JP6276740B2 - Method for producing dried cellulose nanofiber - Google Patents

Description

  The present invention relates to a method for producing a dried cellulose nanofiber.

  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 used for industrial use as a filler for chromatography analysis equipment, a filler for compounding resin and rubber, and for a cosmetic compound such as lipstick, powder cosmetic, emulsified cosmetic, and the like. 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. Accordingly, the cellulose nanofibers obtained are in a water-dispersed state, and such an aqueous 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.

  Under such circumstances, as a technique for obtaining a dried product of cellulose nanofibers that can be easily redispersed, a method of mixing carboxy group-containing cellulose nanofibers and a redispersion accelerator and drying the mixture has been proposed (Japanese Patent Application Laid-Open (JP-A)). 2014-1411821 gazette). In this technique, it is said that a powdery or granular dried body (gel body) can be obtained by using spray drying. However, drying by spray drying consumes a large amount of energy and is not preferable from the viewpoint of cost and environment. In particular, carboxy group-containing cellulose requires a large amount of energy for drying due to the presence of a highly hydrophilic carboxy group. Further, according to spray drying, a fine powdery dried product is obtained, but the redispersibility of the obtained dried product is not good.

  In addition, a technique for drying an aqueous suspension of cellulose nanofibers using a drum dryer is also known (see Japanese Patent Application Laid-Open No. 2015-134873). In the drum drying apparatus, the material to be dried is dried by continuously contacting the material to be dried with the drum surface while rotating the drum. At this time, if the fluidity of the material to be dried is low, the material to be dried does not contact the drum surface continuously and uniformly, and effective drying is not performed. Therefore, it is said that it is necessary to make it the low density | concentration that the aqueous suspension of the cellulose nanofiber which is a to-be-dried material has sufficient fluidity | liquidity. Also in the Example of the said gazette, what added the sodium hydroxide aqueous solution to the 0.7 weight% aqueous suspension of a cellulose nanofiber is used for the drum drying apparatus. However, enormous energy is required to sufficiently dry such a low concentration aqueous suspension.

JP 2014-118521 A Japanese Patent Laying-Open No. 2015-134873

  This invention is made | formed based on the above situations, The objective is to provide the method of manufacturing a cellulose nanofiber dried body with favorable redispersibility with energy saving.

  When the double drum dryer is used, the inventors can normally dry even a mixture of cellulose nanofiber with relatively high concentration and low fluidity, which seems to be difficult to dry, and water. Furthermore, it was found that the resulting dried product has good water dispersibility, and the present invention has been completed.

  That is, the invention made to solve the above problems is a step of drying a mixture containing cellulose nanofibers and water, wherein the cellulose nanofiber content is more than 1% by mass and 50% by mass or less by a double drum dryer. It is a manufacturing method of a cellulose nanofiber dry body provided with this.

  According to the manufacturing method, by using a double drum dryer for drying, the cellulose nanofibers can be gently dried, and a dried body in which aggregation between the cellulose nanofibers is gentle can be obtained. Thereby, the redispersibility of the obtained dry body becomes favorable. Furthermore, according to the said manufacturing method, even if it is a mixture with comparatively high density | concentration and low fluidity or no fluidity, a dry body with favorable redispersibility is obtained by using a double drum dryer. Can do. Moreover, a dried cellulose nanofiber can be obtained with energy saving by drying a mixture having a relatively high concentration.

  As content of the carboxy group in the said cellulose nanofiber, 0.5 mmol / g or less is preferable. As described above, by using cellulose nanofibers having a small content of carboxy groups and having a low affinity for water, the cellulose nanofibers can be more efficiently dried by gentle drying using a double drum dryer. Moreover, the redispersibility of the dry body obtained can be further improved by using such a cellulose nanofiber.

  Before the drying step, the method may further include a step of obtaining an aqueous dispersion of the cellulose nanofibers by a refinement process to a pulp in an aqueous dispersion state, and a step of obtaining the mixture by concentrating the aqueous dispersion. preferable. In this way, by drying the aqueous dispersion of cellulose nanofibers obtained by the micronization treatment before drying and drying the concentrated mixture, a dried product that is sufficiently dry with more energy saving can be obtained.

  It is preferable that the mixture contains a hydroxy acid, a hydroxy acid salt, glycerin, a glycerin derivative or a combination thereof. By further adding these components to the mixture, the redispersibility of the resulting dried product can be further enhanced.

  The surface temperature of the double drum dryer in the drying step is preferably 80 ° C. or higher and 160 ° C. or lower. According to the production method, a sufficiently dried product can be obtained even at such a relatively low drying temperature. Furthermore, by performing drying at such a relatively low temperature, it is possible to further save energy, and by gentle drying, agglomeration of the obtained dried body can be suppressed and redispersibility can be further improved. it can.

  It is preferable that the cellulose nanofiber has one peak in a pseudo particle size distribution curve measured by a laser diffraction method in an aqueous dispersion state, and the particle size of the peak of the pseudo particle size distribution curve is 5 μm or more and 25 μm or less. By using such cellulose nanofibers that are relatively uniform in size and not too fine, drying efficiency is further improved, and drying without uniform unevenness can be achieved, so that redispersibility is more excellent. You can get a body.

  According to the method for producing a dried cellulose nanofiber of the present invention, a dried cellulose nanofiber having good redispersibility can be obtained with energy saving.

  Hereinafter, the method for producing a dried cellulose nanofiber according to an embodiment of the present invention will be described in detail with reference to the drawings as appropriate.

  The manufacturing method of the said cellulose nanofiber dry body is equipped with the process (drying process) which dries the mixture containing a cellulose nanofiber and water with a double drum dryer. The said manufacturing method is the process of obtaining the aqueous dispersion of the said cellulose nanofiber by the refinement process to the pulp of an aqueous dispersion state before the said drying process (miniaturization process), and the concentration of the said aqueous dispersion, It is preferable to further include a step of obtaining the above mixture (concentration step). Hereinafter, each step will be described in detail.

(Miniaturization process)
In this miniaturization process, the cellulose nanofiber of a water dispersion state is obtained by performing a micronization process to the pulp of a water dispersion state. Cellulose nanofiber refers to fine cellulose fiber obtained by defibrating pulp (pulp fiber), which is a plant material, and generally includes cellulose fine fiber having a fiber width of nanosize (1 nm to 1000 nm). Refers to fiber.

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 tea waste paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, leaflet waste paper, office waste paper, corrugated waste paper, Kami white waste paper, Kent waste paper, imitation waste paper, lottery waste paper, waste 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.

  As a method for refining the pulp in this refinement step, for example, water-dispersed pulp may be subjected to fibrillation by mechanical treatment, or by defibration by chemical treatment such as enzyme treatment or acid treatment. However, it is preferable to defibrate by mechanical treatment. Cellulose nanofibers can be obtained more easily and reliably by defibration of pulp by mechanical treatment, and the dispersibility of the resulting dried product can be further increased, thereby obtaining a dried product with less discoloration. You can also.

  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. A grinder method in which raw beaten pulp is preliminarily beaten to 30% or less of the starting raw material in a so-called viscous beater such as a Niagara beater, and then ground between rotating wheels. It is preferable to defibrate until cellulose nanofibers are obtained.

  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.

  The upper limit of the content of carboxy groups in the cellulose nanofibers provided in the drying step obtained by the micronization step is preferably 0.5 mmol / g, more preferably 0.3 mmol / g, 0.1 mmol / g Is more preferable. On the other hand, the lower limit of the carboxy group content may be 0 mmol / g, but may be 0.0001 mmol / g. As described above, by using cellulose nanofibers having a small content of carboxy groups and having a low affinity for water, the cellulose nanofibers can be more efficiently dried by gentle drying using a double drum dryer. The carboxy group is usually introduced into the cellulose nanofiber by an oxidation treatment. Therefore, cellulose nanofibers having a carboxy group content of 0.5 mmol / g or less can be obtained by defibration by mechanical treatment or by controlling oxidation treatment as a pretreatment. The carboxy group content of the cellulose nanofiber can be determined by neutralization titration. In addition, when the amount of carboxy groups does not substantially change before and after the refining treatment step, such as when the refining step is performed only by mechanical treatment, the content of carboxy groups in the cellulose nanofibers is determined based on the carboxy content of the raw material pulp. It is substantially the same as the group content. That is, in this case, the carboxy group content of the cellulose nanofiber can be obtained by neutralization titration with respect to the pulp that is the raw material.

  The water retention of the cellulose nanofiber is preferably, for example, 300% or more and 500% or less. 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 the degree of water retention exceeds the above upper limit, the redispersibility of the obtained dried cellulose nanofiber may be reduced. The water retention (%) of the cellulose nanofiber was determined by JAPAN TAPPI No. 26 is measured.

  The cellulose nanofiber preferably has only one peak in a pseudo particle size distribution curve measured by a laser diffraction method in an aqueous dispersion state. 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. By using such cellulose nanofibers that are relatively uniform in size and not too fine, drying efficiency is further improved, and drying without uniform unevenness can be achieved, so that redispersibility is more excellent. You can get a body. As said particle size, 10 micrometers or more are more preferable, and 15 micrometers or more are further more preferable. The “pseudo particle size distribution curve” means a curve indicating a volume-based particle size distribution measured using a particle size distribution measuring apparatus (for example, a laser diffraction / scattering type particle size distribution measuring instrument manufactured by Seishin Corporation).

  The content (concentration) of cellulose nanofibers in the aqueous dispersion of cellulose nanofibers obtained by the micronization step is, for example, about 0.1% by mass to 5% by mass.

(Concentration process)
In this concentration process, the aqueous dispersion of cellulose nanofibers obtained in the above-described refinement process is concentrated. This concentration means removing a part of water as a dispersion medium in the aqueous dispersion to increase the content (concentration) of cellulose nanofibers. What concentrated the said aqueous dispersion becomes a mixture with which it uses for a drying process. Thus, by using the mixture which passed through the concentration process for a drying process, it can dry efficiently and consume little energy.

  Although it does not specifically limit as a concentration method in this concentration process, From the viewpoint of aiming at energy saving, the method without a heating is preferable. As such a concentration method, aggregation using a flocculant or a coagulant, vertical centrifugal separation, horizontal centrifugal separation, ultracentrifugation, microfiltration, ultrafiltration, filter press, screw press, belt press and these are used. A combined method and the like can be given.

(Drying process)
In this drying process, the mixture containing cellulose nanofibers and water is dried with a double drum dryer. According to the manufacturing method, by using a double drum dryer for drying, the cellulose nanofibers can be gently dried, and a dried body in which aggregation between the cellulose nanofibers is gentle can be obtained. Thereby, the redispersibility of the obtained dry body becomes favorable. In addition, according to the production method, even a mixture having a relatively high concentration and low fluidity or no fluidity can be obtained by using a double drum dryer to obtain a dried product having good redispersibility. Can do.

  The cellulose nanofiber content in this mixture subjected to the drying step is more than 1% by weight. As a minimum of this content, 1.5 mass% is preferred, may be 5 mass%, and may be 10 mass%. On the other hand, as an upper limit of this content, it is 50 mass%, 30 mass% is preferable, 10 mass% may be sufficient, and 5 mass% may be sufficient. According to the said manufacturing method, a cellulose nanofiber can be obtained by energy saving by drying a comparatively high concentration mixture. When the content of the cellulose nanofiber exceeds the above lower limit, the drying efficiency increases and energy saving can be achieved. On the other hand, when the content of the cellulose nanofiber is not more than the above upper limit, the mixture can be dried well with a double drum dryer, and a dry body with low bulk density and high redispersibility can be obtained by gentle aggregation. Can do.

  The mixture subjected to the drying step preferably contains a hydroxy acid, a hydroxy acid salt, glycerin, a glycerin derivative or a combination thereof as a redispersant. By further adding these redispersing agents to the mixture, the redispersibility of the resulting dried product can be further enhanced.

  Hydroxy acid is also referred to as hydroxycarboxylic acid, oxyacid, etc., and refers to a carboxylic acid having a hydroxy group (—OH). Hydroxy acids include glycolic acid, lactic acid, tartronic acid, glyceric acid, hydroxybutyric acid, malic acid, tartaric acid, citric acid, isocitric acid, mevalonic acid, pantoic acid, ricinoleic acid and other aliphatic hydroxy acids, salicylic acid, vanillic acid, Examples thereof include aromatic hydroxy acids such as gallic acid.

  Examples of the hydroxy acid salt include alkali metal salts such as sodium salt and potassium salt, alkaline earth metal salts such as calcium salt, other copper salts, and ammonium salts. Among these, alkali metal salts are preferable, and sodium salts are more preferable. By using such a hydroxy acid salt, it is possible to more suitably exhibit the dispersion performance due to electrostatic action in water.

  As the hydroxy acid, a hydroxy acid salt is preferable because the obtained dried product can exhibit good dispersibility. Similarly, aliphatic hydroxy acids and salts thereof are preferable, and citric acid, isocitric acid, tartaric acid, malic acid and salts thereof are more preferable from the viewpoint that the obtained dried product can exhibit good dispersibility. Citric acid, tartaric acid, malic acid or salts thereof are more preferred, citric acid and salts thereof are more preferred, and citrate is particularly preferred. Moreover, it is also preferable that a citric acid, sodium citrate, and these combination are included from the point which can exhibit favorable dispersibility.

  The number of hydroxy groups contained in the hydroxy acid or salt thereof is preferably 1 or more and 3 or less, and more preferably 1. The number of carboxy groups possessed by the hydroxy acid is preferably 2 or more and 4 or less, more preferably 3. When the hydroxy acid has the number of hydroxy groups and carboxy groups within the above range, the adhesion to the surface of the cellulose nanofiber and the resilience in the water-dispersed state can be satisfactorily exhibited. Dispersibility can be increased.

  The glycerin derivative refers to a compound obtained from glycerin. Examples of glycerin derivatives 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 redispersant contained in the mixture, hydroxy acid salt and glycerin are preferable, and sodium citrate and glycerin are more preferable. In addition, when glycerin is used, the dry body with which coloring was suppressed can be obtained effectively.

  Although it does not specifically limit as a mixing method of each component for obtaining the mixture containing the said cellulose nanofiber, water, and a redispersant, Mixing the mixture of a cellulose nanofiber and water and the aqueous solution of the said redispersant. Is preferred. In addition, you may obtain a mixture by mixing the aqueous dispersion of the cellulose nanofiber before the said concentration process, and the aqueous solution of the said redispersing agent, and using this for a concentration process.

  The content of the redispersant in the mixture is not particularly limited, but the lower limit with respect to 100 parts by mass of cellulose nanofibers is preferably 0.1 parts by mass, more preferably 1 part by mass, and even more preferably 10 parts by mass. Part by mass is particularly preferred. On the other hand, as this upper limit, 200 mass parts is preferable and 100 mass parts is more preferable. When the content of the redispersant is less than the lower limit, a sufficient effect of improving redispersibility due to the use of the redispersant may not appear. On the other hand, when the content of the redispersant exceeds the upper limit, the amount of the redispersant used increases and the cost may increase.

  The above mixture contains water, cellulose nanofibers and preferably the above redispersant (hydroxy acid, hydroxy acid salt, glycerin, glycerin derivative or a combination thereof), but other than the above as long as the effect of the present invention is not impaired. These components may be further contained. However, as content of the other component in the said mixture, 10 mass% or less is preferable, and 1 mass% or less is more preferable.

  A well-known thing can be used for the double drum dryer used at this drying process. This drying process can be normally performed under a normal pressure. As the double drum dryer, an internal drum dryer is usually used. By using an internal rotation type drum dryer, a dry product having good redispersibility can be efficiently obtained even with a mixture having low or no fluidity.

  As a minimum of the surface temperature of a double drum dryer in this drying process, 80 ° C is preferred, 100 ° C is more preferred, and 120 ° C is still more preferred. On the other hand, the upper limit of the surface temperature is preferably 160 ° C and more preferably 145 ° C. According to the production method, a sufficiently dried product can be obtained even at such a relatively low drying temperature. By performing drying at such a relatively low temperature, energy saving can be further achieved, and the redispersibility of the obtained dried product can be further improved by gentle drying. When the surface temperature is less than the above lower limit, there may be a case where a sufficiently dried product cannot be obtained. On the other hand, when the surface temperature exceeds the above upper limit, a rapidly aggregated dried body is obtained by rapid drying, and the redispersibility may be lowered.

  The rotation speed of the double drum dryer in the main drying step is appropriately adjusted depending on the size of the drum, the supply amount of the mixture to be processed, and the like, and can be set to 1 rpm or more and 10 rpm or less, for example.

(Dried cellulose nanofiber)
The dried cellulose nanofiber obtained through each of these steps has good redispersibility. The dried cellulose nanofiber can usually be in the form of powder or flakes.

  The moisture content (water content) of the dried cellulose nanofiber is, for example, less than 50% by mass, preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. A mass% or less is particularly preferred. When the moisture content is less than or equal to the above upper limit, energy consumption in transportation and the like can be reduced, and handling 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 dry body, although it may be 0 mass% substantially, 0.1 mass% may be sufficient and 1 mass% may be sufficient.

  Although it does not specifically limit as the redispersion method of the said cellulose nanofiber dried body, It can carry out by mixing the said cellulose nanofiber dried body and water, and stirring as needed.

  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 method for producing a dried cellulose nanofiber of the present invention is not limited to the above embodiment. For example, the aqueous dispersion (mixture) of cellulose nanofibers obtained by the miniaturization step may be directly subjected to the drying step without going through the concentration step.

  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))
The raw material pulp was precisely weighed, adjusted to pH 2.5 to 3.0, and automatically titrated with 0.05 mol / L sodium hydroxide. Conductivity measurement (measuring at room temperature using a conductivity device “pH / ion / EC / DO meter MN-60R” manufactured by Toa DKK) was performed, and the range where there was no change in conductivity was defined as the amount of carboxyl groups. In addition, in a present Example, carboxy group content of raw material pulp can be considered as carboxy group content of the obtained cellulose nanofiber.

[Example 1]
The raw pulp (LBKP: moisture 97.5 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” by Masuko Sangyo Co., Ltd.) to obtain an aqueous dispersion 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 particle size at the above peak was 20.2 μm. The content of carboxy group was 0.05 mmol / g.

  On the other hand, 70 g of water and 30 g of glycerin were mixed and stirred at 600 rpm for 60 minutes using a magnetic stirrer to obtain a glycerin aqueous solution.

  5,000 g of the obtained aqueous dispersion of cellulose nanofibers with a concentration of 2.5% by mass, 83 g of a glycerin aqueous solution with a concentration of 30% by mass and 1,167 g of water are mixed, and 1,200 rpm for 60 minutes using a magnetic stirrer. To give a mixture. The mixing ratio (mass ratio) of cellulose nanofiber (CNF) and glycerin in the obtained mixture was 100: 20, and the content of CNF was about 2.0 mass%. This mixture was dried with a double drum dryer (“John Milder JM-T type” manufactured by Johnson Boiler) at a drum rotation speed of 3 rpm and a drum surface temperature of 135 ° C. to obtain a dried cellulose nanofiber of Example 1. The moisture content of the obtained dried cellulose nanofiber was 5% by mass.

[Example 2]
The same operation as in Example 1 was carried out except that 5,000 g of the obtained aqueous dispersion of cellulose nanofibers with a concentration of 2.5% by mass, 250 g of a glycerol aqueous solution with a concentration of 30% by mass, and 1,000 g of water were mixed. And dried cellulose nanofibers were obtained. At this time, the mixing ratio (mass ratio) of cellulose nanofibers (CNF) and glycerin in the mixture to be dried was 100: 60, and the content of CNF was 2.0% by mass.

[Example 3]
In the same manner as in Example 1, an aqueous dispersion of cellulose nanofibers having a concentration of 2.5% by mass was obtained. On the other hand, 70 g of water and 30 g of sodium citrate were mixed and stirred at 600 rpm for 60 minutes using a magnetic stirrer to obtain an aqueous sodium citrate solution.

  5,000 g of the obtained aqueous dispersion of cellulose nanofibers with a concentration of 2.5% by mass, 83 g of an aqueous sodium citrate solution with a concentration of 30% by mass, and 1,167 g of water are mixed, and 1 minute for 60 minutes using a magnetic stirrer. The mixture was obtained by stirring at 200 rpm. The mixture ratio (mass ratio) of cellulose nanofiber (CNF) and sodium citrate in the obtained mixture was 100: 20, and the content of CNF was about 2.0 mass%. This mixture was dried with a double drum dryer (“John Milder JM-T type” manufactured by Johnson Boiler) at a drum rotation speed of 3 rpm and a drum surface temperature of 135 ° C. to obtain a dried cellulose nanofiber. The moisture content of the obtained dried cellulose nanofiber was 5% by mass.

[Example 4]
Example 3 except that 5,000 g of the obtained aqueous dispersion of cellulose nanofibers with a concentration of 2.5% by mass, 250 g of a sodium citrate aqueous solution with a concentration of 30% by mass, and 1,000 g of water were mixed. The same operation was performed to obtain a dried cellulose nanofiber. At this time, the mixing ratio (mass ratio) of cellulose nanofiber (CNF) and sodium citrate in the mixture to be dried was 100: 60, and the content of CNF was 2.0% by mass.

[Comparative Example 1]
By the method similar to Example 1, the mixing ratio (mass ratio) of a cellulose nanofiber (CNF) and glycerol was 100: 20, and the liquid mixture with a CNF content of 2.0 mass% was obtained.

  The above mixture was dried with a spray dryer (“PR160” manufactured by Pris) at an atomizer rotational speed of 14,000 rpm, an inlet temperature of 200 ° C., and a supply rate of 3 kg / h to obtain a dried cellulose nanofiber. The moisture content of the obtained cellulose nanofiber was 5% by mass.

[Comparative Example 2]
In the same manner as in Example 3, a mixed solution in which the mixing ratio (mass ratio) of cellulose nanofiber (CNF) and sodium citrate is 100: 20 and the CNF content is 2.0% by mass is obtained. It was.

  The above mixture was dried with a spray dryer (“PR160” manufactured by Pris) at an atomizer rotational speed of 14,000 rpm, an inlet temperature of 200 ° C., and a supply rate of 3 kg / h to obtain a dried cellulose nanofiber. The moisture content of the obtained cellulose nanofiber was 5% by mass.

<Evaluation>
[Supernatant concentration (%)]
0.2 g of each dried cellulose nanofiber obtained 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. 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. The measurement results are shown in Table 1.

[Bulk density (g / ml)]
About each obtained cellulose nanofiber dry body, the bulk density (apparent density) was measured by the stationary method according to JIS-K-5101-12-1 (2004). The measurement results are shown in Table 1. “-” In the table indicates that measurement is not performed.

[shape]
The shape of each dried cellulose nanofiber obtained was visually observed. The shape is shown in Table 1.

  As Table 1 shows, the density | concentration of the supernatant liquid of the redispersion liquid obtained from the cellulose nanofiber dry body of Examples 1-4 is high compared with Comparative Examples 1-2, and it is excellent in redispersibility. Recognize. Further, the drum drying in Examples 1 to 4 was able to reduce the power consumption by about 41% compared to the spray drying in Comparative Examples 1 and 2.

[Example 5]
In the same manner as in Example 1, an aqueous dispersion of cellulose nanofibers having a concentration of 2.5% by mass was obtained. Next, this was diluted with water to obtain an aqueous dispersion (mixture) of cellulose nanofibers having a concentration of 2% by mass. The obtained aqueous dispersion of cellulose nanofibers having a concentration of 2% by mass was dried with a double drum dryer (“John Milder JM-T type” manufactured by Johnson Boiler) at a drum rotation speed of 3 rpm and a drum surface temperature of 135 ° C. The dried cellulose nanofiber of Example 5 was obtained.

[Examples 6 to 7, Comparative Example 3]
Except for diluting or concentrating the obtained aqueous dispersion of cellulose nanofibers to obtain a solid content concentration shown in Table 2, and the aqueous dispersion of cellulose nanofiber was dried with a double drum dryer. The dried cellulose nanofibers of Examples 6 to 7 and Comparative Example 3 were obtained in the same manner as in No. 5. The bulk density and moisture content of each obtained cellulose nanofiber were measured. The measured values are shown in Table 2.

  As shown in Table 2, in Comparative Example 3 in which the dispersion (mixture) having a cellulose nanofiber concentration of 1% by mass was dried, a sufficient dried product was not obtained under the same conditions. On the other hand, in Examples 5-7 using the dispersion liquid (mixture) in which the cellulose nanofiber concentration exceeds 1% by mass, it can be seen that a sufficient dried product is obtained.

The method for producing a dried cellulose nanofiber of the present invention can produce a dried cellulose nanofiber having good redispersibility with low energy. Accordingly, the dried cellulose nanofibers obtained by the production method include a filter medium, a filter aid, a base material for ion exchangers, a filler for chromatography analyzers, a filler for compounding resin and rubber, and a compounding agent for cosmetics. Suitable for use of conventional cellulose nanofibers such as food and paint viscosity retainers, food ingredient dough strengtheners, moisture retainers, food stabilizers, low calorie additives, and emulsion stabilization aids it can.

Claims (5)

Comprising a step of drying a mixture containing cellulose nanofibers and water, wherein the cellulose nanofiber content is more than 1% by mass and 50% by mass or less by a double drum dryer ,
The content of carboxy groups in the cellulose nanofiber is 0.5 mmol / g or less,
The manufacturing method of the cellulose nanofiber dry body whose water retention of the said cellulose nanofiber is 300-500% . Before the drying process,
The cellulose nanofiber according to claim 1, further comprising: a step of obtaining an aqueous dispersion of the cellulose nanofiber by refining the pulp in an aqueous dispersion state; and a step of obtaining the mixture by concentrating the aqueous dispersion. A method for producing a dried body. The method for producing a dried cellulose nanofiber according to claim 1 or 2 , wherein the mixture contains a hydroxy acid, a hydroxy acid salt, glycerin, a glycerin derivative, or a combination thereof. The method for producing a dried cellulose nanofiber according to any one of claims 1 to 3 , wherein a surface temperature of the double drum dryer in the drying step is 80 ° C or higher and 160 ° C or lower. The cellulose nanofiber has one peak in a pseudo particle size distribution curve measured by a laser diffraction method in a water dispersion state, and the particle size in the peak of the pseudo particle size distribution curve is 5 μm or more and 25 μm or less. The manufacturing method of the cellulose nanofiber dry body of any one of Claim 4 .