JP2021091895A - Cellulose nanocrystal dispersion - Google Patents

Abstract

To provide a cellulose nanocrystal dispersion that is excellent in dispersibility of cellulose nanocrystal, can express excellent barrier properties and handleability, and also has excellent productivity and economical efficiency.SOLUTION: A cellulose nanocrystal dispersion contains a sulfate group and/or a sulfo group derived from sulfuric acid treatment, and an anionic functional group derived from hydrophilicization treatment. In a water dispersion with the cellulose nanocrystal of 2 mass% in solid content, a visible light transmittance at 600 nm is 45%T or more.SELECTED DRAWING: None

Description

The present invention relates to a cellulose nanocrystal dispersion, and more specifically, to a cellulose nanocrystal dispersion capable of forming a coating film having excellent dispersibility and coatability, and excellent transparency and gas barrier property.

It has been proposed that nanocellulose is used as an advanced biomass raw material, as a functional additive, as a film composite material, and for various purposes. In particular, materials such as a film made of cellulose nanofibers (CNF) and a laminate containing cellulose nanofibers can suppress the dissolution and diffusion of gas due to hydrogen bonds between cellulose fibers and strong cross-linking interactions, so that oxygen can be suppressed. It is known to have excellent gas barrier properties such as barrier properties, and barrier materials using cellulose nanofibers have been proposed.
In order to make the cellulose fibers finer, a chemical treatment is carried out in which hydrophilic functional groups such as a carboxyl group and a phosphoric acid group are introduced into the hydroxyl groups of the cellulose in addition to the mechanical treatment. The energy required for the treatment can be reduced, and the barrier property and the dispersibility in an aqueous solvent are improved.

A dispersion liquid using such cellulose nanofibers is also known. For example, in Patent Document 1 below, the crystallinity is 70% or more, the degree of polymerization by the viscosity method using a copper ethylenediamine solution is 160 or less, and the degree of polymerization is 160 or less. A dispersion liquid in which cellulose nanofibers having a fiber diameter of 50 nm or less are dispersed in a dispersion medium has been proposed.
Further, Patent Document 2 below proposes a dispersion in which cellulose nanofibers having a number average fiber length of 250 nm or less and a number average fiber diameter of 2 to 5 nm are dispersed in a dispersion medium.

Japanese Unexamined Patent Publication No. 2013-256546 International release 2014/061485

However, in the cellulose nanofiber dispersion liquid described in Patent Document 1, as a step of preparing the cellulose nanofibers to be dispersed in the dispersion medium, a step of reducing the viscosity of the cellulose nanofibers chemically treated using a TEMPO catalyst. Or, a micronization step for making nanofibers is required, and the productivity and economic efficiency are not sufficiently satisfied. In addition, cellulose nanofibers are not satisfactory in terms of gas barrier properties due to their long fiber length, and it is possible to obtain high gas barrier properties by shortening the fiber length, but further treatment is required for that purpose. , Inferior in economy.
Further, in Patent Document 2 above, cellulose nanofibers having a short fiber length capable of lowering the viscosity are prepared in order to improve the dispersibility of the dispersion liquid, but specially for preparing cellulose nanofibers having a short fiber length. It is necessary to use various raw materials, which is also inferior in productivity and economy.

As nanocellulose having a shorter fiber length than cellulose nanofibers, cellulose nanocrystals (CNC) formed by hydrolyzing cellulose fibers with a strong acid are known. Since cellulose nanocrystals have a short fiber length, they are excellent in handleability at the time of coating and also excellent in smoothness of the coated surface. However, in general, cellulose nanocrystals are inferior in gas barrier properties to cellulose nanofibers into which a carboxyl group or the like has been introduced as described above.
The present inventors have found that cellulose nanocrystals can exhibit excellent gas barrier properties by containing a large amount of anionic functional groups (Japanese Patent Application No. 2018-177610).
However, such cellulose nanocrystals are generally solidified in the form of powder from the viewpoint of storage stability, transportability, etc., and in order to obtain a dispersion liquid, powdered cellulose nanocrystals are used as a dispersion medium while suppressing aggregation. It needs to be dispersed, and it is not satisfactory in terms of productivity and economy. Further, according to the research by the present inventors, the dispersion liquid in which such solidified (powder-like) cellulose nanocrystals are dispersed reduces the gas barrier property of the cellulose nanocrystals containing anionic functional groups. I understood.

Therefore, an object of the present invention is to provide a cellulose nanocrystal dispersion liquid which is excellent in dispersibility of cellulose nanocrystals, can exhibit excellent barrier properties and handleability, and is also excellent in productivity and economy. ..

According to the present invention, a cellulose nanocrystal dispersion containing a sulfate group and / or a sulfo group derived from a sulfuric acid treatment and an anionic functional group derived from a hydrophilic treatment, wherein the solid content of the cellulose nanocrystals is 2% by mass. Provided is a cellulose nanocrystal dispersion liquid characterized by having a visible light transmittance at 600 nm of% aqueous dispersion of 45% T or more.

In the cellulose nanocrystal dispersion of the present invention,
1. 1. The average particle size of the cellulose nanocrystals by the laser diffraction type particle size distribution measuring device of the cellulose nanocrystal dispersion is 10.1 μm or less, the median diameter is 10.6 μm or less, and the mode diameter is 10.9 μm or less.
2. The total amount of the sulfate group and / or the sulfo group and the anionic functional group is more than 0.17 mmol / g and 4.0 mmol / g or less.
3. 3. The degree of crystallinity of the cellulose nanocrystal is 60% or more, the fiber width is 50 nm or less, and the aspect ratio is 5 to 50.
4. The anionic functional group is at least one of a sulfuric acid group, a sulfo group, a phosphoric acid group, and a carboxyl group.
5. The hydrophilization treatment is a combination of a never dry treatment or a never dry treatment and a treatment using any one of carbodiimide, sulfuric acid, sulfur trioxide-pyridine complex, phosphoric acid-urea, TEMPO catalyst, and oxidizing agent. ,
Is preferable.

In the cellulose nanocrystal dispersion liquid of the present invention, the cellulose nanocrystals having a short fiber length and a small fiber diameter are uniformly dispersed without agglomeration, so that they are excellent in coatability and handleability and are transparent. It is also excellent in properties, and has excellent transparency with a visible light transmittance of 45% T or more in an aqueous dispersion in which the solid content of the cellulose nanocrystal is 2% by mass.
Further, in the present invention, the cellulose nanocrystals have a sulfuric acid group and / or a sulfo group derived from the sulfuric acid treatment and an anionic functional group derived from the hydrophilic treatment, and are densely self-assembled by charge repulsion between the cellulose nanocrystals. Since the structure is formed, excellent gas barrier properties can be exhibited. Further, since it is composed of cellulose nanocrystals having a short fiber length and these are uniformly dispersed in the dispersion liquid, the gas barrier property is further improved in combination with the above-mentioned self-assembled structure.
As is clear from the results of Examples described later, the cellulose nanocrystal dispersion liquid of the present invention is more transparent (visible light transmission) than the dispersion liquid in which solidified cellulose nanocrystals are dispersed as the same solid content. Excellent rate) and gas barrier properties. Further, it is not necessary to redisperse the solidified cellulose nanocrystals to prepare a dispersion liquid, which is excellent in terms of economy and handleability.
Further, since the cellulose nanocrystals are never-dried without undergoing drying and solidification, it is possible to obtain a dispersion liquid in which the cellulose nanocrystals are in a fine and homogeneous dispersed state.

It is a figure for demonstrating the calculation method of a particle diameter. It is a cryo-SEM photograph which shows the dispersion state of the cellulose nanocrystal in the dispersion liquid of Example 1, (A) is the photograph which is 5000 times the actual size, and (B) is the enlarged photograph of the X part of (A) (A). (20,000 times the actual size), (C) is an enlarged photograph of the Y part of (A) (20,000 times the actual size), (D) is an enlarged photograph of the Z part of (B) (actual size) (100,000 times), (E) is an enlarged photograph (100,000 times the actual size) of the Z portion of (C). It is a cryo-SEM photograph showing the dispersion state of the cellulose nanocrystal in the dispersion liquid of Comparative Example 1, (A) is a photograph which is 5000 times the actual size, and (B) is an enlarged photograph of the X part of (A) (A). (20,000 times the actual size), (C) is an enlarged photograph of the Y part of (A) (20,000 times the actual size), (D) is an enlarged photograph of the Z part of (B) (actual size) (100,000 times), (E) is a double-magnified photograph (100,000 times the actual size) of the Z portion of (C).

In the cellulose nanocrystal dispersion of the present invention, cellol nanocrystals containing a sulfate group and / or a sulfo group derived from a sulfuric acid treatment and an anionic functional group derived from a hydrophilization treatment are uniform without agglomeration in the dispersion medium. Since it is a dispersion liquid dispersed in, it has excellent transparency with a visible light transmittance of 45% T or more in an aqueous dispersion having a solid content of 2% by mass of cellulose nanocrystals.
Further, the gas barrier property of the cellulose nanocrystals is expressed by the self-assembled structure formed by the charge repulsion between the cellulose nanocrystals acting as a barrier of the permeation path of the permeated gas. In the case, since anionic functional groups such as sulfate group and / or sulfo group and carboxyl group are present on the surface of the cellulose nanocrystal, the self-assembled structure is made efficient by the charge (anion) possessed by these anionic functional groups. It is well formed and can exhibit excellent gas barrier properties in combination with the above-mentioned uniform dispersibility.

Further, in the cellulose nanocrystal dispersion liquid of the present invention, the average particle size of the cellulose nanocrystals by the laser diffraction type particle size distribution measuring device is 10.1 μm or less, the median diameter is 10.6 μm or less, and the mode diameter is 10.9 μm or less. Is preferable.
The particle size distribution means that particles of what size (particle size) are included in the sample particle group of the dispersion liquid to be measured, and at what ratio (relative particle amount with the whole as 100%). It is an index showing whether or not it is. The particle size is specified from the light intensity distribution data pattern by the laser diffraction / scattering method using a laser diffraction type particle size distribution device, and the volume-based particle size distribution is obtained by calculation. It is also possible to calculate the number-based particle size distribution based on the volume-based particle size distribution.
In the laser diffraction type particle size distribution measuring device, when the particle group to be measured is irradiated with laser light, a light intensity distribution pattern of diffracted / scattered light is spatially generated, and the light intensity distribution pattern of the forward scattered light is a lens. A ring-shaped diffracted / scattered image is formed on the detection surface at the focal distance. This is detected by a ring sensor in which detection elements are arranged concentrically. Further, the side scattered light and the backscattered light are detected by the side scattered light sensor and the backscattered light sensor, respectively. In this way, the light intensity distribution pattern is detected using various detection elements, and the light intensity distribution data is obtained.
The average particle size, median diameter, and mode diameter of the cellulose nanocrystals can be obtained by analyzing the measurement results of the laser diffraction type particle size distribution device in a state where the cellulose nanocrystals in the dispersion liquid are present at a dilute concentration. .. In a dispersion in which the average particle size, median diameter, and mode diameter of the cellulose nanocrystals in the dispersion are in the above ranges, the dispersibility is good, the gas barrier property and the handling property at the time of coating are excellent, and the coating surface is excellent. It also has the advantage of being excellent in smoothness.

The particle size distribution is usually expressed as a particle size (integration or frequency) relative to the particle size scale. Further, in the laser diffraction / scattering method, which is the measurement principle of the laser diffraction type particle size distribution measuring device, the particle size distribution can be obtained based on the light intensity distribution pattern of the diffraction / scattered light calculated on the assumption that the particles are spherical. .. Therefore, the particle size distribution measurement is always based on the assumption or assumption that the particles are spherical.
In the case of fibrous particles such as cellulose nanocrystals, the obtained particle size distribution is such that the minor axis of the fibrous particles corresponds to the lower limit of the distribution and the major axis substantially corresponds to the upper limit of the distribution. This is because it is considered that the directions of the fibrous particles are random inside the cell, and even if the directions of the particles are constant to some extent, the shape of the sensor that detects diffracted / scattered light is 1/4 yen. As a result, it is not possible to detect diffracted / scattered light only in a certain direction.
When fibrous particles of various shapes and sizes are included, the distribution range of the measurement result extends from the smallest minor axis to the largest major axis, and even in the case of fibrous particles, the particles to be measured. The larger the variation in the shape and size of the particles contained in the group, the wider the distribution range, the smaller the variation, the narrower the distribution range, and the larger the shape and size, the larger the particle size distribution as a whole. As the shape and size become smaller, the particle size distribution shifts to the smaller one as a whole. If the fibrous particles are agglomerated, the particle size distribution moves to the larger side as a whole, and if they are dispersed, the particle size distribution moves to the smaller side as a whole. In this way, the fiber characteristics of the cellulose nanocrystals can be quantitatively evaluated by the laser diffraction type particle size distribution measuring device.

The average particle size is calculated based on a logarithmic scale, and is calculated by multiplying the value of each particle size by the relative particle amount (difference%) and dividing by the total relative particle amount (100%). Specifically, first, the particle size range (maximum particle size: x1, minimum particle size: xn + 1) to be measured is divided into n, and each particle size section is divided into [xj, xj + 1] (j = 1, 2, 2,・ ・ ・ ・ N). The division in this case is an equal division on a logarithmic scale. Further, based on the logarithmic scale, the representative particle size in each particle size section is given by the following equation (1).

で計算する。
この代表粒子径は対数により表されていることからこの時点で粒子径の単位ではなくなる。さらにｑｊ（ｊ＝１，２，・・・・ｎ）を、粒子径区間［ｘｊ、ｘｊ＋１］に対応する相対粒子量（差分％）とし、全区間の合計を１００％とすると、対数スケール上での平均値μは下記式（２）

Calculate with.
Since this representative particle size is represented by a logarithm, it is no longer a unit of particle size at this point. Further, assuming that qj (j = 1, 2, ... n) is the relative particle amount (difference%) corresponding to the particle size interval [xj, xj + 1] and the total of all the intervals is 100%, it is on the logarithmic scale. The average value μ in is calculated by the following equation (2).

で計算できる。
このμは、対数スケール上の数値であり、粒子径としての単位を持たないので、粒子径の単位に戻すために１０^μすなわち１０のμ乗を計算している。この１０^μが平均粒子径となる。

Can be calculated with.
Since this μ is a numerical value on a logarithmic scale and does not have a unit as a particle size, 10 ^μ, that is, 10 μ power is calculated in order to return to the unit of particle size. This 10 ^μ is the average particle size.

The particle size distribution data is expressed as an integrated% or frequency% with respect to the particle size scale, but can also be expressed as a particle size with respect to the integrated% scale. For example, the particle size at the point where the integrated% distribution curve intersects the 10% horizontal axis intersects with the 10% diameter, and the particle size at the point where the 50% horizontal axis intersects with the 50% diameter and 90% horizontal axis. The particle size of the point can be said to be 90%, and an arbitrary integrated% is used if necessary. The calculation method of the arbitrary% particle size is shown in FIG. 1 and the following formulas (3) and (4).

積算％Ｑ_ａにおける任意％粒子径ｘ_ａを求め、このｘ_ａの両側の２つの粒子径ｘ_ｊ＋１およびｘ_ｊにおける積算％Ｑ_ｊ＋１およびＱ_ｊが既知であるとき、積算％Ｑ_ａにおける任意％粒子径ｘ_ａは、上記式（３）及び（４）を用いて計算することができる。５０％粒子径がメディアン径となり、Ｑ_ａを５０％として計算することでメディアン径を求めることができる。また出現される頻度（％）の比率が最も大きい粒径によってモード径を求めることができる。

Obtains any% particle size _{x a} in cumulative% _{Q a,} when _{cumulative% Q j + 1} and _{Q j} in the _x 2 one particle size on either side of _{a x j + 1} and _{x j} are known, any% in cumulative% _{Q a} The particle size x _a can be calculated using the above equations (3) and (4). The 50% particle size becomes the median diameter, and the median diameter can be obtained by calculating with _{Q a as 50%.} Further, the mode diameter can be obtained from the particle size having the largest ratio of appearance frequency (%).

Further, in the cellulose nanocrystal dispersion of the present invention, it is preferable that the cellulose nanocrystals have undergone the never dry treatment, but the cellulose nanocrystals in the cellulose nanocrystal dispersion have undergone the never dry treatment. Or, whether or not the cellulose nanocrystal dispersion has undergone the dry solidification treatment can be evaluated by relaxation time measurement analysis by pulse NMR and cryo-SEM observation for the difference in molecular motility and dispersibility of the cellulose nanocrystal dispersion.
That is, with respect to the cellulose nanocrystal dispersion, the free induction decay (M (t)) measured by the solid echo method of pulse NMR using Bruker's TD-NMR THE MINISPEC MQ20 was subjected to the following formula (5). , Fitting with analysis software (TDNMR-A), and analyze by approximating one component (α) (component (α): the component with low molecular motion and the lowest molecular motion in which molecular motion is constrained). Can be done. Further, by using the following formulas (6) and (7), two or more components (component (α), component (β): a component having higher molecular motility than the component (α) and whose molecular motion is not constrained). , Component (γ): A component with higher motility than component (β)) can be examined, and if an error is returned on the analysis software, it is suggested that two or more components do not exist. To.

M (t) = αexp {-(1 / Wa) x (t / Tα) x Wa} ... (5)
M (t) = αexp {-(1 / Wa) x (t / Tα) x Wa}
+ Βexp {-(1 / Wa) x (t / Tβ) x Wa} ... (6)
M (t) = αexp {-(1 / Wa) x (t / Tα) x Wa}
+ Βexp {-(1 / Wa) x (t / Tβ) x Wa}
+ Γexp {-(1 / Wa) x (t / Tγ) x Wa} ... (7)

The symbols in (5) to (7) above are as follows.
α: Proton ratio (%) of component (α)
Tα: T2 relaxation time (μsec) of component (α)
β: Proton ratio (%) of component (β)
Tβ: T2 relaxation time (μsec) of component (β)
γ: Proton ratio (%) of component (γ)
Tγ: T2 relaxation time (μsec) of component (γ)
t: Observation time (μsec)
Wa: Shape coefficient (1 <Wa <2)

The dispersion obtained by concentrating the cellulose nanocrystals by the never-dry treatment (corresponding to Example 1 described later) is a dispersion treated by spray-drying or the like and then redispersed using a disperser (described later). It becomes a dispersion liquid having higher viscosity and transparency than (corresponding to Comparative Example 1).
That is, as is clear from the results of Examples described later, in Example 1, which is a cellulose nanocrystal dispersion liquid obtained by never-drying, as a result of analysis according to the above formulas (5) to (7), the relaxation time is short. The analysis result of the numerical value with only one component (α) is obtained. This indicates that only the cellulose nanocrystals subjected to the never-dry treatment are present in the solvent and have uniform motility of one component, and the homogeneity of the cellulose nanocrystals in the dispersion is good. Is shown.
Further, as is clear from FIG. 2 showing the cryo-SEM observation image of the cellulose nanocrystal dispersion liquid of Example 1, it was observed that the cellulose nanocrystals subjected to the never-dry treatment were finely and uniformly dispersed in the dispersion liquid. Will be done. It is suggested that this result correlates with the analysis result of pulse NMR.

On the other hand, in Comparative Example 1, which is a cellulose nanocrystal dispersion liquid that has been solidified by a drying treatment, as a result of analysis according to the above formulas (5) to (7), the component (α) having a short relaxation time and the relaxation time Numerical analysis results for the two components of the longer component (β) have been obtained. This indicates that the two components of the cellulose nanocrystals that have undergone dry solidification and the cellulose nanocrystals that have been redispersed and aggregated are present in the solvent and have non-uniform motility. , Shows the inhomogeneity of cellulose nanocrystals in the dispersion.
Further, as is clear from FIG. 3 showing a cryo-SEM observation image of the cellulose nanocrystal dispersion liquid of Comparative Example 1, it was observed that aggregated cellulose nanocrystals were present and the dispersion was not uniform, and the result was pulse NMR. It is suggested that there is a correlation with the analysis results of.

In the dispersion of the present invention, the cellulose nanocrystal has a total amount of anionic functional groups such as sulfate group and / or sulfo group and carboxyl group of more than 0.17 mmol / g and 4.0 mmol / g or less. It is preferable that the mixture is contained, and when the total amount of anionic functional groups is smaller than the above range, a sufficient self-assembled structure is not formed as compared with the case where the total amount of anionic functional groups is in the above range, and a desired gas barrier is not formed. There is a risk that sex cannot be obtained. On the other hand, when the total amount of anionic functional groups is larger than the above range, the crystal structure of the cellulose nanocrystals cannot be maintained, and the gas barrier property may be impaired.
In addition, in this specification, a sulfuric acid group is a concept including a sulfuric acid ester group.

In the present invention, since the cellulose nanocrystal is a cellulose nanocrystal hydrolyzed by sulfuric acid treatment, it already contains a sulfuric acid group and / or a sulfo group that contributes to the formation of a self-assembled structure. preferable. That is, some cellulose nanocrystals acid-hydrolyze cellulose fibers by sulfuric acid treatment or hydrochloric acid treatment, but since cellulose nanocrystals by hydrochloric acid treatment do not have sulfuric acid groups and / or sulfo groups, they have a self-assembled structure. Barrier properties cannot be improved as compared with cellulose nanocrystals treated with sulfuric acid, which have a sulfuric acid group and / or a sulfo group that contribute to the formation.
The anionic functional group contained in the cellulose nanocrystal of the present invention is determined by the method for hydrophilizing the cellulose nanocrystal described later, and is particularly preferably a carboxyl group, a phosphoric acid group, a sulfate group and / or a sulfo group. .. As a result, the above-mentioned self-organizing structure is efficiently formed, and the gas barrier property is improved.

In the present invention, it is desirable that the total amount of the sulfate group and / or the sulfo group and the anionic functional group of the cellulose nanocrystal is in the above range and the crystallinity is in the range of 60% or more.
Further, the cellulose nanocrystal is preferably a cellulose nanocrystal having a fiber diameter of 50 nm or less and an aspect ratio of 5 to 50.

(Manufacturing method of cellulose nanocrystal dispersion)
In the preparation of cellulose nanocrystals, it is important that the cellulose nanocrystal dispersion liquid of the present invention having the above-mentioned characteristics is a cellulose nanocrystal dispersion liquid that has not undergone solidification such as powder (never dry treatment). As described above, when the dispersion liquid is prepared using the solidified cellulose nanocrystals, not only the manufacturing process becomes complicated due to the solidification treatment and the dispersion treatment of the solid cellulose nanocrystals, but also the gas barrier property is lowered. There is a problem. That is, the cellulose nanocrystals that have been subjected to the drying treatment and solidified are difficult to align the fibers in the dispersion liquid, and it is difficult to form a dense self-assembled structure, as compared with the dispersion liquid of the present invention. Poor gas barrier property.
Therefore, in the cellulose nanocrystal dispersion of the present invention, a cellulose nanocrystal containing a sulfuric acid group and / or a sulfo group obtained by treating a cellulose raw material with sulfuric acid is hydrophilized, and after the hydrophilization treatment step, centrifugation is performed. It is a dispersion obtained by subjecting it to a step and a filtration separation step, and does not undergo a spray drying step or the like for solidification.

[Cellulose nanocrystal]
Cellulose nanocrystals are rod-shaped cellulose crystal fibers obtained by acid-hydrolyzing cellulose fibers such as pulp with sulfuric acid or hydrochloric acid, but in the present invention, they can contribute to the formation of a self-assembled structure. Sulfuric acid-treated cellulose nanocrystals with sulfuric acid and / or sulfo groups are used.
Cellulose nanocrystals preferably contain a sulfate group and / or a sulfo group in an amount of 0.18 to 4.0 mmol / g, particularly 0.20 to 2.0 mmol / g. As described above, the cellulose nanocrystals have a fiber diameter of 50 nm or less, particularly in the range of 2 to 50 nm, a fiber length in the range of 100 to 500 nm, an aspect ratio in the range of 5 to 50, and a degree of crystallinity. 60% or more, particularly 70% or more can be preferably used.

[Hydrophilic treatment]
In the present invention, the amount of sulfate group and / or sulfo group is adjusted or anions such as carboxyl group and phosphoric acid group are adjusted by hydrophilizing the cellulose nanocrystal having a sulfate group and / or sulfo group described above. A sex functional group is introduced into the hydroxyl group at the 6-position of cellulose, and the total amount of anionic functional groups such as sulfate group, sulfo group, carboxyl group and phosphoric acid group is more than 0.17 mmol / g and 4.0 mmol / g or less. In particular, cellulose nanocrystals in the range of 0.25 to 2.0 mmol / g are prepared.
The hydrophilization treatment is a combination of a never-dry treatment or a never-dry treatment and a treatment using any of water-soluble carbodiimide, sulfuric acid, sulfur trioxide-pyridine complex, phosphoric acid-urea, TEMPO catalyst, and oxidant. Do. Treatment with any of carbodiimide, sulfuric acid, and sulfur trioxide-pyridine complex adjusts the amount of sulfuric acid group and / or sulfo group of the cellulose nanocrystal, and further shortens the nanocellulose. Further, by treatment with either phosphoric acid-urea, a TEMPO catalyst, or an oxidizing agent, an anionic functional group of a phosphoric acid group or a carboxyl group is introduced, and the total amount of anionic functional groups of the cellulose nanocrystal is within the above range. It will be adjusted.
The hydrophilization treatment may be performed by any one of them as long as the total amount of anionic functional groups is within the above range, but the same treatment may be performed a plurality of times or a plurality of times in combination with other treatments. Good.

<Hydrophilic treatment by never dry treatment>
Cellulose nanocrystals undergo drying treatments such as spray drying, heating, and reduced pressure to solidify powders and the like, but when solidified by drying treatments, some of the anionic functional groups contained in the cellulose nanocrystals are removed. Separation reduces hydrophilicity. That is, a never-drying treatment of cellulose nanocrystals containing anionic functional groups without solidification of powder or the like can be mentioned as a hydrophilic treatment. Examples of the anionic functional group include a sulfate group and / or a sulfo group, a phosphoric acid group, a carboxyl group and the like.

<Hydrophilic treatment using carbodiimide>
In the treatment using carbodiimide, cellulose nanocrystals and carbodiimide are stirred in a solvent such as dimethylformamide, sulfuric acid is added thereto, and then the reaction is carried out at a temperature of 0 to 80 ° C. for 5 to 300 minutes to obtain a sulfuric acid ester. .. Carbodiimide and sulfuric acid are preferably used in an amount of 5 to 30 mmol and 5 to 30 mmol with respect to 1 g (solid content) of cellulose nanocrystals.
Next, it is preferable to add an alkaline compound such as sodium hydroxide to convert the sulfo group introduced into the cellulose nanocrystal from H type to Na type in order to improve the yield. After that, impurities and the like are removed by filtration using a dialysis membrane or the like to prepare cellulose nanocrystals modified with a sulfate group and / or a sulfo group.
Examples of the carbodiimide include 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide, which is a water-soluble compound having a carbodiimide group (-N = C = N-) in the molecule. Further, dicyclohexylcarbodiimide or the like dissolved in an organic solvent can also be used.

<Hydrophilic treatment with sulfuric acid>
The cellulose nanocrystals used in the present invention are formed by hydrolyzing cellulose fibers with sulfuric acid, and the cellulose nanocrystals are further hydrophilized with sulfuric acid. Sulfuric acid is preferably used in an amount of 40 to 60% by mass with respect to 1 g (solid content) of cellulose nanocrystals. Sulfate group and / or sulfo group-modified cellulose nanocrystals are prepared by reacting at a temperature of 40 to 60 ° C. for 5 to 300 minutes and then subjecting to filtration treatment using a dialysis membrane or the like to remove impurities and the like. To.

<Hydrophilic treatment using sulfur trioxide-pyridine complex>
In the treatment using the sulfur trioxide-pyridine complex, the cellulose nanocrystal and the sulfur trioxide-pyridine complex are reacted in dimethylsulfoxide at a temperature of 0 to 60 ° C. for 5 to 240 minutes to form 6 of the cellulose glucose unit. A sulfate group and / or a sulfo group is introduced into the hydroxyl group at the position.
The sulfur trioxide-pyridine complex is preferably blended in a mass of 0.5 to 4 g with respect to 1 g (solid content) of the cellulose nanocrystal.
After the reaction, it is preferable to add an alkaline compound such as sodium hydroxide to convert the sulfate group and / or the sulfo group introduced into the cellulose nanocrystal from the H type to the Na type in order to improve the yield. Then, dimethylformamide or isopropyl alcohol is added, and the mixture is washed by centrifugation or the like, impurities and the like are removed by filtration using a dialysis membrane or the like, and the obtained concentrate is dispersed in water to form a sulfate group. And / or a sulfo group-modified cellulose nanocrystal is prepared.

<Hydrophilic treatment using phosphoric acid-urea>
The hydrophilization treatment using phosphoric acid-urea can be carried out in the same manner as the conventionally known treatment for introducing a phosphoric acid group using phosphoric acid-urea. Specifically, the cellulose nanocrystal and the phosphate group-containing compound are reacted at a temperature of 135 to 180 ° C. for 5 to 120 minutes in the presence of a urea-containing compound to form a phosphate group on the hydroxyl group of the cellulose glucose unit. Introduce.
Examples of the phosphoric acid group-containing compound include phosphoric acid, a lithium salt of phosphoric acid, a sodium salt of phosphoric acid, a potassium salt of phosphoric acid, and an ammonium salt of phosphoric acid. Among them, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid and the like can be preferably used alone or in combination. The phosphoric acid group-containing compound is preferably added in an amount of 10 to 100 mmol with respect to 10 g (solid content) of cellulose nanocrystals.
Examples of the urea-containing compound include urea, thiourea, biuret, phenylurea, benzylurea, and dimethylurea. Among them, urea can be preferably used. The urea-containing compound is preferably used in an amount of 150 to 200 mmol with respect to 10 g (solid content) of cellulose nanocrystals.

<Hydrophilic treatment using TEMPO catalyst>
The hydrophilization treatment using a TEMPO catalyst (2,2,6,6-tetramethylpiperidin-1-oxyl) can be carried out in the same manner as a conventionally known oxidation method using a TEMPO catalyst. Specifically, cellulose nanocrystals having a sulfate group and / or a sulfo group are subjected to TEMPO catalyst (2,2,6,6-tetramethylpiperidine 1-oxyl) under aqueous conditions, normal temperature, and normal pressure. , The hydroxyl group at the 6-position of the cellulose glucose unit is oxidized to a carboxyl group to cause a hydrophilic reaction.
As the TEMPO catalyst, in addition to the above 2,2,6,6-tetramethylpiperidin 1-oxyl, TEMPO derivatives such as 4-acetamido-TEMPO, 4-carboxy-TEMPO, and 4-phosphonoxy TEMPO can also be used.
The amount of the TEMPO catalyst used is 0.01 to 100 mmol, preferably 0.01 to 5 mmol, per 1 g of cellulose nanocrystals (solid content).

Further, at the time of hydrophilization oxidation treatment, it is preferable to use an oxidizing agent, a bromide, an iodide or the like in combination with an oxidizing agent or a TEMPO catalyst.
Examples of the oxidizing agent include known oxidizing agents such as halogen, hypobromous acid, hypochlorous acid, perhalogen acid or salts thereof, halogen oxides, and peroxides, and in particular, sodium hypochlorite and the like. Sodium hypobromite can be preferably used. The amount of the oxidizing agent is 0.5 to 500 mmol, preferably 5 to 50 mmol per 1 g of cellulose nanocrystal (solid content). After a certain period of time has passed after adding the oxidizing agent, the additional oxidation treatment can be performed by further adding the oxidizing agent.
Further, as the copolymerizer, an alkali metal bromide such as sodium bromide and an alkali metal iodide such as sodium iodide can be preferably used. The amount of the copolymer is 0.1 to 100 mmol, preferably 0.5 to 5 mmol, based on 1 g of the cellulose nanocrystal (solid content).
The reaction solution preferably uses water or an alcohol solvent as a reaction medium.

The reaction temperature of the hydrophilization treatment is in the range of 1 to 50 ° C., particularly 10 to 50 ° C., and may be room temperature. The reaction time is preferably 1 to 360 minutes, particularly preferably 60 to 240 minutes.
As the reaction progresses, a carboxyl group is generated in the cellulose, so that the pH of the slurry is lowered. However, in order to promote the oxidation reaction efficiently, a pH adjuster such as sodium hydroxide is used to adjust the pH to 9-12. It is desirable to keep it in the range.

[Washing / defibration treatment]
The cellulose nanocrystals before or after the hydrophilization treatment are washed with water or centrifuged while adding water to wash the acid, catalyst, etc. used in the hydrophilic treatment.
Next, it is preferable to perform a defibration treatment, but since the cellulose nanocrystal has a short fiber length, the defibration treatment does not necessarily have to be performed.
A dispersion liquid may be prepared at the same time as defibration by using an ultra-high pressure homogenizer, a mixer, a grinder or the like as a miniaturization device and performing a defibration treatment using water or the like as a dispersion medium.

[Distributed processing]
Cellulose nanocrystals that have been subjected to a hydrophilization treatment or, if necessary, a defibration treatment, are subjected to a dispersion treatment without being solidified (spray-dried so as to become a powder). Since it is not solidified, there is no need for redispersion, and it is excellent in productivity and economy. Further, since it is not solidified, it is possible to form the above-mentioned dense self-assembled structure, and it is possible to exhibit excellent gas barrier properties.
For the dispersion treatment, a disperser such as an ultrasonic disperser, a homogenizer, or a mixer can be preferably used, and a stirring method using a stirring rod, a stirring stone, or the like may be used.
The dispersion medium of the dispersion may be water alone, or may be a mixed solvent of water with an alcohol such as methanol, ethanol or isopropanol, a ketone such as 2-butanone or acetone, or an aromatic solvent such as toluene.
The cellulose nanocrystal dispersion liquid preferably contains cellulose nanocrystals (solid content) in the range of 0.1 to 90% by mass, and is aqueous dispersion having a solid content of 2% by mass and has a viscosity of 5.5. ~ 40 mPa · s (rotary viscometer, temperature 30 ° C., spindle rotation speed 100 rpm), zeta potential is in the range of -50 to -55 mV, and it is excellent in handleability and coatability. Further, it is excellent in transparency with a visible light transmittance of 45% T or more with water dispersion having a solid content of 2% by mass.

Examples of the present invention will be described below. The following examples are examples of the present invention, and the present invention is not limited to these examples. The measurement method for each item is as follows.

<Amount of anionic functional groups>
The nanocellulose-containing dispersion was weighed, and ion-exchanged water was added to prepare 100 ml of a nanocellulose-containing dispersion of 0.05 to 0.3% by mass. 0.1 g of a cation exchange resin was added and the mixture was stirred. Then, filtration was performed to separate the cation exchange resin and the nanocellulose dispersion. A 0.05 M sodium hydroxide solution was added dropwise to the dispersion after cation exchange using an automatic potential difference titrator (manufactured by Kyoto Electronics Co., Ltd.), and the change in electrical conductivity exhibited by the nanocellulose-containing dispersion was measured. From the obtained conductivity curve, the amount of sodium hydroxide droplets consumed for neutralizing the anionic functional groups was determined, and the amount of anionic functional groups (mmol / g) was calculated using the following formula.
Amount of anionic functional group (mmol / g) = Quantitative amount of sodium hydroxide droplets consumed for neutralization of anionic functional group (ml) × sodium hydroxide concentration (mmol / ml) ÷ solid mass of nanocellulose (g) )

<Visible light transmittance>
Using a spectrophotometer (UV-3100PC, Shimadzu Corporation), the visible light transmittance (% T) at 600 nm when the cellulose nanocrystals were made into an aqueous dispersion having a solid content of 2% by mass was determined.

<Particle size distribution>
Using a laser diffraction type particle size distribution measuring device (SALD-3100, Shimadzu Corporation), the average particle size, median diameter, and mode diameter were determined using an aqueous dispersion containing 2% by mass of solids of cellulose nanocrystals. The light source of the device is a semiconductor laser, and the wavelength is 690 nm. The measurement results at an absorbance of 0.015 or less and a refractive index of 1.55 were used for the analysis.

<Example 1>
Cellulose nanocrystals were prepared by decomposing pulp with 64% by weight sulfuric acid. The cellulose nanocrystals are not dried and solidified, but are concentrated and washed in an ultracentrifuge to prepare cellulose nanocrystals that have been never dried, and finally the cellulose nanocrystals are ionized so that the solid content is 2% by mass. A cellulose nanocrystal dispersion was prepared by treating with an ultrasonic disperser for 10 minutes in addition to the exchanged water.

<Example 2>
A cellulose nanocrystal that has been never-dried in the same manner as in Example 1 is prepared, finally added to ion-exchanged water so that the cellulose nanocrystal has a solid content of 2% by mass, and treated with an ultra-high pressure homogenizer for 10 minutes. A cellulose nanocrystal dispersion was prepared.

<Example 3>
Never-dried cellulose nanocrystals were prepared in the same manner as in Example 1. To an aqueous dispersion containing 10 g (solid content) of cellulose nanocrystals, 0.8 mmol of TEMPO catalyst (manufactured by Sigma-Aldrich) and 12.1 mmol of sodium bromide were added, and ion-exchanged water was added to increase the volume to 1 L. Stirred until uniformly dispersed. Then, 5 mmol of sodium hypochlorite was added to start the oxidation reaction. During the reaction, the pH in the system was maintained from 10.0 to 10.5 with a 0.5 N aqueous sodium hydroxide solution, and the hydrophilization treatment was carried out with stirring at 30 ° C. for 4 hours. The hydrophilized cellulose nanocrystals were washed with an ultracentrifugator (50,000 rpm, 10 minutes) while adding ion-exchanged water until the pH reached 8. After that, it was placed inside a dialysis membrane (manufactured by Spectrum Co., Ltd., molecular weight cut off of 3,000 to 5000D) and allowed to stand in ion-exchanged water to remove impurities and the like to prepare cellulose nanocrystals. By adding ion-exchanged water to the washed cellulose nanocrystal dispersion and dispersing it with an ultrasonic disperser, the solid amount of cellulose nanocrystals oxidized by the TEMPO catalyst without solidifying the cellulose nanocrystals in the process can be obtained. A 2% by mass cellulose nanocrystal dispersion was prepared.

<Comparative example 1>
The pulp was decomposed with 64% by mass of sulfuric acid, washed, and dried and solidified to prepare cellulose nanocrystals that were dried and solidified. By adding 1 g (solid amount) of the cellulose nanocrystals to ion-exchanged water and performing a dispersion treatment with an ultrasonic disperser for 10 minutes, a cellulose nanocrystal dispersion having a solid amount of 2% by mass of the cellulose nanocrystals was obtained. ..

<Comparative example 2>
Cellulose nanocrystals dried and solidified were prepared in the same manner as in Comparative Example 1. The cellulose nanocrystals were oxidized with a TEMPO catalyst in the same manner as in Example 3 to prepare a cellulose nanocrystal dispersion having a solid content of 2% by mass of the cellulose nanocrystals.

<Pulse NMR>
The cellulose nanocrystal dispersions obtained in Example 1 and Comparative Example 1 described above were concentrated to a solid content of 5% by mass, and free induction of the cellulose nanofiber dispersion at 30 ° C. measured by the solid echo method of pulse NMR. The decay (M (t)) was measured under the following conditions.
Measuring device: Bruker TD-NMR the minispec mq20
Sample amount: Approximately 200 mg
Observation nucleus: 1H
Measurement: T2
Measurement method: Solid echo method 90 ° Pulse width: 2.2 μsec
Number of integrations: 32 times Measurement temperature: 30 ° C (15 minutes after the device temperature reached the set temperature, the device temperature was adjusted so that the sample internal temperature reached the measured temperature, and measurement was started).
Repeat time: 8 sec

Further, using the above-mentioned formula (5), fitting was performed by analysis software (TDNMR-A), and the analysis was performed by approximating the above-mentioned component (α). If two or more of the above-mentioned components (α), (β), and (γ) are analyzed using the above-mentioned equations (6) and (7) and an error is returned on the analysis software. It was confirmed that two or more components did not exist.

In the cellulose nanocrystal dispersion of Example 1, the proton ratio of the component (α) was 100 (%) and the T2 relaxation time of the component (α) was 1579 (μsec), and the numerical analysis results of one component were obtained. .. This indicates that only the cellulose nanocrystals obtained by the never-dry treatment are dispersed in the solvent and have uniform motility of one component, and the cellulose nanocrystals have excellent homogeneity in the dispersion liquid. You can see that.
Further, in the cellulose nanocrystal dispersion liquid of Comparative Example 1, the proton ratio of the component (α) was 86.7 (%), the T2 relaxation time of the component (α) was 1519 (μsec), and the proton ratio of the component (β) was 13. The T2 relaxation time of 6 (%) and the component (β) was 7723 (μsec), and the numerical analysis results of the two components of the component (α) and the component (β) were obtained. From this result, there are two components in the solvent, cellulose nanocrystals that have undergone dry solidification and cellulose nanocrystals that have been aggregated and dispersed, and the two components have non-uniform motility and are contained in the dispersion liquid. The inhomogeneity of cellulose nanocrystals can be seen.

<Cryo SEM>
The cellulose nanocrystal dispersions obtained in Example 1 and Comparative Example 1 were concentrated to a solid content of 5% by mass, fractionated, frozen and broken at −160 ° C., sublimated to -80 ° C., and cooled. The fracture surface was adjusted by FIB and FE-SEM observation was performed while maintaining the state. SEM observation photographs are shown in FIGS. 2 and 3.
Equipment: FEI, Helios NanoLab 600, Helios G4
UX
Acceleration voltage: FIB30 kV, SEM 1-2 kV
Observation image: Reflected electron image Processing set temperature: -160 ° C
Observation set temperature: -80 ° C

As is clear from FIG. 2, in the cellulose nanocrystal dispersion liquid of Example 1, it was observed that the cellulose nanocrystals treated with never dry were finely and uniformly dispersed.
Further, as is clear from FIG. 3, it was observed that the cellulose nanocrystal dispersion liquid of Comparative Example 1 had aggregated cellulose nanocrystals and was not uniformly dispersed.

The cellulose nanocrystal dispersion liquid of the present invention is excellent in coatability and handleability, can form a coating film having excellent gas barrier property and transparency, and is used as a coating agent capable of imparting gas barrier performance. .. In addition, it has better dispersibility than the dispersion liquid in which solidified cellulose nanocrystals are dispersed, and by forming a molded product composed of a mixture of a polyvalent cationic resin and a cross-linking agent, it can be used as a gas barrier film or thermoplastic. Since the interfacial peeling strength with a hydrophobic base material made of resin or the like is also improved, it is suitably used as a gas barrier laminate.

Claims (6)

A cellulose nanocrystal dispersion containing a sulfate group and / or a sulfo group derived from a sulfuric acid treatment and an anionic functional group derived from a hydrophilic treatment, wherein the solid content of the cellulose nanocrystals is 600 nm in aqueous dispersion of 2% by mass. A cellulose nanocrystal dispersion liquid having a visible light transmittance of 45% T or more. The first aspect of claim 1, wherein the average particle size of the cellulose nanocrystals by the laser diffraction type particle size distribution measuring device of the cellulose nanocrystal dispersion is 10.1 μm or less, the median diameter is 10.6 μm or less, and the mode diameter is 10.9 μm or less. Cellulose nanocrystal dispersion. The cellulose nanocrystal dispersion according to claim 1, wherein the total amount of the sulfate group and / or the sulfo group and the anionic functional group is more than 0.17 mmol / g and 4.0 mmol / g or less. The cellulose nanocrystal dispersion according to any one of claims 1 to 3, wherein the cellulose nanocrystal has a crystallinity of 60% or more, a fiber width of 50 nm or less, and an aspect ratio of 5 to 50. The cellulose nanocrystal dispersion according to any one of claims 1 to 4, wherein the anionic functional group is at least one of a sulfate group, a sulfo group, a phosphoric acid group, and a carboxyl group. A claim that the hydrophilization treatment is a combination of a never-dry treatment or a never-dry treatment and a treatment using any one of carbodiimide, sulfuric acid, sulfur trioxide-pyridine complex, phosphoric acid-urea, TEMPO catalyst, and an oxidizing agent. Item 2. The cellulose nanocrystal dispersion according to any one of Items 1 to 5.

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