JPWO2010134357A1 - Method for producing cellulose nanofiber dispersion, cellulose nanofiber dispersion, cellulose nanofiber molded body, and cellulose nanofiber composite - Google Patents

Abstract

INDUSTRIAL APPLICABILITY The present invention provides a method for producing a cellulose nanofiber dispersion that can be suitably used for compounding with a wide range of organic solvent-soluble polymer materials. According to the method for producing a cellulose nanofiber dispersion of the present invention, when cellulose nanofibers having a carboxylate group are dispersed in a medium containing an organic solvent, the cellulose nanofibers are dispersed according to the type of the organic solvent. A substitution step of substituting a group from a carboxylate type to a carboxylic acid type is performed.

Description

The present invention relates to a method for producing a cellulose nanofiber dispersion, a cellulose nanofiber dispersion, a cellulose nanofiber molded article, and a cellulose nanofiber composite.
This application claims priority on May 22, 2009 based on Japanese Patent Application No. 2009-124408 for which it applied to Japan, and uses the content here.

  The present inventors oxidize natural fiber materials such as cellulose in the presence of a TEMPO (2,2,6,6-tetramethyl-1-piperidine-N-oxyl) catalyst and perform a mechanical fibrillation treatment. Thus, a method for producing highly crystalline ultrafine fibers (nanofibers) having a diameter of several nanometers has already been proposed (see Patent Document 1). By this production method, each cellulose nanofiber was separated in water, and a cellulose nanofiber dispersion, which was a novel material that could be applied to various uses, could be obtained.

JP 2008-001728 A

  By the way, when cellulose nanofibers are compounded with other materials such as polyvinyl alcohol (PVA), it is necessary to disperse the cellulose nanofibers in the same solvent as the material to be complexed. However, in the cellulose nanofiber dispersion obtained by the production method described in Patent Document 1, since the dispersion medium was water, there were limitations on the materials to be combined. Moreover, even if the cellulose nanofibers obtained by TEMPO catalytic oxidation are simply put into an organic solvent, they are aggregated and precipitated and cannot be uniformly dispersed.

The present invention has been made in view of the above-mentioned problems of the prior art, and is a cellulose nanofiber dispersion that can be suitably used for compounding with a wide range of organic solvent-soluble polymer materials and a method for producing the same. Is one of the purposes.
Another object of the present invention is to provide a cellulose nanofiber molded article and a cellulose nanofiber composite using the cellulose nanofiber dispersion.

According to the method for producing a cellulose nanofiber dispersion of the present invention, when cellulose nanofibers having a carboxylate group are dispersed in a medium containing an organic solvent, the cellulose nanofibers may be dispersed according to the type of the organic solvent. A substitution step of substituting a group from a carboxylate type to a carboxylic acid type is performed.
According to this production method, the carboxylate type group on the surface of the nanofiber is replaced with a carboxylic acid type group according to the type of the organic solvent, so that the cellulose nanofiber is modified according to the nature of the organic solvent. , Cellulose nanofibers can be dispersed in a wide range of solvents. Thereby, the removal of a liquid component is easy and the cellulose nanofiber dispersion liquid which can be used suitably also for composite_combination with a wide range of materials can be manufactured easily.

In the substitution step, the substitution rate of the group to the carboxylic acid type is preferably varied based on the type of the organic solvent.
According to this production method, since the surface state of the cellulose nanofiber is controlled by the substitution rate that can be easily controlled by the condition management of the substitution step, it is possible to easily produce the cellulose nanofiber dispersion using various organic solvents. it can.

The method for producing a cellulose nanofiber dispersion of the present invention comprises a step of dispersing cellulose nanofibers having a carboxylate group in an aqueous solvent to prepare a cellulose nanofiber aqueous dispersion, and the cellulose nanofiber aqueous dispersion. And adding one or two organic solvents selected from dimethyl sulfoxide and N, N-dimethylformamide, and removing the aqueous solvent from the cellulose nanofiber aqueous dispersion to which the organic solvent is added. And a process.
According to this production method, a cellulose nanofiber dispersion using one or two organic solvents selected from dimethyl sulfoxide and N, N-dimethylformamide can be easily produced.

The method for producing a cellulose nanofiber dispersion of the present invention comprises a step of dispersing cellulose nanofibers having a carboxylate group in an aqueous solvent to prepare a cellulose nanofiber aqueous dispersion, and the cellulose nanofiber aqueous dispersion. And adding at least a part of the groups from a carboxylate type to a carboxylic acid type to gel the cellulose nanofibers, and adding the cellulose nanofiber gel to dimethyl sulfoxide, N, A step of adding one or more organic solvents selected from N-dimethylacetamide and N, N-dimethylformamide, and a step of removing water from the gel to which the organic solvent has been added. It is characterized by that.
According to this production method, a cellulose nanofiber dispersion using one or more organic solvents selected from dimethyl sulfoxide, N, N-dimethylacetamide, and N, N-dimethylformamide is easily produced. be able to.

The method for producing a cellulose nanofiber dispersion of the present invention comprises a step of dispersing cellulose nanofibers having a carboxylate group in an aqueous solvent to prepare a cellulose nanofiber aqueous dispersion, and the cellulose nanofiber aqueous dispersion. An acid is added to at least a part of the group from a carboxylate type to a carboxylic acid type, and the cellulose nanofiber is gelled; and the gel is dimethyl sulfoxide, N, N-dimethylacetamide, And supplying one or more organic solvents selected from N, N-dimethylformamide, substituting the solvent contained in the gel, and dispersing the gel after solvent replacement in the organic solvent; It is characterized by having.
According to this production method, a cellulose nanofiber dispersion using one or more organic solvents selected from dimethyl sulfoxide, N, N-dimethylacetamide, and N, N-dimethylformamide is easily produced. be able to.

The method for producing a cellulose nanofiber dispersion of the present invention comprises a step of dispersing cellulose nanofibers having a carboxylate group in an aqueous solvent to prepare a cellulose nanofiber aqueous dispersion, and the cellulose nanofiber aqueous dispersion. 80% or more of the groups are changed from a carboxylate type to a carboxylic acid type by adding an acid to the gel, and the cellulose nanofibers are gelled, and N, N-dimethylacetamide and N, N are added to the gel. -Supplying one or two organic solvents selected from dimethylformamide, replacing the solvent contained in the gel, and dispersing the gel after solvent replacement in the organic solvent. Features.
According to this production method, a cellulose nanofiber dispersion using one or two organic solvents selected from N, N-dimethylacetamide and N, N-dimethylformamide can be easily produced.

The method for producing a cellulose nanofiber dispersion according to the present invention provides a nanofiber of oxidized cellulose by defibrating an oxidized cellulose having a carboxylate group obtained by oxidizing natural cellulose in an organic solvent. It has the process to disperse | distribute. It is characterized by the above-mentioned.
According to this production method, a cellulose nanofiber dispersion using an organic solvent such as dimethylsulfoxide can be easily produced without previously dispersing the cellulose nanofibers in an aqueous solvent.

Prior to the dispersing step, it is preferable to have a step of stirring the oxidized cellulose suspension for a predetermined time.
According to this production method, part of the oxidized cellulose is defibrated by the stirring treatment, so that defibration in an organic solvent is facilitated, and the cellulose nanofiber dispersion can be produced more easily.

The method for producing a cellulose nanofiber dispersion of the present invention comprises adding an acid to an aqueous suspension of oxidized cellulose having carboxylate type groups obtained by oxidizing natural cellulose, so that 80% or more of the groups are added. Replacing the carboxylate type with a carboxylic acid type, and dispersing the oxidized cellulose having the group substituted with a carboxylic acid type in an organic solvent to disperse the oxidized cellulose nanofibers; It is characterized by having.
According to this production method, a cellulose nanofiber dispersion using an organic solvent such as N, N-dimethylformamide can be easily produced without previously dispersing cellulose nanofibers in an aqueous solvent.

Prior to the dispersing step, it is preferable to have a step of stirring the oxidized cellulose suspension for a predetermined time.
According to this production method, part of the oxidized cellulose is defibrated by the stirring treatment, so that defibration in an organic solvent is facilitated, and the cellulose nanofiber dispersion can be produced more easily.

Next, the cellulose nanofiber dispersion of the present invention is a medium containing cellulose nanofibers having carboxylate type groups, one or two organic solvents selected from dimethyl sulfoxide and N, N-dimethylformamide. It is characterized by being dispersed in.
According to this configuration, since the medium is an organic solvent, it is easy to remove the liquid component, and it is possible to provide a cellulose nanofiber dispersion that can be suitably used for compounding with a wide range of materials. .

In the cellulose nanofiber dispersion liquid of the present invention, cellulose nanofibers having a carboxylate type group and a carboxylic acid type group are selected from dimethyl sulfoxide, N, N-dimethylacetamide, and N, N-dimethylformamide. It is characterized by being dispersed in a medium containing one or more organic solvents.
According to this configuration, since the medium is an organic solvent, it is easy to remove the liquid component, and it is possible to provide a cellulose nanofiber dispersion that can be suitably used for compounding with a wide range of materials. .

The cellulose nanofiber dispersion liquid of the present invention comprises a cellulose nanofiber having a carboxylate group, and one or more organic solvents selected from N, N-dimethylacetamide and N, N-dimethylformamide. It is characterized by being dispersed in a medium containing it.
According to this configuration, since the medium is an organic solvent, it is easy to remove the liquid component, and it is possible to provide a cellulose nanofiber dispersion that can be suitably used for compounding with a wide range of materials. .

Next, the cellulose nanofiber molded product of the present invention is obtained by removing the liquid component while holding the cellulose nanofiber dispersion in a predetermined shape.
According to this configuration, it is possible to provide a cellulose nanofiber molded article that can well express the functionality of cellulose nanofibers and is excellent in manufacturability.

Next, the cellulose nanofiber composite of the present invention is a composite dispersion obtained by mixing the cellulose nanofiber dispersion containing the cellulose nanofiber as the first material and the liquid material containing the second material. It was obtained by using.
According to this configuration, it is possible to provide a cellulose nanofiber composite that can favorably exhibit the functionality of cellulose nanofibers and that is excellent in manufacturability.

Moreover, according to the present invention, it is possible to disperse cellulose nanofibers in an organic solvent, which has been impossible in the past, by a simple technique.
Since the cellulose nanofiber dispersion of the present invention is an organic solvent, it becomes a dispersion that can be easily combined with a wide range of organic solvent-soluble polymer materials.
Moreover, according to this invention, the cellulose nanofiber dispersion and the cellulose nanofiber composite_body | complex excellent in manufacturability can be provided using the cellulose nanofiber dispersion liquid of this invention.

It is explanatory drawing which shows the 1st manufacturing method of this invention. It is explanatory drawing which shows the 2nd manufacturing method of this invention. It is explanatory drawing which shows the 4th manufacturing method of this invention. It is explanatory drawing which shows the 5th manufacturing method of this invention. It is explanatory drawing which shows the 6th manufacturing method of this invention. It is explanatory drawing which shows the 7th manufacturing method of this invention. The photograph of the cellulose nanofiber dispersion liquid concerning a 1st example. The light transmittance measurement result of the cellulose nanofiber dispersion liquid which concerns on 1st Example. The photograph of the cellulose nanofiber dispersion liquid concerning a 2nd example. The photograph of the cellulose nanofiber dispersion liquid concerning a 2nd example. The photograph of the cellulose nanofiber dispersion liquid concerning a 3rd example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Method for producing cellulose nanofiber dispersion)
The manufacturing method of the cellulose nanofiber dispersion liquid of the present embodiment selects and uses the following first to third manufacturing methods according to the type of the organic solvent, so that the cellulose nanofibers are uniformly in the organic solvent. A dispersed cellulose nanofiber dispersion is produced.

<First manufacturing method>
The 1st manufacturing method of a cellulose nanofiber dispersion has the following processes 1A-1C. FIG. 1 is an explanatory view showing a first manufacturing method.
(1A) Step of preparing cellulose nanofiber aqueous dispersion by dispersing cellulose nanofiber having carboxylate type group in aqueous solvent (1B) Step of adding organic solvent to cellulose nanofiber aqueous dispersion (1C) A step of removing an aqueous solvent from an aqueous dispersion of cellulose nanofibers to which an organic solvent is added

"Process 1A"
First, step 1A will be described.
Step 1A is a step of preparing an aqueous dispersion of cellulose nanofibers having a carboxylate type group. The method for producing the cellulose nanofiber aqueous dispersion having the above structure is not particularly limited, but the method for producing cellulose nanofiber by TEMPO catalytic oxidation already proposed by the present inventors is used. Is preferred.
That is, natural cellulose is used as a raw material, an N-oxyl compound such as TEMPO (2,2,6,6-tetramethyl-1-piperidine-N-oxyl) is used as an oxidation catalyst in an aqueous solvent, and an oxidizing agent is allowed to act. It is preferable to prepare a cellulose nanofiber aqueous dispersion by a production method including an oxidation treatment step of oxidizing natural cellulose by a method and a dispersion step of dispersing natural cellulose after the oxidation treatment step in a medium.

  In the oxidation treatment step, first, a dispersion in which natural cellulose is dispersed in water is prepared. Natural cellulose is purified cellulose isolated from cellulose biosynthetic systems such as plants, animals, and bacteria-producing gels. Specifically, it is isolated from softwood pulp, hardwood pulp, cotton pulp such as cotton linter and cotton lint, non-wood pulp such as straw pulp and bagasse pulp, bacterial cellulose, cellulose isolated from sea squirt, seaweed A cellulose etc. can be illustrated.

  Moreover, you may give the process which expands surface areas, such as beating, to the natural cellulose isolated and refine | purified. Thereby, reaction efficiency can be improved and productivity can be improved. In addition, it is preferable to use natural cellulose that has been stored in an undried state after isolation and purification. By storing in an undried state, it is possible to keep the microfibril bundle in an easily swellable state, so that the reaction efficiency is improved and cellulose nanofibers with a small fiber diameter are easily obtained.

  In the oxidation treatment step, water is typically used as a dispersion medium for natural cellulose in the reaction solution. The natural cellulose concentration in the reaction solution is not particularly limited as long as the reagent (oxidant, catalyst, etc.) can be sufficiently dissolved. Usually, the concentration is preferably about 5% or less with respect to the weight of the reaction solution.

An N-oxyl compound is used as a catalyst added to the reaction solution. As the N-oxyl compound, TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) and a TEMPO derivative having various functional groups at the C4 position can be used. Examples of the TEMPO derivative include 4-acetamido TEMPO, 4-carboxy TEMPO, 4-phosphonooxy TEMPO, and the like. In particular, TEMPO and 4-acetamido TEMPO have obtained favorable results in the reaction rate.
A catalytic amount is sufficient for the addition of the N-oxyl compound. Specifically, it may be added in a range of 0.1 to 4 mmol / L with respect to the reaction solution. Preferably, it is the addition amount range of 0.1-2 mmol / L.

  Further, depending on the type of oxidizing agent, a catalyst component in which a bromide or iodide is combined with an N-oxyl compound may be used. For example, ammonium salt (ammonium bromide, ammonium iodide), bromide or alkali metal iodide (bromide such as lithium bromide, potassium bromide, sodium bromide, lithium iodide, potassium iodide, sodium iodide, etc. Iodide), bromide or alkaline earth metal iodides (calcium bromide, magnesium bromide, strontium bromide, calcium iodide, magnesium iodide, strontium iodide, etc.) can be used. These bromides and iodides can be used alone or in combination of two or more.

  As the oxidizing agent, hypohalous acid or a salt thereof (hypochlorous acid or a salt thereof, hypobromous acid or a salt thereof, hypoiodous acid or a salt thereof, etc.), a halogenous acid or a salt thereof (chlorous acid or a salt thereof) Salts thereof, bromous acid or salts thereof, iodic acid or salts thereof, perhalogen acids or salts thereof (perchloric acid or salts thereof, periodic acid or salts thereof), halogens (chlorine, bromine, iodine, etc.) ), Halogen oxides (ClO, ClO2, Cl2O6, BrO2, Br3O7, etc.), nitrogen oxides (NO, NO2, N2O3, etc.), peracids (hydrogen peroxide, peracetic acid, persulfuric acid, perbenzoic acid, etc.) It is. These oxidizing agents can be used alone or in combination of two or more. Further, it may be used in combination with an oxidase such as laccase. The content of the oxidizing agent is preferably in the range of 1 to 50 mmol / L.

  As hypohalite, in the case of hypochlorous acid, alkali metal salts such as lithium hypochlorite, potassium hypochlorite, sodium hypochlorite, calcium hypochlorite, hypochlorous acid, etc. Examples include magnesium, alkaline earth metal salts such as strontium hypochlorite, and ammonium hypochlorite. Moreover, hypobromite and hypoiodite corresponding to these can also be used.

  Examples of halous acid salts include, in the case of chlorous acid, alkali metal salts such as lithium chlorite, potassium chlorite, and sodium chlorite, calcium chlorite, magnesium chlorite, and strontium chlorite. Examples thereof include alkaline earth metal salts and ammonium chlorite. In addition, bromite and iodate corresponding to these can also be used.

  As perhalogenates, for example, in the case of perchlorates, alkali metal salts such as lithium perchlorate, potassium perchlorate, sodium perchlorate, calcium perchlorate, magnesium perchlorate, strontium perchlorate Examples thereof include alkaline earth metal salts such as ammonium perchlorate. Moreover, perbromate and periodate corresponding to these can also be used.

As a preferable oxidizing agent in the present invention, an alkali metal hypohalite or an alkali metal halite can be mentioned, and an alkali metal hypochlorite or an alkali metal chlorite is more preferably used. .
The catalyst described above may be appropriately selected according to the kind of the oxidizing agent. For example, when an alkali metal hypochlorite is used as the oxidizing agent, an N-oxyl compound, bromide or iodide, It is preferable to use a catalyst component in combination with N, and when an alkali metal chlorite is used as the oxidizing agent, it is preferable to use an N-oxyl compound alone as the catalyst component.

  Hereinafter, a typical oxidation process will be described with two specific examples.

[First example of oxidation treatment step]
In the first example of the oxidation treatment step, a cellulose raw material suspended in water, an N-oxyl compound (such as TEMPO) and an alkali metal bromide (or alkali metal iodide), and hypochlorous acid as an oxidizing agent A reaction solution to which sodium (hypochlorite) is added is prepared, and the oxidation reaction is allowed to proceed with stirring as necessary under a temperature condition of 0 ° C. to room temperature (10 ° C. to 30 ° C.).

  After the completion of the reaction, a treatment for decomposing an oxidizing agent (such as sodium hypochlorite) is performed as necessary, and then the purified fibrous TEMPO-catalyzed oxidized cellulose (hereinafter referred to as “filtered” TEMPO-catalyzed oxidized cellulose (hereinafter referred to as “filtered cellulose tempo catalyst”) , Referred to as oxidized cellulose).

  In the oxidation treatment process of the first example, a carboxyl group is generated with the progress of the reaction, so that the pH of the reaction solution is lowered. Therefore, in order to sufficiently advance the oxidation reaction, it is preferable to maintain the reaction system in an alkaline region, for example, in the range of pH 9 to 12 (preferably 10 to 11). The pH of the reaction system can be adjusted by appropriately adding an alkali (such as an aqueous solution containing an alkali metal component such as an aqueous sodium hydroxide solution) to the reaction system. Moreover, in the oxidation treatment process of the first example, the pH of the reaction solution decreases with the progress of the oxidation reaction, so that the point in time when the progress of the pH decrease is not recognized can be set as the reaction end point.

  Note that the reaction temperature in the oxidation treatment step of the first example can be higher than room temperature, and the reaction efficiency can be increased by reacting at a high temperature. On the other hand, since chlorine gas is easily generated from sodium hypochlorite, it is preferable to prepare a chlorine gas treatment system when the reaction is performed at a high temperature.

[Second Example of Oxidation Process]
Next, in a second example of the oxidation reaction, a reaction solution in which an N-oxyl compound and sodium chlorite (chlorite) as an oxidizing agent are added to a suspension of a cellulose raw material in water. The oxidation reaction is allowed to proceed with stirring as necessary under a temperature condition of room temperature to about 100 ° C. The process for extracting the oxidized cellulose after completion of the oxidation reaction is the same as in the case of the first example described above.

  In the oxidation treatment process of the second example, the pH of the reaction solution is maintained in a neutral to acidic range. More specifically, a pH range of 4 to 7 is preferable. In particular, care should be taken that the pH of the reaction solution does not exceed 8. This is to prevent a beta elimination reaction due to an aldehyde group temporarily generated at the C6 position of cellulose.

Furthermore, it is preferable to add a buffer to the reaction solution. As the buffer solution, various buffer solutions such as a phosphate buffer solution, an acetate buffer solution, a citrate buffer solution, a borate buffer solution, a tartaric acid buffer solution, and a Tris buffer solution can be used.
By suppressing the pH change during the reaction using a buffer solution, it is not necessary to continuously add acid or alkali to maintain the pH, and it is not necessary to install a pH meter. And since addition of an acid or an alkali is unnecessary, a reaction container can be sealed.

  In the second example, an oxidizing agent that can also oxidize an aldehyde group generated by oxidation of a hydroxyl group is used as the oxidizing agent. Examples of such oxidizing agents include halous acid such as sodium chlorite or salts thereof, a mixture of hydrogen peroxide and oxidase (laccase), peracid (persulfuric acid (such as potassium hydrogen persulfate), peracetic acid, Examples thereof include perbenzoic acid.

By using an oxidizing agent capable of oxidizing an aldehyde group to a carboxyl group, generation of an aldehyde group at the C6 position can be prevented. In the oxidation reaction using an N-oxyl compound as a catalyst, the primary hydroxyl group of the glucose component may be selectively oxidized to produce an intermediate containing an aldehyde group. However, since the oxidation reaction of the second example includes an oxidizing agent that oxidizes an aldehyde group, the intermediate aldehyde group is rapidly oxidized and converted to a carboxyl group.
Therefore, the beta elimination reaction caused by the aldehyde group can be prevented, and high molecular weight cellulose nanofibers can be obtained.

In addition, it is preferable to add hypohalous acid or a salt thereof on the premise that the above-described oxidizing agent is used as the main oxidizing agent. For example, the reaction rate can be greatly improved by adding a small amount of sodium hypochlorite. Sodium hypochlorite added to the reaction solution functions as an oxidizing agent for TEMPO, and the oxidized TEMPO oxidizes the primary hydroxyl group at the C6 position of cellulose to produce an aldehyde group at the C6 position. And the produced | generated aldehyde group is rapidly oxidized to a carboxyl group by the sodium chlorite which is a main oxidizing agent. Further, during the oxidation of the aldehyde group, sodium chlorite changes to sodium hypochlorite. Furthermore, the produced sodium hypochlorite is supplemented as an oxidizing agent for TEMPO.
Thus, by adding sodium hypochlorite or the like to the reaction solution, the oxidation reaction of TEMPO can be promoted and the reaction rate can be increased. The amount of hypohalite added is preferably about 1 mmol / L or less.

  Oxidized cellulose can be obtained through the oxidation treatment steps as described above. In the figure, the oxidized cellulose is indicated by the symbol P.

[Dispersion process]
Next, in the dispersion step, the oxidized cellulose obtained in the oxidation treatment step or the oxidized cellulose that has undergone the purification step is dispersed in the medium.
As a medium (dispersion medium) used for dispersion, an aqueous solvent is used. The aqueous solvent in the present embodiment is a solvent that is only water except for components that are inevitably mixed, or a mixed solvent of water and an organic solvent such as an alcohol compatible with less than 20% by weight of water. Typically, water is used as the dispersion medium. In the figure, water is indicated by the symbol W.

  A cellulose nanofiber dispersion liquid in which cellulose nanofibers are dispersed in a medium is obtained by the dispersion step. In the figure, a dispersion in which cellulose nanofibers are dispersed in an aqueous solvent is indicated by a symbol D1. In the cellulose nanofiber aqueous dispersion prepared in Step 1A, cellulose nanofibers in which a part of the C6-primary hydroxyl group of cellulose is oxidized to sodium carboxylate (sodium salt of carboxyl group) are uniformly in an aqueous solvent. Are distributed.

  In the case of the present embodiment, the concentration of the cellulose nanofiber aqueous dispersion is preferably in the range of 0.05% by weight to 2% by weight. More preferably, it is 0.1 weight% or more and 0.5 weight% or less. By setting it as such a range, substitution to the organic solvent in latter process 1B, 1C can be performed, without gelatinizing a cellulose nanofiber.

  Various devices can be used as a dispersion device (defibration device) used in the dispersion step. For example, a household mixer, an ultrasonic homogenizer, a high-pressure homogenizer, a biaxial kneading device, a defibrating device such as a stone mill can be used. In addition to these, a dispersion of cellulose nanofibers can be easily obtained with a defibrating apparatus generally used for household use or industrial production. In addition, if a defibrating apparatus having a strong and beating ability such as various homogenizers and various refiners is used, cellulose nanofibers having a small fiber diameter can be obtained more efficiently.

"Process 1B"
Next, in Step 1B, an organic solvent is added to the cellulose nanofiber aqueous dispersion.
The organic solvent used in the first production method is an organic solvent that can be dispersed without modifying cellulose nanofibers, and is selected from dimethyl sulfoxide (DMSO) and N, N-dimethylformamide (DMF). A seed or two organic solvents, or a mixed solvent obtained by adding a small amount (30% or less) of water to these organic solvents is used. In the figure, the obtained mixed solvent dispersion is indicated by a symbol D2.
The addition amount of the organic solvent is preferably changed as appropriate according to the type of the organic solvent and the composition of the mixed solvent, and is, for example, in the range of 20% to 80% with respect to the cellulose nanofiber aqueous dispersion.
In addition to the above, any organic solvent that can be dispersed without modifying cellulose nanofibers can be used.

"Process 1C"
Next, in Step 1C, the aqueous solvent is removed from the cellulose nanofiber aqueous dispersion to which the organic solvent has been added.
As the method for removing the aqueous solvent, any method can be used as long as it can selectively remove only the aqueous solvent from the mixed solvent of the aqueous solvent and the organic solvent. As a simple method, the boiling point of the aqueous solvent is usually about 80 to 100 ° C., and the boiling point of the organic solvent is 189 ° C. for dimethyl sulfoxide and 153 ° C. for N, N-dimethylformamide. Then, the method of removing the aqueous solvent by evaporating the solution (depressurizing distillation) can be mentioned. In the case of this embodiment, the heating temperature of the dispersion during evaporation is set to a temperature not exceeding 60 ° C.

Through the above steps 1A to 1C, a cellulose nanofiber dispersion liquid in which cellulose nanofibers are dispersed in an organic solvent can be produced. In the figure, the obtained organic solvent dispersion is indicated by reference numeral D3. The resulting cellulose nanofiber dispersion is a transparent suspension in which each cellulose nanofiber is uniformly dispersed in an organic solvent.
Even if an organic solvent is added to a dried cellulose gel or gel obtained by removing all or part of the liquid components from the aqueous dispersion of cellulose nanofibers obtained in step 1A, the cellulose nanofibers are uniformly in the organic solvent. It cannot be dispersed. Therefore, in the present embodiment, in Step 1A, a cellulose nanofiber aqueous dispersion in which cellulose nanofibers are uniformly dispersed in an aqueous solvent is first prepared, and the aqueous solvent in the aqueous dispersion is replaced with an organic solvent. . By using such a technique, an organic solvent can be added to the system while maintaining the dispersion state of the cellulose nanofibers, which makes it easy to obtain a cellulose nanofiber dispersion in which cellulose nanofibers are dispersed in the organic solvent. I was able to get it.

<Second production method>
The 2nd manufacturing method of a cellulose nanofiber dispersion has the following processes 2A-2D. FIG. 2 is an explanatory view showing a second manufacturing method.
(2A) Step of preparing cellulose nanofiber aqueous dispersion by dispersing cellulose nanofiber having carboxylate type group in aqueous solvent (2B) Adding acid to cellulose nanofiber aqueous dispersion, and carboxylating cellulose nanofiber Step of substituting a part of acid salt type group with carboxylic acid type group (2C) Step of adding organic solvent to gel of cellulose nanofiber in which part of group is substituted with carboxylic acid type (2D) Organic solvent Of removing aqueous solvent from cellulose nanofiber aqueous dispersion with added

"Process 2A"
Step 2A is the same as step 1A in the first manufacturing method described above. By this step 2A, an aqueous dispersion of cellulose nanofibers having a carboxylic acid sodium salt at the C6 position of cellulose is obtained.

"Process 2B"
Step 2B is a step of replacing a part of sodium contained in the cellulose nanofibers with hydrogen to form a carboxylic acid type group (—COOH group).
Cellulose nanofibers having a carboxylic acid sodium salt on the surface can ionize the carboxylic acid in water and disperse the cellulose nanofibers well by the charge repulsion between the carboxylic acid ions. However, since the degree of ionization described above may be low in an organic solvent, cellulose nanofibers aggregate and gel. Therefore, in step 2B, cellulose nanofibers having a carboxylic acid type group by replacing sodium with hydrogen are modified to convert them into a structure dispersible in an organic solvent.

  In the case of this embodiment, since only a part of the carboxylic acid sodium salt contained in the cellulose nanofibers is substituted with a carboxylic acid type group, the cellulose nanofibers are converted into an acidic solution (added with an acid) so as to obtain a desired substitution rate. The time to hold in the dispersion) is managed. In the figure, the acidic solution is indicated by the symbol Wa.

The holding time is set according to the type of acid added, the pH of the acidic solution, the content of cellulose nanofibers, and the like. If the pH of the acidic solution is constant, the substitution rate to the carboxylic acid type group becomes higher as the retention time is increased, and changes monotonously with the change in the retention time. Convenient.
In addition, the ratio of the carboxylate type group (carboxylic acid sodium salt) and the carboxylic acid type group in the cellulose nanofiber after the treatment can be measured using an analyzer such as FT-IR.

  In Step 2B, since the cellulose nanofiber aqueous dispersion may be maintained acidic, the type of acid is not particularly limited, and inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, hydrogen peroxide, citric acid, apple Any organic acid such as acid, lactic acid, adipic acid, sebacic acid, sodium sebacate, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid and gluconic acid can be used. It is preferable to use hydrochloric acid from the viewpoint of avoiding alteration and damage of the cellulose nanofibers due to acid and facilitating waste liquid treatment.

  When an acid is added to the cellulose nanofiber aqueous dispersion to form an acidic solution, the carboxylate ion contributing to the dispersibility of the cellulose nanofibers becomes a base and receives hydrogen to form a carboxylic acid type group. As a result, cellulose nanofibers aggregate and gel. In the figure, the resulting gel is indicated by the symbol G.

After that, when the time required to obtain a predetermined substitution rate has elapsed, the gelatinized cellulose nanofibers are collected by filtration and washed with water to obtain an acid and a reaction product (for example, sodium chloride when hydrochloric acid is used). Remove.

"Process 2C"
Next, in Step 2C, an organic solvent is added to the cellulose nanofiber gel obtained in Step 2B.
The organic solvent used in the second production method is an organic solvent that can disperse cellulose nanofibers containing both carboxylate type groups and carboxylic acid type groups. Dimethyl sulfoxide (DMSO) and water ( A mixed solvent having a content of 10% or more), one or two organic solvents selected from N, N-dimethylformamide (DMF) and N, N-dimethylacetamide (DMAc), or a small amount of these organic solvents ( A mixed solvent to which 30% or less of water is added is used. In the figure, the mixed solvent produced by the addition of the organic solvent is indicated by the symbol M.
The addition amount of the organic solvent is preferably changed as appropriate according to the type of the organic solvent and the composition of the mixed solvent. For example, the amount is 1 mL or more and 20 mL or less, more preferably 5 mL or more, per 1 g of cellulose nanofiber gel weight. 10 mL or less.
In addition to the above, any organic solvent that can disperse cellulose nanofibers partially introduced with a carboxylic acid type group can be used.

"Process 2D"
Next, in Step 2D, the aqueous solvent is removed from the cellulose nanofiber aqueous dispersion to which the organic solvent has been added. Step 2D is the same step as Step 1C in the first production method, and for example, the dispersion added with the organic solvent in Step 2C is evaporated at a temperature not exceeding 60 ° C. The solvent can be selectively removed. Thereafter, a cellulose nanofiber dispersion is obtained by subjecting the dispersion containing cellulose nanofibers and an organic solvent to a defibrating treatment. In the figure, the resulting dispersion is denoted by reference numeral D4. As the above-described defibrating treatment, a defibrating method similar to the dispersion treatment used in the previous step 1A can be used.
The cellulose nanofiber dispersion obtained by the above steps is a transparent suspension in which each cellulose nanofiber is uniformly dispersed in an organic solvent.

  The concentration of the cellulose nanofiber dispersion may be adjusted by adding an organic solvent to the dispersion containing the cellulose nanofiber and the organic solvent. The addition amount of the organic solvent in this case is appropriately set according to the amount of cellulose nanofiber dispersible in the organic solvent. For example, an organic solvent is added so that the concentration (g / mL) of cellulose nanofiber is 1% or less.

<Modification of Second Manufacturing Method>
In the second production method, the method of removing the aqueous solvent after adding the organic solvent to the cellulose nanofiber gel was used, but a method of replacing the solvent of the cellulose nanofiber gel with the organic solvent can also be used. . A production method using this solvent substitution method will be described below. In addition, since this modification has many in common with the said 2nd manufacturing method, description using a figure is abbreviate | omitted.

The manufacturing method according to the modified example includes the following steps 2A, 2B, 2E, and 2F.
(2A) Step of preparing cellulose nanofiber aqueous dispersion by dispersing cellulose nanofiber having carboxylate type group in aqueous solvent (2B) Adding acid to cellulose nanofiber aqueous dispersion, and carboxylating cellulose nanofiber A step of substituting a part of the acid salt type group with a carboxylic acid type group (2E) A step of washing the gel of cellulose nanofiber in which a part of the group is substituted with the carboxylic acid type with an excessive amount of organic solvent (2F) Step of dispersing cellulose nanofiber by adding organic solvent

Since Step 2A and Step 2B are the same as those in the second manufacturing method, description thereof is omitted in this example.
In step 2E, the aqueous solvent of the gelatinized cellulose nanofiber is replaced with an organic solvent. Since the cellulose nanofiber gel collected in the step 2B contains water, the gel is washed with an organic solvent to replace the water contained in the gel with the organic solvent.

In step 2F, the cellulose nanofiber concentration is adjusted by adding a predetermined amount of organic solvent to the cellulose nanofiber gel after solvent substitution in step 2E. Thereafter, a cellulose nanofiber dispersion liquid in which cellulose nanofibers are dispersed in an organic solvent can be produced by performing a fibrillation treatment such as ultrasonic treatment. The resulting cellulose nanofiber dispersion is a transparent suspension in which each cellulose nanofiber is uniformly dispersed in an organic solvent.
In addition, as said defibrating process, the defibrating method similar to the dispersion | distribution process used by previous process 1A can be used.

<Third production method>
The 3rd manufacturing method of a cellulose nanofiber dispersion has the following processes 3A-3D.
(3A) Step of preparing cellulose nanofiber aqueous dispersion by dispersing cellulose nanofiber having carboxylate type group in aqueous solvent (3B) Adding acid to cellulose nanofiber aqueous dispersion, and carboxylating cellulose nanofiber A step of replacing 80% or more of the acid salt group with a carboxylic acid type group (3C) A step of washing a cellulose nanofiber gel in which a part of the group is replaced with a carboxylic acid type with an excess amount of an organic solvent (3D ) Addition of organic solvent to disperse cellulose nanofibers

  In addition, since this modification is the same structure as the modification of the said 2nd manufacturing method except that the substitution rate from the carboxylic acid group to a carboxylic acid group in a cellulose nanofiber differs, description using the figure Is omitted.

"Process 3A"
Step 3A is the same as step 1A in the first manufacturing method described above. In Step 3A, an aqueous dispersion of cellulose nanofibers having a carboxylate type group (carboxylate sodium salt) is obtained.

"Process 3B"
Step 3B has the same procedure as Step 2B in the second manufacturing method, but in the third manufacturing method, 80% or more of sodium contained in cellulose nanofibers is replaced with hydrogen, and carboxylic acid is used. A type group (—COOH group).
In the case of this embodiment as well, a desired substitution rate of 80% or more can be obtained by managing the time for holding the cellulose nanofibers in the acidic solution (dispersed liquid added with acid). For example, when the replacement rate in step 2B of the second manufacturing method is 50%, if the holding time is doubled with the conditions other than the holding time being the same, the replacement rate is almost 100%. Can be obtained.
After maintaining in the acidic solution for a predetermined time, the cellulose nanofibers gelled in the acidic solution are collected by filtration and washed with water to remove the acid and the reaction product (for example, sodium chloride when using hydrochloric acid). Remove.

"Process 3C"
In Step 3C, as in Step 2E in the modification of the second production method, the cellulose nanofiber gel collected in a state containing water is washed with an organic solvent, so that water contained in the gel is obtained. Is replaced with an organic solvent.
The organic solvent used for the substitution in Step 3C is an organic solvent capable of dispersing cellulose nanofibers in which 80% or more of the carboxyl groups are carboxylic acid type groups, and N, N-dimethylformamide (DMF) and N , N-dimethylacetamide (DMAc) or a mixed solvent obtained by adding a small amount (30% or less) of water to these organic solvents.
The addition amount of the organic solvent is preferably changed as appropriate according to the type of the organic solvent and the composition of the mixed solvent. For example, the amount is 1 mL or more and 20 mL or less, more preferably 5 mL or more, per 1 g of cellulose nanofiber gel weight. 10 mL or less.
In addition to the above, any organic solvent that can disperse cellulose nanofibers partially introduced with a carboxylic acid type group can be used.

"Process 3D"
In step 3D, the concentration of cellulose nanofibers is adjusted by adding a predetermined amount of organic solvent to the gel of cellulose nanofibers after solvent replacement, as in step 2F in the modification of the second manufacturing method. To do. Thereafter, a cellulose nanofiber dispersion liquid in which cellulose nanofibers are dispersed in an organic solvent can be produced by performing a fibrillation treatment such as ultrasonic treatment. The resulting cellulose nanofiber dispersion is a transparent suspension in which each cellulose nanofiber is uniformly dispersed in an organic solvent.
In addition, as said defibrating process, the defibrating method similar to the dispersion | distribution process used by previous process 1A can be used.

  In the above first to third manufacturing methods, an aqueous dispersion of cellulose nanofibers is formed in advance, and then the organic solvent dispersion of cellulose nanofibers is replaced with an organic solvent for the dispersion. Decided to get. That is, the above method has an advantage that dispersion in an organic solvent can be easily performed once through the state of an aqueous dispersion of cellulose nanofibers. However, the above manufacturing method still requires room for improvement, such as the need for repeated defibrating treatments and the need to use a large amount of organic solvent for the replacement of the aqueous solvent with the organic solvent. .

In contrast, in the following fourth to seventh manufacturing methods, an organic solvent dispersion can be obtained without going through the state of the cellulose nanofiber aqueous dispersion. Hereinafter, it demonstrates in order.

<Fourth manufacturing method>
The 4th manufacturing method of a cellulose nanofiber dispersion has the following processes 4. FIG. 3 is an explanatory view showing a fourth manufacturing method.
(4) Step of preparing cellulose nanofiber aqueous dispersion by dispersing oxidized cellulose having carboxylate type group in organic solvent

"Process 4"
In step 4, oxidized cellulose or oxidized cellulose that has undergone a purification step is obtained in the same manner as the method shown in step 1A of the first manufacturing method described above.
Next, the obtained oxidized cellulose is fractionated and then dispersed in an organic solvent. In the figure, the organic solvent is indicated by symbol S. The organic solvent used for substitution in Step 4 is an organic solvent that can be obtained by defibrating oxidized cellulose and can disperse cellulose nanofibers, which are carboxylate-type groups, and includes dimethyl sulfoxide (DMSO) and its An aqueous solution, N, N-dimethylformamide (DMF) can be mentioned as a suitable thing. Although dispersion into nanofibers becomes difficult, N, N-dimethylacetamide (DMAc) can also be used.

The oxidized cellulose in the organic solvent is subjected to a defibrating process by the same defibrating method as the dispersion process used in the above-described step 1A, thereby producing a cellulose nanofiber dispersion liquid in which the cellulose nanofibers are dispersed in the organic solvent. . In the figure, the obtained organic solvent dispersion is indicated by reference numeral D5. Transparent cellulose nanofibers in which each cellulose nanofiber is uniformly dispersed in an organic solvent by separating and removing oxidized cellulose that remains undefibrated after defibration treatment by centrifugation A dispersion is obtained.

  As the dispersing device (defibrating device) used at this time, various devices can be used, but a device for defibrating oxidized cellulose by strong mechanical shearing can be suitably used. Various homogenizers and various refiners can be used. Such a strong defibrating device having a beating ability is preferable.

<Fifth manufacturing method>
The fifth production method of the cellulose nanofiber dispersion includes the following steps 5A and 5B. FIG. 4 is an explanatory view showing a fifth manufacturing method.
(5A) A step of adding an acid to an aqueous dispersion of oxidized cellulose having a carboxylate type group and replacing 80% or more of the carboxylate type group of the oxidized cellulose with a carboxylic acid type group. (5B) Carboxylic acid Process for preparing cellulose nanofiber aqueous dispersion by dispersing oxidized cellulose having type group in organic solvent

"Process 5A"
In step 5A, oxidized cellulose or oxidized cellulose that has undergone a purification step is obtained by a method similar to the method shown in step 1A of the first manufacturing method described above. And by adding an acid to the dispersion liquid in which oxidized cellulose is dispersed in an aqueous solvent and maintaining the acidity, a part of sodium contained in the carboxylate group of the oxidized cellulose is replaced with hydrogen, and 80% or more of the carboxyl groups are removed. It is a carboxylic acid type group. Of course, all carboxyl groups may be substituted with carboxylic acid type groups. Here, the acid shown in the above step 2B can be used. In the figure, the oxidized cellulose having a carboxylic acid type group obtained by acid treatment is indicated by symbol Pa.

"Process 5B"
In step 5B, as in step 4 in the fourth production method, cellulose nanofibers are dispersed in an organic solvent by separating the oxidized cellulose and dispersing it in an organic solvent, followed by fibrillation treatment. A cellulose nanofiber dispersion is prepared. In the figure, the obtained organic solvent dispersion is indicated by reference numeral D6.

  The organic solvent used for substitution in Step 5B is an organic solvent capable of dispersing cellulose nanofibers in which 80% or more of the carboxyl groups are carboxylic acid type groups, and N, N-dimethylformamide (DMF) and N N-dimethylacetamide (DMAc) can be mentioned as a suitable example. In addition, although dispersion | distribution to a nanofiber becomes difficult, dimethylsulfoxide (DMSO) and its aqueous solution can also be used.

  Transparent cellulose nanofibers in which each cellulose nanofiber is uniformly dispersed in an organic solvent by separating and removing oxidized cellulose that remains undefibrated after defibration treatment by centrifugation A dispersion is obtained.

  In the first to third production methods described above, the cellulose nanofibers are in a gel state when the cellulose nanofibers are dispersed in advance in an aqueous solvent and then replaced with an organic solvent, and a large amount of aqueous solvent is retained. It was. Therefore, a large amount of organic solvent is required when replacing the aqueous solvent of the gel with an organic solvent. In contrast, in the fourth and fifth production methods, oxidized cellulose is added to an organic solvent, and this is dispersed in the nanofibers in the organic solvent, so that the cellulose nanofibers do not go through the gel state, and the solvent A large amount of organic solvent used for exchange is not necessary.

<Sixth manufacturing method>
The sixth method for producing a cellulose nanofiber dispersion includes the following steps 6A and 6B. FIG. 5 is an explanatory view showing a sixth manufacturing method.
(6A) A step of performing a pretreatment in which an aqueous dispersion of oxidized cellulose having a carboxylate type group is stirred for a predetermined time to partially fibrillate the oxidized cellulose (6B) Dispersing the oxidized cellulose in an organic solvent Process for preparing cellulose nanofiber aqueous dispersion

"Process 6A"
In Step 6A, oxidized cellulose or oxidized cellulose that has undergone a purification step is obtained by the same method as that shown in Step 1A of the first production method described above. And the dispersion liquid which disperse | distributed the oxidized cellulose in the aqueous solvent is stirred for predetermined time beforehand.

  The stirring treatment can be performed using a generally known stirrer. For example, stirring by rotating a stirrer using a magnetic stirrer or a rotary blade type stirrer can be used.

  Part of the oxidized cellulose after the stirring treatment is defibrated. In the figure, the partially defibrated oxidized cellulose obtained by the stirring treatment is indicated by the symbol Pb. It can be detected by measuring the water retention value that the oxidized cellulose is partially defibrated by the stirring treatment.

"Process 6B"
In Step 6B, as in Step 4 in the previous fourth production method, the cellulose oxide after the agitation treatment is separated and dispersed in an organic solvent to perform a fibrillation treatment, whereby cellulose nanofibers are converted into an organic solvent. A dispersed cellulose nanofiber dispersion is prepared. The organic solvent used for substitution in Step 6B is an organic solvent capable of dispersing cellulose nanofibers, which are carboxylate type groups, dimethyl sulfoxide (DMSO) and its aqueous solution, N, N-dimethylformamide (DMF). ) Can be mentioned as suitable. Although dispersion into nanofibers becomes difficult, N, N-dimethylacetamide (DMAc) can also be used.

  If the dispersion becomes thick and stirring becomes difficult as the defibrating process proceeds, the same kind of organic solvent is added to dilute the dispersion, and the defibrating process is performed while decreasing the viscosity. If necessary, each cellulose nanofiber was uniformly dispersed in an organic solvent by separating and removing oxidized cellulose remaining undefibrated even after defibrating treatment by centrifugation. A transparent cellulose nanofiber dispersion is obtained. In the figure, the obtained organic solvent dispersion is denoted by reference numeral D7.

<Seventh manufacturing method>
The 7th manufacturing method of a cellulose nanofiber dispersion has the following processes 7A-7C. FIG. 6 is an explanatory view showing a seventh manufacturing method.
(7A) A step of performing a pretreatment of stirring an aqueous dispersion of oxidized cellulose having a carboxylate type group for a predetermined time and preliminarily partially defibrating the oxidized cellulose (7B) of the oxidized cellulose after the pretreatment (7C) Dispersing oxidized cellulose in an organic solvent to disperse cellulose nanofiber aqueous dispersion by adding acid to aqueous dispersion and replacing 80% or more of carboxylate type groups of oxidized cellulose with carboxylic acid type groups Preparation process

"Process 7A"
In step 7A, a dispersion liquid in which oxidized cellulose is dispersed in an aqueous solvent is agitated for a predetermined time in the same manner as the method shown in step 6A in the sixth production method described above.

  The stirring treatment can be performed using a generally known stirrer. For example, stirring by rotating a stirrer using a magnetic stirrer or a rotary blade type stirrer can be used.

"Process 7B"
In step 7B, an acid is added to the aqueous dispersion in which the oxidized cellulose subjected to stirring treatment is dispersed in the same manner as the method shown in step 5A in the previous fifth production method, and the mixture is kept acidic. A part of sodium contained in the carboxylate group of oxidized cellulose is replaced with hydrogen to form a carboxylic acid type group. In the figure, the oxidized cellulose having a part of fibrillated and having a carboxylic acid type group obtained by acid treatment is indicated by a symbol Pc.

"Process 7C"
In Step 7C, as in Step 4 in the previous fourth production method, the oxidized cellulose after acid treatment is fractionated and then dispersed in an organic solvent and subjected to a fibrillation treatment, whereby cellulose nanofibers are converted into an organic solvent. A dispersed cellulose nanofiber dispersion is prepared. In the figure, the obtained organic solvent dispersion is indicated by reference numeral D8.

  The organic solvent used for substitution in Step 7C is an organic solvent capable of dispersing cellulose nanofibers in which 80% or more of the carboxyl groups are carboxylic acid type groups. For example, N, N-dimethylformamide (DMF) is used. Used.

  Transparent cellulose nanofibers in which each cellulose nanofiber is uniformly dispersed in an organic solvent by separating and removing oxidized cellulose that remains undefibrated after defibration treatment by centrifugation A dispersion is obtained.

  As described above, according to the method for producing a cellulose nanofiber dispersion of this embodiment, depending on the type of the organic solvent in which the cellulose nanofibers are dispersed, the presence or absence of the modification treatment of the cellulose nanofibers and the modification By appropriately selecting and using the first to seventh production methods having different degrees, cellulose nanofibers that have not been obtained conventionally can be produced.

  Since the cellulose nanofiber dispersion obtained by the above production method is obtained by dispersing cellulose nanofibers separated one by one in an organic solvent, the liquid component is removed from the dispersion to form cellulose nanofibers. The body can be made.

In addition, a nanofiber molded object can be manufactured as follows, for example. As a material for the nanofiber molded body, a nanofiber dispersion obtained by the above production method is used. The viscosity of the dispersion at this time is 10 mPa · s or more and 5000 mPa · s or less.
And after apply | coating a nanofiber dispersion liquid on board | substrates, such as a glass plate, the dispersion liquid is dried with drying methods, such as natural drying, ventilation drying, and vacuum drying, and a film | membrane is formed. Thereafter, the film is peeled off from the substrate to obtain a nanofiber molded body (cast method).

Alternatively, the nanofiber layer may be formed on another molded article using the nanofiber dispersion.
In this case, a nanofiber dispersion is deposited on the surface of the molded product by a known method such as a coating method, spraying method, dipping method, preferably by a coating method or spraying method, and this is dried and solidified to form a nanofiber layer. To do. Furthermore, it is also possible to employ a method in which a nanofiber molded body formed in a film shape is bonded to the surface of another molded product. As a bonding method, a method using an adhesive, a heat sealing method, or the like can be employed.

  The molded product may be a film, sheet, woven fabric, nonwoven fabric or other foil having a desired shape and size, or a three-dimensional container such as a box or bottle having various shapes and sizes. As these molded products, those made of paper, paperboard, plastic, metal, and composites thereof can be used. Among these, it is preferable to use plant-derived materials such as paper and paperboard, biodegradable materials such as biodegradable plastics, or biomass-derived materials. The molded product may have a multilayer structure in which the same or different materials are combined.

In addition, when compounding cellulose nanofibers with other materials, it can be easily compounded with materials that can only be dissolved or dispersed in organic solvents, so it can be combined with a wide range of materials. It can be used for forming into a fiber or a film.
For example, synthetic polymers such as polyvinyl alcohol, nylon, polypropylene, polyethylene terephthalate, and polyester can be dissolved in an organic solvent and spun or formed into a film. In this regard, since the cellulose nanofiber dispersion liquid of the present embodiment has cellulose nanofibers dispersed in an organic solvent, it can be easily mixed with these synthetic polymer materials, so that the synthetic polymer and cellulose can be easily used. A fibrous molded product or a film-shaped molded product in which nanofibers are combined can be obtained.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

(First embodiment)
In the first example, a cellulose nanofiber dispersion was prepared using the first manufacturing method of the above embodiment.
First, dry pulp equivalent to 1 g of undried pulp, 5 mmol of sodium hypochlorite, 1 mmol of sodium bromide, 0.1 mmol of TEMPO are dispersed in 100 mL of water and gently stirred at room temperature for 2.5 hours. Then, TEMPO catalyst oxidized pulp (oxidized cellulose) was obtained by washing with water.
Thereafter, distilled water was added to the undried TEMPO catalyst oxidized pulp to prepare an aqueous suspension having a solid concentration of 0.1%. Then, the suspension was subjected to a fibrillation treatment for 1 minute by a household mixer and 8 minutes by ultrasonic treatment to obtain a cellulose nanofiber aqueous dispersion. Thereafter, unfibrillated components were removed from the cellulose nanofiber aqueous dispersion by centrifugation (100 G).
As a result, a cellulose nanofiber aqueous dispersion having a concentration of 0.09%, which is a transparent liquid, was obtained (step 1A).

Next, 25 mL of dimethyl sulfoxide (85% aqueous solution) is added to 100 mL of the cellulose nanofiber aqueous dispersion (Step 1B), and then evaporated and dehydrated at 45 ° C. (Step 1C), with a concentration of 0.25%. A cellulose nanofiber dispersion (g / mL) was obtained.
The obtained dispersion was a transparent suspension as shown in FIG. Moreover, as shown in FIG.7 (b), it showed birefringence in the observation through a polarizing plate, and it was confirmed that it is a dispersion liquid by which the cellulose nanofiber was disperse | distributed in the organic solvent.

  In addition, under the above conditions, when the same dispersion was prepared by replacing the organic solvent to be added with N, N-dimethylformamide, it was confirmed that a cellulose nanofiber dispersion showing transparency and birefringence was obtained. It was done.

[Evaluation of transparency]
Here, FIG. 8 shows the results of measuring the light transmittance of the cellulose nanofiber dispersion prepared in the first example and the cellulose nanofiber dispersion using the dimethyl sulfoxide aqueous solution prepared in the first example. It is a graph to show. All samples were adjusted to a concentration of 0.1% during measurement.
As shown in FIG. 8, the transmittance is the same when water is used as the solvent and when the organic solvent is used. According to the present invention, the dispersibility equivalent to that of the conventional cellulose nanofiber aqueous dispersion is obtained. It was confirmed that the cellulose nanofiber organic solvent dispersion liquid can be produced.

(Second embodiment)
In the second example, a cellulose nanofiber dispersion was prepared using the second production method of the above embodiment.
First, an aqueous cellulose nanofiber dispersion was prepared in the same manner as in the first example (Step 2A).
Next, 1 mL of 1M hydrochloric acid was added to 100 mL of the cellulose nanofiber aqueous dispersion while stirring, and then stirring was continued for 30 minutes (step 2B). Then, the gelatinized cellulose nanofiber was collected by filtration using a membrane filter having a pore size of 0.45 μm, and then washed with distilled water.
Here, when the collected gel was analyzed by FT-IR, the carboxyl group on the cellulose surface had a ratio of the carboxylate type and the carboxylic acid type to the same degree.
In this example, a cellulose nanofiber dispersion was prepared by the following methods (1) and (2) using the gel.

(1) 25 g of dimethyl sulfoxide (85% aqueous solution) is added to 5 g of cellulose nanofiber gel (Step 2C), evaporated at 50 ° C. and dehydrated (Step 2D), and the concentration is 0.25% (g / g). mL) of cellulose nanofiber dispersion.
The obtained dispersion was a transparent suspension similar to the cellulose nanofiber dispersion of Example 1 shown in FIG. 7, and exhibited birefringence.

(2) The cellulose nanofiber gel was washed with each solvent (N, N-dimethylformamide, N, N-dimethylacetamide) on a membrane filter having a pore size of 0.1 μm to replace the gel solvent (step 2E). ).
Thereafter, the same solvent as that used for solvent replacement was added to adjust the concentration to 0.25% (g / mL), and then ultrasonic treatment (for 1 minute) was performed to disperse the cellulose nanofibers (process) 2F).
Through the above steps, a cellulose nanofiber dispersion using N, N-dimethylformamide as a solvent and a cellulose nanofiber dispersion using N, N-dimethylacetamide as a solvent were obtained.

FIG. 9 is a photograph of a cellulose nanofiber dispersion using N, N-dimethylformamide as a solvent. As shown in FIG. 9 (a), the dispersion was a transparent suspension, and as shown in FIG. 9 (b), it showed birefringence.
FIG. 10 is a photograph of a cellulose nanofiber dispersion using N, N-dimethylacetamide as a solvent. As shown in FIG. 10 (a), the dispersion was a transparent suspension, and as shown in FIG. 10 (b), it showed birefringence.

(Third embodiment)
In the third example, a cellulose nanofiber dispersion was prepared using the third manufacturing method of the above embodiment.
First, an aqueous cellulose nanofiber dispersion was prepared in the same manner as in the first example (Step 3A).
Next, 1 mL of 1M hydrochloric acid was added to 100 mL of the cellulose nanofiber aqueous dispersion while stirring, and then stirring was continued for 60 minutes. Thereafter, the gelatinized cellulose nanofibers were collected using a membrane filter having a pore size of 0.45 μm, and then washed with distilled water (step 3B).
Here, when the collected gel was analyzed by FT-IR, 90% or more of the carboxyl groups on the cellulose surface were substituted with a carboxylic acid type.

Next, the gel of the cellulose nanofiber was washed with each solvent (N, N-dimethylformamide, N, N-dimethylacetamide) on a membrane filter having a pore size of 0.1 μm to replace the gel solvent (Step 3C). ).
Thereafter, the same solvent as that used for solvent replacement was added to adjust the concentration to 0.25% (g / mL), and then ultrasonic treatment (for 1 minute) was performed to disperse the cellulose nanofibers (process) 3D).

Through the above steps, a cellulose nanofiber dispersion using N, N-dimethylformamide as a solvent and a cellulose nanofiber dispersion using N, N-dimethylacetamide as a solvent were obtained.
FIG. 11 is a photograph of a cellulose nanofiber dispersion using N, N-dimethylacetamide as a solvent. As shown in FIG. 11 (a), the dispersion was a transparent suspension and exhibited birefringence as shown in FIG. 11 (b). Moreover, the cellulose nanofiber dispersion using N, N-dimethylformamide as a solvent was also a transparent suspension and exhibited birefringence.

Table 1 shows the relationship between the type of organic solvent obtained based on the results of the first to third examples and the dispersibility of cellulose nanofibers.
As shown in Table 1, cellulose nanofiber dispersions using dimethyl sulfoxide and N, N-dimethylformamide were obtained in the first example (first production method), but N, N-dimethylacetamide was used. In some cases, the cellulose nanofibers could not be uniformly dispersed. On the other hand, in the second and third examples, cellulose nanofibers in which cellulose nanofibers were uniformly dispersed using N, N-dimethylacetamide were obtained.
The same applies to the case where other production methods are used. When these are combined, it is uniformly dispersed by selecting and using one of the first to third production methods according to the type of the organic solvent. It turns out that a cellulose nanofiber dispersion liquid is obtained.

Specifically, when the solvent to be used is dimethyl sulfoxide (DMSO), cellulose nanofibers can be obtained by adopting the first production method in which the cellulose nanofibers are dispersed in a state containing carboxylate type groups. A fiber dispersion can be made.
When the solvent to be used is an 85% dimethyl sulfoxide aqueous solution, the first production method or the second production in which a part of the carboxylate type group of the cellulose nanofiber is substituted with a carboxylic acid type group. By using this method, a cellulose nanofiber dispersion can be produced.
When the solvent to be used is N, N-dimethylacetamide (DMAc), the second production method or the third method in which almost all of the carboxylate group of the cellulose nanofiber is substituted with the carboxylic acid type. By using this production method, a cellulose nanofiber dispersion can be produced.
In addition, when the solvent to be used is N, N-dimethylformamide (DMF), the cellulose nanofiber dispersion can be produced by using any of the first to third production methods.

(Fourth embodiment)
In the fourth example, a cellulose nanofiber dispersion was prepared using the fourth production method of the above embodiment.
First, TEMPO-catalyzed oxidized pulp was obtained in the same manner as in the first example, using undried pulp equivalent to 2 g in dry weight.
Thereafter, in a centrifuge tube (50 mL volume), dimethyl sulfoxide was added to the TEMPO catalyst oxidized pulp to prepare 40 mL of a suspension having a solid content concentration of 1%. Then, water was removed from the suspension by three times of centrifugation (100 G).
Thereafter, defibration treatment (10000 rpm, 10 minutes) was applied to 40 mL of the suspension using a homogenizer (Hiscotron, manufactured by Microtech Nichion). Thereafter, undefibrated components were removed by centrifugation (100G) (step 4).

  Through the above steps, a cellulose nanofiber dispersion having a concentration of 0.1% (g / mL) using dimethyl sulfoxide as a solvent was obtained. The obtained dispersion was a transparent suspension similar to the cellulose nanofiber dispersion of Example 1 shown in FIG. 7, and exhibited birefringence.

(5th Example)
In the fifth example, a cellulose nanofiber dispersion was prepared using the fifth production method of the above embodiment.
First, TEMPO-catalyzed oxidized pulp was obtained in the same manner as in the first example, using undried pulp equivalent to 2 g in dry weight.
Thereafter, the undried TEMPO-catalyzed oxidized pulp was stirred in 0.1 M hydrochloric acid for 2 hours, collected by a glass filter (P100 (ISO name)), and washed with 200 mL of 0.1 M hydrochloric acid. The steps of stirring, filtering and washing in hydrochloric acid were repeated twice to obtain a TEMPO-catalyzed oxidized pulp in which the surface carboxyl groups were completely substituted with the carboxylic acid type (step 5A).

Thereafter, in a centrifuge tube (50 mL volume), N, N-dimethylformamide was added to the carboxylic acid type TEMPO-catalyzed oxidized pulp to prepare 40 mL of a suspension having a solid content concentration of 1%. Then, water and hydrochloric acid were removed from the suspension by three times of centrifugation (100 G).
Thereafter, 40 mL of the suspension was defibrated (10000 rpm, 10 minutes) using a homogenizer. Thereafter, undefibrated components were removed by centrifugation (100G) (step 5B).

  Through the above steps, a cellulose nanofiber dispersion having a concentration of 0.05% (g / mL) using N, N-dimethylformamide as a solvent was obtained. The obtained dispersion was a transparent suspension similar to the cellulose nanofiber dispersion of Example 1 shown in FIG. 7, and exhibited birefringence.

(Sixth embodiment)
In the sixth example, a cellulose nanofiber dispersion was prepared using the sixth production method of the above embodiment.
First, TEMPO-catalyzed oxidized pulp was obtained in the same manner as in the first example, using undried pulp equivalent to 2 g in dry weight.
Distilled water was added to the undried TEMPO-catalyzed oxidized pulp to prepare an aqueous suspension with a solid content concentration of 5%, and the mixture was stirred at 400 rpm for 12 hours using a magnetic stirrer. As a result of measuring the water retention value of the TEMPO-catalyzed oxidized pulp after stirring, an increase in the water retention value was confirmed as compared to before stirring (step 6A).
Thereafter, the stirred TEMPO catalyst oxidized pulp was collected by filtration, and dimethyl sulfoxide was added in a centrifuge tube (50 mL volume) to prepare 40 mL of a suspension having a solid content concentration of 1%. Then, water was removed from the suspension by three times of centrifugation (100 G).
Thereafter, defibration treatment (10000 rpm, 10 minutes) was applied to 40 mL of the suspension using a homogenizer. 40 mL of dimethyl sulfoxide was added to the gel-like high-viscosity liquid obtained, and defibration treatment under the same conditions was added again using a homogenizer (step 6B).

  Through the above steps, a cellulose nanofiber dispersion having a concentration of 0.5% (g / mL) using dimethyl sulfoxide as a solvent was obtained. The obtained dispersion was a transparent suspension similar to the cellulose nanofiber dispersion of Example 1 shown in FIG. 7, and exhibited birefringence.

(Seventh embodiment)
In the seventh example, a cellulose nanofiber dispersion was prepared using the seventh manufacturing method of the above embodiment.
First, the TEMPO catalyst oxidized pulp which stirred by the method similar to 6th Example was obtained (process 7A).
Thereafter, the TEMPO-catalyzed oxidized pulp after undried stirring was stirred in 0.1M hydrochloric acid for 2 hours, and then collected by a glass filter (P100 (ISO name)) and washed with 200 mL of 0.1M hydrochloric acid. . The steps of stirring, filtering and washing in hydrochloric acid were repeated twice to obtain a TEMPO-catalyzed oxidized pulp in which the surface carboxyl groups were completely substituted with the carboxylic acid type (step 7B).
Thereafter, in a centrifuge tube (50 mL volume), N, N-dimethylformamide was added to the carboxylic acid type TEMPO-catalyzed oxidized pulp to prepare 40 mL of a suspension having a solid content concentration of 1%. Then, water and hydrochloric acid were removed from the suspension by three times of centrifugation (100 G).
Thereafter, 40 mL of the suspension was defibrated (10000 rpm, 10 minutes) using a homogenizer. Thereafter, undefibrated components were removed by centrifugation (100G) (step 7C).

  Through the above steps, a cellulose nanofiber dispersion having a concentration of 0.1% (g / mL) using N, N-dimethylformamide as a solvent was obtained. The obtained dispersion was a transparent suspension similar to the cellulose nanofiber dispersion of Example 1 shown in FIG. 7, and exhibited birefringence.

  From the above, it was found that an organic solvent dispersion of cellulose nanofibers can be obtained satisfactorily by using the production method of the present invention, and the usefulness of the present invention was confirmed.

  According to the present invention, the cellulose nanofiber dispersion of the present invention can be used to provide a cellulose nanofiber molded article and a cellulose nanofiber composite excellent in manufacturability. Therefore, the present invention is extremely useful industrially. .

  D1 to D8 ... dispersion, G ... gel, P ... oxidized cellulose

Claims (15)

When dispersing cellulose nanofibers having carboxylate type groups in a medium containing an organic solvent,
A method for producing a cellulose nanofiber dispersion, comprising performing a substitution step of substituting the group of the cellulose nanofibers from a carboxylate type to a carboxylic acid type according to the type of the organic solvent.   The method for producing a cellulose nanofiber dispersion according to claim 1, wherein, in the substitution step, the substitution rate of the group to the carboxylic acid type is varied based on the type of the organic solvent. A step of preparing a cellulose nanofiber aqueous dispersion by dispersing cellulose nanofibers having a carboxylate type group in an aqueous solvent;
Adding one or two organic solvents selected from dimethyl sulfoxide and N, N-dimethylformamide to the cellulose nanofiber aqueous dispersion;
Removing the aqueous solvent from the cellulose nanofiber aqueous dispersion to which the organic solvent has been added;
A method for producing a cellulose nanofiber dispersion, comprising: A step of preparing a cellulose nanofiber aqueous dispersion by dispersing cellulose nanofibers having a carboxylate type group in an aqueous solvent;
Adding an acid to the cellulose nanofiber aqueous dispersion, substituting at least a part of the group from a carboxylate type to a carboxylic acid type, and gelling the cellulose nanofiber;
Adding one or more organic solvents selected from dimethyl sulfoxide, N, N-dimethylacetamide, and N, N-dimethylformamide to the cellulose nanofiber gel;
Removing water from the gel to which the organic solvent has been added;
A method for producing a cellulose nanofiber dispersion, comprising: A step of preparing a cellulose nanofiber aqueous dispersion by dispersing cellulose nanofibers having a carboxylate type group in an aqueous solvent;
Adding an acid to the cellulose nanofiber aqueous dispersion, substituting at least a part of the group from a carboxylate type to a carboxylic acid type, and gelling the cellulose nanofiber;
Supplying one or more organic solvents selected from dimethyl sulfoxide, N, N-dimethylacetamide, and N, N-dimethylformamide to the gel, and replacing the solvent contained in the gel;
Dispersing the gel after solvent substitution in an organic solvent;
A method for producing a cellulose nanofiber dispersion, comprising: A step of preparing a cellulose nanofiber aqueous dispersion by dispersing cellulose nanofibers having a carboxylate type group in an aqueous solvent;
Adding an acid to the cellulose nanofiber aqueous dispersion to replace 80% or more of the groups from a carboxylate type to a carboxylic acid type, and gelling the cellulose nanofiber;
Supplying one or two organic solvents selected from N, N-dimethylacetamide and N, N-dimethylformamide to the gel, and replacing the solvent contained in the gel;
Dispersing the gel after solvent substitution in an organic solvent;
A method for producing a cellulose nanofiber dispersion, comprising:   Cellulose nanofibers comprising a step of dispersing oxidized cellulose having carboxylate group obtained by oxidizing natural cellulose in an organic solvent to disperse the oxidized cellulose nanofibers A method for producing a dispersion.   The method for producing a cellulose nanofiber dispersion according to claim 7, further comprising a step of stirring the oxidized cellulose suspension for a predetermined time prior to the dispersing step. A step of replacing 80% or more of the groups from carboxylate type to carboxylic acid type by adding an acid to an aqueous suspension of oxidized cellulose having carboxylate type groups obtained by oxidizing natural cellulose. When,
Disperse the oxidized cellulose having the carboxylic acid type substituted in an organic solvent to disperse the oxidized cellulose as nanofibers;
A method for producing a cellulose nanofiber dispersion, comprising:   The method for producing a cellulose nanofiber dispersion according to claim 9, further comprising a step of stirring the oxidized cellulose suspension for a predetermined time prior to the replacing step.   Dispersing cellulose nanofibers having carboxylate type groups in a medium containing one or two organic solvents selected from dimethyl sulfoxide and N, N-dimethylformamide liquid.   One or more organic solvents selected from cellulose nanofibers having a carboxylate type group and a carboxylic acid type group selected from dimethyl sulfoxide, N, N-dimethylacetamide, and N, N-dimethylformamide A cellulose nanofiber dispersion characterized by being dispersed in a medium containing   A cellulose nanofiber having a carboxylate type group is dispersed in a medium containing one or more organic solvents selected from N, N-dimethylacetamide and N, N-dimethylformamide. Cellulose nanofiber dispersion.   A cellulose nanofiber molded article obtained by removing a liquid component while maintaining the cellulose nanofiber dispersion liquid according to any one of claims 11 to 13 in a predetermined shape.   The composite dispersion liquid which mixes the cellulose nanofiber dispersion liquid of any one of Claim 11 to 13 containing the cellulose nanofiber as a 1st material, and the liquid material containing a 2nd material is used. A cellulose nanofiber composite obtained by