JP2014114332A - Method for producing cellulose nanofiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a cellulose nanofiber, in which micronization of an oxidized cellulose fiber can be promoted by micronization treatment while restraining the oxidized cellulose fiber from becoming a short fiber and the energy required to perform micronization treatment can be saved.SOLUTION: The method for producing the cellulose nanofiber comprises: a step of oxidizing a natural cellulose fiber by using an oxidizer and an N-oxyl compound to obtain a carboxyl group-containing cellulose fiber; a step of adding an anionic cellulose derivative to the obtained carboxyl group-containing cellulose fiber; and a micronization step of performing the micronization treatment on the anionic cellulose derivative-added carboxyl group-containing cellulose fiber.

Description

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

  Conventionally, petroleum-derived polymer materials, which are finite resources, have been widely used, but in recent years, technologies that have a low environmental impact have come to the spotlight. As a material using cellulose fibers, for example, a technology related to cellulose fibers having a nano-sized fiber diameter (cellulose nanofibers) is drawing attention.

As a method for producing hanging cellulose nanofibers, there is known a production method including an oxidation reaction step in which natural cellulose fibers are oxidized to obtain carboxy group-containing cellulose fibers, and a refinement step in which the carboxy group-containing cellulose fibers are refined. For example, Patent Document 1 describes a method in which natural cellulose fibers are oxidized in the presence of an N-oxyl compound and then fibrillated and dispersed with an ultrahigh pressure homogenizer or the like to form nanofibers.
Patent Document 2 discloses a method for producing a dispersion in which cellulose nanofibers are dispersed in a medium, using natural cellulose fiber as a raw material, N-oxyl compound as an oxidation catalyst, and a co-oxidant acting to oxidize. Using a disperser such as an ultra-high pressure homogenizer, the oxidation reaction step for obtaining the reaction product fiber, the purification step for obtaining the reaction product fiber impregnated with water by removing impurities, and the reaction product fiber impregnated with water A production method having a dispersion step of dispersing in a solvent is described.
The production of such conventional cellulose nanofibers has a drawback that a large mechanical energy is required for the process of refining oxidized cellulose fibers. In order to produce cellulose nanofibers, it has also been proposed that cellulase, which is a degrading enzyme, can be produced with low energy, but there is a problem that cellulose fibers are shortened by cellulase to lower the viscosity.

  Patent Document 3 proposes a method using a cationizing agent in the production of fine cellulose fibers, but the produced cellulose fibers are also cation group-containing cellulose fibers. In this method, since the reaction proceeds under strong alkali conditions, there is a possibility that the crystallinity of the cellulose is lowered or eluted.

JP 2010-235679 A JP 2008-1728 A JP 2011-162608 A

  Therefore, the subject of this invention is providing the manufacturing method of the cellulose nanofiber which can solve the solution subject which the prior art mentioned above has.

  The present invention is a method for producing cellulose nanofibers, which comprises producing cellulose nanofibers from carboxy group-containing cellulose fibers obtained by oxidizing natural cellulose fibers using an oxidant and an N-oxyl compound, the carboxy group containing The present invention provides a method for producing cellulose nanofiber, in which an anionic cellulose derivative is added to a cellulose fiber, followed by a refinement process for performing a refinement treatment.

  According to the method for producing cellulose nanofibers of the present invention, it is possible to promote the refinement of oxidized cellulose fibers in the refinement process while suppressing shortening of oxidized cellulose fibers, and the energy required for producing cellulose nanofibers. Can be reduced.

  The cellulose nanofibers produced in the present invention preferably have an average fiber diameter of 200 nm or less. The average fiber diameter of the cellulose nanofiber is preferably 1 nm or more, and preferably 200 nm or less, more preferably 100 nm or less, particularly preferably 50 nm or less, more specifically, preferably 1 nm or more and 200 nm or less, more preferably 1 nm. The thickness is not less than 100 nm and particularly preferably not less than 1 nm and not more than 50 nm. The average fiber diameter is measured by the following measuring method.

<Measurement method of average fiber diameter>
A cellulose nanofiber aqueous dispersion having a solid content of 0.0001% by mass was prepared, and the dispersion was dropped onto mica (mica) and dried, and an observation sample was used as an observation sample. Atomic force microscope (AFM, Nanoscope III) Tapping mode AFM, manufactured by Digital instrument, and the probe uses Point Probe (NCH) manufactured by Nanosensors), and the fiber height of the cellulose nanofiber in the observation sample is measured. And in the microscope image which can confirm a cellulose nanofiber, five or more cellulose nanofibers are extracted, and an average fiber diameter is computed from the height of those fibers. In general, microfibrils, which are the smallest unit of cellulose nanofibers prepared from higher plants, are cellulose nanofibers that can be analyzed by AFM images because 6 × 6 cellulose molecular chains are packed in a shape of a square cross section. The height of the fiber can be regarded as the fiber diameter.

The present invention is a method for producing cellulose nanofibers from carboxy group-containing cellulose fibers obtained by oxidizing natural cellulose fibers using an oxidizing agent and an N-oxyl compound.
The carboxy group-containing cellulose fiber is obtained by oxidizing natural cellulose fiber using an oxidizing agent and an N-oxyl compound.
In this oxidation reaction step, first, a slurry in which natural cellulose fibers are dispersed in water is prepared. The slurry is obtained by adding about 10 to 1000 times (mass basis) of water to the natural cellulose fiber (absolute dry basis) as a raw material, and processing with a mixer or the like. Examples of natural cellulose fibers include wood pulp such as softwood pulp and hardwood pulp; cotton pulp such as cotton linter and cotton lint; non-wood pulp such as straw pulp and bagasse pulp; and bacterial cellulose. These 1 type can be used individually or in combination of 2 or more types. The natural cellulose fiber may be subjected to a treatment for increasing the surface area such as beating.

  Next, using a N-oxyl compound as an oxidation catalyst, natural cellulose fibers are oxidized in water to obtain carboxy group-containing cellulose fibers. Examples of N-oxyl compounds include 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO), 4-acetamido-TEMPO, 4-carboxy-TEMPO, 4-phosphonooxy-TEMPO, and the like. Can be used. A catalytic amount is sufficient for the addition of the N-oxyl compound, and is usually in the range of 0.1 to 10% by mass relative to the natural cellulose fiber (absolute dry basis) used as a raw material.

  In the oxidation treatment of natural cellulose fiber, an oxidizing agent (for example, hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogenic acid or a salt thereof, hydrogen peroxide, a perorganic acid, etc.) and a co-oxidant (For example, alkali metal bromide such as sodium bromide). As the oxidizing agent, alkali metal hypohalites such as sodium hypochlorite and sodium hypobromite are particularly preferable. The amount of the oxidizing agent used is usually in the range of about 1 to 100% by mass with respect to the natural cellulose fiber (absolute dry standard) used as a raw material. Moreover, the usage-amount of a co-oxidant is the range used as about 1-30 mass% normally with respect to the natural cellulose fiber (absolute dry reference | standard) used as a raw material.

  In the oxidation treatment of natural cellulose fibers, it is desirable to maintain the pH of the reaction solution (slurry) in the range of 9 to 12 from the viewpoint of allowing the oxidation reaction to proceed efficiently. The temperature of the oxidation treatment (the temperature of the slurry) is arbitrary at 1 to 50 ° C., but the reaction is possible at room temperature, and no temperature control is required. The reaction time is preferably 1 to 240 minutes.

  A refinement | purification process is implemented after an oxidation reaction process and before a refinement | miniaturization process, and impurities other than the carboxy-group containing cellulose fiber and water contained in the said slurry, such as an unreacted oxidizing agent and various by-products, are removed. Since the carboxy group-containing cellulose fibers are usually not dispersed to the nanofiber unit at this stage, a purification method in which washing and filtration are repeated, for example, can be performed in the purification step. The purification apparatus used in that case is not particularly limited. The refined carboxy group-containing cellulose fibers thus obtained are usually sent to the next step (miniaturization step) impregnated with an appropriate amount of water, but if necessary, dried fibers or powders It is also good.

  In a preferred embodiment of the present invention, an anionic cellulose derivative is added to the carboxy group-containing cellulose fiber obtained by the above-described method, and then a refinement treatment is performed. A cellulose derivative is added to the dispersion liquid which disperse | distributed the carboxy-group containing cellulose fiber which passed through the refinement | purification process mentioned above in solvents, such as water, for example.

As used herein, “anionic” refers to a substance having a charge amount of 0.1 mmol / g or more. Therefore, it can be said that a negative charge of less than 0.1 mmol / g is nonionic.
The charge amount of the anionic cellulose derivative is preferably 1.0 mmol / g or more, more preferably 1.5 mmol / g or more, particularly preferably 1.8 mmol / g or more, and preferably 3.4 mmol. / G or less, more preferably 3.1 mmol / g or less, particularly preferably 3.0 mmol / g or less, and preferably 1.0 mmol / g or more and 3.4 mmol / g or less, more preferably 1 0.5 mmol / g or more and 3.1 mmol / g or less, and particularly preferably 1.8 mmol / g or more and 3.0 mmol / g or less. When the charge amount is within this range, the cleavage between the fibers in the miniaturization process is more reliably promoted, and the cellulose nanofibers can be produced with low energy.

The charge amount of the anionic cellulose derivative is measured by the following method.
<Measurement method of charge amount of anionic cellulose derivative>
A dispersion is prepared by diluting an anionic cellulose derivative to 0.1% by mass with ion-exchanged water. Volume of cationic titration solution (0.001N polydiallyldimethylammonium chloride, purchased from BTG Mutek) consumed to neutralize 10 g of this dispersion using a particle charge meter (PCD 03, Mutek) Measure. The charge amount of the anionic cellulose derivative is calculated by dividing the product of the volume amount and the charge amount of the titration solution by the mass of the anionic cellulose dielectric in the dispersion.

Examples of the anionic cellulose derivative include carboxymethyl cellulose (abbreviation “CMC”), polyuron sun (PUA) obtained from cellulose described in JP-A-2009-298968, and sulfonated cellulose. CMC is preferable from the viewpoints of being easy to promote and miniaturization.
Whether or not the cellulose derivative is anionic is determined based on, for example, that an aqueous solution of the cellulose derivative is measured using the particle charge meter (PCD 03, manufactured by Mutek) described above, and the charge value is negative. Can be determined.

  When CMC is used, the degree of substitution of CMC is preferably 0.1 or more, more preferably 0.45 or more, and preferably 0.9 or less, from the viewpoint of facilitating miniaturization. More preferably, it is 0.8 or less, Preferably it is 0.1 or more and 0.9 or less, More preferably, it is 0.45 or more and 0.8 or less.

<Measurement method of CMC substitution degree>
The degree of substitution of CMC is measured by the following method.
Take CMC with a dry mass of 0.5 g in a 100 ml beaker, add ion exchange water to make a total of 55 ml, add 5 ml of 0.01 M sodium chloride aqueous solution to prepare an aqueous solution, and add the aqueous solution until CMC is fully dissolved. Stir. 0.1M hydrochloric acid is added to this aqueous solution to adjust the pH to 2.5-3, and an automatic titration apparatus (AUT-50, manufactured by Toa DKK Co., Ltd.) is used to wait for a waiting time of 0.05M sodium hydroxide aqueous solution. The solution is dropped into the aqueous solution under the condition of seconds, and the electric conductivity and pH value are measured every minute, and the measurement is continued until the pH is about 11, thereby obtaining an electric conductivity curve. From this conductivity curve, a sodium hydroxide titration amount is obtained, and the carboxy group content of CMC is calculated by the following formula.
Carboxy group content (mmol / g) = sodium hydroxide titration × sodium hydroxide aqueous solution concentration (0.05 M) / mass of CMC (0.5 g)

When the carboxyl group content (mmol / g) is C, the degree of substitution of CMC is obtained by the following formula.
Degree of substitution of CMC = 162 × C / (10 ³ −80 × C)

  The amount of the cellulose derivative added to the carboxy group-containing cellulose fiber dispersion is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, based on the solid content of the carboxy group-containing cellulose fiber. Also, it is preferably 10% by mass or less, more preferably 5% by mass or less, preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 5% by mass or less. It is.

  In a preferred embodiment of the present invention, in this way, the dispersion of the carboxy group-containing cellulose fiber after the addition of the specific cellulose derivative is subjected to a fine treatment. By passing through this refinement | miniaturization process, a fiber nanofiber is cleaved and a cellulose nanofiber is obtained.

  In the above-mentioned micronization treatment, the solvent as the dispersion medium is usually preferably water, but water-soluble organic solvents (alcohols, ethers, ketones, etc.) may be used in addition to water depending on the purpose. These mixtures can also be suitably used. Examples of the disperser used in the miniaturization treatment include a disaggregator, a beater, a low pressure homogenizer, a high pressure homogenizer, a grinder, a cutter mill, a ball mill, a jet mill, a short shaft extruder, a twin screw extruder, an ultrasonic stirrer, and a household. Juicer mixer for use. The solid content concentration of the carboxy group-containing cellulose fiber in the refining treatment is preferably 50% by mass or less.

Cellulose nanofibers obtained after the micronization step are in a state of dispersion with high viscosity and high transparency. A high viscosity means that fiber shortening is suppressed as in the case of using cellulase, and a high transparency means that the fibers are split and the fineness has progressed sufficiently. Means that.
The liquid thus obtained in the form of a dispersion may be in the form of a suspension in which the solid content concentration is adjusted as needed (a liquid that is visually transparent or opaque) or in the form of a powder that has been dried ( However, it is a powder form in which cellulose nanofibers are aggregated and does not mean cellulose particles). When making a suspension, only water may be used as a dispersion medium, or a mixed solvent of water and other organic solvents (for example, alcohols such as ethanol), surfactants, acids, bases, etc. is used. You may do it.
Using the obtained dispersion containing cellulose nanofibers, a film-like product can be formed by a known method as described in, for example, JP-A No. 2010-168573.

  The obtained cellulose nanofibers preferably have a light transmittance of 40% or more, more preferably 60% or more, and still more preferably 80%, in an aqueous dispersion diluted to a solid content concentration of 1% by mass. That's it. A method for measuring the transmittance of cellulose nanofibers will be described later in Examples.

  By the oxidation treatment and refinement treatment of the natural cellulose fiber as described above, the hydroxyl group at the C6 position of the cellulose structural unit is selectively oxidized to a carboxy group via an aldehyde group, and the average fiber diameter is preferably 200 nm or less. It is possible to obtain highly crystalline cellulose fibers that have been refined to a minimum diameter of 5 mm. This highly crystalline cellulose fiber has a cellulose I-type crystal structure. This means that the cellulose nanofiber produced in the present invention is a fiber obtained by surface-oxidizing and refining a naturally-derived cellulose solid raw material having an I-type crystal structure. In other words, natural cellulose fibers have a high-order solid structure formed by a bundle of fine fibers called microfibrils produced in the process of biosynthesis. The mechanical energy applied by a disperser is conventionally reduced by weakening the hydrogen bond between the aldehyde group and carboxy group by the oxidation treatment and further performing the above-described refinement treatment in the presence of the cellulose derivative. Even if the amount is reduced, sufficiently refined highly crystalline cellulose fibers can be obtained. And by adjusting the conditions for the oxidation treatment, the carboxy group content is increased or decreased within a predetermined range.

  In addition to being fine (the average fiber diameter is preferably 200 nm or less), the cellulose nanofiber used in the present invention is preferably within a predetermined range of the carboxy group content of cellulose. Specifically, the carboxy group content of the cellulose constituting the cellulose nanofiber used in the present invention is preferably 0.1 mmol / g or more, more preferably 0.4 mmol / g or more, particularly preferably 0.6 mmol / g. Above, and preferably 3 mmol / g or less, more preferably 2 mmol / g or less, particularly preferably 1.8 mmol / g or less, more specifically preferably 0.1 mmol / g or more and 3 mmol / g or less, more preferably Is 0.4 mmol / g or more and 2 mmol / g or less, particularly preferably 0.6 mmol / g or more and 1.8 mmol / g or less.

  The carboxy group content of cellulose constituting the cellulose nanofiber is preferably 0.1 to 3 mmol / g in order to stably obtain cellulose nanofiber having a fine average fiber diameter of preferably 200 nm or less. It is an important element. That is, in the process of biosynthesis of natural cellulose, usually, nanofibers called microfibrils are first formed, and these are bundled to form a higher-order solid structure. As will be described later, the fiber is obtained by using this in principle, in order to weaken the hydrogen bond between the surfaces, which is the driving force of the strong cohesive force between the microfibrils in the naturally derived cellulose solid raw material. In addition, it is obtained by oxidizing a part thereof and converting it to a carboxy group. Therefore, the larger the total amount of carboxy groups present in cellulose (carboxy group content), the smaller the fiber diameter, the more stable it can exist, and in water, an electric repulsive force is generated. In addition, the tendency of microfibrils to break apart without maintaining agglomeration is increased, and the dispersion stability of nanofibers is further increased. The carboxy group content of the cellulose nanofiber is measured by the following measuring method. “Cellulose fiber” in the following measurement method can be read as “cellulose nanofiber”.

<Measurement method of carboxy group content>
Take a cellulose fiber with a dry mass of 0.5 g in a 100 ml beaker and add ion exchange water to make a total of 55 ml. The dispersion is stirred. 0.1M hydrochloric acid is added to this dispersion to adjust the pH to 2.5-3, and 0.05M sodium hydroxide aqueous solution is waited for using an automatic titrator (AUT-50, manufactured by Toa DKK Co., Ltd.). The solution is dropped into the dispersion under the condition of 60 seconds, and the conductivity and pH values are measured every minute, and the measurement is continued until the pH is about 11, thereby obtaining an conductivity curve. From this conductivity curve, a sodium hydroxide titration amount is obtained, and the carboxy group content of the cellulose fiber is calculated by the following formula.
Carboxy group content (mmol / g) = sodium hydroxide titration × sodium hydroxide aqueous solution concentration (0.05 M) / mass of cellulose fiber (0.5 g)

  The cellulose nanofibers produced by the production method of the present invention can be used without particular limitation for various known uses of cellulose nanofibers. For example, a film-like body obtained by coating a cellulose nanofiber dispersion is excellent in gas barrier properties and mechanical strength in a high-humidity atmosphere. For example, food, cosmetics, medicine, medical equipment, mechanical parts, electronic It is suitably used for applications such as packaging materials for equipment and clothing.

  In relation to the above-described embodiments, the present invention further discloses the following embodiments.

<1> A cellulose nanofiber production method for producing cellulose nanofibers from carboxy group-containing cellulose fibers obtained by oxidizing natural cellulose fibers using an oxidizing agent and an N-oxyl compound,
The manufacturing method of the cellulose nanofiber which performs the refinement | miniaturization process which performs refinement | miniaturization treatment, after adding an anionic cellulose derivative to the said carboxy group containing cellulose fiber.

<2> The method for producing cellulose nanofiber according to <1>, wherein the cellulose derivative is carboxymethylcellulose.
<3> The degree of substitution of the carboxymethyl cellulose is preferably 0.1 or more, more preferably 0.45 or more, and preferably 0.9 or less, more preferably 0.8 or less, specifically Is preferably 0.1 or more and 0.9 or less, more preferably 0.45 or more and 0.8 or less, the method for producing cellulose nanofiber according to <1> or <2>.
<4> The method for producing cellulose nanofiber according to <2> or <3>, wherein the degree of substitution of the carboxymethylcellulose is 0.1 or more and 0.9 or less.
<5> The addition amount of the cellulose derivative is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and preferably 10% with respect to the solid content of the carboxy group-containing cellulose fiber. <1> The mass% or less, more preferably 5 mass% or less, preferably 0.01 mass% or more and 10 mass% or less, more preferably 0.1 mass% or more and 5 mass% or less. The manufacturing method of the cellulose nanofiber any one of-<4>.
<6> The additive according to any one of <1> to <5>, wherein the addition amount of the cellulose derivative is 0.01% by mass or more and 10% by mass or less with respect to the solid content of the carboxy group-containing cellulose fiber. A method for producing cellulose nanofibers.
<7> The charge amount of the anionic cellulose derivative is preferably 1.0 mmol / g or more, more preferably 1.5 mmol / g or more, particularly preferably 1.8 mmol / g or more, and preferably 3.4 mmol / g or less, more preferably 3.1 mmol / g or less, particularly preferably 3.0 mmol / g or less, and preferably 1.0 mmol / g or more and 3.4 mmol / g or less, more The cellulose according to any one of <1> to <6>, preferably 1.5 mmol / g or more and 3.1 mmol / g or less, and more preferably 1.8 mmol / g or more and 3.0 mmol / g or less. Manufacturing method of nanofiber.
<8> The method for producing cellulose nanofiber according to any one of <1> to <7>, wherein a charge amount of the anionic cellulose derivative is 1.0 mmol / g or more and 3.4 mmol / g or less.
<9> Examples of the N-oxyl compound include 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO), 4-acetamido-TEMPO, 4-carboxy-TEMPO, and 4-phosphonooxy. -The manufacturing method of the cellulose nanofiber any one of said <1>-<8> using at least 1 sort (s) chosen from TEMPO.

<10> The cellulose nano according to any one of <1> to <9>, wherein the anionic cellulose derivative is added to the dispersion of the carboxy group-containing cellulose fiber, and then a micronization process is performed to perform micronization. Fiber manufacturing method.
<11> The method for producing cellulose nanofiber according to <10>, wherein water is used as a dispersion medium of the dispersion liquid of the carboxy group-containing cellulose fiber in the miniaturization treatment.
<12> The method for producing cellulose nanofiber according to <10> or <11>, wherein the carboxy group-containing cellulose fiber in the refinement treatment has a solid content concentration of 50% by mass or less.
The manufacturing method of the cellulose nanofiber any one of said <10>-<12> which performs the said refinement | miniaturization process using a <13> homogenizer.
<14> The average fiber diameter of the cellulose nanofiber is preferably 1 nm or more, and preferably 200 nm or less, more preferably 100 nm or less, particularly preferably 50 nm or less, more specifically, preferably 1 nm or more and 200 nm or less, More preferably, it is 1 nm or more and 100 nm or less, Especially preferably, it is 1 nm or more and 50 nm or less, The manufacturing method of the cellulose nanofiber any one of said <1>-<13>.
<15> The carboxy group content of cellulose constituting the cellulose nanofiber is preferably 0.1 mmol / g or more, more preferably 0.4 mmol / g or more, particularly preferably 0.6 mmol / g or more, and preferably Is 3 mmol / g or less, more preferably 2 mmol / g or less, particularly preferably 1.8 mmol / g or less, more specifically preferably 0.1 mmol / g or more and 3 mmol / g or less, more preferably 0.4 mmol / g. The method for producing cellulose nanofiber according to any one of <1> to <14>, wherein g is 2 to 2 mmol / g, particularly preferably 0.6 to 1.8 mmol / g.
<16> The light transmittance of the aqueous dispersion diluted so that the solid content concentration of the cellulose nanofiber is 1% by mass is preferably 40% or more, more preferably 60% or more, and still more preferably 80%. The method for producing cellulose nanofiber according to any one of the above items <1> to <15>.
<17> A cellulose nanofiber dispersion containing cellulose nanofibers produced by the production method according to any one of <1> to <16>.
<18> A film-like molded body formed from the cellulose nanofiber dispersion described in <17>.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to such examples. Hereinafter, unless otherwise specified, “%” means “mass%”.

[Method for producing carboxy-containing cellulose fiber]
Hereinafter, the carboxy-containing cellulose fiber is abbreviated as oxidized cellulose fiber.
Soft cellulose bleached kraft pulp (Fletcher Challenge Canada, CSF 650 ml) is used as the raw natural cellulose fiber, TEMPO (ALDRICH, Free radical, 98%) is used as the oxidation catalyst, and sodium hypochlorite (Japanese sum) Kobunyaku Kogyo Co., Ltd., Cl: 5%) was used, and sodium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a co-oxidant. 9900 g of ion-exchanged water is added to 100 g of natural cellulose fibers and sufficiently stirred to obtain a slurry. In the slurry, TEMPO is 1.25% by mass of pulp, sodium bromide is 12.5% by mass of pulp, hypochlorite. Sodium sulfate was added in an amount of 14.2% by weight to the pulp in this order, and a pH stud was used to maintain the pH of the slurry at 10.5 by dropwise addition of 0.5M sodium hydroxide. Natural cellulose fibers were oxidized. The dropping of sodium hydroxide was stopped after an oxidation time of 60 minutes, and the natural cellulose fiber after the oxidation treatment was sufficiently washed with ion-exchanged water and dehydrated. Thus, an oxidized cellulose fiber having a carboxyl group content of 0.9 mmol / g was obtained.

[Example 1]
[Method for producing cellulose nanofiber]
The oxidized cellulose fiber obtained in the above [Method for producing oxidized cellulose fiber] and ion-exchanged water were mixed so that the solid content concentration of the oxidized cellulose fiber was 0.3% by mass to obtain an oxidized cellulose fiber slurry. Further, CMC having the charge amount shown in Table 1 was dissolved in ion-exchanged water to prepare a 1.0 mass% CMC aqueous solution. Then, 0.15 g of CMC aqueous solution was added to 50 g of the oxidized cellulose fiber slurry described above, and stirred at 15,000 rpm with a small homogenizer (manufactured by Nippon Seiki Seisakusho, Excel Auto Homogenizer ED-4) to produce cellulose nanofibers. did. Stirring was stopped every predetermined time, and a part of the dispersion was collected to measure the transmittance and viscosity.
The results are shown in Table 1.

[Examples 2 to 4]
In Example 1, cellulose nanofibers were produced in the same manner as in Example 1, except that CMC having the charge amount and substitution degree shown in Table 1 was used as an additive.
The following were used as CMC of Examples 1-4.
Example 1: Serogen PL-15, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
Example 2: Serogen WS-C, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
Example 3: Serogen WS-D, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
Example 4: Serogen WS-A, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
[Comparative Example 1]
In Example 1, cellulose nanofibers were produced in the same manner as in Example 1 except that CMC was not added.
[Comparative Examples 2 to 4]
In Example 1, cellulose nanofibers were produced in the same manner as in Example 1 except that the following substances shown in Table 1 were added instead of CMC as an additive. None of the following substances are anionic cellulose derivatives.
PVP: Polyvinylpyrrolidone K30 (manufactured by Wako Pure Chemical Industries, Ltd.)
LAS: Sodium linear alkylbenzene sulfonate (manufactured by Wako Pure Chemical Industries, Ltd.)
MC: methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., Metro's SM-4)
[Evaluation]
Table 1 shows the transmittance and viscosity of the samples of Examples and Comparative Examples when the elapsed time from the start of stirring was 5 minutes and 15 minutes later.

<Measurement method of transmittance>
About the aqueous dispersion liquid of the obtained cellulose nanofiber, it measured with the transmittance | permeability in wavelength 660nm and optical path length 1cm using the ultraviolet visible spectrophotometer (UV-visible spectral hardness meter U-3310, Shimadzu Corp. make). did.

<Measurement method of viscosity>
Using an E-type viscometer VISCONIC manufactured by TOKIMEC, the viscosity of the aqueous dispersion of cellulose nanofibers obtained at 23 ° C. and a rotation speed of 5 rpm was measured.

As is clear from Table 1, in Examples 1 to 4 in which an anionic cellulose derivative was added and subjected to a refinement treatment, the viscosity and transmittance in 5 minutes and 15 minutes after the start of stirring were all All exceeded the comparative example 1 which has not added the anionic cellulose derivative. On the other hand, the viscosity of Comparative Example 2 was lower than that of Comparative Example 1 because the additive was not anionic and not a cellulose derivative. In Comparative Example 3, since the additive was anionic but not a cellulose derivative, the viscosity and transmittance were lower than Comparative Example 1. About Comparative Example 4, although it is a cellulose derivative, it is MC with a low charge amount and is not anionic as referred to in this specification, and therefore the viscosity was lower than that of Comparative Example 1.
Thus, by carrying out the refining treatment by adding the anionic cellulose derivative, a dispersion of cellulose nanofibers having high transmittance and viscosity can be obtained even under the same refining treatment conditions. A high transmittance means that the fiber is becoming finer and a high viscosity means that the fiber is long. That is, the addition of the anionic cellulose derivative in the present invention can promote the refinement of the oxidized cellulose fiber in the refinement process while suppressing the shortening of the oxidized cellulose fiber, and reduce the energy required for the refinement process. It can be seen that

Claims (7)

A cellulose nanofiber production method for producing cellulose nanofibers from carboxy group-containing cellulose fibers obtained by oxidizing natural cellulose fibers using an oxidizing agent and an N-oxyl compound,
The manufacturing method of the cellulose nanofiber which performs the refinement | miniaturization process which performs refinement | miniaturization treatment, after adding an anionic cellulose derivative to the said carboxy group containing cellulose fiber.   The method for producing cellulose nanofiber according to claim 1, wherein the cellulose derivative is carboxymethylcellulose.   The manufacturing method of the cellulose nanofiber of Claim 2 whose substitution degree of the said carboxymethylcellulose is 0.1-0.9.   The cellulose nanofiber production according to any one of claims 1 to 3, wherein an addition amount of the cellulose derivative is 0.01% by mass or more and 10% by mass or less based on a solid content of the carboxy group-containing cellulose fiber. Method.   The manufacturing method of the cellulose nanofiber of any one of Claims 1-4 whose charge amount of the said anionic cellulose derivative is 1 mmol / g or more and 3.4 mmol / g or less.   The cellulose nanofiber dispersion liquid containing the cellulose nanofiber manufactured by the manufacturing method of any one of Claims 1-5.   A film-like molded body formed from the cellulose nanofiber dispersion liquid according to claim 6.