JP7162422B2 - H-type carboxylated cellulose nanofiber - Google Patents

Description

The present invention relates to H-type carboxylated cellulose nanofibers.

When the cellulose raw material is treated in the presence of 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter also referred to as "TEMPO") and sodium hypochlorite, which is an inexpensive oxidizing agent, , carboxyl groups can be efficiently introduced onto the surface of cellulose microfibrils. When the carboxyl group-introduced cellulose is treated in water with a mixer or the like, a highly viscous and transparent aqueous dispersion of cellulose nanofibers can be obtained.

As described above, since carboxyl groups are introduced into the surface of the cellulose nanofibers, the carboxyl groups can be used as starting points to freely modify the surface. In addition, since cellulose nanofibers are in the form of a dispersion, they can be modified by blending them with water-soluble polymers or by combining them with organic or inorganic pigments. Furthermore, cellulose nanofibers can be made into sheets or fibers. Due to these characteristics, the development of new high-performance products applying cellulose nanofibers to high-performance packaging materials, transparent organic substrate members, high-performance fibers, separation membranes, regenerative medicine materials, etc., is being studied.

As an example of the new highly functional product, Patent Document 1 proposes a spray composition containing carboxylated cellulose fibers and water. Since the carboxylated cellulose fibers contained in the composition for spraying described in Patent Document 1 have not undergone a desalting step, it is presumed to be in the sodium salt form from the manufacturing procedure.

Japanese Unexamined Patent Application Publication No. 2010-37200

Patent Literature 1 describes that there are additives whose functions deteriorate in the presence of salts. Therefore, when carboxylated cellulose fibers are used in a spray composition, the carboxylated cellulose fibers are preferably desalted and converted to an acid form.
However, acid-type carboxylated cellulose nanofibers obtained by acid-treating carboxylated cellulose fibers with a mineral acid such as hydrochloric acid have a low shear rate region (hereinafter also referred to as a “low shear region”), Viscosity tended to be low. Therefore, when used in spray compositions, a thickener is sometimes added to prevent dripping.
Therefore, the development of acid-type carboxylated cellulose nanofibers with low shear and high viscosity is desired.

An object of the present invention is to provide acid-type carboxylated cellulose nanofibers with high viscosity in the low shear range.

As a result of intensive studies on the above problems, the present inventors found that acid-type carboxylated cellulose nanofibers obtained by desalting with a cation exchange resin can solve the above problems, and have completed the present invention. Arrived.
That is, the present inventors provide the following [1] to [4].
[1] A carboxylated cellulose nanofiber having a carboxyl group in at least a portion of the constituent units constituting the cellulose molecular chain, wherein the viscosity in an aqueous dispersion having a content of 0.95 to 1.05% by mass is 30 H-type carboxylated cellulose nanofibers (hereinafter also referred to as “nanofibers”) that are more than 925 Pa·s and not more than 100,000 Pa·s at a shear rate of 0.003 to 0.01 s ⁻¹ at ° C.
[2] The above [1], wherein at least part of the cellulose molecular chain is composed of a structural unit having a carboxyl group in which the carbon atom having a primary hydroxyl group at the C6 position of the glucopyranose unit is selectively oxidized. of H-type carboxylated cellulose nanofibers.
[3] The H-type carboxylated cellulose according to [1] or [2] above, wherein the amount of carboxyl groups is 0.6 to 2.0 mmol/g with respect to the absolute dry mass of the carboxylated cellulose nanofibers. nanofibers.
[4] The H-type carboxylated cellulose according to [1] or [2] above, wherein the amount of carboxyl groups is 0.8 to 2.0 mmol/g with respect to the absolute dry mass of the carboxylated cellulose nanofibers. nanofibers.

According to the present invention, it is possible to provide acid-type carboxylated cellulose nanofibers having a low shear region and high viscosity.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in detail with reference to its preferred embodiments. In the present specification, "H-type carboxylated cellulose nanofiber" refers to carboxylated cellulose nanofiber obtained by desalting a metal salt such as sodium salt and converting it into an acid form.

[1. Nanofiber]
The nanofibers of the present invention are H-type carboxylated cellulose nanofibers. In addition, the nanofiber of the present invention has a carboxyl group in at least a part of the constituent units constituting the cellulose molecular chain, and the viscosity in an aqueous dispersion having a carboxyl group content of 0.95 to 1.05% by mass is 30. °C, at a shear rate of 0.003 to 0.01 s ^-1 , it exceeds 925 Pa·s and is 100,000 Pa·s or less.
Therefore, when the nanofiber of the present invention is used, for example, in a composition for spraying, dripping can be prevented without using other thickening agents or even with a small amount of other thickening agents. .

The nanofiber of the present invention has a viscosity exceeding 925 Pa s at a shear rate of 0.003 to 0.01 s ⁻¹ at 30° C. in an aqueous dispersion having a content of 0.95 to 1.05% by mass. is 100,000 Pa·s or less, preferably 930 to 50,000 Pa·s, more preferably 950 to 25,000 Pa·s. The lower limit of viscosity is 925 Pa.s. s and 930 Pa.s. s or more is preferable, and 950 Pa·s or more is more preferable. The upper limit is 100,000 Pa.s. s or less and 50,000 Pa.s or less. s or less, preferably 25,000 Pa.s or less. s or less is more preferable.
In addition, the viscosity is adjusted by, for example, adding water to nanofibers to prepare an aqueous dispersion of 0.95 to 1.05% by mass, and measuring the aqueous dispersion with a viscoelastic rheometer (eg, "MCR301", (manufactured by Anton Paar) at a predetermined shear rate.

The nanofibers of the present invention preferably have an average fiber length of 200 to 2000 nm, more preferably 250 to 1500 nm, even more preferably 300 to 1000 nm, even more preferably 550 to 1000 nm. preferable.
The nanofiber of the present invention preferably has an average fiber diameter of 1.50 to 1000 nm, more preferably 2.00 to 750 nm, even more preferably 2.50 to 500 nm. 0.85 to 500 nm is even more preferred.

The average fiber length of carboxylated cellulose nanofibers can be calculated as follows. Carboxylated cellulose nanofibers can be immobilized on mica sections, 200 fiber lengths can be measured using atomic force microscopy (AFM), and the length (weighted) average fiber length can be calculated. The fiber length is measured within an arbitrary length range using image analysis software WinROOF (manufactured by Mitani Shoji Co., Ltd.).
Also, the average fiber diameter of the carboxylated cellulose nanofibers can be calculated as follows. A diluted carboxylated cellulose nanofiber aqueous dispersion is prepared so that the carboxylated cellulose nanofiber concentration is 0.001% by mass. This diluted dispersion is spread thinly on a mica sample stage and dried by heating at 50° C. to prepare an observation sample. The weighted average fiber diameter can be calculated by measuring the cross-sectional height of the shape image observed with an atomic force microscope (AFM).

In the nanofiber of the present invention, at least a portion of the cellulose molecular chain is preferably composed of structural units having a carboxyl group in which the carbon atom having a primary hydroxyl group at the C6 position of the glucopyranose unit is selectively oxidized. . The cellulose molecular chain may be composed only of structural units having a carboxyl group obtained by selectively oxidizing the carbon atom having a primary hydroxyl group at the C6 position of the glucopyranose unit.
Here, the glucopyranose unit refers to a structural unit represented by the following formula (0).

The nanofiber of the present invention preferably has a carboxyl group content of 0.6 to 2.0 mmol/g, more preferably 0.8 to 2.0 mmol/g, relative to the absolute dry mass of the carboxylated cellulose nanofiber. more preferably 1.2 to 2.0 mmol/g. When the amount of carboxyl groups is 0.6 mmol/g or more, carboxyl groups are introduced to the surface of the cellulose molecular chains, and electrostatic repulsion can be imparted, and nanofibers can be produced by fibrillation. . Further, when the amount of carboxyl groups is 0.8 mmol/g or more, sufficient carboxyl groups are introduced to the surface of the cellulose molecular chains, and nanofibers can be easily produced by fibrillation.
The carboxyl group content can be measured as follows. 60 ml of a 0.5% by weight slurry (aqueous dispersion) of carboxylated cellulose are prepared. After adjusting the pH to 2.5 by adding a 0.1 M hydrochloric acid aqueous solution to the prepared slurry, a 0.05 N sodium hydroxide aqueous solution is added dropwise and the electrical conductivity is measured until the pH reaches 11. From the amount of sodium hydroxide (a) consumed in the neutralization step of a weak acid with a slow change in conductivity, the amount of carboxyl groups can be calculated using the following formula:
Carboxyl group amount [mmol/g carboxylated cellulose] = a [ml] x 0.05/carboxylated cellulose mass [g]
In addition, the amount of carboxyl groups of the carboxylated cellulose nanofiber and the amount of carboxyl groups of the carboxylated cellulose are usually the same value.

[2. Production method]
Carboxylated cellulose nanofibers can be produced, for example, as follows. A cellulose raw material is oxidized to prepare oxidized cellulose (hereinafter also referred to as "oxidation treatment"), the prepared oxidized cellulose is defibrated (hereinafter also referred to as "fibrillation treatment"), and the defibrated oxidized cellulose is treated with cations. Nanofibers can be produced by desalting with an exchange resin (hereinafter also referred to as "desalting").
Acid-type carboxylated cellulose nanofibers can also be produced by desalting the prepared oxidized cellulose or hydrolyzed oxidized cellulose with a cation exchange resin, followed by fibrillation. In the following description, the case of producing acid-type carboxylated cellulose nanofibers by desalting with a cation exchange resin after fibrillation will be described.

[2-1. Oxidation treatment]
Oxidation treatment is a treatment for preparing oxidized cellulose by oxidizing a cellulose raw material. The oxidation method is not particularly limited, but a method using an oxidizing agent in the presence of an N-oxyl compound, a bromide, an iodide, or a mixture thereof is preferred. When the cellulose raw material is oxidized by this method, a structural unit having a carboxyl group can be obtained in which the carbon atom having a primary hydroxyl group at the C6 position of the glucopyranose unit constituting the cellulose molecular chain is selectively oxidized.
The partial structure of oxidized cellulose obtained by this method is shown in the following general formula (1).

（一般式（１）中、Ｍ_１はカチオン塩を示す。）

(In general formula (1), M ₁ represents a cation salt.)

Examples of cation salts represented by M1 in general formula ( ₁ ) include alkali metal salts such as sodium salts and potassium salts, phosphonium salts, imidazolinium salts, ammonium salts and sulfonium salts.

Natural cellulose has a microfibril structure in which a large number of linear cellulose molecular chains converge through hydrogen bonding. When cellulose is oxidized using an N-oxyl compound, as described above, the carbon atom having a primary hydroxyl group at the C6 position of the glucopyranose unit constituting the cellulose molecular chain is selectively oxidized to a carboxyl group via an aldehyde group. . Therefore, carboxyl groups are introduced at a high density on the surface of the microfibril structure. The introduced carboxyl groups have a repulsive action, and cellulose nanofibers separated one by one can be obtained by defibration.

Cellulose raw materials include wood-derived kraft pulp or sulfite pulp, powdered cellulose obtained by pulverizing them with a high-pressure homogenizer, mill, or the like, or microcrystalline cellulose powder obtained by refining them by chemical treatment such as acid hydrolysis. In addition, plant-derived cellulose raw materials such as kenaf, hemp, rice, bagasse, and bamboo can also be used. From the viewpoint of mass production and cost, it is preferable to use powdered cellulose, microcrystalline cellulose powder, or chemical pulp such as kraft pulp or sulfite pulp. When chemical pulp is used, it is preferable to remove lignin by subjecting it to a known bleaching treatment. As the bleached pulp, for example, bleached kraft pulp or bleached sulfite pulp having a brightness (ISO 2470) of 80% or more can be used.

Powdered cellulose is rod-shaped particles made of microcrystalline or crystalline cellulose obtained by removing the non-crystalline portion of wood pulp by acid hydrolysis, followed by pulverization and sieving. In powdered cellulose, the polymerization degree of cellulose is about 100 to 500, the crystallinity of powdered cellulose is 70 to 90% by X-ray diffraction method, and the volume average particle diameter by laser diffraction particle size distribution device is usually 100 μm or less. and preferably 50 μm or less. Such powdered cellulose may be prepared by purifying and drying, grinding and sieving the undegraded residue obtained after acid hydrolysis of the screened pulp, or by KC Floc® (Nippon Paper Industries Co., Ltd.). (manufactured by Asahi Kasei Chemicals), Ceolus (registered trademark) (manufactured by Asahi Kasei Chemicals), and Avicel (registered trademark) (manufactured by FMC).

Bleaching methods include chlorine treatment (C), chlorine dioxide bleaching (D), alkali extraction (E), hypochlorite bleaching (H), hydrogen peroxide bleaching (P), alkaline hydrogen peroxide treatment stage ( Ep), alkaline hydrogen peroxide/oxygen treatment stage (Eop), ozone treatment (Z), chelate treatment (Q), etc. can be combined. For example, C/DEHD, ZEDP, Z/D-Ep-D, Z/D-Ep-DP, D-Ep-D, D-Ep-D- Sequences such as P, D-Ep-PD, Z-Eop-DD, Z/D-Eop-D, Z/D-Eop-DD, etc. can be performed. Note that "/" in the sequence means that the processing before and after "/" is performed continuously without cleaning.

In addition, the above-mentioned cellulose raw material can be used as a cellulose raw material after being finely divided by a dispersing device such as a high-speed rotating type, colloid mill type, high pressure type, roll mill type, ultrasonic type, etc., or a wet high pressure or ultrahigh pressure homogenizer. can also

N-oxyl compounds are compounds that can generate nitroxy radicals. As the N-oxyl compound, any compound can be used as long as it is a compound that undergoes the desired oxidation reaction. Examples of N-oxyl compounds include compounds represented by the following general formulas (2) to (5) and (7) and compounds represented by the following formula (6).

（一般式（２）中、Ｒ^１～Ｒ^４は、同一又は異なっていてもよい炭素原子数１～４のアルキル基を示し、Ｒ^５は、水素原子又はヒドロキシル基を示す。）

(In general formula (2), R ¹ to R ⁴ represent an alkyl group having 1 to 4 carbon atoms which may be the same or different, and R ⁵ represents a hydrogen atom or a hydroxyl group.)

（一般式（３）～（５）中、Ｒ^６は、炭素原子数１～４の直鎖状又は分岐状の炭化水素基を示す。）

(In general formulas (3) to (5), R ⁶ represents a linear or branched hydrocarbon group having 1 to 4 carbon atoms.)

（一般式（７）中、Ｒ^７～Ｒ^８は、同一若しくは異なっていてもよい、水素原子又は炭素原子数１～６の直鎖状若しくは分岐状のアルキル基を示す。）

(In general formula (7), R ⁷ to R ⁸ represent a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms, which may be the same or different.)

Examples of alkyl groups having 1 to 4 carbon atoms represented by R ¹ to R ⁴ in general formula (2) include methyl group, ethyl group, propyl group and butyl group. Among them, a methyl group or an ethyl group is preferable.
Examples of linear or branched hydrocarbon groups having 1 to 4 carbon atoms represented by R ⁶ in general formulas (3) to (5) include methyl group, ethyl group, n-propyl group, Examples include isopropyl, n-butyl, s-butyl and t-butyl groups. Among them, a methyl group or an ethyl group is preferable.
In general formula (7), linear or branched alkyl groups having 1 to 6 carbon atoms represented by R ⁷ to R ⁸ include, for example, methyl group, ethyl group, n-propyl group and isopropyl group. , n-butyl group, s-butyl group, t-butyl group, n-pentyl group and n-hexyl group. Among them, a methyl group or an ethyl group is preferable.

Examples of compounds represented by the general formula (2) include 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter also referred to as “TEMPO”), or 4-hydroxy-2 , 2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter also referred to as “4-hydroxy TEMPO”).
The N-oxyl compound may be a derivative of TEMPO or 4-hydroxy TEMPO. Derivatives of 4-hydroxy TEMPO include, for example, the compound represented by the general formula (3), that is, the hydroxyl group of 4-hydroxy TEMPO has a linear or branched hydrocarbon group having 4 or less carbon atoms. Derivatives obtained by etherification with alcohol, and compounds represented by general formula (4) or (5), ie, derivatives obtained by esterification with carboxylic acid or sulfonic acid, can be mentioned.
When etherifying 4-hydroxy TEMPO, if an alcohol having 4 or less carbon atoms is used, the resulting derivative becomes water-soluble regardless of the presence or absence of saturated or unsaturated bonds in the alcohol, and is good as an oxidation catalyst. function.

When the N-oxyl compound is a compound represented by the formula (6), that is, a compound in which the amino group of 4-amino TEMPO is acetylated, it is imparted with appropriate hydrophobicity, is inexpensive, and can be uniformly oxidized. It is preferable because cellulose can be obtained. Further, the N-oxyl compound is preferably a compound represented by the general formula (7), that is, an azaadamantane-type nitroxy radical, because uniform oxidized cellulose can be obtained in a short time.

The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount that can sufficiently oxidize the cellulose raw material to the extent that the resulting oxidized cellulose can be made into nanofibers. For example, it is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, still more preferably 0.01 to 0.5 mmol with respect to 1 g of absolute dry cellulose raw material.

Bromides used in the oxidation of cellulosic raw materials are compounds containing bromine, examples of which include alkali metal bromides that can be dissociated and ionized in water. Also, iodides are compounds containing iodine, examples of which include alkali metal iodides.
The amount of bromide or iodide used can be adjusted within a range capable of promoting the desired oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, still more preferably 0.5 to 5 mmol, relative to 1 g of absolute dry cellulose raw material.

As the oxidizing agent, for example, known oxidizing agents such as halogens, hypohalous acids, halogenous acids, perhalogenates or salts thereof, halogen oxides and peroxides can be used. Among them, sodium hypochlorite is preferable because it is inexpensive and has less environmental load.
The amount of the oxidizing agent to be used may be any amount as long as it performs the oxidation reaction. .5 to 25 mmol.

Since the oxidation reaction of the cellulose raw material proceeds efficiently even under relatively mild conditions, the reaction temperature may be room temperature of about 15 to 30°C. As the reaction progresses, carboxyl groups are generated in the cellulose, resulting in a decrease in the pH value of the reaction solution. In order to allow the oxidation reaction to proceed efficiently, an alkaline solution such as an aqueous sodium hydroxide solution may be added to the reaction system in a timely manner to maintain the pH value of the reaction solution at about 9-12, preferably about 10-11. preferable. Water is preferable as the reaction medium because it is easy to handle and less likely to cause side reactions.

The reaction time in the oxidation reaction can be appropriately set according to the progress of oxidation, and is usually about 0.5 to 6 hours, preferably about 0.5 to 4 hours.

Moreover, the oxidation reaction may be carried out in two steps. For example, the cation salt of oxidized cellulose obtained by filtration after the completion of the reaction in the first step is again oxidized under the same or different reaction conditions, thereby being inhibited by the salt produced as a by-product in the reaction in the first step. carboxyl groups can be efficiently introduced into the cellulose raw material.

In the oxidized cellulose obtained by the above steps, the carboxyl group introduced into the cellulose raw material is usually an alkyl metal salt such as a sodium salt. Before the following desalting treatment or fibrillation treatment, the alkali metal salt of oxidized cellulose may be replaced with other cation salt such as phosphonium salt, imidazolinium salt, ammonium salt and sulfonium salt. Substitutions can be carried out by known methods.

Another example of the oxidation method is a method of contacting a cellulose raw material with an ozone-containing gas. This oxidation reaction oxidizes at least carbon atoms having hydroxyl groups at the 2- and 6-positions of the glucopyranose ring and causes degradation of the cellulose chain.

The ozone concentration in the ozone-containing gas is preferably 50-250 g/m ³ , more preferably 50-220 g/m ³ . The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by mass, more preferably 5 to 30 parts by mass, when the solid content of the cellulose raw material is 100 parts by mass. The ozone treatment temperature is preferably 0 to 50°C, more preferably 20 to 50°C. The ozone treatment time is not particularly limited, but is usually about 1 to 360 minutes, preferably about 30 to 360 minutes. When the ozone treatment conditions are within these ranges, cellulose can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved.

After the ozone treatment, additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the post-oxidation treatment is not particularly limited, but examples thereof include chlorine-based compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, the additional oxidation treatment can be performed by dissolving these oxidizing agents in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and immersing the cellulose raw material in the solution.

[2-2. defibration treatment]
The defibration treatment is a treatment for fibrillating oxidized cellulose. Oxidized cellulose has carboxyl groups introduced by oxidation treatment, so that it can be easily made into nanofibers by fibrillation treatment.

As the defibration treatment, for example, after sufficiently washing the oxidized cellulose with water, it can be carried out as a physical treatment using a known apparatus such as a high-speed shearing mixer or a high-pressure homogenizer. Examples of the types of defibration equipment include high-speed rotation type, colloid mill type, high pressure type, roll mill type, and ultrasonic type. These devices may be used alone, or two or more of them may be used in combination.

When using a high-speed shear mixer, the shear rate is preferably 1000 sec ^-1 or higher. When the shear rate is 1000 sec ⁻¹ or more, the aggregate structure is small and nanofibers can be formed uniformly.
When using a high-pressure homogenizer, the applied pressure is preferably 50 MPa or higher, more preferably 100 MPa or higher, and even more preferably 140 MPa or higher. When treated with a wet high-pressure or ultra-high-pressure homogenizer at this pressure, nanofiber formation proceeds efficiently, and carboxylated cellulose nanofibers can be obtained efficiently.

Oxidized cellulose is subjected to fibrillation treatment as an aqueous dispersion such as water. If the concentration of oxidized cellulose in the aqueous dispersion is high, the viscosity may excessively increase during the defibration process, which may result in failure to defibrate uniformly, or the apparatus may stop. Therefore, the concentration of oxidized cellulose must be appropriately set according to the treatment conditions for oxidized cellulose. As an example, the concentration of oxidized cellulose is preferably 0.3 to 50% (w/v), more preferably 0.5 to 10% (w/v), and 1.0 to 5% (w/v). More preferred.

[2-3. Desalting treatment]
The desalting treatment is a treatment for desalting the defibrated oxidized cellulose with a cation exchange resin. By this treatment, the cationic salt of the defibrated oxidized cellulose is substituted with protons, so that acid-type carboxylated cellulose nanofibers can be obtained. Since a cation exchange resin is used, unnecessary by-products such as sodium chloride are not generated, and after desalting using a cation exchange resin, the cation exchange resin is filtered through a metal mesh or the like to remove it. An aqueous dispersion of proton-substituted acid-type carboxylated cellulose nanofibers is obtained as a filtrate.

The cation exchange resin is the object to be removed as a filtrate with a metal mesh or the like, and the carboxylated cellulose nanofibers are difficult to remove due to the diameter of the metal mesh or the like, and almost all of the carboxylated cellulose nanofibers are contained in the filtrate. Therefore, the decrease in yield is extremely small.
The filtrate contains a large amount of carboxylated cellulose nanofibers with short fiber length. In addition, since the filtrate does not need to be washed or dehydrated, the acid-type carboxylated cellulose nanofibers are less likely to aggregate. Therefore, it is presumed that the dispersion of carboxylated cellulose nanofibers will have a high viscosity in the low shear region if it is not subjected to alkaline hydrolysis treatment.

For the carboxylated cellulose nanofiber salt, the aqueous dispersion obtained in the fibrillation step can be directly subjected to the desalting step. In addition, water can be added as needed to lower the concentration.

As the cation exchange resin, both strongly acidic ion exchange resins and weakly acidic ion exchange resins can be used as long as the counterion is H ^{2 +} . Among them, it is preferable to use a strongly acidic ion exchange resin. Examples of strongly acidic ion exchange resins and weakly acidic ion exchange resins include those obtained by introducing sulfonic acid groups or carboxyl groups into styrene resins or acrylic resins.
The shape of the cation exchange resin is not particularly limited, and various shapes such as fine granules (granules), membranes, and fibers can be used. Among them, the granular form is preferable from the viewpoint of efficiently desalting the carboxylated cellulose nanofiber salt and facilitating separation after the desalting treatment. A commercial product can be used as such a cation exchange resin. Commercially available products include, for example, Amberjet 1020, Amberjet 1024, Amberjet 1060, Amberjet 1220 (manufactured by Organo Corporation), Amberlite IR-200C, Amberlite IR-120B (manufactured by Tokyo Organic Chemical Co., Ltd.), Lewatit SP 112. , S100 (manufactured by Bayer), GEL CK08P (manufactured by Mitsubishi Chemical), Dowex 50W-X8 (manufactured by Dow Chemical) and the like.

For the desalting treatment, for example, a granular cation exchange resin and an aqueous dispersion of a carboxylated cellulose nanofiber salt are mixed, and the carboxylated cellulose nanofiber salt and the cation are separated while stirring and shaking as necessary. It can be carried out by separating the cation exchange resin from the aqueous dispersion after contacting the exchange resin for a certain period of time.

The concentration of the aqueous dispersion and the ratio to the cation exchange resin are not particularly limited, and those skilled in the art can appropriately set them from the viewpoint of efficient proton substitution. As an example, the concentration of the aqueous dispersion is preferably 0.05 to 10% by mass. If the concentration of the aqueous dispersion is less than 0.05% by mass, the time required for proton substitution may be too long. If the concentration of the aqueous dispersion exceeds 10% by mass, a sufficient effect of proton substitution may not be obtained.
The contact time is also not particularly limited, and can be appropriately set by those skilled in the art from the viewpoint of efficient proton substitution. For example, it can be carried out by contacting for 0.2 to 4 hours.

At this time, after contacting the carboxylated cellulose nanofiber salt or oxidized cellulose with an appropriate amount of cation exchange resin for a sufficient time, the cation exchange resin is removed as a filter with a metal mesh or the like, thereby removing the A salt treatment can be performed.

[3. Application]
The nanofibers of the present invention can be used in spray compositions, rubber reinforcing materials, resin reinforcing materials, cosmetics, medical products, foods, beverages, paints, and the like. Among others, it is preferably used in a spray composition that takes advantage of the characteristics of high viscosity in a low shear region.

(Spray composition)
The spray composition contains the above nanofibers and water. Depending on the application of the spray, the spray composition may also contain functional additives.
Since the nanofibers have a high viscosity in the low shear region, the spray composition can prevent dripping with no or a small amount of a thickening agent.

Examples of functional additives include surfactants, oils, moisturizers, organic fine particles, inorganic fine particles, preservatives, deodorants, fragrances, organic solvents and the like. These can be selected according to the application of the composition for spraying.
In addition, a functional additive may be used individually by 1 type, and may be used in combination of 2 or more type.

Nonionic surfactants include, for example, propylene glycol fatty acid ester, glycerin fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbit fatty acid ester, Polyethylene glycol fatty acid ester, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, polyoxyethylene alkyl ether, polyoxyethylene phytosterol, polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene lanolin, polyoxy Examples include ethylene lanolin alcohol, polyoxyethylene beeswax derivatives, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, polyoxyethylene alkylphenyl formaldehyde condensates and the like.

Examples of oils include jojoba oil, macadamia nut oil, avocado oil, evening primrose oil, mink oil, rapeseed oil, castor oil, sunflower oil, corn oil, cacao oil, coconut oil, rice bran oil, olive oil, almond oil, sesame oil, and coconut oil. Flower oil, soybean oil, camellia oil, persic oil, cottonseed oil, Japanese wax, palm oil, palm kernel oil, egg yolk oil, lanolin, natural animal and plant oils such as squalene; synthetic triglycerides, squalane, liquid paraffin, petroleum jelly, ceresin, microcrystalline wax , isoparaffin and other hydrocarbons; carnauba wax, paraffin wax, whale wax, beeswax, candelilla wax, lanolin and other waxes; higher alcohols (cetanol, stearyl alcohol, lauryl alcohol, cetostearyl alcohol, oleyl alcohol, behenyl alcohol, lanolin alcohol, hydrogenated lanolin alcohol, hexyldecanol, octyldodecanol, etc.); lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, isostearic acid, oleic acid, linolenic acid, linoleic acid, oxystearic acid, undecylenic acid, lanolin Higher fatty acids such as fatty acids, hard lanolin fatty acids, and soft lanolin fatty acids; cholesterol and derivatives thereof such as cholesteryl-octyldodecyl-behenyl; isopropyl myristate, isopropyl palmitate, isopropyl stearate, glycerol 2-ethylhexanoate, butyl stearate, etc. polar oils such as diethylene glycol monopropyl ether, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxypropylene butyl ether, and ethyl linoleate; amino-modified silicone, epoxy-modified silicone, carboxyl-modified silicone, carbinol-modified silicone, methacryl Modified silicone, mercapto-modified silicone, phenol-modified silicone, one-end reactive silicone, different functional group-modified silicone, polyether-modified silicone, methylstyryl-modified silicone, alkyl-modified silicone, higher fatty acid ester-modified silicone, hydrophilic special modified silicone, high grade Silicones such as alkoxy-modified silicones, higher fatty acid-containing silicones, and fluorine-modified silicones can be used.
The details of silicones are dimethylpolysiloxane, methylphenylpolysiloxane, methylpolysiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexanesiloxane, methylcyclopolysiloxane, octamethyltrisiloxane, decamethyl Tetrasiloxane, polyoxyethylene/methylpolysiloxane copolymer, polyoxypropylene/methylpolysiloxane copolymer, poly(oxyethylene/oxypropylene)methylpolysiloxane copolymer, methylhydrogenpolysiloxane, tetrahydrotetramethylcyclo Tetrasiloxane, stearoxymethylpolysiloxane, cethoxymethylpolysiloxane, methylpolysiloxane emulsion, highly polymerized methylpolysiloxane, trimethylsiloxysilicate, crosslinked methylpolysiloxane, crosslinked methylphenylpolysiloxane, and the like.

Moisturizing agents include polyhydric alcohols such as glyceryl trioctanoate, maltitol, sorbitol, glycerin, propylene glycol, 1,3-butylene glycol, polyethylene glycol and glycol; organic acids such as sodium pyrrolidonecarboxylate, sodium lactate and sodium citrate. and salts thereof; hyaluronic acid such as sodium hyaluronate and salts thereof; hydrolysates of yeast and yeast extracts; fermentation metabolites such as yeast cultures and lactic acid bacteria cultures; water-soluble proteins such as collagen, elastin, keratin and sericin; Hydrolysates, casein hydrolysates, silk hydrolysates, peptides such as sodium polyaspartate and salts thereof; derivatives; glycosaminoglycans such as water-soluble chitin, chitosan, pectin, chondroitin sulfate and salts thereof, and salts thereof; Amino acids; Sugar amino acid compounds such as aminocarbonyl reactants; Plant extracts such as aloe and horse chestnut, trimethylglycine, urea, uric acid, ammonia, lecithin, lanolin, squalane, squalene, glucosamine, creatinine, nucleic acid-related substances such as DNA and RNA etc.

Examples of organic fine particles include latex emulsions obtained by emulsion polymerization such as styrene-butadiene copolymer latexes and acrylic emulsions, and aqueous polyurethane dispersions.
Examples of inorganic fine particles include inorganic fine particles such as zeolite, montmorillonite, asbestos, smectite, mica, fumed silica, colloidal silica, and titanium oxide.

Examples of antiseptics include methylparaben and ethylparaben.

Deodorants and fragrances include D-limonene, decylaldehyde, menthone, pulegone, eugenol, cinnamaldehyde, benzaldehyde, menthol, peppermint oil, lemon oil, orange oil, and active deodorizing ingredients extracted from plant organs (e.g. , Deodorant active ingredients extracted from each organ of oxalis, Houttuynia cordata, hemlock, ginkgo, black pine, larch, red pine, paulownia, holly osmanthus, lilac, osmanthus, butterbur, Japanese silverberry, and forsythia with water or hydrophilic organic solvent. ), etc.

Examples of organic solvents include water-soluble alcohols (methanol, ethanol, isopropanol, isobutanol, sec-butanol, tert-butanol, methyl cellosolve, ethyl cellosolve, ethylene glycol, glycerin, etc.), ethers (ethylene glycol dimethyl ether, 1,4-dioxane, tetrahydrofuran, etc.), ketones (acetone, methyl ethyl ketone), N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide and the like.

EXAMPLES The present invention will be described in detail below with reference to examples. The following examples are intended to better illustrate the present invention and are not intended to limit the present invention. Unless otherwise specified, the method for measuring physical properties is the method described above.

[Viscosity (Pa s)]: Water is added to carboxylated cellulose nanofibers to prepare an aqueous dispersion of 1.95 to 1.05% by mass, and the aqueous dispersion is measured using a viscoelastic rheometer. and measured at a given shear rate.

[Carboxyl group content]: The carboxyl group content was measured as follows. 60 ml of a 0.5% by mass slurry (aqueous dispersion) of carboxylated cellulose was prepared, and 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. The electrical conductivity was measured until From the amount (a) of sodium hydroxide consumed in the neutralization step of the weak acid, whose electrical conductivity changes slowly, the amount of carboxyl groups was calculated using the following formula:
Carboxyl group amount [mmol/g carboxylated cellulose] = a [ml] x 0.05/carboxylated cellulose mass [g]

[Average fiber length (nm)]: Carboxylated cellulose nanofibers were fixed on a mica section, the fiber length of 200 fibers was measured using an atomic force microscope (AFM), and the length (weighted) average fiber length was calculated. The fiber length was measured using image analysis software WinROOF (manufactured by Mitani Shoji Co., Ltd.).

[Average fiber diameter (nm)]: A diluted carboxylated cellulose nanofiber aqueous dispersion was prepared so that the concentration of the carboxylated cellulose nanofibers was 0.001% by mass. This diluted dispersion was spread thinly on a mica sample stage and dried by heating at 50° C. to prepare an observation sample. The cross-sectional height of the shape image observed with an atomic force microscope (AFM) was measured to calculate the weighted average fiber diameter.

(Reference example 1)
5 g (absolute dry) of bleached softwood unbeaten pulp (manufactured by Nippon Paper Industries Co., Ltd.) was added to 500 ml of an aqueous solution in which 78 mg (0.5 mmol) of TEMPO (manufactured by Sigma Aldrich) and 754 mg (7.4 mmol) of sodium bromide were dissolved, Stir until the pulp is evenly dispersed. After adding 14 ml of a 2M sodium hypochlorite aqueous solution to the reaction system, the pH was adjusted to 10.3 with a 0.5N hydrochloric acid aqueous solution to initiate an oxidation reaction. Since the pH in the system decreased during the reaction, a 0.5N sodium hydroxide aqueous solution was successively added to maintain the pH at 10. After reacting for 2 hours, the mixture was filtered through a glass filter and thoroughly washed with water to obtain oxidized cellulose having a carboxyl group content of 1.60 mmol/g.

Next, the resulting slurry of oxidized cellulose was adjusted to 1% (w/v) with water and treated with an ultrahigh pressure homogenizer (20°C, 140 MPa) three times to produce a transparent gel-like carboxylated cellulose nanofiber salt. A dispersion (1% (w/v)) was obtained.

A cation exchange resin (“Amberjet 1024” manufactured by Organo Co., Ltd.) was added to the resulting carboxylated cellulose nanofiber salt dispersion, and the mixture was brought into contact with the mixture while stirring at 20° C. for 0.3 hours. Thereafter, the cation exchange resin and the aqueous dispersion were separated with a metal mesh (100 mesh opening) to obtain acid-type carboxylated cellulose nanofibers (nanofibers).

The resulting 1.00% by mass aqueous dispersion of acid-type carboxylated cellulose nanofibers had a viscosity of 925 Pa s under conditions of shear rate (0.00417 s ⁻¹ , 30° C.), and (0.00671 s ⁻¹ , 30° C.) was 920 Pa·s. Table 1 shows the results.
The average fiber length of the obtained acid-type carboxylated cellulose nanofibers was 549 nm, and the average fiber diameter was 2.83 nm.

(Comparative example 1)
Carboxylated cellulose nanofibers were obtained in the same manner as in Reference Example 1, except that the desalting step was changed as follows.
A 10% hydrochloric acid aqueous solution was added to the carboxylated cellulose nanofiber salt dispersion until the pH reached 2.4, and the mixture was stirred at 20° C. for 0.4 hours to bring into contact. After that, washing and dehydration treatment were repeated three times, followed by filtration. Water was added to the filtrate to adjust the concentration to 1.0% (w/v), and treated twice with an ultrahigh pressure homogenizer (20°C, 140 MPa) to disperse transparent gel-like H-type carboxylated cellulose nanofibers. A liquid (1% (w/v)) was obtained.

The resulting 1.00% by mass aqueous dispersion of carboxylated cellulose nanofibers had a viscosity of 336 Pa s under conditions of shear rate (0.00417 s ⁻¹ , 30° C.), and (0.00671 s ⁻¹ , 30° C.) was 350 Pa·s. Table 1 shows the results.
Moreover, the obtained H-type carboxylated cellulose nanofibers had an average fiber length of 503 nm and an average fiber diameter of 2.55 nm.

(Example 1)
5 g (absolute dry) of bleached softwood unbeaten pulp (manufactured by Nippon Paper Industries Co., Ltd.) was added to 500 ml of an aqueous solution in which 78 mg (0.5 mmol) of TEMPO (manufactured by Sigma Aldrich) and 754 mg (7.4 mmol) of sodium bromide were dissolved, Stir until the pulp is evenly dispersed. After adding 11 ml of a 2M sodium hypochlorite aqueous solution to the reaction system, the pH was adjusted to 10.3 with a 0.5N hydrochloric acid aqueous solution to initiate an oxidation reaction. Since the pH in the system decreased during the reaction, a 0.5N sodium hydroxide aqueous solution was successively added to maintain the pH at 10. After reacting for 1.5 hours, the mixture was filtered through a glass filter and thoroughly washed with water to obtain oxidized cellulose having a carboxyl group content of 1.23 mmol/g.

Next, the resulting slurry of oxidized cellulose was adjusted to 1% (w/v) with water and treated twice with an ultrahigh pressure homogenizer (20°C, 140 MPa) to produce a transparent gel-like carboxylated cellulose nanofiber salt. A dispersion (1% (w/v)) was obtained.

A cation exchange resin (“Amberjet 1024” manufactured by Organo Co., Ltd.) was added to the resulting carboxylated cellulose nanofiber salt dispersion, and the mixture was brought into contact with the mixture while stirring at 20° C. for 0.3 hours. Thereafter, the cation exchange resin and the aqueous dispersion were separated with a metal mesh (100 mesh opening) to obtain acid-type carboxylated cellulose nanofibers (nanofibers).

The resulting 1.00% by mass aqueous dispersion of acid-type carboxylated cellulose nanofibers had a viscosity of 18300 Pa s under conditions of shear rate (0.00417 s ⁻¹ , 30° C.), and (0.00671 s ⁻¹ , 30° C.) was 17800 Pa·s. Table 1 shows the results.
The average fiber length of the obtained acid-type carboxylated cellulose nanofibers was 624 nm, and the average fiber diameter was 3.11 nm.

(Example 2)
5 g (absolute dry) of bleached softwood unbeaten pulp (manufactured by Nippon Paper Industries Co., Ltd.) was added to 500 ml of an aqueous solution in which 78 mg (0.5 mmol) of TEMPO (manufactured by Sigma Aldrich) and 754 mg (7.4 mmol) of sodium bromide were dissolved, Stir until the pulp is evenly dispersed. After adding 12 ml of a 2M sodium hypochlorite aqueous solution to the reaction system, the pH was adjusted to 10.3 with a 0.5N hydrochloric acid aqueous solution to initiate an oxidation reaction. Since the pH in the system decreased during the reaction, a 0.5N sodium hydroxide aqueous solution was successively added to maintain the pH at 10. After reacting for 2 hours, the mixture was filtered through a glass filter and thoroughly washed with water to obtain oxidized cellulose having a carboxyl group content of 1.50 mmol/g.

Next, the resulting slurry of oxidized cellulose was adjusted to 1% (w/v) with water and treated with an ultrahigh pressure homogenizer (20°C, 140 MPa) three times to produce a transparent gel-like carboxylated cellulose nanofiber salt. A dispersion (1% (w/v)) was obtained.

A cation exchange resin (“Amberjet 1024” manufactured by Organo Co., Ltd.) was added to the resulting carboxylated cellulose nanofiber salt dispersion, and the mixture was brought into contact with the mixture while stirring at 20° C. for 0.3 hours. Thereafter, the cation exchange resin and the aqueous dispersion were separated with a metal mesh (100 mesh opening) to obtain acid-type carboxylated cellulose nanofibers (nanofibers).

The resulting 1.00% by mass aqueous dispersion of acid-type carboxylated cellulose nanofibers had a viscosity of 995 Pa s under conditions of shear rate (0.00417 s ⁻¹ , 30° C.), and (0.00671 s ⁻¹ , 30° C.) was 970 Pa·s. Table 1 shows the results.
The average fiber length of the obtained acid-type carboxylated cellulose nanofibers was 570 nm, and the average fiber diameter was 2.85 nm.

(Example 3)
5 g (absolute dry) of bleached softwood unbeaten pulp (manufactured by Nippon Paper Industries Co., Ltd.) was added to 500 ml of an aqueous solution in which 78 mg (0.5 mmol) of TEMPO (manufactured by Sigma Aldrich) and 754 mg (7.4 mmol) of sodium bromide were dissolved, Stir until the pulp is evenly dispersed. After adding 6 ml of a 2M sodium hypochlorite aqueous solution to the reaction system, the pH was adjusted to 10.3 with a 0.5N hydrochloric acid aqueous solution to initiate an oxidation reaction. Since the pH in the system decreased during the reaction, a 0.5N sodium hydroxide aqueous solution was successively added to maintain the pH at 10. After reacting for 0.5 hours, the mixture was filtered through a glass filter and thoroughly washed with water to obtain oxidized cellulose having a carboxyl group content of 0.60 mmol/g.

Next, the resulting slurry of oxidized cellulose was adjusted to 1% (w/v) with water and treated twice with an ultrahigh pressure homogenizer (20°C, 140 MPa) to produce a transparent gel-like carboxylated cellulose nanofiber salt. A dispersion (1% (w/v)) was obtained.

A cation exchange resin (“Amberjet 1024” manufactured by Organo Co., Ltd.) was added to the resulting carboxylated cellulose nanofiber salt dispersion, and the mixture was brought into contact with the mixture while stirring at 20° C. for 0.3 hours. Thereafter, the cation exchange resin and the aqueous dispersion were separated with a metal mesh (100 mesh opening) to obtain acid-type carboxylated cellulose nanofibers (nanofibers).

The resulting 1.00% by mass aqueous dispersion of acid-type carboxylated cellulose nanofibers had a viscosity of 24100 Pa s under conditions of shear rate (0.00417 s ⁻¹ , 30° C.), and (0.00671 s ⁻¹ , 30° C.) was 23300 Pa·s. Table 1 shows the results.
The average fiber length of the obtained acid-type carboxylated cellulose nanofibers was 840 nm, and the average fiber diameter was 3.22 nm.

As can be seen from Table 1, in the H-type carboxylated cellulose nanofibers prepared by desalting with a cation exchange resin, when the carboxyl group amount is 1.50 mmol / g, 0.00417 or 0.00671 s ^-1 is 995 or 970 Pa s in the low shear region (see Example 2), and when the carboxyl group amount is 1.23 mmol / g, it is 18300 or 17800 Pa s (see Example 1), and the carboxyl group amount is 0 In the case of 0.60 mmol/g, the viscosity was as high as 24100 or 23300 Pa·s (see Example 3). Moreover, when the amount of carboxyl groups was 1.60 mmol/g, it was 925 or 920 Pa·s (see Reference Example 1).

On the other hand, the H-type carboxylated cellulose nanofibers prepared by desalting with hydrochloric acid have a low carboxyl group content of 0.00417 or 0.00671 s ⁻¹ when the amount of carboxyl groups is 1.60 mmol / g as in Reference Example 1. The viscosity was as low as 336 or 350 Pa·s in the shear region (see Comparative Example 1). From this, it was found that the physical properties of the resulting H-type carboxylated cellulose nanofibers, especially the viscosity in the low shear region, differed depending on the desalting process. Therefore, H-type carboxylated cellulose nanofibers can be expected to be widely used by changing the desalting process according to the application.

Claims (3)

Carboxylated cellulose nanofibers having carboxyl groups in at least some of the structural units constituting the cellulose molecular chain,
The viscosity of the aqueous dispersion with a content of 1.00% by mass is more than 925 Pa s and 50,000 Pa s or less at 30 ° C. and shear rates of 0.00417 s ^-1 and 0.00671 s ^-1 ,
The average fiber length is 550 nm to 2000 nm ,
H-type carboxylated cellulose nanofibers, wherein the amount of carboxyl groups is 0.6 to 2.0 mmol/g relative to the absolute dry mass of the carboxylated cellulose nanofibers. 2. The H-type carboxyl according to claim 1, wherein at least part of the cellulose molecular chain is composed of structural units having a carboxyl group in which the carbon atom having the primary hydroxyl group at the C6 position of the glucopyranose unit is selectively oxidized. modified cellulose nanofibers. The H-type carboxylated cellulose nanofiber according to claim 1 or 2, wherein the amount of carboxyl groups is 0.8 to 2.0 mmol/g relative to the absolute dry weight of the carboxylated cellulose nanofiber.