can be in the form of a dried product. Preferable examples of the dried product include airgel, xerogel and the like. A high level of specific surface area and void ratio can be imparted to the dried body of the cellulose nanofiber dispersion, and it can be advantageously used as a heat insulating material, a catalyst carrier, a catalyst carrier, a sound absorbing material, and an adsorbent.

According to one embodiment of the present invention, the dried product is obtained by drying a cellulose nanofiber dispersion together with an organic solvent. The method for drying the cellulose nanofiber dispersion can be carried out by the method described in the second aspect described later.

Second Embodiment According to the second embodiment of the present invention, there is a method for producing a dried product of cellulose nanofibers, wherein the cellulose nanofiber dispersion is brought into contact with an acid to obtain a gel-like composition. The cellulose nanofiber dispersion comprises a step of drying the gel-like composition to obtain a dried product of cellulose nanofibers, and the cellulose nanofiber dispersion is obtained by introducing a carboxyl group and a quaternary organic onium ion as a counter ion of the carboxyl group. A method comprising a fiber and an organic solvent is provided.
According to the above method, since the drying treatment can be carried out in a substantially anhydrous state, it is particularly advantageous in easily obtaining a dried body of the cellulose nanofiber dispersion while avoiding adsorption of water and the like.

According to one embodiment of the present invention, a cellulose nanofiber dispersion is brought into contact with an acid to obtain a gel-like composition.

According to one embodiment of the present invention, it is preferable that the cellulose nanofiber dispersion is in a substantially anhydrous state. Here, the substantially anhydrous state means that the water content is usually 1% or less, preferably 0.1% or less, more preferably 0.001% or less, still more preferably 0.0001% or less. Means.

The cellulose nanofiber dispersion can be prepared according to the description in the first aspect.

According to one embodiment of the present invention, the quaternary organic onium ion in the cellulose nanofiber dispersion can be the same as that described in the first aspect.

Therefore, according to one embodiment of the present invention, the quaternary organic onium ion is represented by the following formula (1).

[In the formula, M represents a nitrogen atom or a phosphorus ^atom, R ^1, R 2, ^{R 3} and ^{R 4} represents a hydrocarbon ^group, R ^1, R 2, hydrocarbon represented by ^{R 3} and ^{R 4} At least one of the groups has 6 or more carbon atoms. ]

In the formula ^(1), the number of carbon atoms in all of the hydrocarbon groups represented by R ^1, R 2, ^{R 3} and ^{R 4} are usually 6 or more, preferably from 6 to 30, even more preferably 6 It is ~ 20, and even more preferably 6 ~ 15.

Further, in the formula (1), at least one of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ has preferably 8 or more carbon atoms, more preferably 8 to 30 carbon atoms. , Even more preferably 8 to 20, and even more preferably 8 to 15.

Further, in the formula (1), the total number of carbon atoms of the hydrocarbons of R ¹ , R ² , R ³ and R ⁴ is usually 20 or more, preferably 25 or more, and more preferably 30 or more. Further, according to another embodiment, the total number of carbon atoms of the hydrocarbons of R ¹ , R ² , R ³ and R ⁴ is usually 20 to 60, preferably 20 to 50, and more preferably 20. ~ 40.

Further, according to one embodiment, in the formula (1), three or more groups among the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ are aliphatic hydrocarbon groups. Further, according to a preferred embodiment, ^four of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ are aliphatic hydrocarbon groups.

Further, according to one embodiment, in the formula (1), three or more groups among the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ are aliphatic hydrocarbon groups. Moreover, according to another embodiment, all the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ are aliphatic hydrocarbon groups. According to any of the above embodiments, in the formula (1), one or less of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ is an aralkyl group or an aromatic group. is there.

Examples of the aliphatic hydrocarbon group, preferably an aliphatic hydrocarbon group having 6 to 30 carbon atoms, examples of case R ^{1, R 2,} R ³ and R ⁴ is an aliphatic hydrocarbon group, an alkyl, alkenyl, Alkinyl, cycloalkyl, cycloalkenyl, cycloalkynyl and the like can be mentioned, but more preferably alkyl groups (eg, methyl, ethyl, n-propyl, n-butyl, n-dodecyl, n-tridecyl, n-tetradecyl, n- Pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, etc.).

As the aralkyl group, an aralkyl group having 7 to 20 carbon atoms is preferable, and examples thereof include a benzyl group, an o-toluylmethyl group, an m-toluylmethyl group, a p-toluylmethyl group, a 2-phenylethyl group and a 1-naphthylmethyl group. Examples include a group and a 2-naphthylmethyl group. Further, as the aromatic group, an aromatic group having 6 to 20 carbon atoms is preferable, and phenyl group, biphenyl group, benzyl group, tosyl group and the like can be exemplified. R ¹ , R ² , R ³ and R ⁴ may have substituents such as methyl, ethyl, fluorine, chlorine and the like that do not affect their thermal stability.

Further, according to one embodiment, in Formula (1), when M is phosphorus atom, the quaternary organic onium ^ion, excluding R ^1, R 2, ^{R 3} and ^{R 4} are the same.

Further, according to a preferred embodiment of the present invention, in the above formula (1),
M represents a nitrogen atom or a phosphorus ^atom, R ^1, R 2, ^{R 3} and ^{R 4} represents a hydrocarbon group, the carbon of all hydrocarbon groups represented by ^{R 1,} R 2, ^{R 3} and ^{R 4} The number is 6 or more, and at least one of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ has 8 or more carbon atoms.
The total number of carbon atoms in the hydrocarbons of R ¹ , R ² , R ³ and R ⁴ is usually 20 or more, and 3 or more of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ The group is an aliphatic hydrocarbon group,
However, those in which M is a phosphorus atom and R ¹ , R ² , R ³ and R ⁴ are the same are excluded.

In the embodiment of the present invention, the quaternary organic onium ion is preferably water-insoluble at 20 ° C., and more preferably water-insoluble, as a property of the bromide salt. According to a particularly preferred embodiment of the present invention, the quaternary organic onium ion is tetraoctylammonium ion, tetradodecylammonium ion, tributyldodecylphosphonium ion or trihexyltetradecylphosphonium ion.

Further, according to one embodiment of the present invention, the organic solvent in the cellulose nanofiber dispersion can be the same as that described in the first aspect.

Further, according to another embodiment of the present invention, the organic solvent in the cellulose nanofiber dispersion is a solvent that can be mixed with a supercritical fluid (CO _2, etc.) in consideration of the drying step described later. preferable. Preferable examples of such a solvent include ethanol, methanol, acetone and the like.

According to one embodiment of the present invention, the acid to be brought into contact with the cellulose nanofiber dispersion is preferably in a substantially anhydrous state from the viewpoint of avoiding adsorption of water. Preferable examples of the acid include glacial acetic acid, hydrochloric acid, acetic anhydride or a hydrochloric acid-containing organic solvent (hydrochloric acid-methanol solution, etc.).

The amount of the acid used may be appropriately determined according to the content of the carboxyl group in the dispersion of the cellulose nanofibers, etc., but for example, it is usually compared to the carboxyl group in the dispersion of the cellulose nanofibers. It can be 0.5 to 1.5 equivalents, preferably 0.9 to 1.1 equivalents.

The method of contacting the acid with the cellulose nanofiber dispersion is not particularly limited, but it is preferable to directly add the acid or the acid-containing liquid to the cellulose nanofiber dispersion. The temperature at which the acid is brought into contact is not particularly limited, but is, for example, 5 to 40 ° C, preferably room temperature (about 25 ° C). The contact period of the acid is, for example, 0.5 to 3 hours, preferably 1 to 2 hours. During the above contact period, the contact material between the cellulose nanofiber dispersion and the acid may be allowed to stand until a gel-like composition is formed.

In one embodiment of the present invention, the gel-like composition is dried to obtain a dried product of cellulose nanofibers. As the drying, a known drying method can be used, but from the viewpoint of avoiding functional deterioration of the dried body due to mixing of water, it is preferably carried out by a supercritical drying method or an evaporation drying method.

When the above drying method is a supercritical drying method, the drying temperature is usually 35 to 45 ° C, preferably 38 to 42 ° C. Further, supercritical drying is preferably carried out using liquid carbon dioxide under a pressure of usually 5 to 15 MPa, preferably 8 to 12 MPa. The time required for the gel-like composition to be solvent-substituted with liquid carbon dioxide under pressure and to reach drying through a supercritical state by heating is not particularly limited, but is usually 1 to 15 hours, preferably 1 to 8 hours. is there.

When the drying method is a supercritical drying method, a dried product of cellulose nanofibers can be provided as an airgel.

When the above drying method is a freeze-drying method, the gel-like composition is generally frozen using liquid nitrogen or the like. The gel-like composition is preferably quick-frozen.

In the freeze-drying method, it is preferable to carry out under reduced pressure conditions, preferably at a temperature of usually room temperature or lower. The time for freeze-drying is not particularly limited, but is, for example, 24 to 48 hours.

When the drying method is the freeze-drying method, the dried product of cellulose nanofibers can be provided as a cryogel.

When the above drying method is an evaporation drying method, the drying temperature is usually 30 to 110 ° C, preferably 30 to 90 ° C. The drying time is not particularly limited, but is usually 1 to 48 hours, preferably 1 to 12 hours.

When the drying method is the evaporation drying method, the dried product of cellulose nanofibers can be provided as xerogel.

An embodiment of the present invention will be described below. The following examples are examples of the present invention, and the present invention is not limited to these examples.

Example 1
A cellulose modified product and a cellulose nanofiber dispersion were prepared by the following procedure.

(1) Reagents / Materials Cellulose: Bleached Kraft Pulp (Fletcher Challenge Canada "Mackenzie")
TEMPO: Commercial product (manufactured by Tokyo Chemical Industry, 98%)
Sodium hypochlorite: Commercial product (manufactured by Wako Junyakusha, Cl: 5%)
Sodium bromide: Commercial product (manufactured by Wako Junyakusha)

(2) Oxidation Step Bleached kraft pulp having a dry weight of 10 g was allowed to stand overnight in 500 mL of ion-exchanged water in a 2 L glass beaker to swell the pulp. To this, 0.1 g of TEMPO and 1 g of sodium bromide were added and stirred to prepare a pulp suspension. Further, 5 mmoL / g of sodium hypochlorite was added per weight of cellulose with stirring. At this time, about 1N of sodium hydroxide aqueous solution was added to maintain the pH of the pulp suspension at about 10.5. Then, the reaction was carried out for 2 hours, and 10 g of ethanol was added to stop the reaction to obtain oxidized cellulose in which a carboxyl group was introduced into cellulose. The carboxyl group introduced at this time forms a salt having a sodium ion derived from the reaction reagent remaining in the reaction medium as a counter ion.

Subsequently, 0.5 N hydrochloric acid was added dropwise to lower the pH to 2. Cellulose was filtered off using a glass filter, washed 3 times with 0.05 N hydrochloric acid to make the carboxyl group a carboxylic acid, and then washed 5 times with pure water to obtain wet cellulose oxide with a solid content concentration of 20%. Got The obtained oxidized cellulose was calculated to have a carboxyl group amount of 1.6 mmoL per dry weight of cellulose by neutralization titration with sodium hydroxide.

(3) Counterion Substitution Step The cellulose oxide prepared above is added with water so as to have a solid content concentration of 5% to form a suspension, and an organic onium compound as an alkaline species is added thereto with respect to the amount of carboxyl groups of the cellulose oxide. 0.0 equivalent was added. After stirring for 2 hours, the cellulose oxide was filtered off using a glass filter to obtain counterion-substituted cellulose oxide. Here, in the counterion substitution step, it was confirmed that the counterion-substituted oxidized cellulose can be obtained even when ethanol is used instead of water.

Be counterion substitution occurs, by FTIR analysis, pair after ion exchange step to reduce the absorption of acid type carboxyl groups near 1720 cm ^-1 wherein the counterion replacement step before testing samples had the, 1610 cm ^- It was also confirmed by the shift to salt-type absorption near ¹ .

The countercations of the test samples obtained in (1) to (3) above and their properties are as shown in Table 1 below. In Table 1, the test sample of Test Group 1 was obtained by (2) oxidation step without performing (3) counterion substitution step. The test samples in Test Groups 2 to 10 were obtained by using the bromide salt of each counterion in the (3) counterion substitution step as an organic onium compound. The physical properties shown in Table 1 mean the properties of the bromide salt of each counterion.

(4) Solvent Substitution Step The oxidized cellulose counterion-substituted as described above was solvent-substituted using each of the substituted solvents. As each substitution solvent, an organic solvent (methanol, ethanol, isopropyl alcohol, acetone or t-butyl alcohol) or water was used.

When the substitution solvent is an organic solvent, the antiionically substituted cellulose oxide is added to a solution in which water and the substitution solvent are mixed so that the volume fraction is 2: 1 and the mixture is stirred for 30 minutes and then oxidized using a glass filter. Cellulose was filtered and recovered. Subsequently, in the same manner, cellulose oxide was added to a solution in which water and a substitution solvent were 1: 1 and stirred for 30 minutes for filtration and recovery, and then washed and recovered with the substitution solvent three times to replace the solvent. The treated cellulose oxide was obtained.

When the replacement solvent was water, counterion-substituted cellulose oxide was added to water, and after stirring for 30 minutes, the cellulose oxide was filtered and recovered using a glass filter. Subsequently, in the same manner, cellulose oxide was added to water, stirred for 30 minutes, separated and recovered, and then washed and recovered with water three times to obtain solvent-substituted cellulose oxide.

(5) Dispersion Step The solvent-placed cellulose oxide was added to a substitution solvent (dispersion medium) to prepare a mixed solution having a solid content concentration of 0.1%. Then, 25 mL of the mixed solution is defibrated by treating it at 20 ° C. for 16 minutes using an ultrasonic homogenizer, placed in a centrifuge tube having a volume of 50 mL, centrifuged (12000 g, 10 minutes), and a residue (precipitate). ) And the dispersion (supernatant) were separated by decantation, and the weight of each was measured.

(6) Evaluation of dispersion yield Next, the dispersion yield was calculated according to the following formula.

Note that FIG. 1 is a photograph of the cellulose nanofiber dispersion (dispersion liquid) described in Test Group 10 dispersed in each organic solvent. As shown in FIG. 1A, the dispersion of this example was a transparent dispersion. Further, as shown in FIG. 1 (b), it is confirmed that it exhibits birefringence, and it can be seen that it is completely nano-dispersed in each organic solvent. In addition, in the test groups 7 to 9, it was confirmed that the birefringence was completely nano-dispersed in each organic solvent.

Example 2
Ethanol dispersion of cellulose oxide nanofibers is carried out in the same manner as in Test Group 5, except that the defibration treatment (150 Pa, 5 times) is performed using a high-pressure homogenizer (Star Burst, Sugino Machine) in the dispersion step (5) of Example 1. The liquid was prepared.

Next, the obtained ethanol dispersion was concentrated under reduced pressure to a concentration of cellulose nanofibers of 0.5%. Next, 5 mL of glacial acetic acid was added to 10 g of the ethanol dispersion to obtain a gel (also referred to as “cellulose nanofiber arcogel”).

The obtained cellulose nanofiber arcogel was placed in a supercritical drying device, subjected to solvent substitution with liquefied CO2 for 8 hours, dried in a supercritical state (40 ° C., 10 MPa) for 1 hour, and the cellulose nanofiber airgel (aerogel of cellulose nanofibers). 0.05 g) was obtained. The morphology of the cellulose nanofiber airgel was as shown in FIG.

It was also confirmed that the cellulose nanofiber arcogel can be evaporated and dried by heating to obtain a cellulose nanofiber xerogel.

Example 3
An aqueous dispersion of cellulose oxide nanofibers was prepared in the same manner as in Test Group 1 of Example 1 without performing a counterion exchange step.

Next, the obtained aqueous dispersion was concentrated under reduced pressure to a concentration of cellulose nanofibers of 0.5%. Next, 5 mL of hydrochloric acid was added to 10 g of the water spray to gel. When the obtained gel was allowed to stand in 100 mL of ethanol for solvent substitution to obtain a cellulose nanofiber alcohol gel, it was necessary to leave the gel in ethanol for 8 hours 6 times. there were. It was confirmed that the raw material cellulose nanofiber arcogel for obtaining the cellulose nanofiber airgel by supercritical drying can be obtained more efficiently by performing the counterion substitution step as described in Example 2.

According to the first aspect of the present invention, it is possible to provide cellulose nanofibers having excellent dispersibility in an organic solvent.
Further, according to the second aspect of the present invention, the cellulose nanofibers can be efficiently dried.

Claims (18)

1. A cellulose nanofiber in which a carboxyl group and a quaternary organic onium ion as a counter ion of the carboxyl group are introduced.
   When the quaternary organic onium ion forms a salt together with the bromide ion, the melting point of the salt measured according to JIS-K7121 is 100 ° C. or lower.
   The dispersion yield of the cellulose nanofibers measured by the following test method is higher when the dispersion medium is an organic solvent than when the dispersion medium is water.
   Test method: At 25 ° C., cellulose nanofibers having a solid content concentration of 0.1% by weight in a dispersion medium were centrifuged at 12,000 g for 10 minutes to separate the precipitate from the supernatant, and the obtained precipitate was obtained. Based on the weight of the product and the supernatant, the dispersion yield is calculated according to the following formula.
   

   
2. The cellulose nanofiber according to claim 1, wherein the quaternary organic onium ion is at least one selected from a quaternary ammonium ion and a quaternary phosphonium ion.
3. The cellulose nanofiber according to claim 1 or 2, wherein the quaternary organic onium ion is represented by the following formula (1).
   

   

   [In the formula, M represents a nitrogen atom or a phosphorus ^atom, R ^1, R 2, ^{R 3} and ^{R 4} represents a hydrocarbon ^group, R ^1, R 2, hydrocarbon represented by ^{R 3} and ^{R 4} At least one of the groups has 6 or more carbon atoms. ]
4. All hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ have 6 or more carbon atoms, and at least among the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ^4. One carbon number is 8 or more,
   The cellulose nanofiber according to claim 3, wherein the total number of carbon atoms of all the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ is 30 or more.
5. The cellulose nanofiber according to claim 3 or 4, wherein three or more of the hydrocarbon groups represented by R ¹ , R ² , R ³ and R ⁴ are aliphatic hydrocarbon groups.
6. M excluding quaternary organic onium ion is and R ¹ a phosphorus ^atom, R ^2, R ³ and R ⁴ are the same, the cellulose nanofiber according to any one of claims 3-5.
7. The cellulose nanofiber according to any one of claims 1 to 6, which contains an organic solvent as a dispersion medium.
8. The cellulose nanofiber according to any one of claims 1 to 7, wherein the relative permittivity of the organic solvent is 75 or less.
9. The cellulose nanofiber according to any one of claims 1 to 8, wherein the organic solvent is a water-soluble organic solvent.
10. The organic solvent is methanol, ethanol, isopropyl alcohol, t-butyl alcohol, acetone, ethyl acetate, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone and N-methyl. The cellulose nanofiber according to any one of claims 1 to 9, which is at least one selected from the group consisting of acetamide.
11. The cellulose nanofiber according to any one of claims 1 to 10, wherein the dispersion yield is 25% or more when the dispersion medium is an organic solvent.
12. The cellulose nanofiber according to any one of claims 1 to 11, wherein the dispersion yield when the dispersion medium is water is 20% or less.
13. The cellulose nanofiber according to any one of claims 1 to 12, wherein the content of the carboxyl group is 0.1 mm or more and 3.0 mm or less per dry weight of the cellulose nanofiber.
14. The dried cellulose nanofiber according to any one of claims 1 to 13.
15. A method for producing a dried product of cellulose nanofibers.
    Including a step of contacting a cellulose nanofiber dispersion with an acid to obtain a gel-like composition and a step of drying the gel-like composition to obtain a dried cellulose nanofiber.
    A method, wherein the cellulose nanofiber dispersion contains a cellulose nanofiber in which a carboxyl group and a quaternary organic onium ion as a counterion of the carboxyl group are introduced, and an organic solvent as a dispersion medium.
16. The method according to claim 15, wherein the drying is carried out by a supercritical drying method, a freeze drying method or an evaporation drying method.
17. The method according to claim 15 or 16, wherein the acid is brought into contact with the cellulose nanofiber dispersion in a substantially anhydrous state.
18. The method according to any one of claims 15 to 17, wherein the dried body of the cellulose nanofiber is airgel, cryogel or xerogel.

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