Method for producing a powder containing chitin or partially deacetylated chitin nanofibers, and the powder containing chitin or partially deacetylated chitin nanofibers

Abstract

The present invention provides a powder containing chitin or partially deacetylated chitin nanofibers that are excellent in terms of storage and handling properties and can be redispersed in water. [Solution] An aqueous solution or aqueous dispersion of dextrin is mixed with a nanofiber dispersion of chitin or partially deacetylated chitin, and the resulting mixture is dried to obtain a powder containing nanofibers of chitin or partially deacetylated chitin.

Description

Technical Field

[0001] The present invention relates to a method for producing a powder containing nanofibers of chitin or partially deacetylated chitin, and a powder containing nanofibers of chitin or partially deacetylated chitin produced by the above method.

Background Art

[0002] Chitin nanofibers are chitin (poly-β1-4-N-acetylglucosamine) fibers whose fiber diameter is refined to about 2 nm to 200 nm, and have been reported to have a wound healing effect, an intestinal inflammation suppressing effect, a promoting effect on the production of fibroblast growth factor in the skin, an improvement effect on bread-making properties, a plant disease resistance inducing effect, etc. (Non-Patent Document 1), and their applications have been studied in various fields such as medical materials, cosmetics, and foods. Chitin nanofibers are produced by defibrating chitin extracted and purified from the shells of crustaceans such as shrimps and crabs by wet grinding or the like (Patent Document 1), but are usually provided in the state of a dispersion liquid dispersed in water. When chitin nanofibers are dried, they hydrogen-bond and strongly aggregate, and even if they are dispersed in water again, they do not return to a clean dispersed state. Therefore, it is necessary to store and distribute them in an environment that is not dried, that is, in a state dispersed in a solvent such as water, and there are various restrictions when handling and applying them to various materials.

[0003] Also, regarding nanofibers of partially deacetylated chitin obtained by partially deacetylating chitin, their applications have been studied in various fields in the same manner as chitin nanofibers, but there were the same problems as chitin nanofibers.

[0004] Therefore, there is a demand for a powdery chitin or nanofibers of partially deacetylated chitin that is excellent in storage stability and handling properties, can be redispersed in water, and has few restrictions and convenience when applied in distribution and various fields.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] International Publication No. 2010 / 073758 [Non-patent literature]

[0006] [Non-Patent Document 1] Chemistry and Biology 53(7) 473-477 (2015) [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Therefore, the present invention aims to provide powdered chitin or partially deacetylated chitin nanofibers that are excellent in terms of storage and handling, can be redispersed in water, and have fewer restrictions and convenience in terms of distribution and application in various fields, that is, to provide a powder containing chitin or partially deacetylated chitin nanofibers at a certain concentration or higher. [Means for solving the problem]

[0008] The present inventors, after diligently studying to solve the above problems, discovered that by mixing an aqueous solution or aqueous dispersion of dextrin with a dispersion of chitin or partially deacetylated chitin nanofibers, and drying the resulting mixed dispersion by means of spray drying, freeze-drying, or other means, a powder containing chitin or partially deacetylated chitin nanofibers at a high concentration can be obtained, and that the powder can be redispersed in water. Further studies led to the completion of the present invention.

[0009] In other words, the present invention relates to the following: [1] A method for producing a powder containing chitin or partially deacetylated chitin nanofibers, comprising the steps of mixing an aqueous solution or aqueous dispersion of dextrin with an aqueous dispersion of chitin or partially deacetylated chitin nanofibers, and drying the mixture obtained in the first step. [2] The method for producing a powder containing 1.2% to 87.5% by weight of chitin or partially deacetylated chitin nanofibers, as described in [1]. [3] The method for producing the product according to [1] or [2], wherein the dextrin is a dextrin or maltodextrin having a dextrose equivalent (DE) of 2 to 20 and an average molecular weight of 1,000 to 11,000. [4] The manufacturing method according to any one of [1] to [3], wherein the dextrin concentration of the aqueous solution or aqueous dispersion of dextrin is 2% to 30% by weight. [5] The method for producing nanofibers of chitin or partially deacetylated chitin, wherein the aqueous dispersion of chitin or partially deacetylated chitin nanofibers is 0.1% to 30% by weight. [6] A method for producing a product according to any one of [1] to [5], wherein the mixing ratio of dextrin and chitin or partially deacetylated chitin nanofibers (dextrin:chitin nanofibers) is 85:1 to 1:7 by weight. [7] A method for producing an aqueous dispersion of a powder containing nanofibers of chitin or partially deacetylated chitin, wherein the median diameter measured at 25°C by laser diffraction / scattering particle size distribution analysis is 20 μm to 80 μm, according to any one of [1] to [6]. [8] A powder containing chitin or partially deacetylated chitin nanofibers and dextrin. [9] The powder according to [8], containing 1.2% to 87.5% by weight of chitin or partially deacetylated chitin nanofibers.

[10] The powder according to [8] or [9], wherein the dextrin is a dextrin or maltodextrin having a dextrose equivalent (DE) of 2 to 20 and an average molecular weight of 1,000 to 11,000.

[11] The powder according to any one of [8] to

[10] , wherein the median diameter of the aqueous dispersion is 20 μm to 80 μm as measured at 25°C by laser diffraction / scattering particle size distribution analysis. [Effects of the Invention]

[0010] The present invention provides a method for producing a powder containing nanofibers of chitin or partially deacetylated chitin, and also provides a powder containing nanofibers of chitin or partially deacetylated chitin. The powder containing chitin or partially deacetylated chitin nanofibers produced by the present invention has excellent storage and handling properties and can be redispersed in water. The redispersed solution obtained by redispersing the powder containing chitin or partially deacetylated chitin nanofibers produced by the present invention in water exhibits similar dispersion behavior to the aqueous dispersion of chitin or partially deacetylated chitin nanofibers before powdering. Furthermore, the redispersed solution obtained by redispersing the powder containing chitin or partially deacetylated chitin nanofibers produced by the present invention in water has lower viscosity compared to the aqueous dispersion of chitin or partially deacetylated chitin nanofibers before powdering. In addition, the redispersed solution obtained by redispersing the powder containing chitin or partially deacetylated chitin nanofibers produced by the present invention in water exhibits thixotropy similar to the aqueous dispersion of chitin or partially deacetylated chitin nanofibers before powdering, but has the characteristic of exhibiting less viscosity reduction due to shear compared to the aqueous dispersion of chitin or partially deacetylated chitin nanofibers before powdering. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows the change in viscosity when shear force is applied to the aqueous dispersions of each powder prepared in Examples 1 to 4, as well as the aqueous dispersion of partially deacetylated chitin nanofibers used as raw materials, in Test Example 5. [Modes for carrying out the invention]

[0012] The present invention provides a method for producing a powder containing nanofibers of chitin or partially deacetylated chitin (hereinafter also referred to as "the method of the present invention" in this specification). The method of the present invention comprises the steps of mixing an aqueous solution or aqueous dispersion of dextrin with an aqueous dispersion of chitin or partially deacetylated chitin nanofibers, and drying the mixture obtained in the first step.

[0013] The dextrin used in the method of the present invention is obtained by hydrolyzing starch or glycogen with acid or enzyme to reduce its molecular weight, and includes dextrin with a dextrose equivalent (DE) of 10 or less, and maltodextrin with a dextrose equivalent (DE) of about 10 to 20. In the present invention, dextrin or maltodextrin with a dextrose equivalent (DE) of 2 to 20 and an average molecular weight of 1,000 to 11,000 is preferably used, and dextrin or maltodextrin with a dextrose equivalent (DE) of 4 to 11 and an average molecular weight of 1,900 to 6,000 is more preferably used. The above dextrin is preferably used as an aqueous solution or aqueous dispersion in an amount of 2% to 30% by weight, more preferably 2% to 20% by weight.

[0014] The chitin nanofibers used in the method of the present invention are ultrafine fibers made by micronizing chitin (poly-β1-4-N-acetylglucosamine) to a fiber diameter of typically 2 nm to 200 nm, preferably 2 nm to 40 nm, and more preferably 2 nm to 20 nm, and can be manufactured by known methods. For example, they can be obtained by the method described in Patent Document 1, that is, by purifying a material derived from a chitin-containing organism such as crustaceans, insects, or krill by subjecting it to at least one deproteinization step (such as alkali treatment) and at least one demineralization step (such as acid treatment), and then subjecting it to a defibration treatment (such as grinding with a millstone grinder, high-pressure homogenizer treatment, or freeze-drying treatment). Natural chitin contains not only N-acetylglucosamine but also glucosamine as a constituent, and the degree of deacetylation is about 10%. Further, when preparing chitin nanofibers from a biological material containing chitin as described above, partial elimination of acetyl groups may occur by protein removal treatment. Therefore, the chitin nanofibers used in the method of the present invention may include nanofibers of chitin in which a part of the chitin structure is deacetylated. In the method of the present invention, as the chitin nanofibers, deacetylated chitin present in naturally occurring chitin or chitin deacetylated in a purification process or the like of chitin may be washed and removed, and nanofibers of chitin with the degree of deacetylation reduced to near 0% can be used.

[0015] The nanofibers of partially deacetylated chitin used in the method of the present invention are obtained by defibrating chitin that has been partially deacetylated by boiling in concentrated alkali or the like after being purified as described above from a material derived from a chitin-containing organism. The degree of deacetylation can be adjusted by adjusting the conditions of the deacetylation treatment. The nanofibers of partially deacetylated chitin used in the method of the present invention are nanofibers of chitin that have been deacetylated beyond the degree of deacetylation normally observed in chitin obtained by purifying a material derived from a chitin-containing organism, and are nanofibers of chitin with a degree of deacetylation usually exceeding 10%. Further, in the method of the present invention, nanofibers of partially deacetylated chitin with a degree of deacetylation of 60% or less can preferably be used. The degree of deacetylation (degree of deacetylation) can be measured by NMR spectroscopy, infrared absorption spectroscopy, colloidal titration method, or the like. In another aspect of the method of the present invention, nanofibers of deacetylated chitin with a degree of deacetylation exceeding 60% can also be used, and nanofibers obtained by defibrating commercially available chitosan or chitin deacetylated to the same extent as commercially available chitosan (degree of deacetylation = 70% - 95%) can also be used.

[0016] The nanofibers of the above chitin or partially deacetylated chitin are produced as a dispersion liquid dispersed in water or a wet cake-like dispersion, and are used in such a state of the dispersion liquid or the dispersion. As the aqueous dispersion of the nanofibers of chitin or partially deacetylated chitin, commercially available products provided by companies such as Marine Nanofiber Co., Ltd. can be used, or a high-concentration dispersion of the nanofibers of chitin or partially deacetylated chitin can be prepared and used. The aqueous dispersion of the nanofibers of chitin or partially deacetylated chitin is preferably used as an aqueous dispersion of 0.1% to 30% by weight, more preferably 0.5% to 25% by weight.

[0017] The mixing of the aqueous solution or aqueous dispersion of dextrin and the aqueous dispersion of the nanofibers of chitin or partially deacetylated chitin is preferably carried out so that the mixing ratio by weight (dextrin: nanofibers of chitin or partially deacetylated chitin) is 85:1 to 1:7, more preferably 25:1 to 1:7, and even more preferably 10:1 to 1:3. The mixing of the aqueous dextrin solution or aqueous dispersion and the aqueous dispersion of the nanofibers of chitin or partially deacetylated chitin is preferably carried out at a temperature of about 15°C to 40°C, more preferably about 20°C to 30°C, and preferably stirred for about 10 minutes to 120 minutes, more preferably about 30 minutes to 120 minutes. In order to mix dextrin and the nanofibers of chitin or partially deacetylated chitin more uniformly, it is preferable to carry out stirring with a stirrer or homogenization with a homogenizer.

[0018] The step of drying the mixed solution obtained in the above step can be carried out by commonly used means as long as it can remove moisture and make it in a dry state without adversely affecting the physical properties of the nanofibers of chitin or partially deacetylated chitin and dextrin contained in the mixed solution, but spray drying and freeze drying are mentioned as preferable means. Spray drying is a method of rapidly drying a liquid or a mixture of liquid and solid by spraying it into a gas. It can be carried out using a commonly used spray dryer under normal conditions, but is preferably performed for 30 to 120 minutes at a spray rate of 15 mL / min to 30 mL / min, an atomizer rotation speed of 15,000 rpm to 30,000 rpm, and an inlet temperature of 130°C to 180°C. Freeze-drying is a method of drying a sample by freezing the water content below its freezing point (eutectic point) and then removing the water by sublimation. Using general equipment, the sample is pre-frozen at approximately -80°C to -30°C, followed by primary drying (sublimation drying of the frozen sample under high vacuum) and secondary drying (heating to approximately 30°C to 60°C and removing bound water under high vacuum). The freeze-dried material is then pulverized in a blender and sieved to obtain a powder containing chitin or partially deacetylated chitin nanofibers. Spray drying is a more preferable drying method than freeze-drying because it can be performed in a shorter time and does not require pulverizing the dried material.

[0019] The present invention provides a method for obtaining a powder containing chitin or partially deacetylated chitin nanofibers. The powder containing chitin or partially deacetylated chitin nanofibers produced by the present invention preferably contains 1.2% to 87.5% by weight, more preferably 1.2% to 26% by weight (all on a dry weight basis), of chitin or partially deacetylated chitin nanofibers. Furthermore, a 1% or 10% by weight aqueous dispersion of the powder containing chitin or partially deacetylated chitin nanofibers is prepared and further diluted as appropriate. The particle size (median diameter) measured at 25°C by laser diffraction / scattering particle size distribution analysis is preferably 20 μm to 80 μm, more preferably 25 μm to 70 μm. Note that the particle size measured for the aqueous dispersion is not the same as the particle size of the dried powder, but is considered to be proportional. The powder containing chitin or partially deacetylated chitin nanofibers obtained by the method of the present invention can be redispersed in water. The redispersed solution obtained by redispersing the powder containing chitin or partially deacetylated chitin nanofibers obtained by the method of the present invention in water may exhibit dispersion behavior similar to that of a dispersion in which the raw material chitin or partially deacetylated chitin nanofibers are dispersed in water. Furthermore, the redispersed solution obtained by redispersing the powder containing chitin or partially deacetylated chitin nanofibers obtained by the method of the present invention in water exhibits lower viscosity compared to the aqueous dispersion of chitin or partially deacetylated chitin nanofibers used as raw materials. Moreover, the redispersed solution obtained by redispersing the powder containing chitin or partially deacetylated chitin nanofibers obtained by the method of the present invention in water exhibits thixotropy similar to the aqueous dispersion of chitin or partially deacetylated chitin nanofibers used as raw materials, but has the characteristic of exhibiting less viscosity reduction due to shear compared to the aqueous dispersion of chitin or partially deacetylated chitin nanofibers used as raw materials.

[0020] In another embodiment of the method of the present invention, a powder containing deacetylated chitin nanofibers can be produced using nanofibers obtained by defibrating deacetylated chitin having a degree of deacetylation of more than 60% as a raw material. When commercially available chitosan or nanofibers obtained by defibrating chitin that has been deacetylated to the same extent as commercially available chitosan (degree of deacetylation = 70% to 95%) are used as raw materials, a powder containing chitosan nanofibers can be obtained.

[0021] The powder containing deacetylated chitin nanofibers obtained by the method described above can also be redispersed in water, and the redispersed solution obtained by redispersing the powder containing deacetylated chitin nanofibers in water may exhibit dispersion behavior similar to that of the dispersion of deacetylated chitin nanofibers used as raw materials in water. Furthermore, the redispersed solution obtained by redispersing the powder containing deacetylated chitin nanofibers obtained by the above method in water has a lower viscosity than the aqueous dispersion of deacetylated chitin nanofibers used as the raw material, and exhibits thixotropy similar to the aqueous dispersion of deacetylated chitin nanofibers used as the raw material, but has the characteristic of exhibiting less viscosity reduction due to shear compared to the aqueous dispersion of deacetylated chitin nanofibers used as the raw material.

[0022] Accordingly, the present invention also provides a powder containing nanofibers of chitin or partially deacetylated chitin (hereinafter also referred to as "the powder of the present invention" in this specification). The powder of the present invention contains chitin or partially deacetylated chitin nanofibers and dextrin. The chitin or partially deacetylated chitin nanofibers and dextrin are as described above in the method of the present invention. The powder of the present invention preferably contains 1.2% to 87.5% by weight, more preferably 1.2% to 26% by weight, of chitin or partially deacetylated chitin nanofibers, and is produced by the method of the present invention described above. Furthermore, when a 1% by weight or 10% by weight aqueous dispersion of the powder of the present invention is prepared and further diluted as appropriate, and the particle size is measured by laser diffraction / scattering particle size distribution analysis, the median diameter measured at 25°C is preferably 20 μm to 80 μm, and more preferably 25 μm to 70 μm. When the powder of the present invention is dispersed in water, a redispersion solution can be obtained in which chitin or partially deacetylated chitin nanofibers are well dispersed in water. The redispersion solution obtained by dispersing the powder of the present invention in water exhibits dispersion behavior similar to that of the aqueous dispersion of chitin or partially deacetylated chitin nanofibers before powdering, but has a lower viscosity than the aqueous dispersion of chitin or partially deacetylated chitin nanofibers before powdering. Furthermore, the redispersion solution obtained by dispersing the powder of the present invention in water has thixotropy similar to that of the aqueous dispersion of chitin or partially deacetylated chitin nanofibers before powdering, but has the characteristic of less viscosity reduction due to shear compared to the aqueous dispersion of chitin or partially deacetylated chitin nanofibers before powdering.

[0023] In another embodiment of the present invention, a powder containing nanofibers of deacetylated chitin with a degree of deacetylation exceeding 60% can be provided. Such a powder containing nanofibers of deacetylated chitin includes a powder containing chitosan nanofibers with a degree of deacetylation of 70% to 95%.

[0024] The median diameter of the aqueous dispersion of the powder containing the deacetylated chitin nanofibers described above, measured at 25°C by laser diffraction / scattering particle size distribution analysis, is comparable to that of the aqueous dispersion of the powder containing chitin or partially deacetylated chitin nanofibers. Furthermore, the content of deacetylated chitin nanofibers in the powder containing deacetylated chitin nanofibers is comparable to that of chitin or partially deacetylated chitin nanofibers in the powder containing chitin or partially deacetylated chitin nanofibers. Furthermore, powders containing deacetylated chitin nanofibers can also be redispersed in water, and the redispersed solution obtained by redispersing powder containing deacetylated chitin nanofibers in water may exhibit similar dispersion behavior to the dispersion solution in which the deacetylated chitin nanofibers used as raw materials are dispersed in water. Furthermore, the redispersed solution obtained by redispersing the powder containing deacetylated chitin nanofibers in water has a lower viscosity than the aqueous dispersion of deacetylated chitin nanofibers used as the raw material, and exhibits thixotropy similar to the aqueous dispersion of deacetylated chitin nanofibers used as the raw material, but has the characteristic of less viscosity reduction due to shear compared to the aqueous dispersion of deacetylated chitin nanofibers used as the raw material. [Examples]

[0025] The present invention will be described in more detail below with reference to examples.

[0026] [Example 1] Preparation of powder containing partially deacetylated chitin nanofibers: Preparation by spray drying 90g of dextrin ("Pinex #2", Matsutani Chemical Industry Co., Ltd.) (DE=11) was added to 500g of distilled water and stirred at room temperature for 30 minutes to dissolve. To the dextrin aqueous solution, 1kg of a 1% by weight aqueous dispersion of partially deacetylated chitin (degree of deacetylation = 60% or less) nanofibers derived from crab shells ("S-HL-02", Lot No.: F323052301, Marine Nanofiber Co., Ltd.) was added and stirred at room temperature for 30 minutes to obtain approximately 1,600mL of a mixed dispersion of dextrin and partially deacetylated chitin nanofibers. The dispersion obtained above was spray-dried for 80 minutes using a spray dryer ("Spray Dryer L-8i" model, Okawara Chemical Machinery Co., Ltd.) at a spray rate of 19 mL / min, an inlet temperature of 140°C, and an atomizer rotation speed of 25,000 rpm. 94.8 g of powder containing 10% by weight of partially deacetylated chitin nanofibers at a final concentration was recovered. The time required to prepare the powder containing partially deacetylated chitin nanofibers was 2.5 hours.

[0027] [Example 2] Preparation of powder containing partially deacetylated chitin nanofibers: Preparation by freeze-drying In Example 1 described above, approximately 1600 mL of the mixed dispersion of dextrin and partially deacetylated chitin nanofibers was divided into two portions and pre-dried at -30°C in a freeze-dryer ("TF20-85ATANC", Takara ATM Co., Ltd.), followed by freeze-drying at -30°C to +40°C for 3 days. The obtained freeze-dried product (110.4 g) was pulverized using a blender ("Oster Blender ST-2", Osaka Chemical Co., Ltd.), and then sieved through a 30-mesh sieve using an electromagnetic sieve shaker ("AS200 Digit Type", Retsch Co., Ltd.). 109.4 g of powder containing 10% by weight of partially deacetylated chitin nanofibers at a final concentration was recovered. The time required to prepare the powder containing partially deacetylated chitin nanofibers was 3.5 days.

[0028] [Example 3] Preparation of powder containing partially deacetylated chitin nanofibers using a real-world instrument (scale-up) 1.8 kg of dextrin ("Pinex #2", Matsutani Chemical Industry Co., Ltd.) (DE=11) was added to 60 kg of tap water and stirred at room temperature for 1 hour to dissolve. 20 kg of a 1 wt% aqueous dispersion of partially deacetylated chitin (deacetylation degree = 60% or less) nanofibers derived from crab shells ("S-HL-02", Lot No.: F324020501, Marine Nanofiber Co., Ltd.) was added to the dextrin aqueous solution and stirred at room temperature for 1 hour to obtain approximately 81.8 kg of a mixed dispersion of dextrin and partially deacetylated chitin nanofibers. The dispersion obtained above was heat-sterilized at 95°C for 30 minutes, and then spray-dried using a spray dryer (custom-made by Yamano Co., Ltd., manufactured by Kitano Seisakusho Co., Ltd.) at a spray rate of 1.7 L / hour and an inlet temperature of 170°C for 30 minutes. The mixture was then sieved through a 42-mesh sieve using an electromagnetic sieve shaker "AS200 Digit Type," manufactured by Retsch Co., Ltd.) to recover 14 kg of powder containing 10% by weight of partially deacetylated chitin nanofibers at a final concentration. The time required to prepare the powder containing partially deacetylated chitin nanofibers was 3.5 hours.

[0029] [Example 4] Preparation of powder containing partially deacetylated chitin nanofibers: Preparation using high-molecular-weight dextrin 45 g of dextrin ("Pinex #100", Matsutani Chemical Industry Co., Ltd.) (DE=4) was added to 1,500 g of tap water and stirred at room temperature for 30 minutes to dissolve. 500 g of a 1 wt% aqueous dispersion of partially deacetylated chitin (degree of deacetylation = 60% or less) nanofibers derived from crab shells ("S-HL-02F", Lot No.: F323121801, Marine Nanofiber Co., Ltd.) was added to the dextrin aqueous solution and stirred at room temperature for 2 hours to obtain approximately 2,000 mL of a mixed dispersion of dextrin and partially deacetylated chitin nanofibers. The dispersion obtained above was spray-dried for 2 hours using a spray dryer ("Spray Dryer L-8i" model, Okawara Chemical Machinery Co., Ltd.) at a spray rate of 17 mL / min, an inlet temperature of 140°C, and an atomizer rotation speed of 25,200 rpm. 46 g of powder containing 10% by weight of partially deacetylated chitin nanofibers at a final concentration was recovered. The time required to prepare the powder containing partially deacetylated chitin nanofibers was 4.5 hours.

[0030] [Test Example 1] The powders containing partially deacetylated chitin nanofibers prepared in Examples 1-4 above were dried at 105°C for 3 hours. The drying loss was measured to determine the drying loss rate, and the amount of powder recovered after drying was calculated to determine the recovery rate. The calculated recovery rates for each powder are shown in Table 1.

[0031] [Table 1]

[0032] As shown in Table 1, when dextrin with a dextrose equivalent (DE) of 11 was used as the dextrin, a powder containing partially deacetylated chitin nanofibers could be obtained with a high recovery rate regardless of whether spray drying or freeze-drying was used as the means of drying the mixed dispersion of dextrin and partially deacetylated chitin nanofibers (Examples 1 and 2). As a means of drying a mixed dispersion of dextrin and partially deacetylated chitin nanofibers, spray drying requires fewer steps and takes less time to prepare the powder containing partially deacetylated chitin nanofibers compared to freeze-drying, suggesting that it is more practical. The recovery rate in the case of preparation using an actual machine (scale-up) (Example 3) was somewhat low at approximately 70%. In Example 3, since it was a prototype with the smallest lot size using a large machine, powder adhesion to the walls of the drying chamber and the exhaust port was observed, and it was considered that the recovery rate decreased due to production losses caused by these factors. In preparation using an actual machine, it is thought that production losses can be reduced by drying with equipment appropriate to the amount of the mixed dispersion of dextrin and partially deacetylated chitin nanofibers used as raw materials, or by increasing the amount of the dispersion. Even when a high-polymerization dextrin (dextrose equivalent (DE) = 4) was used as the dextrin (Example 4), a powder containing partially deacetylated chitin nanofibers was obtained with a high recovery rate of 80% or more.

[0033] [Test Example 2] Evaluation of redispersibility in water The redispersibility of the partially deacetylated chitin nanofiber-containing powders prepared in Examples 1-4 in water was evaluated as follows. The powder containing partially deacetylated chitin nanofibers prepared in Examples 1-4 was gradually added to water at 25°C or 40°C, respectively, and stirred at 1,000 rpm with a hot stirrer. After uniform dispersion was observed visually, the powder was further added and the dispersion process was repeated to prepare dispersions with a final concentration of 1% by weight or 10% by weight. A "○" in Table 2 indicates when a clear and uniform dispersion was obtained visually. The solubility of the dextrin used to prepare the powder containing partially deacetylated chitin nanofibers in Examples 1-4 was similarly evaluated and is also shown in Table 2.

[0034] [Table 2]

[0035] As shown in Table 2, the powders containing 10% by weight of partially deacetylated chitin nanofibers prepared in Examples 1-4 showed good redispersibility in water. In all cases, stirring with a stirrer required a considerable amount of time to obtain a dispersion with a final concentration of 10% by weight at 25°C, but a transparent and uniform dispersion was obtained visually.

[0036] [Test Example 3] Measurement of particle size For the powders containing partially deacetylated chitin nanofibers prepared in Examples 1-4, particle size measurements were performed using a laser diffraction / scattering particle size distribution analyzer ("LA-960V2", Horiba, Ltd.) with 1% by weight or 10% by weight aqueous dispersions prepared in Test Example 2. The measured median diameter and span values ​​are shown in Table 3. For the dextrin used in the preparation of the powders containing partially deacetylated chitin nanofibers in Examples 1-4, particle size measurements were performed using a 10% by weight aqueous solution, and for the partially deacetylated chitin nanofibers, particle size measurements were performed using a 1% by weight aqueous dispersion, and these results are also shown in Table 3.

[0037] [Table 3]

[0038] As shown in Table 3, the powder containing partially deacetylated chitin nanofibers prepared in Example 1 showed a median diameter of 39 μm to 41 μm when dispersed in water, while the powder containing partially deacetylated chitin nanofibers prepared in Example 2 showed a median diameter of 28 μm to 35 μm when dispersed in water. This suggests that the powder obtained by spray drying in the drying process has a slightly larger particle size than the powder obtained by freeze-drying. Furthermore, the powder containing partially deacetylated chitin nanofibers prepared in Example 3 using the actual equipment had a larger particle size compared to the powder containing partially deacetylated chitin nanofibers prepared in Example 1, and a tendency for the particle size to increase with scale-up was observed. In Example 4, a powder containing partially deacetylated chitin nanofibers prepared using a dextrin with a higher degree of polymerization than the dextrin used in Example 1 showed a median diameter of 24 μm to 30 μm when dispersed in water, indicating that the particle size was slightly smaller.

[0039] [Test Example 4] Measurement of Zeta Potential The zeta potential of aqueous dispersions of the partially deacetylated chitin nanofiber powders prepared in Examples 1-4 at a final concentration of 10% by weight at 25°C was measured. The zeta potential was measured using a "Zetasizer Nano ZSP" (Malballoon Panalytical Co.) by adding the aqueous dispersion of each powder to a 10 mM potassium chloride aqueous solution to a pH of around 7. Similarly, the zeta potential of aqueous solutions prepared by dissolving the dextrin used in the preparation of the partially deacetylated chitin nanofiber powders in Examples 1-4 at a final concentration of 10% by weight at 40°C, and of a 1% by weight aqueous dispersion of partially deacetylated chitin nanofibers ("S-HL-02", Marine Nanofiber Co., Ltd.) were also measured. The measurement results are shown in Table 4.

[0040] [Table 4]

[0041] As shown in Table 4, in Example 4, although the zeta potential of the aqueous dispersion of powder containing partially deacetylated chitin nanofibers prepared using high-molecular-weight dextrin was slightly lower, the zeta potential of the aqueous dispersions of powder containing partially deacetylated chitin nanofibers prepared in Examples 1 to 4 was almost the same as that of the aqueous dispersion of partially deacetylated chitin nanofibers contained in the aforementioned powders. The results of Test Example 4 suggest that the powder containing chitin or partially deacetylated chitin nanofibers of the present invention exhibits dispersion behavior almost identical to that of an aqueous dispersion of chitin or partially deacetylated chitin nanofibers contained in the powder when dispersed in water.

[0042] [Test Example 5] Evaluation of Thixotropy The partially deacetylated chitin nanofiber powders prepared in Examples 1-4 were dispersed in 10% by weight aqueous dispersions at 25°C. Shear force was applied to these dispersions, and the viscosity was measured using a Type B viscometer ("VISCOMETER TVB-10", Toki Sangyo Co., Ltd.). Viscosity was measured at 25°C using a Spindle Rotor TM4. The measurement results are shown in Figure 1, based on a comparison with a 1% by weight aqueous dispersion of partially deacetylated chitin nanofibers ("S-HL-02", Marine Nanofiber Co., Ltd.).

[0043] As shown in Figure 1, a 1% by weight aqueous dispersion of partially deacetylated chitin nanofibers exhibited thixotropy, where viscosity decreased as shear force was applied. On the other hand, aqueous dispersions of the partially deacetylated chitin nanofiber powders prepared in Examples 1-4, each at a concentration of 10% by weight in water, showed lower viscosity compared to a 1% by weight aqueous dispersion of partially deacetylated chitin nanofibers. Furthermore, the aqueous dispersions of the partially deacetylated chitin nanofiber powders prepared in Examples 1-4 also showed a decrease in viscosity as shear force was applied, indicating thixotropy. However, the decrease in viscosity due to shear was smaller than that of a 1% by weight aqueous dispersion of partially deacetylated chitin nanofibers. Furthermore, the powder containing partially deacetylated chitin nanofibers prepared using high-molecular-weight dextrin (the powder prepared in Example 4) showed higher viscosity at each rotational speed and a greater decrease in viscosity with increasing applied shear force (increasing rotational speed) compared to the powder containing partially deacetylated chitin nanofibers prepared using low-molecular-weight dextrin (the powder prepared in Example 1), indicating more pronounced thixotropy. [Industrial applicability]

[0044] As described in detail above, the present invention provides a method for producing a powder containing nanofibers of chitin or partially deacetylated chitin, and a powder containing nanofibers of chitin or partially deacetylated chitin. The powder containing chitin or partially deacetylated chitin nanofibers provided by the present invention has excellent storage and handling properties and can be redispersed in water. The dispersion obtained by redispersing the powder containing chitin or partially deacetylated chitin nanofibers provided by the present invention in water exhibits dispersion behavior similar to that of the chitin or partially deacetylated chitin nanofibers before powdering. However, it has a lower viscosity than the aqueous dispersion of chitin or partially deacetylated chitin nanofibers before powdering, and exhibits thixotropy similar to the aqueous dispersion of chitin or partially deacetylated chitin nanofibers before powdering. However, it has the characteristic of exhibiting less viscosity reduction due to shear compared to the aqueous dispersion of chitin or partially deacetylated chitin nanofibers before powdering.

Claims

1. A method for producing a powder containing chitin or partially deacetylated chitin nanofibers, comprising the steps of: mixing an aqueous solution or aqueous dispersion of dextrin with an aqueous dispersion of chitin or partially deacetylated chitin nanofibers; and drying the mixture obtained in the first step.

2. The method for producing a powder containing 1.2% to 87.5% by weight of chitin or partially deacetylated chitin nanofibers, as described in claim 1.

3. The method for producing the product according to claim 1 or 2, wherein the dextrin is a dextrin or maltodextrin having a dextrose equivalent (DE) of 2 to 20 and an average molecular weight of 1,000 to 11,000.

4. The manufacturing method according to claim 1 or 2, wherein the dextrin concentration of the aqueous solution or aqueous dispersion of dextrin is 2% by weight to 30% by weight.

5. The method for producing nanofibers of chitin or partially deacetylated chitin according to claim 1 or 2, wherein the aqueous dispersion of chitin or partially deacetylated chitin nanofibers is 0.1% to 30% by weight.

6. The manufacturing method according to claim 1 or 2, wherein the mixing ratio of dextrin to chitin or partially deacetylated chitin nanofibers (dextrin: chitin or partially deacetylated chitin nanofibers) is 85:1 to 1:7 by weight.

7. The manufacturing method according to claim 1 or 2, wherein the median diameter of an aqueous dispersion of a powder containing nanofibers of chitin or partially deacetylated chitin is 20 μm to 80 μm, as measured at 25°C by laser diffraction / scattering particle size distribution analysis.

8. A powder containing chitin or partially deacetylated chitin nanofibers and dextrin.

9. The powder according to claim 8, comprising 1.2% to 87.5% by weight of chitin or partially deacetylated chitin nanofibers.

10. The powder according to claim 8 or 9, wherein the dextrin is a dextrin or maltodextrin having a dextrose equivalent (DE) of 2 to 20 and an average molecular weight of 1,000 to 11,000.

11. The powder according to claim 8 or 9, wherein the median diameter of the aqueous dispersion is 20 μm to 80 μm, as measured at 25°C by laser diffraction / scattering particle size distribution analysis.

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