JP2022132151A - Ionic functional group-introduced cellulose nanocrystals and method of producing the same, and dispersion liquids, sheets, and powders containing the same - Google Patents

Abstract

To provide cellulose nanocrystals which, when made into aqueous dispersion liquids, have low viscosity, are highly transparent, have excellent salinity tolerance, and have a large amount of ionic functional groups introduced thereinto, and a method of producing the same, and further to provide dispersion liquids, sheets, and powders containing the cellulose nanocrystals.SOLUTION: Provided is a method of producing an ionic functional group-introduced cellulose nanocrystal, comprising the following steps A to C in this order. Step A: Ionic functional group introduction step of introducing ionic functional groups into cellulose fibers. Step B: Hydrolysis step of hydrolyzing the cellulose fibers, into which ionic functional groups are introduced, with an acidic aqueous solution having a concentration of 5 mol/L or more. C: Fibrillation step of fibrillating cellulose fibers into which hydrolyzed ionic functional groups are introduced.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to an ionic functional group-introduced cellulose nanocrystal, a method for producing the same, and a dispersion, sheet and powder containing the ionic functional group-introduced cellulose nanocrystal.

In recent years, attention has been paid to materials using reproducible natural fibers due to the replacement of petroleum resources and the growing awareness of the environment. Among natural fibers, fibrous cellulose having a fiber diameter of 10 μm or more and 50 μm or less, especially wood-derived fibrous cellulose (pulp) has been widely used mainly as paper products.

In Patent Document 1, for the purpose of obtaining cellulose nanofibers having a low viscosity even at a high concentration, a cellulosic material is oxidized using an oxidizing agent, and the oxidized cellulosic material is treated with cellulase and/or hemicellulose. A method for producing cellulose nanofibers is described, which comprises treating with a homogenizer in the presence of cellulase, defibrating and dispersing to form cellulose nanofibers.
Non-Patent Document 1 describes hydrolysis of undenatured cotton pulp with high-concentration phosphoric acid to obtain phosphorylated cellulose nanocrystals.
Non-Patent Document 2 describes that a phosphate group is introduced into cellulose nanocrystals by (i) phosphorylation in an aqueous system or (ii) phosphorylation in a molten urea system.

WO2011/118746

Biomacromolecules, vol.14, 1223-1230, 2013 Carbohydrate Polymers, vol.125, 301-313, 2015

The short nanocellulose fibers as described in Patent Document 1 were not sufficiently low in viscosity when made into an aqueous dispersion.
Cellulose nanocrystals have a lower viscosity when made into an aqueous dispersion, but when the amount of ionic functional groups introduced is small, there is a problem that transparency and salt resistance are not sufficient. However, since phosphate groups are introduced during hydrolysis, it is not possible to sufficiently introduce ionic functional groups into cellulose nanocrystals. In addition, the method described in Non-Patent Document 2 also introduces phosphate groups into cellulose nanocrystals, and the method (i) cannot sufficiently introduce ionic functional groups, and (ii) Although the method (i) can introduce more ionic functional groups than the method (i), it is presumed that a large amount of unintended functional groups (carbamide groups) are also included. In addition, in both methods (i) and (ii), since an ionic functional group is introduced into the cellulose nanocrystals, a large amount of reagent must be used to react a low-concentration cellulose nanocrystal dispersion. Therefore, there is room for improvement from the viewpoint of industrialization.
An object of the present invention is to provide cellulose nanocrystals that have a low viscosity when made into an aqueous dispersion, high transparency, excellent salt resistance, and a large amount of ionic functional groups introduced, and a method for producing the same. . A further object of the present invention is to provide dispersions, sheets, and powders containing the cellulose nanocrystals.

The present inventors have found that the above problems can be solved by producing cellulose nanocrystals by a specific production method, or by using cellulose nanocrystals in which the amount of ionic functional groups introduced is a specific value or more. .
The present invention relates to the following <1> to <19>.
<1> A method for producing ionic functional group-introduced cellulose nanocrystals, comprising the following steps A to C in this order.
Step A: Ionic functional group introduction step of introducing ionic functional groups into cellulose fibers Step B: Hydrolysis step of hydrolyzing cellulose fibers introduced with ionic functional groups with an acidic aqueous solution having a concentration of 5 mol/L or more C: defibration step of fibrillating the cellulose fiber into which the hydrolyzed ionic functional group has been introduced <2> The ionic functional group is a phosphorous acid group, a group derived from a phosphoroxoacid group, a carboxyl group, a sulfone group, The production method according to <1>, wherein the group is at least one selected from the group consisting of a sulfur oxoacid group, a group derived from a sulfur oxoacid group, and a cationic group.
<3> The production method according to <1> or <2>, wherein the ionic functional group is at least one selected from the group consisting of a phosphorous acid group and a group derived from a phosphorous acid group.
<4> The production method according to any one of <1> to <3>, wherein in step A, the amount of the ionic functional group introduced into the cellulose fiber is 0.5 mmol/g or more.
<5> The production method according to any one of <1> to <4>, wherein the amount of ionic functional group introduced in the ionic functional group-introduced cellulose nanocrystal is 0.1 mmol/g or more.
<6> The production method according to any one of <1> to <5>, wherein the amount of carbamide groups in the ionic functional group-introduced cellulose nanocrystals is 0.06 mmol/g or less.
<7> Any one of <1> to <6>, wherein the acidic aqueous solution used in step B is an aqueous solution of an acid compound selected from the group consisting of phosphoric acid, sulfuric acid, diphosphorus pentoxide, and hydrochloric acid. The manufacturing method described in .
<8> An ionic functional group-introduced cellulose nanocrystal having an ionic functional group introduction amount of 0.1 mmol/g or more (however, cellulose in which only the carbon atom at the 6-position of cellulose is oxidized and a carboxy group is introduced excluding nanocrystals).
<9> The ionic functional group is selected from the group consisting of a phosphorus oxoacid group, a group derived from a phosphorus oxoacid group, a carboxy group, a sulfone group, a sulfur oxoacid group, a group derived from a sulfur oxoacid group, and an ammonium group. The ionic functional group-introduced cellulose nanocrystal according to <8>, which is at least one of
<10> The ionic functional group-introduced cellulose according to <8> or <9>, wherein the ionic functional group is at least one selected from the group consisting of a phosphorous acid group and a group derived from a phosphorous acid group. nano crystals.
<11> The ionic functional group-introduced cellulose nanocrystal according to any one of <8> to <10>, wherein the amount of the ionic functional group introduced is 0.5 mmol/g or more.
<12> The ionic functional group according to any one of <8> to <11>, wherein the ionic functional group is introduced to at least one of the carbon atoms at the 2nd and 3rd positions of cellulose. Introducing cellulose nanocrystals.
<13> The ionic functional group-introduced cellulose nanocrystal according to any one of <8> to <12>, wherein the amount of carbamide groups in the ionic functional group-introduced cellulose nanocrystal is 0.06 mmol/g or less. .
<14> The ionic functional group according to any one of <8> to <13>, wherein a 1.5% by mass aqueous dispersion of the ionic functional group-introduced cellulose nanocrystals has a viscosity of 100 mPa s or less. Introducing cellulose nanocrystals.
<15> The ionic functional group-introduced cellulose nanocrystals according to any one of <8> to <14>, wherein the total light transmittance of the 0.2% by mass aqueous dispersion of the cellulose nanocrystals is 95.5% or more. Cellulose nanocrystals with ionic functional groups.
<16> When sodium chloride is added to a 0.2% by mass aqueous dispersion of the ionic functional group-introduced cellulose nanocrystals so as to be 100 mmol / L, the total light transmittance after adding sodium chloride is T, chloride The ionic functional group-introduced cellulose nanostructure according to any one of <8> to <15>, wherein T/ _T0 is 0.98 or more, where _T0 is the total light transmittance before the addition of sodium. crystal.
<17> A dispersion containing the ionic functional group-introduced cellulose nanocrystals according to any one of <8> to <16>.
<18> A sheet containing the ionic functional group-introduced cellulose nanocrystal according to any one of <8> to <16>.
<19> A powder containing the ionic functional group-introduced cellulose nanocrystals according to any one of <8> to <16>.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a cellulose nanocrystal which has a low viscosity when made into an aqueous dispersion, has high transparency, has excellent salt resistance, and has a large amount of ionic functional groups introduced, and a method for producing the same. Furthermore, according to the present invention, dispersions, sheets, and powders containing the cellulose nanocrystals can be provided.

FIG. 1 is a graph showing the relationship between the amount of dropped NaOH and pH for a slurry containing cellulose fibers having a phosphorous acid group. FIG. 2 is a graph showing the relationship between the amount of dropped NaOH and pH for a slurry containing cellulose fibers having carboxyl groups.

[Method for Producing Ionic Functional Group-Introduced Cellulose Nanocrystals]
The method for producing the ionic functional group-introduced cellulose nanocrystals of the present invention (hereinafter, "ionic functional group-introduced cellulose nanocrystals" is also simply referred to as "ionic functional group-introduced CNC" or "CNC") comprises the following step A: to step C in this order.
Step A: Ionic functional group introduction step of introducing ionic functional groups into cellulose fibers Step B: Hydrolysis step of hydrolyzing cellulose fibers introduced with ionic functional groups with an acidic aqueous solution having a concentration of 5 mol/L or more C: defibration step of fibrillating cellulose fibers into which hydrolyzed ionic functional groups have been introduced According to the production method of the present invention, the aqueous dispersion has low viscosity, high transparency, and salt resistance. A cellulose nanocrystal with excellent ionic functional group introduction is provided.
Cellulose nanocrystals are fibrillated to a nano level with a fiber width of 1000 nm or less, and are highly crystallized by removing amorphous regions by acid hydrolysis.
The reason why the above effect can be obtained by the manufacturing method of the present embodiment is considered as follows. Conventionally, as described in Patent Document 1, attempts have been made to obtain low-viscosity nanocellulose when an aqueous dispersion is prepared by shortening cellulose nanofibers. It has been difficult to achieve a sufficiently low viscosity in the case of forming an aqueous dispersion by shortening the fibers.
For the purpose of achieving a sufficiently low viscosity in the case of an aqueous dispersion, cellulose nanocrystals are produced by hydrolyzing the amorphous portion by acid hydrolysis of cellulose and then fibrillating. Although the cellulose nanocrystals obtained by this method achieve a low viscosity when made into an aqueous dispersion, there are problems with the transparency and salt resistance of the aqueous dispersion. To solve this problem, ionic functional groups have been introduced into cellulose nanocrystals obtained by acid hydrolysis and fibrillation. However, in the method of introducing an ionic functional group into cellulose nanocrystals, the concentration of the cellulose nanocrystal dispersion is low, chemical treatment at a high concentration is difficult, and the reaction efficiency is low. The amount was too small to sufficiently improve the transparency and salt resistance. There is also a problem that functional groups other than ionic functional groups remain as impurities. Furthermore, in the method of obtaining cellulose nanocrystals and then introducing the phosphorous acid groups, the condensation of phosphorous acid groups and the reaction of one molecule of phosphorous acid with multiple hydroxyl groups of cellulose give rise to strong acid groups and weak acid groups. There was a case where there was a difference in the introduction amount between
In the present invention, by hydrolyzing and fibrillating after introducing an ionic functional group into cellulose fibers, it is possible to increase the amount of ionic functional groups introduced into the resulting cellulose nanocrystals, and as a result, It is considered that the transparency and salt resistance are improved. In addition, functional groups other than ionic functional groups can be reduced by acid hydrolysis after the introduction of ionic functional groups into cellulose fibers, and cellulose nanocrystals introduced with ionic functional groups with higher purity can be obtained. It is thought that Furthermore, by hydrolyzing after introducing the ionic functional group, even when the phosphorus oxoacid group is introduced, there is little or no difference in the amount of introduction between the strongly acidic group and the weakly acidic group. A functional group-introduced cellulose nanocrystal is obtained.
In addition, by performing defibration after hydrolyzing the cellulose fibers to which the ionic functional groups have been introduced, the defibration efficiency is increased due to the electrical repulsion of the ionic functional groups of the hydrolyzed cellulose fibers. A cellulose nanocrystal with a smaller fiber width is obtained.
The present invention will be described in more detail below.

<Process A>
Step A is an ionic functional group introduction step of introducing ionic functional groups into cellulose fibers.
[Cellulose fiber]
Cellulose fiber is a fiber raw material containing cellulose, and the cellulose fiber is not particularly limited, but it is preferable to use pulp because it is readily available and inexpensive. Pulp includes, for example, wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), and unbleached kraft pulp (UKP). ) and chemical pulp such as oxygen bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemigroundwood pulp (CGP), groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP) A mechanical pulp etc. are mentioned. Examples of non-wood pulps include, but are not limited to, cotton-based pulps such as cotton linters and cotton lints, and non-wood-based pulps such as hemp, straw, bamboo, and bagasse. Examples of deinked pulp include, but are not limited to, deinked pulp made from waste paper. The pulp of this embodiment may be used alone or in combination of two or more.
Among the above pulps, wood pulp and deinked pulp are preferable, for example, from the viewpoint of availability. In addition, among wood pulps, chemical pulps are more preferable, for example, from the viewpoints that the cellulose ratio is high and the yield of CNC at the time of defibration treatment is high, and the decomposition of cellulose in the pulp is small, for example, kraft pulp, sulfite pulp. is more preferred.
As the cellulose fiber, for example, cellulose contained in sea squirts and bacterial cellulose produced by acetic acid bacteria can be used.
Also, instead of cellulose fibers, fibers formed by linear nitrogen-containing polysaccharide polymers such as chitin and chitosan may be used.

[Ionic functional group]
In step A, an ionic functional group is introduced into the cellulose fibers. By introducing an ionic functional group into the cellulose fibers, the defibration efficiency in the fibrillation treatment can be increased, and the transparency and salt resistance of the obtained cellulose nanocrystals can be improved.
The ionic functional group can include, for example, either one or both of an anionic functional group and a cationic functional group. In this embodiment, it is particularly preferable to have an anionic functional group as the ionic functional group.

The anionic functional group as the ionic functional group includes, for example, a phosphorous acid group or a group derived from a phosphoroxo acid group (sometimes simply referred to as a phosphorous acid group), a carboxy group or a group derived from a carboxy group (simply referred to as a carboxy group). ), a sulfur oxoacid group or a group derived from a sulfur oxoacid group (sometimes referred to simply as a sulfur oxoacid group), a xanthate group, a phosphon group, a phosphine group, a sulfone group, a carboxyalkyl group, and the like. can.
Cationic functional groups as ionic functional groups include, for example, an ammonium group, a phosphonium group, and a sulfonium group. Among them, the cationic functional group is preferably an ammonium group.
Among them, the ionic functional group includes a phosphorous acid group, a group derived from a phosphorous acid group, a carboxy group, a sulfone group, a sulfur oxoacid group, a group derived from a sulfur oxoacid group, a carboxymethyl group, a carboxyethyl group, and a cation. It is preferably at least one selected from the group consisting of a functional group consisting of a phosphorous oxoacid group, a group derived from a phosphorous oxoacid group, a carboxyl group, a sulfur oxoacid group, and a group derived from a sulfur oxoacid group. It is more preferably at least one selected from the group, more preferably at least one selected from the group consisting of a phosphorous acid group and a group derived from a phosphorous acid group, and is preferably a phosphorous acid group. Even more preferable. By introducing a phosphorous acid group as an anionic functional group, cellulose nanocrystals with excellent transparency and salt resistance can be obtained.

A phosphorous acid group or a group derived from a phosphorous acid group is, for example, a substituent represented by the following formula (1). A plurality of substituents represented by the following formula (1) may be introduced into each cellulose fiber. In this case, the plural introduced substituents represented by the following formula (1) may be the same or different.

In formula (1), a, b and n are natural numbers, and m is an arbitrary number (where a=b×m). At least one of n α and α' is O 2 ^- , and the rest are R or OR. Note that all of α and α' may be O 2 ⁻ . All of the n αs may be the same or different. β ^b+ is a cation having a valence of 1 or more, which is composed of an organic substance or an inorganic substance.

Each R is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated-branched hydrocarbon group A hydrogen group, an unsaturated-cyclic hydrocarbon group, an aromatic group, or a derivative group thereof. Also, in formula (1), n is preferably 1.

Examples of the saturated straight-chain hydrocarbon group include, but are not limited to, methyl group, ethyl group, n-propyl group, n-butyl group, and the like. The saturated-branched hydrocarbon group includes, but is not particularly limited to, i-propyl group, t-butyl group, and the like. The saturated cyclic hydrocarbon group includes, but is not particularly limited to, a cyclopentyl group, a cyclohexyl group, and the like. The unsaturated straight-chain hydrocarbon group includes, but is not particularly limited to, a vinyl group, an allyl group, and the like. The unsaturated-branched hydrocarbon group includes i-propenyl group, 3-butenyl group and the like, but is not particularly limited. Examples of the unsaturated-cyclic hydrocarbon group include, but are not particularly limited to, a cyclopentenyl group, a cyclohexenyl group, and the like. Aromatic groups include, but are not particularly limited to, phenyl groups, naphthyl groups, and the like.

In addition, the derivative group in R is selected from functional groups such as carboxy group, carboxylate group (-COO-), hydroxy group, amino group and ammonium group for the main chain or side chain of the above various hydrocarbon groups. functional groups to which at least one type of is added or substituted, but is not particularly limited. Although the number of carbon atoms constituting the main chain of R is not particularly limited, it is preferably 20 or less, more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorous oxoacid group can be set within an appropriate range, facilitating penetration into cellulose fibers and increasing the yield of cellulose nanocrystals. can also In addition, when a plurality of R are present in the formula (1) or when a plurality of types of substituents represented by the above formula (1) are introduced into the cellulose fiber, the plurality of Rs present are the same. may be different.

β ^b+ is a cation having a valence of 1 or more, which is composed of an organic substance or an inorganic substance. An organic onium ion can be mentioned as a cation having a valence of 1 or more composed of an organic substance. Organic onium ions include, for example, organic ammonium ions and organic phosphonium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of monovalent or higher valent cations composed of inorganic substances include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, and ammonium ions. When a plurality of β ^b+ are present in the formula (1) or when a plurality of types of substituents represented by the above formula (1) are introduced into the cellulose fiber, the plurality of β ^b+ are the same. may be different. As the cation having a valence of 1 or more composed of an organic substance or an inorganic substance, sodium or potassium ions are preferable, but not particularly limited, because cellulose fibers containing β ^b+ are not easily yellowed when heated and are easily industrially available. .

More specifically, the phosphoric acid group or the substituent derived from the phosphoric acid group includes a phosphoric acid group (—PO ₃ H ₂ ), a salt of a phosphoric acid group, a phosphorous acid group (phosphonic acid group) (—PO ₂ H ₂ ), salts of phosphite group (phosphonic acid group). In addition, the phosphoric acid group or the substituent derived from the phosphoric acid group includes a condensed phosphoric acid group (e.g., pyrophosphate group), a condensed phosphonic acid group (e.g., polyphosphonic acid group), a phosphoric acid ester group ( For example, it may be a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkylphosphonic acid group (eg, a methylphosphonic acid group), or the like.

Further, the sulfur oxoacid group (a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). Each cellulose fiber may contain a plurality of substituents represented by the following formula (2). In this case, the plural introduced substituents represented by the following formula (2) may be the same or different.

In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (where 1=b×m). In addition, when n is 2 or more, multiple p may be the same number or may be different numbers. In the above structural formula, β ^b+ is a monovalent or higher cation composed of an organic substance or an inorganic substance. An organic onium ion can be mentioned as a cation having a valence of 1 or more composed of an organic substance. Organic onium ions include, for example, organic ammonium ions and organic phosphonium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of monovalent or higher-valent cations composed of inorganic substances include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, and ammonium ions. When multiple types of substituents represented by the above formula (2) are introduced into fibrous cellulose, the multiple β ^b+ may be the same or different. As the cation having a valence of 1 or more composed of an organic substance or an inorganic substance, sodium or potassium ions are preferable, but are not particularly limited, because cellulose fibers containing β ^b+ are not easily yellowed when heated and are easily industrially available. .

The amount of the ionic functional group introduced into the cellulose fiber is, for example, preferably 0.30 mmol/g or more, more preferably 0.50 mmol/g or more, more preferably 0.80 mmol/g per 1 g (mass) of fibrous cellulose. g or more, and even more preferably 1.00 mmol/g or more. In addition, the amount of the ionic functional group introduced into the cellulose fiber is, for example, preferably 5.20 mmol/g or less, more preferably 3.65 mmol/g or less per 1 g (mass) of fibrous cellulose. It is more preferably 50 mmol/g or less, and even more preferably 3.00 mmol/g or less. By setting the amount of the ionic functional group to be introduced within the above range, the ionic functional group-introduced cellulose nanocrystals to be obtained have good transparency and salt resistance.
Here, the denominator in units of mmol/g indicates the mass of fibrous cellulose when the counter ion of the ionic functional group is hydrogen ion (H ⁺ ).

The amount of ionic functional groups introduced into cellulose fibers and cellulose nanocrystals into which ionic functional groups have been introduced can be measured, for example, by neutralization titration or elemental analysis. In the measurement by the neutralization titration method, the introduction amount is measured by determining the pH change while adding alkali such as sodium hydroxide aqueous solution to the obtained slurry containing the cellulose fibers or the ionic functional group-introduced cellulose nanocrystals. do.

FIG. 1 is a graph showing the relationship between the amount of dropped NaOH and pH for a slurry containing cellulose fibers having a phosphorous acid group. The amount of phosphorus oxoacid groups introduced into cellulose fibers is measured, for example, as follows. The amount of phosphorous acid groups in the ionic functional group-introduced cellulose nanocrystals is also measured in the same manner.
First, a slurry containing cellulose fibers is treated with a strongly acidic ion exchange resin. In addition, before the treatment with the strongly acidic ion exchange resin, a defibration treatment similar to the fibrillation treatment step described below may be performed on the object to be measured, if necessary.
Next, the change in pH is observed while adding sodium hydroxide aqueous solution, and a titration curve as shown in the upper part of FIG. 1 is obtained. The titration curve shown in the upper part of FIG. 1 plots the measured pH against the amount of alkali added, and the titration curve shown in the lower part of FIG. 1 plots the pH against the amount of alkali added. The increment (differential value) (1/mmol) is plotted. In this neutralization titration, two points where the increment (the differential value of the pH with respect to the amount of alkali dropped) are maximized are confirmed in the curve obtained by plotting the measured pH against the amount of alkali added. Among these, the maximum point of the increment obtained first when the alkali is first added is called the first end point, and the maximum point of the increment obtained next is called the second end point. The amount of alkali required from the start of titration to the first end point is equal to the first dissociated acid amount of fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the first end point to the second end point The amount is equal to the second dissociated acid amount of fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second end point is equal to the amount of fibrous cellulose contained in the slurry used for titration. equal to the total dissociated acid content of A value obtained by dividing the amount of alkali required from the start of titration to the first end point by the solid content (g) in the slurry to be titrated is the amount of phosphorus oxoacid group introduced (mmol/g). In addition, when simply referring to the amount of phosphorus oxoacid groups introduced (or the amount of phosphorus oxoacid groups), it means the amount of the first dissociated acid.
In FIG. 1, the region from the start of titration to the first end point is called the first region, and the region from the first end point to the second end point is called the second region. For example, when the phosphoric acid group is a phosphoric acid group, and the phosphoric acid group causes condensation, it appears that the amount of weakly acidic groups in the phosphoric acid group (also referred to herein as the second dissociated acid amount) is The amount of alkali required in the second region is less than that required in the first region. On the other hand, the amount of strongly acidic groups in the phosphorus oxoacid group (also referred to herein as the amount of first dissociated acid) matches the amount of phosphorus atoms regardless of the presence or absence of condensation. In addition, when the phosphorous acid group is a phosphorous acid group, the weakly acidic group does not exist in the phosphorous acid group, so the amount of alkali required for the second region is reduced, or the amount of alkali required for the second region is may be zero. In this case, the titration curve has one point at which the pH increment is maximum.
In addition, since the denominator of the above-described phosphorus oxoacid group introduction amount (mmol/g) indicates the mass of acid-type cellulose fibers, the amount of phosphorus oxoacid groups possessed by acid-type cellulose fibers (hereinafter referred to as the amount of phosphorus oxoacid groups (acid type)). On the other hand, when the counterion of the phosphate group is substituted with an arbitrary cation C so as to have a charge equivalent, the denominator is converted to the mass of the cellulose fiber when the cation C is the counterion. , the amount of phosphorous acid groups (hereinafter referred to as the amount of phosphorous acid groups (C type)) possessed by the cellulose fiber having the cation C as a counter ion can be obtained.
That is, it is calculated by the following formula.
Phosphorus oxo acid group amount (C type) = Phosphorus oxo acid group amount (acid type) / {1 + (W-1) × A / 1000}
A [mmol/g]: total amount of anions derived from the phosphate groups possessed by the cellulose fiber (value obtained by adding the amount of strongly acidic groups and the amount of weakly acidic groups of phosphate groups)
W: Formula weight per valence of cation C (for example, 23 for Na and 9 for Al)

FIG. 2 is a graph showing the relationship between the dropping amount of NaOH and pH for cellulose fibers having a carboxyl group.
The amount of carboxyl groups introduced into cellulose fibers is measured, for example, as follows. The amount of carboxyl groups in the ionic functional group-introduced cellulose nanocrystals is also measured in the same manner.
First, a slurry containing cellulose fibers is treated with a strongly acidic ion exchange resin. In addition, before the treatment with the strongly acidic ion exchange resin, a fibrillation treatment similar to the fibrillation treatment step described below may be performed on the object to be measured, if necessary. Next, the change in pH is observed while adding an aqueous sodium hydroxide solution to obtain a titration curve as shown in FIG.
As shown in FIG. 2, in this neutralization titration, there is one point where the increment (differential value of pH with respect to the amount of alkali added) is maximum in the curve plotting the measured pH against the amount of alkali added. Observed. The maximum point of this increment is called the first end point. Here, the region from the start of titration to the first end point in FIG. 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the slurry used for titration. Then, by dividing the alkali amount (mmol) required in the first region of the titration curve by the solid content (g) in the cellulose fiber-containing slurry to be titrated, the introduction amount (mmol/g) of the carboxy group was calculated. Calculated.
The amount of carboxyl groups introduced above (mmol/g) is the amount of substituents per 1 g of mass of cellulose fibers when the counterion of the carboxyl group is hydrogen ion (H ⁺ ) (hereinafter referred to as the amount of carboxyl groups (acid type )).

In addition, since the denominator of the above-mentioned carboxy group introduction amount (mmol / g) is the mass of the acid-type cellulose fiber, the amount of carboxy groups possessed by the acid-type cellulose fiber (hereinafter referred to as the amount of carboxy groups (acid type) call). On the other hand, when the counter ion of the carboxy group is substituted with an arbitrary cation C so as to have a charge equivalent, the denominator is converted to the mass of the cellulose fiber when the cation C is the counter ion. , the amount of carboxy groups (hereinafter referred to as the amount of carboxy groups (C-type)) (mmol/g) possessed by cellulose fibers having cations C as counter ions can be obtained.
That is, it is calculated by the following formula.
Carboxy group amount (C type) = carboxy group amount (acid form) / {1 + (W-1) x (carboxy group amount (acid form)) / 1000}
W: Formula weight per valence of cation C (for example, 23 for Na and 9 for Al)

In addition, the amounts of sulfur oxoacid groups and sulfone groups introduced into cellulose fibers and cellulose nanocrystals introduced with an ionic functional group were determined by exposing the obtained cellulose fibers or cellulose nanocrystals introduced with an ionic functional group to perchloric acid and concentrated nitric acid. After wet ashing, the mixture is diluted by a suitable factor and the amount of sulfur is measured by ICP emission spectrometry.
The sulfur oxoacid group amount/sulfonic acid group amount (unit: mmol/g) is obtained by dividing this sulfur amount by the absolute dry mass of the cellulose fiber or cellulose nanocrystal having an ionic functional group introduced therein.

In addition, in measuring the amount of substituents by the titration method, if the amount of dropping of one drop of sodium hydroxide solution is too large, or if the titration interval is too short, the amount of substituents will be lower than the original value, and an accurate value cannot be obtained. sometimes not. Appropriate dropping amount and titration interval are, for example, titration of 10 to 50 μL of 0.1N sodium hydroxide aqueous solution in 5 to 30 seconds. In addition, in order to eliminate the influence of carbon dioxide dissolved in the cellulose fiber-containing slurry, for example, it is desirable to measure while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration to the end of titration.

Cellulose fibers may have carbamide groups derived from urea and/or urea derivatives that are added in the production process of the ionic functional group-introduced cellulose fibers described below. In this case, the amount of carbamide groups introduced into the cellulose fibers (the amount of carbamide groups) is, for example, preferably 1.50 mmol/g or less, more preferably 1.00 mmol/g or less per 1 g (mass) of cellulose fibers. , is more preferably 0.30 mmol/g or less, and particularly preferably 0.20 mmol/g or less. The amount of carbamide groups introduced into the cellulose fiber (carbamide group amount) may be 0.00 mmol/g. Since the carbamide group and the phosphorus oxoacid group are groups introduced by reacting with the hydroxyl groups of cellulose, the more the amount of the carbamide group introduced, the smaller the amount of the phosphorus oxoacid group introduced. Therefore, by setting the amount of the carbamide group to be introduced within the above range, the amount of the phosphorus oxoacid group to be introduced can be increased and brought into an appropriate range. In addition, since the carbamide group itself has no electrical conductivity, the cellulose introduced with the ionic functional group cannot be obtained by introducing the carbamide group. Therefore, by setting the amount of carbamide groups to be introduced within the above range and increasing the amount of phosphorus oxoacid groups to be introduced, the transparency and salt resistance of the resulting ionic functional group-introduced cellulose nanocrystals can be improved. .

The amount of carbamide groups introduced into the cellulose fibers and the cellulose nanocrystals introduced with an ionic functional group is determined by measuring the amount of nitrogen covalently bound to cellulose. Specifically, after liberating and removing ionic nitrogen (ammonium ion) from a measurement object containing cellulose fibers or cellulose nanocrystals introduced with an ionic functional group, the amount of nitrogen is measured by trace nitrogen analysis. Liberation of ionic nitrogen (ammonium ion) is carried out under conditions in which substantially no nitrogen covalently bound to cellulose is removed. For example, after the phosphorus oxoacid group-introducing step, ammonium ions may be liberated by alkali treatment, washed and removed, and then step B described later may be performed, or after step B or step C, ammonium ions may be dissolved by a strongly acidic ion exchange resin. Ions may be removed by adsorption. As a device for measuring the amount of nitrogen by the trace nitrogen analysis method, for example, a trace total nitrogen analyzer TN-110 manufactured by Mitsubishi Chemical Analytech Co., Ltd. can be used. The cellulose fibers or the ionic functional group-introduced cellulose nanocrystals are dried at a low temperature (for example, in a vacuum dryer at 40° C. for 24 hours) before the measurement until they become absolutely dry. The amount (mmol/g) of carbamide groups introduced per unit mass of cellulose fibers or cellulose nanocrystals introduced with an ionic functional group is the amount per unit mass of cellulose fibers or cellulose nanocrystals introduced with an ionic functional group obtained by trace nitrogen analysis. is calculated by dividing the nitrogen content (g/g) by the atomic weight of nitrogen.

[Ionic functional group introduction step]
In order to introduce an ionic functional group into the cellulose fiber, the ionic functional group introduction step of introducing the ionic functional group into the cellulose fiber described above is provided, and the step B is preceded by a washing step and an alkali treatment step. in this order, and may have an acid treatment step instead of or in addition to the washing step. The ionic functional group introduction step includes a phosphorus oxoacid group introduction step, a carboxyl group introduction step, a sulfur oxoacid group introduction step, an oxidation step with a chlorine-based oxidizing agent, a xanthate group introduction step, a sulfone group introduction step, a carboxyalkylation step, are exemplified. Each of these will be described below.

-Phosphorus oxoacid group introduction step-
In the phosphorus oxoacid group-introducing step, at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing a phosphorus oxoacid group by reacting with a hydroxyl group possessed by the cellulose fiber is applied to the cellulose fiber. It is a process to let Through this step, the phosphate group-introduced fiber is obtained.
In the phosphate group-introducing step according to the present embodiment, the reaction between the cellulose fiber and compound A may be performed in the presence of at least one selected from urea and derivatives thereof (hereinafter also referred to as "compound B"). . On the other hand, the cellulose fiber and compound A may be reacted in the absence of compound B.
An example of a method of allowing compound A to act on cellulose fibers in the presence of compound B is a method of mixing compound A and compound B with cellulose fibers in a dry state, in a wet state, or in a slurry state. Among these, it is preferable to use cellulose fibers in a dry state or a wet state, and it is particularly preferable to use cellulose fibers in a dry state, because the uniformity of the reaction is high. Although the form of the cellulose fiber is not particularly limited, it is preferably, for example, cotton-like or thin sheet-like. The compound A and compound B can be added to the cellulose fiber in the form of a powder, a solution dissolved in a solvent, or a melted state by heating to a melting point or higher. Among these, it is preferable to add in the form of a solution dissolved in a solvent, particularly in the form of an aqueous solution, since the uniformity of the reaction is high. Moreover, the compound A and the compound B may be added simultaneously to the cellulose fiber, may be added separately, or may be added as a mixture. The method of adding compound A and compound B is not particularly limited, but when compound A and compound B are in the form of a solution, the cellulose fibers may be immersed in the solution to absorb the liquid and then taken out. The solution may be added dropwise to the Further, the required amount of compound A and compound B may be added to the cellulose fiber, or after adding the excess amount of compound A and compound B to the cellulose fiber, the excess compound A and compound B are removed by pressing or filtering. may be removed.

The compound A used in the present embodiment may be any compound having a phosphorus atom and capable of forming an ester bond with cellulose. Salts, phosphoric anhydride (diphosphorus pentoxide) and the like can be mentioned, but are not particularly limited. Phosphoric acid of various purities can be used, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid can be used. Phosphorous acid includes, for example, 99% phosphorous acid (phosphonic acid). Dehydration-condensed phosphoric acid is obtained by condensing two or more molecules of phosphoric acid by dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts and ammonium salts of phosphoric acid, phosphorous acid or dehydrated condensed phosphoric acids. It can be a degree of harmony.
Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, or ammonium salt of phosphoric acid from the viewpoint of high efficiency of introduction of a phosphoric acid group, low cost, and easy industrial application is preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or ammonium dihydrogen phosphate is more preferred.
The amount of compound A added to the cellulose fibers is not particularly limited, but for example, when the amount of compound A added is converted to the amount of phosphorus atoms, the amount of phosphorus atoms added to the cellulose fibers (absolute dry mass) is 0.5% by mass or more. It is preferably 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the cellulose fiber within the above range, the transparency and salt resistance of the ionic functional group-introduced cellulose nanocrystals to be obtained can be further improved. On the other hand, by setting the amount of phosphorus atoms to be added to the cellulose fiber to the above upper limit or less, it is possible to balance the effect of improving the yield and the cost.

Compound B used in this embodiment is at least one selected from urea and derivatives thereof as described above. Compound B includes, for example, urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea.
From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. From the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.
The amount of compound B added to cellulose fibers (absolute dry mass) is not particularly limited, but is preferably, for example, 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, More preferably, it is 100% by mass or more and 350% by mass or less.

In the reaction of cellulose fiber and compound A, in addition to compound B, for example, amides or amines may be included in the reaction system. Examples of amides include formamide, dimethylformamide, acetamide, dimethylacetamide and the like. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine and hexamethylenediamine. Among these, triethylamine in particular is known to work as a good reaction catalyst.

In the phosphorus oxoacid group-introducing step, it is preferable to heat-treat the cellulose fibers after the compound A or the like is added to or mixed with the cellulose fibers. As the heat treatment temperature, it is preferable to select a temperature that can efficiently introduce phosphorus oxoacid groups while suppressing thermal decomposition and hydrolysis reaction of cellulose fibers. The heat treatment temperature is, for example, preferably 50° C. or higher and 300° C. or lower, more preferably 100° C. or higher and 250° C. or lower, and even more preferably 130° C. or higher and 200° C. or lower. In addition, for the heat treatment, equipment having various heat media can be used, for example, a stirring dryer, a rotary dryer, a disc dryer, a roll heater, a plate heater, a fluidized bed dryer, and a band dryer. A mold drying device, a filter drying device, a vibrating fluidized drying device, a flash drying device, a vacuum drying device, an infrared heating device, a far infrared heating device, a microwave heating device, and a high frequency drying device can be used.

In the heat treatment according to the present embodiment, for example, the compound A is added to the thin sheet-like cellulose fiber by a method such as impregnation, and then heated, or the cellulose fiber and the compound A are heated while kneading or stirring with a kneader or the like. method can be adopted. This makes it possible to suppress concentration unevenness of the compound A in the cellulose fibers and to more uniformly introduce the phosphate groups to the cellulose fiber surfaces. This is because when water molecules move to the cellulose fiber surface during drying, the dissolved compound A is attracted to the water molecules by surface tension and similarly moves to the cellulose fiber surface (that is, the concentration unevenness of the compound A is It is thought that this is due to the fact that it is possible to suppress the occurrence of
In addition, the heating apparatus used for the heat treatment constantly removes the moisture retained by the slurry and the moisture generated due to the dehydration condensation (phosphoric acid esterification) reaction between the compound A and the hydroxyl groups contained in the cellulose in the cellulose fibers, for example. A device that can be discharged to the outside is preferable. As such a heating device, for example, an air-blowing oven can be used. In addition to being able to suppress the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of phosphorylation, by constantly discharging the water in the device system, it is possible to suppress the acid hydrolysis of the sugar chains in the cellulose fibers. can also
The heat treatment time is, for example, preferably 1 second or more and 300 minutes or less after water is substantially removed from the cellulose fibers, more preferably 1 second or more and 1,000 seconds or less, and 10 seconds or more and 800 seconds or less. Seconds or less is more preferable. In the present embodiment, the amount of phosphorus oxoacid groups to be introduced can be set within a preferable range by setting the heating temperature and the heating time within appropriate ranges.

The phosphorus oxoacid group-introducing step may be performed at least once, but may be performed repeatedly two or more times. By performing the step of introducing phosphate groups two or more times, many phosphate groups can be introduced into the cellulose fibers. In the present embodiment, as an example of a preferred aspect, the case where the step of introducing a phosphorus oxoacid group is performed twice is mentioned.

The amount of phosphorus oxoacid groups introduced into cellulose fibers is, for example, preferably 0.30 mmol/g or more, more preferably 0.50 mmol/g or more, and 0.80 mmol/g or more per 1 g (mass) of cellulose fibers. is more preferably 1.00 mmol/g or more, and particularly preferably 1.25 mmol/g or more. In addition, the amount of phosphorus oxoacid groups introduced into cellulose fibers is, for example, preferably 5.20 mmol/g or less, more preferably 3.65 mmol/g or less per 1 g (mass) of cellulose fibers, and more preferably 3.00 mmol/g. g or less is more preferable. By setting the amount of the phosphorus oxoacid group to be introduced within the above range, the transparency and salt resistance of the resulting ionic functional group-introduced cellulose nanocrystal can be improved.

-Carboxy group introduction step-
In the carboxyl group introduction step, the cellulose fiber is subjected to oxidation treatment such as ozone oxidation, oxidation by the Fenton method, TEMPO oxidation treatment, a compound having a carboxylic acid-derived group or a derivative thereof, or an acid of a compound having a carboxylic acid-derived group. This is done by treatment with an anhydride or derivative thereof.
The compound having a carboxylic acid-derived group is not particularly limited. Examples include tricarboxylic acid compounds. Derivatives of compounds having a carboxylic acid-derived group are not particularly limited, but include, for example, imidized acid anhydrides of compounds having a carboxy group and derivatives of acid anhydrides of compounds having a carboxy group. Examples of imidized acid anhydrides of compounds having a carboxy group include, but are not particularly limited to, imidized dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

The acid anhydride of the compound having a group derived from carboxylic acid is not particularly limited. acid anhydrides; In addition, the acid anhydride derivative of the compound having a carboxylic acid-derived group is not particularly limited. Acid anhydrides in which at least some of the hydrogen atoms are substituted with substituents such as alkyl groups and phenyl groups can be mentioned.

In the carboxyl group introduction step, when the TEMPO oxidation treatment is performed, it is preferable to perform the treatment, for example, under the condition of pH 6 or more and 8 or less. Such treatment is also referred to as neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment includes, for example, sodium phosphate buffer (pH = 6.8), pulp as cellulose fiber, and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as catalyst. This can be done by adding sodium hypochlorite as a nitroxy radical, sacrificial reagent. Furthermore, coexistence of sodium chlorite enables efficient oxidation of aldehydes generated in the process of oxidation to carboxyl groups.
Moreover, the TEMPO oxidation treatment may be performed under the condition that the pH is 10 or more and 11 or less. Such treatment is also called alkali TEMPO oxidation treatment. Alkaline TEMPO oxidation treatment can be performed, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a cocatalyst, and sodium hypochlorite as an oxidizing agent to pulp as cellulose fibers. .
The amount of carboxyl groups to be introduced into cellulose fibers varies depending on the type of substituents. It is more preferably 0.50 mmol/g or more, further preferably 0.80 mmol/g or more, even more preferably 0.90 mmol/g or more, and particularly preferably 1.00 mmol/g or more. preferable. Also, it is preferably 2.5 mmol/g or less, more preferably 2.20 mmol/g or less, and even more preferably 2.00 mmol/g or less. In addition, when the substituent is a carboxymethyl group, it may be 5.8 mmol/g or less per 1 g (mass) of fibrous cellulose.

-Sulfur oxoacid group introduction step-
The production process of the ionic functional group-introduced cellulose nanocrystals may include, for example, a sulfur oxoacid group-introducing process as the ionic functional group-introducing process. In the step of introducing sulfur oxo acid groups, hydroxyl groups of cellulose fibers and sulfur oxo acids react with each other to obtain cellulose fibers having sulfur oxo acid groups (sulfur oxo acid group-introduced fibers).

In the sulfur oxoacid group-introducing step, at least one selected from compounds capable of introducing sulfur oxoacid groups by reacting with the hydroxyl groups of the cellulose fibers in place of compound A in the <phosphorus oxoacid group-introducing step>. (hereinafter also referred to as "compound C") is used. Compound C is not particularly limited as long as it has a sulfur atom and is capable of forming an ester bond with cellulose, and includes sulfuric acid or its salts, sulfurous acid or its salts, and sulfate amides. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid) can be used. Sulfurous acid includes 5% sulfurous acid water. Sulfates or sulfites include lithium, sodium, potassium, ammonium salts, etc. of sulfates or sulfites, which can be of varying degrees of neutralization. As the sulfate amide, sulfamic acid or the like can be used. In the sulfur oxoacid group-introducing step, it is preferable to use compound B in the same manner as in <phosphorus oxoacid group-introducing step>.

In the sulfur oxoacid group-introducing step, it is preferred that the cellulose fibers are mixed with an aqueous solution containing sulfur oxoacid and urea and/or a urea derivative, and then the cellulose fibers are heat-treated. As the heat treatment temperature, it is preferable to select a temperature at which sulfur oxoacid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis reaction of the fiber. The heat treatment temperature is preferably 100° C. or higher, more preferably 120° C. or higher, and even more preferably 150° C. or higher. The heat treatment temperature is preferably 300° C. or lower, more preferably 250° C. or lower, and even more preferably 200° C. or lower.

In the heat treatment step, it is preferable to heat until the moisture is substantially removed. For this reason, the heat treatment time varies depending on the amount of water contained in the cellulose fibers, the amount of sulfur oxo acid, and the added amount of the aqueous solution containing urea and/or urea derivatives, but for example, 10 seconds to 10,000 seconds It is preferable to: Equipment having various heat media can be used for the heat treatment, for example, a stirring dryer, a rotary dryer, a disk dryer, a roll heater, a plate heater, a fluidized bed dryer, and a band dryer. An apparatus, filter drying apparatus, vibrating fluidized drying apparatus, air flow drying apparatus, vacuum drying apparatus, infrared heating apparatus, far infrared heating apparatus, microwave heating apparatus, and high frequency drying apparatus can be used.

The amount of sulfur oxoacid groups introduced into the cellulose fiber is preferably 0.05 mmol/g or more, more preferably 0.10 mmol/g or more, further preferably 0.20 mmol/g or more, It is more preferably 0.50 mmol/g or more, even more preferably 0.80 mmol/g or more, and particularly preferably 0.90 mmol/g or more. The amount of sulfur oxoacid groups introduced into the cellulose fibers is preferably 5.00 mmol/g or less, more preferably 3.00 mmol/g or less. By setting the amount of sulfur oxoacid groups to be introduced within the above range, it is possible to improve defibration properties and obtain ionic functional group-introduced cellulose nanocrystals with a smaller fiber width.

-Oxidation step with a chlorine-based oxidizing agent (second carboxyl group introduction step)-
The step of introducing an ionic functional group may include, for example, an oxidation step using a chlorine-based oxidizing agent. In the oxidation step using a chlorine-based oxidizing agent, a carboxyl group is introduced into the cellulose fibers by adding the chlorine-based oxidizing agent to cellulose fibers having hydroxyl groups in a wet or dry state and performing a reaction.

Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorite, chlorous acid, chlorite, chloric acid, chlorate, perchloric acid, perchlorate, and chlorine dioxide. Sodium hypochlorite, sodium chlorite, and chlorine dioxide are preferable from the viewpoints of the efficiency of introduction of the ionic functional group and the transparency, salt resistance, cost, and ease of handling of the resulting ionic functional group-introduced cellulose nanocrystals. .
The chlorine-based oxidizing agent may be added to the cellulose fiber as it is, or may be dissolved in an appropriate solvent and added.

The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent is preferably 1% by mass or more and 1,000% by mass or less, for example, in terms of effective chlorine concentration, and 5% by mass or more and 500% by mass. It is more preferably 10% by mass or more and 100% by mass or less.
The amount of the chlorine-based oxidizing agent added to 100 parts by mass of cellulose fibers is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 10 parts by mass or more and 10,000 parts by mass or less, and 100 parts by mass. It is more preferable that it is 5,000 parts by mass or less.

The reaction time with the chlorine-based oxidizing agent in the oxidation step with the chlorine-based oxidizing agent may vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, and 10 minutes or more and 500 minutes or less. More preferably, the time is 20 minutes or more and 400 minutes or less.
The pH during the reaction is preferably 5 or more and 15 or less, more preferably 7 or more and 14 or less, and even more preferably 9 or more and 13 or less. Moreover, at the start of the reaction, the pH during the reaction is preferably kept constant (for example, pH 11) while appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products and the like may be washed with water and removed by filtration or the like.

-Xanthate Group Introduction Step (Xanthate Esterification Step)-
The ionic functional group introduction step may include, for example, a xanthate group introduction step (hereinafter also referred to as a xanthate formation step). In the xanthate-forming step, carbon disulfide and an alkali compound are added to cellulose fibers having hydroxyl groups in a wet or dry state and reacted to introduce xanthate groups into the cellulose fibers. Specifically, carbon disulfide is added to the cellulose fibers converted to alkali cellulose by the method described later, and the reaction is carried out.

≪Alkaline Celluloseization≫
When introducing an ionic functional group into the cellulose fiber, it is preferable to react the cellulose contained in the cellulose fiber with an alkaline solution to convert the cellulose into alkali cellulose. This treatment causes ion dissociation of some of the hydroxyl groups of cellulose, and can enhance nucleophilicity (reactivity). The alkali compound contained in the alkali solution is not particularly limited, and may be an inorganic alkali compound or an organic alkali compound. For example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide are preferably used because of their high versatility. Alkali cellulose conversion may be performed simultaneously with the introduction of the ionic functional group, may be performed as a preceding step, or may be performed at both timings.

The temperature of the solution when alkali cellulose conversion is started is preferably 0° C. or higher and 50° C. or lower, more preferably 5° C. or higher and 40° C. or lower, and even more preferably 10° C. or higher and 30° C. or lower.

As the concentration of the alkaline solution, the molar concentration is preferably 0.01 mol/L or more and 4 mol/L or less, more preferably 0.1 mol/L or more and 3 mol/L or less, and 1 mol/L or more and 2.5 mol/L. L or less is more preferable. In particular, when the treatment temperature is less than 10°C, it is preferably 1 mol/L or more and 2 mol/L or less.

The treatment time for alkali cellulose conversion is preferably 1 minute or longer, more preferably 10 minutes or longer, and even more preferably 30 minutes or longer. Also, the alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less, and even more preferably 4 hours or less.

By adjusting the type of alkaline solution, treatment temperature, concentration, and immersion time as described above, it is possible to suppress the penetration of the alkaline solution into the crystalline region of cellulose, and the crystalline structure of cellulose type I can be easily maintained, and the ionic functionality is improved. The yield of group-introduced cellulose nanocrystals can be increased.

If the introduction of ionic functional groups and conversion to alkali cellulose are not performed at the same time, the alkali cellulose obtained by the alkali treatment is subjected to solid-liquid separation and moisture is removed by general deliquoring methods such as centrifugation and filtration. It is preferable to keep This improves the reaction efficiency in the subsequent step of introducing an ionic functional group. The cellulose fiber concentration after solid-liquid separation is preferably 5% or more and 50% or less, more preferably 10% or more and 40% or less, and even more preferably 15% or more and 35% or less.

- Phosphonic group or phosphine group introduction step (phosphoalkylation step) -
The step of introducing an ionic functional group may include a step of introducing a phosphone group or a phosphine group (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phospho group or a phosphine group (compound E _A ) as an essential component, an alkali compound as an optional component, and a compound B selected from the aforementioned urea and its derivatives are wetted. Alternatively, a phosphonic group or a phosphine group is introduced into the cellulose fiber by adding it to the cellulose fiber having hydroxyl groups in a dry state and performing a reaction.

Examples of reactive groups include halogenated alkyl groups, vinyl groups, epoxy groups (glycidyl groups), and the like.
Compound EA includes, for example, _{vinylphosphonic} acid, phenylvinylphosphonic acid, phenylvinylphosphinic acid and the like. The compound _EA is preferably vinyl phosphonic acid from the viewpoints of the efficiency of introduction of substituents, the transparency and salt resistance of the ionic functional group-introduced cellulose nanocrystals to be obtained, the cost, and the ease of handling.
Further, as an optional component, it is preferable to use the compound B in the above-described <Phosphorus oxoacid group-introducing step> in the same manner, and the addition amount is preferably as described above.

When compound _EA is added, it may be added as a reagent (solid or liquid) to the cellulose fibers as it is, or it may be dissolved in an appropriate solvent and added. Cellulose fibers are preferably converted to alkali cellulose in advance or are converted to alkali cellulose simultaneously with the reaction. The method of alkali cellulose conversion is as described above.

The temperature during the reaction is, for example, preferably 50° C. or higher and 300° C. or lower, more preferably 100° C. or higher and 250° C. or lower, and even more preferably 130° C. or higher and 200° C. or lower.

The amount of Compound E _A added to 100 parts by mass of cellulose fibers is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and 5 parts by mass. It is more preferable that the amount is 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and 20 minutes or more and 400 minutes or less. is more preferred. After the reaction, excess reaction reagents, by-products and the like may be washed with water and removed by filtration or the like.

-Sulfone Group Introduction Step (Sulfoalkylation Step)-
The ionic functional group introduction step may include, for example, a sulfone group introduction step (sulfoalkylation step). In the sulfoalkylation, a compound having a reactive group and a sulfone group (compound E _B ) as essential components, an alkali compound as an optional component, and the above-described compound B selected from urea and its derivatives are wetted or dried. A sulfone group is introduced into the cellulose fiber by reacting it in addition to the cellulose fiber having a hydroxyl group in the state.

Examples of reactive groups include halogenated alkyl groups, vinyl groups, epoxy groups (glycidyl groups), and the like.
Compound E _B includes sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid and the like. Among them, sodium vinyl sulfonate is preferable from the viewpoints of the efficiency of introduction of substituents, the transparency and salt resistance of the resulting ionic functional group-introduced cellulose nanocrystals, the cost, and the ease of handling.
Furthermore, as an optional component, it is preferable to use compound B in the same manner as in the above-described <Phosphorus oxoacid group-introducing step>, and the amount added is preferably as described above.

The compound _EB may be added as a reagent to the cellulose fiber, or may be dissolved in an appropriate solvent and added. It is preferable that the cellulose fibers are converted to alkali cellulose in advance or to be converted to alkali cellulose simultaneously with the reaction. The method of alkali cellulose conversion is as described above.

The temperature during the reaction is, for example, preferably 50° C. or higher and 300° C. or lower, more preferably 100° C. or higher and 250° C. or lower, and even more preferably 130° C. or higher and 200° C. or lower.

The amount of compound _EB added to 100 parts by mass of cellulose fibers is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and 5 parts by mass. It is more preferable that the content is 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and 15 minutes or more and 400 minutes or less. is more preferred.
After the reaction, excess reaction reagents, by-products and the like may be washed with water and removed by filtration or the like.

-Carboxyalkylation step (third carboxy group introduction step)-
The ionic functional group introduction step may include, for example, a carboxyalkylation step. A compound having a reactive group and a carboxyl group (compound E _C ) as an essential component, an alkali compound as an optional component, and the above-described compound B selected from urea and its derivatives, in a wet or dry state, having a hydroxyl group A carboxy group is introduced into the cellulose fiber by performing a reaction in addition to the cellulose fiber.

Examples of reactive groups include halogenated alkyl groups, vinyl groups, epoxy groups (glycidyl groups), and the like.
As the compound E _C , monochloroacetic acid, sodium monochloroacetate, and 2-chloropropionic acid are selected from the viewpoints of efficiency of introduction of substituents, transparency and salt resistance of the resulting ionic functional group-introduced cellulose nanocrystals, cost, and ease of handling. , 3-chloropropionic acid, sodium 2-chloropropionate, sodium 3-chloropropionate are preferred.
Further, as an optional component, it is preferable to use the compound B in the above-described <Phosphorus oxoacid group-introducing step> in the same manner, and the addition amount is preferably as described above.

The compound E _C may be added as a reagent to the cellulose fibers, or may be added after being dissolved in an appropriate solvent. Cellulose fibers are preferably converted to alkali cellulose in advance or are converted to alkali cellulose simultaneously with the reaction. The method of alkali cellulose conversion is as described above.

The temperature during the reaction is, for example, preferably 50° C. or higher and 300° C. or lower, more preferably 100° C. or higher and 250° C. or lower, and even more preferably 130° C. or higher and 200° C. or lower.

The amount of compound E _C added to 100 parts by mass of cellulose fibers is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and 5 parts by mass. It is more preferable that the amount is 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 3 minutes or more and 500 minutes or less, and 5 minutes or more and 400 minutes or less. is more preferred.
After the reaction, excess reaction reagents, by-products and the like may be washed with water and removed by filtration or the like.

- Cationic group introduction step (cationization step) -
A compound having a reactive group and a cationic group (compound E _D ) as an essential component, an alkali compound as an optional component, the above-described compound B selected from urea and its derivatives, and a hydroxyl group in a wet or dry state. A cationic group is introduced into the cellulose fibers by performing a reaction in addition to the cellulose fibers possessed.

Examples of reactive groups include halogenated alkyl groups, vinyl groups, epoxy groups (glycidyl groups), and the like.

As the compound E _D , glycidyltrimethylammonium chloride, 3-chloro-2-hydroxy Propyltrimethylammonium chloride and the like are preferred.

Furthermore, as an optional component, it is also preferable to use compound B in the above-described <Phosphorus oxoacid group-introducing step> in the same manner. It is preferable that the amount to be added is also as described above.

Compound E _D may be added as a reagent to the cellulose fiber, or may be dissolved in an appropriate solvent and added. Cellulose fibers are preferably converted to alkali cellulose in advance or are converted to alkali cellulose simultaneously with the reaction. The method of alkali cellulose conversion is as described above.

The temperature during the reaction is, for example, preferably 50° C. or higher and 300° C. or lower, more preferably 100° C. or higher and 250° C. or lower, and even more preferably 130° C. or higher and 200° C. or lower.

The amount of compound E _D added to 100 parts by mass of cellulose fibers is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and 5 parts by mass. It is more preferable that the amount is 1,000 parts by mass or less.

The reaction time may vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 5 minutes or more and 500 minutes or less, and 10 minutes or more and 400 minutes or less. is more preferred.
After the reaction, excess reaction reagents, by-products and the like may be washed with water and removed by filtration or the like.

[Washing process]
In the production method of the present embodiment, the ionic functional group-introduced fiber can be subjected to a washing step, if necessary, before step B described later. The washing step is performed by washing the ionic functional group-introduced cellulose fiber with water or an organic solvent, for example. Moreover, the washing process may be performed after each process described later, and the number of times of washing performed in each washing process is not particularly limited.

[Alkaline treatment step]
An alkali treatment may be performed on the ionic functional group-introduced cellulose fiber between step A (ionic functional group introduction step) and step B (hydrolysis step) to be described later. The method of alkali treatment is not particularly limited, but includes, for example, a method of immersing the ionic functional group-introduced cellulose fibers in an alkali solution.
The alkali compound contained in the alkali solution is not particularly limited, and may be an inorganic alkali compound or an organic alkali compound. In the present embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of its high versatility. Moreover, the solvent contained in the alkaline solution may be either water or an organic solvent. Among them, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent exemplified by alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is preferable because of its high versatility.
Although the temperature of the alkaline solution in the alkaline treatment step is not particularly limited, it is preferably 5° C. or higher and 80° C. or lower, more preferably 10° C. or higher and 60° C. or lower. The immersion time of the ionic functional group-introduced fiber in the alkali solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes or more and 30 minutes or less, more preferably 10 minutes or more and 20 minutes or less. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but for example, it is preferably 100% by mass or more and 100,000% by mass or less with respect to the absolute dry mass of the ionic functional group-introduced fiber, and 1,000% by mass. It is more preferable that the content is not less than 10,000% by mass or less.
When the cellulose fiber into which an ionic functional group is introduced has an anionic group, the alkali treatment may be neutralization treatment or ion exchange treatment of the anionic group. In this case, the temperature of the alkaline solution is preferably room temperature.

In order to reduce the amount of alkaline solution used in the alkaline treatment step, the ionic functional group-introduced cellulose fibers may be washed with water or an organic solvent after the ionic functional group-introducing step and before the alkaline treatment step. . After the alkali treatment step and before step B, it is preferable to wash the alkali-treated ionic functional group-introduced cellulose fibers with water or an organic solvent from the viewpoint of improving handleability.

[Acid treatment process]
The ionic functional group-introduced cellulose fiber may be subjected to an acid treatment between the ionic functional group-introducing step and the hydrolysis step described below. For example, the ionic functional group introduction step, acid treatment step, alkali treatment step, step B and step C may be performed in this order.
The method of acid treatment is not particularly limited, but includes, for example, a method of immersing the ionic functional group-introduced cellulose fiber in an acid solution containing an acid. Although the concentration of the acid liquid used is not particularly limited, it is preferably 10% by mass or less, more preferably 5% by mass or less. Moreover, the pH of the acidic liquid to be used is not particularly limited. Examples of the acid contained in the acid solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acid include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid and the like. Carboxylic acids include, for example, formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, it is particularly preferable to use hydrochloric acid or sulfuric acid.
The temperature of the acid solution in the acid treatment is not particularly limited. The immersion time in the acid solution in the acid treatment is not particularly limited, but is preferably 5 minutes or more and 120 minutes or less, more preferably 10 minutes or more and 60 minutes or less. The amount of the acid solution used in the acid treatment is not particularly limited. % or more and 10,000 mass % or less.
When the cellulose fiber into which an ionic functional group is introduced has a cationic group, the acid treatment may be neutralization treatment or ion exchange treatment of the cationic group. In this case, the temperature of the acid solution is preferably room temperature.

<Process B>
Step B is a hydrolysis step of hydrolyzing the cellulose fiber into which the ionic functional group has been introduced with an acidic aqueous solution having a concentration of 5 mol/L or more.
It is preferable that the above-mentioned cellulose fiber into which an ionic functional group has been introduced (ionic functional group-introduced cellulose fiber) has a washing step after step A and before step B.
The hydrolysis step removes the amorphous portion in the cellulose fiber into which the ionic functional group has been introduced, thereby improving the crystallinity. Further, in the hydrolysis step, for example, the condensed portion in the phosphonic acid is hydrolyzed, and the difference between the first dissociated amount and the second dissociated amount in the resulting ionic functional group-introduced cellulose nanocrystal becomes smaller or equal. Become.
In the hydrolysis step, the ionic functional groups introduced into the amorphous sites in the cellulose fibers are removed along with the hydrolysis of the cellulose fibers. The amount of ionic functional groups introduced into the ionic functional group-introduced cellulose nanocrystals obtained through Steps B and C is smaller than the amount of ionic functional groups introduced into the cellulose nanocrystals. In addition, carbamide groups and the like introduced into the amorphous sites of the cellulose fibers are also removed by the hydrolysis step, yielding ionic functional group-introduced cellulose nanocrystals of higher purity.

[Aqueous aqueous solution]
In step B, an acidic aqueous solution with a concentration of 5 mol/L or more is used.
Examples of the acid contained in the acidic aqueous solution include inorganic acids and organic acids such as sulfonic acids and carboxylic acids.
Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid.
Examples of sulfonic acid include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid and the like. Carboxylic acids include, for example, formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid.
Also, the aqueous solution of phosphoric acid may be an aqueous solution of diphosphorus pentoxide. The use of diphosphorus pentoxide is preferable in that it is possible to obtain a highly concentrated acidic aqueous solution, and that it can be recovered and reused as regenerated diphosphorus pentoxide after being used in the hydrolysis treatment.
Among these, the acidic aqueous solution used in step B is preferably an aqueous solution of an acid compound selected from the group consisting of phosphoric acid, sulfuric acid, diphosphorus pentoxide, and hydrochloric acid.

The concentration of the acidic aqueous solution used in step B is 5 mol/L or higher, preferably 7 mol/L or higher, more preferably 9 mol/L or higher, still more preferably 10 mol/L or higher, and from the viewpoint of ease of operation. Therefore, it is preferably 30 mol/L or less, more preferably 25 mol/L or less, and still more preferably 20 mol/L or less.

[Hydrolysis step]
The concentration of the ionic functional group-introduced cellulose fiber in step B is preferably 1% by mass or more, more preferably 1.5% by mass or more, and preferably 10% by mass, from the viewpoint of hydrolysis reaction reactivity. Below, more preferably 7.5% by mass or less, still more preferably 5% by mass or less.
The reaction temperature in step B is preferably 50° C. or higher, more preferably 70° C. or higher, still more preferably 90° C. or higher, and preferably 100° C. or lower, from the viewpoint of hydrolysis reaction reactivity.
The reaction time in step B is preferably 5 minutes or longer, more preferably 15 minutes or longer, and still more preferably 30 minutes or longer, from the viewpoint of hydrolysis reaction reactivity and production time reduction. It is 12 hours or less, more preferably 6 hours or less, still more preferably 3 hours or less.

After step B and before step C, it is preferable to have a purification step.
In the purification step, it is preferable to remove the acidic aqueous solution used for hydrolysis by repeating solid-liquid separation and re-dispersion in water.
Further, after the above treatment, it is preferable to purify the slurry by bringing it into contact with a strongly basic ion-exchange resin and treating it until there is no fluctuation in the electrical conductivity and pH of the slurry.

<Process C>
Step C is a defibration step of fibrillating the hydrolyzed ionic functional group-introduced fibers obtained in step B.
In the defibration step, the hydrolyzed ionic functional group-introduced fibers obtained in step B are preferably made into a dispersion (slurry) and subjected to fibrillation.

[Fibrillation process]
By defibrating the hydrolyzed ionic functional group-introduced cellulose fibers in the fibrillation treatment step, ionic functional group-introduced cellulose nanocrystals are obtained.
In the defibration treatment process, for example, a fibrillation treatment device can be used. The fibrillation treatment device is not particularly limited, but for example, a high-speed fibrillator, a grinder (stone mill type pulverizer), a high-pressure homogenizer, an ultra-high pressure homogenizer, a high-pressure collision type pulverizer, a ball mill, a bead mill, a disk-type refiner, a conical refiner, and a biaxial refiner. A kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, a beater, or the like can be used. Among the above fibrillation treatment devices, it is more preferable to use a high-speed fibrillation machine, a high-pressure homogenizer, and an ultrahigh-pressure homogenizer, which are less affected by the pulverization media and less likely to cause contamination.

In the fibrillation treatment step, for example, the hydrolyzed ionic functional group-introduced cellulose fibers are preferably diluted with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from organic solvents such as water and polar organic solvents can be used. The polar organic solvent is not particularly limited, but alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents and the like are preferable. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, isobutyl alcohol and the like. Examples of polyhydric alcohols include ethylene glycol, propylene glycol and glycerin. Ketones include acetone, methyl ethyl ketone (MEK), and the like. Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether and the like. Examples of esters include ethyl acetate and butyl acetate. Aprotic polar solvents include dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP) and the like.
Among these, water is preferable as the dispersion medium.

The concentration of the dispersion (slurry) during defibration treatment is preferably 0.3% by mass or more, more preferably 1.0% by mass or more, and still more preferably 1.5% by mass, from the viewpoint of efficient fibrillation. and preferably 10% by mass or less, more preferably 6% by mass or less, and even more preferably 3% by mass or less.

<Ionic Functional Group-Introduced Cellulose Nanocrystals>
The ionic functional group-introduced cellulose nanocrystals obtained through Steps A to C are highly crystallized while having ionic functional groups introduced therein.
The amount of ionic functional groups introduced into the ionic functional group-introduced cellulose nanocrystals is preferably 0.10 mmol/g or more, more preferably 0.20 mmol/g or more, and still more preferably 0.20 mmol/g or more, from the viewpoint of transparency and salt resistance. It is 0.30 mmol/g or more, more preferably 0.40 mmol/g or more, and particularly preferably 0.50 mmol/g or more, and the upper limit is not particularly limited, and is, for example, 3.00 mmol/g or less.

From the viewpoint of improving the purity of the ionic functional group-introduced cellulose nanocrystals, the amount of carbamide groups in the ionic functional group-introduced cellulose nanocrystals is preferably low, preferably 0.06 mmol/g or less, more preferably 0.06 mmol/g or less. 05 mmol/g or less, more preferably 0.04 mmol/g or less, and even more preferably 0.03 mmol/g or less. The lower limit is not particularly limited, and may be 0.00 mmol/g.
As described above, carbamide groups may be introduced when urea and/or urea derivatives are used to introduce ionic functional groups into cellulose fibers. Carbamide groups introduced into the crystalline portion are removed along with the amorphous portion.

The fiber width of the ionic functional group-introduced cellulose nanocrystals is 1000 nm or less. The fiber width of cellulose nanocrystals can be measured, for example, by electron microscope observation.
The fiber width of the ionic functional group-introduced cellulose nanocrystal is 1,000 nm or less, for example, preferably 2 nm or more and 1,000 nm or less, more preferably 2 nm or more and 100 nm or less, and 2 nm or more and 50 nm or less. is more preferable, and it is particularly preferable to be 2 nm or more and 30 nm or less. By setting the fiber width of the ionic functional group-introduced cellulose nanocrystals within the above range, the dissolution of cellulose molecules in water is suppressed, and the effect of lowering the viscosity of the ionic functional group-introduced cellulose nanocrystal dispersion liquid is enhanced. It can be made easy to express.

The average fiber width of the ionic functional group-introduced cellulose nanocrystals is, for example, 1,000 nm or less. The average fiber width of the ionic functional group-introduced cellulose nanocrystal is preferably 2 nm or more and 1,000 nm or less, more preferably 2 nm or more and 100 nm or less, further preferably 2 nm or more and 50 nm or less, and 2 nm or more. 30 nm or less is particularly preferred. By setting the average fiber width of the ionic functional group-introduced cellulose nanocrystals within the above range, the dissolution of cellulose molecules in water is suppressed, and the effect of lowering the viscosity of the ionic functional group-introduced cellulose nanocrystal dispersion liquid is achieved. It can be made easier to express.

The average fiber width of cellulose nanocrystals is measured, for example, using an electron microscope as follows. First, an aqueous suspension of cellulose nanocrystals having a concentration of 0.05% by mass or more and 0.1% by mass or less was prepared, and this suspension was cast on a hydrophilized carbon film-coated grid to prepare a sample for TEM observation. and SEM images of surfaces cast on glass may be observed if they contain wide fibers. Then, an electron microscope image is observed at a magnification of 1,000, 5,000, 10,000 or 50,000 times depending on the width of the fiber to be observed. However, the sample, observation conditions and magnification are adjusted so as to satisfy the following conditions.
(1) A single straight line X is drawn at an arbitrary point in the observed image, and 20 or more fibers intersect the straight line X.
(2) Draw a straight line Y that intersects the straight line perpendicularly in the same image, and 20 or more fibers intersect the straight line Y.

Widths of fibers intersecting the straight lines X and Y are visually read from the observation image satisfying the above conditions. In this way, at least three sets of observed images of surface portions that do not overlap each other are obtained. Then, for each image, the width of the fiber that crosses straight line X and straight line Y is read. This gives at least 20 x 2 x 3 = 120 fiber width readings. Then, the average value of the read fiber widths is taken as the average fiber width of the cellulose nanocrystals.

In addition, the fiber diameter and average fiber width of cellulose nanocrystals may be measured using an atomic force microscope (AFM) as follows. First, an aqueous suspension of cellulose nanocrystals with a concentration of 0.0001% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast on mica cleaved with a tape to obtain a sample for AFM observation. . Then, according to the width of the fiber to be observed, AFM observation is performed at a magnification of 5 μm square field of view, 2 μm square field of view, or 1 μm square field of view. At least three sets of observed images of surface portions that do not overlap each other are obtained, fibers that do not overlap each other are randomly selected, and the height of the fibers in the Z-axis direction is read to determine the fiber width. After measuring the width of at least 100 fibers, the average value of the obtained fiber widths is taken as the average fiber width of the cellulose nanocrystals.

Although the fiber length of the ionic functional group-introduced cellulose nanocrystal is not particularly limited, it is preferably, for example, 30 nm or more and 1,000 nm or less, more preferably 40 nm or more and 800 nm or less, and 50 nm or more and 500 nm or less. More preferred. By setting the fiber length within the above range, it is also possible to set the slurry viscosity of the ionic functional group-introduced cellulose nanocrystals within an appropriate range. The fiber length of the ionic functional group-introduced cellulose nanocrystal can be determined by image analysis using, for example, TEM, SEM, and AFM.

The ionic functional group-introduced cellulose nanocrystals preferably have a type I crystal structure. Here, the fact that the cellulose nanocrystals introduced with an ionic functional group have a type I crystal structure can be identified in the diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. . Specifically, it can be identified by having typical peaks at two positions near 2θ=14° or more and 17° or less and 2θ=22° or more and 23° or less.
The proportion of the I-type crystal structure in the ionic functional group-introduced cellulose nanocrystals is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This can be expected to reduce the viscosity of the aqueous dispersion. The degree of crystallinity is determined by a conventional method from the pattern of X-ray diffraction profiles (Seagal et al., Textile Research Journal, vol. 29, p. 786, 1959).

Although the axial ratio (fiber length/fiber width) of the ionic functional group-introduced cellulose nanocrystals is not particularly limited, it is preferably 5 or more and 500 or less, more preferably 10 or more and 250 or less. By setting the axial ratio within the above range, a low-viscosity dispersion can be easily obtained when a solvent dispersion is produced.

Unlike cellulose nanofibers, cellulose nanocrystals typically have a needle-like or spindle-like shape with few folds.
This is probably because the hydrolysis of the amorphous portion in the step B increases the crystallinity, and a person skilled in the art can distinguish between cellulose nanocrystals and cellulose nanofibers also from shape observation.
When 100 cellulose nanocrystals are randomly observed with an atomic force microscope, the number of fibers bent at 30° or more in the middle is preferably 20 or less, more preferably 10 or less, and still more preferably 5. It is 3 or less, more preferably 3 or less.

[Ionic Functional Group-Introduced Cellulose Nanocrystals]
The ionic functional group-introduced cellulose nanocrystal of the present embodiment has an ionic functional group introduction amount of 0.1 mmol/g or more (however, only the carbon atom at the 6-position of cellulose is oxidized and a carboxy group is introduced). cellulose nanocrystals).
Note that the cellulose nanocrystals introduced with an ionic functional group of the present embodiment exclude cellulose nanocrystals in which only the 6-position carbon atom of cellulose is oxidized and a carboxy group is introduced, as described above. Specifically, in the carboxy group-introduced cellulose nanocrystals obtained by TEMPO oxidation, a carboxy group is introduced only at the 6-position, and an ionic functional group can be introduced at least one of the carbon atoms at the 2- and 3-positions. Can not. Therefore, the degree of freedom in introducing ionic functional groups is low. Conventionally, in the introduction of carboxyl groups by TEMPO oxidation, a relatively high amount of carboxyl groups was obtained even when the carboxyl groups were introduced after the cellulose nanocrystals were formed by hydrolysis reaction and fibrillation treatment. However, in the case of other ionic functional groups, it has been difficult to introduce a sufficient amount of ionic functional groups.

Examples of the ionic functional groups introduced into the ionic functional group-introduced cellulose nanocrystals of the present embodiment include the ionic functional groups exemplified in the method for producing the ionic functional group-introduced cellulose nanocrystals described above. is also the same.
The ionic functional group can include, for example, either one or both of an anionic functional group and a cationic functional group. In this embodiment, it is particularly preferable to have an anionic functional group as the ionic functional group.
The anionic functional group as the ionic functional group includes, for example, a phosphorous acid group or a group derived from a phosphoroxo acid group (sometimes simply referred to as a phosphorous acid group), a carboxy group or a group derived from a carboxy group (simply referred to as a carboxy group). ), a sulfur oxoacid group or a group derived from a sulfur oxoacid group (sometimes referred to simply as a sulfur oxoacid group), a xanthate group, a phosphon group, a phosphine group, a sulfone group, a carboxyalkyl group, and the like. can.
Cationic functional groups as ionic functional groups include, for example, an ammonium group, a phosphonium group, and a sulfonium group. Among them, the cationic functional group is preferably an ammonium group.
Among them, the ionic functional group is selected from the group consisting of a phosphorous oxoacid group, a group derived from a phosphorous oxoacid group, a carboxyl group, a sulfone group, a sulfur oxoacid group, a group derived from a sulfur oxoacid group, and a cationic functional group. at least one selected from the group consisting of a phosphorous oxoacid group, a group derived from a phosphorous oxoacid group, a carboxy group, a sulfur oxoacid group, and a group derived from a sulfur oxoacid group is more preferably at least one selected from the group consisting of a phosphate group and a group derived from a phosphate group, and even more preferably a phosphate group. By introducing a phosphorous acid group as an anionic functional group, cellulose nanocrystals with excellent transparency and salt resistance can be obtained.

In the ionic functional group-introduced cellulose nanocrystal of the present embodiment, the amount of ionic functional group introduced is 0.20 mmol/g or more, preferably 0.40 mmol/g or more, more preferably 0.50 mmol/g or more, More preferably 0.60 mmol/g or more, still more preferably 0.70 mmol/g or more, still more preferably 0.80 mmol/g or more, still more preferably 0.90 mmol/g or more, still more preferably 1.00 mmol/g /g or more, more preferably 1.10 mmol/g or more, still more preferably 1.20 mmol/g or more. Although the upper limit is not particularly limited, since an excessive introduction amount causes destruction and dissolution of cellulose crystals, it is preferably 5.00 mmol/g or less, more preferably 4.00 mmol/g or less, and still more preferably 3.00 mmol/g. It is below.

The amount of carbamide groups in the ionic functional group-introduced cellulose nanocrystals of the present embodiment is preferably low, preferably 0.06 mmol/g or less, from the viewpoint of improving the purity of the ionic functional group-introduced cellulose nanocrystals. It is preferably 0.05 mmol/g or less, more preferably 0.04 mmol/g or less, still more preferably 0.03 mmol/g or less. The lower limit is not particularly limited, and may be 0.00 mmol/g.
As described above, when urea and/or urea derivatives are used to introduce ionic functional groups into cellulose fibers, they may be introduced. In the case of production by the crystal production method, at least the carbamide groups introduced into the amorphous portion of the cellulose fiber are removed together with the amorphous portion in the step B, resulting in a low carbamide group content, which is preferable. .

The ionic functional group-introduced cellulose nanocrystal of the present embodiment has an ionic functional group introduced into at least one of the 2-position and 3-position carbon atoms of cellulose in addition to the 6-position carbon atom of cellulose. preferably.
In addition to the carbon atom at the 6-position of cellulose, an ionic functional group is introduced to at least one carbon atom selected from the group consisting of the carbon atom at the 2-position and the carbon atom at the 3-position. It is possible to increase the amount of the ionic functional group to be introduced, and improve the degree of freedom in the amount of the ionic functional group to be introduced.
In addition, compared to the case where the ionic functional group is introduced only at the 6-position, the ionic functional group is formed in the cellulose nanocrystal with the ionic functional group introduced, and the ionic functional group is more densely packed, and the cellulose nanocrystal has excellent dissociation properties and a small fiber diameter. It is believed that nanocrystals are obtained.
Introduction of an ionic functional group to at least one carbon atom selected from the group consisting of the carbon atom at the 2-position and the carbon atom at the 3-position can be detected by ¹³ C NMR, for example, ¹³ It can be detected by C CP/MAS NMR (Cross Polarization Magic Angle Spinning-NMR (Nuclear Magic Resonance)).

The ionic functional group-introduced cellulose nanocrystals of the present embodiment are preferably obtained by the above-described method for producing ionic functional group-introduced cellulose nanocrystals, which includes steps A to C in this order. However, the method for producing the ionic functional group-introduced nanocrystals of the present embodiment is not limited to this, and other methods may be used.

The ionic functional group-introduced cellulose nanocrystals of the present embodiment have a low viscosity when made into an aqueous dispersion.
The ionic functional group-introduced cellulose nanocrystals of the present embodiment have a viscosity of a 1.5% by mass aqueous dispersion at 23° C. of preferably 100 mPa·s or less, more preferably 50 mPa·s or less, and even more preferably 30 mPa·s. Below, more preferably 15 mPa·s or less. Although the lower limit is not particularly limited, it is preferably 1 mPa·s or more, more preferably 2 mPa·s or more, from the viewpoint of ease of production.
The viscosity of the aqueous dispersion of ionic functional group-introduced cellulose nanocrystals is measured by the method described in Examples.

The ionic functional group-introduced cellulose nanocrystals of the present invention are excellent in transparency. Specifically, the total light transmittance at 23° C. of a 0.2% by mass aqueous dispersion of cellulose nanocrystals containing an ionic functional group is preferably 95.5% or more, more preferably 96.0% or more, and further It is preferably 96.5% or more, and the upper limit is not particularly limited, and may be 100%.
Here, the total light transmittance is a value measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with, for example, JIS K 7361-1:1997.

The ionic functional group-introduced cellulose nanocrystals of this embodiment are excellent in salt resistance.
Specifically, it is preferable that the change in the total light transmittance at 23° C. of the 0.2% by mass aqueous dispersion of the ionic functional group-containing cellulose nanocrystals due to the addition of sodium chloride is suppressed, and sodium chloride is added. When T ₀ is the total light transmittance before adding sodium chloride, and T is the total light transmittance after adding sodium chloride, the sodium chloride concentration at which T/T ₀ is 0.98 or less is preferably 100 mmol/L or more, or more. Preferably it is 300mmol/L or more.

The ionic functional group-introduced cellulose nanocrystals of the present embodiment preferably have excellent purity, and are evaluated by coloring by wet heating. Nitrogen-containing structures such as carbamide groups are believed to promote coloring.
Specifically, it is evaluated by visually judging the degree of coloring when a 1% by mass dispersion is heated at 95° C. for 10 hours.

The range of the fiber width and fiber length of the ionic functional group-introduced cellulose nanocrystals of the present embodiment is the same as that of the ionic functional group-introduced cellulose nanocrystals obtained by the production method of the present embodiment, and the preferred ranges are also the same. be.
In addition, as described above, unlike cellulose nanofibers, cellulose nanocrystals typically have a needle-like or spindle-like shape with few folds.
When 100 cellulose nanocrystals are randomly observed with an atomic force microscope, the number of fibers bent by 30° or more in the middle is preferably 20 or less, more preferably 10 or less, and still more preferably 5. It is 3 or less, more preferably 3 or less.

[Dispersion]
The dispersion of this embodiment contains ionic functional group-introduced cellulose nanocrystals.
The ionic functional group-introduced cellulose nanocrystals of the present embodiment have low viscosity even when made into a dispersion, and can be used as a dispersion with a higher concentration than conventional cellulose nanofibers. be.

[Sheet]
The sheet of this embodiment contains ionic functional group-introduced cellulose nanocrystals.
In this embodiment, the sheet is formed by using a liquid composition containing, for example, the above-described ionic functional group-introduced cellulose nanocrystals, and, if necessary, a hydrophilic polymer and other components. can be obtained by
The sheet manufacturing process preferably includes at least a coating step of coating the composition on a substrate, or a papermaking step of papermaking the composition, and a coating step of coating the composition on the substrate. It is more preferable to have a step. As a result, a sheet containing ionic functional group-introduced cellulose nanocrystals is obtained.
The thickness of the sheet is not particularly limited.

[powder]
The powder of the present embodiment contains ionic functional group-introduced cellulose nanocrystals.
In the present embodiment, the powder is obtained by drying an ionic functional group-introduced cellulose nanocrystal dispersion. Specifically, a dispersion containing ionic functional group-introduced cellulose nanocrystals is dried with a spray dryer. A method of spray drying is exemplified.
The moisture content of the powder is preferably 50% or less, more preferably 30% or less, still more preferably 25% or less, and preferably 5% or more, more preferably 10% or more.
The particle size of the powder is preferably 1 μm or more, more preferably 3 μm or more, still more preferably 5 μm or more, and is preferably 1000 μm or less, more preferably 300 μm or less, and still more preferably, from the viewpoint of ease of production. is 100 μm or less.

[Application of ionic functional group-introduced cellulose nanocrystals]
The ionic functional group-introduced cellulose nanocrystals of the present embodiment can be used, for example, in cosmetics, medical compositions, paints, metal surface treatment agents, abrasives, foods, rubbers, resins, drilling compositions, and concrete hydration compositions. materials, concrete precursors, dental materials, cell growth promoters, antifreeze agents, coating stripping agents, insecticides/insect repellents, agricultural chemicals, molding compositions, lubricants, pipe frictional resistance reducers, fragrances/extinguishing agents It can be used as an additive for odorants. The ionic functional group-introduced cellulose nanocrystals of this embodiment are excellent in transparency and salt resistance, and yellowing due to wet heating is suppressed. It is also suitable for use.
Further, by making it into a sheet form, it is suitable for optical members such as display devices and various solar cells. Furthermore, it is also suitable for applications such as substrates for electronic devices, separators for electrochemical devices, members for home appliances, window materials for various vehicles and buildings, interior materials, exterior materials, packaging materials, and the like.

The features of the present invention will be described more specifically below with reference to examples and comparative examples. The materials, amounts used, proportions, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed to be limited by the specific examples shown below.

<Example A1>
As raw material pulp (cellulose fiber), softwood bleached kraft pulp manufactured by Oji Paper Co., Ltd. (NBKP, solid content 93% by mass, basis weight 245 g / m ² sheet, defibered and measured according to JIS P 8121-2: 2012 Canadian Standard Freeness (CSF) of 700 mL) was used.
The raw material pulp was subjected to phosphorus oxo oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea is added to 100 parts by mass (absolute dry mass) of the raw material pulp to obtain 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water. A chemical-impregnated pulp was obtained by adjusting as follows. Next, the resulting chemical solution-impregnated pulp was heated in a hot air dryer at 165° C. for 250 seconds to introduce phosphoric acid groups into cellulose in the pulp to obtain phosphorylated pulp.
Then, the obtained phosphorylated pulp was washed. In the washing treatment, a pulp dispersion liquid obtained by pouring 10 L of ion-exchanged water into 100 g (absolute dry mass) of phosphorylated pulp is stirred so that the pulp is uniformly dispersed, and then filtration and dehydration are repeated. gone. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.
Next, the washed phosphorylated pulp was neutralized as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1N sodium hydroxide aqueous solution was added little by little while stirring to obtain a phosphorylated pulp slurry having a pH of 12 or more and 13 or less. . Next, the phosphorylated pulp slurry was dehydrated and washed to obtain neutralized phosphorylated pulp.

The obtained phosphorylated pulp was subjected to high-concentration acid hydrolysis treatment.
Specifically, 85% phosphoric acid (14.7 mol/L phosphoric acid) was added little by little to the obtained phosphorylated pulp, and the phosphorylated pulp was suspended at 4% by mass in 10.7 mol/L phosphoric acid. A cloudy slurry was obtained. This suspended slurry was a stringy and viscous liquid. The obtained suspension slurry was placed in a glass container and heated and hydrolyzed in a hot bath at 95° C. for 90 minutes while stirring.
The obtained slurry after high-concentration acid hydrolysis had a light brown color and decreased viscosity, and no stringiness was observed. The obtained post-reaction slurry was purified by removing the dissolved components and acid in the following procedure. That is, the obtained post-reaction slurry was ice-cooled and subjected to solid-liquid separation by centrifugation (12,000 G, 5 minutes). After centrifugation, the supernatant was removed, the same volume of ion-exchanged water was added, and the sediment was thoroughly kneaded and dispersed, and then subjected to centrifugation again. After repeating this operation three times, the precipitate was again suspended in ion-exchanged water and brought into contact with a strongly basic ion-exchange resin (Amberjet 4400; Organo Co., Ltd., conditioned), and the electrical conductivity of the slurry and the treatment was continued until the fluctuation of pH disappeared.
Ion-exchanged water was added to the obtained slurry after purification to prepare a slurry having a solid content concentration of 2% by mass, and the following defibration treatment was performed. Specifically, this slurry is treated 6 times with a wet atomization device (Beryu-Mini, high-pressure homogenizer, manufactured by Misayu Co., Ltd.) at a pressure of 100 MPa to defibrate and disperse the phosphorylated cellulose nanocrystals. I got the liquid.

Infrared absorption spectra of the obtained phosphorylated pulp and phosphorylated cellulose nanocrystals were measured using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. Further, when the obtained phosphorylated pulp and phosphorylated cellulose nanocrystals were tested and analyzed with an X-ray diffractometer, 2θ was around 14° or more and 17° or less and 2θ was around 22° or more and 23° or less. Typical peaks were confirmed at two positions of , and it was confirmed to have cellulose type I crystals. The phosphate group content (first dissociated acid content) measured by the measurement method described in [Measurement of phosphate group content] described later was 1.45 mmol/g for phosphorylated pulp, and 1.45 mmol/g for phosphorylated cellulose nanocrystals. It was 0.60 mmol/g. The total amount of dissociated acid was 2.45 mmol/g (the amount of the second dissociated acid was 1.00 mmol/g) for the phosphorylated pulp, and 1.20 mmol/g (the amount of the second dissociated acid was 0 mmol/g) for the phosphorylated cellulose nanocrystals. .60 mmol/g). Also, the fiber width of the cellulose nanocrystals was measured using an atomic force microscope and found to be 3 to 20 nm.

<Example A2>
A dispersion containing phosphorylated pulp and phosphorylated cellulose nanocrystals was prepared in the same manner as in Example A1, except that the washed phosphorylated pulp was further subjected to the phosphorylation treatment and the washing treatment twice in this order. got
The obtained phosphorylated pulp and phosphorylated cellulose nanocrystals were subjected to infrared absorption spectrum measurement using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. X-ray diffraction confirmed that the resulting phosphorylated pulp and phosphorylated cellulose nanocrystals maintained cellulose type I crystals. The phosphate group content (first dissociated acid content) measured by the measurement method described in [Measurement of phosphate group content] described later was 2.00 mmol/g for phosphorylated pulp and 0.0 mmol/g for phosphorylated cellulose nanocrystals. It was 85 mmol/g. The total amount of dissociated acid was 3.30 mmol/g (the amount of the second dissociated acid was 1.30 mmol/g) in the phosphorylated pulp, and 1.65 mmol/g (the amount of the second dissociated acid was 0 in the phosphorylated cellulose nanocrystals). .80 mmol/g). Further, the fiber width of the phosphorylated cellulose nanocrystals was measured using an atomic force microscope and found to be 3 to 20 nm.

<Example A3>
In Example A1, phosphorylated pulp and phosphorylated A dispersion containing cellulose nanocrystals was obtained.

The obtained phosphorylated pulp and phosphorylated cellulose nanocrystals were subjected to infrared absorption spectrum measurement using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. X-ray diffraction confirmed that the resulting phosphorylated pulp and phosphorylated cellulose nanocrystals maintained cellulose type I crystals. The phosphoric acid group content (first dissociated acid content) measured by the measuring method described later in [Measurement of Phosphorus Acid Group Content] was 2.53 mmol/g for phosphorylated pulp and 1.5 mmol/g for phosphorylated cellulose nanocrystals. It was 25 mmol/g. The total amount of dissociated acid was 4.22 mmol/g (the amount of the second dissociated acid was 1.69 mmol/g) in the phosphorylated pulp, and 2.39 mmol/g (the amount of the second dissociated acid was 1.69 mmol/g) in the phosphorylated cellulose nanocrystals. .14 mmol/g). Further, the fiber width of the phosphorylated cellulose nanocrystals was measured using an atomic force microscope and found to be 3 to 20 nm.

<Example A4>
A dispersion containing phosphorylated cellulose nanocrystals was obtained in the same manner as in Example A1, except that diphosphorus pentoxide was used instead of 85% phosphoric acid.

The obtained phosphorylated cellulose nanocrystals were subjected to infrared absorption spectrum measurement using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. It was confirmed by X-ray diffraction that cellulose type I crystals were maintained. The phosphate group content (first dissociated acid content) measured by the measurement method described in [Measurement of Phosphorus Acid Group Content] described later was 0.60 mmol/g. The total amount of dissociated acid was 1.20 mmol/g (the amount of second dissociated acid was 0.60 mmol/g). Also, the fiber width was measured using an atomic force microscope and found to be 3 to 20 nm.

<Example A5>
The supernatant obtained by centrifuging the slurry after high-concentration acid hydrolysis obtained in Example A1 was recovered and dried overnight in a hot air oven at 105°C. Organic matter was removed from the dried product by burning it in a hot air drying oven at 650° C., and the sublimated phosphorus component was recovered. The X-ray diffraction pattern of the obtained phosphorus component was similar to that of commercially available diphosphorus pentoxide, indicating that regenerated diphosphorus pentoxide was obtained.
A dispersion containing phosphorylated cellulose nanocrystals was obtained in the same manner as in Example A4, except that this regenerated diphosphorus pentoxide was used.

The obtained phosphorylated cellulose nanocrystals were subjected to infrared absorption spectrum measurement using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. It was confirmed by X-ray diffraction that cellulose type I crystals were maintained. The phosphate group content (first dissociated acid content) measured by the measurement method described in [Measurement of Phosphorus Acid Group Content] described later was 0.60 mmol/g. The total amount of dissociated acid was 1.20 mmol/g (the amount of second dissociated acid was 0.60 mmol/g). Also, the fiber width was measured using an atomic force microscope and found to be 3 to 20 nm.

<Example A6>
Example except that concentrated sulfuric acid (18.7 mol/L sulfuric acid) was used instead of 85% phosphoric acid to obtain a slurry in which phosphorylated pulp was suspended at 4% by mass in 10.7 mol/L sulfuric acid. A dispersion containing phosphorylated cellulose nanocrystals was obtained in the same manner as in A1.

The obtained phosphorylated cellulose nanocrystals were subjected to infrared absorption spectrum measurement using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. It was confirmed by X-ray diffraction that cellulose type I crystals were maintained. The phosphate group content (first dissociated acid content) measured by the measurement method described in [Measurement of Phosphorus Acid Group Content] described later was 0.53 mmol/g. The total amount of dissociated acid was 1.06 mmol/g (the amount of second dissociated acid was 0.53 mmol/g). Also, the fiber width was measured using an atomic force microscope and found to be 3 to 20 nm.

<Example A7>
Example except that concentrated hydrochloric acid (11.2 mol/L hydrochloric acid) was used instead of 85% phosphoric acid to obtain a slurry in which phosphorylated pulp was suspended at 2% by mass in 10.7 mol/L hydrochloric acid. A dispersion containing phosphorylated cellulose nanocrystals was obtained in the same manner as in A1.

The obtained phosphorylated cellulose nanocrystals were subjected to infrared absorption spectrum measurement using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. It was confirmed by X-ray diffraction that cellulose type I crystals were maintained. The phosphate group content (first dissociated acid content) measured by the measurement method described in [Measurement of phosphate group content] described later was 0.66 mmol/g. The total amount of dissociated acid was 1.32 mmol/g (the amount of second dissociated acid was 0.66 mmol/g). Also, the fiber width was measured using an atomic force microscope and found to be 3 to 20 nm.

<Example A8>
A dispersion containing phosphorylated cellulose nanocrystals was obtained in the same manner as in Example A4, except that a slurry in which 4% by mass of phosphorylated pulp was suspended in 16 mol/L phosphoric acid was obtained.

The obtained phosphorylated cellulose nanocrystals were subjected to infrared absorption spectrum measurement using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. It was confirmed by X-ray diffraction that cellulose type I crystals were maintained. The phosphate group content (first dissociated acid content) measured by the measurement method described later in [Measurement of Phosphorus Acid Group Content] was 0.48 mmol/g. The total amount of dissociated acid was 0.96 mmol/g (the amount of second dissociated acid was 0.48 mmol/g). Also, the fiber width was measured using an atomic force microscope and found to be 3 to 20 nm.

<Example B1>
The procedure of Example A1 was repeated except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate, and a dispersion containing phosphorous acid pulp and cellulose phosphorous nanocrystals was prepared. Obtained.

The obtained phosphorylated pulp and phosphorylated cellulose nanocrystals were subjected to infrared absorption spectrum measurement using FT-IR. As a result, an absorption based on P=O of a phosphonic acid group, which is a tautomer of a phosphite group, was observed near 1210 cm ⁻¹ , confirming that a phosphite group (phosphonic acid group) was added. was done. It was confirmed by X-ray diffraction that the resulting phosphorous oxidized pulp and phosphorous cellulose nanocrystals maintained cellulose type I crystals. The amount of phosphite groups (the amount of first dissociated acid) measured by the measurement method described in [Measurement of the amount of phosphorous acid groups] described later is 1.51 mmol/g in phosphorous oxidized pulp, and 1.51 mmol/g in phosphorous cellulose. It was 0.67 mmol/g for nanocrystals. The total amount of dissociated acid was 1.54 mmol/g (the amount of the second dissociated acid was 0.03 mmol/g) in the phosphorous oxidized pulp, and 0.68 mmol/g (the amount of the second dissociated acid was was 0.01 mmol/g). In addition, the fiber width of the cellulose phosphite nanocrystal was measured using an atomic force microscope and found to be 3 to 20 nm.
In the phosphorous pulp and the phosphorous cellulose nanocrystals, the total amount of dissociated acid is larger than the amount of the first dissociated acid due to slight oxidation of phosphorous acid and carboxy groups derived from amorphous hemicellulose. It is thought that

<Example C1>
Sulfated pulp and sulfated cellulose nanocrystals were prepared in the same manner as in Example A1 except that 38 parts by mass of amidosulfuric acid (sulfamic acid) was used instead of ammonium dihydrogen phosphate and the heating time was extended to 20 minutes. A dispersion liquid containing was obtained.

The obtained sulfated pulp and sulfated cellulose nanocrystals were subjected to infrared absorption spectrum measurement using FT-IR. As a result, an absorption due to S=O of the sulfate ester group was observed near 1220-1260 cm ⁻¹ , confirming the addition of the sulfate ester group. X-ray diffraction confirmed that the obtained sulfated pulp and sulfated cellulose nanocrystals maintained cellulose type I crystals. The amount of sulfate ester groups measured by the measurement method described in [Measurement of Sulfur Oxoacid Group/Sulfone Group Content] described later is 1.47 mmol/g for sulfated pulp and 0.68 mmol/g for sulfated cellulose nanocrystals. /g. Also, the fiber width of the sulfated cellulose nanocrystals was measured using an atomic force microscope and found to be 3 to 20 nm.

<Example D1>
As raw material pulp, bleached softwood kraft pulp (NBKP, undried, Canadian standard freeness (CSF) measured according to JIS P 8121-2: 2012: 700 mL) manufactured by Oji Paper Co., Ltd. was used. Alkaline TEMPO oxidation treatment was performed on this raw material pulp as follows.
First, the raw pulp equivalent to 100 parts by mass of dry mass, 1.6 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), 10 parts by mass of sodium bromide, and 10000 parts by mass of water distributed in parts. Then, a 13% by mass sodium hypochlorite aqueous solution was added to 10 mmol per 1.0 g of pulp to initiate the reaction. During the reaction, a 0.5 M sodium hydroxide aqueous solution was added dropwise to maintain the pH at 10 or more and 10.5 or less, and the reaction was considered completed when no change in pH was observed.
Then, the obtained TEMPO oxidized pulp was washed. The washing treatment is performed by dehydrating the pulp slurry after TEMPO oxidation to obtain a dehydrated sheet, pouring 5000 parts by mass of ion-exchanged water, stirring to uniformly disperse, and then filtering and dehydrating repeatedly. rice field. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.

This dehydrated sheet was subjected to a post-oxidation treatment for residual aldehyde groups as follows. The dehydrated sheet equivalent to 100 parts by mass of dry mass was dispersed in 10000 parts by mass of 0.1 mol/L acetate buffer (pH 4.8). Next, 113 parts by mass of 80% by mass sodium chlorite was added, and the mixture was immediately sealed, followed by reaction at room temperature for 48 hours while stirring at 500 rpm using a magnetic stirrer to obtain a pulp slurry.
Then, the obtained after-oxidized TEMPO oxidized pulp was washed. The washing treatment is carried out by dehydrating the post-oxidized pulp slurry to obtain a dehydrated sheet, pouring 5000 parts by mass of ion-exchanged water, stirring to uniformly disperse, and then filtering and dehydrating repeatedly. rice field. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.
Except for using the obtained TEMPO-oxidized pulp, the high-concentration acid hydrolysis treatment and subsequent treatments were performed in the same manner as in Example A1 to obtain a dispersion containing TEMPO-oxidized cellulose nanocrystals.

X-ray diffraction confirmed that the resulting TEMPO-oxidized pulp and TEMPO-oxidized cellulose nanocrystals maintained cellulose type I crystals. The amount of carboxyl groups measured by the measurement method described below was 1.80 mmol/g for the TEMPO-oxidized pulp and 0.86 mmol/g for the TEMPO-oxidized cellulose nanocrystals. In addition, the fiber width of the TEMPO-oxidized cellulose nanocrystals was measured using an atomic force microscope and found to be 3 to 20 nm.

<Example E1>
[Hypochlorous acid oxidation]
A sheet of softwood bleached kraft pulp (NBKP) (solid content concentration 90% by mass) is processed with a hand mixer (Labo Milcer PLUS, manufactured by Osaka Chemical Co., Ltd.) at a rotation speed of 20000 rpm for 15 seconds to form a flocculent. Fluffing pulp (solid content concentration 90% by mass) was prepared. Next, sodium hypochlorite pentahydrate was added to the ion-exchanged water to prepare an aqueous solution having a sodium hypochlorite solid content concentration of 22% by mass. 9000 parts by mass of a 22% by mass sodium hypochlorite aqueous solution was added to 100 parts by mass of cotton-like fluffing pulp, and the mixture was reacted for 2 hours while adjusting the temperature to 30°C in a hot bath to obtain a carboxy group-introduced pulp. The pH was maintained at 11 by appropriately adding 1N sodium hydroxide aqueous solution during the reaction.
Next, the obtained carboxy group-introduced pulp was washed. The washing treatment was carried out by repeating an operation of filtering and dehydrating a pulp dispersion liquid obtained by pouring ion-exchanged water into the obtained carboxy group-introduced pulp, stirring the pulp so that the pulp is uniformly dispersed, and then filtering and dehydrating the pulp. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.
Except for using the obtained carboxy group-introduced pulp, the treatment after the high-concentration acid hydrolysis treatment was performed in the same manner as in Example A1 to obtain a dispersion containing carboxy group-introduced cellulose nanocrystals.

It was confirmed by X-ray diffraction that the obtained carboxy group-introduced pulp and carboxy group-introduced cellulose nanocrystals maintained cellulose type I crystals. The amount of carboxyl groups measured by the method described later was 0.70 mmol/g in the carboxyl-introduced pulp and 0.33 mmol/g in the carboxyl-introduced cellulose nanocrystals. Further, when the fiber width of the carboxy group-introduced cellulose nanocrystal was measured using an atomic force microscope, it was 3 to 20 nm.

<Example F1>
[Maleic acid esterification]
A sheet (solid content concentration 90% by mass) made from bleached softwood (NBKP) is treated with a hand mixer (Labo Milcer PLUS, manufactured by Osaka Chemical Co., Ltd.) at a rotation speed of 20,000 rpm for 15 seconds to produce a flocculent fluffing. It was made into pulp (solid content concentration 90% by mass). An autoclave was charged with 100 parts by mass of cotton-like fluffing pulp and 50 parts by mass of maleic anhydride and treated at 150° C. for 2 hours to obtain a carboxy group-introduced pulp.
Next, the obtained carboxy group-introduced pulp was washed. The washing treatment was carried out by repeating an operation of filtering and dehydrating a pulp dispersion obtained by pouring ion-exchanged water into the obtained carboxy group-introduced pulp, stirring the pulp so that the pulp is uniformly dispersed, and then filtering and dehydrating. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.
Except for using the obtained carboxy group-introduced pulp, the treatment after the high-concentration acid hydrolysis treatment was performed in the same manner as in Example A1 to obtain a dispersion containing carboxy group-introduced cellulose nanocrystals.

It was confirmed by X-ray diffraction that the obtained carboxy group-introduced pulp and carboxy group-introduced cellulose nanocrystals maintained cellulose type I crystals. The amount of carboxyl groups measured by the measuring method described later was 1.22 mmol/g in the carboxyl group-introduced pulp and 0.49 mmol/g in the carboxyl group-introduced cellulose nanocrystals. Further, when the fiber width of the carboxy group-introduced cellulose nanocrystal was measured using an atomic force microscope, it was 3 to 20 nm.

<Example G1>
[Carboxyethylation]
As raw material pulp, softwood bleached kraft pulp manufactured by Oji Paper Co., Ltd. (NBKP, solid content 93% by mass, basis weight 245 g / m ² sheet, defibered and measured according to JIS P 8121-2: 2012 Canadian standard Freeness (CSF) of 700 mL) was used.
To 100 parts by mass (absolute dry mass) of this raw pulp, a chemical solution consisting of 250 parts by mass of 12N NaOH aqueous solution, 163 parts by mass of 2-chloropropionic acid, and 140 parts by mass of ion-exchanged water (total 553 parts by mass) was added. An impregnated pulp was obtained. Next, the resulting chemical solution-impregnated pulp was heated in a hot air dryer at 165° C. for 10 minutes to introduce carboxyethyl groups (carboxy groups) into the cellulose in the pulp to obtain carboxy group-introduced pulp.
Next, the obtained carboxy group-introduced pulp was washed. The washing treatment was carried out by repeating an operation of filtering and dehydrating a pulp dispersion liquid obtained by pouring ion-exchanged water into the obtained carboxy group-introduced pulp, stirring the pulp so that the pulp is uniformly dispersed, and then filtering and dehydrating the pulp. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.
Next, the washed carboxy group-introduced pulp was neutralized as follows. First, after diluting the washed carboxy group-introduced pulp with 10 L of deionized water, a 1 N sodium hydroxide aqueous solution was added little by little while stirring to prepare a carboxy group-introduced pulp slurry having a pH of 12 or more and 13 or less. Obtained. Next, the carboxyl group-introduced pulp slurry was dewatered and washed to obtain neutralized carboxyl group-introduced pulp.
Except for using the obtained carboxy group-introduced pulp, the treatment after the high-concentration acid hydrolysis treatment was performed in the same manner as in Example A1 to obtain a dispersion containing carboxy group-introduced cellulose nanocrystals.

It was confirmed by X-ray diffraction that the obtained carboxy group-introduced pulp and carboxy group-introduced cellulose nanocrystals maintained cellulose type I crystals. The amount of carboxyl groups measured by the measuring method described later was 1.41 mmol/g in the carboxyl group-introduced pulp and 0.65 mmol/g in the carboxyl group-introduced cellulose nanocrystals. Further, when the fiber width of the carboxy group-introduced cellulose nanocrystal was measured using an atomic force microscope, it was 3 to 20 nm.

<Example H1>
[Carboxymethylation]
As raw material pulp, softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solid content 93% by mass, basis weight 245 g / m ² sheet, disaggregated and Canadian standard freeness measured according to JIS P 8121-2: 2012 (CSF) is 700 mL) was used.
To 100 parts by mass (absolute dry mass) of this raw material pulp, a chemical solution consisting of 83 parts by mass of 12N NaOH aqueous solution, 175 parts by mass of sodium monochloroacetate, and 313 parts by mass of ion-exchanged water (total 571 parts by mass) was added to obtain a chemical solution-impregnated pulp. got Next, the resulting chemical solution-impregnated pulp was placed in a polyethylene container and heated in a hot bath at 95° C. for 60 minutes to introduce carboxymethyl groups (carboxy groups) into the cellulose in the pulp to obtain carboxy group-introduced pulp.
Next, the obtained carboxy group-introduced pulp was washed. The washing treatment was carried out by repeating an operation of filtering and dehydrating a pulp dispersion liquid obtained by pouring ion-exchanged water into the obtained carboxy group-introduced pulp, stirring the pulp so that the pulp is uniformly dispersed, and then filtering and dehydrating the pulp. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.
Except for using the obtained carboxy group-introduced pulp, the treatment after the high-concentration acid hydrolysis treatment was performed in the same manner as in Example A1 to obtain a dispersion containing carboxy group-introduced cellulose nanocrystals.

It was confirmed by X-ray diffraction that the obtained carboxy group-introduced pulp and carboxy group-introduced cellulose nanocrystals maintained cellulose type I crystals. The amount of carboxyl groups measured by the measuring method described later was 1.21 mmol/g in the carboxyl group-introduced pulp and 0.41 mmol/g in the carboxyl group-introduced cellulose nanocrystals. Further, when the fiber width of the carboxy group-introduced cellulose nanocrystal was measured using an atomic force microscope, it was 3 to 20 nm.

<Example J1>
[Sulfoethylation]
As raw material pulp, softwood bleached kraft pulp manufactured by Oji Paper Co., Ltd. (NBKP, solid content 93% by mass, basis weight 245 g / m ² sheet, defibered and measured according to JIS P 8121-2: 2012 Canadian standard Freeness (CSF) of 700 mL) was used.
To 100 parts by mass (absolute dry mass) of this raw material pulp, a chemical solution consisting of 180 parts by mass of a 2N NaOH aqueous solution and 780 parts by mass of a 25% by mass sodium vinylsulfonate aqueous solution (960 parts by mass in total) was added to obtain a chemical solution-impregnated pulp. Obtained. Next, the resulting chemical solution-impregnated pulp was heated in a hot air dryer at 165° C. for 16 minutes to introduce sulfoethyl groups (sulfone groups) into the cellulose in the pulp to obtain sulfoethyl group-introduced pulp (sulfone group-introduced pulp).
Next, the resulting sulfoethyl group-introduced pulp was washed. The washing treatment was carried out by repeating an operation of filtering and dehydrating a pulp dispersion liquid obtained by pouring ion-exchanged water into the resulting sulfoethyl group-introduced pulp, stirring the pulp to uniformly disperse the pulp, and then filtering and dehydrating the pulp. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.
Except for using the obtained sulfoethyl group-introduced pulp, the treatment after the high-concentration acid hydrolysis treatment was performed in the same manner as in Example A1 to obtain a dispersion liquid containing sulfoethyl group-introduced cellulose nanocrystals.

X-ray diffraction confirmed that the obtained sulfoethyl group-introduced pulp and sulfoethyl group-introduced cellulose nanocrystals maintained cellulose type I crystals. The sulfoethyl group content (sulfone group content) measured by the method described later was 1.48 mmol/g for the sulfoethyl group-introduced pulp and 0.71 mmol/g for the sulfoethyl group-introduced cellulose nanocrystals. Further, when the fiber width of the sulfoethyl group-introduced cellulose nanocrystal was measured using an atomic force microscope, it was 3 to 20 nm.

<Example K1>
[Cationization treatment]
As raw material pulp, softwood bleached kraft pulp manufactured by Oji Paper Co., Ltd. (NBKP, solid content 93% by mass, basis weight 245 g / m ² sheet, defibered and measured according to JIS P 8121-2: 2012 Canadian standard Freeness (CSF) of 700 mL) was used.
To 100 parts by mass (absolute dry mass) of this raw material pulp, 180 parts by mass of 1N NaOH aqueous solution and a cationizing agent (Catiomaster G, manufactured by Yokkaichi Gosei Co., Ltd., glycidyltrimethylammonium chloride, pure content 73.1% by mass, moisture content 20.2% by mass) 325 parts by mass (505 parts by mass in total) of the chemical solution was added to obtain a chemical solution-impregnated pulp. Next, the resulting chemical solution-impregnated pulp was heated in a hot air dryer at 165° C. for 12 minutes to introduce cationic groups into the cellulose in the pulp to obtain cationic group-introduced pulp.
Next, the resulting cationic group-introduced pulp was washed. The washing treatment was carried out by repeating an operation of filtering and dehydrating a pulp dispersion obtained by pouring ion-exchanged water into the obtained cationic group-introduced pulp, stirring the pulp so that the pulp is uniformly dispersed, and then filtering and dehydrating. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.
Next, the cationic group-introduced pulp after washing was neutralized as follows. First, the cationic group-introduced pulp after washing was diluted with 10 L of deionized water, and then 1N hydrochloric acid was added little by little while stirring to obtain a cationic group-introduced pulp slurry having a pH of 1 or more and 2 or less. Next, the cationic group-introduced pulp slurry was dehydrated and washed to obtain a neutralized cationic group-introduced pulp.

Concentrated hydrochloric acid (11.2 mol/L hydrochloric acid) was added little by little to the resulting cationic group-introduced pulp to obtain a slurry in which 2% by mass of the cationized pulp was suspended in 10.7 mol/L hydrochloric acid. This suspended slurry was a stringy and viscous liquid. The obtained suspension slurry was placed in a glass container and heated and hydrolyzed in a hot bath at 95° C. for 90 minutes while stirring. (High-concentration acid hydrolysis treatment)
The treatment after the high-concentration acid hydrolysis treatment was performed in the same manner as in Example A1 to obtain a dispersion containing cationic group-introduced cellulose nanocrystals.

X-ray diffraction confirmed that the resulting cationic group-introduced pulp and cationic group-introduced cellulose nanocrystals maintained cellulose type I crystals. The amount of cationic groups measured by the method described below was 1.45 mmol/g for the cationic group-introduced pulp and 0.71 mmol/g for the cationic group-introduced cellulose nanocrystals. In addition, the fiber width of the cationic group-introduced cellulose nanocrystal was measured using an atomic force microscope and found to be 3 to 20 nm.

<Comparative Example 1>
Instead of phosphorylated pulp, softwood bleached kraft pulp manufactured by Oji Paper Co., Ltd. (NBKP, solid content 93% by mass, basis weight 245 g / m ² sheet, defibered and measured according to JIS P 8121-2: 2012 A dispersion containing cellulose nanocrystals was obtained in the same manner as in Example A1, except that the Canadian standard freeness (CSF) of 700 mL) was used.
The amount of phosphate groups in the obtained cellulose nanocrystals was less than 0.01 mmol/g. The fiber width was measured using an atomic force microscope to be 10-30 nm.

<Comparative Example 2>
85% phosphoric acid was added to the dispersion (solid content concentration 2%) containing the cellulose nanocrystals obtained in Comparative Example 1 until the phosphoric acid concentration reached 10.7 mol/L, and then in a hot bath at 95°C. Treatment was carried out for 90 minutes. The obtained post-reaction slurry was purified by removing the dissolved components and acid in the following procedure. That is, the obtained post-reaction slurry was ice-cooled and subjected to solid-liquid separation by centrifugation (12,000 G, 5 minutes). After centrifugation, the supernatant was removed, the same volume of ion-exchanged water was added, and the sediment was thoroughly kneaded and dispersed, and then subjected to centrifugation again. After repeating this operation three times, the precipitate was again suspended in ion-exchanged water and brought into contact with a strongly basic ion-exchange resin (Amberjet 4400; Organo Co., Ltd., conditioned), and the electrical conductivity of the slurry and the treatment was continued until the fluctuation of pH disappeared.
Ion-exchanged water was added to the obtained purified slurry to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated six times at a pressure of 100 MPa with a wet-type atomizer (Beryu-Mini, manufactured by Biryu Co., Ltd.) to obtain a dispersion containing phosphorylated cellulose nanocrystals.

The infrared absorption spectrum of the obtained phosphorylated cellulose nanocrystals was measured using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. It was confirmed by X-ray diffraction that cellulose type I crystals were maintained. The phosphate group content (first dissociated acid content) measured by the measurement method described in [Measurement of phosphate group content] described later was 0.24 mmol/g. The total amount of dissociated acid was 0.40 mmol/g (the amount of second dissociated acid was 0.16 mmol/g). Also, the fiber width of the cellulose nanocrystals was measured using an atomic force microscope and found to be 10 to 20 nm.

<Comparative Example 3>
The dispersion containing cellulose nanocrystals obtained in Comparative Example 1 (solid concentration: 2%) was allowed to stand in a constant temperature and humidity chamber (23°C, 50% RH) and air-dried until the solid concentration reached 42%. 24 parts by mass of the obtained cellulose nanocrystals having a solid concentration of 42% and 51 parts by mass of 85% phosphoric acid were added to 64 parts by mass of urea melted in a glass flask set in an oil bath at 140°C. . Then, it was heated to 150° C. and heat-treated for 30 minutes.
After the heat treatment, 500 parts by mass of water was added to obtain a post-reaction slurry. This slurry was subjected to the same refining operation as in Comparative Example 2 and the treatment with a wet micronization apparatus to obtain a dispersion containing phosphorylated cellulose nanocrystals.

The infrared absorption spectrum of the obtained phosphorylated cellulose nanocrystals was measured using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. It was confirmed by X-ray diffraction that cellulose type I crystals were maintained. The phosphate group content (first dissociated acid content) measured by the measurement method described in [Measurement of phosphate group content] described later was 1.03 mmol/g. The total amount of dissociated acid was 1.77 mmol/g (the amount of second dissociated acid was 0.74 mmol/g). Also, the fiber width of the cellulose nanocrystals was measured using an atomic force microscope and found to be 3 to 20 nm.

<Reference example 1>
The dispersion containing cellulose nanocrystals obtained in Comparative Example 1 (solid concentration: 2%) was subjected to alkali TEMPO oxidation treatment as follows.
First, the above cellulose nanocrystals equivalent to 100 parts by weight of dry weight, 1.6 parts by weight of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by weight of sodium bromide are added to 10,000 parts of water. Dispersed in parts by mass. Then, a 13% by mass sodium hypochlorite aqueous solution was added to 2 mmol per 1.0 g of pulp to initiate the reaction. During the reaction, a 0.5 M sodium hydroxide aqueous solution was added dropwise to maintain the pH at 10 or more and 10.5 or less, and the reaction was considered completed when no change in pH was observed.
The obtained slurry was subjected to the same refining operation as in Comparative Example 2 and to a treatment using a wet micronization apparatus to obtain a dispersion containing TEMPO-oxidized cellulose nanocrystals.

X-ray diffraction confirmed that the resulting TEMPO-oxidized pulp and TEMPO-oxidized cellulose nanocrystals maintained cellulose type I crystals. The amount of carboxyl groups measured by the measurement method described below was 0.86 mmol/g in the TEMPO-oxidized cellulose nanocrystals. In addition, the fiber width of the TEMPO-oxidized cellulose nanocrystals was measured using an atomic force microscope and found to be 3 to 20 nm.

<Comparative Example 4>
As raw material pulp, softwood bleached kraft pulp manufactured by Oji Paper Co., Ltd. (NBKP, solid content 93% by mass, basis weight 245 g / m ² sheet, defibered and measured according to JIS P 8121-2: 2012 Canadian standard Freeness (CSF) of 700 mL) was used.
The raw material pulp was subjected to phosphorus oxo oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea is added to 100 parts by mass (absolute dry mass) of the raw material pulp to obtain 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water. A chemical-impregnated pulp was obtained by adjusting as follows. Next, the resulting chemical solution-impregnated pulp was heated in a hot air dryer at 165° C. for 250 seconds to introduce phosphoric acid groups into cellulose in the pulp to obtain phosphorylated pulp.
Then, the obtained phosphorylated pulp was washed. In the washing treatment, a pulp dispersion liquid obtained by pouring 10 L of ion-exchanged water into 100 g (absolute dry mass) of phosphorylated pulp is stirred so that the pulp is uniformly dispersed, and then filtration and dehydration are repeated. gone. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.

Ion-exchanged water and 85% phosphoric acid were added to the washed phosphorylated pulp to adjust the solid content concentration to 2% and the phosphoric acid concentration to 1 mol/L. was subjected to heat hydrolysis treatment for 90 minutes. (dilute acid hydrolysis treatment)

Then, the obtained hydrolyzed phosphorylated pulp was subjected to a washing treatment. In the washing treatment, a pulp dispersion liquid obtained by pouring 10 L of ion-exchanged water into 100 g (absolute dry mass) of phosphorylated pulp is stirred so that the pulp is uniformly dispersed, and then filtration and dehydration are repeated. gone. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.

Next, the washed phosphorylated pulp was neutralized as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1N sodium hydroxide aqueous solution was added little by little while stirring to obtain a phosphorylated pulp slurry having a pH of 12 or more and 13 or less. . Next, the phosphorylated pulp slurry was dehydrated and washed to obtain neutralized phosphorylated pulp.
Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated six times at a pressure of 100 MPa with a wet atomization device (Beryu-Mini, manufactured by Biryu Co., Ltd.) to obtain a dispersion liquid mainly containing phosphorylated cellulose nanofibers.

The infrared absorption spectrum of the obtained phosphorylated cellulose nanofiber was measured using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. In addition, when the obtained phosphorylated cellulose nanofibers were tested and analyzed with an X-ray diffraction device, two points near 2θ = 14° or more and 17° or less and 2θ = 22° or more and 23° or less were found. A typical peak was confirmed at the position, and it was confirmed to have cellulose type I crystals. The phosphate group content (first dissociated acid content) measured by the measurement method described in [Measurement of phosphate group content] described later was 0.93 mmol/g. The total amount of dissociated acid was 1.56 mmol/g (the amount of second dissociated acid was 0.63 mmol/g). Further, when the fiber width of the cellulose nanofiber was measured using an atomic force microscope, it was 3 to 5 nm.

<Comparative Example 5>
Same as Comparative Example 4, except that the dilute acid hydrolysis treatment and the washing treatment after the dilute acid hydrolysis treatment were performed not on the phosphorylated pulp after washing but on the bleached softwood kraft pulp before phosphorylation. Then, a dispersion containing mainly phosphorylated cellulose nanofibers was obtained.

The infrared absorption spectrum of the obtained phosphorylated cellulose nanofiber was measured using FT-IR. As a result, absorption based on P=O of the phosphate group was observed near 1230 cm ^-1 , confirming that the phosphate group was added. In addition, when the obtained phosphorylated cellulose nanofibers were tested and analyzed with an X-ray diffractometer, two points near 2θ = 14° or more and 17° or less and 2θ = 22° or more and 23° or less were analyzed. A typical peak was confirmed at the position, and it was confirmed to have cellulose type I crystals. The phosphate group content (first dissociated acid content) measured by the measurement method described in [Measurement of phosphate group content] described later was 1.45 mmol/g. The total amount of dissociated acid was 2.45 mmol/g (the amount of second dissociated acid was 1.00 mmol/g). Further, when the fiber width of the cellulose nanofiber was measured using an atomic force microscope, it was 3 to 5 nm.

<Comparative Example 6>
Ion-exchanged water was added to the neutralized phosphorylated pulp obtained in Example A1 to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated six times at a pressure of 100 MPa with a wet atomization device (Beryu-Mini, manufactured by Biryu Co., Ltd.) to obtain a dispersion containing phosphorylated cellulose nanofibers.

An enzyme (cellulase) was added to the obtained phosphorylated cellulose nanofiber dispersion liquid so that 550 nkat per 1 g of phosphorylated cellulose nanofibers, and enzyme treatment was performed at a temperature of 50° C. (Step D). The temperature of the resulting dispersion was adjusted to 100° C. to heat-inactivate the enzyme. Further, this slurry was treated 6 times with a wet-type atomization device (Beryu-Mini, manufactured by Biryu Co., Ltd.) at a pressure of 100 MPa to obtain a dispersion containing enzyme-treated phosphorylated cellulose nanofibers. The phosphate group content (first dissociated acid content) measured by the measurement method described in [Measurement of Phosphorus Acid Group Content] described later was 1.45 mmol/g. The total amount of dissociated acid was 2.45 mmol/g.

[Preparation of sheet]
Various cellulose nanocrystals obtained in Examples A1 to A8, B1, C1, D1, E1, F1, G1, H1, J1, and K1 were diluted with deionized water so that the solid content concentration was 0.6% by mass. did. The mixed liquid was weighed so that the finished basis weight of the sheet was 70 g/m ² and spread on a commercially available acrylic plate. A damming frame (inner dimensions: 250 mm×250 mm, height: 5 cm) was arranged on the acrylic plate so as to obtain a predetermined basis weight. After that, it was dried in a drier at 70° C. for 24 hours and peeled off from the acrylic plate. Sheets containing cellulose nanocrystals were obtained from all cellulose nanocrystals. The thickness of the sheet was 50 μm.

[Preparation of powder]
2% by mass dispersions of various cellulose nanocrystals obtained in Examples A1 to A8, B1, C1, D1, E1, F1, G1, H1, J1, and K1 were spray-dried with a spray dryer whose outlet temperature was set to 150°C. did. Powders containing cellulose nanocrystals were obtained from all cellulose nanocrystals. The powder had a particle size of 20 μm or less and a moisture content of 20% or less.

[evaluation]
<Measurement of phosphorus oxoacid group content>
The amount of phosphorous acid groups in cellulose nanocrystals, cellulose nanofibers, and cellulose fibers with ionic functional groups varies depending on the target cellulose ) was added to the dispersion containing ion-exchanged water to make the content 0.2% by mass, treated with an ion-exchange resin, and then titrated with an alkali.
In the treatment with an ion-exchange resin, 1/10 by volume of the various celluloses described above is added with a strongly acidic ion-exchange resin (Ambarjet 1024; manufactured by Organo Co., Ltd., conditioned), shaken for 1 hour, and then opened. Separation of the resin and the slurry was done by pouring over a 90 μm mesh.
In the titration using an alkali, while adding 10 μL of 0.1N sodium hydroxide aqueous solution every 5 seconds to various cellulose-containing slurries after treatment with an ion exchange resin, the change in the pH value indicated by the slurry is measured. I went by. The titration was performed while nitrogen gas was blown into the slurry from 15 minutes before the start of the titration. In this neutralization titration, two points where the increment (the differential value of the pH with respect to the amount of alkali added) are maximized are observed in the curve obtained by plotting the measured pH against the amount of alkali added. Among these, the maximum point of the increment obtained first when the alkali is first added is called the first end point, and the maximum point of the increment obtained next is called the second end point (Fig. 1). The amount of alkali required from the start of titration to the first end point is equal to the amount of first dissociated acid in the slurry used for titration. Also, the amount of alkali required from the start of titration to the second end point is equal to the total amount of dissociated acid in the slurry used for titration. The amount of alkali (mmol) required from the start of titration to the first end point is divided by the solid content (g) in the slurry to be titrated, and the amount of phosphorous acid groups (first dissociated acid amount) (mmol/g ). Further, the value obtained by dividing the amount of alkali (mmol) required from the start of titration to the second end point by the solid content (g) in the slurry to be titrated was defined as the total amount of dissociated acid (mmol/g). Further, a value obtained by subtracting the first dissociated acid amount from the total dissociated acid amount is the second dissociated acid amount.

<Measurement of carboxy group content>
The amount of carboxyl groups in cellulose nanocrystals, cellulose nanofibers, and cellulose fibers introduced with an ionic functional group was adjusted to 0.2% by mass by adding ion-exchanged water to various cellulose dispersions containing various types of target cellulose. was treated with an ion-exchange resin, followed by titration with an alkali.
Treatment with an ion-exchange resin is performed by adding 1/10 by volume of a strongly acidic ion-exchange resin (Amberjet 1024; manufactured by Organo Co., Ltd., conditioned) to 0.2% by mass of various cellulose-containing slurries, followed by shaking for 1 hour. After that, the slurry was separated from the resin by pouring it onto a mesh with an opening of 90 μm.
In addition, the titration using an alkali was performed by measuring the change in the pH value of the slurry while adding a 0.1N sodium hydroxide aqueous solution to the fibrous cellulose-containing slurry after treatment with the ion-exchange resin. . Observing the change in pH while adding an aqueous sodium hydroxide solution yields a titration curve as shown in FIG. As shown in FIG. 2, in this neutralization titration, in the curve plotting the measured pH against the amount of alkali added, there is one point where the increment (the differential value of pH with respect to the amount of alkali added) is maximum. Observed. The maximum point of this increment is called the first end point. Here, the region from the start of titration to the first end point in FIG. 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the slurry used for titration. Then, by dividing the alkali amount (mmol) required in the first region of the titration curve by the solid content (g) in the various cellulose-containing slurries to be titrated, the introduction amount (mmol/g) of the carboxy group is calculated. Calculated.
The amount of carboxyl groups introduced (mmol/g) described above is the amount of substituents per 1 g of mass of fibrous cellulose (hereinafter referred to as the amount of carboxyl groups ( ^acid type)).

<Measurement of Sulfur Oxoacid Group/Sulfone Group Amount>
The amounts of sulfur oxoacid groups and sulfone groups of the pulps and cellulose nanocrystals obtained in Examples C1 and J1 were measured. That is, the obtained various celluloses were subjected to wet incineration using perchloric acid and concentrated nitric acid, diluted at appropriate ratios, and the amount of sulfur was measured by ICP emission spectrometry. The sulfur oxoacid group content and the sulfone group content (unit: mmol/g) were obtained by dividing this sulfur content by the absolute dry mass of each type of cellulose tested.

<Measurement of cationic group amount>
The cationic group content of the pulp and cellulose nanocrystals obtained in Example K1 was measured. That is, the freeze-dried and pulverized sample was subjected to measurement using a trace total nitrogen analyzer TN-110 manufactured by Mitsubishi Chemical Analytic Tech. Ionic nitrogen was removed in the process of neutralization and washing. The introduction amount (mmol/g) of cationic groups per unit mass of various celluloses is obtained by dividing the nitrogen content (g/g) per unit mass of various celluloses obtained by trace nitrogen analysis by the atomic weight of nitrogen. Calculated by

<Measurement of carbamide group amount>
The carbamide group content of the pulps, cellulose nanocrystals, and cellulose nanofibers obtained in Examples A1 to A8, B1, C1 and Comparative Examples 3 to 6 was measured. That is, the freeze-dried and pulverized sample was subjected to measurement using a trace total nitrogen analyzer TN-110 manufactured by Mitsubishi Chemical Analytic Tech. Ionic nitrogen was removed during the neutralization and washing processes. The introduction amount (mmol/g) of carbamide groups per unit mass of various celluloses was obtained by dividing the nitrogen content (g/g) per unit mass of various celluloses obtained by trace nitrogen analysis by the atomic weight of nitrogen. Calculated.

<Measurement of Viscosity of Dispersion>
First, dispersions of various cellulose nanocrystals and cellulose nanofibers were diluted with ion-exchanged water so that the solid content concentration was 1.5% by mass, and then stirred at 1500 rpm for 5 minutes with a disperser. Then, the viscosity of the resulting dispersion was measured using a Brookfield viscometer (manufactured by BLOOKFIELD, analog viscometer T-LVT). The measurement conditions were a rotation speed of 3 rpm, and the viscosity value after 3 minutes from the start of measurement was taken as the viscosity of the dispersion. In addition, the dispersion liquid to be measured was allowed to stand in an environment of 23° C. and 50% relative humidity for 24 hours before the measurement. The liquid temperature of the dispersion liquid at the time of measurement was 23°C.

<Measurement of Total Light Transmittance of Dispersion>
The total light transmittance of the dispersion is measured by diluting various cellulose dispersions with deionized water to a concentration of 0.2% by mass, and then using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.). Measurement was performed according to 7361-1:1997 using a liquid glass cell (manufactured by Fujiwara Seisakusho Co., Ltd., MG-40, reverse optical path) with an optical path length of 1 cm. The zero point measurement was performed with ion-exchanged water in the same glass cell. That is, the total light transmittance measured only with ion-exchanged water was taken as 100%. In addition, the dispersion liquid to be measured was allowed to stand in an environment of 23° C. and 50% relative humidity for 24 hours before the measurement. The liquid temperature of the dispersion liquid at the time of measurement was 23°C.

<Salt resistance>
The total light transmittance was measured when a predetermined amount of sodium chloride was added to the resulting 0.2% by mass dispersion of cellulose nanocrystals and cellulose nanofibers, and the total light transmittance hardly changed due to the addition of sodium chloride. was used as a cellulose nanocrystal and cellulose nanofiber dispersion with high salt resistance. Specifically, evaluation was performed using the following indices.
A: T / T ₀ is 0.98 or more at a sodium chloride concentration of 300 mmol / L B: T / T ₀ is less than 0.98 at a sodium chloride concentration of 300 mmol / L, but the sodium chloride concentration is T/T ₀ is 0.98 or more at 100 mmol/L. C: T/T ₀ is less than 0.98 at a sodium chloride concentration of 100 mmol/L. Light transmittance, T ₀ : Total light transmittance before adding sodium chloride.
Moreover, the specific measurement procedure of the total light transmittance after adding sodium chloride is as follows.
(1) Add a predetermined amount of solid sodium chloride to a 0.2% by mass dispersion of cellulose nanocrystals and cellulose nanofibers (2) Manually stir with a Teflon (registered trademark) rod until the sodium chloride is dissolved. (3) After dissolving sodium chloride, stir at 4000 rpm for 1 minute with a rotating disperser. (4) Measure total light transmittance by the method described in <Measurement of total light transmittance of dispersion>.

<Presence or absence of modification other than C6 position>
A freeze-dried sample of the obtained cellulose nanocrystal and cellulose nanofiber dispersion was analyzed by ¹³ C CP/MAS NMR. 68-80 ppm corresponding to the C2, C3, C5 positions, 80-91 ppm corresponding to the C4 position adjacent to the C3 position, and corresponding to the C1 position adjacent to the C2 position when compared to the results of the sample of Comparative Example 1. A change in the peak at the chemical shift of 101-109 ppm was considered to be a modification other than at the C6 position.

<Purity>
The purity of the obtained cellulose nanocrystals and cellulose nanofibers was judged from whether or not they contained functional groups other than ionic functional groups, and from the coloration during wet heating.
A: Does not contain functional groups other than ionic functional groups, or contains functional groups other than ionic functional groups, but is hardly colored by wet heating B: Contains functional groups other than ionic functional groups, by wet heating Slightly yellowish C: Contains functional groups other than ionic functional groups, and becomes strong yellow to light brown when heated by wet heating. Coloring during wet heating is 1 mass% concentration of cellulose nanocrystals and cellulose nanofiber dispersion. The degree of coloration when the liquid was heated at 95° C. for 10 hours was judged visually. A nitrogen-containing structure capable of liberating ammonia by hydrolysis or the like, such as a carbamide group, is thought to promote formation of a colored structure.

<Bend of fiber>
Images of cellulose nanocrystals and cellulose nanofibers are taken with an atomic force microscope, and 100 fibers are randomly selected, and those with one or more bends (angle of 30° or more) in the middle are examined. were counted and judged according to the following criteria.
A: The number of bent fibers is less than 10. B: The number of bent fibers is 10 or more and less than 20. C: The number of bent fibers is 20 or more.

Regarding the ionic functional group-introduced cellulose fibers, ionic functional group-introduced cellulose nanofibers, and ionic functional group-introduced cellulose nanocrystals shown in Tables 1-1 and 1-2, ion When the amount of functional group introduced was measured, the results of the first dissociated acid amount and the second dissociated acid amount of the measurement results were described in the respective columns. In addition, when the amount of ionic functional groups is measured by <measurement of carboxyl group amount> and <measurement of sulfur oxoacid group/sulfone group amount> described above, the measurement results are described in the first dissociated acid amount column. . In addition, when the amount of introduced ionic functional groups was measured by <measurement of amount of cationic group> described above, the measurement result was described in the column of amount of cationic group.

According to Tables 1-1 and 1-2, the ionic functional group-introduced cellulose nanocrystals obtained by the production method having steps A to C in this order have a low viscosity when made into an aqueous dispersion, High transparency and excellent salt resistance. In addition, the purity is high.
On the other hand, as shown in Comparative Examples, Comparative Example 1, which does not include the step of introducing an ionic functional group, was inferior in transparency and salt resistance. Also, when the ionic functional groups were introduced after fibrillation as shown in Comparative Examples 2 and 3, the amount of ionic functional groups introduced was low, and the transparency and salt resistance were poor (Comparative Example 2). ), and the purity was poor (Comparative Example 3).
Further, as shown in Comparative Examples 4 and 5, in the step B, when the concentration of the acidic aqueous solution used for hydrolysis was less than 5 mol/L, the viscosity of the aqueous solution was high. Moreover, as shown in Comparative Example 6, when the step B was not performed, the viscosity of the aqueous solution was high even if the enzyme treatment was performed.

Claims (19)

A method for producing an ionic functional group-introduced cellulose nanocrystal, comprising the following steps A to C in this order.
Step A: Ionic functional group introduction step of introducing ionic functional groups into cellulose fibers Step B: Hydrolysis step of hydrolyzing cellulose fibers introduced with ionic functional groups with an acidic aqueous solution having a concentration of 5 mol/L or more C: Defibrillation step of fibrillating cellulose fibers into which hydrolyzed ionic functional groups have been introduced The ionic functional group is selected from the group consisting of a phosphorous oxoacid group, a group derived from a phosphorous oxoacid group, a carboxy group, a sulfone group, a sulfur oxoacid group, a group derived from a sulfur oxoacid group, and a cationic functional group. The manufacturing method according to claim 1, wherein at least one of the 3. The production method according to claim 1 or 2, wherein the ionic functional group is at least one selected from the group consisting of a phosphorous acid group and a group derived from a phosphorous acid group. 4. The production method according to any one of claims 1 to 3, wherein in step A, the amount of the ionic functional group introduced into the cellulose fiber is 0.50 mmol/g or more. The production method according to any one of claims 1 to 4, wherein the amount of ionic functional group introduced in the ionic functional group-introduced cellulose nanocrystal is 0.10 mmol/g or more. The production method according to any one of claims 1 to 5, wherein the amount of carbamide groups in the ionic functional group-introduced cellulose nanocrystals is 0.06 mmol/g or less. The production method according to any one of claims 1 to 6, wherein the acidic aqueous solution used in step B is an aqueous solution of an acid compound selected from the group consisting of phosphoric acid, sulfuric acid, diphosphorus pentoxide, and hydrochloric acid. . An ionic functional group-introduced cellulose nanocrystal having an ionic functional group introduction amount of 0.10 mmol/g or more (however, a cellulose nanocrystal in which only the carbon atom at the 6-position of cellulose is oxidized and a carboxy group is introduced) except). The ionic functional group is at least selected from the group consisting of a phosphorous acid group, a group derived from a phosphorous acid group, a carboxy group, a sulfone group, a sulfur oxoacid group, a group derived from a sulfur oxoacid group, and an ammonium group. The ionic functional group-introduced cellulose nanocrystal according to claim 8, which is one. 10. The ionic functional group-introduced cellulose nanocrystal according to claim 8 or 9, wherein the ionic functional group is at least one selected from the group consisting of a phosphorous acid group and a group derived from a phosphorous acid group. The ionic functional group-introduced cellulose nanocrystal according to any one of claims 8 to 10, wherein the amount of the ionic functional group introduced is 0.50 mmol/g or more. The ionic functional group-introduced cellulose nanocrystal according to any one of claims 8 to 11, wherein the ionic functional group is introduced to at least one of carbon atoms at the 2- and 3-positions of cellulose. The ionic functional group-introduced cellulose nanocrystal according to any one of claims 8 to 12, wherein the amount of carbamide groups in the ionic functional group-introduced cellulose nanocrystal is 0.06 mmol/g or less. The ionic functional group-introduced cellulose nanocrystals according to any one of claims 8 to 13, wherein a 1.5% by mass aqueous dispersion of the ionic functional group-introduced cellulose nanocrystals has a viscosity of 100 mPa·s or less. The ionic functional group-introduced cellulose nanocrystals according to any one of claims 8 to 14, wherein a total light transmittance of a 0.2% by mass aqueous dispersion of the ionic functional group-introduced cellulose nanocrystals is 95.5% or more. cellulose nanocrystals. When sodium chloride is added to a 0.2% by mass aqueous dispersion of the ionic functional group-introduced cellulose nanocrystals to a concentration of 100 mmol/L, the total light transmittance after addition of sodium chloride is T, and sodium chloride is added. The cellulose nanocrystal with introduced ionic functional groups according to any one of claims 8 to 15, wherein T/T ₀ is 0.98 or more, where T ₀ is the total light transmittance before. A dispersion containing the ionic functional group-introduced cellulose nanocrystals according to any one of claims 8 to 16. A sheet containing the ionic functional group-introduced cellulose nanocrystals according to any one of claims 8 to 16. A powder containing the ionic functional group-introduced cellulose nanocrystals according to any one of claims 8 to 16.

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