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 technology]

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

[0003] The main metabolic decomposition products of low-substituted cellulose acetate are acetic acid and propionic acid. Propionic acid is thought to be produced from glucose, which constitutes cellulose, via phosphoenolpyruvic acid and succinic acid (Non-Patent Documents 2 and 3). Acetic acid is thought to be produced by the release of acetic acid bound to cellulose in low-substituted cellulose acetate, and is also thought to be produced from glucose, which constitutes cellulose, via phosphoenolpyruvic acid (Non-Patent Documents 2 and 3).

[0004] It is known that acetic acid and propionic acid, which are produced by intestinal bacteria metabolically decomposing low-substituted cellulose acetate, act on the nuclear receptor GPR43 and the like in intestinal L cells to produce the incretin GLP-1, thereby affecting appetite and glucose metabolism (Non-Patent Document 4), and also act on the hypothalamus to suppress appetite, suppress weight gain, and affect glucose metabolism and lipid metabolism (Non-Patent Document 5).

[0005] It is known that the enzyme acetyl xylan esterase is involved in the deacetylation of low-substituted cellulose acetate (Non-Patent Document 6). Note that Bacteroides xylanisolvens (Patent Document 1, Non-Patent Document 1), which grows in the intestines of rats fed low-substituted cellulose acetate, has been well studied as a xylan-decomposing bacterium and is thought to have acetyl xylan esterase. From these facts, it is presumed that the initial decomposition in the metabolic decomposition of low-substituted cellulose acetate by intestinal bacteria is deacetylation, and that acetyl xylan esterase is involved in this decomposition.

[0006] Glucose, which is the main structural unit of cellulose, has hydroxyl groups at the 2-, 3-, and 6-positions. In low-substituted cellulose acetate, some of these hydroxyl groups are acetylated. Acetyl xylan esterase selectively removes the acetyl group at the 2- or 3-position, but hardly removes the acetyl group at the 6-position (Non-Patent Document 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). Summary of the Invention [Problem to be solved by the invention]

[0009] It is believed that low-substituted cellulose acetate exerts its physiological effects through metabolic decomposition by intestinal bacteria.Low-substituted cellulose acetate, which is biodegradable and susceptible to metabolic decomposition by intestinal bacteria, is expected to exert excellent physiological effects.

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

[0011] However, in conventional methods, it has not been possible to reduce the degree of acetyl substitution at the 6-position of the glucose ring in cellulose acetate having a low total degree of acetyl substitution relative to the degrees of acetyl substitution at the 2- and 3-positions.

[0012] Furthermore, the more water-soluble the low-substituted cellulose acetate is, the more biodegradable it is. Therefore, low-substituted cellulose acetate having a low degree of acetyl substitution at the 6-position and excellent water-solubility is particularly excellent in biodegradability.

[0013] However, such a low-substituted cellulose acetate having a low degree of acetyl substitution at the 6-position and excellent water solubility has not been known. For example, the low-substituted cellulose acetate disclosed in Patent Document 1 has a high degree of acetyl substitution at the 6-position. Non-Patent Document 7 discloses low-substituted cellulose acetates having a low degree of acetyl substitution at the 6-position as Experiment No. 6 and Experiment No. 7, but these have poor water solubility.

[0014] An object of the present invention is to provide a cellulose acetate which has a low total degree of acetyl substitution, a low degree of acetyl substitution at the 6-position of the glucose ring relative to the degrees of acetyl substitution at the 2- and 3-positions, and excellent water solubility. [Means for solving the problem]

[0015] A first aspect of the present disclosure relates to a 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 acetyl substitution at the 6-position 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 wt % aqueous solution of the cellulose acetate is 5% or more.

[0016] In the cellulose acetate, the 4 wt % aqueous solution may have a light transmittance of 80% or more at 660 nm.

[0017] A second aspect of the present disclosure relates to a method for producing cellulose acetate, comprising the steps of deacetylating a starting cellulose acetate having a total degree of acetyl substitution of 1.5 to 3.0 by solvolysis and precipitating the cellulose acetate produced by the deacetylation of the starting cellulose acetate, wherein the solvolysis of the starting cellulose acetate proceeds in the presence of a solvent containing an alcohol having 3 or less carbon atoms and an acid catalyst at a temperature equal to or higher than the boiling point of the alcohol.

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

[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 the steps of dissolving the precipitated cellulose acetate in water and removing a residue, and precipitating the dissolved cellulose acetate.

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

[0024] Effects of the Invention According to the present invention, it is possible to provide cellulose acetate which has a low total degree of acetyl substitution, a low degree of acetyl substitution at the 6-position of the glucose ring relative to the degrees of acetyl substitution at the 2- and 3-positions, and excellent water solubility. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0026] [Total degree of acetyl substitution] The cellulose acetate of the present disclosure has a total acetyl substitution degree of 0.4 or more and 0.9 or less. When the total acetyl substitution degree is within this range, the cellulose acetate of the present disclosure has excellent water solubility and biodegradability. Note that the cellulose acetate of the present disclosure has a total acetyl substitution degree of 0.4 or more and 0.9 or less, and may be referred to as low-substituted cellulose acetate.

[0027] [Acetyl substitution at 6th position] The cellulose acetate according to the present disclosure has a ratio of the acetyl substitution degree at the 6-position to the total acetyl substitution degree of 0% or more and 18% or less, and the ratio of the acetyl substitution degree at the 6-position is preferably 14% or less, and more preferably 10% or less. The ratio of the acetyl substitution degree at the 6-position is most preferably 0%, but may be more than 0% and may be 4% or more. By being 18% or less, it is easily degraded by enzymes present in the intestine (e.g., acetyl xylan esterase, etc.) and is easily metabolized in the body.

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

[0029] First, the degree of acetyl substitution at the 2nd, 3rd, and 6th positions of the glucose ring of cellulose acetate is measured by NMR according to the method of Tezuka (Tezuka, Carbonydr. Res. 273, 83 (1995)). That is, the free hydroxyl groups of cellulose acetate are propionylated with propionic anhydride in pyridine. The obtained sample is dissolved in deuterated chloroform and 13 The C-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 2nd, 3rd, and 6th positions from the high magnetic field, and the signals of the carbonyl carbon of the propionyl group appear in the same order in the region from 172 ppm to 174 ppm. From the abundance ratio of the acetyl group and the propionyl group at the corresponding positions, the degree of acetyl substitution at the 2nd, 3rd, and 6th positions of the glucose ring of the cellulose acetate can be calculated. The degree of acetyl substitution can also be calculated by 13 In addition to C-NMR, 1 It can also be analyzed by H-NMR.

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

[0031] The total degree of acetyl substitution can be converted into the degree of acetylation using the following formula. DS=162.14×AV×0.01 / (60.052-42.037×AV×0.01) DS: Total degree of acetyl substitution AV: Acetyl content (%)

[0032] [Light transmittance] The cellulose acetate according to the present disclosure has a light transmittance of 5% or more at 660 nm in a 4% by weight aqueous solution of the cellulose acetate, and the light transmittance is 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 water solubility of the cellulose acetate is poor.

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

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

[0035] The viscosity average degree of polymerization (DP) can be evaluated as the 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 a method based on JIS-K-7367-1 and ISO1628-1, the viscosity average molecular weight is calculated according to the document by Kamide et al., and the viscosity average degree of polymerization can be calculated from the viscosity average molecular weight.

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

[0037] The cellulose acetate of the present disclosure has a low total degree of acetyl substitution and a low degree of acetyl substitution at the 6-position relative to the 2- and 3-positions of the glucose ring. Therefore, it is highly degradable by enzymes present in the intestine (e.g., acetyl xylan esterase, etc.) and is easily metabolized in the body, making it usable as a food product.

[0038] [Method of manufacturing cellulose acetate] The method for producing cellulose acetate disclosed herein comprises a step of deacetylating a starting cellulose acetate having a total degree of acetyl substitution of 1.5 to 3.0 by solvolysis, and a step of precipitating the cellulose acetate produced by deacetylation of the starting cellulose acetate, in which the solvolysis of the starting cellulose acetate proceeds in the presence of a solvent containing an alcohol having 3 or less carbon atoms and an acid catalyst, at a temperature equal to or higher than the boiling point of the alcohol.

[0039] [Deacetylation process] In the deacetylation step in the method for producing cellulose acetate of the present disclosure, raw cellulose acetate is subjected to solvolysis. In the deacetylation step of the present disclosure, deacetylation proceeds by solvolysis. The solvolysis may involve only a solvent containing an alcohol having 3 or less carbon atoms, or may involve a solvent containing an alcohol having 3 or less carbon atoms and other solvents such as water. Solvolysis also includes hydrolysis.

[0040] (Raw cellulose acetate) As the raw cellulose acetate, cellulose acetate having a medium to high degree of substitution can be used. The total acetyl substitution degree of the medium to high acetyl substitution cellulose acetate used as the raw material is 1.5 to 3.0, preferably 1.5 to 2.5. As the raw cellulose acetate, commercially available cellulose diacetate (total acetyl substitution degree 2.20 to 2.56) or cellulose triacetate (total acetyl substitution degree over 2.56 to 3) can be used.

[0041] The raw cellulose acetate may be produced by a conventionally known production method. For example, it can be produced through a series of steps including a step of disintegrating pulp, which is a cellulose material, a step of pretreatment, a step of acetylation, a step of hydrolysis, a step of precipitation, and a step of adding a stabilizer. Each of these steps will be described below. For a general method of producing cellulose acetate, see "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 contains little hemicellulose. This is because the amount of these impurities is small, which is why cellulose acetate, which is particularly excellent in water solubility and biodegradability, can be obtained.

[0043] The α-cellulose content can be determined as follows. A pulp with a known weight is successively extracted with 17.5% and 9.45% aqueous sodium hydroxide solutions at 25°C, 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 the oxidation. The weight of the insoluble portion of the pulp, or α-cellulose, is determined by subtracting the weight of β,γ-cellulose from the initial weight of the pulp (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 (wt%).

[0044] As the pulp, wood pulp (softwood pulp, hardwood pulp), cotton linters, etc. These celluloses may be used alone or in combination of two or more kinds, for example, softwood pulp may be used in combination with cotton linters or hardwood pulp.

[0045] Wood pulp is preferred because it is available as a stable raw material and is more cost effective than linters. Examples of wood pulp include hardwood prehydrolyzed kraft pulp.

[0046] In the step of crushing the pulp, for example, the pulp can be crushed in a dry manner using a disc refiner.

[0047] In the pretreatment step, the disintegrated pulp is contacted with acetic acid or sulfur-containing acetic acid. The acetic acid to be used may be 96 to 100% by weight, and the sulfur-containing acetic acid is acetic acid containing sulfuric acid, and preferably contains 1 to 10% by weight of sulfuric acid.

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

[0049] In the hydrolysis step, a neutralizing agent such as water, dilute acetic acid, or magnesium acetate aqueous solution is added to neutralize the sulfuric acid (complete or partial neutralization) and inactivate the acetic anhydride, thereby terminating the acetylation reaction. This allows the fully tri-substituted cellulose acetate (primary cellulose acetate) to be hydrolyzed to obtain cellulose acetate (secondary cellulose acetate) with a desired degree of substitution. Here, dilute acetic acid refers to an aqueous solution of acetic acid with a concentration of 1 to 50% by weight. The magnesium acetate concentration of the aqueous magnesium acetate solution is preferably 5 to 30% by weight.

[0050] In the precipitation step, a mixture containing cellulose acetate is mixed with a precipitant such as water, dilute acetic acid, a dilute aqueous solution of calcium hydroxide, or an aqueous solution of magnesium acetate to precipitate cellulose acetate. The resulting cellulose acetate (precipitate) is then separated and washed with water to remove free metal components, sulfuric acid components, and the like.

[0051] In the step of adding a stabilizer, in addition to washing with water, an alkali metal compound and / or an alkaline earth metal compound, in particular a calcium compound such as calcium hydroxide, may be added as a stabilizer as necessary. A stabilizer may also be used during washing with water.

[0052] (Solvolysis of raw cellulose acetate) The solvolysis of the raw cellulose acetate proceeds in the presence of a solvent containing an alcohol having 3 or less carbon atoms and an acid catalyst at a temperature equal to or higher than the boiling point of the alcohol.

[0053] The solvent containing an alcohol having 3 or less carbon atoms may be any solvent that contains an alcohol having 3 or less carbon atoms and is capable of dissolving the raw cellulose acetate. Being capable of dissolving the raw cellulose acetate means that the raw cellulose acetate can be molecularly dispersed in part or in whole, either with or without heating, and a clear change or disappearance in the form of the solid raw cellulose acetate can be visually observed.

[0054] The alcohol having 3 or less carbon atoms contained 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 the alcohol having 3 or less carbon atoms in the solvent is preferably 70% by weight or more, more preferably 80% by weight or more, and may be 100% by weight or less.

[0056] The solvent may contain, as optional components, for example, acetate esters, acetic acid, acetone, etc., in addition to the alcohol having 3 or less carbon atoms. Among these, acetate esters are preferred, and among acetate esters, ethyl acetate and methyl acetate are more preferred. This is because they increase the solubility of the starting material (cellulose acetate raw material) and / or the reaction intermediate in the reaction bath, and cellulose acetate with excellent water solubility and biodegradability can be obtained.

[0057] The content of optional components other than the alcohol having 3 or less 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 contained 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 the solvent containing an alcohol having 3 or less 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, relative to 1 part by weight of the raw cellulose acetate.

[0059] The catalyst may be an acid catalyst that is generally used as a deacetylation catalyst. Examples of the acid catalyst 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 alone or in combination of two or more.

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

[0061] The acid catalyst is preferably sulfuric acid. Concentrated sulfuric acid may be used as an aqueous solution of sulfuric acid having a sulfuric acid concentration of 98% by weight. The catalyst may be mixed in advance with a solvent containing an alcohol having 3 or less carbon atoms and used for the solvolysis of the raw cellulose acetate.

[0062] The amount of the acid catalyst used is, for example, preferably 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, relative to 1 part by weight of the raw cellulose acetate. If the amount of the catalyst is too small, the time for solvolysis becomes too long, which is economically undesirable, although it has the advantage of making it easier to control the end point of the reaction. On the other hand, if the amount of the catalyst is too large, the degree of change in the depolymerization rate relative to the solvolysis temperature becomes large, making it difficult to control the end point of the reaction, and it becomes difficult to obtain cellulose acetate having the total substitution degree of the present disclosure. In addition, it is likely to result in a non-uniform cellulose acetate with a fluctuating degree of acetyl substitution.

[0063] The water content in the solvolysis reaction system is preferably as small as possible, and is preferably 2 parts by weight or less, more preferably 1 part by weight or less, and even more preferably 0.5 parts by weight or less, per part by weight of the starting cellulose acetate. As long as the solvolysis of the starting cellulose acetate is initiated and progresses, there is no lower limit to the water content in the solvolysis reaction system, but it may be, for example, 0.01 part by weight or more per part by weight of the starting cellulose acetate.

[0064] When subjecting the raw cellulose acetate to solvolysis, the moisture originally contained in the raw cellulose acetate may or may not be removed in advance. The moisture content of the raw 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 moisture content of raw cellulose acetate can be measured by the following method. It can be measured using a Kett moisture meter (METTLER TOLEDO HB43). Approximately 2.0 g of a wet sample is placed on the aluminum tray of the Kett moisture meter and heated at 120°C until the weight stops changing, and the moisture content (wt%) in the sample can be calculated from the change in weight before and after heating.

[0066] In the step of deacetylating the raw cellulose acetate by solvolysis, water may be added to the system in addition to the water originally contained in the raw cellulose acetate. The entire amount may be present in the system at the start of the reaction, or a part 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 or several portions.

[0067] The content of water 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 part by weight of the solvent.

[0068] The temperature in the solvolysis reaction system is adjusted to a temperature equal to or higher than the boiling point of the alcohol having 3 or less carbon atoms. For example, when methanol is used as the alcohol having 3 or less carbon atoms, the temperature is 65° C. or higher, when ethanol is used, 78° C. or higher, when 1-propanol is used, 97° C. or higher, and when 2-propanol is used, 82° C. or higher. The raw cellulose acetate can be sufficiently dissolved in the solvent, and the solvolysis reaction can proceed uniformly.

[0069] The temperature in the solvolysis reaction system is not limited as long as it is equal to or higher than the boiling point of the alcohol having 3 or less carbon atoms, but is preferably equal to or lower than 105° C., more preferably equal to or lower than 100° C., and even more preferably equal to or lower than 95° C. If the temperature exceeds 105° C., the degree of polymerization of the resulting cellulose acetate and the yield decrease significantly.

[0070] The gauge pressure in the solvolysis reaction system is preferably 0.2 MPaG to 1 MPaG. It is preferably 0.2 MPaG to 0.7 MPaG, and more preferably 0.2 MPaG to 0.5 MPaG. By setting the pressure at 0.2 MPaG or more, the raw cellulose acetate can be sufficiently dissolved in the solvent, and the solvolysis reaction can proceed particularly uniformly. If the pressure exceeds 1 MPaG, the degree of polymerization of the obtained cellulose acetate and the yield decrease significantly.

[0071] The time for the solvolysis reaction may be from 20 minutes to 300 minutes, from 30 minutes to 240 minutes, or from 60 minutes to 200 minutes. By being within this range, the total degree of acetyl substitution can be easily adjusted to from 0.4 to 0.9.

[0072] The solvolysis reaction time herein refers to the time during which the temperature is maintained after the temperature in the solvolysis reaction system is reached.

[0073] In conventional deacetylation of raw cellulose acetate, the raw cellulose acetate is dissolved in a mixed solvent of acetic acid and water, and the raw cellulose acetate is hydrolyzed using a sulfuric acid catalyst. In this process, the elimination of acetyl groups proceeds in roughly the same manner at the 2-, 3-, and 6-positions of the glucose ring of cellulose acetate. On the other hand, in the method for producing cellulose acetate disclosed herein, the acetyl group at the 6-position is preferentially eliminated, resulting in cellulose acetate having a lower degree of acetyl substitution at the 6-position relative to the 2- and 3-positions of the glucose ring.

[0074] In conventional deacetylation of raw cellulose acetate, acetic acid is used as a reaction solvent, and the reaction proceeds while acetic acid is preferentially reacetylated at the 6-position during the deacetylation process, so that the elimination of acetyl groups apparently proceeds in roughly the same manner at the 2-, 3-, and 6-positions of the glucose ring of cellulose acetate. Cellulose acetate with a low degree of substitution at the 6-position can be obtained by suppressing the reacetylation at the 6-position, but in that case, a solvent to replace acetic acid is required. As a result of extensive investigations, the present inventors have found that a solvent containing an alcohol having 3 or less carbon atoms is suitable as a reaction solvent for this purpose at or above its boiling point. A solvent containing an alcohol having 3 or less carbon atoms dissolves or highly swells the starting cellulose acetate with a medium to high degree of substitution at or above its boiling point.

[0075] The solvolysis of the raw cellulose acetate can be terminated by the addition of a neutralizing agent. Neutralizing agents include salts of weak acids, such as acetates, e.g., sodium acetate and magnesium acetate, and carbonates, e.g., sodium carbonate and magnesium carbonate. The neutralizing agent may be added together with a solvent containing an alcohol having 3 or less carbon atoms.

[0076] The amount of the neutralizing agent used may be 1.0 to 5.0 equivalents relative to 1 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 the 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 the neutralizing agent is too large, a large amount of solvents will be used to wash off the neutralizing agent, which is economically undesirable.

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

[0078] As a method of precipitation, for example, after the completion of the solvolysis reaction of the raw cellulose acetate, the temperature of the reaction system is cooled to room temperature to precipitate cellulose acetate with a low degree of substitution. In this way, the precipitation method using cooling does not require the addition of a precipitating solvent and is economically preferable. However, the addition of a precipitating solvent may be allowed since it may promote the precipitation of cellulose acetate with a low degree of substitution and increase the yield.

[0079] Examples of the precipitating solvent include a solvent containing an alcohol having 3 or less 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 precipitating solvents may be used alone or in combination with a mixed solvent containing two or more solvents. Among these, the solvent containing an alcohol having 3 or less carbon atoms is preferred because using the same solvent as the reaction solvent as the precipitating solvent may facilitate recovery and reuse of waste solvent.

[0080] The precipitation solvent preferably contains the following basic substances, since neutralization can be carried out simultaneously with precipitation.

[0081] [Optional process] (Cleaning process, neutralization process) The precipitated cellulose acetate is preferably washed with an organic solvent (poor solvent) such as an alcohol such as methanol or a ketone such as acetone. It is also preferable to wash and neutralize with an organic solvent containing a salt of a weak acid or a basic substance (for example, an alcohol such as methanol or a ketone such as acetone). By washing and neutralization, impurities such as the catalyst (sulfuric acid, etc.) used in the solvolysis step can be efficiently removed.

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

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

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

[0085] The cellulose acetate may be dissolved by stirring at an appropriate temperature (e.g., 20 to 80° C., preferably 25 to 60° C.) and the concentration (mixture ratio) of the cellulose acetate in the aqueous solution may be adjusted to an appropriate concentration (e.g., 2 to 10% by weight, preferably 3 to 8% by weight).

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

[0087] After removing the residue, the dissolved cellulose acetate may be precipitated. Precipitation methods include reprecipitation and spray drying. Precipitation solvents used for reprecipitation include solvents containing the alcohols having 3 or less 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 alone or as mixed solvents containing two or more solvents.

[0088] (stabilizer added) After precipitation of cellulose acetate, a stabilizer may be added to the precipitated cellulose acetate to enhance the thermal stability of the cellulose acetate. The stabilizer is preferably an alkali metal compound and / or an alkaline earth metal compound, particularly a calcium compound such as calcium hydroxide.

[0089] The amount of stabilizer 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 stabilizer may be added at the same time as removing free metal components, sulfuric acid components, etc. by washing the precipitate with a poor solvent such as the precipitating solvent.

[0091] After the step of precipitating the deacetylated cellulose acetate, or after the optional step if the method includes such an optional step, it is preferable to dry the cellulose acetate. When drying the cellulose acetate, the drying method is not particularly limited, and a conventionally known method can be used. For example, drying methods include air drying such as hot air drying, reduced pressure drying, and vacuum drying. The temperature and pressure may be appropriately adjusted.

[0092] After drying, the cellulose acetate may be pulverized. For pulverization, a conventional pulverizer such as a sample mill, a hammer mill, a turbo mill, an atomizer, a cutter mill, a bead mill, a ball mill, a roll mill, a jet mill, and a pin mill may be used. In addition, freeze pulverization, dry pulverization at room temperature, or wet pulverization may be used. EXAMPLES

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

[0094] <Preparation and properties of cellulose acetate> For the cellulose acetates of the Examples and Comparative Examples, the physical properties shown in Table 1 were measured as follows.

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

[0097] (Total degree of acetyl substitution, degree of acetyl substitution at 2-position, 3-position and 6-position (DS2, DS3 and DS6), proportion of degree of acetyl substitution at 6-position in total degree of acetyl substitution) According to the literature of Tezuka et al. (Carbohydrate Research, 273, 83-91 (1995)), the sample was propionylated with propionic anhydride in pyridine solvent, and then dehydrated with chloroform solvent. 13 The C-NMR spectrum was measured, and the intensities of three signals of acetyl carbonyl carbon appearing in the vicinity of 169.1 to 170.2 ppm were integrated, and the intensities of three signals of propionyl carbonyl carbon appearing in the vicinity of 172.7 to 173.6 ppm were integrated.

[0098] 13 In the C-NMR spectrum, the three acetyl carbonyl carbon signals appearing in the vicinity of 169.1 to 170.2 ppm are assigned to the 2nd, 3rd, and 6th positions from the high magnetic field side. The intensity of each signal was integrated within the range of ±0.2 ppm from the maximum, and this was defined as the integrated intensity of each acetyl carbonyl carbon signal. The DS was calculated from the following formula: i (i is 2, 3 or 6). DS i=DS × (integral intensity of acetyl carbonyl carbon signal at i-position) / (sum of integral intensities of acetyl carbonyl carbon signals at 2-, 3- and 6-positions)

[0099] The NMR measurement conditions are as follows. Measurement solvent: CDCl3 (approximately 3 ml) Measurement temperature: 40℃ Sample size: 160-180mg (φ10mm) Observed nucleus: 13C (1H fully decoupled) Number of data points: 32768 Pulse angle and time: 45°, 9μsec Data capture time: 0.9667 sec Waiting time: 2.0333sec Number of times: 18,000

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

[0101] The ratio (%) of the degree of acetyl substitution at the 6-position to the total degree of acetyl substitution was calculated by the following formula. Percentage of acetyl substitution at 6-position (%) = acetyl substitution at 6-position (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, first, the intrinsic viscosity number of cellulose acetate was determined in accordance with JIS-K-7367-1 and ISO1628-1, using a size 1C Ubbelohde viscometer as the 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 calculated using the following formula according to the literature by Kamide et al. Viscosity average molecular weight = (limiting viscosity number [η] / 0.171) (1 / 0.61)

[0105] The degree of polymerization (viscosity average degree of polymerization) of cellulose acetate was 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 for 2 hours with a magnetic stirrer, left to stand overnight, and stirred again for 2 hours. The transmittance (%) of the 4% aqueous solution of cellulose acetate thus obtained was measured at 660 nm with a spectrophotometer (Shimadzu Corporation, UV-1800 ultraviolet-visible spectrophotometer, cell material polystyrene, cell length 10 mm).

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

[0108] Precipitation step: The reaction mixture was cooled to room temperature, and a mixture of 14.6 parts by weight of sodium acetate trihydrate and 55 parts by weight of methanol was added to neutralize the sulfuric acid. The white solid suspended in the reaction mixture was filtered off by suction. 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 the methanol was filtered off by suction.

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

[0110] (Example A-2) Deacetylation and Precipitation Steps: In the same manner as in Example A-1, 60 parts by weight of low-substituted cellulose acetate was obtained.

[0111] Purification process: Further, 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 12,600G for 30 minutes to obtain a supernatant of the suspension. This supernatant was dropped into 10,000 parts by weight of acetone under stirring to obtain a white precipitate. This white precipitate was filtered by suction filtration and dried under reduced pressure at 60°C until it reached a constant weight, obtaining 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 and Precipitation Steps: Cellulose acetate manufactured by Eastman Chemical Company (product name "CA-320S", moisture content 3% by weight, total acetyl substitution degree 1.80, 2-position acetyl substitution degree 0.61, 3-position acetyl substitution degree 0.56, 6-position acetyl substitution degree 0.63) was used instead of cellulose diacetate (manufactured by Daicel Corporation, product name "L-50", moisture content 3% by weight), and 68 parts by weight of low-substituted cellulose acetate was obtained in the same manner as in Example A-1, except that the temperature adjustment time at 90°C was changed to 80 minutes. The physical properties of the obtained low-substituted cellulose acetate were measured and the results are shown in Table 1.

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

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

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

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

[0117] Deacetylation step: A mixture of 510 parts by weight of acetic acid and 95 parts by weight of water was added to 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 2-position 0.86, acetyl substitution degree at 3-position 0.82, acetyl substitution degree at 6-position 0.75), and stirred at 70°C for 3 hours to obtain a cellulose diacetate solution. The 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 heated to 70°C while continuing to stir, and 3 hours after the addition of sulfuric acid, 67 parts by weight of water was added over 5 minutes, and further, 8 hours after the addition of sulfuric acid, 133 parts by weight of water was added over 10 minutes. The reaction mixture was heated to 70°C while continuing to stir, and 10 hours (600 minutes) after the addition of sulfuric acid, the reaction mixture was cooled to 25°C to essentially stop the reaction.

[0118] Precipitation step: The reaction mixture was dropped into 1,500 parts by weight of acetone under stirring to obtain a white precipitate. The white precipitate was filtered, dispersed in 800 parts by weight of acetone, and filtered again, 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, two times. The filtered white precipitate was dried under reduced pressure at 60°C until it reached a constant weight. 960 parts by weight of a 20% by weight aqueous acetone solution was added to 64 parts by weight of the dried product, and the mixture was stirred at 40°C for 8 hours. The thick phase was removed by centrifugation, and parts by weight of acetone was added to the dilute phase to obtain a white precipitate. The white precipitate was filtered, 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 it reached a constant weight to obtain 59 parts by weight of low-substituted cellulose acetate. The results of measuring the 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 a constant weight was reached) was suspended in 237 parts by weight of methanol, 0.2 parts by weight of molybdenum hexacarbonyl (Mo(CO)6) was added, and the internal pressure was adjusted to 200 psi using nitrogen in a sealed reactor, followed by heating 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 a constant weight was reached, yielding 29 parts by weight of low-substituted cellulose acetate. The results of measuring the 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 a constant weight was reached) was suspended in 237 parts by weight of methanol, 0.2 parts by weight of molybdenum oxide (VI) (MoO3) was added, and the internal pressure was adjusted to 1,000 psi using nitrogen in a sealed reactor, and the mixture was heated 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 a constant weight was reached, yielding 37 parts by weight of low-substituted cellulose acetate. The results of measuring the physical properties of the obtained low-substituted cellulose acetate are shown in Table 1.

[0123] [Table 1]

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

[0125] The cellulose acetate of Comparative Example A-3 has a degree of acetyl substitution at the 6-position of 0.05 and a ratio of the degree of acetyl substitution at the 6-position to the total degree of acetyl substitution of 10.4%, while the cellulose acetate of Comparative Example A-4 has a degree of acetyl substitution at the 6-position of 0.06 and a ratio of the degree of acetyl substitution at the 6-position to the total degree of acetyl substitution of 12.0%, so that the degrees of acetyl substitution at the 6-position of the cellulose acetates of Comparative Examples A-3 and A-4 are lower than the degrees of acetyl substitution at positions 2 and 3. However, the light transmittance at 660 nm of a 4 wt % aqueous solution is low, and the water solubility is poor.

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

[0127] <Animal experiments (acetyl group residual rate, feed intake, weight gain, blood sugar level, cholesterol, triglyceride, epididymal fat)> Animal experiments were started using nine 7-week-old (body weight 150-170g) male Wistar rats (Japan SLC Co., Ltd.) housed individually in stainless steel cages under conditions of room temperature of 24±1°C, relative humidity of 55±5°C, and a 12-hour light / dark cycle (lights on from 7:00 to 19:00).

[0128] After the rats were brought in, they were acclimated to a purified diet, AIN-93G (Reeves et al., Journal of Nutrition, 123, 1939-1951 (1993)) for 3 days with tap water, and then divided into 3 groups based on body weight (so as to eliminate bias in the total body weight of the rats in each group). The first group was given AIN-93G (sometimes called the "control group"), the second group was given AIN-93G containing 5% by weight of low-substituted cellulose acetate of Example A-2 (sometimes called the "test group"), and the third group was given AIN-93G containing 5% by weight of low-substituted cellulose acetate of Comparative Example A-1 (sometimes called the "comparison group"), each of which was given ad libitum access to tap water for 14 days. Each group consisted of 3 rats. The first group corresponds to Reference Example B-1, the second group to Example B-1, and the third group to Comparative Example B-1.

[0129] The rats were divided into three groups, and on the 3rd, 7th, and 13th days after starting to feed on each diet, the total amount of feces was collected for one day and used to analyze the residual rate of acetyl groups. The analytical method is as follows. In addition, the amount of food intake and the amount of body weight gain were measured throughout the feeding period.

[0130] On the 14th day of feeding, rats were fasted from 7:00 a.m. and autopsy was performed from 3:00 p.m. The rats were anesthetized with isoflurane and the abdomen was opened, and about 2 mL of blood was collected from the abdominal aorta into a heparinized test tube (Venoject II heparin sodium, for 3 mL blood collection: Terumo Corporation). The rats were then euthanized by exsanguination, and the epididymal fat (left and right) was promptly removed. The weight of the epididymal fat was then measured.

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

[0132] <Acetyl group remaining 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-nitrophenylhydrazide using the method of Miwa et al. (Journal of Chromatography, 321, 165-174 (1985)). The acetic acid concentration in the rat feces was then determined by quantifying the amount of 2-nitrophenylhydrazide of acetic acid using HPLC analysis.

[0133] In addition, 0.1 g of rat feces was suspended in 150 mM aqueous sodium hydroxide 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-nitrophenylhydrazide using the method of Miwa et al. (Journal of Chromatography, 321, 165-174 (1985)), and the 2-nitrophenylhydrazide of acetic acid was quantified by HPLC analysis to determine the acetic acid concentration in the sodium hydroxide-treated rat feces.

[0134] The difference between the acetic acid concentration in the rat feces treated with sodium hydroxide and the acetic acid concentration in the rat feces was taken as the acetyl group concentration (moles per unit weight) of the rat feces. The residual acetyl group rate was calculated using the following formula: Acetyl group remaining rate (mol%) = 100 × (acetyl group concentration in rat feces) × A / (B × C / D) A: Fecal mass (weight) of rats from 0 to 24 hours B: Food intake (weight) of rats from -24 hours to 0 hours C: Concentration of cellulose acetate in the feed (wt%) D: Number of moles of acetyl groups per unit weight of cellulose acetate =DS / (162.14+42.037×DS) DS: Total degree of acetyl substitution

[0135] [Table 2]

[0136] The residual acetyl group rate in feces of rats fed cellulose acetate of Example A-2 (the proportion of acetyl substitution at the 6-position in the total acetyl substitution degree is 18% or less) on days 3, 7, and 13 of feeding (Example B-1) was lower than that of rats fed cellulose acetate of Comparative Example A-1 (the proportion of acetyl substitution at the 6-position in the total acetyl substitution degree is 36.9% or less) (Comparative Example B-1). This indicates that the cellulose acetate of the Example with a low proportion of acetyl substitution at the 6-position is highly degradable and easily metabolized in the body.

[0137] The feed intake of the rats in Comparative Example B-1 (comparison group) was significantly lower than that of Reference Example B-1 (control group), but no significant difference was observed in the weight gain. On the other hand, the feed intake and weight gain of the rats in Example B-1 (test group) were both lower than those 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 tendency to decrease compared to those in Reference Example B-1 (control group), although the difference was not significant.

[0139] In addition, the neutral fat of the rats of Comparative Example B-1 (comparison group) was not significantly different from that of Reference Example B-1 (control group). On the other hand, the neutral fat of the rats of Example B-1 (test group) was lower than that of Reference Example B-1 (control group), and a significant difference was observed.

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

[0141] As described above, the cellulose acetate of the Examples having a low degree of acetyl substitution at the 6-position is highly degradable and easily metabolized in the body, and is particularly effective in suppressing appetite (suppressing feed intake), weight gain, neutral fat, and fat accumulation (suppressing epididymal fat) 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.