Cellulose acetate and method for producing cellulose acetate

Abstract

To provide a cellulose acetate that has a low total degree of acetyl substitution and a degree of acetyl substitution at 6-position that is lower than the degrees of acetyl substitution at 2-position and 3-position of a glucose ring, and has excellent water solubility.SOLUTION: In the cellulose acetate, the total degree of acetyl substitution is from 0.4 to 0.9 inclusive; the ratio of a degree of acetyl substitution at 6-position to the total degree of acetyl substitution is from 0% to 18% inclusive; and the light transmittance at 660 nm in a 4-wt.% aqueous solution is 5% or greater.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to cellulose acetate and a method for producing cellulose acetate.

Background Art

[0002] It is known that low-substitution-degree cellulose acetate with a total degree of acetylation of 0.4 to 1.1 and water-soluble cellulose acetate (low-substitution-degree cellulose acetate) with a total degree of acetylation of approximately 0.8 are metabolized and decomposed by intestinal bacteria and exhibit physiological effects such as suppression of weight gain and reduction of blood cholesterol (Patent Document 1 and Non-Patent Document 1).

[0003] The main metabolites of low-substitution-degree cellulose acetate are acetic acid and propionic acid. Propionic acid is thought to be produced from glucose constituting cellulose via phosphoenolpyruvate and succinic acid (Non-Patent Document 2 and Non-Patent Document 3). Acetic acid is thought to be produced by the release of acetic acid bound to cellulose in low-substitution-degree cellulose acetate, and is also thought to be produced from glucose constituting cellulose via phosphoenolpyruvate (Non-Patent Document 2 and Non-Patent Document 3).

[0004] Acetic acid and propionic acid produced by the metabolic decomposition of low-substitution-degree cellulose acetate by intestinal bacteria act on the nuclear receptor GPR43 of intestinal L cells, etc. on the one hand, and affect appetite and glucose metabolism by generating incretin GLP-1 (Non-Patent Document 4), and on the other hand, act on the hypothalamus and are known to affect appetite suppression, weight gain suppression, glucose metabolism, and lipid metabolism (Non-Patent Document 5).

[0005] It is known that the enzyme acetylxylanesterase is involved in the deacetylation of low-substituted cellulose acetate (Non-Patent Literature 6). Furthermore, Bacteroides xylanisolvens (Patent Literature 1, Non-Patent Literature 1), which proliferates in the intestines of rats fed low-substituted cellulose acetate, is a well-studied xylan-degrading bacterium and is thought to possess acetylxylanesterase. From these findings, it is presumed that the initial degradation of low-substituted cellulose acetate by intestinal bacteria is deacetylation, and that acetylxylanesterase is involved in this degradation.

[0006] Glucose, a major component of cellulose, has hydroxyl groups at positions 2, 3, and 6. In low-substituted cellulose acetate, some of these hydroxyl groups are acetylated. Acetylxylanesterase selectively removes the acetyl group at positions 2 or 3, but hardly removes the acetyl group at position 6 (Non-patent Literature 6). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6453851 [Non-patent literature]

[0008] [Non-Patent Document 1] Genda et al., Journal of Agricultural and Food Chemistry, 66, 11909-11916 (2018). [Non-Patent Document 2] Gijs den Besten et al., Journal of Lipid Research, 54, 2325-2340 (2013). [Non-Patent Document 3] Strobel, Applied and Environmental Microbiology, 58, 2331-2333 (1992). [Non-Patent Document 4] Sleeth et al., Nutrition Research Reviews, 23, 135-145 (2010). [Non-Patent Document 5] Frost et al., Nature Communications, DOI: 10.1038 (2014). [Non-Patent Document 6] Puls et al., Mactomolecular Symposia, 208, 239-253 (2004). [Non-Patent Document 7] Buchanan et al, Macromolecules, 24, 3060-3064 (1991). [Overview of the project] [Problems that the invention aims to solve]

[0009] Low-substituted cellulose acetate is thought to exert its physiological effects through metabolic degradation by intestinal bacteria. Because it is biodegradable and readily undergoes metabolic degradation by intestinal bacteria, low-substituted cellulose acetate is expected to exhibit excellent physiological effects.

[0010] Since acetylxylanesterase hardly removes the acetyl group at position 6, in order to improve the biodegradability of low-substituted cellulose acetate, it is necessary to relatively reduce the degree of acetyl substitution at position 6 of the glucose ring of cellulose acetate compared to the degree of acetyl substitution at positions 2 and 3.

[0011] However, conventional methods have not been able to make the degree of acetyl substitution at position 6 of the glucose ring relatively low compared to the degrees of acetyl substitution at positions 2 and 3 in cellulose acetate, which has a low total degree of acetyl substitution.

[0012] In addition, cellulose acetate with a low degree of substitution is more excellent in biodegradability when it has excellent water solubility. Therefore, cellulose acetate with a low degree of substitution, having a low degree of 6-position acetyl substitution and excellent water solubility, is particularly excellent in biodegradability.

[0013] However, such cellulose acetate with a low degree of 6-position acetyl substitution and excellent water solubility has not been known conventionally. For example, the degree of 6-position acetyl substitution of the cellulose acetate disclosed in Patent Document 1 is not low. Although cellulose acetate with a low degree of 6-position acetyl substitution is disclosed as Experimental No. 6 and Experimental No. 7 in Non-Patent Document 7, its water solubility is poor.

[0014] An object of the present invention is to provide cellulose acetate having a low total degree of acetyl substitution, a low degree of 6-position acetyl substitution with respect to the degrees of acetyl substitution at the 2- and 3-positions of the glucose ring, and further excellent water solubility.

Means for Solving the Problems

[0015] The first aspect of the present disclosure relates to cellulose acetate having a total degree of acetyl substitution of 0.4 or more and 0.9 or less, a ratio of the degree of 6-position acetyl substitution in the total degree of acetyl substitution of 0% or more and 18% or less, and a light transmittance at 660 nm of a 4% by weight aqueous solution of 5% or more.

[0016] In the cellulose acetate, the light transmittance at 660 nm of the 4% by weight aqueous solution may be 80% or more.

[0017] The second aspect of the present disclosure has a step of subjecting a raw material cellulose acetate having a total degree of acetyl substitution of 1.5 to 3.0 to solvolysis for deacetylation, and a step of precipitating the cellulose acetate generated by the deacetylation of the raw material cellulose acetate. The solvolysis of the raw material cellulose acetate proceeds at a temperature not lower than the boiling point of the alcohol in the presence of a solvent containing an alcohol having 3 or less carbon atoms and an acid catalyst. The present disclosure relates to a method for producing the cellulose acetate.

[0018] In the method for producing the cellulose acetate, the acid dissociation constant pKa of the acid catalyst in water at 25°C may be 0 or less.

[0019] In the method for producing cellulose acetate, the acid catalyst may be sulfuric acid.

[0020] In the method for producing cellulose acetate, the alcohol may be methanol.

[0021] In the method for producing cellulose acetate, the solvent may contain an acetate ester.

[0022] The method for producing cellulose acetate may include a step of dissolving the precipitated cellulose acetate in water to remove residues, and a step of precipitating the dissolved cellulose acetate.

[0023] The method for producing cellulose acetate may include a step of dissolving the precipitated cellulose acetate in water, centrifuging to remove residues, and a step of reprecipitating the dissolved cellulose acetate. [Advantages of the Invention]

[0024] According to the present invention, it is possible to provide cellulose acetate having a low total degree of acetyl substitution, a low degree of acetyl substitution at the 6-position with respect to the degrees of acetyl substitution at the 2- and 3-positions of the glucose ring, and excellent water solubility. [Embodiments for Carrying Out the Invention]

[0025] [Cellulose Acetate] The cellulose acetate of the present disclosure has a total degree of acetyl substitution of 0.4 or more and 0.9 or less, the ratio of the degree of acetyl substitution at the 6-position in the total degree of acetyl substitution is 0% or more and 18% or less, and the light transmittance at 660 nm of a 4% by weight aqueous solution is 5% or more.

[0026] [Total Degree of Acetyl Substitution] The cellulose acetate of this disclosure has a total acetyl substitution degree of 0.4 to 0.9. When the total acetyl substitution degree is within this range, the cellulose acetate of this disclosure has excellent water solubility and biodegradability. The cellulose acetate of this disclosure, with a total acetyl substitution degree of 0.4 to 0.9, may be referred to as low-substituted cellulose acetate.

[0027] [Percentage of acetyl substitution degree for the 6th position] The cellulose acetate relating to this disclosure has a acetyl substitution at position 6 of the total acetyl substitution degree of 0% or more and 18% or less, with the acetyl substitution at position 6 being preferably 14% or less, and more preferably 10% or less. The acetyl substitution at position 6 is most preferably 0%, but may exceed 0%, and may be 4% or more. Having a acetyl substitution at position 18% or less results in excellent degradability by enzymes present in the intestines (e.g., acetylxylanesterase, etc.) and is easily metabolized in the body.

[0028] The total degree of acetyl substitution and the proportion of the acetyl substitution at position 6 within the total degree of acetyl substitution can be determined by the following method.

[0029] First, the degrees of acetyl substitution at positions 2, 3, and 6 of the glucose ring of cellulose acetate are measured by NMR according to the method of Tezuka (Carbonydr. Res. 273, 83 (1995)). Specifically, the free hydroxyl groups of cellulose acetate are propionized with propionic anhydride in pyridine. The obtained sample is dissolved in deuterated chloroform, 13 The 1C-NMR spectrum is measured. The carbon signals of the acetyl group appear in the region from 169 ppm to 171 ppm in the order of positions 2, 3, and 6 from the highest magnetic field, and the signals of the carbonyl carbons of the propionyl group appear in the region from 172 ppm to 174 ppm in the same order. From the relative abundance of acetyl and propionyl groups at the corresponding positions, the degrees of acetyl substitution at positions 2, 3, and 6 of the glucose ring of cellulose acetate can be determined. Furthermore, the degrees of acetyl substitution are... 13 In addition to CNMR, 1 It can also be analyzed using 1H-NMR.

[0030] The degree of acetyl substitution at position i is the value obtained by dividing the number of moles of acetyl groups at position i by the sum of the number of moles of acetyl groups at position i and the number of moles of hydroxyl groups, and is a real number between 0 and 1. Here, i is either 2, 3, or 6. The sum of the degrees of acetyl substitution at positions 2, 3, and 6 of the glucose ring of cellulose acetate is the total degree of acetyl substitution. The proportion of the degree of acetyl substitution at position 6 in the sum of the degrees of acetyl substitution at positions 2, 3, and 6 of the glucose ring of cellulose acetate is the proportion (%) of the degree of acetyl substitution at position 6 in the total degree of acetyl substitution.

[0031] The total degree of acetyl substitution can be converted to the degree of acetic acid using the following formula. DS=162.14×AV×0.01 / (60.052-42.037×AV×0.01) DS: Degree of total acetyl substitution AV: Degree of acetic acid (%)

[0032] [Light transmittance] The cellulose acetate relating to this disclosure has a light transmittance of 5% or more at 660 nm in a 4% by weight aqueous solution of cellulose acetate, preferably 10% or more, more preferably 30% or more, even more preferably 50% or more, and most preferably 80% or more. The light transmittance may be 99% or less, 98% or less, or 95% or less. If the light transmittance of the 4% by weight aqueous solution at 660 nm is less than 5%, the cellulose acetate has poor water solubility.

[0033] The light transmittance at 660 nm of a 4 wt% aqueous solution of cellulose acetate can be determined using a spectrophotometer (Shimadzu Corporation, UV-1800 ultraviolet-visible spectrophotometer, polystyrene cell material, 10 mm cell length).

[0034] [Degree of polymerization (viscosity average degree of polymerization)] The viscosity-average degree of polymerization of the cellulose acetate in this disclosure is not particularly limited, but is preferably 3 to 400, more preferably 10 to 200, and even more preferably 15 to 150. Having a viscosity-average degree of polymerization within this range provides particularly excellent water solubility and biodegradability.

[0035] The viscosity-average degree of polymerization (DP) can be evaluated as a viscosity-average degree of polymerization based on the intrinsic viscosity number ([η], unit: g / ml), as shown below. Specifically, the intrinsic viscosity number is determined by methods conforming to JIS-K-7367-1 and ISO1628-1, the viscosity-average molecular weight is calculated according to the literature by Kamide et al., and the viscosity-average degree of polymerization can be calculated from this viscosity-average molecular weight.

[0036] The cellulose acetate of this disclosure can be produced by the following manufacturing method.

[0037] The cellulose acetate of this disclosure has a low total degree of acetyl substitution, and the degree of acetyl substitution at position 6 of the glucose ring is lower than the degree of acetyl substitution at positions 2 and 3. Therefore, it is highly biodegradable by enzymes present in the intestines (e.g., acetylxylanesterase), is easily metabolized in the body, and can be used as a food.

[0038] [Method for producing cellulose acetate] The present disclosure provides a method for producing cellulose acetate, comprising the steps of solvolysis and deacetylation of raw material cellulose acetate having a total acetyl substitution degree of 1.5 to 3.0, and precipitation of the cellulose acetate produced by the deacetylation of the raw material cellulose acetate, wherein the solvolysis of the raw material cellulose acetate proceeds in the presence of a solvent containing an alcohol having 3 or fewer carbon atoms and an acid catalyst, at a temperature above the boiling point of the alcohol.

[0039] [Deacetylation process] In the deacetylation step of the method for producing cellulose acetate according to this disclosure, the raw material cellulose acetate is solvolytically broken down. In the deacetylation step of this disclosure, deacetylation proceeds by solvolytic breakdown. This solvolytic breakdown may involve only a solvent containing an alcohol having 3 or fewer carbon atoms, or it may involve a solvent containing an alcohol having 3 or fewer carbon atoms and other solvents such as water. Solvolytic breakdown also includes hydrolysis.

[0040] (Raw material: cellulose acetate) As the raw material cellulose acetate, cellulose acetate with a moderate to high degree of substitution can be used. The total degree of acetyl substitution of the moderate to high degree of substitution cellulose acetate used as a raw material is 1.5 to 3.0, with 1.5 to 2.5 being preferred. As the raw material cellulose acetate, commercially available cellulose diacetate (total degree of acetyl substitution 2.20 to 2.56) or cellulose triacetate (total degree of acetyl substitution greater than 2.56 to 3) can be used.

[0041] When producing cellulose acetate as a raw material, it is acceptable to use conventionally known production methods. For example, it can be produced by a series of steps including crushing the pulp, which is the cellulose material, pretreatment, acetylation, hydrolysis, precipitation, and addition of a stabilizer. Next, each of these steps will be explained. For general methods of producing cellulose acetate, please refer to "Wood Chemistry" (Vol. 1) (Migita et al., Kyoritsu Shuppan Co., Ltd., 1968, pp. 180-190).

[0042] The α-cellulose content of the pulp is preferably 92% by weight or more, more preferably 93% by weight or more, and even more preferably 94% by weight or more. There is no particular upper limit, but it may be 99% by weight or less. Such high-purity pulp contains almost no lignin derived from wood, and also little hemicellulose. Because of these low levels of impurities, cellulose acetate with particularly excellent water solubility and biodegradability can be obtained.

[0043] The α-cellulose content can be determined as follows: Pulp of known weight is successively extracted at 25°C with 17.5% and 9.45% sodium hydroxide aqueous solutions. The soluble portion of the extract is oxidized with potassium dichromate, and the weight of β,γ-cellulose is determined from the volume of potassium dichromate required for oxidation. The value obtained by subtracting the weight of β,γ-cellulose from the initial weight of the pulp is taken as the weight of the insoluble portion of the pulp and the weight of α-cellulose (TAPPI T203). The ratio of the weight of the insoluble portion of the pulp to the initial weight of the pulp is the α-cellulose content (weight %).

[0044] As pulp, wood pulp (coniferous pulp, hardwood pulp) and cotton linters can be used. These celluloses may be used individually or in combination of two or more types; for example, coniferous pulp may be used in combination with cotton linters or hardwood pulp.

[0045] Wood pulp is preferred because it offers a stable supply of raw materials and is cost-effective compared to linters. Examples of wood pulp include pre-hydrolyzed hardwood kraft pulp.

[0046] In the pulp crushing process, for example, it can be crushed dry using a disc refiner.

[0047] In the pretreatment step, the crushed pulp is brought into contact with acetic acid or sulfur-containing acetic acid. Acetic acid can be 96-100% by weight, and sulfur-containing acetic acid is acetic acid containing sulfuric acid, preferably containing 1-10% by weight of sulfuric acid.

[0048] In the acetylation step, the pre-treated pulp is contacted with a mixed solution of acetic acid and acetic anhydride to acetylate the pulp with acetic anhydride, thereby obtaining fully trisubstituted cellulose acetate (primary cellulose acetate). The mixed solution preferably contains sulfuric acid as a catalyst. In the acetylation step, 96-100% by weight acetic acid can be used, and concentrated sulfuric acid is preferred.

[0049] In the hydrolysis step, a neutralizing agent such as water, dilute acetic acid, or an aqueous magnesium acetate solution is added to neutralize the sulfuric acid (completely or partially neutralize it) and deactivate the acetic anhydride, thereby stopping the acetylation reaction. This hydrolyzes the fully trisubstituted cellulose acetate (primary cellulose acetate) to obtain cellulose acetate of the desired degree of substitution (secondary cellulose acetate). Here, dilute acetic acid refers to an aqueous acetic acid solution of 1 to 50% by weight. Furthermore, the magnesium acetate concentration in the aqueous magnesium acetate solution is preferably 5 to 30% by weight.

[0050] In the precipitation process, a mixture containing cellulose acetate is mixed with a precipitating agent such as water, dilute acetic acid, dilute calcium hydroxide aqueous solution, or magnesium acetate aqueous solution to precipitate the cellulose acetate. Furthermore, the resulting cellulose acetate (precipitate) is separated and washed with water to remove free metal components, sulfuric acid components, etc.

[0051] In the step of adding stabilizers, in addition to washing with water, alkali metal compounds and / or alkaline earth metal compounds, particularly calcium compounds such as calcium hydroxide, may be added as stabilizers as needed. Stabilizers may also be used during washing with water.

[0052] (Solvolysis of raw material cellulose acetate) The solvolysis of the raw material cellulose acetate proceeds at a temperature above the boiling point of the alcohol in the presence of a solvent containing an alcohol with 3 or fewer carbon atoms and an acid catalyst.

[0053] The solvent containing an alcohol with 3 or fewer carbon atoms is any solvent that contains an alcohol with 3 or fewer carbon atoms and can dissolve the raw material cellulose acetate. "Can dissolve the raw material cellulose acetate" means that, under either heated or unheated conditions, some or all of the raw material cellulose acetate can be molecularly dispersed, and a clear change or disappearance of the solid raw material cellulose acetate can be observed visually.

[0054] The alcohol containing three or fewer carbon atoms in the solvent is not particularly limited. Examples include methanol, ethanol, 1-propanol, and 2-propanol. Among these, methanol and ethanol are preferred, and methanol is more preferred.

[0055] The content of alcohols having 3 or fewer carbon atoms in the solvent is preferably 70% by weight or more, and more preferably 80% by weight or more. It may also be 100% by weight or less.

[0056] The solvent may contain, in addition to alcohols with 3 or fewer carbon atoms, optional components such as acetate esters, acetic acid, and acetone. Among these, acetate esters are preferred, and among acetate esters, ethyl acetate and methyl acetate are more preferred. This is because it increases the solubility of the starting material (raw material cellulose acetate) and / or reaction intermediates in the reaction bath, resulting in cellulose acetate with excellent water solubility and biodegradability.

[0057] The content of optional components other than alcohols with 3 or fewer carbon atoms in the solvent is preferably 30% by weight or less, and more preferably 20% by weight or less. In particular, when an acetate ester is included as an optional component, the content of the acetate ester in the solvent is preferably 10% by weight or more and 5% by weight or less.

[0058] The amount of solvent containing an alcohol with 3 or fewer carbon atoms used is, for example, 0.5 to 50 parts by weight, preferably 1 to 20 parts by weight, and more preferably 3 to 10 parts by weight, per 1 part by weight of the raw material cellulose acetate.

[0059] As a catalyst, an acid catalyst commonly used as a deacetylation catalyst can be used. Examples of acid catalysts include inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid; and organic acids such as trifluoroacetic acid and formic acid. These acid catalysts may be used individually or in combination of two or more.

[0060] The acid catalyst preferably has an acid dissociation constant pKa of 0 or less in water at 25°C, more preferably -0.5 or less, and even more preferably -1.0 or less. The acid dissociation constant pKa may be -6.0 or higher.

[0061] Sulfuric acid is preferred as the acid catalyst. Alternatively, concentrated sulfuric acid, specifically an aqueous sulfuric acid solution with a sulfuric acid concentration of 98% by weight, can be used. The catalyst may be pre-mixed with a solvent containing an alcohol with 3 or fewer carbon atoms and used for solvolysis of the raw material cellulose acetate.

[0062] The amount of acid catalyst used is preferably, for example, 0.005 to 1 part by weight, more preferably 0.01 to 0.5 parts by weight, and even more preferably 0.02 to 0.3 parts by weight, per 1 part by weight of the raw material cellulose acetate. If the amount of catalyst is too small, the solvolysis time becomes too long, which has the advantage of making it easier to control the reaction endpoint, but is not economically desirable. On the other hand, if the amount of catalyst is too large, the degree of change in the depolymerization rate with respect to the solvolysis temperature becomes large, making it difficult to control the reaction endpoint, and making it difficult to obtain cellulose acetate having the total degree of substitution of the present disclosure. In addition, it is easy to obtain heterogeneous cellulose acetate with varying degrees of acetyl substitution.

[0063] The water content in the solvolysis reaction system should be as low as possible, preferably 2 parts by weight or less per 1 part by weight of the raw material cellulose acetate, more preferably 1 part by weight or less, and even more preferably 0.5 parts by weight or less. Furthermore, there is no lower limit to the water content in the solvolysis reaction system, as long as the solvolysis of the raw material cellulose acetate starts and proceeds, but for example, it may be 0.01 parts by weight or more per 1 part by weight of the raw material cellulose acetate.

[0064] When solvolysis of the raw material cellulose acetate, the water originally contained in the raw material cellulose acetate may or may not be removed beforehand. The water content of the raw material cellulose acetate may be, for example, 5% by weight or less, 4% by weight or less, or 3% by weight or less, or 1% by weight or more.

[0065] The water content in raw cellulose acetate can be measured by the following method. It can be measured using a Kett moisture meter (METTLER TOLEDO HB43). Place approximately 2.0 g of the sample in a hydrated state on the aluminum tray of the Kett moisture meter and heat it at 120°C until the weight stops changing. The water content (weight %) in the sample can be calculated from the weight change before and after heating.

[0066] In the process of solvolysis and deacetylation of the raw material cellulose acetate, water may be added to the system in addition to the water originally contained in the raw material cellulose acetate. The entire amount may be present in the system at the start of the reaction, or some of the water to be used may be present in the system at the start of the reaction, and the remaining water may be added to the system in one to several portions.

[0067] The water content in the solvolysis reaction system is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 5 parts by weight or less, per 1 part by weight of solvent.

[0068] The temperature within the solvolysis reaction system is adjusted to be above the boiling point of the alcohol with 3 or fewer carbon atoms. For example, when using methanol, the temperature should be 65°C or higher; when using ethanol, 78°C or higher; when using 1-propanol, 97°C or higher; and when using 2-propanol, 82°C or higher. This allows the raw material cellulose acetate to be sufficiently dissolved in the solvent, enabling the solvolysis reaction to proceed uniformly.

[0069] The temperature within the solvolysis reaction system is not limited as long as it is above the boiling point of alcohols with 3 or fewer carbon atoms, but it is preferably 105°C or lower, more preferably 100°C or lower, and even more preferably 95°C or lower. Above 105°C, a significant decrease in the degree of polymerization and yield of the resulting cellulose acetate occurs.

[0070] The gauge pressure in the solvolysis reaction system is preferably between 0.2 MPaG and 1 MPaG. Preferably between 0.2 MPaG and 0.7 MPaG, and more preferably between 0.2 MPaG and 0.5 MPaG. A pressure of 0.2 MPaG or higher allows the raw material cellulose acetate to dissolve sufficiently in the solvent, enabling the solvolysis reaction to proceed particularly uniformly. If the pressure exceeds 1 MPaG, a significant decrease in the degree of polymerization and yield of the resulting cellulose acetate becomes apparent.

[0071] The duration of the solvolysis reaction may be between 20 minutes and 300 minutes, between 30 minutes and 240 minutes, or between 60 minutes and 200 minutes. Within this range, it is easy to adjust the total degree of acetyl substitution to between 0.4 and 0.9.

[0072] Here, the time of the solvolysis reaction refers to the time from when the temperature in the solvolysis reaction system is reached until that temperature is maintained.

[0073] In conventional deacetylation of raw material cellulose acetate, the raw material cellulose acetate is dissolved in a mixed solvent of acetic acid and water, and hydrolyzed using a sulfuric acid catalyst. In this process, the elimination of acetyl groups proceeds generally similarly at positions 2, 3, and 6 of the glucose ring of the cellulose acetate. On the other hand, in the method for producing cellulose acetate of the present disclosure, the acetyl group at position 6 is preferentially eliminated, resulting in cellulose acetate with a lower degree of acetyl substitution at position 6 compared to positions 2 and 3 of the glucose ring.

[0074] In conventional deacetylation of cellulose acetate, acetic acid is used as the reaction solvent. During the deacetylation process, acetic acid preferentially reacetylates at the 6-position, so the elimination of the acetyl group appears to proceed similarly at the 2, 3, and 6 positions of the glucose ring of cellulose acetate. Suppressing the reacetylation at the 6-position yields cellulose acetate with a low degree of substitution at the 6-position, but in that case, a solvent other than acetic acid is required. As a result of diligent research, the inventors have found that a solvent containing alcohols with 3 or fewer carbon atoms is suitable as a reaction solvent for this purpose at or above its boiling point. A solvent containing alcohols with 3 or fewer carbon atoms dissolves or greatly swells cellulose acetate with a moderate to high degree of substitution in the starting material at or above its boiling point.

[0075] The solvolysis of the raw material cellulose acetate can be completed by adding a neutralizing agent. Examples of neutralizing agents include salts of weak acids, such as acetates like sodium acetate and magnesium acetate, and carbonates like sodium carbonate and magnesium carbonate. The neutralizing agent may be added together with a solvent containing an alcohol with 3 or fewer carbon atoms.

[0076] The amount of neutralizing agent used may be 1.0 to 5.0 equivalents per equivalent of the acid catalyst, preferably 1.1 to 3.0 equivalents, and more preferably 1.2 to 2.0 equivalents. If the amount of neutralizing agent is too small, the acid catalyst may remain in the low-substituted cellulose acetate, causing decomposition of the low-substituted cellulose acetate. On the other hand, if the amount of neutralizing agent is too large, a large amount of solvent will be used to wash away the neutralizing agent, which is economically undesirable.

[0077] [Precipitation process] In the precipitation step of the method for producing cellulose acetate according to the present disclosure, the cellulose acetate produced by deacetylation of the raw material cellulose acetate is precipitated.

[0078] One precipitation method involves, for example, cooling the reaction system to room temperature after the solvolysis of the raw material cellulose acetate is complete, thereby precipitating the cellulose acetate with a low degree of substitution. This precipitation method using cooling does not require the addition of a precipitation solvent and is therefore economically preferable. However, adding a precipitation solvent may promote the precipitation of cellulose acetate with a low degree of substitution and increase the yield, so a precipitation solvent may be added.

[0079] Examples of precipitation solvents include solvents containing alcohols with 3 or fewer carbon atoms; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate and methyl acetate; nitrogen-containing compounds such as acetonitrile; ethers such as tetrahydrofuran; and mixed solvents thereof. These precipitation solvents may be used individually or as a mixed solvent containing two or more solvents. Among these, solvents containing alcohols with 3 or fewer carbon atoms are preferred because using the same solvent as the reaction solvent as the precipitation solvent can facilitate the recovery and reuse of waste solvents.

[0080] The precipitation solvent preferably contains the following basic substances, as this allows for neutralization to occur simultaneously with precipitation.

[0081] [Optional process] (Washing process, neutralization process) The precipitated cellulose acetate is preferably washed with an organic solvent (poor solvent) such as methanol or an alcohol, or acetone or a ketone. It is also preferable to wash and neutralize it with an organic solvent containing a salt of a weak acid or a basic substance (e.g., methanol or other alcohol, acetone or a ketone). Washing and neutralization efficiently remove impurities such as catalysts (sulfuric acid, etc.) used in the solvolysis step.

[0082] Examples of the weak acid salts include acetate salts such as sodium acetate and magnesium acetate, and carbonate acetate hydrates such as sodium carbonate and magnesium carbonate. As the basic substance, alkali metal compounds such as alkali metal hydroxides such as calcium hydroxide can be used.

[0083] (purification process) Further purification of the precipitated cellulose acetate can yield cellulose acetate with excellent water solubility. In particular, the higher the total acetyl substitution degree of the raw material cellulose acetate, the lower the water solubility of the resulting cellulose acetate tends to be, so purification is preferable. Purification can be carried out, for example, by precipitation fractionation (fractional precipitation) and / or dissolution fractionation (fractional dissolution).

[0084] Dissolution and fractionation can be carried out, for example, by dissolving the precipitated cellulose acetate (solid) in water or a mixed solvent of water and a hydrophilic organic solvent (e.g., acetone) to form an aqueous solution, and then removing the residue (in other words, the insoluble components). Centrifugation may be used to remove the residue.

[0085] Cellulose acetate can be dissolved by stirring at an appropriate temperature (for example, 20-80°C, preferably 25-60°C). The concentration (mixing ratio) of cellulose acetate in the aqueous solution can be adjusted to an appropriate concentration (for example, 2-10% by weight, preferably 3-8% by weight).

[0086] Furthermore, when using a mixed solvent of water and a hydrophilic organic solvent, the concentration of the organic solvent in the mixed solvent may be, for example, 5 to 50% by weight, preferably 10 to 40% by weight.

[0087] After removing the residue, the dissolved cellulose acetate can be precipitated. Methods of precipitation include reprecipitation and spray drying. Examples of precipitation solvents used for reprecipitation include solvents containing alcohols with 3 or fewer carbon atoms; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate and methyl acetate; nitrogen-containing compounds such as acetonitrile; ethers such as tetrahydrofuran; and mixed solvents thereof. These precipitation solvents may be used individually or as a mixed solvent containing two or more solvents.

[0088] (Stabilizer added) After precipitation of cellulose acetate, a stabilizer may be added to the precipitated cellulose acetate. This is to improve the thermal stability of cellulose acetate. As a stabilizer, alkali metal compounds and / or alkaline earth metal compounds, particularly calcium compounds such as calcium hydroxide, are preferred.

[0089] The amount of stabilizer to be added is preferably such that the reaction mixture containing cellulose acetate and an aqueous calcium hydroxide solution adjusted to 0.2 to 1.0% by weight are added in a volume ratio of 100:1 to 10.

[0090] The addition of the stabilizer may be carried out in conjunction with the removal of free metal components, sulfuric acid components, etc., by washing the precipitate with a poor solvent such as a precipitation solvent.

[0091] It is preferable to dry the cellulose acetate after the step of precipitating the deacetylated cellulose acetate, or after any optional step if one is included. When drying the cellulose acetate, there are no particular limitations on the drying method, and conventionally known methods can be used. Examples include blown air drying such as hot air drying, reduced pressure drying, and vacuum drying. The temperature and pressure can be adjusted as appropriate.

[0092] After drying the cellulose acetate, it may be ground. For grinding, conventional grinders such as sample mills, hammer mills, turbo mills, atomizers, cutter mills, bead mills, ball mills, roll mills, jet mills, and pin mills can be used. Alternatively, freeze grinding, dry grinding at room temperature, or wet grinding may be performed. [Examples]

[0093] The present invention will be specifically described below with reference to examples, but the technical scope of the present invention is not limited by these examples.

[0094] <Preparation and physical properties of cellulose acetate> The physical properties of the cellulose acetate in the examples and comparative examples, as shown in Table 1, were measured as follows.

[0095] (Yield of reaction products) The reaction product yield (yield of cellulose acetate before the purification step) (weight %) was calculated as follows. Reaction product yield (weight %) = Actual yield of solvolysis reaction product (cellulose acetate before purification step, if purification step is included) / Theoretical yield of solvolysis reaction product (cellulose acetate before purification step, if purification step is included)

[0096] (Purified product yield) The yield of the purified product (by weight %) was calculated as follows: Purified product yield (yield of cellulose acetate after the purification process) (weight %) = Actual yield of purified product (cellulose acetate after the purification process, if the purification process is included) / Actual yield of solvolysis reaction product (cellulose acetate before the purification process, if the purification process is included)

[0097] (Total degree of acetyl substitution, degrees of acetyl substitution at positions 2, 3, and 6 (DS2, DS3, and DS6), and the percentage of the degree of acetyl substitution at position 6 in the total degree of acetyl substitution) Following the literature by Tezuka et al. (Carbohydrate Research, 273, 83-91 (1995)), the sample was propionized with propionic anhydride in pyridine solvent, and then in chloroform solvent... 13 The 1C-NMR spectrum was measured, and the intensities of the three signals of the acetylcarbonyl carbon appearing around 169.1–170.2 ppm were integrated. Additionally, the intensities of the three signals of the propionylcarbonyl carbon appearing around 172.7–173.6 ppm were integrated.

[0098] 13 In the 1C-NMR spectrum, the three acetylcarbonyl carbon signals appearing around 169.1–170.2 ppm are assigned to positions 2, 3, and 6, respectively, from the high-field side. The intensity within a range of ±0.2 ppm for each signal's maximum is integrated and defined as the integrated intensity of each acetylcarbonyl carbon signal. The DS is then calculated using the following equation. i We found (i is 2, 3, or 6). DS i=DS × (integrated signal intensity of the acetylcarbonyl carbon at position i) / (sum of integrated signal intensities of the acetylcarbonyl carbons at positions 2, 3, and 6)

[0099] The NMR measurement conditions are as follows: Measurement solvent: CDCl3 (approximately 3 ml used) Measurement temperature: 40℃ Sample size: 160-180 mg (φ10 mm) Observed nucleus: 13C (1H complete decoupling) Number of data points: 32768 Pulse angle and time: 45°, 9μsec Data acquisition time: 0.9667 sec Waiting time: 2.0333 sec Total number of times: 18,000

[0100] The total degree of acetyl substitution (DS) was calculated using the following formula, where X is the integrated signal intensity of the acetylcarbonyl carbon and Y is the integrated signal intensity of the propionylcarbonyl carbon. Total degree of acetyl substitution (DS) = 3 × [X / (X + Y)]

[0101] The percentage of acetyl substitution at position 6 in the total acetyl substitution degree was calculated using the following formula. Percentage of acetyl substitution at position 6 (%) = Percentage of acetyl substitution at position 6 (DS6) / Total acetyl substitution (DS) × 100

[0102] (Degree of polymerization (viscosity average degree of polymerization)) The degree of polymerization of cellulose acetate was evaluated as the viscosity-average degree of polymerization based on the intrinsic viscosity number ([η], unit: g / ml).

[0103] Specifically, the intrinsic viscosity of cellulose acetate was determined in accordance with JIS-K-7367-1 and ISO1628-1, using a size 1C Ubbelohde viscometer and dimethyl sulfoxide (DMSO) as the solvent, based on the value obtained by dividing the logarithmic relative viscosity at 25°C by the concentration.

[0104] Next, the molecular weight (viscosity-average molecular weight) of cellulose acetate was determined using the following formula, in accordance with the literature by Kamide et al. Viscosity average molecular weight = (intrinsic viscosity number [η] / 0.171) (1 / 0.61)

[0105] The degree of polymerization (viscosity-average degree of polymerization) of cellulose acetate was then calculated using the following formula. Degree of polymerization (viscosity average degree of polymerization) = viscosity average molecular weight / (162.14+42.037×DS)

[0106] (Transmittance (4wt% aqueous solution transmittance)) 0.4 g of cellulose acetate was dispersed in 10 ml of water, stirred with a magnetic stirrer for 2 hours, allowed to stand overnight, and then stirred again for 2 hours. The transmittance (%) at 660 nm of the resulting 4% aqueous solution of cellulose acetate was measured using a spectrophotometer (Shimadzu Corporation, UV-1800 ultraviolet-visible spectrophotometer, polystyrene cell material, 10 mm cell length).

[0107] (Example A-1) Deacetylation process: 70 parts by weight of cellulose diacetate (manufactured by Daicel Corporation, trade name "L-50", water content 3% by weight, total acetyl substitution degree 2.43, acetyl substitution degree at position 2 0.86, acetyl substitution degree at position 3 0.82, acetyl substitution degree at position 6 0.75) was added to 554 parts by weight of methanol as a solvent at room temperature, and then 3.5 parts by weight of sulfuric acid was added as a catalyst. The mixture was heated to 90°C for 50 minutes while stirring, and then maintained at 90°C for 100 minutes.

[0108] Sedimentation process: The reaction mixture was cooled to room temperature, and the sulfuric acid was neutralized by adding a mixture of 14.6 parts by weight of sodium acetate trihydrate and 55 parts by weight of methanol. The white solid suspended in this reaction mixture was filtered off by suction filtration. The filtered white solid was suspended in 277 parts by weight of methanol and stirred at room temperature for 1 hour. The white solid in methanol was filtered off by suction filtration.

[0109] The filtered white solid was resuspended in 277 parts by weight of methanol and stirred at room temperature for 1 hour. The white solid in methanol was filtered off by suction filtration. The methanol-washed white solid was dried under reduced pressure at 60°C until a constant weight was obtained, yielding 60 parts by weight of low-substituted cellulose acetate. The results of measuring the various physical properties of the obtained low-substituted cellulose acetate are shown in Table 1.

[0110] (Example A-2) Deacetylation step and precipitation step: 60 parts by weight of low-substituted cellulose acetate were obtained using the same method as in Example A-1.

[0111] Purification process: Furthermore, this low-substituted cellulose acetate was added to 1,440 parts by weight of water, stirred at room temperature for 8 hours, and allowed to stand overnight. This suspension was centrifuged at 12,600 G for 30 minutes to obtain the supernatant. This supernatant was added dropwise to 10,000 parts by weight of acetone with stirring to obtain a white precipitate. This white precipitate was filtered off by suction filtration and dried under reduced pressure at 60°C until a constant weight was obtained to obtain 54 parts by weight of low-substituted cellulose acetate. The results of measuring the various physical properties of the obtained low-substituted cellulose acetate are shown in Table 1.

[0112] (Example A-3) Deacetylation step and precipitation step: 68 parts by weight of low-substituted cellulose acetate was obtained using the same method as in Example A-1, except that Eastman Chemical's cellulose acetate (product name "CA-320S", moisture content 3% by weight, total acetyl substitution degree 1.80, acetyl substitution degree at position 2 0.61, acetyl substitution degree at position 3 0.56, acetyl substitution degree at position 6 0.63) was used instead of cellulose diacetate (manufactured by Daicel Corporation, product name "L-50", moisture content 3% by weight), and the temperature setting time at 90°C was 80 minutes. The results of measuring the various physical properties of the obtained low-substituted cellulose acetate are shown in Table 1.

[0113] (Comparative example A-1) Deacetylation process: 100 parts by weight of cellulose diacetate (manufactured by Daicel Corporation, trade name "L-50", water content 3% by weight, total acetyl substitution degree 2.43, acetyl substitution degree at position 2 0.86, acetyl substitution degree at position 3 0.82, acetyl substitution degree at position 6 0.75) was added as the raw material cellulose acetate to a mixture of 358 parts by weight of acetic acid and 95 parts by weight of water (mixed solvent), stirred at 70°C for 5 hours, and then allowed to stand overnight at room temperature (approximately 25°C). The mixture was then heated to 70°C, and 178 parts by weight of water was added to obtain a cellulose diacetate solution.

[0114] The cellulose diacetate solution was heated to 50°C, and a mixture of 12.6 parts by weight of 98% sulfuric acid (catalyst) and 57 parts by weight of acetic acid (solvent) was added. The reaction mixture was heated to 50°C while stirring, and 137 parts by weight of water was added over 30 minutes 4 hours after the addition of sulfuric acid, and then 111 parts by weight of water was added over 30 minutes 8 hours after the addition of sulfuric acid. The reaction mixture was continued to be heated to 50°C while stirring, and 23 hours and 40 minutes (1,420 minutes) after the addition of sulfuric acid, a mixture of 72 parts by weight of sodium acetate trihydrate and 109 g of water was added to stop the reaction.

[0115] Sedimentation process: This reaction mixture was added dropwise to 4,700 parts by weight of methanol under stirring to obtain a white precipitate. This white precipitate was filtered off, dispersed in 1,100 parts by weight of methanol, and filtered again. This process was repeated five times. The filtered white precipitate was dried under reduced pressure at 60°C until a constant weight was obtained, yielding 64 parts by weight of low-substituted cellulose acetate. The results of measuring the various properties of the obtained low-substituted cellulose acetate are shown in Table 1.

[0116] (Comparative example A-2) Low-substituted cellulose acetate was obtained by a method similar to Example 17 of Japanese Patent No. 6378712. Specifically, the method is as follows:

[0117] Deacetylation process: 100 parts by weight of cellulose diacetate (manufactured by Daicel Corporation, trade name "L-50", water content 3% by weight, total acetyl substitution degree 2.43, 2-acetyl substitution degree 0.86, 3-acetyl substitution degree 0.82, 6-acetyl substitution degree 0.75) were added to a mixture of 510 parts by weight of acetic acid and 95 parts by weight of water, and the mixture was stirred at 70°C for 3 hours to obtain a cellulose diacetate solution. This cellulose diacetate solution was heated to 70°C while stirring, and 13 parts by weight of 98% sulfuric acid was added. The reaction mixture was continued to be heated to 70°C while stirring, and 67 parts by weight of water was added over 5 minutes 3 hours after the addition of sulfuric acid, and then 133 parts by weight of water was added over 10 minutes 8 hours after the addition of sulfuric acid. The reaction mixture was continued to be heated to 70°C while stirring, and 10 hours (600 minutes) after the addition of sulfuric acid, the reaction mixture was cooled to 25°C to substantially stop the reaction.

[0118] Sedimentation process: This reaction mixture was added dropwise to 1,500 parts by weight of acetone under stirring to obtain a white precipitate. This white precipitate was filtered off, dispersed in 800 parts by weight of acetone, and filtered again. This process was repeated three times. The filtered white precipitate was dispersed in 800 parts by weight of methanol containing 0.004% by weight of potassium acetate, and filtered again. This process was repeated twice. The filtered white precipitate was dried under reduced pressure at 60°C until a constant weight was obtained. To 64 parts by weight of this dried product, 960 parts by weight of 20% by weight of aqueous acetone solution was added, and the mixture was stirred at 40°C for 8 hours. The concentrated phase was removed by centrifugation, and parts by weight of acetone were added to the dilute phase to obtain a white precipitate. This white precipitate was filtered off, dispersed in 3,000 parts by weight of acetone, and filtered again. The filtered white precipitate was dried under reduced pressure at 60°C until a constant weight was obtained to obtain 59 parts by weight of low-substituted cellulose acetate. The results of measuring the various physical properties of the obtained low-substituted cellulose acetate are shown in Table 1.

[0119] (Comparative example A-3) Low-substituted cellulose acetate was obtained according to the conditions of experiment number 6 in Edgar et al., Macromolecules, 24, 3060 (1991).

[0120] Specifically, 60 parts by weight of cellulose diacetate (manufactured by Daicel Corporation, trade name "L-50", dried under reduced pressure at 60°C until constant weight is achieved) was suspended in 237 parts by weight of methanol, and 0.2 parts by weight of hexacarbonylmolybdenum (Mo(CO)6) was added. The internal pressure was adjusted to 200 psi using nitrogen in a sealed reactor, and the temperature was maintained at 140°C for 7 hours (420 minutes). The reaction mixture was cooled to room temperature, and the solid in the reaction mixture was filtered off by suction filtration. The filtered solid was dried under reduced pressure at 60°C until constant weight was achieved to obtain 29 parts by weight of low-substituted cellulose acetate. The results of measuring the various physical properties of the obtained low-substituted cellulose acetate are shown in Table 1.

[0121] (Comparative example A-4) Low-substituted cellulose acetate was obtained according to the conditions of experiment number 7 in Edgar et al., Macromolecules, 24, 3060 (1991).

[0122] Specifically, 60 parts by weight of cellulose diacetate (manufactured by Daicel Corporation, trade name "L-50", dried under reduced pressure at 60°C until constant weight is achieved) was suspended in 237 parts by weight of methanol, and 0.2 parts by weight of molybdenum(VI) oxide (MoO3) was added. The internal pressure was adjusted to 1,000 psi using nitrogen in a sealed reactor, and the temperature was maintained at 155°C for 3 hours (180 minutes). The reaction mixture was cooled to room temperature, and the solid in the reaction mixture was filtered off by suction filtration. The filtered solid was dried under reduced pressure at 60°C until constant weight was achieved to obtain 37 parts by weight of low-substituted cellulose acetate. The results of measuring the various physical properties of the obtained low-substituted cellulose acetate are shown in Table 1.

[0123] [Table 1]

[0124] In Comparative Example A-1, the cellulose acetate had a degree of acetyl substitution at position 6 of 0.24, and the proportion of the degree of acetyl substitution at position 6 to the total degree of acetyl substitution was 36.9%. In Comparative Example A-2, the cellulose acetate had a degree of acetyl substitution at position 6 of 0.28, and the proportion of the degree of acetyl substitution at position 6 to the total degree of acetyl substitution was 35.9%. Thus, in Comparative Examples A-1 and A-2, the degree of acetyl substitution at position 6 is higher than the degree of acetyl substitution at positions 2 and 3.

[0125] In Comparative Example A-3, the cellulose acetate had a degree of acetyl substitution at position 6 of 0.05, and the proportion of the degree of acetyl substitution at position 6 to the total degree of acetyl substitution was 10.4%. In Comparative Example A-4, the cellulose acetate had a degree of acetyl substitution at position 6 of 0.06, and the proportion of the degree of acetyl substitution at position 6 to the total degree of acetyl substitution was 12.0%. Thus, in Comparative Examples A-3 and A-4, the degree of acetyl substitution at position 6 was lower than that at positions 2 and 3. However, the light transmittance of the 4 wt% aqueous solution at 660 nm was low, indicating poor water solubility.

[0126] On the other hand, the cellulose acetate of Examples A-1 to A-3 has a low acetyl substitution rate at the 6th position in the total acetyl substitution rate, which is 18% or less, and the light transmittance at 660 nm of the 4 wt% aqueous solution is 5% or more, indicating excellent water solubility. In particular, the 4 wt% aqueous solutions of cellulose acetate of Examples A-2 and A-3 have a light transmittance at 660 nm of 92% or more, indicating particularly excellent water solubility.

[0127] <Animal experiments (acetyl group retention rate, feed intake, weight gain, blood glucose levels, cholesterol, triglycerides, epididymal fat)> Animal experiments were initiated using nine 7-week-old (weight 150-170g) male Wistar rats (Nippon SLC Co., Ltd.) that were individually housed in stainless steel cages under conditions of room temperature 24±1℃, relative humidity 55±5℃, and a 12-hour light-dark cycle (lights on from 7:00 to 19:00).

[0128] After arrival, the rats were acclimatized for 3 days by feeding them purified feed AIN-93G (Reeves et al., Journal of Nutrition, 123, 1939-1951 (1993)) with tap water. Then, they were divided into three groups based on body weight (to eliminate imbalances in the total body weight of the rats in each group). Group 1 was given AIN-93G (sometimes referred to as the "control group"), Group 2 was given AIN-93G containing 5% by weight of low-substituted cellulose acetate from Example A-2 (sometimes referred to as the "test group"), and Group 3 was given AIN-93G containing 5% by weight of low-substituted cellulose acetate from Comparative Example A-1 (sometimes referred to as the "comparison group"), each group being given free access to tap water for 14 days. Each group consisted of 3 rats. Group 1 corresponds to Reference Example B-1, Group 2 to Example B-1, and Group 3 to Comparative Example B-1.

[0129] Rats were divided into three groups, and on the 3rd, 7th, and 13th days after the start of feeding with each diet, the entire daily fecal sample was collected and used for analysis of acetyl group retention rates. The analytical method is as follows. In addition, feed intake and body weight gain were measured throughout the feeding period.

[0130] On the 14th day of rearing, the rats were fasted from 7:00 AM, and a necropsy was performed at 3:00 PM. The rats were opened under isoflurane anesthesia, and approximately 2 mL of blood was collected from the abdominal aorta into a heparinized test tube (Venoject II heparin sodium, 3 mL for blood collection: Terumo Corporation). The rats were then euthanized by bleeding, and the epididymal fat (both sides) was promptly removed. The weight of the epididymal fat was then measured.

[0131] The collected blood was centrifuged at room temperature at 2,380G for 10 minutes to separate the plasma. On the day of collection, blood glucose levels were measured in the separated plasma using Sikariliquid GLU (Kanto Chemical Co., Ltd.), triglycerides using Sikariliquid-N TG (Kanto Chemical Co., Ltd.), and cholesterol (also referred to as plasma cholesterol) using Sikariliquid-N CHO (Kanto Chemical Co., Ltd.).

[0132] <Acetyl group retention rate> 0.1 g of rat feces was suspended in 10 ml of water, and the acetic acid contained in the rat feces was derivatized to the corresponding 2-nitrophenyl hydrazide using the method of Miwa et al. (Journal of Chromatography, 321, 165-174 (1985)). The concentration of acetic acid in the rat feces was determined by quantifying the 2-nitrophenyl hydrazide of acetic acid by HPLC analysis.

[0133] Furthermore, 0.1 g of rat feces was suspended in a 150 mM sodium hydroxide aqueous solution and incubated at 70°C for 4 hours. The acetic acid contained in the sodium hydroxide-treated rat feces was derivatized to the corresponding 2-nitrophenyl hydrazide using the method of Miwa et al. (Journal of Chromatography, 321, 165-174 (1985)), and the concentration of acetic acid in the sodium hydroxide-treated rat feces was determined by quantifying the 2-nitrophenyl hydrazide of acetic acid by HPLC analysis.

[0134] The difference between the acetic acid concentration in rat feces treated with sodium hydroxide and the acetic acid concentration in rat feces was defined as the acetyl group concentration (moles per unit weight) in the rat feces. The acetyl group retention rate was calculated using the following formula. Acetyl group retention rate (mol%) = 100 × (acetyl group concentration in rat feces) × A / (B × C / D) A: Rat fecal volume (weight) over 0-24 hours B: Rat feed intake (weight) from -24 hours to 0 hours C: Concentration of cellulose acetate in feed (weight %) D: Number of moles of acetyl groups per unit weight of cellulose acetate =DS / (162.14+42.037×DS) DS: Degree of total acetyl substitution

[0135] [Table 2]

[0136] When rats were fed cellulose acetate from Example A-2 (where the proportion of acetyl substitution at position 6 in the total acetyl substitution degree was 18% or less) on days 3, 7, and 13 of rearing (Example B-1), the remaining acetyl group percentage in the feces was lower in all cases compared to when rats were fed cellulose acetate from Comparative Example A-1 (where the proportion of acetyl substitution at position 6 in the total acetyl substitution degree was 36.9% or less) (Comparative Example B-1). This indicates that the cellulose acetate from the example with a low proportion of acetyl substitution at position 6 is highly degradable and easily metabolized in the body.

[0137] In Comparative Example B-1 (comparison group), the feed intake of rats was significantly lower than in Reference Example B-1 (control group), but there was no significant difference in weight gain. On the other hand, in Example B-1 (test group), both the feed intake and weight gain of rats were lower than in Comparative Example B-1 (comparison group), and a clear significant difference was observed compared to Reference Example B-1 (control group).

[0138] The blood glucose and cholesterol levels of the rats in Example B-1 (test group) showed a decreasing trend compared to Reference Example B-1 (control group), although the difference was not statistically significant.

[0139] Furthermore, there was no significant difference in triglyceride levels between rats in Comparative Example B-1 (comparison group) and those in Reference Example B-1 (control group). On the other hand, the triglyceride levels in rats in Example B-1 (test group) were lower than those in Reference Example B-1 (control group), and a significant difference was observed.

[0140] Furthermore, the epididymal fat levels of rats in Comparative Example B-1 (comparison group) and Example B-1 (test group) were both lower than those of Reference Example B-1 (control group), and a statistically significant difference was observed.

[0141] As described above, the cellulose acetate in the example with a low degree of acetyl substitution at position 6 exhibits excellent degradability and is easily metabolized in the body, contributing particularly to appetite suppression (reduced feed intake), suppression of weight gain, suppression of triglycerides, and suppression of fat accumulation (superdidymal fat suppression) in rats.

Claims

1. An appetite suppressant, a fat accumulation inhibitor, or a weight gain inhibitor comprising cellulose acetate, The cellulose acetate has a total acetyl substitution degree of 0.4 or more and 0.9 or less. An appetite suppressant, fat accumulation inhibitor, or weight gain inhibitor, wherein the proportion of acetyl substitution at the 6th position in the total degree of acetyl substitution is greater than 0% and 18% or less, the viscosity-average degree of polymerization is 3 or more and 400 or less, and the light transmittance of a 4% by weight aqueous solution at 660 nm is 5% or more.

2. The appetite suppressant, fat accumulation inhibitor, or weight gain inhibitor according to Claim 1, wherein the light transmittance of the 4% by weight aqueous solution at 660 nm is 80% or more.

3. A method for producing cellulose acetate for use in an appetite suppressant, fat accumulation inhibitor, or weight gain inhibitor according to Claim 1 or 2, A process of deacetylating raw material cellulose acetate having a total acetyl substitution degree of 1.5 to 3.0 by solvolysis, and The process includes a step of precipitating cellulose acetate produced by deacetylation of the raw material cellulose acetate, The solvolysis of the aforementioned raw material cellulose acetate proceeds in the presence of a solvent containing an alcohol having 3 or fewer carbon atoms and an acid catalyst, at a temperature above the boiling point of the alcohol. The acid catalyst is sulfuric acid, and the solvent contains any element other than an alcohol having 3 or fewer carbon atoms. The content of this component is 30% by weight or less. A method for producing cellulose acetate, comprising washing the precipitated cellulose acetate with a poor solvent.

4. The method for producing cellulose acetate according to claim 3, wherein the acid dissociation constant pKa of the acid catalyst in water at 25°C is 0 or less.

5. The method for producing cellulose acetate according to claim 3 or 4, wherein the alcohol is methanol.

6. The method for producing cellulose acetate according to any one of claims 3 to 5, wherein the solvent comprises an acetate ester.

7. A step of dissolving the precipitated cellulose acetate in water and removing the residue, A method for producing cellulose acetate according to any one of claims 3 to 6, comprising the step of precipitating the dissolved cellulose acetate.

8. A method for producing cellulose acetate according to any one of claims 3 to 7, comprising the steps of dissolving the precipitated cellulose acetate in water, centrifuging it to remove the residue, and reprecipitating the dissolved cellulose acetate.

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