Microcrystalline cellulose fiber and microcrystalline cellulose fiber composition

Abstract

To provide microcellulose fiber inhibiting reduction in the viscosity and reduction in the pH when the microcellulose fiber is dispersed in water after the microcellulose fiber is stored in a powder form at high temperature.SOLUTION: One embodiment is microcellulose fiber with a sulfate group represented by general formula (1) in the figure. In general formula (1): n is an integer from 1 to 3 inclusive; Mn+ are n-valent cations, where at least some of the Mn+ are quaternary ammonium cations in which four groups bonded to nitrogen (N+) each have a main chain with 12 or less carbon atoms; and the wavy line is a binding site to another atom.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to finely divided cellulose fibers and finely divided cellulose fiber compositions. [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 sulfated cellulose fibers when stored in a powdered state at high temperatures (for example, at 50°C to 100°C). As a result, they have found that when sulfated cellulose fibers are stored in a powdered state at high temperatures and then dispersed in water, the viscosity and pH are significantly reduced (acidified) compared to when the fibers are not stored at high temperatures.

[0007] According to the studies of the present inventors, it has been found that even in the case of sulfated fibrous cellulose disclosed in Patent Document 1, when it is stored in a powder state at high temperature and then dispersed in water, the viscosity is significantly reduced and the pH is significantly reduced (acidified) compared to when it is not stored at high temperature.

[0008] Therefore, an object of the present disclosure is to provide fine cellulose fibers that suppress a decrease in viscosity and a decrease in pH when the fine cellulose fibers are stored in a powder state at high temperatures and then dispersed in water. [Means for solving the problem]

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

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

[0011] [1] Fine cellulose fibers having sulfate ester groups represented by the following general formula (1): [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 M n+ at least a portion of which are quaternary ammonium cations; The nitrogen (N +) each of the four groups bonded to the main chain has 12 or less carbon atoms, The wavy lines are the bonding sites to other atoms.) [2] Said M n+ The fine cellulose fibers according to [1], wherein at least a portion of the cations is a quaternary ammonium cation derived from a zwitterion. [3] Said M n+ The fine cellulose fibers according to [1] or [2], 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 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.) [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 ) [4] 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 fibers according to [3], wherein the group represented by the general formula (5) is a group represented by the formula (5') or (5''). [ka] [5] A fine cellulose fiber composition comprising the fine cellulose fiber according to any one of [1] to [4] and a salt having a buffering effect. [6] The salt having the buffering effect is NH4 + The fine cellulose fiber composition according to [5], which does not contain ammonium ions represented by the formula: [7] The fine cellulose fiber composition according to [5] or [6], 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. [8] The fine cellulose fiber composition according to [5], 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. [Effects of the Invention]

[0012] The present disclosure makes it possible to provide fine cellulose fibers that are inhibited from decreasing in viscosity and pH when the fine cellulose fibers are dispersed in water after being stored in a powder state at high temperatures. DETAILED DESCRIPTION OF THE INVENTION

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

[0014] One aspect of this embodiment is fine cellulose fibers having sulfate ester groups represented by the following general formula (1).

[0015] Another aspect of the present embodiment is a fine cellulose fiber composition containing the fine cellulose fibers and a salt having a buffering effect.

[0016] The microfibrillated cellulose fibers of this embodiment can suppress a decrease in viscosity and a decrease in pH when the microfibrillated cellulose fibers are stored in a powder state at high temperatures and then dispersed in water. The microfibrillated cellulose fibers of this embodiment are suppressed from decreasing in physical properties due to high-temperature storage, and therefore can be used as 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 for evaluating storage stability. This is because when microfibrillated cellulose fibers, microfibrillated cellulose fiber compositions, or aqueous dispersions thereof are stored in warehouses in summer or inside vehicles during transportation, the temperatures can reach high temperatures of, for example, 40°C to 60°C. 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 of the microfibrillated cellulose fibers were evaluated when stored at high temperatures (80°C in the examples).

[0017] The fine cellulose fiber composition of this embodiment can suppress a decrease in viscosity and a decrease in pH when the fine cellulose fiber composition is stored in powder form at high temperatures and then dispersed in water. The inventors have also investigated the stability of aqueous dispersions containing sulfated cellulose fibers when stored at high temperatures (e.g., at 50°C to 100°C). As a result, they have found that when a typical aqueous dispersion containing sulfated cellulose fibers is stored at high temperatures, its viscosity and pH are significantly decreased and its pH significantly decreased (acidified) compared to when it is not stored at high temperatures (e.g., before high-temperature storage). The fine cellulose fiber composition of this embodiment can also suppress 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. In other words, the fine cellulose fiber composition of this embodiment suppresses a decrease in physical properties when the powder of the composition is stored at high temperatures and when the aqueous dispersion is stored at high temperatures, and therefore can be used as a fine cellulose fiber composition of stable quality in a variety of usage environments and in a variety of fields.

[0018] This embodiment will be described in detail below.

[0019] (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).

[0020] [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 M n+ at least a portion of which are quaternary ammonium cations; The nitrogen (N + ) each of the four groups bonded to the main chain has 12 or less carbon atoms, The wavy lines are the bonding sites to other atoms.)

[0021] Ordinary cellulose (unmodified cellulose) is a polysaccharide in which glucose is linked via β-1,4-glycosidic bonds (C6H 10 O5) n The fine cellulose fibers in this embodiment are fibers made of modified cellulose, as is clear from the fact that they have sulfate ester groups.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] M n+ is an n-valent cation, and when n is 2 or 3, that is, M n+ If is a polyvalent cation, M n+ is two or three -OSO3 - It forms an ionic bond with M n+ As n is 1, that is, Mn+ M + (monovalent cation) is one of the preferred embodiments.

[0026] Said M n+ At least a part of the nitrogen (N + 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.

[0027] As a result of studies by the present inventors, it was found that when conventional sulfated cellulose nanofibers are stored at high temperatures 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 that constitute the sulfated cellulose nanofibers. Furthermore, it has been confirmed by analysis that the amount of sulfate ester groups bonded to cellulose in conventional sulfated cellulose nanofibers 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 nanofibers, the viscosity and pH of the aqueous dispersion are inhibited from decreasing when the powder is stored at high temperatures and then dispersed in water. This is a phenomenon not observed with tertiary amines (or their ions) or quaternary ammonium cations not included in the present embodiment. The reason for this is unclear, but the inventors speculate that the specific quaternary ammonium cations, due to their hydrophilicity and hygroscopicity, act as a desiccant within the molecules of the sulfated cellulose nanofibers, preventing water molecules from attacking the sulfate ester groups and suppressing hydrolysis of the sulfate ester groups.

[0028] The quaternary ammonium cation is preferably 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.

[0029] Said M n+ In one preferred embodiment, at least a portion of M is a quaternary ammonium cation derived from a zwitterion. 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.

[0030] 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.

[0031] The zwitterion is not particularly limited, but examples thereof include betaine (trimethylglycine), carnitine, acetylcarnitine, lauryldimethylaminoacetic acid, and the like.

[0032] 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).

[0033] [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.)

[0034] [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 )

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 4 The 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).

[0040] 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.

[0041] M n+ As mentioned above, at least a portion of M is 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.

[0042] 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.

[0043] Examples of metal ions include alkali metal ions, alkaline earth metal ions, transition metal ions, and other metal ions.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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'').

[0048] [ka]

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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)

[0054] The method for producing fine cellulose fibers is not particularly limited, and can be carried out by selecting a reagent such that at least a portion of the neutralization (neutralization of sulfate ester groups) is carried out with quaternary ammonium cations in a conventional method for producing fine cellulose fibers having sulfate ester groups. For example, when defibrating (unmodified) cellulose fibers 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.

[0055] 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.

[0056] 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.

[0057] (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.

[0058] A 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. That is, the fine cellulose fiber composition of the present embodiment is preferable because it not only has high-temperature storage stability as a powder, which is a characteristic of fine cellulose fibers described above, but also has excellent high-temperature storage stability when made into an aqueous dispersion. The inventors speculate that the reason for the excellent high-temperature storage stability when made into an aqueous dispersion is that when a salt having a buffering effect is included, the pH of the aqueous dispersion can be maintained near neutral, thereby suppressing hydrolysis of sulfate esters, specifically, the catalytic action of hydrolysis by acid.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] (Additives) The fine cellulose fiber composition may contain other additives. Furthermore, the fine cellulose fibers may be used for various purposes as a composition containing additives. The additives may be inorganic or organic.

[0065] 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.

[0066] 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.

[0067] The fine cellulose fibers and fine cellulose fiber composition of the present embodiment have excellent storage stability, in other words, there is less deterioration in quality than conventional ones, and therefore they can be used in various applications in which fine cellulose fibers are used. [Example]

[0068] The present embodiment will be described below with reference to examples, but the present disclosure is not limited to these examples.

[0069] [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.

[0070] 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 choline (choline hydroxide) solution was added until the pH reached 7 to neutralize the sulfuric acid. The supernatant was then removed by centrifugation. Note that the centrifugation speed for each step was 12,000 rpm, and the centrifugation time was 50 minutes.

[0071] 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.

[0072] 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.

[0073] The same procedure was repeated three times to obtain 15 g of dried fine cellulose fibers. The 15 g of dried fine cellulose fibers was then processed for 3 minutes in a dry grinder (Wonder Blender WB1, manufactured by Osaka Chemical Co., Ltd.) to obtain Sample No. 1, a fine cellulose fiber powder.

[0074] [Example 2] The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous choline solution to an aqueous tetrapropylammonium hydroxide solution, and sample No. 2, which was a powder of fine cellulose fibers, was obtained.

[0075] [Example 3] The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from the aqueous choline solution to an aqueous benzyltrimethylammonium hydroxide solution, and sample No. 3, which was a powder of fine cellulose fibers, was obtained.

[0076] [Example 4] The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from the aqueous choline solution to an aqueous tetraethylammonium hydroxide solution, and sample No. 4, which was a powder of fine cellulose fibers, was obtained.

[0077] [Example 5] Sample No. 5, a powder of fine cellulose fibers, was obtained in the same manner as in Example 1, except that the neutralization reagent was changed from the aqueous choline solution to a mixed aqueous solution of tetraethylammonium hydroxide and sodium hydroxide. The molar ratio of tetraethylammonium hydroxide to sodium hydroxide, tetraethylammonium hydroxide (mol) / sodium hydroxide (mol), was 1 / 1.

[0078] [Example 6] The procedure of Example 1 was repeated except that the neutralization reagent was changed from the aqueous choline solution to a mixed aqueous solution of carnitine and sodium hydroxide, to obtain Sample No. 6, a fine cellulose fiber powder. The molar ratio of carnitine to sodium hydroxide, carnitine (mol) / sodium hydroxide (mol), was 1 / 1.

[0079] [Example 7] The procedure of Example 1 was repeated except that the neutralization reagent was changed from the aqueous choline solution to a mixed aqueous solution of lauryldimethylaminoacetic acid and sodium hydroxide, to obtain Sample No. 7, a fine cellulose fiber powder. The molar ratio of lauryldimethylaminoacetic acid to sodium hydroxide, lauryldimethylaminoacetic acid (mol) / sodium hydroxide (mol), was 1 / 1.

[0080] [Example 8] The procedure of Example 1 was repeated except that the neutralization reagent was changed from the aqueous choline solution to a mixed aqueous solution of betaine (trimethylglycine) and sodium hydroxide, to obtain Sample No. 8, a fine cellulose fiber powder. The molar ratio of betaine to sodium hydroxide, betaine (mol) / sodium hydroxide (mol), was 4 / 1.

[0081] [Example 9] The procedure of Example 1 was repeated except that the neutralization reagent was changed from the aqueous choline solution to a mixed aqueous solution of betaine and sodium hydroxide, to obtain Sample No. 9, a fine cellulose fiber powder. The molar ratio of betaine to sodium hydroxide, betaine (mol) / sodium hydroxide (mol), was 1 / 1.

[0082] [Example 10] The procedure of Example 1 was repeated except that the neutralization reagent was changed from the aqueous choline solution to a mixed aqueous solution of betaine and sodium hydroxide, to obtain Sample No. 10, a fine cellulose fiber powder. The molar ratio of betaine to sodium hydroxide, betaine (mol) / sodium hydroxide (mol), was 1 / 4.

[0083] [Example 11] The procedure of Example 1 was repeated except that the neutralization reagent was changed from the aqueous choline solution to a mixed aqueous solution of betaine and sodium hydroxide, to obtain Sample No. 11, a fine cellulose fiber powder. The molar ratio of betaine to sodium hydroxide, betaine (mol) / sodium hydroxide (mol), was 1 / 9.

[0084] [Example 12] The same procedure as in Example 9 was carried out, except that the stirring time when 5.0 g of softwood kraft pulp NBKP (manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution was changed from 120 minutes to 30 minutes, and sample No. 12, a powder of fine cellulose fibers, was obtained.

[0085] [Example 13] The same procedure as in Example 9 was carried out, except that the stirring time when 5.0 g of softwood kraft pulp NBKP (manufactured by Nippon Paper Industries Co., Ltd.) was added to the defibrating solution was changed from 120 minutes to 180 minutes, and sample No. 13, a powder of fine cellulose fibers, was obtained.

[0086] [Example 14] The same procedure as in Example 4 was carried out to produce Sample No. 4, which is a powder of fine cellulose fibers. 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 Sample No. 4 and mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 14.

[0087] [Example 15] Sample No. 4, a fine cellulose fiber powder, was produced by the same procedure as in Example 4. 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 Sample No. 4, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 15.

[0088] [Example 16] The same procedure as in Example 4 was carried out to produce a fine cellulose fiber powder, Sample No. 4. Furthermore, 1 part by mass of sodium acetate was added to 100 parts by mass of Sample No. 4, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 16.

[0089] [Example 17] Sample No. 4, a powder of fine cellulose fibers, was produced by the same procedure as in Example 4. 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 Sample No. 4, and the mixture was mixed in a mortar. The resulting fine cellulose fiber composition was designated Sample No. 17. Tetraethylammonium acetate was obtained by neutralizing an aqueous acetic acid solution with tetraethylammonium hydroxide to pH 7, followed by evaporation of the water.

[0090] [Example 18] The same procedure as in Example 4 was carried out to produce a fine cellulose fiber powder, Sample No. 4. Furthermore, 0.5 parts by mass of tetraethylammonium acetate was added to 100 parts by mass of Sample No. 4, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 18.

[0091] [Example 19] Sample No. 9, a fine cellulose fiber powder, was produced by the same procedure as in Example 9. 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 Sample No. 9, and the mixture was mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 19.

[0092] [Example 20] The same procedure as in Example 9 was carried out to produce Sample No. 9, which is a fine cellulose fiber powder. Furthermore, 1 part by mass of sodium acetate was added to 100 parts by mass of Sample No. 9 and mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 20.

[0093] [Example 21] Sample No. 9, which is a fine cellulose fiber powder, was produced by the same procedure as in Example 9. Furthermore, 1 part by mass of ammonium acetate was added to 100 parts by mass of Sample No. 9 and mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 21.

[0094] [Example 22] Sample No. 9, which is a fine cellulose fiber powder, was produced by the same procedure as in Example 9. Furthermore, 1 part by mass of ammonium carbonate was added to 100 parts by mass of Sample No. 9 and mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 22.

[0095] [Example 23] The same procedure as in Example 9 was carried out to produce Sample No. 9, which is a fine cellulose fiber powder. Furthermore, 1 part by mass of ammonium hydrogen carbonate was added to 100 parts by mass of Sample No. 9 and mixed in a mortar. The obtained fine cellulose fiber composition was designated Sample No. 23.

[0096] [Comparative Example 1] The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from the aqueous choline solution to an aqueous hexadecyltrimethylammonium hydroxide solution, and a fine cellulose fiber powder, Sample No. 1c, was obtained. The fine cellulose fibers obtained in Comparative Example 1 had poor dispersibility in water, and therefore the fine cellulose fibers were prone to settling in water.

[0097] Comparative Example 2 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from the choline aqueous solution to a sodium hydroxide aqueous solution, and sample No. 2c, which was a powder of fine cellulose fibers, was obtained.

[0098] Comparative Example 3 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous choline solution to an aqueous monoethylamine solution, and sample No. 3c, which was a powder of fine cellulose fibers, was obtained.

[0099] Comparative Example 4 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous choline solution to an aqueous diethylamine solution, and sample No. 4c, which was a powder of fine cellulose fibers, was obtained.

[0100] Comparative Example 5 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous choline solution to an aqueous triethylamine solution, and sample No. 5c, which was a powder of fine cellulose fibers, was obtained.

[0101] Comparative Example 6 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous choline solution to an aqueous monoethanolamine solution, and sample No. 6c, which was a powder of fine cellulose fibers, was obtained.

[0102] Comparative Example 7 The same procedure as in Example 1 was carried out except that the neutralization reagent was changed from an aqueous choline solution to an aqueous diethanolamine solution, and sample No. 7c, which was a powder of fine cellulose fibers, was obtained.

[0103] [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.

[0104] [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.

[0105] [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.

[0106] 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.

[0107] [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).

[0108] 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).

[0109] [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.

[0110] 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.

[0111] [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.

[0112] 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.

[0113] [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.

[0114] <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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] <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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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 to 1-3, and the type and amount of salt added to the microfibrillated cellulose fibers in Examples 14 to 23 are shown in Table 2. Tables 3-1 to 3-3 show the storage stability of the powdered samples obtained in the Examples and Comparative Examples, and Tables 4-1 to 4-3 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.

[0123] [Table 1-1]

[0124] [Table 1-2]

[0125] [Table 1-3]

[0126] [Table 2]

[0127] [Table 3-1]

[0128] [Table 3-2]

[0129] [Table 3-3]

[0130] [Table 4-1]

[0131] [Table 4-2]

[0132] [Table 4-3]

[0133] In all examples, the samples obtained were excellent in storage stability in powder form. This is because the M n+ This is thought to be due to the fact that at least a part of the M is a specific quaternary ammonium cation. n+ at least a portion of which is a quaternary ammonium cation derived from a zwitterion, and Mn+ Even when the proportion of quaternary ammonium cations in the powder was small, the powder still had excellent storage stability.

[0134] The samples obtained in Examples 14 to 23 were fine cellulose fiber compositions containing fine cellulose fibers and a salt with buffering properties. Because of the salt, the samples not only had excellent storage stability in powder form, but also had excellent storage stability as aqueous dispersions. Examples 21 to 23 were examples in which the salt with buffering properties did not fall under any of disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium acetate, and quaternary ammonium acetate. These samples had excellent storage stability, but discoloration occurred when stored in powder form. On the other hand, Comparative Examples 1 to 8, which do not fall under the present embodiment, clearly had poor storage stability.

[0135] 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.

[0136] 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. Fine cellulose fibers having sulfate ester groups represented by the following general formula (1): 【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, and the M ｎ+ At least a part of the atoms in the ammonium cations is a quaternary ammonium cation represented by the following general formula (2), and the wavy lines represent bonding sites with other atoms. 【Chemistry 2】 (In general formula (2), R 1 , R 2 , and R 3 each independently represent a group having at least one partial structure selected from an ethylene oxide moiety and a glyceryl moiety, an alkyl group, or a monohydroxyalkyl group having 12 or less carbon atoms; 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′) or (3″), (4′) or (4″), or (5′) or (5″), and the group represented by —CH 2 —R 4 —Z has 12 or less carbon atoms; Two of R 1 , R 2 , R 3 , and R 4 may be bonded to each other to form a ring. 【Transformation 3】 (The wavy line indicates the bonding site with R 4 .)

2. The fine cellulose fiber described in claim 1, wherein at least a portion of the M n+ is a quaternary ammonium cation derived from one or more selected from the group consisting of carnitine and acetylcarnitine.

3. Fine cellulose fibers having sulfate ester groups represented by the following general formula (1): 【Chemistry 4】 In the general formula (1), n ​​is an integer of 1 or more and 3 or less, M n+ is an n-valent cation, and at least a part of the M n+ is a quaternary ammonium cation derived from at least one selected from the group consisting of choline, tetramethylammonium, tetraethylammonium, tetrapropylammonium, benzyltrimethylammonium, trimethylglycine, carnitine, acetylcarnitine, and lauryldimethylaminoacetic acid; The wavy lines indicate the bond sites with other atoms.)

4. A fine cellulose fiber composition comprising the fine cellulose fibers according to claim 1 and a salt having a buffering effect.

5. The salt having a buffering effect is NH ４ ＋ The fine cellulose fiber composition according to claim 4, which does not contain ammonium ions represented by the formula:

6. The fine cellulose fiber composition according to claim 4, 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.

7. The fine cellulose fiber composition according to claim 4, 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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