High-concentration dispersion of nano-sized chitin

Abstract

To provide a high-concentration dispersion of nanosized chitin having a uniform and fine fiber width.SOLUTION: A dispersion of nanosized chitin contains nanosized chitin with a fiber width of 20 nm or less in a concentration of 10 wt.%-30 wt.%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a high-concentration dispersion of nanochitin, and more particularly to a dispersion containing nanochitin having a uniform fiber width at a high concentration.

Background Art

[0002] Chitin nanofibers obtained by defibrating chitin abundantly contained in the shells of crustaceans such as shrimps and crabs exhibit transparency and high water swelling properties, and their use in various fields has been studied. As a method for producing chitin nanofibers, for example, a method of immersing purified β-chitin having a crystallinity of 90% or less in an acidic liquid having a pH of 5 or less and then defibrating the immersed β-chitin (Patent Document 1), a method of partially deacetylating purified α-chitin, immersing it in an acidic liquid having a pH of 5 or less, and then defibrating it (Patent Document 2), etc. have been proposed. In the methods for producing chitin nanofibers described in Patent Documents 1 and 2, it has been proposed to impart a positive charge to glucosamine residues considered to be distributed on the surface of chitin nanofibrils, cause a charge repulsion between the microfibrils of chitin nanofibrils, and facilitate the defibrillation of microfibrils.

[0003] In the methods for producing chitin nanofibers described in Patent Documents 1 and 2, the defibrillation treatment of purified β-chitin or a partially deacetylated product of purified α-chitin is performed using defibrillation and pulverization equipment such as a propeller mixer, a cutter mixer, an ultrasonic homogenizer, a high-pressure homogenizer, and a twin-screw kneader. Also, as a method for defibrating chitin microfibrils, a method of applying the technology of a water jet for defibrillation has been proposed (Patent Document 3).

[0004] As described in Patent Documents 1 to 3, chitin nanofibers are generally obtained by mechanically or physically defibrating purified chitin. However, with this method, it is difficult to easily obtain chitin nanofibers with a uniform fiber width, and it was necessary to repeat the defibration process to make the fiber width of the chitin nanofibers uniform. Furthermore, in the manufacturing methods disclosed in Patent Documents 1 to 3, etc., a chitin aqueous dispersion is subjected to the defibrillation treatment, resulting in chitin nanofibers being obtained in a dispersed state in water. It is difficult to obtain chitin nanofibers as a high-concentration dispersion, and therefore, it cannot be said to be economically superior for use as a raw material for N-acetylglucosamine and oligosaccharides, or for use in medical materials, functional foods, cosmetics, animal feed, etc.

[0005] Therefore, there is a need for a dispersion containing nano-sized chitin with a uniform fiber width at a high concentration, which offers excellent applicability in various fields. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2009-102782 [Patent Document 2] Japanese Patent Publication No. 2010-180309 [Patent Document 3] Japanese Patent Publication No. 2011-056456 [Overview of the project] [Problems that the invention aims to solve]

[0007] In view of the above, the present invention aims to provide a dispersion containing nano-sized chitin having a uniform fiber width at a high concentration. [Means for solving the problem]

[0008] The inventors of the present invention conducted diligent studies to solve the above problems and found that the chitin precipitate obtained by treating it with a high concentration of alkali or acid at low temperature, followed by dilution and neutralization, is nano-sized chitin. Further studies led to the creation of a dispersion containing nano-sized chitin with a fiber width of 20 nm or less at a concentration of 10% to 30% by weight, thus completing the present invention.

[0009] In other words, the present invention relates to the following: [1] A dispersion of nano-sized chitin containing nano-sized chitin with a fiber width of 20 nm or less at a concentration of 10% to 30% by weight. [2] The dispersion according to [1], wherein the concentration of nano-sized chitin is 15% to 25% by weight. [3] The dispersion according to [1] or [2], wherein the fiber width of the nano-sized chitin is 10 nm or less. [4] The dispersion according to any one of [1] to [3], wherein the degree of deacetylation of nano-sized chitin is 8% or less. [5] A dispersion that is in the form of a wet cake, as described in any of [1] to [4]. [6] Dispersion of deacetylated nano-chitin. [7] The dispersion described in [6], wherein the degree of deacetylation is 10% to 50%. A gel containing the dispersion described in [8][6] or [7]. [Effects of the Invention]

[0010] The present invention makes it possible to provide a dispersion containing a high concentration of nano-sized chitin having a uniform fiber width. The nano-sized chitin contained in the dispersion of the present invention can be deacetylated while maintaining the nano-sized chitin form. The dispersion of the deacetylated nano-sized chitin can form a gel at low concentrations by making the solution acidic or by dispersing it in an acidic aqueous solution. The above dispersion is useful as a raw material for N-acetylglucosamine and oligosaccharides, as well as for medical materials, plastic materials, and as an ingredient in functional foods, cosmetics, and animal feed. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a diagram showing an image of the dispersion of nano chitin of Example 1 observed by a transmission electron microscope. The bar in the figure indicates 100 nm. [Figure 2] Figure 2 is a diagram showing the appearance of a gel formed when the dispersion of the deacetylated nano chitin of Example 2 is made acidic. [Figure 3] Figure 3 is a diagram showing the appearance of a gel formed when the dispersion of the deacetylated nano chitin of Example 3 is made acidic. [Figure 4] Figure 4 is a diagram showing the appearance of a gel formed when the dispersion of the deacetylated nano chitin of Example 4 is made acidic. [Figure 5] Figure 5 is a diagram showing an image of the gel formed when the dispersion of the deacetylated nano chitin of Example 4 is made acidic, observed by a transmission electron microscope. The bar in the figure indicates 100 nm.

Mode for Carrying Out the Invention

[0012] The present invention provides a dispersion containing a high concentration of nano chitin having a uniform fiber width (hereinafter also referred to as "the dispersion of the present invention" in this specification). The dispersion of the present invention contains nano chitin having a fiber width of 20 nm or less at a concentration of 10% by weight to 30% by weight.

[0013] Here, "nano chitin" refers to chitin having a fiber width on the order of nanometers, that is, less than 1 μm is chitin. The fiber width of the nano chitin contained in the dispersion of the present invention is 20 nm or less, preferably 10 nm or less. Further, the average fiber width of the nano chitin contained in the dispersion of the present invention is usually 3 nm to 10 nm, preferably 3 nm to 5 nm. The fiber width of the nano chitin contained in the dispersion of the present invention is measured from an image when the dispersion of the present invention is appropriately diluted with water or the like and observed with a transmission electron microscope. On the one hand, when the nano-sized chitin contained in the dispersion of the present invention was observed under a transmission electron microscope, it was found that it was twisted spirally in the longitudinal direction, and the fiber length could not be clearly measured. However, as described later, when the dispersion of the present invention was prepared, although the molecular weight of the nano-sized chitin contained in the dispersion decreased compared to the chitin used as the starting material, the degree was the same as that in the case of preparation by a normal physical fibrillation method, and it was presumed that it was almost the same as the fiber length of the chitin nanofibers prepared by the physical fibrillation method.

[0014] The nano-sized chitin contained in the dispersion of the present invention may be obtained from any chitin, such as α-chitin present in crustaceans such as crabs and shrimps, or β-chitin present in the cuttlebone of squids and the body of mealworms.

[0015] The dispersion of the present invention contains the above-mentioned nano-sized chitin at a concentration of usually 10% to 30% by weight, preferably 15% to 25% by weight. Here, the concentration of the nano-sized chitin contained in the dispersion of the present invention is calculated from the chitin content in the dispersion of the present invention, which is quantified as a solid content by the normal pressure heating drying method, and the obtained quantified value and the weight of the dispersion of the present invention before drying.

[0016] The degree of deacetylation of the nano-sized chitin contained in the dispersion of the present invention is preferably 8% or less, more preferably 5% or less. Also, considering the degree of deacetylation of the chitin used as the raw material, the degree of deacetylation of the nano-sized chitin contained in the dispersion of the present invention is usually about 1% to 5%. The degree of deacetylation of nano-sized chitin can be measured by colloidal titration with a 1 / 400N aqueous solution of potassium polyvinyl sulfate using toluidine blue as an indicator.

[0017] In the dispersion of the present invention, as described above, nano-sized chitin having a fine and uniform fiber width is dispersed in a solvent such as water at a high concentration of 10% to 30% by weight, presenting a wet cake-like appearance.

[0018] The dispersion of the present invention can be prepared, for example, by grinding chitin to the extent that it can pass through a 42-mesh sieve, immersing the chitin powder in a highly concentrated alkaline aqueous solution, letting it stand at a temperature below room temperature, diluting it with ice, neutralizing it with a highly concentrated acid to precipitate the chitin, washing the chitin dispersion with water to desalt it, and dehydrating it if necessary. Furthermore, the dispersion of the present invention can also be prepared by immersing pulverized chitin powder in a highly concentrated aqueous acid solution and neutralizing it with a highly concentrated alkali. However, considering the desired reduction of nano-sized chitin molecules, it is preferable to immerse the powder in an alkaline aqueous solution and neutralize it with acid.

[0019] Chitin can be ground using conventional grinders, such as cutter mills, hammer mills, rolling ball mills, dry air mills, and counter-air dry mills.

[0020] As a high-concentration alkaline aqueous solution, a sodium hydroxide aqueous solution or potassium hydroxide aqueous solution of about 40% to 48% by weight can be used. The amount of high-concentration alkaline aqueous solution used should be sufficient to completely immerse the chitin powder. The immersion treatment of chitin powder in a high-concentration alkaline aqueous solution is preferably carried out at a temperature of room temperature (25°C) or lower, more preferably 20°C or lower, and even more preferably 15°C or lower, for 10 to 24 hours, and more preferably 15 to 20 hours.

[0021] After the immersion treatment described above, when ice is added, the chitin will dissolve in a viscous state, so stir until the chitin immersion solution becomes clear. The dilution treatment by adding ice described above should be carried out at 25°C or below, preferably 0°C or below, and more preferably -10°C or below, until the immersed chitin powder becomes a uniform solution (until the alkali concentration reaches about 10(w / v)%). The neutralization of the chitin solution obtained by the above dilution treatment is carried out by adding an acid of about 30% to 40% by weight, such as concentrated hydrochloric acid, at a temperature of 25°C or lower, preferably 0°C or lower, so that the pH of the solution becomes about 7 to 8.5. By performing the immersion treatment with the above-mentioned alkaline aqueous solution at a low temperature of preferably 25°C or lower, more preferably 20°C or lower, and by performing dilution and neutralization at a low temperature of 25°C or lower, more preferably 0°C or lower, the deacetylation of chitin can be suppressed.

[0022] Washing with water is performed with 250 to 500 times the weight of water relative to the precipitated chitin dispersion, and this washing operation is usually repeated 10 to 20 times. This washing operation is sufficient to desalinate the precipitated chitin dispersion. In this invention, washing with water is performed until the salt concentration of the precipitated chitin dispersion is usually 0.01% by weight or less. The degree of desalination can be confirmed by measuring the salt concentration using a digital salinity meter.

[0023] The precipitated chitin dispersion can be dehydrated using conventional dehydration methods, but it can be preferably carried out by, for example, centrifugal filtration or pressure filtration.

[0024] The nano-sized chitin contained in the dispersion of the present invention has the characteristics of being easily degradable by enzymes such as chitinase and being easily chemically modified, such as by deacetylation. Furthermore, because the dispersion of the present invention contains nano-sized chitin with minute and uniform fiber widths at an unprecedentedly high concentration, it can be efficiently utilized as a raw material for N-acetylglucosamine and oligosaccharides, as a medical material, as a filler for plastic materials, and as an ingredient in functional foods, cosmetics, and animal feed.

[0025] Furthermore, the present invention provides, as one embodiment of the chemical modification of nano-sized chitin contained in the dispersion of the present invention, a dispersion of a deacetylated nano-sized chitin (hereinafter also referred to as "dispersion of a deacetylated nano-sized chitin of the present invention" in this specification). In the present invention, the degree of deacetylation of the nano-sized chitin deacetylated product is preferably 10% to 50%, and more preferably 15% to 40%.

[0026] The dispersion of the nano-sized chitin deacetylate of the present invention can be made acidic by adding a small amount of acid, or by dispersing it in an acidic aqueous solution. This improves the dispersibility of the nano-sized chitin deacetylate, and a uniform gel can be formed at a low concentration of 1% to 2% by weight of the nano-sized chitin deacetylate. When the degree of deacetylation of the nano-sized chitin exceeds 18%, the transparency of the formed gel increases, and when the degree of deacetylation of the nano-sized chitin reaches about 40%, a viscous gel exhibiting nearly transparent thixotropy is obtained. The acid added to improve the dispersibility of the dispersion of the nano-sized chitin deacetylated product of the present invention, or to form a gel, is not particularly limited as long as it can make the liquid of the dispersion acidic. However, from the viewpoint of suppressing the demolecularization of the nano-sized chitin deacetylated product, a weak acid is preferred, and an organic acid is more preferred. Furthermore, for use as a food ingredient, an edible acid is preferred. Examples of edible organic acids include lactic acid and citric acid. These are some examples. Furthermore, the amount of acid added to the dispersion of the nano-sized chitin deacetylated product of the present invention is small, and it is sufficient if the concentration of the acid in the dispersion is about 0.5% to 1% by weight. When dispersing the deacetylated nano-chitin product of the present invention in an acidic aqueous solution, the above-mentioned acid aqueous solution can be used as the acidic aqueous solution, and its concentration can be as low as 0.5% to 1% by weight.

[0027] The dispersion of the deacetylated nano-chitin of the present invention can be obtained by heating or inducing the above-described dispersion of nano-chitin of the present invention in an alkaline aqueous solution and then washing it with water. As the alkaline aqueous solution, aqueous solutions of sodium hydroxide, potassium hydroxide, etc., are preferably used. The concentration of the alkaline aqueous solution is appropriately set according to the desired degree of deacetylation, within a range in which the crystalline structure of chitin does not swell. Typically, an alkaline aqueous solution with a concentration of 10(w / v)% to 55(w / v)%, preferably 10(w / v)% to 40(w / v)%, and more preferably 30(w / v)% to 36(w / v)%, is used. The heating or heating temperature in the alkaline aqueous solution is set appropriately according to the desired degree of deacetylation, and is usually 45°C to 80°C, preferably 45°C to 60°C. The heating or heating time in the alkaline aqueous solution is also set appropriately according to the desired degree of deacetylation, and is usually 5 to 72 hours, preferably 5 to 17 hours, and more preferably 5 to 6 hours. The degree of deacetylation of nano-sized chitin can be adjusted by controlling the concentration of the alkaline aqueous solution, the heating temperature, and the heating time. For example, when the deacetylation reaction is carried out in a 30(w / v)%~36(w / v)% sodium hydroxide aqueous solution at 60°C for 5 hours, the degree of deacetylation is 15%~16%; when the deacetylation reaction is carried out at 80°C for 5 hours, the degree of deacetylation is 18%~19%; and when the deacetylation reaction is carried out at 45°C for 72 hours, the degree of deacetylation is 25%~26%.

[0028] After heating or invigorating in an alkaline aqueous solution, neutralization treatment with an acid may be performed. However, as described above, since the deacetylated nano-chitin of the present invention forms a gel with low concentrations of acid, it is preferable to repeatedly wash the dispersion of the deacetylated nano-chitin 10 to 20 times with water at a ratio of approximately 250 to 500 times by weight in order to remove alkali from the dispersion. Furthermore, if the dispersion of the nano-sized chitin deacetylated product of the present invention becomes weakly acidic, it may swell and gel, making recovery by filtration impossible. Therefore, it is preferable to end the washing with water when the pH of the filtered filtrate is approximately 8.5 to 9.

[0029] As described above, when the dispersion of nano-sized chitin deacetylate of the present invention is made acidic or dispersed in an acidic aqueous solution, the dispersibility of the nano-sized chitin deacetylate is improved, allowing for the formation of a uniform gel at low concentrations. By adjusting the degree of deacetylation, highly transparent gels and gels exhibiting thixotropy can be obtained. The dispersion of deacetylated nano-chitin of the present invention can be further subjected to chemical modification. [Examples]

[0030] The present invention will be described in detail below with reference to examples.

[0031] [Example 1] Dispersion containing nano-sized chitin at a high concentration (wet cake-like nano-sized chitin) A dispersion containing nano-sized chitin at a high concentration was prepared as described below. α-chitin powder derived from crab shells (42-mesh sieved product, degree of deacetylation = 1.0%~2%). To 0% ("Chitin L-PC", manufactured by Koyo Chemical Co., Ltd.), a 48% sodium hydroxide aqueous solution (10 times its original weight) was added. After thoroughly permeating the chitin powder with the sodium hydroxide aqueous solution, the mixture was left to stand at 20°C overnight. Next, crushed ice was added until the sodium hydroxide concentration reached approximately 10 (w / v)%, and the mixture was stirred at -10°C or below until it became a uniform liquid. Next, concentrated hydrochloric acid was added while ice was added to neutralize the solution until the pH reached approximately 8.0-8.5, allowing chitin to precipitate. The precipitated chitin dispersion was repeatedly washed with a large amount of water to desalinate it until the salinity, as measured by a digital salinity meter ("ES-421", manufactured by Atago Co., Ltd.), was 0.01% by weight or less. The desalted chitin dispersion was dewatered by pressure filtration (filter press) (manufactured by Yabuta Machinery Co., Ltd.) to obtain a wet cake-like dispersion.

[0032] The wet cake-like dispersion obtained above was observed using a transmission electron microscope (TEM). Specifically, the dispersion obtained above was diluted with purified water to a chitin concentration of approximately 2.5% by weight to prepare a sample for TEM observation, which was then observed at a magnification of 50,000x using a "JEM-2100" (manufactured by JEOL Ltd.). The TEM observation image is shown in Figure 1.

[0033] As shown in Figure 1, the obtained dispersion was confirmed to be a dispersion of nano-sized chitin, in which chitin was defibrated down to elementary microfibril units. From the observation images of nano-sized chitin shown in Figure 1, the fiber width of the nano-sized chitin was measured to be less than 10 nm, and the fiber length could not be accurately measured. Furthermore, the average fiber width calculated from the measured fiber width was 3 nm to 5 nm. On the other hand, the observed nano-sized chitin was twisted in a spiral manner along its length, and as mentioned above, it was not possible to accurately measure the fiber length.

[0034] [Test Example 1] Measurement of nano-chitin content concentration and degree of nano-chitin deacetylation in the nano-chitin dispersion of Example 1 The nano-chitin content and the degree of deacetylation of the nano-chitin were measured for the nano-chitin dispersion of Example 1 as follows.

[0035] (1) Measurement of nano-sized chitin content For the nano-sized chitin dispersion of Example 1, the solid content was determined by atmospheric pressure heating and drying, and the concentration of nano-sized chitin was calculated from the weight of the dispersion before drying.

[0036] (2) Measurement of the degree of deacetylation 1380g of N,N-dimethylacetamide was weighed into a 2L glass beaker that had been pre-filled with a stirrer, stirred with the stirrer, and then 120g of lithium chloride was added and dissolved to prepare a chitin solution. The nano-sized chitin dispersion from Example 1 was heated and dried at atmospheric pressure. 2.5 g of the resulting solid content was weighed out and added to the chitin solution to make a total volume of 500 g. The mixture was stirred overnight to dissolve the chitin. 1.0 g of the resulting nano-sized chitin solution was weighed out, deionized water was added to make a total volume of 50 mL, 3 drops of 0.1 (w / v)% toluidine blue were added and mixed, and the solution was titrated with 1 / 400 N potassium polyvinyl sulfate aqueous solution (PVSK) (the endpoint was defined as the point when the solution color changed from blue to reddish-purple and remained reddish-purple for 3 seconds or more). The molar masses of glucosamine units and acetylglucosamine units in nano-sized chitin were set to 161 and 203, respectively, and the degree of deacetylation was calculated from the titration values.

[0037] The measurement results for (1) and (2) above are shown in Table 1.

[0038] [Table 1]

[0039] As shown in Table 1, the nano-chitin dispersion of Example 1 contained nano-chitin at a high concentration of 20% by weight. Furthermore, as shown in Table 1, the degree of deacetylation of the nano-chitin in the nano-chitin dispersion of Example 1 was 5%, indicating that deacetylation had not progressed as much as with the chitin powder used as the starting material.

[0040] [Example 2] Dispersion of deacetylated nano-chitin The nano-sized chitin dispersion from Example 1 was diluted, and 9.0 g (nano-sized chitin content = 7 wt%) was dispersed in water to a total volume of 30 mL. 30 mL of 48 wt% sodium hydroxide was added and the mixture was stirred. The mixture was then heated to 60°C and the deacetylation reaction was carried out for 5 hours. The sodium hydroxide concentration during the reaction was approximately 36 (w / v)%. After the reaction, the dispersion of deacetylated nano-chitin was repeatedly washed with a large amount of water until the pH of the washing solution (filtrate) reached 8.5 to 9.0. The degree of deacetylation of the nano-sized chitin in the obtained dispersion was measured using the same method as in the measurement of the degree of deacetylation in Test Example 1 above, and was found to be 15.7% to 16.2%. When a few drops of acetic acid were added to the resulting deacetylated dispersion to make it acidic, gelation was observed at low concentrations of nano-sized chitin (1.0% to 2.0% by weight). The appearance of the resulting deacetylated gel is shown in Figure 2. As shown in Figure 2, when the dispersion of the deacetylated nano-chitin from Example 2 was made acidic, the dispersion exhibited a uniform, viscous gel-like state.

[0041] [Example 3] Dispersion of deacetylated nano-chitin A dispersion of deacetylated nano-chitin was prepared in the same manner as in Example 2, except that the deacetylation reaction was carried out at 80°C for 5 hours. The degree of deacetylation of the deacetylated nano-chitin in the obtained dispersion was measured using the same method as in the measurement of the degree of deacetylation in Test Example 1 above, and was found to be 18.8%. The reason why deacetylation does not proceed very much under the above deacetylation conditions is thought to be that the inside of the crystalline structure of nano-chitin does not swell, and the acetamide on the fiber surface or amorphous parts is deacetylated. When a few drops of acetic acid were added to the dispersion of deacetylated nano-chitin from Example 3 to make it acidic, a highly transparent gel was formed at a nano-chitin concentration of 1.6% by weight (Figure 3).

[0042] [Example 4] Dispersion of deacetylated nano-chitin A dispersion of deacetylated nano-chitin was prepared in the same manner as in Example 2, except that the deacetylation reaction was carried out in a 52.7 (w / v)% aqueous sodium hydroxide solution at 60°C for 5 hours. The degree of deacetylation of the nano-sized chitin in the obtained dispersion was measured using the same method as in the measurement of the degree of deacetylation in Test Example 1 above, and it was found to be 40%. When a few drops of acetic acid were added to the dispersion of deacetylated nano-chitin from Example 4 to make it acidic, a nearly transparent gel was formed at a nano-chitin concentration of 1.2% by weight (Figure 4). The gel formed by the deacetylated nano-chitin of Example 4 exhibits thixotropy, as shown in Figure 4, and even when the bottle filled with the gel is inverted, the gel does not fall out. It exhibited a strong viscosity, though not excessive. Furthermore, the gel formed by the deacetylated nano-chitin of Example 4 was observed using TEM, similar to the case of the nano-chitin dispersion in Example 1. The results are shown in Figure 5. As shown in Figure 5, although a uniform dispersion of nano-sized chitin was observed in the TEM observation image, many short crystals were observed in the axial direction.

[0043] [Example 5] Dispersion of deacetylated nano-chitin A dispersion of deacetylated nano-chitin was prepared in the same manner as in Example 2, except that the deacetylation reaction was carried out in a 30 (w / v)% aqueous sodium hydroxide solution at 45°C for 72 hours. The degree of deacetylation of the nano-sized chitin in the obtained dispersion was measured using the same method as in the measurement of the degree of deacetylation in Test Example 1 above, and was found to be 26.4%. When a few drops of acetic acid were added to the dispersion of the deacetylated nano-chitin from Example 5 to make it acidic, a gel was formed at a nano-chitin concentration of 1.8% by weight.

[0044] [Test Example 2] Measurement of molecular weight of nano-sized chitin and deacetylated nano-sized chitin The molecular weights of nano-chitin and nano-chitin deacetylated contained in the nano-chitin dispersion of Example 1 and the nano-chitin deacetylated dispersion of Example 5 were measured as follows. The dispersion of nano-sized chitin from Example 1 and the dispersion of deacetylated nano-sized chitin from Example 5 were immersed in a 48 wt% sodium hydroxide aqueous solution, respectively, and deacetylated at 85°C for 17 hours. After neutralization, the deacetylated product (degree of deacetylation ≥ 85%) was recovered, dissolved in a 0.5 wt% acetic acid aqueous solution, and analyzed by gel permeation chromatography (GPC) under the following conditions. For comparison, the starting materials used chitin ("Chitin L-PC," manufactured by Koyo Chemical Co., Ltd.) and purified chitin ("Chitin TC-L," manufactured by Koyo Chemical Co., Ltd.) were also processed in the same manner and their molecular weights were measured. <Molecular weight measurement conditions> (i) Columns: TSK Gel G6000PWXL-CP and TSK Gel G3000PWXL-CP (Tosoh Corporation) (ii) Eluent: 0.25M acetic acid - 0.25M sodium acetate buffer (iii) Flow rate: 0.5mL / min (iv) Sample injection volume: 200 μL (v) Oven temperature: 40°C (vi) Detector: RI (differential refraction) detector (vii) Standard sample: pullulan (viii) Analysis time: 60min The measurement results are shown in Table 2.

[0045] [Table 2]

[0046] As mentioned above, the TEM image shown in Figure 1 did not confirm the presence of fibers of sufficient length in the nano-chitin dispersion of Example 1, but the molecules shown in Table 2... The measurement results showed no significant decrease in average molecular weight (low molecular weight) in the nano-sized chitin, suggesting that fiber cleavage was not significant. Furthermore, in the deacetylated nano-chitin present in the dispersion of Example 5, no significant decrease in average molecular weight (low molecular weight) was observed, suggesting that the nano-chitin was deacetylated while maintaining its morphology.

[0047] As described above, the dispersion in Example 1 was a dispersion in which nano-sized chitin, which had a uniform fiber width of 10 nm or less and had been defibrated to almost elementary microfibril units, was dispersed at an unprecedentedly high concentration of 20% by weight. Since such dispersions contain a high concentration of uniform nano-sized chitin, as shown in Examples 2 to 5, they can be used as a raw material or starting material to deacetylate nano-sized chitin while maintaining its form. When the deacetylated nano-sized chitin is dispersed in an acidic solution or in an acidic aqueous solution, it can form a gel at low concentrations. Depending on the degree of deacetylation of the nano-sized chitin, a highly transparent gel or a gel with high viscosity and thixotropy can be obtained. Furthermore, it is possible to explore further derivatization from deacetylated nano-sized chitin products. The dispersion of the present invention is also useful as a raw material for N-acetylglucosamine and oligosaccharides. Furthermore, the dispersion of the present invention is useful as a medical material, a filler in resins, a paper quality improver, etc., and can also be used as an ingredient in functional foods (especially as a prebiotic), cosmetics, animal feed, etc. [Industrial applicability]

[0048] As described in detail above, the present invention makes it possible to provide a nano-chitin dispersion containing nano-chitin having a uniform fiber width at a high concentration. The nano-sized chitin contained in the dispersion of the present invention can be deacetylated while maintaining the nano-sized chitin form. The dispersion of the deacetylated nano-sized chitin can form a gel at low concentrations by making the solution acidic or by dispersing it in an acidic aqueous solution. The dispersion of the present invention can be suitably used as a raw material for N-acetylglucosamine and oligosaccharides, as well as a medical material, a plastic material, and as an ingredient in functional foods, cosmetics, animal feed, etc.

Claims

1. A method for producing a dispersion of deacetylated nanochitin, comprising heating or heating a wet cake-like dispersion containing nanochitin having a fiber width of 20 nm or less at a concentration of 10% to 30% by weight, in an alkaline aqueous solution, and washing it with water.

2. The manufacturing method according to claim 1, wherein the content concentration of nano-sized chitin in the wet cake-like dispersion is 15% to 25% by weight.

3. The manufacturing method according to claim 1 or 2, wherein the fiber width of the nano-sized chitin contained in the wet cake-like dispersion is 10 nm or less.

4. The manufacturing method according to any one of claims 1 to 3, wherein the concentration of the alkaline aqueous solution is 10 (w / v)% to 40 (w / v)%.

5. The manufacturing method according to any one of claims 1 to 4, wherein the heating or heating temperature in the alkaline aqueous solution is 45°C to 80°C.

6. The manufacturing method according to any one of claims 1 to 5, wherein the heating or heating time in an alkaline aqueous solution is 5 hours to 72 hours.

7. The manufacturing method according to any one of claims 1 to 6, wherein the degree of deacetylation of the deacetylated nano-chitin is 10% to 50%.

8. A method for producing a gel containing a dispersion of nano-sized chitin deacetylated product, wherein the dispersion of the nano-sized chitin deacetylated product produced by the manufacturing method described in any one of claims 1 to 7 is made acidic, or the dispersion is dispersed in an acidic aqueous solution.

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