Cellulose nanocrystal composite and dispersion of same

Abstract

Provided is a cellulose nanocrystal composite that can be favorably dispersed in a low-polarity solvent such as toluene.　A cellulose nanocrystal composite according to the present invention includes: cellulose nanocrystals that include an anionic functional group that includes at least a sulfate group and / or a sulfo group; and a cationic surfactant. The cellulose nanocrystal composite is characterized in that the cationic surfactant is a quaternary ammonium salt that satisfies any of (i)–(iii): (i) Has 4 at least C4 alkyl groups, (ii) has 2 or 3 at least C10 alkyl groups, (iii) has 1 at least C14 alkyl group.

Description

Cellulose nanocrystal composite and its dispersion

[0001] The present invention relates to a cellulose nanocrystal composite and a dispersion thereof, and more specifically to a cellulose nanocrystal composite and a dispersion thereof that can be well dispersed in a low-polarity solvent and can provide a dispersion having excellent transparency.

[0002] Nanocellulose has been proposed for use in a variety of applications, including as an advanced biomass raw material, functional additive, and film composite material. In particular, nanocellulose, which has been mechanically treated to refine the cellulose fibers and introduce hydrophilic anionic functional groups such as carboxyl groups or phosphate groups into the hydroxyl groups of the cellulose, has excellent gas barrier properties and excellent dispersibility in aqueous solvents. For example, Patent Document 1 below describes a gas barrier material containing cellulose fibers with an average fiber diameter of 200 nm or less, in which the carboxyl group content of the cellulose constituting the cellulose fibers is 0.4 to 2 mmol / g.

[0003] Furthermore, Patent Document 2 below describes a fine cellulose fiber dispersion having a pH of 4 to 12, which contains at least fine cellulose fibers in which a carboxyl group has been selectively introduced to the hydroxyl group at the 6-position of the pyranose ring by an oxidation reaction, and an organic alkali, wherein the organic alkali is either an amine or an organic onium compound having a hydroxide ion as a counterion. Furthermore, Patent Document 3 below describes a fine cellulose fiber composite in which a cationic surfactant is adsorbed to fine cellulose fibers having a carboxyl group content of 0.1 to 3.0 mmol / g, the cationic surfactant being chemically adsorbed to the carboxyl group at the C6 position of the cellulose structural unit in the fine cellulose fiber, and the cationic surfactant is one or more quaternary ammonium compounds selected from the group consisting of lauryltrimethylammonium chloride, dilauryldimethylchloride, distearyldimethylammonium chloride, cetyltrimethylammonium chloride, and alkylbenzyldimethylammonium chloride.

[0004] Patent No. 4965528 Patent No. 5765331 Patent No. 6261652

[0005] Although the nanocellulose described in the above patent documents has excellent dispersion stability in organic solvents, the organic solvents that can be used are limited to polar solvents such as alcohols, and it is difficult to disperse it well in low-polarity solvents such as toluene. That is, low-polarity solvents such as toluene are soluble in alcohols and oils, even though they are poorly soluble in water. Therefore, they are widely used as solvents in various fields such as paints, adhesives, and printing inks. Even in such applications, it is required to disperse nanocellulose in a low-polarity solvent and composite it with a polymer that dissolves in the low-polarity solvent.

[0006] Therefore, an object of the present invention is to provide a cellulose nanocrystal composite that can be well dispersed in a low-polarity solvent such as toluene. Another object of the present invention is to provide a dispersion in which the cellulose nanocrystal composite is well dispersed in a low-polarity solvent and has excellent transparency.

[0007] According to the present invention, there is provided a cellulose nanocrystal composite comprising a cellulose nanocrystal having an anionic functional group containing at least a sulfate group and / or a sulfo group and at least one of a phosphate group and a carboxyl group, and a cationic surfactant, wherein the cationic surfactant is a quaternary ammonium salt that satisfies any one of the following (i) to (iii): (i) having four alkyl groups each having 8 or more carbon atoms, (ii) having two or three alkyl groups each having 10 or more carbon atoms, or (iii) having one alkyl group each having 14 or more carbon atoms.

[0008] The present invention also provides a cellulose nanocrystal composite comprising a cellulose nanocrystal containing only sulfate and / or sulfo groups as anionic functional groups and a cationic surfactant, wherein the cationic surfactant is a quaternary ammonium salt that satisfies any one of the following conditions (i') to (iii): (i') having four alkyl groups each having 4 or more carbon atoms, (ii) having two or three alkyl groups each having 10 or more carbon atoms, or (iii) having one alkyl group each having 14 or more carbon atoms.

[0009] In the cellulose nanocrystal composite of the present invention, (1) the quaternary ammonium salt is a quaternary ammonium salt represented by the following formula: In the formula, R １ ~R ４ When the anionic functional groups of the cellulose nanocrystal contain at least one of a sulfate group and / or a sulfo group and a phosphate group or a carboxyl group, all of them are alkyl groups having 8 or more carbon atoms, or two or three of them are alkyl groups having 10 or more carbon atoms, or at least one of them is an alkyl group having 14 or more carbon atoms and the remainder are benzyl groups or alkyl groups having 1 to 4 carbon atoms, or all of them are alkyl groups having 4 or more carbon atoms; and X － is Cl or Br. When the anionic functional groups of the cellulose nanocrystals are only sulfate groups and / or sulfo groups, all of them are alkyl groups having 4 or more carbon atoms, or two or three of them are alkyl groups having 10 or more carbon atoms, or at least one of them is an alkyl group having 14 or more carbon atoms, and the remainder are benzyl groups or alkyl groups having 1 to 4 carbon atoms; －is Cl or Br. (2) The cationic surfactant is at least one selected from dimethyldimyristyl ammonium bromide, dimethyldimyristyl ammonium chloride, dimethyldipalmityl ammonium bromide, dimethyldipalmityl ammonium chloride, benzyldimethylstearyl ammonium chloride, and benzyldimethylstearyl ammonium bromide. (3) The total amount of anionic functional groups in the cellulose nanocrystals is preferably more than 0.20 mmol / g and not more than 4.00 mmol / g.

[0010] The present invention also provides a cellulose nanocrystal dispersion, characterized in that the cellulose nanocrystal composite is dispersed in an organic solvent.

[0011] In the above-mentioned cellulose nanocrystal dispersion, it is preferable that: (1) the organic solvent is a low-polarity organic solvent having a relative dielectric constant of 20 or less at 25°C, particularly any one of toluene, benzene, xylene, cyclohexane, and hexane; (2) the light transmittance of the cellulose nanocrystal dispersion when made into a toluene dispersion with a solids content of 1.4% by mass is 40%T or more; and (3) the viscosity of the cellulose nanocrystal dispersion when made into a toluene dispersion with a solids content of 1% by mass is in the range of 0.1 to 100 mPa·sec (rotational viscometer, temperature 30°C, spindle rotation speed 100 rpm).

[0012] The present invention further provides a method for producing the above-mentioned cellulose nanocrystal composite, which comprises hydrophilizing cellulose nanocrystals containing sulfate and / or sulfo groups to prepare an aqueous cellulose nanocrystal dispersion containing anionic functional groups in an amount greater than 0.20 mmol / g and less than 4.00 mmol / g, and then mixing the aqueous cellulose nanocrystal dispersion with an alcohol-based solvent containing a quaternary ammonium salt as a cationic surfactant to produce the cellulose nanocrystal composite. In the method for producing the cellulose nanocrystal composite of the present invention, the hydrophilization treatment is preferably a treatment using any of NeverDry treatment, carbodiimide, sulfuric acid, sulfur trioxide-pyridine complex, phosphoric acid-urea, TEMPO catalyst, and oxidizing agent.

[0013] The cellulose nanocrystal composite of the present invention has cellulose nanocrystals containing anionic functional groups such as sulfate groups, to which quaternary ammonium ions, which are counterions of the anionic functional groups, are adsorbed or ionically bonded. This allows the polymer chains of the quaternary ammonium salt to extend into the dispersion medium, increasing the repulsive potential due to steric hindrance between the polymer chains and preventing the cellulose nanocrystal composite particles from approaching each other. This effectively prevents aggregation of the cellulose nanocrystal composite particles, enabling them to be uniformly dispersed even in low-polarity solvents such as toluene. Furthermore, the quaternary ammonium salt has a specific alkyl chain, which improves its affinity with low-polarity solvents, and this, combined with the aggregation-inhibiting effect due to the steric hindrance of the polymer chains, enables the cellulose nanocrystal composite particles to exhibit excellent dispersibility.

[0014] Furthermore, by using cellulose nanocrystals with short fiber lengths, the self-organized structure due to charge repulsion between the cellulose nanocrystals can be made denser. This also allows resin molded articles, etc., formed using a dispersion in which the cellulose nanocrystal composite of the present invention and various resins are dispersed in an organic solvent to exhibit excellent mechanical strength. Furthermore, by having the total amount of anionic functional groups in the cellulose nanocrystals be greater than 0.20 mmol / g and less than 4.00 mmol / g, the content of quaternary ammonium salts, which serve as counterions to the anionic functional groups, can be set within a range that provides particularly good dispersibility in low-polarity solvents. Furthermore, by using cellulose nanocrystals that have been subjected to an acid hydrolysis treatment process for cellulose fibers or a hydrophilization treatment process for cellulose nanocrystals at temperatures, for example, 100°C or less, a cellulose nanocrystal composite can be provided in which yellowing, thermal decomposition, and loss of dispersibility due to heat treatment are suppressed.

[0015] Dispersions of the present invention, obtained by dispersing the cellulose nanocrystal composite in a low-polarity organic solvent, have excellent transparency because the cellulose nanocrystal composite is well-dispersed uniformly without aggregation. Furthermore, the dispersions of the present invention also have excellent stability over time, maintaining good dispersibility over long periods of time. Furthermore, the dispersions of the present invention use cellulose nanocrystals with short fiber lengths, which reduces thixotropy and provides relatively low viscosity, making them easy to handle. This is evident from the fact that the viscosity of the cellulose nanocrystal dispersion, when dispersed in toluene at a solids content of 1% by mass, is in the range of 0.1 to 100 mPa·sec. Furthermore, dispersions in which the cellulose nanocrystal composite is well-dispersed uniformly exhibit birefringence (polarized light) due to the chiral nematic liquid crystal structure derived from the cellulose nanocrystals.

[0016] (Cellulose Nanocrystal Composite) The cellulose nanocrystal composite (hereinafter sometimes referred to as "CNC composite") of the present invention has an important feature in that it contains a cellulose nanocrystal (hereinafter sometimes referred to as "CNC") having an anionic functional group containing at least a sulfate group and / or a sulfo group and at least one of a phosphate group and a carboxyl group, and a cationic surfactant that is a quaternary ammonium salt that satisfies any one of the following (i) to (iii): (i) having four alkyl groups having 8 or more carbon atoms; (ii) having two or three alkyl groups having 10 or more carbon atoms; and (iii) having one alkyl group having 14 or more carbon atoms.

[0017] Furthermore, an important feature of the cellulose nanocrystal composite of the present invention is that it contains cellulose nanocrystals containing only sulfate and / or sulfo groups as anionic functional groups, and a cationic surfactant that is a quaternary ammonium salt that satisfies any one of the following conditions (i') to (iii): (i') having four alkyl groups with 4 or more carbon atoms; (ii) having two or three alkyl groups with 10 or more carbon atoms; or (iii) having one alkyl group with 14 or more carbon atoms.

[0018] As described above, in the cellulose nanocrystal composite of the present invention, the quaternary ammonium ion, which is the counterion of the anionic functional group of the cellulose nanocrystal, is adsorbed or ionically bonded. The alkyl chains (i) to (iii) of the quaternary ammonium salt extend into the dispersion medium, enhancing the repulsive potential due to steric hindrance between the polymer chains, effectively preventing aggregation of the cellulose nanocrystal composite particles. This allows for good, uniform dispersion even in low-polarity solvents such as toluene. Furthermore, the improved hydrophobicity of the polymer chains (i) to (iii) of the quaternary ammonium salt improves affinity with low-polarity solvents. This, combined with the aggregation-inhibiting effect due to the steric hindrance of the polymer chains, allows for excellent dispersibility in low-polarity solvents such as toluene. Furthermore, when the anionic functional groups of the cellulose nanocrystal are sulfate groups and / or sulfo groups only, even a quaternary ammonium salt having four alkyl groups with relatively short chains and a carbon number of 4 to 8 can exhibit the same effects as those described above in (i) to (iii). Furthermore, by using cellulose nanocrystals that have been subjected to the acid hydrolysis treatment process of cellulose fibers or the hydrophilization treatment process of cellulose nanocrystals described below at temperatures of, for example, 100°C or less as the cellulose nanocrystals that form the cellulose nanocrystal composite of the present invention, it is possible to form a cellulose nanocrystal composite that is suppressed from yellowing, thermal decomposition, and loss of dispersibility due to heat treatment.

[0019] [Cellulose Nanocrystals] The cellulose nanocrystals that make up the cellulose nanocrystal composite of the present invention are rod-shaped cellulose crystals obtained by acid hydrolysis of the amorphous portions of cellulose fibers such as pulp with a strong acid and extracting the crystalline portions. In the present invention, it is preferable to use cellulose nanocrystals hydrolyzed by sulfuric acid treatment, which contain sulfate and / or sulfo groups that can be advantageously complexed with a cationic surfactant. That is, cellulose nanocrystals can be obtained by acid hydrolysis of cellulose fibers by sulfuric acid treatment, hydrochloric acid treatment, phosphoric acid treatment, formic acid treatment, etc., but cellulose nanocrystals obtained by sulfuric acid treatment themselves contain sulfate and / or sulfo groups, which allows them to easily form complexes with quaternary ammonium salts, which are cationic surfactants.

[0020] Before hydrophilization, cellulose nanocrystals preferably contain sulfate groups and / or sulfo groups in an amount of 0.01 to 0.60 mmol / g, more preferably 0.10 to 0.50 mmol / g, and even more preferably 0.20 to 0.45 mmol / g. Cellulose nanocrystals whose sulfate groups and / or sulfo groups have been adjusted to within the above ranges by sulfuric acid treatment can be stably dispersed in water even at high concentrations, allowing for efficient hydrophilization and production of cellulose nanocrystal composites. Furthermore, the cellulose nanocrystals are cellulose fibers with an average fiber length in the range of 100 to 500 nm, an average fiber diameter of 50 nm or less, an aspect ratio in the range of 5 to 50, and a degree of crystallinity of 60% or more. The average fiber diameter is preferably in the range of 2 to 50 nm, and the degree of crystallinity is preferably 70% or more. The average fiber length and average fiber diameter of cellulose nanocrystals can be determined by known methods. For example, it can be determined by observing with an electron microscope such as AFM, SEM, or TEM and calculating the average value of 10 or more fibers at any magnification at which 10 or more fibers can be observed.

[0021] Furthermore, in the present invention, the cellulose nanocrystals are further subjected to a hydrophilization treatment described below, which allows the total amount of anionic functional groups to be adjusted to a preferred range of more than 0.20 mmol / g and not more than 4.00 mmol / g. If the total amount of anionic functional groups is less than the above range, the cellulose nanocrystal composite may not be as well dispersible in low-polarity solvents as when the total amount is within the above range. On the other hand, if the total amount of anionic functional groups is greater than the above range, it becomes difficult to maintain the crystalline structure of the cellulose nanocrystals, which may diminish the benefits of using cellulose nanocrystals. When the anionic functional groups of the cellulose nanocrystals include sulfate groups and / or sulfo groups and at least one of phosphate groups and carboxyl groups, the total amount of anionic functional groups is more preferably in the range of 0.50 to 2.00 mmol / g, and particularly preferably in the range of 1.20 to 1.60 mmol / g. When the anionic functional groups of the cellulose nanocrystals are sulfate groups and / or sulfo groups only, the total amount of anionic functional groups is more preferably in the range of 0.10 to 1.80 mmol / g, and particularly preferably in the range of 0.20 to 0.45 mmol / g.

[0022] The anionic functional groups possessed by the cellulose nanocrystals of the present invention may be any groups capable of dissociating in water and forming ionic bonds with the cationic surfactant. These groups are determined by the hydrophilization treatment method described below. They may contain either carboxyl groups or phosphate groups in addition to sulfate groups and / or sulfo groups, or may contain only sulfate groups and / or sulfo groups. When anionic functional groups are present in addition to sulfate groups and / or sulfo groups, the proportion (molar ratio) of sulfate groups and / or sulfo groups to the total amount of anionic functional groups is typically 0.2% or more, preferably 2.0% or more, and more preferably 4.5% or more. The dispersibility of the cellulose nanocrystal composite is improved when the sulfate groups and / or sulfo groups are within the above range. Furthermore, when the anionic functional groups are only sulfate groups and / or sulfo groups, it is easy to adjust the amount of anionic functional groups and to control the quality of the cellulose nanocrystals. Furthermore, this is preferable because it is less likely to cause gelation or aggregation under acidic conditions and provides stable dispersibility. In this specification, the term "sulfate group" includes a sulfate ester group, and the term "phosphate group" includes a phosphate ester group.

[0023] As described above, the cellulose nanocrystals used in the cellulose nanocrystal composite of the present invention are preferably obtained by treating a cellulose raw material with sulfuric acid to obtain sulfate and / or sulfo group-containing cellulose nanocrystals, which are then subjected to a hydrophilization treatment to adjust the amount of anionic functional groups within the above range. Furthermore, before or after the hydrophilization treatment, the cellulose nanocrystals can also be subjected to defibration or dispersion treatment as necessary.

[0024] [Measurement of Amount of Functional Groups] The method for measuring the amount of anionic functional groups contained in the cellulose nanocrystals of the present invention is not particularly limited, but for example, the amount can be measured by the following method.

[0025] <Measurement of sulfate and / or sulfo group content> Cellulose nanocrystals are frozen in a freezer and then dried for 3 days in a vacuum freeze dryer (FD-1BU-S, manufactured by Nippon Techno Service Co., Ltd.). The resulting freeze-dried material is ground into powder using a dry grinder (manufactured by IKA, Tube Mill control) at 20,000 rpm for 60 seconds. The freeze-dried and ground sample is subjected to pressure-heat decomposition using nitric acid in a sealed container. The sample is then appropriately diluted and the sulfur content is measured using ICP-OES. The value calculated by dividing by the bone-dry mass of the cellulose nanocrystals tested is taken as the sulfate and / or sulfo group content (mmol / g) of the cellulose nanocrystals.

[0026] <Measurement of the amount of anionic functional groups> The cellulose nanocrystal-containing dispersion was weighed and ion-exchanged water was added to prepare 100 mL of a 0.05 to 0.3 mass% cellulose nanocrystal-containing dispersion. 0.1 g of cation exchange resin was added to the dispersion and stirred. Filtration was then performed to separate the cation exchange resin from the cellulose nanocrystal dispersion. A 0.05 M sodium hydroxide solution was added dropwise to the dispersion after cation exchange using an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd.), and the change in the electrical conductivity of the cellulose nanocrystal-containing dispersion was measured. The amount of sodium hydroxide consumed for neutralization of the anionic functional groups was determined from the resulting conductivity curve, and the total amount of anionic functional groups (mmol / g) was calculated using the following formula: Total amount of anionic functional groups (mmol / g) = amount of sodium hydroxide consumed for neutralization of the anionic functional groups (mL) × sodium hydroxide concentration (mmol / mL) ÷ solid mass of cellulose nanocrystals (g).

[0027] <Hydrophiliza- tion Treatment> In the present invention, cellulose nanocrystals are subjected to a hydrophilic treatment to adjust the amount of sulfate groups and / or sulfo groups, or to introduce anionic functional groups such as sulfate groups, sulfo groups, carboxyl groups, and phosphate groups into hydroxyl groups or hydrogen atoms of cellulose. The total amount of anionic functional groups such as sulfate groups, sulfo groups, carboxyl groups, and phosphate groups is preferably adjusted to more than 0.2 mmol / g and not more than 4.0 mmol / g. The hydrophilic treatment is preferably carried out using any of the following: Never-Dry treatment, water-soluble carbodiimide, sulfuric acid, sulfur trioxide-pyridine complex, phosphoric acid-urea, TEMPO catalyst, and oxidizing agent. Treatment using any of Never-Dry treatment, carbodiimide, sulfuric acid, and sulfur trioxide-pyridine complex adjusts the amount of sulfate groups and / or sulfo groups in the cellulose nanocrystals and further shortens the cellulose nanocrystals. When using cellulose nanocrystals hydrolyzed by a method other than sulfuric acid treatment, it is preferable to introduce sulfate groups and / or sulfo groups into the cellulose nanocrystals at a concentration of 0.01 mmol / g or more by hydrophilization treatment using either carbodiimide, sulfuric acid, or a sulfur trioxide-pyridine complex. Furthermore, if necessary, phosphate groups or carboxyl groups are introduced by treatment using either phosphoric acid-urea, a TEMPO catalyst, or an oxidizing agent, thereby adjusting the total amount of anionic functional groups in the cellulose nanocrystals to the above range. It should be noted that, as long as the total amount of anionic functional groups falls within the above range, any one of the hydrophilization treatments may be performed, but the same treatment may be performed multiple times, or multiple times in combination with other treatments. Furthermore, as described below, the above hydrophilization treatments, except for the hydrophilization treatment using phosphoric acid-urea, can be performed at temperatures below 100°C, particularly below 60°C. The ability to perform hydrophilization treatments at such low temperatures makes it possible to adjust the amount of anionic functional groups without causing yellowing or thermal decomposition due to heat treatment or reducing dispersibility.

[0028] <Hydrophilic treatment using never-drying treatment> Cellulose nanocrystals are solidified into powder or the like by drying treatment such as spray drying, heating, or reduced pressure, but during solidification by drying treatment, some of the anionic functional groups contained in the cellulose nanocrystals are eliminated, resulting in a decrease in hydrophilicity. In other words, never-drying treatment, which does not solidify cellulose nanocrystals into powder or the like, for anionic functional groups, can be exemplified as a hydrophilic treatment. Examples of anionic functional groups include sulfate groups and / or sulfo groups, phosphate groups, and carboxyl groups.

[0029] <Hydrophilic Treatment Using Carbodiimide> In the treatment using carbodiimide, cellulose nanocrystals and carbodiimide are stirred in a solvent such as dimethylformamide, sulfuric acid is added, and the mixture is allowed to react at a temperature of 0 to 80°C for 5 to 300 minutes to form sulfate esters. The carbodiimide and sulfuric acid are preferably used in amounts of 5 to 30 mmol and 5 to 30 mmol per gram (solids) of cellulose nanocrystals. To improve yield, it is preferable to subsequently add an alkaline compound such as sodium hydroxide to convert the sulfo groups introduced into the cellulose nanocrystals from the H-type to the Na-type. The mixture is then subjected to filtration using a dialysis membrane or the like to remove impurities, thereby preparing sulfo-modified cellulose nanocrystals. This allows the preparation of cellulose nanocrystals containing only sulfate and / or sulfo groups as anionic functional groups within the above range. Examples of carbodiimides include 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, a water-soluble compound containing a carbodiimide group (—N═C═N—) in the molecule. Also, dicyclohexylcarbodiimide, which is soluble in organic solvents, can be used.

[0030] <Hydrophilic Treatment Using Sulfuric Acid> In the hydrophilic treatment using sulfuric acid, it is preferable to use 40 to 60 mass % of sulfuric acid per 1 g (solid content) of cellulose nanocrystals. The reaction is carried out at a temperature of 40 to 60°C for 5 to 300 minutes, and then the mixture is subjected to a filtration treatment using a dialysis membrane or the like to remove impurities, thereby introducing sulfate groups and / or sulfo groups as anionic functional groups.

[0031] <Hydrophilic Treatment Using Sulfur Trioxide-Pyridine Complex> In the treatment using a sulfur trioxide-pyridine complex, cellulose nanocrystals are reacted with a sulfur trioxide-pyridine complex in dimethyl sulfoxide at a temperature of 0 to 60°C for 5 to 240 minutes to introduce sulfate and / or sulfo groups into the hydroxyl groups at the 6-position of the cellulose glucose units. The sulfur trioxide-pyridine complex is preferably incorporated at a mass of 0.5 to 4 g per 1 g (solid content) of cellulose nanocrystals. After the reaction, it is preferable to add an alkaline compound such as sodium hydroxide to convert the sulfate and / or sulfo groups introduced into the cellulose nanocrystals from the H-type to the Na-type, which improves yield. Subsequently, dimethylformamide or isopropyl alcohol is added, and the cellulose nanocrystals are washed by centrifugation or the like, followed by filtration using a dialysis membrane or the like to remove impurities. The resulting concentrate is dispersed in water to prepare cellulose nanocrystals containing only sulfate and / or sulfo groups as anionic functional groups within the above range.

[0032] <Hydrophilic Treatment Using Phosphoric Acid-Urea> The hydrophilic treatment using phosphoric acid-urea can be carried out in the same manner as the conventionally known treatment of introducing phosphate groups using phosphoric acid-urea. Specifically, cellulose nanocrystals and a phosphate group-containing compound are reacted in the presence of a urea-containing compound at a temperature of 135 to 180°C for 5 to 120 minutes to introduce phosphate groups into the hydroxyl groups of the cellulose glucose units. Examples of the phosphate group-containing compound include phosphoric acid, lithium salts of phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid. Among these, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid are preferred for use alone or in combination. The phosphate group-containing compound is preferably added in an amount of 10 to 100 mmol per 10 g (solids content) of cellulose nanocrystals. Examples of the urea-containing compound include urea, thiourea, biuret, phenylurea, benzylurea, and dimethylurea. Of these, urea is preferred. The urea-containing compound is preferably used in an amount of 150 to 200 mmol per 10 g (solid content) of cellulose nanocrystals.

[0033] <Hydrophiliza- tion Treatment Using TEMPO Catalyst> The hydrophiliza- tion treatment using the TEMPO catalyst (2,2,6,6-tetramethylpiperidine-1-oxyl) can be carried out in the same manner as conventionally known oxidation methods using a TEMPO catalyst. Specifically, cellulose nanocrystals having sulfate groups and / or sulfo groups are subjected to a hydrophiliza- tion reaction in which the hydroxyl group at the 6-position of the cellulose glucose unit is oxidized to a carboxyl group in an aqueous system mediated by the TEMPO catalyst (2,2,6,6-tetramethylpiperidine-1-oxyl) under conditions of room temperature and normal pressure. In addition to the above-mentioned 2,2,6,6-tetramethylpiperidine-1-oxyl, TEMPO derivatives such as 4-acetamido-TEMPO, 4-carboxy-TEMPO, and 4-phosphonoxy-TEMPO can also be used as the TEMPO catalyst. The amount of the TEMPO catalyst used is 0.01 to 100 mmol, preferably 0.01 to 5 mmol, per gram of cellulose nanocrystal (solid content).

[0034] During the hydrophilic oxidation treatment, it is preferable to use an oxidizing agent, bromide, iodide, or other co-oxidizing agent, either alone or in combination with the TEMPO catalyst. Examples of oxidizing agents include known oxidizing agents such as halogens, hypohalous acids, halous acids, perhalogen acids or their salts, halogen oxides, and peroxides. Sodium hypochlorite and sodium hypobromite are particularly suitable. The amount of oxidizing agent is 0.5 to 500 mmol, preferably 5 to 50 mmol, per gram of cellulose nanocrystals (solid content). Additional oxidation treatment can be performed by adding additional oxidizing agent after a certain period of time has elapsed since the addition of the oxidizing agent. Alkali metal bromides such as sodium bromide and alkali metal iodides such as sodium iodide are also suitable as co-oxidizing agents. The amount of co-oxidizing agent is 0.1 to 100 mmol, preferably 0.5 to 5 mmol, per gram of cellulose nanocrystals (solid content). Water or an alcohol solvent is preferably used as the reaction medium for the reaction solution.

[0035] The reaction temperature for the hydrophilization treatment is in the range of 1 to 50°C, particularly 10 to 50°C, but may also be room temperature. The reaction time is preferably 1 to 360 minutes, particularly 60 to 240 minutes. As the reaction proceeds, carboxyl groups are generated in the cellulose, causing a decrease in the pH of the slurry. However, to ensure efficient oxidation reaction, it is desirable to maintain the pH in the range of 9 to 12 using a pH adjuster such as sodium hydroxide. After the oxidation treatment, the catalyst and other components used are removed by washing with water or the like.

[0036] <Defibrillation Treatment / Dispersion Treatment> Because the cellulose nanocrystal composite of the present invention uses cellulose nanocrystals with short fiber lengths as raw materials, defibration treatment can be performed after hydrophilization treatment, although this is not necessarily required. Defibration treatment can be performed by conventionally known methods, specifically, using an ultra-high-pressure homogenizer, ultrasonic homogenizer, grinder, high-speed blender, bead mill, ball mill, jet mill, disintegrator, beater, twin-screw extruder, etc. to achieve finer pulverization. Defibration treatment can be performed either dry or wet, depending on the state of the CNC after hydrophilization treatment. Since CNC is preferably mixed with a cationic surfactant in the form of a dispersion, it is preferable to defibrate it using an ultra-high-pressure homogenizer or the like using water or the like as a dispersion medium, and it can also be subjected to a further dispersion treatment. Dispersion treatment can be performed using a dispersing machine such as an ultrasonic disperser, homogenizer, or mixer, and stirring methods using a stirring rod, stirring stone, etc. may also be used.

[0037] The hydrophilic CNC dispersion has excellent dispersibility, ease of handling, and the like, since it contains cellulose nanocrystals with a small fiber length and fiber diameter. In the state of an aqueous dispersion with a solid content of 1% by mass, it is preferable that the viscosity is 0.1 to 100 mPa s (rotational viscometer, temperature 30°C, spindle rotation speed 100 rpm) and the zeta potential is in the range of -60 to -10 mV.

[0038] [Cationic Surfactant (Hydrophobizing Agent)] In the cellulose nanocrystal composite of the present invention, the cationic surfactant used is a cationic surfactant having a quaternary ammonium ion that serves as a counterion to the anionic functional group of the cellulose nanocrystal. When the anionic functional group of the cellulose nanocrystal contains a sulfate group and / or a sulfo group and at least one of a phosphate group and a carboxyl group, it is important that the quaternary ammonium salt satisfies any one of the following conditions (i) to (iii): (i) having four alkyl groups each having 8 or more carbon atoms; (ii) having two or three alkyl groups each having 10 or more carbon atoms; or (iii) having one alkyl group each having 14 or more carbon atoms. When the anionic functional groups of the cellulose nanocrystals are sulfate groups and / or sulfo groups only, it is important that the quaternary ammonium salt satisfies any one of the following conditions (i') to (iii): (i') having four alkyl groups having 4 or more carbon atoms; (ii) having two or three alkyl groups having 10 or more carbon atoms; or (iii) having one alkyl group having 14 or more carbon atoms. Note that the carbon number of the alkyl group refers to the number of carbon atoms in the main chain, not the total number of carbon atoms in one alkyl group. The number of carbon atoms in the alkyl group is usually 20 or less, preferably 18 or less, and more preferably 16 or less. Furthermore, the alkyl group may have a side chain, an unsaturated bond, or a functional group, as long as the effects of the present invention are not impaired.

[0039] The polymer chains (i) to (iii) of the quaternary ammonium salt extend into the dispersion medium, increasing the repulsive potential due to steric hindrance, thereby effectively preventing aggregation of the cellulose nanocrystal composite particles. Specifically, the quaternary ammonium salt is preferably a quaternary ammonium salt represented by the following formula:

[0040] In the formula, R １ ~R ４When the anionic functional groups of the cellulose nanocrystal contain at least one of a sulfate group and / or a sulfo group and a phosphate group or a carboxyl group, all of them are alkyl groups having 8 or more carbon atoms, or two or three of them are alkyl groups having 10 or more carbon atoms, or at least one of them is an alkyl group having 14 or more carbon atoms, and the remainder are benzyl groups or alkyl groups having 1 to 4 carbon atoms; and X － is Cl or Br. When the anionic functional groups of the cellulose nanocrystals are only sulfate groups and / or sulfo groups, all of them are alkyl groups having 4 or more carbon atoms, or two or three of them are alkyl groups having 10 or more carbon atoms, or at least one of them is an alkyl group having 14 or more carbon atoms, and the remainder are benzyl groups or alkyl groups having 1 to 4 carbon atoms; － is Cl or Br.

[0041] In order to improve the dispersibility of cellulose nanocrystals in low-polarity solvents, it is important that the quaternary ammonium salt used as the cationic surfactant in the present invention satisfy any one of the above conditions (i) to (iii). However, since the specific polymer chain possessed by the quaternary ammonium salt improves affinity with low-polarity solvents, it is desirable to select a molecular chain that is compatible with the low-polarity solvent to be used as the solvent. As is clear from the results of the examples described below, it can be seen that particularly excellent dispersibility is obtained by using a quaternary ammonium salt having an alkyl group with 14 or 16 carbon atoms (Examples 5 and 6), or by using a quaternary ammonium salt that satisfies any one of the above conditions (i) to (iii) and has a benzyl group (Example 12).

[0042] The quaternary ammonium salt, which is the cationic surfactant used in the present invention, is particularly preferably at least one selected from dimethyldimyristylammonium bromide, dimethyldimyristylammonium chloride, dimethyldipalmitylammonium bromide, dimethyldipalmitylammonium chloride, benzyldimethylstearylammonium chloride, and benzyldimethylstearylammonium bromide. When the anionic functional groups of the cellulose nanocrystals are sulfate groups and / or sulfo groups only, tetrabutylammonium bromide and tetrabutylammonium chloride are also suitable as the quaternary ammonium salt.

[0043] The molecular weight of the cationic surfactant, the quaternary ammonium salt, is not particularly limited, but is preferably in the range of 200 to 1200, which improves the handleability of the cellulose nanocrystal composite. In the cellulose nanocrystal composite of the present invention, the content of the cationic surfactant is determined by the content of the anionic functional groups in the cellulose nanocrystals, and it is preferably contained in an amount of 0.01 to 10 times the equivalent of the anionic functional groups in the cellulose nanocrystals, and particularly 0.1 to 3 times the equivalent. If the amount of cationic surfactant is less than the above range, the cellulose nanocrystal composite cannot be sufficiently hydrophobicized and its dispersibility in low-polarity solvents cannot be improved. On the other hand, if the amount is greater than the above range, further improvement in dispersibility cannot be obtained, resulting in poor economic efficiency.

[0044] (Method for Producing Cellulose Nanocrystal Composite) The cellulose nanocrystal composite of the present invention can be produced by preparing an aqueous cellulose nanocrystal dispersion in which the total amount of anionic functional groups containing at least sulfate groups and / or sulfo groups is adjusted to more than 0.2 mmol / g and not more than 4.0 mmol / g, and then adding and mixing an alcohol solution containing a cationic surfactant to this aqueous cellulose nanocrystal dispersion. The concentration of the aqueous cellulose nanocrystal dispersion is not limited thereto, but it is preferable that the solids concentration be in the range of 0.5 to 10% by mass. Examples of alcohol-based solvents used in the cationic surfactant-containing solution include methanol, ethanol, n-propanol, and isopropanol, with ethanol being particularly preferable. A mixed solvent of this alcohol-based solvent and water can also be used. The concentration of the alcohol solution containing the cationic surfactant is not limited thereto, but it is preferable that the solids concentration be in the range of 0.5 to 10% by mass. The cellulose nanocrystal composite of the present invention (hereinafter sometimes referred to as "hydrophobized cellulose nanocrystal") can be obtained by removing the aqueous solvent from the liquid in which the cellulose nanocrystal composite obtained as described above has precipitated, using a known separation method such as filtration or centrifugation.

[0045] (Cellulose Nanocrystal Composite Dispersion) A dispersion of the cellulose nanocrystal composite of the present invention dispersed in a low-polarity solvent can be obtained by adding the cellulose nanocrystal composite obtained as described above to a low-polarity solvent and mixing. Alternatively, a dispersion of the cellulose nanocrystal composite dispersed in a low-polarity solvent can be obtained by replacing the aqueous solvent in the solution in which the cellulose nanocrystal composite precipitated with a low-polarity solvent. Low-polarity solvents in which the cellulose nanocrystal composite of the present invention can be dispersed include, but are not limited to, low-polarity solvents having a dielectric constant of 20 or less at 25°C, preferably 1 to 5. Specific examples include toluene, benzene, xylene, diethyl ether, cyclohexane, and hexane. This cellulose nanocrystal composite dispersion has excellent transparency because the cellulose nanocrystals are uniformly dispersed in the low-polarity solvent. It also has excellent stability over time, and since excellent dispersibility can be maintained over a long period of time, excellent transparency can also be maintained over a long period of time.

[0046] In the dispersion of the present invention, it is preferable to use toluene as the low-polarity solvent, and when the CNC composite dispersion is made into a toluene dispersion with a solids content of 1.4% by mass, the light transmittance is 40% T or more, and the dispersion has excellent transparency. Furthermore, since the CNC composite dispersion of the present invention is a dispersion of cellulose nanocrystals with short fiber length, it has a lower viscosity and is easier to handle than when cellulose nanofibers with long fiber length are used, and the viscosity of the cellulose nanocrystal dispersion when made into a toluene dispersion with a solids content of 1% by mass is in the range of 0.1 to 100 mPa·sec (rotational viscometer, temperature 30°C, spindle rotation speed 100 rpm).

[0047] Examples of the present invention will be described below. Note that the following examples are merely examples of the present invention, and the present invention is not limited to these examples. The measurement methods for each item are as follows.

[0048] <Materials> In this example, cellulose nanocrystals were used, which were obtained by decomposing pulp by sulfuric acid treatment and extracting the crystalline portion, and had sulfate groups and / or sulfo groups of 0.28 mmol / g, an average fiber length of 100 nm, and an average fiber diameter of 5 nm.

[0049] <Hydrophilication Treatment Using TEMPO Catalyst> Cellulose nanocrystals (30 g) were added to 2 L of ion-exchanged water containing the TEMPO catalyst 2,2,6,6-tetramethylpiperidine-1-oxyl (2.4 mmol) and sodium bromide (36.4 mmol), and the mixture was stirred until uniformly dispersed. Subsequently, an aqueous solution of sodium hypochlorite (5%, 45 mmol) was added, and the pH of the system was maintained at 10.0 to 10.5 by successively adding an aqueous solution of sodium hydroxide (0.5 M) dropwise. The mixture was stirred at 25°C for 2 hours and 30 minutes. The resulting aqueous dispersion was dialyzed using a dialysis membrane (molecular weight cutoff 1000 D; manufactured by SPECTRUM) until the pH reached 8 or less, and then concentrated using an evaporator to obtain a hydrophilic cellulose nanocrystal aqueous dispersion A.

[0050] <Unmodified Treatment> Cellulose nanocrystals (10 g) were added to ion-exchanged water and stirred with a mixer to obtain a cellulose nanocrystal aqueous dispersion B.

[0051] <HydrophiliZation Treatment Using Sulfur Trioxide-Pyridine Complex> Cellulose nanocrystals (3 g) Were dispersed in dimethyl sulfoxide (200 ml). Sulfur trioxide-pyridine complex (Tokyo Chemical Industry Co., Ltd., 3 g) Was added little by little to the cellulose nanocrystal dispersion, and the cellulose nanocrystals Were hydrophiliZed While stirring at 25°C for 60 minutes. Sodium hydroxide solution Was then added, and impurities Were removed in ion-exchange Water using a dialysis membrane (molecular Weight cut-off 1000 D; SPECTRUM). The mixture Was then concentrated using an evaporator to obtain hydrophiliZed cellulose nanocrystal Water Dispersion C.

[0052] <Hydrophiliza- tion Treatment Using Sulfur Trioxide-Pyridine Complex> Cellulose nanocrystals (10 g) were dispersed in dimethyl sulfoxide (200 ml). Sulfur trioxide-pyridine complex (Tokyo Chemical Industry Co., Ltd., 10 g) was gradually added to the cellulose nanocrystal dispersion, and the cellulose nanocrystals were hydrophilized while stirring at 25°C for 60 minutes. Sodium hydroxide solution was then added, and impurities were removed in ion-exchange water using a dialysis membrane (molecular weight cutoff 1000 D; Spectrum). The mixture was then concentrated using an evaporator to obtain hydrophilized cellulose nanocrystal aqueous dispersion D.

[0053] <Hydrophobization Treatment> [Example 1] Trimethylmyristylammonium chloride was used as a cationic surfactant (hereinafter referred to as "hydrophobizing agent") and dissolved in ethanol (41.4 mM) to prepare a hydrophobizing agent solution. The hydrophobizing agent solution was added to the hydrophilized cellulose nanocrystal aqueous dispersion A (solid content 2.8% by mass) at a volume ratio of 1:1 and stirred. Next, hydrophobized cellulose nanocrystals were obtained by washing with ethanol using a centrifuge. Further, toluene was added as a solvent and ultrasonic treatment was performed to obtain a hydrophobized cellulose nanocrystal solvent dispersion. This was the sample of Example 1.

[0054] Example 2 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that trimethylpalmitylammonium bromide was used as the hydrophobizing agent. This was used as the sample of Example 2.

[0055] [Example 3] A hydrophobized cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that trimethylstearylammonium chloride was used as the hydrophobizing agent and benzene was used as the solvent. This was used as the sample of Example 3.

[0056] Example 4 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that dimethyldidecylammonium bromide was used as the hydrophobizing agent. This was used as the sample of Example 4.

[0057] Example 5 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that dimethyldimyristylammonium bromide was used as the hydrophobizing agent. This was designated as the sample of Example 5.

[0058] Example 6 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that dimethyldipalmitylammonium bromide was used as the hydrophobizing agent and toluene or benzene was used as the solvent. This was designated as the sample of Example 6.

[0059] Example 7 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that dimethyl distearyl ammonium chloride was used as the hydrophobizing agent. This was designated as the sample of Example 7.

[0060] Example 8 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that tetra-n-octylammonium bromide was used as the hydrophobizing agent. This was designated as the sample of Example 8.

[0061] Example 9 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that tetra(decyl)ammonium bromide was used as the hydrophobizing agent. This was designated as the sample of Example 9.

[0062] Example 10 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that tetradodecylammonium bromide was used as the hydrophobizing agent. This was designated as the sample of Example 10.

[0063] Example 11 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that benzyldimethylmyristylammonium chloride was used as the hydrophobizing agent. This was designated as the sample of Example 11.

[0064] Example 12 A hydrophobized cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that benzyldimethylstearylammonium chloride was used as the hydrophobizing agent and toluene or benzene was used as the solvent. This was designated as the sample of Example 12.

[0065] Example 13: Trimethylmyristylammonium chloride was used as a hydrophobizing agent, and this was dissolved in ethanol (41.4 mM) to prepare a hydrophobizing agent solution. The hydrophobizing agent solution was added to the cellulose nanocrystal aqueous dispersion B (solid content 2.8% by mass) at a volume ratio of 1:1 and stirred. Next, hydrophobized cellulose nanocrystals were obtained by washing with ethanol using a centrifuge. Furthermore, toluene was added as a solvent and ultrasonic treatment was performed to obtain a hydrophobized cellulose nanocrystal solvent dispersion. This was the sample of Example 13.

[0066] Example 14 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 13, except that dimethyldidecylammonium bromide was used as the hydrophobizing agent. This was used as the sample of Example 14.

[0067] Example 15 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 13, except that tetrabutylammonium chloride was used as the hydrophobizing agent. This was designated as the sample of Example 15.

[0068] Example 16 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 13, except that tetra-n-octylammonium bromide was used as the hydrophobizing agent. This was designated as the sample of Example 16.

[0069] Example 17 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 13, except that tetradodecylammonium bromide was used as the hydrophobizing agent. This was designated as the sample of Example 17.

[0070] Example 18: Tetradodecylammonium bromide was used as a hydrophobizing agent, and this was dissolved in ethanol (41.4 mM) to prepare a hydrophobizing agent solution. The hydrophobizing agent solution was added to the hydrophilized cellulose nanocrystal aqueous dispersion C (solid content 2.8% by mass) at a volume ratio of 1:1 and stirred. Next, hydrophobized cellulose nanocrystals were obtained by washing with ethanol using a centrifuge. Furthermore, toluene was added as a solvent and ultrasonic treatment was performed to obtain a hydrophobized cellulose nanocrystal solvent dispersion. This was the sample for Example 18.

[0071] Example 19: Dimethyldipalmitylammonium bromide was used as the hydrophobizing agent, and this was dissolved in ethanol (41.4 mM) to prepare a hydrophobizing agent solution. The hydrophobizing agent solution was added to the hydrophilized cellulose nanocrystal aqueous dispersion D (solid content 2.8% by mass) at a volume ratio of 1:1 and stirred. Next, hydrophobized cellulose nanocrystals were obtained by washing with ethanol using a centrifuge. Furthermore, toluene was added as a solvent and ultrasonic treatment was performed to obtain a hydrophobized cellulose nanocrystal solvent dispersion. This was the sample for Example 19.

[0072] Example 20 The same procedure as in Example 19 was carried out except that tetradodecylammonium bromide was used as the hydrophobizing agent, to obtain a hydrophobized cellulose nanocrystal solvent dispersion. This was designated as the sample of Example 20.

[0073] Comparative Example 1 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that trimethyldodecylammonium chloride was used as the hydrophobizing agent. This was used as the sample of Comparative Example 1.

[0074] Comparative Example 2 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that dimethyldioctylammonium bromide was used as the hydrophobizing agent. This was designated as the sample of Comparative Example 2.

[0075] Comparative Example 3 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that tetrabutylammonium chloride was used as the hydrophobizing agent. This was designated as the sample of Comparative Example 3.

[0076] Comparative Example 4 A hydrophobized cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that tributyl palmityl phosphonium bromide was used as the hydrophobizing agent. This was designated as the sample of Comparative Example 4.

[0077] Comparative Example 5 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that tetra-n-octylphosphonium bromide was used as the hydrophobizing agent. This was designated as the sample of Comparative Example 5.

[0078] Comparative Example 6 A hydrophobic cellulose nanocrystal solvent dispersion was obtained in the same manner as in Example 1, except that benzyltriphenylphosphonium bromide was used as the hydrophobizing agent. This was designated as the sample of Comparative Example 6.

[0079] <Measurement of Anionic Functional Group Amount> 0.1 g of cation exchange resin was added to a hydrophilized cellulose nanocrystal aqueous dispersion (solid content 0.05% by mass, 100 mL) and stirred. The cation exchange resin was then separated by filtration to obtain an H-type hydrophilized cellulose nanocrystal aqueous dispersion. Aqueous sodium hydroxide solution (0.05 M) was added dropwise to the aqueous dispersion, and the change in electrical conductivity was measured using an automatic potentiometric titrator (AT-710, manufactured by Kyoto Electronics Manufacturing Co., Ltd.). The titration amount of the aqueous sodium hydroxide solution consumed for neutralization of the anionic functional groups was determined from the resulting conductivity curve, and the amount of anionic functional groups (mmol / g) was calculated using the following formula:

[0080] In the formula, c: concentration of the aqueous sodium hydroxide solution (mmol / mL), v: titration amount of the aqueous sodium hydroxide solution consumed for neutralizing the anionic functional groups (mL), w: solid mass of cellulose nanocrystals in the system (g).

[0081] <Light Transmittance Measurement> The light transmittance (% T) of the hydrophobic cellulose nanocrystal solvent dispersion (solid content 1.4%) at a wavelength of 660 nm was measured using an ultraviolet-visible-near infrared spectrophotometer (UV-3600i Plus; manufactured by Shimadzu Corporation).

[0082] <Presence or absence of birefringence> The hydrophobic cellulose nanocrystal solvent dispersion (solid content 1.4%) was shaken and the dispersion was visually observed through crossed polarizers to confirm the presence or absence of birefringence. Dispersions in which interference colors were observed throughout the solution were evaluated as having "birefringence," while dispersions in which interference colors were partially or not observed were evaluated as having "no birefringence."

[0083] <Evaluation of Dispersibility> The dispersion was evaluated based on the light transmittance and the presence or absence of birefringence as follows: S: Light transmittance of 60% or more and birefringence present A: Light transmittance of 40% or more and less than 60% and no birefringence B: Light transmittance of less than 40%

[0084]

[0085] The CNC composite of the present invention has excellent dispersibility in low-polarity solvents such as toluene and can be easily composited with polymers soluble in toluene, etc. Therefore, a dispersion of this CNC composite in a low-polarity solvent can be suitably used as a solvent for hydrophobic resins. Furthermore, the dense self-organized structure formed by the cellulose nanocrystals can impart excellent mechanical strength to molded articles made from the above polymers.

Claims

1. A cellulose nanocrystal composite comprising a cellulose nanocrystal containing an anionic functional group containing at least a sulfate group and / or a sulfo group and at least one of a phosphate group and a carboxyl group, and a cationic surfactant, wherein the cationic surfactant is a quaternary ammonium salt that satisfies any one of the following (i) to (iii): (i) having four alkyl groups with 8 or more carbon atoms, (ii) having two or three alkyl groups with 10 or more carbon atoms, or (iii) having one alkyl group with 14 or more carbon atoms.

2. A cellulose nanocrystal composite comprising a cellulose nanocrystal containing only sulfate and / or sulfo groups as anionic functional groups and a cationic surfactant, wherein the cationic surfactant is a quaternary ammonium salt that satisfies any one of the following (i') to (iii): (i') has four alkyl groups with 4 or more carbon atoms, (ii) has two or three alkyl groups with 10 or more carbon atoms, or (iii) has one alkyl group with 14 or more carbon atoms.

3. The cellulose nanocrystal composite according to claim 1, wherein the quaternary ammonium salt is a quaternary ammonium salt represented by the following formula: In the formula, R １ ~R ４ are all alkyl groups having 8 or more carbon atoms, or two or three are alkyl groups having 10 or more carbon atoms, or at least one is an alkyl group having 14 or more carbon atoms, and the remainder are benzyl groups or alkyl groups having 1 to 4 carbon atoms; and X － is Cl or Br.

4. The cellulose nanocrystal composite according to claim 2, wherein the quaternary ammonium salt is a quaternary ammonium salt represented by the following formula: In the formula, R １ ~R ４ are all alkyl groups having 4 or more carbon atoms, or two or three are alkyl groups having 10 or more carbon atoms, or at least one is an alkyl group having 14 or more carbon atoms, and the remainder are benzyl groups or alkyl groups having 1 to 4 carbon atoms; and X － is Cl or Br.

5. A cellulose nanocrystal composite according to claim 1 or 2, wherein the cationic surfactant is at least one selected from the group consisting of dimethyldimyristyl ammonium bromide, dimethyldimyristyl ammonium chloride, dimethyldipalmityl ammonium bromide, dimethyldipalmityl ammonium chloride, benzyldimethylstearyl ammonium chloride, and benzyldimethylstearyl ammonium bromide.

6. The cellulose nanocrystal composite according to claim 1 or 2, wherein the total amount of anionic functional groups in the cellulose nanocrystal is more than 0.20 mmol / g and not more than 4.00 mmol / g.

7. A cellulose nanocrystal dispersion, characterized in that the cellulose nanocrystal complex according to claim 1 or 2 is dispersed in an organic solvent.

8. The cellulose nanocrystal dispersion according to claim 7, wherein the organic solvent is a low-polarity organic solvent having a relative dielectric constant of 20 or less at 25°C.

9. The cellulose nanocrystal dispersion according to claim 7, wherein the organic solvent is any one of toluene, benzene, xylene, cyclohexane, and hexane.

10. The cellulose nanocrystal dispersion according to claim 7, wherein the cellulose nanocrystal dispersion has a light transmittance of 40%T or more when dispersed in toluene with a solid content of 1.4% by mass.

11. The cellulose nanocrystal dispersion according to claim 7, wherein the viscosity of the cellulose nanocrystal dispersion when dispersed in toluene with a solid content of 1% by mass is in the range of 0.1 to 100 mPa·sec (rotational viscometer, temperature 30°C, spindle rotation speed 100 rpm).

12. A method for producing a cellulose nanocrystal composite according to claim 1 or 2, characterized in that cellulose nanocrystals having sulfate groups and / or sulfo groups are hydrophilized to prepare an aqueous dispersion of cellulose nanocrystals in which the total amount of anionic functional groups is adjusted to more than 0.20 mmol / g and not more than 4.00 mmol / g, and then an alcoholic solution containing a quaternary ammonium salt as a cationic surfactant is added to the aqueous dispersion of cellulose nanocrystals to produce the cellulose nanocrystal composite.

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