JP2017101184A - Cellulose nanofiber-containing dried material and production method thereof, and method for producing cellulose nanofiber fluid dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cellulose nanofiber-containing dried material that is excellent in dispersibility in water and has less discoloration, and to provide a production method thereof; also to provide a method for producing a cellulose nanofiber fluid dispersion using said cellulose nanofiber-containing dried material.SOLUTION: A cellulose nanofiber-containing dried material of the present invention is a cellulose nanofiber-containing dried material containing a cellulose nanofiber having a content of carboxylic group by 0.1 mmol/g or less, and glycerin or glycerin derivative. The method for producing cellulose nanofiber-containing dried material of the present invention is a method for producing cellulose nanofiber-containing dried material including a step of producing a mixture by mixing a fluid dispersion of a cellulose nanofiber having a content of carboxylic acid by 0.1 mmol/g or less, and an aqueous solution of glycerin or glycerin derivative, and a step of drying the mixture.SELECTED DRAWING: None

Description

  The present invention relates to a cellulose nanofiber-containing dried product, a method for producing the same, and a method for producing a cellulose nanofiber dispersion.

  In recent years, nanotechnology that aims to refine materials to the nanometer level and obtain new physical properties that are different from conventional properties of materials has attracted attention. Cellulose nanofibers produced from pulp, which is a cellulosic raw material by chemical treatment, pulverization treatment, etc., are excellent in strength, elasticity, thermal stability, etc., so filter media, filter aids, ion exchanger substrates, It is expected to be used in industrial applications as fillers for chromatography analyzers, fillers for blending resins and rubbers, and for cosmetics such as lipsticks, powder cosmetics, and emulsified cosmetics. Yes. Cellulose nanofibers are excellent in water-based dispersibility, so they have viscosity retention agents for foods, cosmetics, paints, etc., food material dough strengtheners, moisture retention agents, food stabilizers, low calorie additives, emulsification It is expected to be used in many applications such as stabilizing aids.

  Cellulose nanofibers are usually obtained by refining water-dispersed pulp and the like. Therefore, the cellulose nanofibers obtained are in a water-dispersed state, and such a dispersion of cellulose nanofibers requires a great deal of energy during transportation. Also, cellulose nanofibers containing moisture can induce a water vapor explosion during melt kneading with the resin. Therefore, in view of commercialization, it is important to dry the dispersion of cellulose nanofibers. However, when the cellulose nanofibers are dried, the cellulose nanofibers strongly aggregate due to hydrogen bonding between the cellulose nanofibers. For this reason, when the dried cellulose nanofiber is dispersed again in water, there is a disadvantage that the dispersibility does not sufficiently return to the state before drying. Moreover, when a cellulose nanofiber is simply dried, the obtained dried product may be discolored (colored). A dried product of cellulose nanofibers that has undergone discoloration is not preferred because undesired coloration occurs when used as an additive.

  On the other hand, as a technique for improving the redispersibility of cellulose nanofibers in a dispersion medium, a step of mixing cellulose nanofibers having a carboxy group and a redispersion accelerator to obtain a gel-like body, and this gel-like body and organic A method for producing a cellulose nanofiber dispersion has been proposed, which comprises a step of mixing a functional liquid and a dispersant to redisperse cellulose nanofibers (see JP 2014-118521 A). However, this technique does not sufficiently dry the cellulose nanofibers, but forms a gel. In addition, cellulose nanofibers having a carboxy group generated by oxidation treatment are used, and such cellulose nanofibers have disadvantages such as time-consuming drying, low heat resistance, and not economical. . In addition, it is known that cellulose nanofibers having a carboxy group are produced in a trace amount of aldehyde groups and ketone groups as side reactions during the production process, and the aldehyde groups and ketone groups are colored yellow by heating. However, in the above technique, no consideration is given to the presence or absence of coloring of the resulting dried product.

  Further, as a technique for obtaining a dried product of bacterial cellulose having high redispersibility, a method of dehydrating and drying after adding a hydrophilic liquid or solid such as glycerin to an aqueous suspension containing bacterial cellulose has been proposed ( JP, 9-165402, A). However, bacterial cellulose is cellulose produced by microorganisms and has different physical properties from cellulose nanofibers that can be obtained by defibrating pulp. Therefore, even if this technique for drying bacterial cellulose is transferred to cellulose nanofibers, the same effect is not always produced.

  In addition, as a drying method of cellulose nanofibers, a freeze drying method, a critical point drying method, a method of drying after a substitution treatment with an organic solvent, and the like have been proposed (see Japanese Patent Application Laid-Open No. 6-233691). However, the freeze drying method and the critical point drying method require a great deal of energy. Further, the method of substitution with an organic solvent also requires the use of a nonpolar solvent in order to weaken the hydrogen bond, and it is difficult to say that it is preferable from the viewpoint of efficiency and economy.

JP 2014-118521 A JP-A-9-165402 Japanese Patent Laid-Open No. 6-233691

  This invention is made | formed based on the above situations, The objective is to provide the cellulose nanofiber containing dry body which is excellent in the dispersibility with respect to water, and has little discoloration, and its manufacturing method. Another object of the present invention is to provide a method for producing a cellulose nanofiber dispersion using such a cellulose nanofiber-containing dried product.

  The invention made in order to solve the said subject is a cellulose nanofiber containing dried body containing the cellulose nanofiber whose content of a carboxy group is 0.1 mmol / g or less, and glycerol or a glycerol derivative.

  Since the cellulose nanofiber-containing dried product contains glycerin or a glycerin derivative (hereinafter also referred to as “glycerin”) together with the cellulose nanofiber, it is excellent in water dispersibility. Although this reason is not certain, it is possible that the hydrogen bond between cellulose nanofibers will weaken because glycerol adheres to the cellulose nanofiber surface. In addition, by using cellulose nanofibers and glycerins having a small amount of carboxy groups, discoloration hardly occurs during drying, and a dried product with little discoloration can be obtained. Furthermore, since the combination of cellulose nanofibers and glycerin having a small amount of carboxy groups is not an ionic compound with each other, they can be mixed uniformly, and as a result, redispersibility is improved.

  As content of glycerol or a glycerol derivative with respect to 100 mass parts of said cellulose nanofibers, 0.1 to 200 mass parts is preferable. By making content of glycerol into the said range, dispersibility can be improved more, suppressing the high cost.

  Another invention made to solve the above problems is a step of obtaining a mixed solution by mixing a dispersion of cellulose nanofibers having a carboxy group content of 0.1 mmol / g or less and an aqueous solution of glycerin or a glycerin derivative. And the manufacturing method of a cellulose nanofiber containing dried body provided with the process of drying the said liquid mixture. According to the production method, a cellulose nanofiber-containing dry product having excellent water dispersibility and little discoloration can be obtained by a simple method. In addition, in the said manufacturing method, since the dispersion liquid of cellulose nanofiber and the aqueous solution of glycerol are mixed, the dry body with which the cellulose nanofiber and glycerol were mixed uniformly can be obtained.

  Yet another invention made to solve the above-described problems is a method for producing a cellulose nanofiber dispersion comprising a step of mixing the cellulose nanofiber-containing dried product with water. According to the method for producing a cellulose nanofiber dispersion, a cellulose nanofiber dispersion with high dispersibility, high concentration and little discoloration can be easily obtained.

  The cellulose nanofiber-containing dried product of the present invention has excellent water dispersibility and little discoloration. According to the method for producing a cellulose nanofiber-containing dry body of the present invention, a cellulose nanofiber-containing dry body having excellent dispersibility in water and no discoloration can be obtained. According to the method for producing a cellulose nanofiber dispersion of the present invention, a cellulose nanofiber dispersion with high dispersibility, high concentration and little discoloration can be easily obtained.

  Hereinafter, a method for producing a cellulose nanofiber-containing dried product, a cellulose nanofiber-containing dried product, and a method for producing a cellulose nanofiber dispersion according to an embodiment of the present invention will be described in detail.

<Method for Producing Cellulose Nanofiber-Containing Dry Body>
The method for producing a cellulose nanofiber-containing dry body according to an embodiment of the present invention,
A step of obtaining a mixed solution by mixing a dispersion of cellulose nanofibers having a carboxy group content of 0.1 mmol / g or less and an aqueous solution of glycerin or a glycerin derivative, and a step of drying the mixed solution (B )
Is provided.

(Cellulose nanofiber)
First, the cellulose nanofiber contained in the dispersion liquid used for a process (A) is demonstrated. Cellulose nanofibers refer to fine cellulose fibers obtained by defibrating plant raw materials such as pulp (pulp fibers), and generally cellulose containing cellulose fine fibers with a fiber width of nanosize (1 nm to 1000 nm). Refers to fiber. Cellulose nanofibers can usually be obtained by fibrillating plant materials (fiber materials) by a known method.

Examples of the pulp used as a raw material for cellulose nanofiber include hardwood kraft pulp (LKP) such as hardwood bleached kraft pulp (LBKP), hardwood unbleached kraft pulp (LUKP), softwood bleached kraft pulp (NBKP), and softwood unbleached kraft pulp. Chemical pulp such as conifer kraft pulp (NKP) such as (NUKP);
Stone Grand Pulp (SGP), Pressurized Stone Grand Pulp (PGW), Refiner Grand Pulp (RGP), Chemi Grand Pulp (CGP), Thermo Grand Pulp (TGP), Grand Pulp (GP), Thermo Mechanical Pulp (TMP), Mechanical pulp such as chemi-thermomechanical pulp (CTMP) and bleached thermomechanical pulp (BTMP);
Waste paper pulp made from waste tea paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, corrugated waste paper, Kami white waste paper, Kent waste paper, imitation waste paper, local paper waste paper, recycle paper waste paper, etc .;
Examples include deinked pulp (DIP) obtained by deinking waste paper pulp. These may be used singly or may be used in combination of plural kinds as long as the effects of the present invention are not impaired.

  Among these, chemical pulp is preferable, and hardwood kraft pulp (LKP) is more preferable from the viewpoint of easy drying. Such a pulp also has the advantage that it has few impurities.

  Examples of other plant materials include linter pulp, hemp, bagasse, kenaf, esparto grass, pulp obtained from bamboo, rice husk, straw and the like. Further, wood, hemp, bagasse, kenaf, esparto grass, bamboo, rice husk, straw, etc., which are raw materials for pulp, can also be used directly as plant raw materials. Hereinafter, although the manufacturing method of the cellulose nanofiber at the time of using a pulp as a plant raw material is demonstrated, also in the case of plant raw materials other than a pulp, a cellulose nanofiber can be obtained with the same method.

  As a manufacturing method of a cellulose nanofiber, unless the effect of this invention is impaired, it does not specifically limit, A well-known method can be used. For example, water-dispersed pulp may be subjected to defibration by mechanical treatment, and may be subjected to defibration by chemical treatment such as enzyme treatment, acid treatment, etc., but is preferably defibrated by mechanical treatment. . By defibrating the pulp by mechanical treatment, cellulose nanofibers can be obtained more easily and reliably, and the dispersibility of the dried product obtained using glycerins can be further increased, and the discoloration can be improved. A small dry body can also be obtained.

  Examples of the defibrating method by mechanical treatment include a grinder method in which pulp is ground between rotating grindstones, an opposing collision method using a high-pressure homogenizer, a grinding method using a ball mill, a roll mill, a cutter mill, and the like. Usually, the defibrating process is repeated until the cellulose nanofibers obtained by defibrating the pulp have a desired size.

  The pulp may be subjected to preliminary beating before defibration. Pre-beating (mechanical pretreatment) is not particularly limited, and a known method can be used. As an example of a specific method, it is preferable to proceed with defibration step by step. Grinder that grinds between unrotated raw pulp in advance with a so-called viscous beating facility such as a Niagara beater, and preliminarily beats the freeness (Canadian Freeness) to 30% or less of the starting raw material, and then rotates between rotating wheels. It is preferable to defibrate until cellulose nanofibers are obtained by the method.

  The pulp may be subjected to chemical pretreatment before defibration. Examples of the chemical pretreatment include hydrolysis treatment using an acid such as sulfuric acid or an enzyme. By performing chemical pretreatment in this way, cellulose nanofibers can be efficiently obtained by mechanical or chemical defibrating treatment.

  In addition, the cellulose nanofiber used for the manufacturing method of the said cellulose nanofiber containing dried body has a carboxy group content of 0.1 mmol / g or less. As described above, by using the cellulose nanofibers with low ionicity in which the carboxy group is not substantially modified, it is possible to improve the uniform mixing property with non-ionic or low ionic glycerins. Moreover, discoloration of the dried body obtained can be reduced or discoloration can be completely eliminated. Furthermore, by using cellulose nanofibers that are not substantially modified with a carboxy group, drying can be performed relatively easily, the heat resistance of the molded body using cellulose nanofibers is increased, and economic efficiency is excellent. There are advantages such as.

  The carboxy group is introduced into the raw material pulp using surface oxidation with an N-oxyl compound or the like and various oxidizing agents. Therefore, cellulose nanofibers having a carboxy group content of 0.1 mmol / g or less can be obtained by controlling surface oxidation with an N-oxyl compound or the like as pretreatment or oxidation treatment with an oxidizing agent. As an upper limit of content of the carboxy group of cellulose nanofiber, 0.05 mmol / g is preferable. On the other hand, the lower limit may be 0 mmol / g, but may also be 0.0001 mmol / g. The carboxy group content of the cellulose nanofiber can be determined by neutralization titration. In addition, when the amount of carboxy groups is not substantially changed before and after the defibrating treatment, such as when the pulp is defibrated only by mechanical treatment, the carboxy group content of the cellulose nanofibers is It is substantially the same as the carboxy group content of the pulp. That is, in this case, the carboxy group content of the cellulose nanofiber can be determined by neutralization titration on the pulp before the defibrating treatment.

  The water retention of the cellulose nanofiber is preferably, for example, from 250% to 500%. When the water retention is less than the above lower limit, it may not be a sufficiently fine cellulose nanofiber. On the other hand, when a water retention degree exceeds the said upper limit, there exists a possibility that the redispersibility of the obtained cellulose nanofiber containing dried body may fall. The water retention (%) of the cellulose nanofiber was determined by JAPAN TAPPI No. 26 is measured.

  The cellulose nanofibers preferably have a single peak in a pseudo particle size distribution curve measured by a laser diffraction method in an aqueous dispersion state. Thus, the cellulose nanofiber having one peak has been sufficiently refined, and can exhibit good physical properties as a cellulose nanofiber. Moreover, as a particle size (mode) of the cellulose nanofiber which becomes this peak, 5 micrometers or more and 25 micrometers or less are preferable, for example. Various characteristics peculiar to a cellulose nanofiber can be exhibited more favorably because a cellulose nanofiber is the said size. The “pseudo particle size distribution curve” means a curve showing a volume-based particle size distribution measured using a particle size distribution measuring device (for example, a laser diffraction / scattering type particle size distribution measuring instrument manufactured by Seishin Corporation).

(Process (A))
In the step (A), a mixed liquid is obtained by mixing a dispersion of cellulose nanofibers and an aqueous solution of glycerol.

  The dispersion includes cellulose nanofibers and a dispersion medium of cellulose nanofibers. The dispersion medium is usually water. The dispersion may further contain other components as long as the effects of the present invention are not impaired. Although it does not specifically limit as content of the cellulose nanofiber in this dispersion liquid, For example, it can be 0.1 mass% or more and 5 mass% or less.

  The aqueous solution contains glycerin and water as a solvent. However, other components may be further contained as long as the effects of the present invention are not impaired. Although it does not specifically limit as content of glycerol in this aqueous solution, For example, it can be 0.1 mass% or more and 5 mass% or less.

  Among the glycerins, a glycerin derivative refers to a compound obtained from glycerin. Examples of the glycerin derivative include glycerin esters such as glycerol monoacetate, glycerol diacetate, glycerol triacetate, glycerol tributyrate, and glycerol ether acetate, and polyglycerin obtained by polymerizing glycerin.

  As the glycerins, glycerin is preferable because the obtained dried product can exhibit good dispersibility.

  By mixing the dispersion of cellulose nanofibers and an aqueous solution of glycerols, the cellulose nanofibers and glycerols can be uniformly mixed. In addition, after mixing, it is preferable to stir the mixed solution using a known stirrer or the like as necessary.

  In the mixed solution obtained by mixing, the mixing ratio of cellulose nanofibers and glycerols is not particularly limited. As a minimum of content of glycerol with respect to 100 mass parts of cellulose nanofibers in a liquid mixture, 0.1 mass part is preferred, 1 mass part is more preferred, 10 mass parts is still more preferred, 50 mass parts is still more preferred, 80 Part by mass is particularly preferred. On the other hand, as this upper limit, 200 mass parts is preferable, 150 mass parts is more preferable, and 120 mass parts is further more preferable. When content of glycerol is less than the said minimum, the obtained cellulose nanofiber containing dried body may not exhibit favorable dispersibility. On the other hand, when the content of glycerin exceeds the above upper limit, the amount of glycerin used increases and the cost may increase.

  Although the said liquid mixture contains water, a cellulose nanofiber, and glycerol, unless the effect of this invention is inhibited, it may further contain other components other than water, a cellulose nanofiber, and glycerol. However, as content of the other component in a liquid mixture, 10 mass% or less is preferable and 1 mass% or less is more preferable.

  Although it does not specifically limit as solid content concentration in the said liquid mixture, As a minimum, 0.1 mass% is preferable and 0.5 mass% is more preferable. On the other hand, as this upper limit, 5 mass% is preferable and 3 mass% is more preferable. When solid content concentration is less than the said minimum, it exists in the tendency for drying efficiency to fall. On the other hand, when the solid content concentration exceeds the above upper limit, it may be difficult to prepare a mixed solution.

(Process (B))
In the step (B), the liquid mixture obtained in the step (A) is dried. Thereby, a cellulose nanofiber containing dried product can be obtained. In such a drying process, it is guessed that glycerols precipitate on the surface of a cellulose nanofiber, and can obtain the cellulose nanofiber containing dried body of the state by which each cellulose nanofiber was coat | covered with glycerol. The cellulose nanofiber-containing dried product thus obtained can exhibit high redispersibility because hydrogen bonds between the cellulose nanofibers are inhibited by glycerins. Further, the cellulose nanofiber-containing dried product thus obtained is a dried product with little discoloration, preferably substantially free from discoloration.

  The method for drying the mixed solution is not particularly limited, and can be performed by a known method such as natural drying, heat drying, vacuum drying, freeze drying, spray drying and the like. In addition, the particulate cellulose nanofiber containing dried body which is especially excellent in redispersibility can be obtained by spray drying.

  As a minimum of the drying temperature in a process (B), 80 ° C is preferred and 90 ° C is more preferred. On the other hand, as this upper limit, 160 degreeC is preferable and 120 degreeC is more preferable. When the drying temperature is less than the above lower limit, it may be difficult to obtain a sufficiently dried cellulose nanofiber-containing dried product. Conversely, when the drying temperature exceeds the above upper limit, the cellulose nanofibers may be discolored by heat.

  Although it changes with drying temperature etc. as drying time in a process (B), it can be 1 hour or more and 24 hours or less, for example.

<Cellulose nanofiber-containing dried product>
The cellulose nanofiber-containing dry body according to the embodiment of the present invention is a cellulose nanofiber-containing dry body containing cellulose nanofibers having a carboxy group content of 0.1 mmol / g or less and glycerin or a glycerin derivative. As will be described in detail later, the cellulose nanofiber-containing dried product can be used as a dispersion remixed with water and redispersed. The said cellulose nanofiber containing dried body can be suitably obtained with the manufacturing method of the cellulose nanofiber containing dried body mentioned above.

  Specific examples and preferred examples of the cellulose nanofibers and the production method thereof contained in the cellulose nanofiber-containing dry body are the same as those exemplified in the description of the production method of the cellulose nanofiber-containing dry body. Moreover, the specific example and suitable example of glycerol contained in the said cellulose nanofiber containing dried body are the same as what was illustrated in description of the manufacturing method of a cellulose nanofiber containing dried body.

  As a minimum of content of glycerol with respect to 100 mass parts of cellulose nanofibers in the dry body containing cellulose nanofibers, 0.1 mass part is preferred, 1 mass part is more preferred, 10 mass parts is still more preferred, and 50 mass parts. Is more preferable, and 80 parts by mass is particularly preferable. On the other hand, as this upper limit, 200 mass parts is preferable, 150 mass parts is more preferable, and 120 mass parts is further more preferable. If the glycerin content is less than the lower limit, good dispersibility may not be exhibited. On the contrary, when content of glycerol exceeds the said upper limit, content of a cellulose nanofiber falls relatively, and a use and a function may be restrict | limited.

  The moisture content (water content) of the cellulose nanofiber-containing dry body is, for example, less than 80% by mass, preferably 50% by mass or less, more preferably 20% by mass or less, and further preferably 15% by mass or less, 10 mass% or less is especially preferable. When the moisture content is less than or equal to the above upper limit, energy consumption during transportation and the like can be further reduced, and handling properties and storage properties are improved. Moreover, the danger of the steam explosion at the time of melt-kneading with resin can be reduced. In addition, as a minimum of the moisture content of the said cellulose nanofiber containing dried body, although it may be 0 mass% substantially, 0.1 mass%, 1 mass%, and 3 mass% may be sufficient.

  Although it does not specifically limit as a shape of the said cellulose nanofiber containing dried body, It is preferable that it is a particulate form and a film form. The dispersibility with respect to water can be improved more because a cellulose nanofiber containing dried body is a particulate form or a film form. In the case where the cellulose nanofiber-containing dried product is in the form of particles, the average particle size can be, for example, 1 μm or more and 5 mm or less. “Average particle size” is calculated in accordance with JIS-Z-8819-2 (2001) based on the particle size distribution measured by the laser diffraction / scattering method in accordance with JIS-Z-8815 (2013). The volume reference cumulative distribution is 50%. When the said cellulose nanofiber containing dried body is a film form, as this average thickness, it can be set as 0.1 micrometer or more and 1 mm or less, for example.

  The cellulose nanofiber-containing dried product is substantially composed of cellulose nanofibers and glycerins. The cellulose nanofiber-containing dried product may contain other components (solid content) other than cellulose nanofibers and glycerin as long as the effects of the present invention are not impaired. As content of other components (solid content) other than a cellulose nanofiber and glycerol in the said cellulose nanofiber containing dried body, when the total amount of a cellulose nanofiber and glycerol is 100 mass parts, it is 10 mass. Part or less is preferable, and 5 parts by weight or less is more preferable. When the content of other components exceeds the above lower limit, these components may affect the dispersibility of cellulose nanofibers.

<Method for producing cellulose nanofiber dispersion>
The manufacturing method of the cellulose nanofiber dispersion which concerns on embodiment of this invention is equipped with the process of mixing the said cellulose nanofiber containing dried body and water. According to the method for producing a cellulose nanofiber dispersion, since a highly dispersible cellulose nanofiber-containing dried product is used, a highly dispersible and highly concentrated cellulose nanofiber dispersion can be easily obtained. Moreover, the cellulose nanofiber dispersion liquid without coloring can be obtained. The water mixed with the cellulose nanofiber-containing dried product may be pure water, or an aqueous solution or water dispersion containing other components. In mixing the cellulose nanofiber-containing dried product and water, stirring is preferably performed as necessary.

  It does not specifically limit as a stirring method, Well-known methods, such as stirring using a stirring blade and a rotor and stirring by an ultrasonic wave, can be used. As a stirrer used for stirring, an automatic or manual shaker, a magnetic stirrer, an ultrasonic vibrator, a stirrer having other various stirrers, a media mill such as a bead mill, a static stirrer such as a static mixer, etc. Can be mentioned.

  Although it does not specifically limit as a density | concentration of the cellulose nanofiber in the obtained cellulose nanofiber dispersion liquid, As a minimum, it is 0.1 mass%, for example, and 0.5 mass% is preferable. On the other hand, as this upper limit, it is 5 mass%, for example, and can be 3 mass%.

  The cellulose nanofiber-containing dried product of the present invention, the production method thereof, and the production method of the cellulose nanofiber dispersion are not limited to the above embodiment. For example, the cellulose nanofiber-containing dried product can be used by being redispersed in a dispersion medium other than water. Further, it may be redispersed in a mixed solvent of water and another dispersion medium. Examples of the dispersion medium other than water include alcohols, ethers, ketones, esters, and hydrocarbons. Moreover, the said cellulose nanofiber containing dried body can also be mixed and used for resin etc., for example.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

<Evaluation method>
Various physical properties of Examples and Comparative Examples were measured according to the following evaluation methods.

(Pseudo particle size distribution curve)
In accordance with ISO-13320 (2009), a curve indicating a volume-based particle size distribution is measured using a particle size distribution measuring device (“Laser diffraction / scattering particle size distribution measuring instrument” manufactured by Seishin Enterprise Co., Ltd.), and the number of peaks is determined. I counted.

(Water retention (%))
The water retention (%) of the cellulose nanofiber is determined by JAPAN TAPPI No. 26: 2000.

(Carboxy group content (mmol / g))
Pulp (raw pulp or oxidized pulp) before defibration was precisely weighed, adjusted to pH 2.5 to 3.0, and automatically titrated with 0.05 mol / L sodium hydroxide. Conductivity measurement (measurement at room temperature using a conductivity device “pH / ion / EC / DO meter MN-60R” manufactured by Toa DKK Co., Ltd.) was performed, and the range where there was no change in conductivity was defined as the amount of carboxy groups.

[Example 1]
The raw pulp (LBKP: moisture 98 mass%) was preliminarily beaten for 2 hours 30 minutes using a Niagara beater. Subsequently, the fiber was disentangled twice using a stone mill type disperser (“Supermass colloider” manufactured by Masuko Sangyo Co., Ltd.) to obtain an aqueous dispersion (concentration 2% by mass) of cellulose nanofibers. Cellulose nanofibers contained in this aqueous dispersion had one peak in the pseudo particle size distribution of particle size distribution measurement using laser diffraction, and the water retention was 350% or more. The content of carboxy group was 0.05 mmol / g.

  98 g of water and 2 g of glycerin were mixed and stirred at 600 rpm for 60 minutes using a magnetic stirrer to obtain an aqueous glycerin solution.

  25 g of the obtained aqueous dispersion of cellulose nanofibers having a concentration of 2% by mass and 25 g of an aqueous glycerin solution having a concentration of 2% by mass were mixed and stirred at 1200 rpm for 60 minutes using a magnetic stirrer to obtain a mixed solution. The mixing ratio (mass ratio) of cellulose nanofiber (CNF) and glycerin is 100: 100. This mixed solution was dried at 105 ° C. for 6 hours to obtain a film-like cellulose nanofiber-containing dried product. The water content of the obtained cellulose nanofiber was 5.0% by mass.

[Examples 2-3, Comparative Examples 1-9, 11]
The same as in Example 1 except that the compound shown in Table 1 was used as a redispersant (glycerin or an alternative component thereof), and the mixing ratio with cellulose nanofiber was changed to the ratio shown in Table 1. The cellulose nanofiber containing dried body of Examples 2-3 and Comparative Examples 1-9, 11 was obtained. In Comparative Example 11, a cellulose nanofiber-containing dried product was obtained by drying an aqueous dispersion of cellulose nanofibers as it was without mixing glycerin or an alternative component thereof.

[Comparative Example 10]
After mixing 10 g raw pulp (LBKP: moisture 98 mass%), 0.16 g TEMPO and 1.0 g sodium bromide in 500 ml water, add 25 ml of 12 mass% sodium hypochlorite aqueous solution. Reacted. During the reaction, a 0.5 M (molar concentration) aqueous sodium hydroxide solution was added so that the pH would not be lower than 10. The reaction was terminated when the pH change ceased, washed with water, filtered, and oxidized pulp was obtained. At this time, the introduction amount of the carboxy group was 1.29 mmol / g. The obtained oxidized pulp was diluted to a solid content concentration of 2% by mass and dispersed with a homomixer at 12,000 rpm for 6 hours to obtain a cellulose nanofiber aqueous dispersion (concentration of 2% by mass). The same as in Example 1 except that this aqueous dispersion of cellulose nanofibers having a carboxy group content of 1.29 mmol / g was used and the mixing ratio of cellulose nanofibers and redispersant was set to the ratio shown in Table 1. Thus, a dried cellulose nanofiber of Comparative Example 10 was obtained.

<Evaluation>
(concentration(%))
0.2 g of each obtained cellulose nanofiber-containing dried product was added to 9.8 g of water, and then stirred at 800 rpm for 60 minutes using a magnetic stirrer to obtain a redispersion of each cellulose nanofiber. After the obtained redispersion was allowed to stand for 10 minutes, the concentration of the supernatant was measured by the following method. The measurement results are shown in Table 1. In addition, if it is in a completely redispersed state, the concentration is 2.0% by mass.

  Collect 1 g of cellulose nanofiber redispersion liquid (supernatant liquid if there is a precipitate) and transfer to a container. After drying at 105 ° C. for 2 hours, the mass was measured with an electronic balance, and the concentration was calculated. This was performed twice to obtain an average value.

(With or without discoloration)
Each obtained cellulose nanofiber-containing dried product was observed with the naked eye, and the one that was colorless and transparent or white was evaluated as having no discoloration (coloring). On the other hand, those with yellow, brown, etc. were evaluated as having discoloration (coloring). The evaluation results are shown in Table 1.

  As shown in Table 1, in Examples 1 to 3, cellulose nanofiber-containing dry bodies without discoloration were obtained. Moreover, the density | concentration of the supernatant liquid of the re-dispersed liquid obtained from the cellulose nanofiber containing dried body of Examples 1-3 is high compared with Comparative Examples 1-11, and it turns out that it is excellent in redispersibility.

  The cellulose nanofiber-containing dried product of the present invention can be used for conventional uses of cellulose nanofibers as cellulose nanofibers having excellent dispersibility in water, little discoloration, and excellent handleability. Specifically, the cellulose nanofiber-containing dry product of the present invention comprises a filter medium, a filter aid, a base material for an ion exchanger, a filler for a chromatographic analyzer, a filler for compounding resin and rubber, and a cosmetic composition. It can be suitably used for many applications such as agents, viscosity retainers for foods and paints, food material dough strengtheners, moisture retention agents, food stabilizers, low calorie additives, and emulsion stabilization aids.

Claims (4)

Cellulose nanofibers having a carboxy group content of 0.1 mmol / g or less;
A cellulose nanofiber-containing dried product comprising glycerin or a glycerin derivative.   The cellulose nanofiber-containing dry product according to claim 1, wherein the content of glycerin or a glycerin derivative with respect to 100 parts by mass of the cellulose nanofiber is 0.1 parts by mass or more and 200 parts by mass or less. Cellulose nanofibers comprising: a step of obtaining a mixture by mixing a dispersion of cellulose nanofibers having a carboxy group content of 0.1 mmol / g or less and an aqueous solution of glycerin or a glycerin derivative; and a step of drying the mixture. A method for producing a dried product. A method for producing a cellulose nanofiber dispersion comprising the step of mixing the cellulose nanofiber-containing dried product according to claim 1 or 2 and water.