JP7103850B2 - Carboxymethylated cellulose nanofibers - Google Patents

Description

The present invention relates to carboxymethylated cellulose nanofibers. More specifically, the present invention relates to carboxymethylated cellulose nanofibers, which have a high degree of crystallinity of cellulose type I, exhibit high transparency when used as an aqueous dispersion, and have a small loss tangent (high elasticity).

Carboxymethylated cellulose is a derivative of cellulose, and is obtained by ether-bonding a carboxymethyl group to a part of hydroxyl groups in glucose residues constituting the skeleton of cellulose. As the amount of carboxymethyl groups increases (ie, the degree of carboxymethyl substitution increases), the carboxymethylated cellulose becomes soluble in water. On the other hand, by adjusting the degree of carboxymethyl substitution to an appropriate range, the fibrous shape of carboxymethylated cellulose can be maintained even in water. Carboxymethylated cellulose having a fibrous shape can be converted into nanofibers having a nanoscale fiber diameter by mechanically defibrating (Patent Document 1).

As a method for producing carboxymethylated cellulose, generally, cellulose is treated with an alkali (mercerization) and then treated with an etherifying agent (also referred to as carboxymethylating agent) (carboxymethylation, also referred to as etherification). Known methods include a method in which both mercerization and carboxymethylation are carried out using water as a solvent, and a method in which both mercerization and carboxymethylation are carried out in a solvent mainly containing an organic solvent (Patent Document 2). It is known that the former is called "water medium method" and the latter is called "solvose method".

As a method for producing cellulose nanofibers having a nanoscale fiber diameter, not only mechanical defibration of carboxymethylated cellulose but also mechanical defibration of cellulose having a carboxyl group introduced is known (Patent Document 3). ..

International Publication No. 2014/088072 JP-A-2017-149901 Japanese Unexamined Patent Publication No. 2008-1728

It is known that the aqueous dispersion of cellulose nanofibers obtained by defibrating cellulose having a carboxyl group introduced as described in Patent Document 3 has high transparency. On the other hand, the aqueous dispersion of cellulose nanofibers obtained by defibrating carboxymethylated cellulose obtained by the solvent method is different from the aqueous dispersion of cellulose nanofibers obtained by defibrating cellulose having a carboxyl group introduced. It was less transparent. In addition, the aqueous dispersion of cellulose nanofibers obtained by defibrating carboxymethylated cellulose obtained by the aqueous medium method uses a large amount of chemicals such as a mercerizing agent and a carboxymethylating agent in order to enhance transparency. It was necessary and had major manufacturing and economic challenges. Since transparent materials are suitable for various uses, transparency of cellulose nanofibers is required. In particular, since carboxymethylated cellulose is a highly safe material, carboxymethylated cellulose is used to make it transparent. It is required to obtain high cellulose nanofibers. An object of the present invention is to provide cellulose nanofibers having novel characteristics, which are carboxymethylated cellulose nanofibers that form highly transparent aqueous dispersions.

As a result of diligent studies on the above objectives, the present inventors performed mercellization (alkaline treatment of cellulose) under a solvent mainly containing water in carboxymethylation of cellulose, and then carboxymethylation (ether). By performing the chemical conversion under a mixed solvent of water and an organic solvent, the conventional water medium method (a method in which both marcellation and carboxymethylation are carried out using water as a solvent) and the solvent method (mercellization and carboxylation) are performed. Compared to the carboxymethylated cellulose obtained by (a method in which both methylation is performed under a solvent mainly composed of an organic solvent), a cellulose nanofiber dispersion having extremely high transparency when defibrated is obtained as a carboxymethylating agent. It was found that it can be manufactured economically with a high effective utilization rate of. Such carboxymethylated cellulose nanofibers have a relatively high degree of crystallinity of cellulose type I, have high elasticity when formed into an aqueous dispersion (small loss tangent), and exhibit unprecedented high transparency. It was a novel carboxymethylated cellulose nanofiber. In the conventional aqueous medium method, by increasing the amount of a drug such as a carboxymethylating agent to increase the degree of carboxymethyl substitution, carboxymethylated cellulose capable of forming a highly transparent nanofiber dispersion can be obtained. However, the carboxymethylated cellulose (water medium method) thus obtained had a low degree of crystallization of cellulose type I. On the other hand, the carboxymethylated cellulose obtained by performing marcellation under a solvent mainly containing water and then performing carboxymethylation under a mixed solvent of water and an organic solvent is a crystal having a high cellulose type I. It is possible to maintain high transparency while maintaining the degree of conversion, and the transparency when made into a nanofiber dispersion is much higher than that of carboxymethylated cellulose produced by the conventional solvent method, and the loss is positive. It had the characteristic of being small (high elasticity).

The present invention includes, but is not limited to, the following.
(1) The degree of crystallization of cellulose type I is 60% or more, and the loss tangent at an angular frequency of 3.87s ^-1 when an aqueous dispersion having a solid content of 1% (w / v) is 0.070 or less. A carboxymethylated cellulose nanofiber having a light transmittance of 60% or more at a wavelength of 660 nm when made into an aqueous dispersion having a solid content of 1% (w / v).
(2) The carboxymethylated cellulose nanofiber according to (1), which has an average fiber diameter of 3 nm to 500 nm.
(3) The carboxymethylated cellulose nanofiber according to (1) or (2), wherein the degree of carboxymethyl substitution is 0.60 or less.
(4) The carboxymethylated cellulose nanofiber according to any one of (1) to (3), which has a structure in which a carboxymethyl group is ether-bonded to a part of a hydroxyl group in a glucose residue constituting cellulose. ..

The present invention provides nanofibers of carboxymethylated cellulose that form highly transparent aqueous dispersions. Further, the carboxymethylated cellulose nanofiber of the present invention is characterized in that the degree of crystallinity of cellulose type I is relatively high and the loss tangent is small. When the degree of crystallinity of cellulose type I is high, the proportion of cellulose that does not dissolve in a solvent such as water and maintains the crystal structure is high, so that high viscosity can be imparted, and a thickener or the like can be imparted. It becomes suitable for viscosity adjusting applications, and when added to gel-like substances (foods, pharmaceuticals, etc.), it has an advantage of improving shape retention. Further, the small loss tangent when used as an aqueous dispersion means that the aqueous dispersion shows the properties of an elastic body more strongly than that of a viscous body, and has high gel-forming property, and is not limited to these, for example. However, when added to foods such as gummy, a feeling of elasticity can be given, and when added to paints, inks and the like, it is possible to obtain the advantage that the paints and the like do not easily drip after application.

<Nanofibers of carboxymethylated cellulose>
The present invention relates to carboxymethylated cellulose nanofibers. Carboxymethylated cellulose has a structure in which some of the hydroxyl groups in the glucose residues constituting the cellulose are ether-bonded to the carboxymethyl group.

The carboxymethylated cellulose nanofibers are those obtained by converting carboxymethylated cellulose having the above structure into nanofibers having a nanoscale fiber diameter. The carboxymethylated cellulose may take the form of a salt such as a metal salt such as a sodium salt of the carboxymethylated cellulose, and the nanofibers of the carboxymethylated cellulose may also take the form of a salt.

The nanofibers of the carboxymethylated cellulose of the present invention maintain at least a part of the fibrous shape even when dispersed in water. That is, when the aqueous dispersion of carboxymethylated cellulose nanofibers is observed with an electron microscope, a fibrous substance can be observed. Further, when the carboxymethylated cellulose nanofibers are measured by X-ray diffraction, the peak of the cellulose type I crystal can be observed.

<Crystallinity of cellulose type I>
The crystallinity of cellulose in the carboxymethylated cellulose nanofibers of the present invention is 60% or more, preferably 65% or more for crystal type I. When the crystallinity of cellulose type I is as high as 60% or more, the proportion of cellulose that does not dissolve in a solvent such as water and maintains the crystal structure is high, so that the thixotropy becomes high (thixotropy), and the thickener, etc. Becomes suitable for viscosity adjustment applications. Further, for example, when added to, for example, but not limited to, a gel-like substance (for example, food or cosmetics), there is an advantage that excellent shape retention can be imparted. The crystallinity of cellulose can be controlled by the concentration of the mercerizing agent, the temperature during treatment, and the degree of carboxymethylation. Since a high concentration of alkali is used in mercerization and carboxymethylation, type I crystals of cellulose are easily converted to type II, but they are modified by adjusting the amount of alkali (mercerizing agent) used. By adjusting the degree, the desired crystallinity can be maintained. The upper limit of the crystallinity of cellulose type I is not particularly limited. In reality, about 90% is considered to be the upper limit.

The method for measuring the crystallinity of cellulose type I of carboxymethylated cellulose nanofibers is as follows:
The sample is placed on a glass cell and measured using an X-ray diffraction measuring device (LabX XRD-6000, manufactured by Shimadzu Corporation). The crystallinity is calculated using a method such as Segal, and the diffraction intensity of the 002 surface at 2θ = 22.6 ° and 2θ = are based on the diffraction intensity of 2θ = 10 ° to 30 ° in the X-ray diffraction diagram. It is calculated by the following formula from the diffraction intensity of the amorphous portion of 18.5 °.

Xc = (I002c-Ia) / I002c × 100
Xc = Cellulose type I crystallinity (%)
I002c: 2θ = 22.6 °, diffraction intensity of 002 surface Ia: 2θ = 18.5 °, diffraction intensity of amorphous part.

The proportion of type I crystals in the nanofibers of carboxymethylated cellulose is usually the same as that in the carboxymethylated cellulose before making the nanofibers.
<Transparency in aqueous dispersion>
The nanofibers of carboxymethylated cellulose of the present invention have a feature of exhibiting high transparency when water is used as a dispersion medium as a dispersion (aqueous dispersion). In the present specification, the transparency refers to the transmittance of light having a wavelength of 660 nm when carboxymethylated cellulose nanofibers are used as an aqueous dispersion having a solid content of 1% (w / v). The method for measuring the transparency of carboxymethylated cellulose nanofibers is as follows:
A cellulose nanofiber dispersion (solid content 1% (w / v), dispersion medium: water) was prepared, and a square cell with an optical path length of 10 mm was prepared using a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation). It is used to measure the transmittance of 660 nm light.

The transparency of the carboxymethylated cellulose nanofibers of the present invention is 60% or more. It is more preferably 60 to 100%, still more preferably 70 to 100%, still more preferably 80 to 100%, still more preferably 90 to 100%. Such cellulose nanofibers can be optimally used in applications where transparency is required.

<Lost tangent in aqueous dispersion>
The carboxymethylated cellulose nanofibers of the present invention are characterized by exhibiting low loss tangent when water is used as a dispersion medium as a dispersion (aqueous dispersion). In the present specification, the loss tangent means the loss tangent at an angular frequency of 3.87s ^-1 when the carboxymethylated cellulose nanofiber is used as an aqueous dispersion having a solid content of 1% (w / v). Specifically, the method of measuring the loss tangent is as follows:
A cellulose nanofiber dispersion (solid content 1% (w / v), dispersion medium: water) is prepared and allowed to stand for 16 hours. A sample solution is placed in a dynamic viscoelasticity measuring device (Anton Pearl Co., Ltd., MCR301) and measured under the following conditions to determine the loss tangent (tan δ) at an angular frequency of 3.87s ^-1 .
Number of intervals: 1
Application: RHEOPLUS / 32 V2.62 21001935-33024
Equipment: MCR301 SN823982; FW2.66; Slot4
Measuring jig: PP25-SN5316 d = READ
Access: TU1 = P-PTD200-SN771412
Number of data points: 18
Measurement conditions: Swing angle gumma = 1%
Angular frequency omega = 100 to 0.1 1 / s logarithm.

Loss tangent at an angular frequency of 3.87s ^-1 when an aqueous dispersion having a solid content of 1% (w / v) of the carboxymethylated cellulose nanofiber of the present invention is used (also simply referred to as "loss tangent" in the present specification. (Call) is 0.070 or less. It is more preferably 0.065 or less, still more preferably 0.060 or less. The tangent loss is the tan value of the phase difference δ between the measured sinusoidal strain wave and the detection limiting stress wave in the dynamic viscoelasticity of the aqueous dispersion, and corresponds to the loss elastic modulus / storage elastic modulus. The storage elastic modulus is a component of the energy generated by external force and strain on the object that is stored inside the object, and the loss elastic modulus is a component that diffuses to the outside. It can be said that the larger the loss tangent, the stronger the viscous property, and the closer it is to 0, the stronger the elastic property. A dispersion having a loss tangent of 0.070 or less has high elasticity and high stability after deformation. Such cellulose nanofibers are not limited to these, but can be said to have a high effect of imparting shape retention, thixotropy, and elasticity to various products such as foods and paints. The lower limit of the loss tangent is not particularly limited, but in reality, it is about 0.005 or more. Carboxymethylated cellulose nanofibers that provide an aqueous dispersion showing such loss tangent can be produced, for example, by a production method described later.

<Carboxymethyl degree of substitution>
In the carboxymethylated cellulose nanofiber of the present invention, the degree of carboxymethyl substitution per anhydrous glucose unit of cellulose is preferably 0.60 or less. If the degree of substitution exceeds 0.60, it is considered that the fiber is dissolved in water and the fiber shape cannot be maintained. Considering operability, the degree of substitution is preferably 0.02 to 0.50, more preferably 0.05 to 0.50, still more preferably 0.10 to 0.40. It is more preferably 0.20 to 0.40. By introducing a carboxymethyl group into cellulose, the celluloses electrically repel each other and can be defibrated into nanofibers, but the degree of carboxymethyl substitution per anhydrous glucose unit is 0.02 or more. If it is too small, defibration may be insufficient and highly transparent cellulose nanofibers may not be obtained. In the conventional aqueous medium method, it is difficult to obtain carboxymethylated cellulose nanofibers having a cellulose type I crystallinity of 60% or more in the range of 0.20 to 0.40 carboxymethyl substitution. However, the present inventors have carboxymethylation in which the degree of carboxymethyl substitution is in the range of 0.20 to 0.40 and the degree of crystallization of cellulose type I is 60% or more by, for example, a method described later. We have found that we can produce cellulose nanofibers. The degree of carboxymethyl substitution can be adjusted by controlling the amount of the carboxymethylating agent to be reacted, the amount of the mercerizing agent, the composition ratio of water and the organic solvent, and the like.

In the present invention, the anhydrous glucose unit means individual anhydrous glucose (glucose residue) constituting cellulose. The degree of carboxymethyl substitution (also referred to as the degree of etherification) is the ratio of hydroxyl groups in glucose residues constituting cellulose that are substituted with carboxymethyl ether groups (carboxymethyl per glucose residue). The number of ether groups) is shown. The degree of carboxymethyl substitution may be abbreviated as DS.

The method for measuring the degree of carboxymethyl substitution is as follows:
Weigh about 2.0 g of the sample and place it in a 300 mL Erlenmeyer flask with a stopper. Add 100 mL of a solution of 100 mL of special grade concentrated nitric acid to 1000 mL of methanol nitrate and shake for 3 hours to convert the salt (CMC) of carboxymethylated cellulose nanofibers into H-CMC (hydrogen-type carboxymethylated cellulose nanofibers). .. Weigh 1.5 to 2.0 g of the absolutely dry H-CMC and place it in an Erlenmeyer flask with a 300 mL stopper. Wet H-CMC with 15 mL of 80% methanol, add 100 mL of 0.1N-NaOH, and shake at room temperature for 3 hours. Using phenolphthalein as an indicator, back titrate excess NaOH with 0.1 N-H ₂ SO ₄ , and calculate the degree of carboxymethyl substitution (DS value) by the following formula.
A = [(100 x F'-0.1N-H ₂ SO ₄ (mL) x F) x 0.1] / (absolute dry mass (g) of H-CMC)
Degree of substitution of carboxymethyl = 0.162 × A / (1-0.058 × A)
F': 0.1N-H ₂ SO ₄ factor F: 0.1N-NaOH factor.

The degree of carboxymethyl substitution in nanofibers of carboxymethylated cellulose is usually the same as the degree of carboxymethyl substitution in carboxymethylated cellulose before being made into nanofibers.

<Fiber diameter, aspect ratio>
The carboxymethylated cellulose nanofibers of the present invention have nanoscale fiber diameters. The average fiber diameter is preferably 3 nm to 500 nm, more preferably 3 nm to 150 nm, still more preferably 3 nm to 20 nm, still more preferably 5 nm to 19 nm, still more preferably 5 nm to 15 nm.

The aspect ratio of the carboxymethylated cellulose nanofibers of the present invention is preferably 350 or less. It is more preferably 300 or less, still more preferably less than 200, and even more preferably less than 120. When the aspect ratio is 350 or less, the fibers are not excessively long, the entanglement between the fibers is reduced, and the occurrence of lumps (lumps) of cellulose nanofibers can be reduced. Further, since the fluidity is high, it is easy to use even at a high concentration, and there is an advantage that it is easy to use even in an application requiring a high solid content. The lower limit of the aspect ratio is not particularly limited, but is preferably 25 or more, and more preferably 30 or more. When the aspect ratio is 25 or more, the fibrous shape provides an effect of improving thixotropy. The aspect ratio can be controlled by the mixing ratio of solvent and water at the time of carboxymethylation, the amount of chemicals added, and the degree of carboxymethylation.

For the average fiber diameter and average fiber length of the carboxymethylated cellulose nanofibers, use an interatomic force microscope (AFM) when the diameter is 20 nm or less, and use an electroemission scanning electron microscope (FE-SEM) when the diameter is 20 nm or more. The measurement can be performed by analyzing 200 randomly selected fibers and calculating the average. The aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length / average fiber diameter.

<Others>
The nanofibers of carboxymethylated cellulose may be in the form of a dispersion obtained after production, but may be dried if necessary, or may be redispersed in water. The drying method is not limited in any way, but for example, a freeze-drying method, a spray-drying method, a shelf-stage drying method, a drum drying method, a belt drying method, a method of thinly stretching and drying on a glass plate, a fluidized bed drying method, a microwave drying method, etc. Known methods such as the method and the heating fan type vacuum drying method can be used. After drying, it may be crushed with a cutter mill, a hammer mill, a pin mill, a jet mill or the like, if necessary. Further, the method of redispersion in water is not particularly limited, and a known disperser can be used.

The use of the carboxymethylated cellulose nanofibers is not particularly limited, but the carboxymethylated cellulose nanofibers of the present invention have the above-mentioned loss tangent of 0.070 or less and a cellulose type I crystallinity of 60%. As described above, since the transparency is 60% or more, it is excellent in fluidity, thickening, and transparency, and affects the applications in which these are required (for example, the transparency and color tone of the composition). It is considered that it can be used particularly optimally for non-thickening agents, etc.). However, it may be used for other purposes. The fields in which carboxymethylated cellulose nanofibers are used are not particularly limited, and various fields in which additives are generally used, such as foods, beverages, cosmetics, pharmaceuticals, papermaking, various chemical supplies, paints, sprays, and pesticides. , Civil engineering, construction, electronic materials, flame retardants, household goods, adhesives, cleaning agents, fragrances, lubricating compositions, etc., thickeners, gelling agents, glues, food additives, excipients, paints, etc. Can be used as additives for adhesives, additives for adhesives, additives for papermaking, abrasives, compounding materials for rubber and plastics, water retention agents, shape retention agents, muddy water conditioners, filtration aids, mud prevention agents, etc. It is thought that it can be done.

<Manufacturing method of carboxymethylated cellulose nanofibers>
Cellulose type I has a crystallinity of 60% or more, and a loss tangent at an angular frequency of 3.87s ^-1 when made into an aqueous dispersion having a solid content of 1% (w / v) is 0.070 or less, and is solid. Nanofibers of carboxymethylated cellulose having a light transmittance of 60% or more at a wavelength of 660 nm when made into an aqueous dispersion of 1% (w / v) are produced by the following method, but not limited to this. It can be produced by defibrating carboxymethylated cellulose.

In general, carboxymethylated cellulose is obtained by treating cellulose with an alkali (mercerization), and then reacting the obtained mercerized cellulose (also referred to as alkali cellulose) with a carboxymethylating agent (also referred to as etherifying agent). It can be manufactured by. The carboxymethylated cellulose capable of forming nanofibers having the above-mentioned characteristics of the present invention is subjected to mercerization (alkaline treatment of cellulose) under a solvent mainly containing water, and then carboxymethylated (also referred to as etherification). ) Can be produced by carrying out under a mixed solvent of water and an organic solvent. The carboxymethylated cellulose thus obtained can be obtained by using a conventional water medium method (a method in which both marcelation and carboxymethylation are carried out using water as a solvent) and a solvent method (both marcelation and carboxymethylation are carried out using an organic solvent). Compared to the carboxymethylated cellulose obtained by (the method performed under the main solvent), the cellulose nanofibers have high transparency and small loss tangent when defibrated while having a high effective utilization rate of the carboxymethylating agent. It can be converted into a dispersion.

<Cellulose>
In the present invention, cellulose means a polysaccharide having a structure in which D-glucopyranose (simply referred to as “glucose residue” or “anhydrous glucose”) is linked by β-1,4 bonds. Cellulose is generally classified into natural cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose excluding amorphous regions, etc., based on the origin, manufacturing method, and the like. In the present invention, any of these celluloses can be used as a raw material for mercellized cellulose, but in order to maintain a crystallinity of cellulose type I of 60% or more in carboxymethylated cellulose nanofibers, cellulose I It is preferable to use cellulose having a high degree of crystallinity of the mold as a raw material. The crystallinity of cellulose type I of the raw material cellulose is preferably 70% or more, and more preferably 80% or more. The method for measuring the crystallinity of cellulose type I is as described above.

Examples of natural cellulose include bleached pulp or unbleached pulp (bleached wood pulp or unbleached wood pulp); linters, purified linters; cellulose produced by microorganisms such as acetic acid bacteria. The raw material of bleached pulp or unbleached pulp is not particularly limited, and examples thereof include wood, cotton, straw, bamboo, hemp, jute, and kenaf. Further, the method for producing bleached pulp or unbleached pulp is not particularly limited, and a mechanical method, a chemical method, or a method in which the two are combined may be used. The bleached pulp or unbleached pulp classified according to the production method includes, for example, mechanical pulp (thermomechanical pulp (TMP), crushed wood pulp), chemical pulp (conifer unbleached sulphite pulp (NUSP), conifer bleached sulphite pulp (NBSP). ) And the like, unbleached coniferous kraft pulp (NUKP), bleached coniferous kraft pulp (NBKP), unbleached broadleaf kraft pulp (LUKP), kraft pulp such as broadleaf bleached kraft pulp (LBKP)) and the like. Further, dissolved pulp may be used in addition to the pulp for papermaking. Dissolving pulp is chemically refined pulp, which is mainly dissolved in chemicals and used as a main raw material for artificial fibers, cellophane, and the like.

Examples of the regenerated cellulose include those obtained by dissolving cellulose in a solvent such as a cuprammonium solution, a cellulose zantate solution, or a morpholine derivative and spinning it again.
The fine cellulose is obtained by subjecting a cellulosic material such as the above-mentioned natural cellulose and regenerated cellulose to a depolymerization treatment (for example, acid hydrolysis, alkali hydrolysis, enzymatic decomposition, blasting treatment, vibration ball mill treatment, etc.). Examples thereof include those obtained by mechanically processing the cellulosic material.

<Mercerization>
The above-mentioned cellulose is used as a raw material, and mercerized cellulose (also referred to as alkaline cellulose) is obtained by adding a mercerizing agent (alkali). According to the method described in the present specification, water is mainly used as a solvent in this marcelation reaction, and a mixed solvent of an organic solvent and water is used in the next carboxymethylation, so that the fiber is very defibrated. Carboxymethylated cellulose, which can be a cellulose nanofiber dispersion having high transparency, can be economically obtained.

The term "water-based solvent" as a solvent mainly uses water means a solvent containing water in a proportion higher than 50% by mass. The water in the solvent mainly containing water is preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, and more preferably 80% by mass or more. It is more preferably 90% by mass or more, and further preferably 95% by mass or more. Particularly preferably, the solvent mainly containing water is 100% by mass (that is, water) of water. The higher the proportion of water during mercerization, the higher the transparency of the cellulose nanofiber dispersion obtained by defibrating carboxymethylated cellulose. Examples of the solvent other than water (used by mixing with water) in the solvent mainly containing water include an organic solvent used as a solvent at the time of carboxymethylation in the subsequent stage. For example, alcohols such as methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol and tertiary butanol, ketones such as acetone, diethyl ketone and methyl ethyl ketone, and dioxane, diethyl ether, benzene and dichloromethane. And the like, these alone or a mixture of two or more kinds can be added to water in an amount of less than 50% by mass and used as a solvent for marcel formation. The organic solvent in the solvent mainly containing water is preferably 45% by mass or less, more preferably 40% by mass or less, further preferably 30% by mass or less, still more preferably 20% by mass or less. , More preferably 10% by mass or less, further preferably 5% by mass or less, and even more preferably 0% by mass.

Examples of the mercerizing agent include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, and any one or a combination of two or more of these can be used. The Marcel agent is not limited to this, but these alkali metal hydroxides are used in the reactor as an aqueous solution of, for example, 1 to 60% by mass, preferably 2 to 45% by mass, and more preferably 3 to 25% by mass. Can be added.

The amount of the marcel agent used is an amount capable of maintaining a degree of crystallization of cellulose type I in carboxymethylated cellulose of 60% or more, and in one embodiment, 0.1 mol or more per 100 g (absolute dry) of cellulose 2 It is preferably 5.5 mol or less, more preferably 0.3 mol or more and 2.0 mol or less, and further preferably 0.4 mol or more and 1.5 mol or less.

The amount of the solvent mainly containing water at the time of mercerization is preferably 1.5 to 20 times by mass, more preferably 2 to 10 times by mass with respect to the cellulose raw material. With such an amount, the raw materials can be easily stirred and mixed, and the reaction can be uniformly caused.

In the mercerization treatment, the bottoming material (cellulose) and a solvent mainly composed of water are mixed, and the temperature of the reactor is adjusted to 0 to 70 ° C., preferably 10 to 60 ° C., more preferably 10 to 40 ° C. Then, an aqueous solution of the mercerizing agent is added, and the mixture is stirred for 15 minutes to 8 hours, preferably 30 minutes to 7 hours, and more preferably 30 minutes to 3 hours. As a result, mercerized cellulose (alkaline cellulose) is obtained.

The pH at the time of mercerization is preferably 9 or more, whereby the mercerization reaction can proceed. The pH is more preferably 11 or more, still more preferably 12 or more, and may be 13 or more. The upper limit of pH is not particularly limited.

Mercerization can be carried out using a reactor capable of mixing and stirring each of the above components while controlling the temperature, and various reactors conventionally used for the mercerization reaction can be used. For example, a batch type agitator in which two shafts agitate and each of the above components is mixed is preferable from the viewpoint of both uniform mixing property and productivity.

<Carboxymethylation>
Carboxymethylated cellulose is obtained by adding a carboxymethylating agent (also referred to as an etherifying agent) to mercerized cellulose. According to the method described in the present specification, water is used as the main solvent for marcel formation, and a mixed solvent of water and an organic solvent is used for carboxymethylation. Carboxymethylated cellulose, which can be a cellulose nanofiber dispersion having high transparency, can be economically obtained.

Examples of the carboxymethylating agent include monochloroacetic acid, sodium monochloroacetate, methyl monochloroacetate, ethyl monochloroacetate, isopropyl monochloroacetate and the like. Of these, monochloroacetic acid or sodium monochloroacetate is preferable in terms of availability of raw materials.

The amount of the carboxymethylating agent used is an amount capable of maintaining a crystallization degree of cellulose type I of 60% or more, and preferably an amount capable of maintaining a carboxymethyl substitution degree of 0.20 to 0.40. Although not particularly limited, in one embodiment, it is preferable to add in the range of 0.5 to 1.5 mol per anhydrous glucose unit of cellulose. The lower limit of the above range is more preferably 0.6 mol or more, further preferably 0.7 mol or more, and the upper limit is more preferably 1.3 mol or less, still more preferably 1.1 mol or less. The carboxymethylating agent can be added to the reactor as an aqueous solution of, for example, 5 to 80% by mass, more preferably 30 to 60% by mass, without being dissolved, and is added in a powder state. You can also do it.

The molar ratio of the mercelling agent to the carboxymethylating agent (merselling agent / carboxymethylating agent) is generally 0.9 to 2.45 when monochloroacetic acid or sodium monochloroacetate is used as the carboxymethylating agent. Will be adopted by. The reason is that if it is less than 0.9, the carboxymethylation reaction may be insufficient, and unreacted monochloroacetic acid or sodium monochloroacetate may remain, resulting in waste, and 2.45. If the amount exceeds the above, a side reaction between the excess marcel agent and monochloroacetic acid or sodium monochloroacetate may proceed to form an alkali metal glycolic acid salt, which may be uneconomical.

In carboxymethylation, the effective utilization rate of the carboxymethylating agent is preferably 15% or more. It is more preferably 20% or more, further preferably 25% or more, and particularly preferably 30% or more. The effective utilization rate of the carboxymethylating agent refers to the ratio of the carboxymethyl group introduced into cellulose among the carboxymethyl groups in the carboxymethylating agent. By using a solvent mainly containing water for marcel formation and using a mixed solvent of water and an organic solvent for carboxymethylation, a high effective utilization rate of the carboxymethylating agent (that is, a carboxymethylating agent) It is possible to produce carboxymethylated cellulose capable of obtaining a cellulose nanofiber dispersion having high transparency when defibrated (economically) without significantly increasing the amount of the solvent used. The upper limit of the effective utilization rate of the carboxymethylating agent is not particularly limited, but in reality, the upper limit is about 80%. The effective utilization rate of the carboxymethylating agent may be abbreviated as AM.

The method for calculating the effective utilization rate of the carboxymethylating agent is as follows:
AM = (DS x number of moles of cellulose) / number of moles of carboxymethylating agent DS: degree of carboxymethyl substitution (measurement method is as described above)
Number of moles of cellulose: Pulp mass (dry mass when dried at 100 ° C. for 60 minutes) / 162
(162 is the molecular weight of cellulose per glucose unit).

The concentration of the cellulose raw material in the carboxymethylation reaction is not particularly limited, but is preferably 1 to 40% (w / v) from the viewpoint of increasing the effective utilization rate of the carboxymethylating agent.

At the same time as the addition of the carboxymethylating agent, or immediately before or after the addition of the carboxymethylating agent, an organic solvent or an aqueous solution of the organic solvent is appropriately added to the reactor, or water other than the water used for the marcelification treatment by reducing the pressure or the like. The organic solvent and the like of the above are appropriately reduced to form a mixed solvent of water and the organic solvent, and the carboxymethylation reaction is allowed to proceed under the mixed solvent of the water and the organic solvent. The timing of addition or reduction of the organic solvent may be between the end of the mercerization reaction and immediately after the addition of the carboxymethylating agent, and is not particularly limited, but for example, 30 minutes before and after the addition of the carboxymethylating agent. Within is preferable.

Examples of the organic solvent include alcohols such as methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol and tertiary butanol, ketones such as acetone, diethyl ketone and methyl ethyl ketone, and dioxane and diethyl ether. Examples thereof include benzene and methanol, and these alone or a mixture of two or more thereof can be added to water and used as a solvent for carboxymethylation. Of these, monohydric alcohols having 1 to 4 carbon atoms are preferable, and monohydric alcohols having 1 to 3 carbon atoms are more preferable because of their excellent compatibility with water.

The ratio of the organic solvent in the mixed solvent at the time of carboxymethylation is preferably 20% by mass or more, more preferably 30% by mass or more, based on the total amount of water and the organic solvent. It is more preferably 40% by mass or more, further preferably 45% by mass or more, and particularly preferably 50% by mass or more. The higher the proportion of the organic solvent, the higher the transparency of the cellulose nanofiber dispersion. The upper limit of the proportion of the organic solvent is not limited and may be, for example, 99% by mass or less. Considering the cost of the organic solvent to be added, it is preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less, still more preferably 70% by mass or less.

The reaction medium for carboxymethylation (a mixed solvent of water and an organic solvent that does not contain cellulose) has a smaller proportion of water than the reaction medium for mercerization (in other words, the proportion of the organic solvent is higher). Many) is preferable. By satisfying this range, it becomes easy to increase the carboxymethyl substitution degree while maintaining the crystallinity of the obtained carboxymethylated cellulose, and the carboxymethylated cellulose becomes a highly transparent cellulose nanofiber dispersion when defibrated. Can be obtained more efficiently. In addition, when the reaction medium for carboxymethylation has a smaller proportion of water (more proportion of organic solvent) than the reaction medium for marcellation, the transition from the marcellation reaction to the carboxymethylation reaction occurs. Another advantage is that a mixed solvent for the carboxymethylation reaction can be formed by a simple means of adding a desired amount of an organic solvent to the reaction system after the completion of the marcellation reaction.

After forming a mixed solvent of water and an organic solvent and adding a carboxymethylating agent to the mercerized cellulose, the temperature is preferably kept constant in the range of 10 to 40 ° C. for 15 minutes to 4 hours, preferably 15 Stir for about 1 minute to 1 hour. The mixing of the liquid containing mercerized cellulose and the carboxymethylating agent is preferably carried out in a plurality of times or by dropping in order to prevent the reaction mixture from becoming hot. After adding the carboxymethylating agent and stirring for a certain period of time, the temperature is raised if necessary, and the reaction temperature is set to 30 to 90 ° C., preferably 40 to 90 ° C., more preferably 60 to 80 ° C. for 30 minutes to The etherification (carboxymethylation) reaction is carried out for 10 hours, preferably 1 to 4 hours to obtain carboxymethylated cellulose.

At the time of carboxymethylation, the reactor used for mercerization may be used as it is, or another reactor capable of mixing and stirring each of the above components while controlling the temperature may be used. ..

After completion of the reaction, the remaining alkali metal salt may be neutralized with a mineral acid or an organic acid. Further, if necessary, the by-produced inorganic salts, organic acid salts and the like may be washed with hydrous methanol to remove them, and then dried, pulverized and classified to obtain carboxymethylated cellulose or a salt thereof. When washing for removing by-products, the acid type may be formed in advance to form a linear shape, and the salt type may be returned after washing. Examples of the device used for dry crushing include impact mills such as hammer mills and pin mills, medium mills such as ball mills and tower mills, and jet mills. Examples of the device used in the wet pulverization include devices such as a homogenizer, a mass colloider, and a pearl mill.

<Dissolution into nanofibers>
By defibrating the carboxymethylated cellulose obtained by the above method, it can be converted into cellulose nanofibers having a nanoscale fiber diameter.

At the time of defibration, a dispersion of carboxymethylated cellulose obtained by the above method is prepared. Water is preferable as the dispersion medium because of its ease of handling. The concentration of carboxymethylated cellulose in the dispersion at the time of defibration is preferably 0.01 to 10% (w / v) in consideration of the efficiency of defibration and dispersion.

The apparatus used for defibrating carboxymethylated cellulose is not particularly limited, but an apparatus such as a high-speed rotary type, a colloid mill type, a high-pressure type, a roll mill type, and an ultrasonic type can be used. At the time of defibration, it is preferable to apply a strong shearing force to the dispersion of carboxymethylated cellulose. In particular, in order to efficiently defibrate, it is preferable to use a wet high-pressure or ultra-high-pressure homogenizer capable of applying a pressure of 50 MPa or more to the dispersion and applying a strong shearing force. The pressure is more preferably 100 MPa or more, still more preferably 140 MPa or more. Further, prior to the defibration and dispersion treatment with a high-pressure homogenizer, the dispersion may be pretreated, if necessary, using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer. ..

A high-pressure homogenizer is a pump that pressurizes (high pressure) a fluid and ejects it from a very delicate gap provided in the flow path, so that it is emulsified and dispersed by the total energy such as collision between particles and shearing force due to pressure difference. , A device for crushing, crushing, and ultra-fine particles.

It is not clear why the above method can economically obtain cellulose nanofibers having high transparency and low loss tangent while maintaining high crystallinity of cellulose type I. Therefore, it is possible to maintain a relatively high degree of crystallinity of cellulose type I, and therefore, it is possible to maintain the fibrous shape of carboxymethylated cellulose even if the degree of carboxymethyl substitution is relatively high. Those are confirming. It is considered that the ability to increase the degree of carboxymethyl substitution while maintaining the fibrous shape (that is, the introduction of many carboxymethyl groups) leads to the improvement of the fibrillation property of carboxymethylated cellulose, which is a highly transparent nano. It is presumed to be one of the reasons why the fiber dispersion can be obtained. Also, in the above method, it is considered that the carboxymethyl group is uniformly (not locally) introduced throughout the cellulose, so that there are few places where it dissolves or swells locally, and the nanofibers are entangled with each other. Is likely to occur, and it is considered that elasticity is likely to occur. However, it is not limited to this.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Unless otherwise specified, parts and% indicate parts by mass and% by mass.

(Example 1)
To a biaxial kneader whose rotation speed is adjusted to 150 rpm, 130 parts of water and 20 parts of sodium hydroxide dissolved in 100 parts of water are added, and hardwood pulp (LBKP manufactured by Nippon Paper Industries Co., Ltd.) is added at 100 ° C. 100 parts were charged by the dry mass when dried for 60 minutes. Mercerized cellulose was prepared by stirring and mixing at 35 ° C. for 80 minutes. Further, 230 parts of isopropanol (IPA) and 60 parts of sodium monochloroacetate were added with stirring, and after stirring for 30 minutes, the temperature was raised to 70 ° C. and a carboxymethylation reaction was carried out for 90 minutes. The concentration of IPA in the reaction medium during the carboxymethylation reaction is 50%. After completion of the reaction, the reaction was neutralized with acetic acid until the pH reached 7, washed with hydrous methanol, deflated, dried and pulverized to obtain a sodium salt of carboxymethylated cellulose.

The obtained sodium salt of carboxymethylated cellulose was dispersed in water to prepare an aqueous dispersion having a solid content of 1% (w / v). This was treated three times with a 140 MPa high-pressure homogenizer to obtain a dispersion of nanofibers of carboxymethylated cellulose. The transparency and loss tangent of the obtained dispersion, the degree of carboxymethyl substitution of the cellulose nanofibers, the degree of crystallinity of cellulose type I, and the average fiber diameter were measured by the above-mentioned methods.

(Comparative Example 1)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the solvent used in the mercerization reaction was 10% water and 90% IPA, and the solvent having the same composition was also used in the carboxymethylation reaction. The obtained sodium salt of carboxymethylated cellulose was defibrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethylated cellulose.

As shown in Table 1, in Example 1 in which marcellation was carried out under a solvent mainly containing water and carboxymethylation was carried out under a mixed solvent of water and an organic solvent, the degree of crystallization of cellulose type I was 60. % Or more, and a loss tangent at an angular frequency of 3.87 s ^-1 when an aqueous dispersion having a solid content of 1% (w / v) is 0.070 or less, and a solid content of 1% (w / v). It can be seen that the carboxymethylated cellulose nanofibers having a light transmittance (transparency) of 60% or more at a wavelength of 660 nm when used as an aqueous dispersion could be produced. On the other hand, in Comparative Example 1 using the solvent method which is a conventional method, it can be seen that the degree of crystallization of cellulose type I is 60% or more, but the transparency is extremely low and the loss tangent is large. The degree of crystallization of cellulose type I of the present invention is 60% or more, and the loss tangent at an angular frequency of 3.87 s ^-1 when an aqueous dispersion having a solid content of 1% (w / v) is 0.070 or less. The nanofiber of carboxymethylated cellulose, which has a light transmittance of 60% or more at a wavelength of 660 nm when made into an aqueous dispersion having a solid content of 1% (w / v), is a new material having unprecedented characteristics. Therefore, it is expected to be a new option in applications that require a high degree of transparency, and applications that require chic properties, shape retention, and elasticity.

Claims (4)

Cellulose type I has a crystallinity of 60% or more,
The loss tangent at an angular frequency of 3.87s ^-1 when an aqueous dispersion having a solid content of 1% (w / v) is 0.070 or less.
When an aqueous dispersion having a solid content of 1% (w / v) is used, the transmittance of light having a wavelength of 660 nm is 60% or more .
Carboxymethylated cellulose nanofibers having a carboxymethyl substitution degree of 0.10 to 0.40 . The carboxymethylated cellulose nanofiber according to claim 1, wherein the average fiber diameter is 3 nm to 500 nm. The carboxymethylated cellulose nanofiber according to claim 1 or 2, wherein the degree of carboxymethyl substitution is 0.20 to 0.40 . The carboxymethylated cellulose nanofiber according to any one of claims 1 to 3, which has a structure in which a carboxymethyl group is ether-bonded to a part of a hydroxyl group of cellulose.