JP6249441B2 - Method for producing cellulose nanofiber dispersion - Google Patents

Description

The present invention relates to a cellulose nanofiber dispersion and a method for producing the same, a cellulose nanofiber modified product, and a cellulose nanofiber composite.
This application claims priority based on Japanese Patent Application No. 2011-254945 for which it applied to Japan on November 22, 2011, 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, the cellulose nanofibers obtained by the above production method are hydrophilic, have low compatibility with hydrophobic synthetic polymers such as polyethylene terephthalate (PET) and polylactic acid (PLA), and are in a nano-dispersed state (nanofibers). It was not possible to obtain a composite material in a state in which each of these was dispersed while being separated.

  The present invention has been made in view of the above-mentioned problems of the prior art, and provides a cellulose nanofiber dispersion that can be suitably used for complexing with a hydrophobic polymer material and a method for producing the same. One of the purposes.

The method for producing a cellulose nanofiber dispersion of the present invention comprises a step of holding cellulose nanofibers having a carboxylate type group in an acidic solution, and substituting the carboxylate type group with a carboxylic acid type group; The cellulose nanofiber having the carboxylic acid type group, a dispersion medium containing an organic solvent, and an amine having a linear or branched molecule having an average molecular weight of 300 or more are mixed, and the cellulose nanofiber is dispersed. dispersed in medium, comprising the steps of obtaining a dispersion of cellulose nanofibers, wherein the linear or branched molecules, polyethylene glycol, branched and straight chain-like type cationic polyacrylamide, cationic polyacrylamide -Polyethylene glycol copolymer and polypropylene polyethylene having terminal amino groups Characterized in that at least one selected from the group consisting of glycol copolymer.

  The cellulose nanofiber composite of the present invention is characterized in that the above-mentioned modified cellulose nanofiber is combined with another material.

Since the cellulose nanofiber dispersion of the present invention is a dispersion of cellulose nanofibers modified with linear or branched molecules, it can be easily combined with a hydrophobic polymer material. It becomes.
According to the present invention, a dispersion of cellulose nanofibers modified with linear or branched molecules can be produced by a simple method.
ADVANTAGE OF THE INVENTION According to this invention, the cellulose nanofiber modified body which is excellent in affinity with a hydrophobic polymer material, and can form a complex with a polymer material easily, and a cellulose nanofiber composite using the same are provided. The

The figure which shows the manufacturing method of the cellulose nanofiber dispersion liquid of embodiment. The figure which shows the modification aspect of a cellulose nanofiber. The FT-IR spectrum about the cellulose nanofiber of an Example. The figure which expands and shows a part of spectrum of FIG. Photo of cellulose nanofiber dispersion. The graph which shows the transmittance | permeability measurement result of a cellulose nanofiber composite film. The graph which shows the tensile test result (stress distortion diagram) of a cellulose nanofiber composite film. The graph which shows the tensile test result (Young's modulus) of a cellulose nanofiber composite film. The graph which shows the tensile test result (yield stress) of a cellulose nanofiber composite film. The graph which shows the tensile test result (fracture work) of a cellulose nanofiber composite film.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a method for producing a cellulose nanofiber dispersion according to the present embodiment. FIG. 2 is a diagram showing a modification mode of cellulose nanofibers.

The manufacturing method of the cellulose nanofiber dispersion liquid of the present embodiment includes the following steps 1A to 1D.
(1A) Step of preparing cellulose nanofiber aqueous dispersion by dispersing cellulose nanofibers having carboxylate type groups in an aqueous solvent (1B) Adding acid to cellulose nanofiber aqueous dispersion, carboxyl of cellulose nanofiber A step of substituting an acid salt type group with a carboxylic acid type group (1C) After washing the cellulose nanofiber gel substituted with a carboxylic acid type, substituting the solvent with ethanol to prepare an ethanol dispersion (1D ) The step of solvent substitution of the cellulose nanofiber gel substituted with ethanol with a hydrocarbon-based or ether-based organic solvent to prepare an organic solvent dispersion (1E) Mix and disperse linear or branched molecules having an amino group and an average molecular weight of 300 or more Process for preparing cellulose nanofiber dispersion

"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, ClO ₂ , Cl ₂ O ₆ , BrO ₂ , Br ₃ O ₇ etc.), nitrogen oxides (NO, NO ₂ , N ₂ O ₃ etc.), peracids (hydrogen peroxide, hydrogen peroxide, Acetic acid, persulfuric acid, perbenzoic acid, etc.). 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.

  Through the oxidation treatment step as described above, oxidized cellulose 10A in which sodium carboxylate is bonded to cellulose main chain 10 as shown in FIG. 2A can be obtained. In FIG. 1, oxidized cellulose is indicated by a 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 FIG. 1, water is indicated by a 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, the acid treatment in latter process 1B can be performed efficiently. For example, when the amount is less than 0.05% by weight, the processing amount of cellulose nanofiber is small and the working efficiency is lowered. In addition, if the concentration is higher than 2% by weight, gelation occurs early in the acid treatment of Step 1B, and untreated cellulose nanofibers may be included in the gel that is produced. .

  Various devices can be used as a dispersion device (defibration device) used in the dispersion step. For example, a household mixer, an ultrasonic disperser, an ultrasonic homogenizer, a high-pressure homogenizer, a biaxial kneading device, a defibrating device such as a stone mortar 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, sodium contained in the cellulose nanofiber is replaced 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 organic solvents generally have a smaller polarity than water, the degree of ionization described above may be low in organic solvents, and cellulose nanofibers tend to aggregate and gel.

  Therefore, in the present invention, by replacing the counter ion of the carboxylate type group with a linear molecule or a branched molecule (branched molecule) that easily develops hydrophobicity, hydrophobicity such as PET and PLA is obtained. It was decided to increase the affinity with other polymer materials.

  In Step 1B, as a pretreatment for the treatment for exchanging with a linear or branched molecule, cellulose nanofibers having a carboxylic acid type group are modified by replacing sodium of the carboxylate type group with hydrogen. The structure is converted into a structure that can be easily exchanged with a linear or branched molecule.

  In the case of this embodiment, the carboxylic acid sodium salt contained in the cellulose nanofibers is substituted with a carboxylic acid type group, so that the cellulose nanofibers are converted into an acidic solution (dispersed liquid with an acid) so as to obtain a desired substitution rate. Manage the retention time. In FIG. 1, 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 1B, 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. Thereby, the oxidized cellulose 10B having the carboxylic acid type group shown in FIG. 2B is formed. In this oxidized cellulose 10B, the charge repulsion between carboxylic acid ions is lost, and the cellulose nanofibers aggregate and gel. In FIG. 1, the resulting gel is indicated by the symbol G.

Next, the cellulose nanofiber gel is collected.
First, after the time for obtaining a predetermined substitution rate has elapsed, the gelatinized cellulose nanofibers are collected by centrifugation and then washed with an acid (for example, 1M hydrochloric acid). Thereafter, the recovered cellulose nanofibers are washed with distilled water.

"Process 1C"
Next, in Step 1C, the cellulose nanofibers are solvent-substituted with ethanol.
Specifically, the cellulose nanofibers after washing with water obtained in step 1B are dispersed in ethanol at a concentration of about 0.1 to 1% (g / mL), and the cellulose nanogel that is gelled in ethanol The step of collecting the fiber by centrifugation is repeated several times (about 2 to 10 times) until the water contained in the cellulose nanofiber is replaced with ethanol. In the figure, a dispersion in which cellulose nanofibers are dispersed in ethanol is indicated by reference numeral D2. The dispersion D2 is a dispersion in which a fine gel of cellulose nanofibers is suspended in ethanol.

  Step 1C may be performed as necessary. That is, if direct solvent replacement with a hydrocarbon-based or ether-based organic solvent used in the subsequent step 1D is possible, step 1C may be omitted.

"Process 1D"
Next, in Step 1D, the cellulose nanofibers are solvent-substituted with a hydrocarbon-based or ether-based organic solvent. What is necessary is just to select the organic solvent to substitute according to the use of the cellulose nanofiber dispersion liquid to produce. For example, when using for the use which combines cellulose nanofiber and a resin material, the organic solvent which dissolves the resin material to be combined is selected. In addition, even if it is organic solvents other than a hydrocarbon type or an ether type, if the nano dispersion of a cellulose nanofiber is possible, it can be used. For example, acetonitrile or methyl ethyl ketone may be used.

  Hydrocarbon organic solvents include benzene, toluene, xylene, n-hexane, n-octane, cyclohexane, methylcyclohexane, dichloromethane, dichloroethane, chloroform, methylene chloride, carbon tetrachloride, fluorotrichloromethane, trichlorotrifluoromethane, hexa Examples include fluorobenzene.

  Examples of ether organic solvents include tetrahydrofuran (THF), 1,2-dimethoxyethane (DME), cyclopentyl methyl ether (CPME), methyl tertiary butyl ether (MTBE), 1,4-dioxane, methyl cellosolve (2-methoxy). Ethanol) and the like.

  In Step 1D, the cellulose nanofibers after ethanol substitution obtained in Step 1C are dispersed in the organic solvent at a concentration of about 0.1 to 1% (g / mL), and gelled in the organic solvent. The step of collecting the cellulose nanofibers by centrifugation is repeated several times (about 2 to 10 times) until the ethanol contained in the cellulose nanofibers is replaced with the organic solvent. In the figure, a dispersion in which cellulose nanofibers are dispersed in an organic solvent is indicated by a symbol D3. The dispersion D3 is a dispersion in which a fine gel of cellulose nanofibers is suspended in an organic solvent.

"Process 1E"
Next, in Step 1E, the cellulose nanofiber organic solvent dispersion obtained in Step 1D is mixed with a linear or branched molecule having an amino group at the terminal and having an average molecular weight of 300 or more to disperse the cellulose. Redisperse the nanofibers.

  The linear or branched molecule used in Step 1E is a linear molecule having a large molecular weight, such as polyethylene glycol, and reacts with the carboxyl group of cellulose nanofiber to form a salt with respect to this polyethylene glycol. An amino group that can be attached. The addition amount of the amine containing a linear or branched molecule may be appropriately changed according to the kind of the amine. For example, the addition amount is in the range of equivalent to 10 times the amount of carboxyl groups of the cellulose nanofiber. is there.

  Examples of the linear or branched molecule used in Step 1E include branched and linear cationic polyacrylamide, cationic polyacrylamide-polyethylene glycol copolymer, and polypropylene polyethylene glycol copolymer having an amino group at the terminal. May be used.

In the present embodiment, the linear or branched molecule has an average molecular weight (weight average molecular weight) of 300 or more, more preferably a linear or branched molecule having an average molecular weight of 500 or more. Preferably, the average molecular weight is 1000 or more. By modifying cellulose nanofibers using linear molecules with a large molecular weight in this way, the surface of cellulose nanofibers that are originally hydrophilic are hydrophobic (or amphiphilic) linear or branched molecules. Covered. As a result, when mixed with a hydrophobic polymer material such as PET or PLA, the hydrophilic cellulose main chain portion is less likely to be exposed to the hydrophobic polymer material, and aggregation of cellulose nanofibers is prevented. The
In addition, since the linear or branched molecule extending from the surface of the cellulose nanofiber to the outside becomes longer as the molecular weight of the linear or branched molecule is larger, the hydrophilicity of the cellulose main chain part is more difficult to express, Dispersibility in a hydrophobic polymer can be increased.

After adding the above-mentioned amines, each fiber nanofiber modified by a linear or branched molecule bonded through a carboxyl group and an amino group is subjected to mechanical defibration treatment one by one It is possible to obtain a dispersion liquid dispersed in a separated state.
As the defibrating apparatus used in this step, the one exemplified in the dispersion step of step 1A can be used.

By the steps 1A to 1E described above, for example, a cellulose nanofiber dispersion liquid in which cellulose nanofibers modified with polyethylene glycolamine are dispersed in a hydrocarbon-based or ether-based organic solvent can be produced. The resulting cellulose nanofiber dispersion is a transparent suspension in which each cellulose nanofiber is uniformly dispersed in an organic solvent.
In FIG. 1, the obtained organic solvent dispersion is indicated by reference numeral D4. FIG.2 (c) is a figure which shows the cellulose nanofiber modification 10E modified with polyethyleneglycolamine. “PEG” shown in FIG. 2C indicates polyethylene glycol.

  In this embodiment, after solvent substitution with a hydrocarbon-based or ether-based organic solvent (step 1D), polyethylene glycolamine is added and redispersed (step 1E). However, the order of the steps is limited. Not. For example, after modification of cellulose nanofiber by adding polyethylene glycolamine, the obtained modified cellulose nanofiber may be dispersed in a hydrocarbon-based or ether-based organic solvent.

  In the present embodiment, the cellulose nanofiber gel is sequentially solvent-substituted to obtain a dispersion liquid in which the cellulose nanofiber gel is dispersed in the target organic solvent (chloroform, THF, etc.). The dried fiber may be directly dispersed in a hydrocarbon-based or ether-based organic solvent.

  In addition, a nanofiber molded object can be manufactured as follows, for example. As a material of the nanofiber molded body, a cellulose 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 the cellulose nanofiber dispersion liquid on 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).

Or you may form a nanofiber layer on another shaping | molding device using a cellulose nanofiber dispersion liquid. In this case, the cellulose nanofiber dispersion is attached to the surface of the molding machine 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. Form.
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.

  As said shaping | molding machine, foil-like objects, such as a film, a sheet | seat, a woven fabric, a nonwoven fabric, etc. which have a desired shape and a magnitude | size, solid containers, such as a box and a bottle of various shapes and a magnitude | size, etc. can be used. These molding machines may be made of paper, paperboard, plastic, metal, and composites thereof. 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 molding device 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 (registered trademark), polypropylene, polyethylene terephthalate, polyester, and polylactic acid can be dissolved in an organic solvent to be spun (solution spinning) 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.
It is also possible to form a composite of cellulose nanofibers and synthetic polymers by mixing monomers and nanodispersed cellulose nanofibers in an organic solvent and polymerizing the monomers to synthesize polymers. It is.

  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 this example, a cellulose nanofiber dispersion was prepared using the manufacturing method of the above embodiment.
First, softwood bleached kraft pulp equivalent to 1 g by dry weight, 10 mmol sodium hypochlorite, 0.1 g (1 mmol) sodium bromide, 0.16 g (1 mmol) TEMPO were dispersed in 100 mL water, The mixture was gently stirred for 4 hours, washed with distilled water and washed with water to obtain a TEMPO-catalyzed oxidized pulp (oxidized cellulose).
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 with a home mixer and 2 minutes with ultrasonic treatment to obtain a cellulose nanofiber aqueous dispersion. Thereafter, undefibrated components were removed from the cellulose nanofiber aqueous dispersion by centrifugation (12000 g).
Thus, a cellulose nanofiber aqueous dispersion having a concentration of 0.1%, which is a transparent liquid, was obtained (Step 1A).

  Next, 1 M hydrochloric acid was added to 100 mL of the cellulose nanofiber aqueous dispersion to adjust the pH to 1, 1 mL was added with stirring, and stirring was continued for 60 minutes (step 1B). Then, after the gelatinized cellulose nanofibers were collected by centrifugation (12000 g), the cellulose nanofiber gel collected with 1M hydrochloric acid was washed, and then washed with distilled water. Through the above steps, 90% or more of the carboxyl groups on the cellulose surface were substituted with carboxylic acid type.

  Next, ethanol is added to the collected cellulose nanofiber gel to obtain a gel dispersion (concentration of about 0.1% (g / mL)), and then the step of collecting by centrifugation (12000 g) is repeated five times. The cellulose nanofiber was solvent-substituted with ethanol (Step 1C).

  Next, chloroform is added to the gel of cellulose nanofibers solvent-substituted with ethanol to obtain a gel dispersion (concentration of about 0.1% (g / mL)), and then recovered by centrifugation (12000 g) five times. By repeating, the solvent substitution of the cellulose nanofiber was carried out with chloroform (process 1D).

  Next, polyethylene glycol amine (molecular weight 2000) in an equimolar amount with respect to the carboxyl group of the cellulose nanofiber was added to the chloroform dispersion of cellulose nanofiber (0.1% (g / mL)). Then, the cellulose nanofiber dispersion liquid of 1st Example was produced by performing the ultrasonic treatment for 3 minutes (process 1E).

(Second embodiment)
In Step 1D, a cellulose nanofiber dispersion of Example 2 was prepared in the same manner as Example 1 except that tetrahydrofuran was used as the organic solvent.

(Third embodiment)
In Step 1D, a cellulose nanofiber dispersion of Example 3 was prepared in the same manner as Example 1 except that toluene was used as the organic solvent.

FIG. 3 is an FT-IR spectrum for the cellulose nanofibers of the first to third examples. FIG. 4 is an enlarged view showing a part of the spectrum of FIG.
3 and 4, the sample indicated as “original TOCN” is a cellulose nanofiber having a carboxylate type group prepared in Step 1A. The sample indicated as “PEG-NH ₂ ” is polyethylene glycol amine.

  As shown in FIG. 4, when the cellulose nanofibers of each Example were analyzed by FT-IR, the vibration absorption of the carboxyl group disappeared, and a clear amine salt peak that appeared to be derived from polyethylene glycolamine appeared. From the results, it was found that the total amount of carboxyl groups on the cellulose surface was a carboxylic acid amine salt.

  FIG. 5 is a photograph of the dispersion of cellulose nanofibers having carboxylate-type groups obtained in step 1A and the cellulose nanofiber dispersions of the first to third examples. As shown in the photograph of FIG. 5A, all of the dispersions were transparent suspensions. Moreover, as shown in FIG.5 (b), it was confirmed that all the dispersion liquids show birefringence, and it turned out that the cellulose nanofiber is nanodispersed.

(Comparative example)
In Step 1E, except that dodecylamine (C ₁₂ H ₂₅ NH ₂ ) and stearylamine (C ₁₈ H ₃₇ NH ₂ ) were used, a cellulose nanofiber dispersion of Comparative Example ₂ was prepared in the same manner as in the first example. Kinds were made. As for the obtained cellulose nanofiber, it was confirmed that the alkylamine salt was introduce | transduced by the ionic bond in almost all the carboxyl groups on the surface (FT-IR measurement). However, these cellulose nanofibers were not nanodispersed in chloroform. This is because the length of the alkyl chain bonded to the surface of the cellulose nanofiber is short, and the hydrophilic surface of the cellulose nanofiber cannot be sufficiently covered with the alkyl chain, and the affinity with chloroform is sufficient. It is thought that this is because of

(Fourth embodiment)
Cellulose nanofiber composite film (cellulose nanofiber) using 0.1% (g / mL) chloroform dispersion of cellulose nanofiber prepared in the first example and chloroform solution of poly-L-lactic acid (PLLA) Composite).

  The PLLA solution is a PLLA chloroform solution having a concentration of 2% (w / v). Mw (weight average molecular weight) of poly-L-lactic acid used in the PLLA solution is 110,000, and the polydispersity Mw / Mn, which is a ratio to Mn (number average molecular weight), is 1.4.

  And after mixing a cellulose nanofiber dispersion and PLLA solution, the resin solution sample was produced by stirring for 30 minutes. In this example, four types of resin solution samples were prepared by changing the mixing ratio of the cellulose nanofiber dispersion and the PLLA solution. As a control sample, a PLLA solution not mixed with the cellulose nanofiber dispersion was prepared.

  After applying the above five types of resin solution samples on a substrate to form a thin film, vacuum drying (30 ° C., 24 hours) and vacuum drying (30 ° C., 48 hours) were sequentially performed, and then the film was peeled off. A self-supporting film was obtained. Thereafter, a hot press process (175 ° C., 1 minute) and a cooling process (quenching process by ice cooling) were sequentially performed on the self-supporting film.

  Through the above steps, a composite film of cellulose nanofibers and PLLA (cellulose nanofibril content: 0 to 1.0 mass%, thickness 150 to 200 μm) and PLLA film (control sample) not containing cellulose nanofibers are prepared. did.

(1) Transmittance measurement The transmittance of the produced cellulose nanofiber composite film and PLLA film was measured using a spectrophotometer. FIG. 6 is a graph showing the transmittance of each film at a wavelength of 600 nm.
As shown in FIG. 6, all the cellulose nanofiber composite films had the same transmittance as the PLLA film not containing cellulose nanofibers.

(2) Tensile test A tensile test was performed on the produced cellulose nanofiber composite film and PLLA film. 7 to 10 are graphs showing the measurement results. FIG. 7 is a stress strain diagram of each film. FIG. 8 is a graph showing the relationship between the cellulose nanofibril content and the Young's modulus. FIG. 9 is a graph showing the relationship between cellulose nanofibril content and yield stress. FIG. 10 is a graph showing the relationship between cellulose nanofibril content and fracture work.

  As shown in FIGS. 7 to 10, the cellulose nanofiber composite film in which cellulose nanofibers and PLLA are combined had improved mechanical properties compared to the control PLLA film in any film content. .

Conventionally, there have been a plurality of reports on the combination of cellulose nanofibers and resins (see, for example, the following references 1 and 2). However, the conventional composite material has the following two problems.
(1) The dispersibility of cellulose nanofibers in the composite material is poor.
(2) Since the interaction between hydrophobic polylactic acid (PLA) and hydrophilic cellulose is weak, the material becomes brittle. Specifically, when a force is applied to the composite material, cracks are likely to occur between PLA and cellulose, and the material breaks from there.

  In the present invention, PEG was grafted on the surface of the cellulose nanofiber, and thus it could be dispersed well in an organic solvent such as chloroform. Thereby, the dispersion liquid in which cellulose nanofibers are dispersed can be uniformly mixed with a solution in which PLA is dissolved in an organic solvent. As a result, the cellulose nanofibers and PLA could be mixed uniformly, and the problem (1) could be solved.

  Further, in the present invention, since amphiphilic PEG is graphed on the cellulose surface, the interaction between PLA / cellulose is improved via PEG. Thereby, since the adhesive strength between PLA and cellulose in the composite material is increased, cracks between PLA and cellulose in the problem (2) are less likely to occur.

  According to the present invention having the above-described action, cellulose nanofibers having an addition amount (1% by mass or less) significantly smaller than the cellulose nanofiber addition amount (3 to 25% by mass) in References 1 and 2 Even if it is a composite film, the outstanding reinforcement effect can be acquired.

[Reference 1] Suryanegara L, Nakagaito AN, Yano H. The effect of crystallization of PLA on the thermal and mechanical properties of microfibrillated cellulose-reinforced PLA composites. Comp Sci Technol 2009; 69: 1187-1192.
[Reference 2] Mathew, AP; Oksman, K .; Sain, M. Mechanical properties of biodegradable composites from poly lactic acid (PLA) and microcrystalline cellulose (MCC). J. Appl. Polym. Sci. 2005, 97, 2014 -2025.

ADVANTAGE OF THE INVENTION According to this invention, the cellulose nanofiber modified body which is excellent in affinity with a hydrophobic polymer material, and can form a complex with a polymer material easily, and a cellulose nanofiber composite using the same are provided. The Therefore, the present invention is extremely useful industrially.

  10A, 10B ... oxidized cellulose, 10E ... modified cellulose nanofiber, D1-D4 ... dispersion, G ... gel, P ... oxidized cellulose

Claims (4)

Holding a cellulose nanofiber having a carboxylate type group in an acidic solution, substituting the carboxylate type group with a carboxylic acid type group;
The cellulose nanofiber having the carboxylic acid type group, a dispersion medium containing an organic solvent, and an amine having a linear or branched molecule having an average molecular weight of 300 or more are mixed, and the cellulose nanofiber is dispersed. dispersed in medium, comprising the steps of obtaining a dispersion of cellulose nanofibers, a,
The linear or branched molecule is selected from polyethylene glycol, branched and linear cationic polyacrylamide, cationic polyacrylamide-polyethylene glycol copolymer, and polypropylene polyethylene glycol copolymer having an amino group at the terminal. A method for producing a cellulose nanofiber dispersion, wherein the cellulose nanofiber dispersion is at least one selected from the group consisting of: The cellulose nanofibers having a carboxylic acid type groups, after solvent replacement with a dispersion medium containing an organic solvent, wherein the average molecular weight is added an amine having a linear or branched molecules is 300 or more, claim 2. A method for producing a cellulose nanofiber dispersion according to 1. The method for producing a cellulose nanofiber dispersion according to claim 1 or 2 , wherein the linear or branched molecule is polyethylene glycol. The method for producing a cellulose nanofiber dispersion according to any one of claims 1 to 3 , wherein the dispersion medium is a hydrocarbon-based or ether-based organic solvent.