Fine cellulose fiber composition

Abstract

To provide a microcellulose fiber composition inhibiting reduction in the viscosity and reduction in the pH when an aqueous dispersion prepared using the microcellulose fiber composition is stored at high temperature.SOLUTION: A microcellulose fiber composition of one embodiment contains microcellulose fiber with a sulfate group represented by general formula (1) in the figure, and a salt having a buffering effect. In general formula (1): n is an integer from 1 to 3 inclusive; Mn+ are n-valent cations; and the wavy line is a binding site to another atom.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a finely divided cellulose fiber composition. [Background technology]

[0002] Due to growing environmental awareness, research is being conducted around the world to put biomass-derived materials to practical use. For example, much of the cellulose extracted from wood (wood chips) is used to make paper, which contributes greatly to both people's lives and CO2 fixation.

[0003] Cellulose nanofibers (fine cellulose fibers) are known, which are cellulose fibers broken down into nano-sized fibers. It has been proposed that cellulose nanofibers can be used by blending them with water, solvents, resins, rubber, etc., or by molding the cellulose nanofibers themselves into powders, films, nonwoven fabrics, etc., and their thickening, emulsifying, cell activating, and antiviral properties are utilized for applications in various fields, such as cosmetics, medical products, and food.

[0004] For example, Patent Document 1 discloses sulfated fibrous cellulose containing carbamide groups and having a fiber width of 1000 nm or less, in which the amount of the carbamide groups introduced is 0.05 mmol / g or more. Patent Document 1 also discloses that the sulfated fibrous cellulose is a fine fibrous cellulose that has a high mass loss peak temperature and is resistant to thermal decomposition. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-042350 Summary of the Invention [Problem to be solved by the invention]

[0006] The present inventors have investigated the stability of aqueous dispersions containing sulfated cellulose fibers when stored at high temperatures (for example, at 50°C to 100°C). As a result, they have found that when the viscosity and pH of a typical aqueous dispersion containing sulfated cellulose fibers is measured after high-temperature storage, the viscosity is significantly reduced and the pH is significantly reduced (acidified) compared to when the dispersion is not stored at high temperatures (for example, before high-temperature storage).

[0007] According to the studies of the present inventors, even in the case of the sulfated fibrous cellulose disclosed in Patent Document 1, when an aqueous dispersion containing the sulfated fibrous cellulose was stored at a high temperature and then the viscosity and pH of the aqueous dispersion were measured, it was found that the viscosity was significantly reduced and the pH was significantly reduced (acidified) compared to when the aqueous dispersion was not stored at a high temperature.

[0008] Therefore, an object of the present disclosure is to provide a fine cellulose fiber composition that suppresses a decrease in viscosity and a decrease in pH when an aqueous dispersion prepared using the fine cellulose fiber composition is stored at high temperatures. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems and have found that a specific fine cellulose fiber composition can achieve the above object, leading to the present disclosure.

[0010] An example aspect of this embodiment is described as follows.

[0011] [1] A fine cellulose fiber composition comprising fine cellulose fibers having sulfate ester groups represented by the following general formula (1) and a salt having a buffering effect: [ka] (In the general formula (1), n ​​is an integer of 1 or more and 3 or less, and M n+ is an n-valent cation, and the wavy lines are bonding sites to other atoms.) [2] The salt having the buffering effect is NH4+ The fine cellulose fiber composition according to [1], which does not contain ammonium ions represented by the formula: [3] The fine cellulose fiber composition according to [1] or [2], wherein the salt having a buffering effect is at least one salt selected from disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium acetate, and acetate salts of quaternary ammonium. [4] The fine cellulose fiber composition according to any one of [1] to [3], wherein the salt having a buffering effect is contained in an amount of 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the fine cellulose fibers. [5] Said M n+ At least a portion of the quaternary ammonium cations is a nitrogen (N + ) and the number of carbon atoms in the main chain of each of the four groups bonded to said cellulose fiber compound is 12 or less. [6] Said M n+ At least a portion of the quaternary ammonium cations is derived from a zwitterion, and the nitrogen (N + ) and the number of carbon atoms in the main chain of each of the four groups bonded to said cellulose fiber compound is 12 or less. [7] Said M n+ The fine cellulose fiber composition according to any one of [1] to [6], wherein at least a part of the cations is a quaternary ammonium cation represented by the following general formula (2): [ka] (In the general formula (2), R 1 , R 2 , and R 3 are each independently a group having 12 or less carbon atoms selected from a group having at least one partial structure selected from an ethylene oxide moiety and a glyceryl moiety, an alkyl group, and a monohydroxyalkyl group, R 4is an alkylene group or a hydroxyalkylene group, and the alkylene group or the hydroxyalkylene group may be substituted with an acetoxy group or an acetyl group; Z is a group represented by the following general formula (3), (4), or (5), and —CH—R 4 the carbon number of the group represented by -Z is 12 or less, R 1 , R 2 , R 3 , and R 4 may be bonded to each other to form a ring.) [ka] (In general formulas (3), (4), and (5), m is an integer of 1 or more and 3 or less, and X m+ is an m-valent cation, The wavy line is R 4 ) [8] The group represented by the general formula (3) is a group represented by the formula (3') or (3''), The group represented by the general formula (4) is a group represented by the formula (4') or (4''), The fine cellulose fiber composition according to [7], wherein the group represented by the general formula (5) is a group represented by the formula (5') or (5''). [ka] [Effects of the Invention]

[0012] According to the present disclosure, it is possible to provide a fine cellulose fiber composition in which the decrease in viscosity and decrease in pH are suppressed when an aqueous dispersion prepared using the fine cellulose fiber composition is stored at high temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0013] The fine cellulose fiber composition of the present embodiment will be described in detail below.

[0014] One aspect of this embodiment is a fine cellulose fiber composition containing fine cellulose fibers having sulfate ester groups represented by the following general formula (1) and a salt having a buffering effect.

[0015] The microfibrillated cellulose fiber composition of this embodiment can suppress a decrease in viscosity and a decrease in pH when an aqueous dispersion prepared using the microfibrillated cellulose fiber composition is stored at high temperatures. The microfibrillated cellulose fiber composition of this embodiment suppresses a decrease in physical properties when stored at high temperatures as an aqueous dispersion, making it possible to provide an aqueous dispersion of microfibrillated cellulose fibers of stable quality in a variety of usage environments and fields. The inventors' studies have shown that evaluation at room temperature (e.g., 20°C to 30°C) is insufficient when evaluating storage stability. This is because when an aqueous dispersion prepared using the microfibrillated cellulose fiber composition is stored, the temperature can reach high temperatures, such as 40°C to 60°C, in a warehouse in summer or inside a vehicle during transportation. Even if there are no problems with storage stability at room temperature, exposure to such temperatures can cause problems to become apparent. Therefore, in this disclosure, the physical properties when stored at high temperatures (80°C in the examples) were evaluated.

[0016] This embodiment will be described in detail below.

[0017] (fine cellulose fiber) The fine cellulose fibers of the present embodiment are fine cellulose fibers having sulfate ester groups represented by the following general formula (1).

[0018] [ka] (In the general formula (1), n ​​is an integer of 1 or more and 3 or less, and M n+ is an n-valent cation, and the wavy lines are bonding sites to other atoms.)

[0019] Ordinary cellulose (unmodified cellulose) is a polysaccharide in which glucose is linked via β-1,4-glycosidic bonds (C6H 10 O5) nThe fine cellulose fibers in this embodiment are fibers made of modified cellulose, as is clear from the fact that they have sulfate ester groups.

[0020] The average fiber width of the fine cellulose fibers is 1 nm to 1000 nm, preferably 1 nm to 100 nm, and more preferably 2 nm to 10 nm. The average fiber length of the fine cellulose fibers is not particularly limited, but is usually 0.1 μm to 6 μm, and preferably 0.1 μm to 2 μm.

[0021] The average fiber width and average fiber length can be measured by, for example, using an atomic force microscope (SPM-9700HT, manufactured by Shimadzu Corporation) to measure the fiber width (fiber diameter (equivalent circle diameter)) and fiber length of 50 arbitrarily selected fibers and calculating the arithmetic mean value. The average fiber width and average fiber length can be set within the desired range by adjusting the sulfuric acid esterification reaction time and the compounding ratio of the reagents.

[0022] The fine cellulose fibers have sulfate ester groups represented by the general formula (1). The fine cellulose fibers are also referred to as sulfated cellulose nanofibers. The sulfate ester groups are usually introduced into the fine cellulose fibers by substituting some of the OH groups in the cellulose that constitutes the fibers with the sulfate ester groups represented by the general formula (1). In this case, the wavy line in the general formula (1) represents the bonding site to the carbon atom to which the OH group was bonded.

[0023] M n+ is an n-valent cation, and when n is 2 or 3, that is, M n+ If is a multivalent cation, M n+ is two or three -OSO3 - It forms an ionic bond with M n+ As n is 1, that is, M n+ M + (monovalent cation) is one of the preferred embodiments.

[0024] Said M n+At least a portion of the quaternary ammonium cations is a nitrogen (N + In one preferred embodiment, the number of carbon atoms in the main chain of each of the four groups bonded to M is 12 or less. The quaternary ammonium cation may be one type or two or more types. n+ The storage stability of the powder is improved when at least a portion of the cations is a specific quaternary ammonium cation. The reason for this is not clear, but the present inventors have obtained the following findings.

[0025] As a result of studies by the present inventors, it was found that when a conventional sulfated cellulose nanofiber composition is stored at high temperature and then dispersed in water, the viscosity and pH of the aqueous dispersion decrease compared to when high-temperature storage is not performed. This is because high-temperature storage causes hydrolysis of some of the sulfate ester groups constituting the sulfated cellulose nanofiber. Furthermore, it has been confirmed by analysis that the amount of sulfate ester groups bonded to cellulose in the conventional sulfated cellulose nanofiber composition decreases before and after high-temperature storage. Further studies by the present inventors have revealed that the above M n+ It was found that by using a specific quaternary ammonium cation as at least a portion of the cellulose nanofiber, the viscosity and pH of the aqueous dispersion are inhibited from decreasing when the nanofiber is dispersed in water after high-temperature storage in powder form. This is a phenomenon not observed with tertiary amines (or their ions), etc. The reason for this is unclear, but the inventors speculate that the specific quaternary ammonium cation, due to its hydrophilicity and hygroscopicity, acts as a desiccant within the molecules of the sulfated cellulose nanofiber, preventing water molecules from attacking the sulfate ester groups and suppressing hydrolysis of the sulfate ester groups.

[0026] Said M n+ At least a portion of the quaternary ammonium cations is derived from a zwitterion, and the nitrogen (N + In one preferred embodiment, the number of carbon atoms in the main chain of each of the four groups bonded to M is 12 or less.n+ When at least a part of the quaternary ammonium cations is derived from a zwitterion, M n+ This is preferable because a sufficient effect can be achieved even when the amount of the quaternary ammonium cation is small, compared to when the quaternary ammonium cation is not derived from a zwitterion.

[0027] The quaternary ammonium cations and quaternary ammonium cations derived from zwitterions include nitrogen (N + ) are preferably all 10 or less carbon atoms in the main chain of the four groups bonded to the aryl group, and are preferably all 8 or less carbon atoms.

[0028] The term "quaternary ammonium cation" encompasses quaternary ammonium cations derived from zwitterions, and includes both quaternary ammonium cations derived from zwitterions and quaternary ammonium cations not derived from zwitterions.

[0029] The quaternary ammonium cation not derived from a zwitterion is not particularly limited, but for example, choline ((CH3)3N + —C2H4—OH), tetramethylammonium, tetraethylammonium, tetrapropylammonium, benzyltrimethylammonium, etc.

[0030] The zwitterion is not particularly limited, but examples thereof include betaine (trimethylglycine), carnitine, acetylcarnitine, lauryldimethylaminoacetic acid, and the like.

[0031] Said M n+ In one preferred embodiment, at least a part of the above is a quaternary ammonium cation represented by the following general formula (2).

[0032] [ka] (In the general formula (2), R 1 , R 2 , and R3 are each independently a group having 12 or less carbon atoms selected from a group having at least one partial structure selected from an ethylene oxide moiety and a glyceryl moiety, an alkyl group, and a monohydroxyalkyl group, R 4 is an alkylene group or a hydroxyalkylene group, and the alkylene group or the hydroxyalkylene group may be substituted with an acetoxy group or an acetyl group; Z is a group represented by the following general formula (3), (4), or (5), and —CH—R 4 the carbon number of the group represented by -Z is 12 or less, R 1 , R 2 , R 3 , and R 4 may be bonded to each other to form a ring.)

[0033] [ka] (In general formulas (3), (4), and (5), m is an integer of 1 or more and 3 or less, and X m+ is an m-valent cation, The wavy line is R 4 )

[0034] R 1 , R 2 , and R 3 are each independently a group having 12 or less carbon atoms selected from a group having at least one partial structure selected from an ethylene oxide moiety and a glyceryl moiety, an alkyl group, and a monohydroxyalkyl group.

[0035] The ethylene oxide moiety means an oxyethylene moiety (-CH2-CH2-O-), and the glyceryl moiety means -O-CH2-CH(-O-)-CH2-O-. Examples of groups having at least one partial structure selected from an ethylene oxide moiety and a glyceryl moiety include groups having 0 to 3 ethylene oxide moieties and 0 or 1 glyceryl moiety, provided that the number of ethylene oxide moieties and the number of glyceryl moieties are not simultaneously 0, and substituted alkyl groups having 0 to 3 ethylene oxide moieties and 0 or 1 glyceryl moiety, provided that the number of ethylene oxide moieties and the number of glyceryl moieties are not simultaneously 0.

[0036] Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, and a dodecyl group. The alkyl group may be a linear alkyl group or a branched alkyl group. Examples of the monohydroxyalkyl group include a group in which one of the hydrogen atoms of the above-mentioned alkyl group is substituted with a hydroxy group.

[0037] As the group having 12 or less carbon atoms selected from a group having at least one partial structure selected from an ethylene oxide moiety and a glyceryl moiety, an alkyl group, and a monohydroxyalkyl group, an embodiment having 10 or less carbon atoms, and an embodiment having 8 or less carbon atoms are also preferred.

[0038] R 4 is an alkylene group or a hydroxyalkylene group, and the alkylene group or the hydroxyalkylene group may be substituted with an acetoxy group or an acetyl group. 4 Z bonded to is a group represented by the above general formula (3), (4) or (5). 4 The group represented by -Z has 12 or less carbon atoms. 4 The alkylene group or hydroxyalkylene group is —CH—R 4The alkyl group or monohydroxyalkyl group described above may have one hydrogen atom removed, provided that the carbon number of the group represented by -Z is 12 or less. The alkylene group or hydroxyalkylene group may be substituted with an acetoxy group or an acetyl group, and for example, one to three, preferably one, of the hydrogen atoms constituting the alkylene group or hydroxyalkylene group may be substituted with an acetoxy group (-O-C(=O)-CH3) or an acetyl group (-C(=O)-CH3).

[0039] X m+ is an m-valent cation, and when m is 2 or 3, that is, X m+ If is a polyvalent cation, X m+ Two or three -CO2 - , -SO3 - , or -OSO3 - It forms an ionic bond with X. m+ As m is 1, that is, X m+ is X + In one preferred embodiment, X is a monovalent cation. m+ As for hydrogen ions (H + ), metal ions, ammonium ions, etc. The m-valent cation may be one type or two or more types.

[0040] M n+ As mentioned above, at least a portion of M is preferably a quaternary ammonium cation. n+ may all be quaternary ammonium cations, and M n+ A part of the cations may be quaternary ammonium cations, and a part (the remainder) may be an n-valent cation other than the quaternary ammonium cation. Examples of n-valent cations other than the quaternary ammonium cation include hydrogen ions (H + ), metal ions, ammonium ions (excluding quaternary ammonium cations), etc. The n-valent cations other than quaternary ammonium cations may be one type or two or more types.

[0041] M n+When a portion of the quaternary ammonium cations is a quaternary ammonium cation and the remaining portion (the remainder) is an n-valent cation other than a quaternary ammonium cation, the molar ratio of quaternary ammonium cations to n-valent cations other than a quaternary ammonium cation is not particularly limited, but the molar ratio of quaternary ammonium cations to n-valent cations other than a quaternary ammonium cation is preferably 0.5:9.5 to 9.9:0.1, more preferably 0.8:9.2 to 9.5:0.5, and particularly preferably 1:9 to 9:1. When the quaternary ammonium cations are quaternary ammonium cations derived from zwitterions, sufficient effects can be achieved regardless of the molar ratio. On the other hand, when the quaternary ammonium cations are quaternary ammonium cations not derived from zwitterions, a small amount of quaternary ammonium cations not derived from zwitterions may result in insufficient effects, so the molar ratio is preferably 1:9 to 9.9:0.1, more preferably 1.5:8.5 to 9.5:0.5, and particularly preferably 2:8 to 9:1.

[0042] Examples of metal ions include alkali metal ions, alkaline earth metal ions, transition metal ions, and other metal ions.

[0043] The alkali metal ions include lithium ions (Li + ), sodium ions (Na + ), potassium ions (K + ), rubidium ion (Rb + ), cesium ions (Cs + ) and the like. Examples of alkaline earth metal ions include calcium ions (Ca 2+ ), strontium ions (Sr 2+ ) and the like. Examples of transition metal ions include iron ions, nickel ions, palladium ions, copper ions, and silver ions. Examples of other metal ions include beryllium ions, magnesium ions, zinc ions, and aluminum ions.

[0044] The ammonium ion is NH4 + Not only NH4 +Ammonium ions derived from various amines in which one or more hydrogen atoms are replaced by organic groups are also included. Ammonium ions include, for example, NH4 + , primary to tertiary ammonium cations, alkanolamine ions, pyridinium ions, etc. However, NH4 + The presence of ammonium ions may deteriorate the storage stability of the powder or cause discoloration such as browning. + In one preferred embodiment, this is not the case.

[0045] X m+ and M n+ As the n-valent cation other than the quaternary ammonium cation, hydrogen ion, sodium ion, potassium ion and calcium ion are preferred from the viewpoint of processability in each application of the fine cellulose fiber, particularly from the viewpoint of excellent storage stability, and hydrogen ion, sodium ion (Na + ) is particularly preferred. n+ and X m+ The number of types may be one or more.

[0046] That is, in one preferred embodiment, the group represented by the general formula (3) is a group represented by formula (3') or (3''); in one preferred embodiment, the group represented by the general formula (4) is a group represented by formula (4') or (4''); and in one preferred embodiment, the group represented by the general formula (5) is a group represented by formula (5') or (5'').

[0047] [ka]

[0048] The fine cellulose fibers may have other substituents in addition to the sulfate ester group represented by the general formula (1). When the fine cellulose fibers have a group other than the sulfate ester group represented by the general formula (1), i.e., other substituents, the other substituents typically substitute for at least one of the OH groups in the cellulose constituting the fine cellulose fibers. Examples of other substituents include, but are not limited to, anionic substituents and their salts, ester groups, ether groups, acyl groups, aldehyde groups, alkyl groups, alkylene groups, aryl groups, and combinations of two or more of these. When two or more other substituents are used in combination, the content ratio of each substituent is not limited. Among the other substituents, anionic substituents and their salts, or acyl groups are preferred from the viewpoint of nano-dispersibility. As the anionic substituents and their salts, carboxyl groups, phosphate ester groups, phosphite ester groups, and xanthate groups are particularly preferred. When the anionic substituent is in the form of a salt, sodium salts, potassium salts, and calcium salts are particularly preferred from the viewpoint of nano-dispersibility. Furthermore, an acetyl group is a particularly preferred acyl group from the viewpoint of nano-dispersibility.

[0049] The amount of sulfur introduced into the fine cellulose fiber due to sulfate ester groups is 0.3 mmol / g or more and 3.0 mmol / g or less. The amount of sulfate ester groups introduced can be set to any appropriate value within the above range depending on the application, etc. The amount of sulfur introduced into the fine cellulose fiber due to sulfate ester groups can be expressed as the sulfur content (mmol) per 1 g of fine cellulose fiber. The amount of sulfur introduced is preferably 0.5 mmol / g or more and 3.0 mmol / g or less, and more preferably 0.7 mmol / g or more and 3.0 mmol / g or less. When the amount of sulfur introduced is within the above range, the fine cellulose fiber tends to have high water dispersibility, which is preferable.

[0050] The amount of sulfur introduced can be determined, for example, by the combustion absorption-ion chromatography (IC) method (combustion absorption-IC method, combustion IC method) described in the Examples. The amount of sulfur introduced can be adjusted, for example, by controlling the concentration of a reagent such as sulfuric acid in the solution (defibration solution) used to defibrate the pulp, the amount of pulp relative to the defibration solution, the reaction time, temperature, etc.

[0051] The fine cellulose fibers are dispersed in water to a concentration of 0.6% by mass, and the viscosity of an aqueous dispersion containing 0.6% by mass of fine cellulose fibers measured at 6 rpm at 25°C is preferably 1000 mPa·s or more, more preferably 3000 mPa·s or more, and particularly preferably 5000 mPa·s or more. The viscosity is preferably 70000 mPa·s or less, and more preferably 50000 mPa·s or less.

[0052] The thixotropic index (TI value) calculated from the viscosity measured at 6 rpm and 60 rpm of an aqueous dispersion containing 0.6% by mass of fine cellulose fibers at 25°C is preferably 3 to 30, more preferably 3.5 to 20, and particularly preferably 3.8 to 15. The TI value can be calculated using the following formula: 6 rpm and 60 rpm refer to the rotation speeds of a viscometer (e.g., a B-type viscometer) used to measure the viscosity. TI value = (viscosity measured at 6 rpm) / (viscosity measured at 60 rpm)

[0053] The method for producing fine cellulose fibers is not particularly limited, and can be carried out by referring to a conventional method for producing fine cellulose fibers having sulfate ester groups. For example, by selecting a reagent so that at least a part of the neutralization (neutralization of sulfate ester groups) is carried out with a quaternary ammonium cation, M n+It is possible to obtain fine cellulose fibers in which at least a portion of the groups is a quaternary ammonium cation. For example, when cellulose (unmodified) fibers are defibrated to nanosize, sulfate ester groups are introduced, neutralized, purified, and dispersed in water or a dispersing medium other than water to prepare a dispersion of fine cellulose fibers, and the dispersing medium is removed from the dispersion to obtain fine cellulose fibers. For example, as shown in the examples, fine cellulose fibers may be produced by sulfate esterifying and defibrating raw pulp, or the method shown in the examples may be modified and carried out.

[0054] Examples of dispersion media other than water include dimethyl sulfoxide, polar organic solvents such as alcohols and polyols, and ionic liquids such as quaternary ammonium compounds. However, it is preferable to use water or a mixed solvent of water and an organic solvent as the dispersion medium, and it is preferable to use water from the viewpoint of safety, etc.

[0055] Drying is an example of a method for removing the dispersion medium from a dispersion of fine cellulose fibers. A dried product of fine cellulose fibers can be obtained by drying. Known drying methods can be used and are not particularly limited. Examples include freeze-drying, spray-drying, squeezing, air drying, hot-air drying, crystallization, and vacuum drying. The drying apparatus is not particularly limited, but a conical dryer, a continuous tunnel dryer, a band dryer, a vertical dryer, a vertical turbo dryer, a multi-stage disk dryer, a through-flow dryer, a rotary dryer, a flash dryer, a spray dryer, a spray dryer, a cylindrical dryer, a drum dryer, a belt dryer, a screw conveyor dryer, a rotary dryer with a heating tube, a vibration transport dryer, a batch-type box dryer, a vacuum box dryer, and an agitator dryer can be used alone or in combination of two or more. As the drying method, freeze-drying, crystallization and vacuum drying (a combination of crystallization and vacuum drying), and spray-drying are preferred because they are less likely to damage the fine cellulose fibers and can produce a porous dried product that is easily powdered. The dried product can be pulverized as needed, preferably by a dry pulverizer, to obtain fine cellulose fibers in a powder form.

[0056] (Fine cellulose fiber composition) The fine cellulose fiber composition of the present embodiment is a fine cellulose fiber composition containing the above-mentioned fine cellulose fibers and a salt having a buffering effect.

[0057] The fine cellulose fiber composition containing a salt having a buffering effect can suppress a decrease in viscosity and a decrease in pH when an aqueous dispersion prepared using the composition is stored at high temperatures. n+When at least a part of the cations is a specific quaternary ammonium cation, the fine cellulose fiber composition of the present embodiment is preferable because it has excellent high-temperature storage stability when prepared as a powder as well as excellent high-temperature storage stability when prepared as an aqueous dispersion. The present inventors speculated that the reason for the excellent high-temperature storage stability when prepared as an aqueous dispersion is that the inclusion of a salt having a buffering action makes it possible to maintain the pH of the aqueous dispersion near neutral, thereby suppressing the hydrolysis of sulfate esters, specifically the catalytic action of acid on hydrolysis.

[0058] Examples of salts with buffering properties include sodium acetate, tetraethylammonium acetate, phosphoric acid, disodium hydrogen phosphate, sodium dihydrogen phosphate, citric acid, sodium citrate, sodium borate, sodium carbonate, sodium bicarbonate, ammonium acetate, ammonium carbonate, ammonium bicarbonate, disodium ethylenediaminetetraacetate, and sodium tartrate. From the viewpoints of stability and excellent buffering properties near neutrality, sodium acetate, disodium hydrogen phosphate, and sodium dihydrogen phosphate are particularly preferred. Furthermore, in the examples described below, quaternary ammonium carboxylates (e.g., quaternary ammonium acetates) and sulfates obtained by neutralizing the carboxylic acid components and sulfuric acid components used in synthesis with quaternary ammonium hydroxides are also suitable as buffering salts and may be used.

[0059] Buffering salts include NH4 + In one preferred embodiment, the salt does not contain ammonium ions and is represented by the formula: NH4 + Salts containing ammonium ions, represented by the formula, decompose when heated, generating ammonia. As a result, the cellulose sulfate ester turns yellow or brown, making it unusable for applications requiring colorless transparency, and may impair its value as a product. + A salt containing no ammonium ion represented by the formula: is preferred.

[0060] In a particularly preferred embodiment, the salt having a buffering effect is at least one salt selected from disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium acetate, and acetate salts of quaternary ammonium.

[0061] The amount of the salt with buffering effect is preferably from 0.01 to 20 parts by mass, more preferably from 0.1 to 15 parts by mass, and even more preferably from 0.5 to 10 parts by mass, relative to 100 parts by mass of the fine cellulose fibers. Within the above range, the buffering effect when the fine cellulose fiber composition is dispersed in water and stability when stored at high temperatures can be ensured, and viscosity reduction can be sufficiently suppressed, which is preferable.

[0062] The method for producing the fine cellulose fiber composition of this embodiment is not particularly limited, and can be obtained, for example, by mixing the above-mentioned fine cellulose fibers with a salt having a buffering effect. Since the fine cellulose fibers are usually in a powder form and the salt having a buffering effect is a solid (for example, powder, granules, or lumps), the fine cellulose fiber composition can be obtained by mixing them using a mixer, a mortar, or the like.

[0063] (Additives) The fine cellulose fiber composition may contain other additives, which may be inorganic or organic.

[0064] Examples of inorganic additives include inorganic fine particles, such as silica, mica, talc, clay, carbon, carbonates (e.g., calcium carbonate, magnesium carbonate), oxides (e.g., aluminum oxide, titanium oxide, zinc oxide, iron oxide), ceramics (e.g., ferrite), and mixtures thereof.

[0065] The organic additive may be, for example, at least one substance selected from the group consisting of resins and rubbers. Examples of resins and rubbers include phenolic resins, melamine resins, urea resins, alkyd resins, epoxy resins, unsaturated polyester resins, polyurethane resins, polyethylene resins (e.g., high-density polyethylene, medium-density polyethylene, and low-density polyethylene), polypropylene resins, polystyrene resins, acrylic resins, polyvinyl alcohol, acrylamide resins, silicone resins, natural rubber, and synthetic rubber. The fine cellulose fiber composition may also contain a functional compound as an organic additive. Examples of functional compounds include pigments, UV absorbers, antioxidants, antistatic agents, and surfactants.

[0066] The fine cellulose fiber composition of the present embodiment has excellent storage stability, in other words, its quality is less likely to deteriorate than conventional compositions, and therefore it can be used in various applications in which fine cellulose fiber compositions are used. [Example]

[0067] The present embodiment will be described below with reference to examples, but the present disclosure is not limited to these examples.

[0068] [Example 1] 150 g of dimethyl sulfoxide (DMSO), 16.5 g of acetic anhydride (concentration in defibration solution: 14% by mass), and 3.35 g of sulfuric acid (concentration in defibration solution: 1.87% by mass) were placed in a 300 ml sample bottle and stirred for approximately 30 seconds using a magnetic stirrer at room temperature of 23°C to prepare a defibration solution.

[0069] Next, 5.0 g of softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution and stirred for an additional 120 minutes at a room temperature of 23°C. After stirring, 250 ml of distilled water was added to the cellulose-containing defibrating solution to stop the reaction, and then an aqueous solution of tetraethylammonium hydroxide was added until the pH reached 7 to neutralize the sulfuric acid. The supernatant was then removed by centrifugation. Note that the centrifugation speed in each operation was 12,000 rpm, and the centrifugation time was 50 minutes.

[0070] An additional 1350 ml of distilled water and 1350 ml of ethanol were added and stirred until uniformly dispersed, then centrifuged to remove the supernatant. The same procedure was repeated three times for washing. After washing by centrifugation, distilled water was added and the total weight was diluted to 1000 g.

[0071] Next, 1000 g of an aqueous dispersion of fine cellulose fibers having a uniform sulfate ester group concentration of 0.5% by mass was obtained by stirring for 3 minutes using a mixer (G5200, manufactured by Biolomix). The obtained aqueous dispersion of fine cellulose fibers was then dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai) to obtain 5 g of dried fine cellulose fibers.

[0072] The same procedure was repeated three times to obtain 15 g of dried fine cellulose fibers. Next, 15 g of the dried fine cellulose fibers were processed in a dry grinder (Wonder Blender WB1, manufactured by Osaka Chemical Co., Ltd.) for 3 minutes to obtain fine cellulose fiber powder.

[0073] Furthermore, 10 parts by mass of a mixed powder of disodium hydrogen phosphate and sodium dihydrogen phosphate (molar ratio of disodium hydrogen phosphate:sodium dihydrogen phosphate = 3:2) was added to 100 parts by mass of the obtained fine cellulose fiber powder and mixed in a mortar. The obtained fine cellulose fiber composition was designated as Sample No. 1.

[0074] [Example 2] A fine cellulose fiber powder was obtained by the same operation as in Example 1. Furthermore, 1 part by mass of a mixed powder of disodium hydrogen phosphate and sodium dihydrogen phosphate (molar ratio of disodium hydrogen phosphate:sodium dihydrogen phosphate = 3:2) was added to 100 parts by mass of the obtained fine cellulose fiber powder, and mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 2.

[0075] [Example 3] A fine cellulose fiber powder was obtained by the same operation as in Example 1. Furthermore, 1 part by mass of sodium acetate was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 3.

[0076] [Example 4] The same procedure as in Example 1 was carried out to obtain a fine cellulose fiber powder. Furthermore, 1 part by mass of a salt of acetic acid and tetraethylammonium hydroxide (TEAH) (tetraethylammonium acetate) was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 4. Tetraethylammonium acetate was obtained by neutralizing an aqueous acetic acid solution with tetraethylammonium hydroxide to a pH of 7, followed by evaporating the water.

[0077] [Example 5] The same procedure as in Example 1 was carried out to obtain a fine cellulose fiber powder. Further, 0.5 parts by mass of tetraethylammonium acetate was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 5.

[0078] [Example 6] A fine cellulose fiber powder was obtained in the same manner as in Example 1, except that the neutralization reagent was changed from an aqueous tetraethylammonium hydroxide solution to a mixed aqueous solution of betaine (trimethylglycine) and sodium hydroxide. The molar ratio of betaine to sodium hydroxide, betaine (mol) / sodium hydroxide (mol), was 1 / 1.

[0079] Furthermore, 1 part by mass of a mixed powder of disodium hydrogen phosphate and sodium dihydrogen phosphate (molar ratio of disodium hydrogen phosphate:sodium dihydrogen phosphate = 3:2) was added to 100 parts by mass of the obtained fine cellulose fiber powder and mixed in a mortar. The obtained fine cellulose fiber composition was designated as Sample No. 6.

[0080] [Example 7] The same procedure as in Example 6 was carried out to obtain a fine cellulose fiber powder. Furthermore, 1 part by mass of sodium acetate was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 7.

[0081] [Example 8] The same procedure as in Example 6 was carried out to obtain a fine cellulose fiber powder. Furthermore, 1 part by mass of ammonium acetate was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 8.

[0082] [Example 9] The same procedure as in Example 6 was carried out to obtain a fine cellulose fiber powder. Furthermore, 1 part by mass of ammonium carbonate was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 9.

[0083] [Example 10] The same procedure as in Example 6 was carried out to obtain a fine cellulose fiber powder. Furthermore, 1 part by mass of ammonium hydrogen carbonate was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 10.

[0084] [Example 11] The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous tetraethylammonium hydroxide solution to an aqueous sodium hydroxide solution, and fine cellulose fiber powder was obtained.

[0085] Furthermore, 10 parts by mass of a mixed powder of disodium hydrogen phosphate and sodium dihydrogen phosphate (molar ratio of disodium hydrogen phosphate:sodium dihydrogen phosphate = 3:2) was added to 100 parts by mass of the obtained fine cellulose fiber powder and mixed in a mortar. The obtained fine cellulose fiber composition was designated as Sample No. 11.

[0086] [Example 12] The same procedure as in Example 11 was carried out to obtain a fine cellulose fiber powder. Furthermore, 1 part by mass of a mixed powder of disodium hydrogen phosphate and sodium dihydrogen phosphate (molar ratio of disodium hydrogen phosphate:sodium dihydrogen phosphate = 3:2) was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 12.

[0087] [Example 13] The same procedure as in Example 11 was carried out to obtain a fine cellulose fiber powder. Furthermore, 1 part by mass of tetraethylammonium acetate was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 13.

[0088] [Example 14] The same procedure as in Example 11 was carried out to obtain a fine cellulose fiber powder. Further, 0.5 parts by mass of tetraethylammonium acetate was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 14.

[0089] [Example 15] The same procedure as in Example 11 was carried out to obtain a fine cellulose fiber powder. Furthermore, 1 part by mass of ammonium acetate was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 15.

[0090] [Example 16] The same procedure as in Example 11 was carried out to obtain a fine cellulose fiber powder. Furthermore, 1 part by mass of ammonium carbonate was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 16.

[0091] [Example 17] The same procedure as in Example 11 was carried out to obtain a fine cellulose fiber powder. Furthermore, 1 part by mass of ammonium hydrogen carbonate was added to 100 parts by mass of the obtained fine cellulose fiber powder, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 17.

[0092] [Comparative Example 1] The same procedure as in Example 1 was carried out, except that the neutralization reagent was changed from an aqueous tetraethylammonium hydroxide solution to an aqueous hexadecyltrimethylammonium hydroxide solution, to obtain Sample No. 1c, which is a powder of fine cellulose fibers. The fine cellulose fibers obtained in Comparative Example 1 had poor dispersibility in water, so the fine cellulose fibers were prone to settling in water. In Comparative Examples 1 to 7, no salt was added after producing the powder of fine cellulose fibers.

[0093] Comparative Example 2 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous solution of tetraethylammonium hydroxide to an aqueous solution of sodium hydroxide, and sample No. 2c, which was a powder of fine cellulose fibers, was obtained.

[0094] Comparative Example 3 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous tetraethylammonium hydroxide solution to an aqueous monoethylamine solution, and sample No. 3c, which was a powder of fine cellulose fibers, was obtained.

[0095] Comparative Example 4 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous solution of tetraethylammonium hydroxide to an aqueous solution of diethylamine, and sample No. 4c, which was a powder of fine cellulose fibers, was obtained.

[0096] Comparative Example 5 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous tetraethylammonium hydroxide solution to an aqueous triethylamine solution, and sample No. 5c, which was a powder of fine cellulose fibers, was obtained.

[0097] Comparative Example 6 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous tetraethylammonium hydroxide solution to an aqueous monoethanolamine solution, and sample No. 6c, which was a powder of fine cellulose fibers, was obtained.

[0098] Comparative Example 7 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous solution of tetraethylammonium hydroxide to an aqueous solution of diethanolamine, and sample No. 7c, which was a powder of fine cellulose fibers, was obtained.

[0099] [Comparative Example 8] A slurry of fine cellulose fibers (Na neutralized, containing carbamide groups) obtained according to Example 1 of JP 2021-42350 was dried for 72 hours using a freeze dryer (FDU-2110, manufactured by Tokyo Rikakikai) to obtain a dried fine cellulose fiber body, and the dried fine cellulose fiber body was then processed for 3 minutes in a dry grinder (Wonder Blender WB1, manufactured by Osaka Chemical) to obtain a powder of fine cellulose fiber, Sample No. 8c.

[0100] [Amount of sulfur introduced] The amount of sulfur incorporated into the fine cellulose fiber in the sample was quantified by combustion absorption-IC method using an ICS-1500 manufactured by Nippon Dionex Co., Ltd. Dried fine cellulose fiber (0.01 g) was placed on a magnetic board and burned in a circular furnace (1350 °C) in an oxygen atmosphere (flow rate: 1.5 L / min). The generated gas components were absorbed in 3% hydrogen peroxide solution (20 ml) to obtain an absorbed solution. The resulting absorbed solution was diluted to 100 ml with pure water, and the diluted solution was subjected to ion chromatography. The sulfate ion concentration (wt%) in the fine cellulose fiber was measured from the measurement results, and the amount of sulfuric acid incorporated per 1 g of fine cellulose fiber (mmol / g) was calculated. The dried fine cellulose fiber was obtained by drying the sample in an atmosphere at 105 °C until it reached a constant weight.

[0101] [Average fiber width] The average fiber width of the fine cellulose fibers in the samples obtained in the examples and comparative examples was measured by measuring the fiber widths of 50 arbitrarily selected fibers using an atomic force microscope (SPM-9700HT, manufactured by Shimadzu Corporation) and calculating the arithmetic mean value. The evaluation samples were prepared by the following method.

[0102] A sample was weighed to obtain 3 g of fine cellulose fiber, and the sample was added to 1000 g of distilled water. The mixture was stirred for 3 minutes using a mixer (G5200, Biolomix) to obtain a 0.3% by mass uniform aqueous dispersion of fine cellulose fiber (fine cellulose fiber aqueous dispersion). A high-pressure homogenizer (M-110EH-30, Microfluidics) equipped with a 200 μm auxiliary processing module and an 87 μm interaction chamber was then used to perform high-dispersion processing by three passes at 200 MPa. Next, 149.0 g of distilled water was added to 1.0 g of the 0.3% by mass uniform aqueous dispersion of fine cellulose fiber after high-dispersion processing, and the mixture was stirred for 3 minutes using a mixer (G5200, Biolomix) to obtain a 0.002% by mass uniform aqueous dispersion of fine cellulose fiber. Next, 30 μL of a 0.002 mass% uniform aqueous dispersion of fine cellulose fibers was dropped onto a natural mica (natural muscovite) substrate (15 mm x 15 mm x 0.15 mm thick) using a micropipette, and the substrate was allowed to dry naturally for 0.5 hours to obtain an evaluation sample.

[0103] [Preparation of fine cellulose fiber aqueous dispersion] Aqueous dispersions of fine cellulose fibers were prepared using the samples obtained in the Examples and Comparative Examples, and samples obtained in the Examples and Comparative Examples after storing at high temperature (80°C).

[0104] The sample was weighed so that the fine cellulose fiber content was 0.6 g, and the sample was added to distilled water weighed so that the total weight including the sample was 100 g. The sample was stirred for 3 minutes using a mixer (G5200, manufactured by Biolomix) to obtain a 0.6% by mass uniform aqueous dispersion of fine cellulose fiber (aqueous dispersion of fine cellulose fiber).

[0105] [viscosity] The viscosities of the fine cellulose fiber aqueous dispersions prepared from the samples obtained in the Examples and Comparative Examples, and from the samples obtained in the Examples and Comparative Examples after storing them at high temperatures (80°C), were determined by degassing under the following conditions, leaving them to stand for 24 hours, and then recording the viscosities (N=3) 10 minutes after the start of viscosity measurement (after rotation started) using a B-type viscometer and calculating the average value.

[0106] 100 g of the aqueous dispersion of fine cellulose fiber was degassed for 10 seconds using a degassing device (Awatori Rentaro ARE-310, manufactured by Thinky) and allowed to stand for 24 hours. Subsequently, viscosity measurements were performed at rotation speeds of 6 rpm and 60 rpm using a B-type viscometer (DV-II+, manufactured by Brookfield), and the viscosity was recorded 10 minutes after the start of measurement (after the start of rotation). Viscosity measurements of three aqueous dispersions of fine cellulose fiber prepared separately using the same method were recorded (N=3), and the average value of the three measurements was used as the viscosity of the aqueous dispersion of fine cellulose fiber. The measurements were performed in an environment where the temperature of the aqueous dispersion was 25°C.

[0107] [pH (hydrogen ion concentration)] The pH of the fine cellulose fiber aqueous dispersions prepared from the samples obtained in the Examples and Comparative Examples, and from the samples obtained in the Examples and Comparative Examples after storing them at high temperature (80°C), was determined under the following conditions.

[0108] 100 g of the fine cellulose fiber aqueous dispersion was degassed for 10 seconds using a degassing device (Awatori Rentaro ARE-310, manufactured by Thinky) and allowed to stand for 24 hours. Subsequently, the pH was measured using a pH meter (905 Titrando, manufactured by Metrohm), and the pH was recorded 10 minutes after the start of the measurement. The pH measurements of three fine cellulose fiber aqueous dispersions prepared separately using the same method were recorded (N=3), and the average value of the three measurements was used as the pH of the fine cellulose fiber aqueous dispersion. The measurements were carried out in an environment where the temperature of the aqueous dispersion was 25°C.

[0109] [Storage stability] In order to determine the storage stability at high temperatures in the powder state and in the aqueous dispersion state, the following tests were carried out.

[0110] <Storage stability in powder form> First, the viscosity and pH of the aqueous dispersion of microfibrillated cellulose fiber prepared by the above-mentioned method using the samples obtained in the Examples and Comparative Examples without storing them at high temperatures were measured by the above-mentioned measuring methods. The physical properties measured using the samples not stored at high temperatures were defined as the initial physical properties.

[0111] Another sample was placed in a powder state in an oven kept at a stable temperature of 80°C, and removed after 12 or 24 hours to serve as a sample after high-temperature storage (12 hours or 24 hours of high-temperature storage). The samples after 24 hours of high-temperature storage were visually observed, and samples with no coloration were rated as not colored, and samples with coloration such as yellow or brown were rated as colored.

[0112] The viscosity and pH of the fine cellulose fiber aqueous dispersion prepared by the method described above were measured using the samples after high-temperature storage. The physical properties measured using the samples after high-temperature storage were defined as the physical properties after 12 hours of high-temperature storage and the physical properties after 24 hours of high-temperature storage.

[0113] Stability was judged as good (AA) if the viscosity measured at 6 rpm was 3000 mPa·s or higher and the pH was 4 or higher after 24 hours of high-temperature storage. Stability was judged as poor (BB) if the viscosity measured at 6 rpm was less than 1000 mPa·s and the pH was less than 4 after 24 hours of high-temperature storage.

[0114] <Storage stability in aqueous dispersion> First, the viscosity and pH of the aqueous dispersion of microfibrillated cellulose fiber prepared by the above-mentioned method using the samples obtained in the Examples and Comparative Examples without storing them at high temperatures were measured by the above-mentioned measuring methods. The physical properties measured using the samples not stored at high temperatures were defined as the initial physical properties.

[0115] Next, the samples obtained in the Examples and Comparative Examples were used without being stored at high temperatures, and the aqueous dispersion of fine cellulose fibers prepared by the above-mentioned method was placed in an oven stabilized at a temperature of 80°C, and removed after 12 or 24 hours to obtain the aqueous dispersion of fine cellulose fibers after high-temperature storage (12 hours or 24 hours of high-temperature storage). The viscosity and pH of the aqueous dispersion after high-temperature storage were measured using the above-mentioned measurement methods. The physical properties measured using the aqueous dispersion after high-temperature storage were defined as the physical properties after 12 hours of high-temperature storage and the physical properties after 24 hours of high-temperature storage.

[0116] Stability was judged as good (AA) if the viscosity measured at 6 rpm was 3000 mPa·s or higher and the pH was 4 or higher after 24 hours of high-temperature storage. Stability was judged as poor (BB) if the viscosity measured at 6 rpm was less than 1000 mPa·s and the pH was less than 4 after 24 hours of high-temperature storage.

[0117] In the overall evaluation of storage stability, a product that exhibited good (AA) storage stability in both the powder state and the aqueous dispersion state was evaluated as having particularly excellent storage stability.

[0118] The microfibrillated cellulose fibers, sulfur content of the microfibrillated cellulose fiber compositions, and average fiber width of the samples obtained in the Examples and Comparative Examples are shown in Tables 1-1 and 1-2, and the types and amounts of salts added to the microfibrillated cellulose fibers in Examples 1 to 17 are shown in Table 2. Tables 3-1 and 3-2 show the storage stability of the powdered samples obtained in the Examples and Comparative Examples, and Tables 4-1 and 4-2 show the storage stability of the aqueous dispersions of the samples obtained in the Examples and Comparative Examples. In the tables, a viscosity (mPa / s) of 0 means that the viscosity was below the lower limit of the measurement range (100 mPa / s at a rotation speed of 6 rpm, 10 mPa / s at a rotation speed of 60 rpm), and therefore could not be measured.

[0119] [Table 1-1]

[0120] [Table 1-2]

[0121] [Table 2]

[0122] [Table 3-1]

[0123] [Table 3-2]

[0124] [Table 4-1]

[0125] [Table 4-2]

[0126] In all Examples, the storage stability of the obtained aqueous dispersion was excellent. This is thought to be due to the effect of containing a salt having a buffering action. Examples 1 to 10 are n+ At least a portion of the compound is a specific quaternary ammonium cation, and the compound contains a salt with a buffering effect, so that the aqueous dispersion has excellent storage stability, and the powder also has excellent storage stability.

[0127] Examples 8 to 10 and 15 to 17 are examples in which the salt having a buffering effect is not disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium acetate, or a quaternary ammonium acetate, and discoloration occurred when stored in powder form. On the other hand, Comparative Examples 1 to 8, which do not correspond to the present embodiment, were clearly inferior in storage stability.

[0128] The upper and / or lower limits of the numerical ranges described herein can be arbitrarily combined to define a preferred range. For example, the upper and lower limits of the numerical ranges can be arbitrarily combined to define a preferred range, the upper limits of the numerical ranges can be arbitrarily combined to define a preferred range, and the lower limits of the numerical ranges can be arbitrarily combined to define a preferred range. Furthermore, in this application, numerical ranges expressed using the symbol "to" include the numerical values ​​written before and after the symbol "to" as the upper and lower limits, respectively.

[0129] Although the present embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and even if there are design changes within the scope that do not deviate from the gist of this disclosure, they are included in this disclosure.

Claims

1. A fine cellulose fiber composition comprising fine cellulose fibers having sulfate ester groups represented by the following general formula (1) and a salt having a buffering effect, The salt having a buffering effect is at least one salt selected from disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium acetate, and acetate salts of quaternary ammonium. Fine cellulose fiber composition. 【Chemistry 1】 (In the general formula (1), n ​​is an integer of 1 or more and 3 or less, and M ｎ+ is an n-valent cation, at least a portion of the M n+ is a cation selected from the group consisting of alkali metal ions and quaternary ammonium cations derived from at least one selected from the group consisting of choline, tetramethylammonium, tetraethylammonium, tetrapropylammonium, benzyltrimethylammonium, trimethylglycine, carnitine, acetylcarnitine, and lauryldimethylaminoacetic acid, and the wavy lines represent bonding sites to other atoms.

2. The fine cellulose fiber composition described in claim 1, wherein at least a portion of the M n+ is a cation selected from the group consisting of sodium ions and quaternary ammonium cations derived from at least one type selected from the group consisting of tetraethylammonium and trimethylglycine.

3. The fine cellulose fiber composition according to claim 1, wherein the salt having a buffering effect is contained in an amount of 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the fine cellulose fibers.

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