Dispersants and dispersions for poorly soluble or insoluble substances

Abstract

To provide a dispersant and a fluid dispersion having excellent dispersibility and friendliness to an environment by using carboxymethylated xylan obtained by methylating xylan to disperse poor solubility or insoluble substance.SOLUTION: A fluid dispersion is characterized by the use of carboxymethylated xylan in which xylan is carboxymethylated. In this case, the xylan may be glucuronoxylan. Further, it is preferable that the degree of CM of the carboxymethyl xylan be 0.1 or more and 0.4 or less. When glucuronoxylan is carboxymethylated with carboxymethylated xylan and the degree of CM is 0.1 or more and 0.4 or less, a dispersant excellent in dispersibility is formed. The poorly soluble or insoluble substance may be carbon nanotubes, graphene, β-carotene or phthalocyanines.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention primarily relates to a dispersant and a dispersion for dispersing poorly soluble or insoluble substances such as carbon nanotubes in water. Background Art

[0002] A carbon nanotube (hereinafter referred to as "CNT") is a cylindrical (tube-shaped) substance composed entirely of carbon with a diameter on the nanometer scale, and has a structure obtained by cylindrically rolling a sheet in which benzene rings with carbon atoms arranged in hexagons are all arranged adjacent to each other on a plane. Those with a single such cylindrical layer are called single-walled carbon nanotubes (hereinafter referred to as "SWCNT"), and those with a plurality of cylinders of different diameters stacked in layers are called multi-walled carbon nanotubes (hereinafter referred to as "MWCNT").

[0003] Carbon nanotubes have high conductivity and great mechanical strength, and applications utilizing these properties in conductive paints, conductive resins, electromagnetic shielding sheets, heater members and the like are under study. What is important for these applications is the dispersibility of CNTs. In the solid state, CNTs form bundled structures due to strong π-π interactions and van der Waals forces, making them difficult to disperse in most solvents. Therefore, to enable the dispersion of CNTs in solvents and facilitate various applications, excellent dispersants that assist in this process are required.

[0004] For example, it is disclosed that a sheet with excellent electromagnetic wave suppression and heat generation capabilities is produced by coating a sheet substrate with an aqueous dispersion obtained by adding and dispersing CNTs in an aqueous solution containing a dispersant consisting of a specific anionic surfactant and a specific polysaccharide. The aqueous dispersion uses one or more dispersants from group A of anionic surfactants consisting of methylnaphthalene sulfonic acid formalin condensate salt, naphthalene sulfonic acid formalin condensate salt, and alkylene maleic acid copolymer salt, and from group B of polysaccharides consisting of water-soluble xylan, xanthan gums, guar gums, gellan gums, and carboxymethylcellulose (see, for example, Patent Document 1).

[0005] Furthermore, it has been discovered that by using water-soluble xylan, the affinity of the solvent to the surface of poorly soluble or insoluble substances can be improved, and a solution of such substances can be obtained by improving the affinity of the solvent to the surface of poorly soluble or insoluble water substances (see, for example, Patent Document 2).

[0006] Furthermore, researchers, including the present inventors, have discovered that methylglucuronoxylan, a hemicellulose, has the function of dispersing hydrophobic substances in water, and have investigated the dispersion mechanism of CNTs, as well as conducting research on its application to electromagnetic wave shielding silicone rubber (see, for example, Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2013-082610 [Patent Document 2] Japanese Patent Publication No. 2007-215542 [Non-patent literature]

[0008] [Non-Patent Document 1] Applied Carbohydrate Science, Vol. 12, No. 1, 27-32 (2022) [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The invention described in Patent Document 1 discloses a carbon nanotube aqueous dispersion using one or more specific anionic surfactants from group A and specific polysaccharides from group B as dispersants. This invention aims to suppress the increase in viscosity of the CNT dispersion when the CNT concentration is increased when using only polysaccharides such as carboxymethylcellulose as a dispersant, by mixing in anionic surfactants to enable coating treatment. However, the addition of surfactants may cause bubbles to form, which presents a problem as it requires careful attention to ensure good coating film formation.

[0010] The invention described in Patent Document 2 enables the dispersion of poorly soluble or insoluble substances using water-soluble xylan. However, when applying CNT dispersions to electronic materials, it is often necessary to increase the degree of dispersion of CNTs. However, there is a challenge in that it is difficult to further increase the degree of dispersion using water-soluble xylan alone.

[0011] In the invention described in Non-Patent Document 1, an example is shown of using a dispersion of SWCNTs (silicon carbonate nanotubes) prepared by dispersing them with water-soluble xylan, a natural product, as a dispersant for electronic materials, and using it as a paint. However, there is a challenge in that it is difficult to further increase the degree of dispersion by using only natural products.

[0012] Furthermore, environmental issues are a very important topic today, and even materials with excellent properties cannot be used if they have a significant environmental impact. When considering environmental impact and biocompatibility, water is the most suitable solvent. In addition, it is desirable that dispersants used to dissolve poorly soluble substances be environmentally friendly or biocompatible. For this reason, dispersants used to disperse poorly soluble or insoluble substances are preferably natural products or biodegradable compounds.

[0013] The present invention relates to the dispersion of poorly soluble or insoluble substances using xylan. CarboxylateThe objective is to provide a dispersant and dispersion that offers good dispersibility and is environmentally friendly by using methylated carboxymethylated xylan. [Means for solving the problem]

[0014] To solve the above-mentioned conventional problems, the dispersant for poorly soluble or insoluble substances of the present invention is characterized by using carboxymethylated xylan, which is obtained by carboxymethylating xylan.

[0015] In this case, xylan may be glucuronoxylan. Furthermore, it is preferable that the degree of carboxymethylation (hereinafter referred to as "CM degree") of the carboxymethylated xylan is 0.1 or higher and 0.4 or lower.

[0016] When xylan, particularly glucuronoxylan, is subjected to carboxymethylation to obtain carboxymethylated xylan, and the degree of CMization is set to 0.1 or higher and 0.4 or lower, it can be used as a dispersant with excellent dispersibility.

[0017] In this case, the poorly soluble or insoluble substance may be carbon nanotubes, graphene, β-carotene, or phthalocyanines. Although these substances possess various high-performance properties, their applications are limited because they cannot be dispersed in solvents such as water. By using the dispersant of the present invention, applications in a wide range of fields become possible.

[0018] Furthermore, the carbon nanotube dispersion of the present invention comprises the dispersant described above, a sparingly soluble or insoluble substance consisting of carbon nanotubes, and water. Because it can disperse carbon nanotubes and has stable dispersibility, it can be applied to a wide range of fields, such as electronic materials such as conductive materials and electromagnetic shielding sheets, and batteries.

[0019] Further, the graphene dispersion of the present invention comprises the dispersant described above, a poorly soluble or insoluble substance composed of graphene, and water. When such a graphene dispersion is used, it can be applied onto the surface of a substrate and used as a conductive coating, an electromagnetic wave shielding material, a field emission material, or the like.

[0020] Further, the β-carotene dispersion of the present invention comprises the dispersant described above, a poorly soluble or insoluble substance composed of β-carotene, and water. Carboxymethylated xylan obtained by subjecting glucuronoxylan to carboxymethylation treatment is also a material that has little impact on human safety and the environment, so the β-carotene dispersion using this dispersant can be applied as a cosmetic raw material or a food additive.

[0021] Further, the phthalocyanine dispersion of the present invention comprises the dispersant described above, a poorly soluble or insoluble substance composed of phthalocyanines, and water. Phthalocyanines are often used as pigments, but when a dispersion with improved dispersibility is used, application to various dyes is facilitated. [Effects of the Invention]

[0022] The dispersant for poorly soluble or insoluble substances and the dispersion of the present invention can easily disperse poorly soluble or insoluble substances such as CNT, and in particular, a dispersion in which CNT is dispersed exerts a great effect in the field of electronic components. [Brief Description of Drawings]

[0023] [Figure 1] This figure shows the results obtained from examining the relationship between the degree of dispersion of MWCNT and the degree of CM modification of carboxymethylated xylan in Example 1 according to the present embodiment. [Figure 2] This figure shows the results of examining the degree of dispersion and viscosity relative to the concentration of CM-GX (carboxymethylated xylan) when the addition amount of MWCNT is small (0.1 wt%) in Example 1 according to the present embodiment. [Figure 3]In Example 1 of this embodiment, the dispersion and viscosity with respect to the CM-GX (carboxymethylated xylan) concentration were investigated when the amount of MWCNT added was large (1 wt%). [Figure 4] This figure shows the results of dispersion using SWCNTs in Example 2 of this embodiment, compared with the results of dispersion using MWCNTs. [Figure 5] This figure shows the results of dispersion using graphene in Example 3 of this embodiment, compared with the MWCNT dispersion results. [Figure 6] This figure shows the results of dispersing copper phthalocyanine in Example 4 of this embodiment, and evaluating the results by measuring the absorption spectrum using a UV-Vis spectrophotometer. [Figure 7] This figure shows the results of dispersing with β-carotene in Example 5 of this embodiment, and the absorption spectrum was measured and evaluated using a UV-Vis spectrophotometer. [Modes for carrying out the invention]

[0024] (Embodiment)

[0025] The following describes an embodiment of the present invention of a dispersant for poorly soluble or insoluble substances. The dispersant for poorly soluble or insoluble substances of the present invention is characterized by using carboxymethylated xylan, which is obtained by carboxymethylating xylan. The inventors have already found that glucuronoxylan has good properties as a dispersant for poorly soluble or insoluble substances, but have made various efforts to further improve dispersibility and dispersion stability. As a result, they have found that carboxymethylated xylan, obtained by using glucuronoxylan as the xylan and subjecting it to carboxymethylation, has even better properties as a dispersant. Furthermore, they have found that it is preferable to set the degree of carboxymethylation to 0.1 or higher and 0.4 or lower, and have completed the present invention. It should be noted that the present invention is not limited to glucuronoxylan as the xylan, and similar effects can be obtained with arabinoglucuronoxylan, glucuronarabinoxylan, and arabinoxylan, which will be described later.

[0026] In the above invention, the poorly soluble or insoluble substance may be carbon nanotubes, graphene, β-carotene, or phthalocyanines. These substances are known to be poorly soluble or insoluble in water, and there is a need for a good dispersant. By using the dispersant of the present invention, dispersion with a high degree of dispersion in water becomes possible. Furthermore, carboxymethylated xylan is obtained by carboxymethylating glucuronoxylan, and is an environmentally friendly material. When used as a dispersant, it is possible to not only improve the dispersibility of poorly soluble substances such as carbon nanotubes, graphene, β-carotene, or phthalocyanines, but also to produce an environmentally friendly dispersion.

[0027] Furthermore, the carbon nanotube dispersion of the present invention comprises the dispersant described above, a sparingly soluble or insoluble substance consisting of carbon nanotubes, and water. Such a carbon nanotube dispersion can be used for purposes such as conductive coatings, electromagnetic shielding materials, field emission materials, and negative electrode materials for batteries.

[0028] Furthermore, the graphene dispersion of the present invention comprises the dispersant described above, a sparingly soluble or insoluble substance made of graphene, and water. Such a graphene dispersion can be used by coating it onto the surface of a substrate to serve as a conductive coating, an electromagnetic shielding material, or an electrolytic emission material.

[0029] Furthermore, the β-carotene dispersion of the present invention comprises the dispersant described above, a poorly soluble or insoluble substance consisting of β-carotene, and water. Since carboxymethylated xylan, obtained by carboxymethylating glucuronoxylan, is also a material with low safety for humans and low environmental impact, the β-carotene dispersion using this dispersant can be applied as a cosmetic ingredient or food additive.

[0030] Furthermore, the phthalocyanine dispersion of the present invention comprises the dispersant described above, a sparingly soluble or insoluble substance consisting of phthalocyanines, and water. Phthalocyanines are commonly used as pigments, but using a dispersion with improved dispersibility makes it easier to apply them to various dyes.

[0031] Phthalocyanines are chemically cyclic compounds containing four isoindole groups. When there is no metal at the center, it is chemically called phthalocyanine, but there are many that do have a metal at the center, with copper phthalocyanine being a typical example. In this invention, copper phthalocyanine, cobalt phthalocyanine, zinc phthalocyanine, magnesium(II) phthalocyanine, tin(II) phthalocyanine, metal-free phthalocyanines, low-chlorinated phthalocyanines, etc., will be referred to as phthalocyanines. The degree of carboxymethylation of carboxymethylated xylan refers to the number of carboxymethyl groups that are substituted for the two hydroxyl groups present per xylose unit.

[0032] Furthermore, xylan refers to a molecule containing two or more xylose residues linked by β-1,4 bonds. Not only molecules composed solely of xylose residues (i.e., pure xylose polymers), but also those to which 4-O-methylglucuronic acid residues and acetyl groups are bonded are generally called glucuronoxylans. It is well known that glucuronoxylan is the main component of hemicellulose found in hardwoods. Glucuronoxylan found in hardwoods is often composed of xylose residues 10: 4-O-methylglucuronic acid 1: acetyl groups 6. There are also molecules to which arabinose residues and 4-O-methylglucuronic acid are bonded to xylose polymers. These are generally called arabinoglucuronoxylans or glucuronarabinoxylans. Molecules to which arabinose residues are bonded are generally called arabinoxylans. In this invention, these are collectively referred to as xylans. (Example 1)

[0033] In this example, glucuronoxylan is used as the xylan, and the results of dispersing MWCNTs using carboxymethylated xylan are described. First, the procedure for carboxymethylation of glucuronoxylan is explained.

[0034] 10 g of glucuronoxylan was mixed with 100 g of ethanol, 10 g of 30% sodium hydroxide aqueous solution, and 3 g of sodium monochloroacetate, and stirred at 45°C. After 15, 30, and 60 minutes, a portion of the reaction solution was taken, and ethanol was added to obtain a precipitate. This precipitate was washed with 90% ethanol and then dried at 70°C to prepare carboxymethylated xylanes with different degrees of carboxymethylation.

[0035] The degree of carboxymethylation (hereinafter sometimes referred to as "CM degree") of the prepared carboxymethylated xylan was calculated by the following method. 200 mg each of carboxymethylated xylan with different CM degrees were suspended in 2 mL of 80% ethanol. Then, 2 mL of hydrochloric acid (HCl) was added and the mixture was stirred for 1 hour, after which a precipitate was obtained by centrifugation at 6000 G for 10 min. These precipitates were washed twice with 80% ethanol, and then 20 mL of purified water was added and the mixture was stirred. Furthermore, 25 mL of 0.1 M sodium hydroxide (NaOH) aqueous solution was added and heated for 15 minutes. These solutions were then titrated with 0.1 M hydrochloric acid (HCl) aqueous solution, and the degree of etherification was calculated from the amount of hydrochloric acid added. Subsequently, the degree of CM was calculated from the difference between the degree of etherification of the sample before carboxymethylation and the degree of etherification of the sample before carboxymethylation.

[0036] Figure 1 shows the relationship between the degree of carboxymethylation of carboxymethylated xylan and the degree of dispersion of MWCNTs. 50 mg of MWCNTs were added to 50 mL of aqueous solutions of carboxymethylated xylans with different degrees of carboxymethylation, as described above, and dispersed using an ultrasonic homogenizer (600 W). Then, the solutions were separated using a centrifuge (Eppendorf Hi-Mac Technologies, CT18R) at 10,000 G for 1 hour, and the supernatant was used as the sample. The absorbance of this supernatant at a wavelength of 500 nm was measured using a UV-Vis spectrophotometer (Shimadzu Corporation, UV-1900), and the value calculated based on the obtained absorbance was defined as the degree of dispersion.

[0037] As can be seen from the figure, it was found that the dispersion can be improved when the degree of CM is 0, i.e., when glucuronoxylan is used, compared to the dispersion when the degree of CM is 0. Furthermore, although not shown in the figure, when a carboxymethylated xylan with a high degree of CM was prepared and the dispersion of MWCNTs was determined, it was found that the dispersion decreased when the degree of CM exceeded 0.4. As a result of these findings, it was found that the degree of CM is preferably in the range of 0.1 to 0.4. In particular, 0.1 to 0.2 is more preferable.

[0038] Furthermore, the molecular weight of the carboxymethylated xylan can be used without particular restrictions as long as it is in the range of 1,000 to 1,000,000. A range of 1,000 to 30,000 is particularly preferred, but 5,000 to 25,000 is even more preferred.

[0039] Figures 2 and 3 show the results of determining the dispersion and viscosity when the concentration of carboxymethylated xylan relative to water and the amount of MWCNT added were varied, using carboxymethylated xylan with a CM degree of 0.2.

[0040] Figure 2 shows the results when the amount of MWCNT added is small (0.1 wt%). CM-GX( Carboxymethylated xylan concentration This is the result of investigating the degree of dispersion and viscosity for [the substance]. For this, aqueous solutions were prepared using carboxymethylated xylan with a CM degree of 0.2, with concentrations of carboxymethylated xylan in water of 0.01 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%, and 1.0 wt%, and these water soluble This shows the dispersion degree and viscosity of a dispersion prepared by adding 0.1 wt% MWCNTs to a liquid.

[0041] It was found that when the concentration of carboxymethylated xylan in water was 0.01 wt%, MWCNTs hardly dispersed, but when 0.1 wt% or more was added, the degree of dispersion increased rapidly. Furthermore, in the range of carboxymethylated xylan concentration from 0.1 wt% to 1.0 wt%, the degree of dispersion showed a gradual increasing trend. On the other hand, the viscosity was 0.9 mPa·s when the concentration of carboxymethylated xylan was 0.01 wt%, approximately 1.1 mPa·s at 0.1 wt%, and approximately 1.7 mPa·s at 1.0 wt%. When the amount of MWCNT added is small, a concentration of carboxymethylated xylan in water of about 0.1 wt% can be used to obtain sufficient dispersion, and using carboxymethylated xylan when manufacturing conductive materials can prevent viscosity increases and gelation of the dispersion. It also makes the dispersion easier to handle.

[0042] Figure 3 shows the results when the amount of MWCNT added is large (1 wt%). CM-GX (Cal (Voxymethylated xylan) concentration This is the result of investigating the degree of dispersion and viscosity with respect to [the substance]. Specifically, using carboxymethylated xylan with a CM degree of 0.2, aqueous solutions were prepared with concentrations of carboxymethylated xylan in water of 0.5 wt%, 1.0 wt%, and 2.0 wt%, and these [results] water soluble This shows the dispersion and viscosity of a dispersion prepared by adding 1 wt% MWCNTs (10 times the amount used in Figure 2) to the liquid.

[0043] For the concentrations of carboxymethylated xylan in Figure 2 (0.5 wt%) and 1.0 wt%), and in Figure 3 (0.5 wt%), the concentration of carboxymethylated xylan relative to water is exactly the same. When the amount of MWCNT added was 1 wt%, the degree of dispersion increased with increasing amount, and the degree of dispersion became significantly larger compared to the case of 0.1 wt%. Specifically, a value of 370 was obtained for a carboxymethylated xylan concentration of 0.5 wt%, 405 for 1.0 wt%, and 430 for 2.0 wt%. Furthermore, it was found that the viscosity of the dispersion increased even when the concentration of carboxymethylated xylan was the same as in Figure 2, due to the increased degree of dispersion of MWCNT. Specifically, a value of 4 mPa·s was obtained for a carboxymethylated xylan concentration of 0.5 wt%, and 5.5 mPa·s for a carboxymethylated xylan concentration of 1.0 wt%.

[0044] The results showed that adding a large amount of MWCNTs significantly increases the degree of dispersion while also lowering the viscosity, compared to adding a small amount, making it effective for applications in conductive materials and the like. In particular, when the viscosity of the dispersion is 6 mPa·s or less, it exhibits high fluidity, improves work efficiency during coating, and is easy to handle, making it preferable. (Example 2)

[0045] This example describes the case where SWCNTs are used as CNTs. Figure 4 shows the results of dispersion using SWCNTs in comparison with the results of dispersion using MWCNTs. The degree of CMization of carboxymethylated xylan was set to 0.2, and the concentration of the dispersant relative to water was 0.2 wt%. water soluble A liquid was used. water soluble 50 mg of SWCNTs were added to 50 mL of solution and dispersed using an ultrasonic homogenizer (600 W). This procedure is the same as for MWCNTs, so the explanation is omitted. Figure 4 also shows the dispersion degree of MWCNTs for comparison.

[0046] As can be seen from Figure 4, the dispersion of SWCNTs is 28.5, which is smaller than that of MWCNTs, but still a dispersion level suitable for practical use was achieved. SWCNTs with an aspect ratio in the range of 5,000 to 100,000 are particularly preferred. (Example 3)

[0047] This example describes the case using graphene. Figure 5 shows the results of dispersion using graphene in comparison with the MWCNT dispersion results. The degree of CMization of carboxymethylated xylan was set to 0.2, and the concentration of the dispersant relative to water was set to 0.2 wt As a percentage water soluble A liquid was used. water soluble 50 mg of graphene was added to 50 mL of liquid and dispersed using an ultrasonic homogenizer (600 W). This procedure is the same as that for MWCNTs, so the explanation is omitted. Figure 5 also shows the dispersion degree of MWCNTs for comparison. As can be seen from Figure 5, the dispersion degree of graphene was 18.9, which is lower than that of MWCNTs, but a dispersion degree sufficient for practical use was obtained.

[0048] In this example, we will describe the case in which copper phthalocyanine(II) (β-type) is used as the phthalocyanine. In this example, a dispersant was prepared using carboxymethylated xylan with a CM degree of 0.2. This dispersant was dissolved in water at a rate of 0.2 wt % added to 0.2 wtA % aqueous solution was prepared. 1 mg of copper phthalocyanine(II) (β-type) was added to this solution and dispersed using an ultrasonic homogenizer (600W). In this example, instead of determining the degree of dispersion, the absorption spectrum was measured and evaluated using a UV-Vis spectrophotometer (Shimadzu Corporation, UV-1900). The results are shown in Figure 6.

[0049] As can be seen in Figure 6, when copper phthalocyanine(II)(β-type) was added directly to water without a dispersant, the copper phthalocyanine(II)(β-type) did not dissolve in water, and therefore almost no absorption was observed in the UV-Vis spectrophotometer measurement. However, in the case of a dispersion with a dispersant added, the absorbance at a wavelength of 500 nm was approximately 0.17, confirming that dispersion was possible, although the degree of dispersion was smaller than that of CNTs. (Example 5)

[0050] This example describes the case using β-carotene. In this example, a dispersant was prepared using carboxymethylated xylan with a CM degree of 0.2. This dispersant was dissolved in water at a rate of 0.2 wt % added to 0.2 wt A % aqueous solution was prepared. 10 mg of β-carotene was added to this solution and dispersed using an ultrasonic homogenizer (600 W). In this example, instead of determining the degree of dispersion, the absorption spectrum was measured and evaluated using a UV-Vis spectrophotometer (Shimadzu Corporation, UV-1900). The results are shown in Figure 7.

[0051] As can be seen in Figure 7, when β-carotene was added directly to water without a dispersant, β-carotene did not dissolve in water, so almost no absorption occurred in the UV-Vis spectrophotometer measurement. However, in the case of the dispersion with a dispersant added, the absorbance at a wavelength of 500 nm was 0.275, indicating that good dispersion was achieved.

[0052] In this invention, the term "xylan" includes not only glucuronoxylan but also arabinoglucuronoxylan, glucuronarabinoxylan, and arabinoxylan. While this embodiment and examples describe the use of carboxymethylated xylan, obtained by carboxymethylating glucuronoxylan, as a dispersant, the invention is not limited to this. Other xylans besides glucuronoxylan, such as arabinoxylan and arabinoglucuronoxylan, obtained by carboxymethylating, can also be used as good dispersants for poorly soluble or insoluble substances. [Industrial applicability]

[0053] The dispersants and dispersions for poorly soluble or insoluble substances of the present invention are useful in the field of electronic components such as electromagnetic wave shielding sheets that take advantage of conductivity when using carbon nanotubes (CNTs), in the food and cosmetics fields when using beta-carotene, and in the paint field when using phthalocyanines.

Claims

1. A carboxymethylated xylan obtained by carboxymethylating xylan, The xylan is a glucuronoxylan obtained by bonding a 4-O-methylglucuronic acid residue and an acetyl group to a xylose polymer. The degree of carboxymethylation during the carboxymethylation treatment was set to be between 0.1 and 0.

4. A dispersant for poorly soluble or insoluble substances comprising carbon nanotubes, graphene, β-carotene, or phthalocyanines, characterized by using the carboxymethylated xylan.

2. The dispersant for poorly soluble or insoluble substances according to Claim 1, characterized in that the molecular weight of the carboxymethylated xylan is in the range of 1,000 to 30,000.

3. A carbon nanotube dispersion comprising the dispersant according to claim 1 or 2, a poorly soluble or insoluble substance consisting of carbon nanotubes, and water.

4. A graphene dispersion comprising the dispersant according to claim 1 or 2, a sparingly soluble or insoluble substance made of graphene, and water.

5. A β-carotene dispersion comprising the dispersant according to claim 1 or 2, a poorly soluble or insoluble substance consisting of β-carotene, and water.

6. A phthalocyanine dispersion comprising the dispersant according to claim 1 or 2, a sparingly soluble or insoluble substance consisting of phthalocyanines, and water.

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