JP7350570B2 - Modified cellulose nanofiber and method for producing the same - Google Patents

Description

The present invention relates to modified cellulose nanofibers whose fiber surfaces are esterified with a dibasic carboxylic acid anhydride, and a method for producing the same.

Cellulose fibers (cell wall units) are aggregates of cellulose fine fibers (microfibrils). Cellulose fine fibers have mechanical properties comparable to steel and have a nanostructure with a diameter of about 30 nm, so they are attracting hot social attention as reinforcing agents. However, cellulose fine fibers are bound together by hydrogen bonds, and in order to extract the fine fibers, it is necessary to break the hydrogen bonds and separate (fibrillate) the microfibrils. Therefore, such separation of microfibrils is called fibrillation, and a mechanical fibrillation method in which intense physical force is applied has been developed as a method for defibrating cellulose fine fibers (cellulose nanofibers).

The most commonly used mechanical defibration method is the underwater mechanical defibration method, in which cellulose fibers are mechanically defibrated in water. It is nano-ized by strong mechanical shearing using a homogenizer or the like. However, natural cellulose microfibrils are composed of a crystalline zone (crystalline region) and an amorphous zone (amorphous region), but when the amorphous zone absorbs a swelling solvent such as water and becomes swollen, , deformed by strong shear. Therefore, the cellulose fibers are damaged by shearing and take on a branched shape that is likely to become entangled or caught. In addition, a strong mechanical grinding method such as a ball mill causes a mechanochemical reaction peculiar to the solid state, and this action inevitably destroys or dissolves the crystal structure of cellulose. As a result, the yield is low and the degree of crystallinity tends to be low. Furthermore, cellulose fine fibers can be used as reinforcing materials for resins, but in order to form composites with resins, underwater mechanical defibration requires dehydration after defibration to modify the fiber surface to make it hydrophobic. This dehydration process requires high energy.

Therefore, as a method for producing cellulose fine fibers that have excellent dispersibility in organic media such as resins and organic solvents by esterifying the fiber surface, JP 2010-104768A (Patent Document 1) discloses butyl chloride methyl imidazo A method for producing polysaccharide nanofibers is disclosed in which a cellulose-based material is swollen and/or partially dissolved using a mixed solvent containing an ionic liquid such as chlorine and an organic solvent, and then esterified. In the examples of this document, acetic anhydride and butyric anhydride are used as esterifying agents.

Additionally, the TEMPO oxidation method using 2,2,6,6-tetramethyl-1-piperidine-N-oxyradical (TEMPO) is also attracting attention as a chemical defibration method that does not require strong defibration or crushing. There is. WO2010/116794 pamphlet (Patent Document 2) describes cellulose in which a cellulose raw material is oxidized using an oxidizing agent in the presence of an N-oxyl compound such as TEMPO and bromide and/or iodide, and then subjected to wet atomization treatment. A method of making a nanofiber dispersion is disclosed.

Furthermore, as a method for easily and efficiently producing uniform nano-sized cellulose particles, JP 2017-82188A (Patent Document 3) discloses a method that uses a catalyst containing a base catalyst or an acid catalyst and a dibasic carboxylic acid anhydride. Disclosed is a method for producing modified cellulose fine fibers, which includes a modified defibration step of impregnating cellulose with a reactive fibrillation liquid containing the above, esterifying and chemically defibrating the cellulose, and obtaining carboxyl group-containing cellulose fine fibers. . Furthermore, in JP 2017-190437 A (Patent Document 4), cellulose (raw material cellulose) is infiltrated with a reactive fibrillation liquid containing a catalyst containing a base or acid catalyst and a dibasic carboxylic acid anhydride. A modified defibration step in which cellulose is esterified and chemically defibrated to obtain carboxyl group-containing cellulose fine fibers, and the obtained carboxyl group-containing cellulose fine fibers and a dispersion medium are stirred at a rotational speed of 2000 rpm or more to obtain carboxyl group-containing cellulose fine fibers. A method for producing modified cellulose fine fibers is disclosed, which includes a stirring step to obtain cellulose fine fibers. Patent Documents 2 and 3 describe that pyridines are preferable as catalysts; Examples of Patent Document 3 use pyridine or toluenesulfonic acid, and Examples of Patent Document 4 use pyridine.

Japanese Patent Application Publication No. 2010-104768 WO2010/116794 pamphlet JP2017-82188A JP 2017-190437 Publication

However, the manufacturing method of Patent Document 1 requires the use of a special ionic liquid, and the purification process for recovering and reusing the ionic liquid increases the manufacturing cost of cellulose nanofibers and complicates the manufacturing process. .

Further, cellulose nanofibers obtained by the TEMPO method of Patent Document 2 have high hydrophilicity and water dispersibility, but have low dispersibility in organic media. Furthermore, since an expensive TEMPO catalyst and a large amount of alkaline substances are used, the cost efficiency is low, wastewater treatment is difficult, and the burden on the environment is large.

Furthermore, although the manufacturing methods of Patent Documents 3 and 4 can produce uniform cellulose nanofibers more easily and efficiently than Patent Documents 1 and 2, the manufacturing methods of Patent Documents 3 and 4 can sufficiently produce uniform cellulose nanofibers. could not be manufactured. Furthermore, although the manufacturing method of Patent Document 4 provides more uniform cellulose nanofibers than that of Patent Document 3, stirring treatment is required in the defibration step, and it is not a simple method.

Therefore, an object of the present invention is to provide a modified cellulose nanofiber that can be easily and efficiently produced, has a uniform nanosize, a high degree of crystallinity, little damage to the fiber shape, a large aspect ratio, and a high water absorption capacity. The purpose is to provide a manufacturing method.

Another object of the present invention is to provide modified cellulose nanofibers that can be produced in an energy-saving manner without strong mechanical shearing, and a method for producing the same.

Still another object of the present invention is to provide a method for producing modified cellulose nanofibers with excellent transparency.

Another object of the present invention is to provide highly modified cellulose nanofibers with excellent thixotropy, film-forming properties, and dispersibility in organic solvents, and a method for producing the same.

As a result of intensive studies to achieve the above-mentioned object, the present inventors have chemically defibrated the cellulose by infiltrating the cellulose with a reactive defibrating liquid containing a metal compound and a dibasic carboxylic acid anhydride to esterify the cellulose. After that, by adding a dispersion medium to the obtained modified cellulose fine fibers and stirring them, a specific modified cellulose nanofiber, that is, a uniform nanosize, high crystallinity, less damage to the fiber shape, and a high aspect ratio. The present invention was completed based on the discovery that modified cellulose nanofibers with large water absorption properties can be easily and efficiently produced.

That is, the method for producing modified cellulose nanofibers of the present invention involves infiltrating cellulose with a reactive defibrating liquid containing a catalyst containing a metal compound and a dibasic carboxylic acid anhydride, esterifying the cellulose, and chemically defibrating it. , a modified fibrillation step for obtaining modified cellulose fine fibers modified with dibasic acid carboxylic acid anhydride and formed of cellulose containing a metal salt form, and adding a dispersion medium to the obtained modified cellulose fine fibers. and a stirring step of stirring to obtain modified cellulose nanofibers. The metal compound may be, for example, an alkali metal compound (particularly an alkali metal hydrogen carbonate). The metal compound may be a weakly basic metal compound. The reactive defibration liquid further includes at least one aprotic solvent having a donor number of 25 or more, such as at least one solvent selected from the group consisting of alkyl sulfoxides, alkylamides, and pyrrolidones (particularly diC _1-2 alkyl sulfoxide). The dibasic carboxylic anhydride is at least one selected from the group consisting of aliphatic dicarboxylic anhydrides, alicyclic dicarboxylic anhydrides, and aromatic dicarboxylic anhydrides (particularly saturated dicarboxylic anhydrides having 4 to 6 carbon atoms). aliphatic dicarboxylic acid anhydride). The proportion of the catalyst may be 100 parts by mass or more with respect to 100 parts by mass of the dibasic carboxylic acid anhydride. The proportion of the dibasic carboxylic acid anhydride may be 60 parts by mass or more based on 100 parts by mass of cellulose. In the stirring step, the modified cellulose fine fibers may be subjected to liquid-liquid shearing.

The present invention also includes modified cellulose nanofibers that are modified with a dibasic carboxylic acid anhydride and are formed of cellulose containing a metal salt form, and that satisfy the following characteristics (1) to (4).
(1) The average degree of substitution is 0.05 to 2. (2) The average fiber diameter is 150 nm or less. (3) The number of fibers with a fiber diameter of 300 nm or more is 5% or less of the total number of fibers. (4) Average fiber length is 1 μm or more

In the present invention, a reactive defibration liquid containing a metal compound and a dibasic carboxylic acid anhydride is permeated into cellulose to esterify and chemically defibrate the cellulose, and then a dispersion medium is applied to the obtained modified cellulose fine fibers. Since it is added and stirred, it can be defibrated without destroying the naturally derived cellulose crystal structure or microfibril structure. In particular, in the present invention, the cellulose can be swollen as the reactive fibrillation liquid permeates, and the fibrillation efficiency of cellulose can be improved without strong mechanical shearing. Therefore, modified cellulose nanofibers with uniform nanosize, high crystallinity, little damage to fiber shape, large aspect ratio, and high water absorption can be easily and efficiently produced using an energy-saving method. Moreover, since it is nano-sized and has a high uniformity in fiber diameter, it has high transparency and can improve thixotropy and film-forming properties.

FIG. 1 is a scanning electron microscope (SEM) photograph (10,000 times magnification) of cellulose pulp, which is the raw material used in the examples. FIG. 2 is a SEM photograph (10,000 times magnification) of the modified cellulose nanofibers obtained in Example 1. FIG. 3 is a SEM photograph (10,000x magnification) of the modified cellulose nanofibers obtained in Example 2. FIG. 4 is a SEM photograph (10,000 times magnification) of the modified cellulose nanofibers obtained in Example 3. FIG. 5 is a SEM photograph (10,000x magnification) of the modified cellulose nanofibers obtained in Example 4. FIG. 6 is a SEM photograph (10,000 times) of the modified cellulose nanofibers obtained in Example 5. FIG. 7 is a SEM photograph (10,000x magnification) of the modified cellulose nanofibers obtained in Example 6. FIG. 8 is a SEM photograph (10,000 times magnification) of the modified cellulose nanofibers obtained in Example 7. FIG. 9 is a SEM photograph (1000x magnification) of the treated cellulose obtained in Comparative Example 1. FIG. 10 is a SEM photograph (1000x magnification) of the treated cellulose obtained in Comparative Example 2.

[Modified defibration process]
The method for producing modified cellulose nanofibers of the present invention includes a reactive fibrillation solution (reactive fibrillation solution or mixed liquid) containing a catalyst containing an inorganic base catalyst and a dibasic carboxylic acid anhydride (alkanedioic anhydride). The method includes a modified defibration step of infiltrating cellulose to esterify the cellulose and chemically defibrate it to obtain modified cellulose fine fibers. In the present invention, the reason why cellulose is modified and at the same time defibrated in this step can be presumed as follows. That is, the reactive defibration solution containing the catalyst and the dibasic carboxylic acid anhydride (especially an aprotic solvent) is a solution with low solubility for cellulose, and this solution penetrates between the microfibrils of cellulose. to swell cellulose and modify the hydroxyl groups on the surface of microfibrils. Furthermore, this modification breaks the hydrogen bonds between microfibrils, and the microfibrils easily separate from each other and become fibrillated. Further, since the solution does not penetrate into the crystalline zone (domain) of the microfibrils, the obtained modified cellulose fine fibers have less damage and have a structure close to that of natural microfibrils. At the same time, in this step, cellulose can be defibrated without using mechanical defibration means using strong shearing force, so there is little damage caused by physical action. In particular, since the catalyst includes an inorganic base catalyst, the inorganic base forms an inorganic salt with the carboxyl group of the modified cellulose fine fibers. In the method of the present invention, this inorganic salt causes strong electrostatic repulsion between the fibers, so that the reactive defibration liquid permeates uniformly between the cellulose fibers, and fibrillation progresses rapidly. It can be estimated. Therefore, it can be estimated that the obtained modified cellulose fine fibers maintain high strength.

(cellulose)
The cellulose used as a raw material may be in the form of cellulose alone, or may be in the form of a mixture containing non-cellulose components such as lignin and hemicellulose.

Cellulose in its own form (or cellulose with a small content of non-cellulose components) includes, for example, pulp (for example, wood pulp, bamboo pulp, straw pulp, bagasse pulp, linter pulp, flax pulp, hemp pulp, mulberry pulp, mitsumata pulp, etc.) ), ascidian cellulose, bacterial cellulose, cellulose powder, crystalline cellulose, etc.

Mixed forms of cellulose (cellulose compositions) include, for example, wood [e.g., conifers (pine, fir, spruce, hemlock, cedar, etc.), hardwoods (beech, birch, poplar, maple, etc.)], herbs [hemp, etc.] (hemp, flax, Manila hemp, ramie, etc.), straw, bagasse, mitsumata, etc.], seed wool fibers (cotton linters, bombax cotton, kapok, etc.), bamboo, sugar cane, paper, etc.

These celluloses can be used alone or in combination of two or more. In the mixed form of cellulose, the proportion of non-cellulose components may be 90% by weight or less, for example 1 to 90% by weight, preferably 3 to 80% by weight, more preferably 5 to 70% by weight. If the proportion of other components is too large, it may become difficult to produce modified cellulose fine fibers.

The cellulose preferably includes crystalline cellulose (especially type I crystalline cellulose), and may be a combination of crystalline cellulose and amorphous cellulose (such as amorphous cellulose). The proportion of crystalline cellulose (especially type I crystalline cellulose) may be 10% by mass or more based on the whole cellulose, for example 30 to 99% by mass, preferably 50 to 98.5% by mass, more preferably 60% by mass. ~98% by mass. If the proportion of crystalline cellulose is too small, there is a risk that the heat resistance and strength of the modified cellulose fine fibers will decrease.

Among these, cellulose, a raw material derived from plants, is commonly used and is easy to modify and defibrate, resulting in wood pulp (e.g., softwood pulp, hardwood pulp, etc.), pulp of seed hair fibers (e.g., cotton linter pulp), and cellulose powder. etc. are commonly used. Note that the pulp may be mechanical pulp obtained by mechanically processing pulp material, but chemical pulp obtained by chemically processing pulp material is preferable because the content of non-cellulose components is low.

The water content of cellulose (mass ratio of water to dry cellulose) may be 1% by mass or more, for example 1 to 100% by mass, preferably 2 to 80% by mass, more preferably 3 to 60% by mass, most preferably is 5 to 50% by mass. In the present invention, from the viewpoint of the degree of fibrillation and the efficiency of fibrillation, cellulose preferably contains water within this range. For example, in the case of commercially available cellulose pulp, the cellulose pulp can be used as it is without drying. You may. If the water content is too low, there is a risk that the fibrillation properties of cellulose will decrease.

The average fiber diameter of cellulose as a raw material is usually 1 μm or more, for example 5 to 500 μm, preferably 10 to 300 μm, more preferably 20 to 100 μm, and most preferably 30 to 50 μm. In this specification and claims, the average fiber diameter of the raw material cellulose may be calculated by randomly selecting 50 fibers from an optical micrograph and averaging them.

The mass ratio of cellulose and reactive defibration liquid can be selected from the range of former/latter = 1/99 to 30/70, for example 1.2/98.8 to 25/75, preferably 1.3/ 98.7 to 20/80, more preferably 1.5/98.5 to 15/85, most preferably 2/98 to 10/90. If the proportion of cellulose is too small, the production amount of modified cellulose fine fibers will be low, and if it is too large, the reaction time will become long, so there is a risk that productivity will decrease in any case. Furthermore, if the proportion of cellulose is too high, the uniformity of the size and modification rate of the obtained fine fibers may decrease.

The saturated absorption rate of cellulose with respect to the reactive defibration liquid is, for example, 10 times or more (for example, about 10 to 200 times), preferably 20 times or more (for example, about 20 to 150 times), and more preferably 30 times or more (for example, 30 to 200 times). (approximately 100 times). If the saturated absorption rate is too low, there is a risk that the fibrillation properties of cellulose and the uniformity of the obtained fine fibers will deteriorate.

(Dibasic carboxylic acid anhydride)
Dibasic carboxylic acid anhydrides (esterifying agents) include aliphatic dicarboxylic anhydrides, alicyclic dicarboxylic anhydrides, and aromatic dicarboxylic anhydrides.

Examples of aliphatic dicarboxylic anhydrides include saturated aliphatic dicarboxylic anhydrides such as succinic anhydride; unsaturated aliphatic dicarboxylic anhydrides such as maleic anhydride and itaconic anhydride. Examples of the alicyclic dicarboxylic anhydride include 1-cyclohexene-1,2-dicarboxylic anhydride, hexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride. Examples of the aromatic dicarboxylic anhydride include phthalic anhydride and naphthalic anhydride. These dibasic carboxylic acid anhydrides can be used alone or in combination of two or more.

Among these dibasic carboxylic acid anhydrides, saturated or unsaturated aliphatic dicarboxylic acid anhydrides having 4 to 8 carbon atoms, such as succinic anhydride and maleic anhydride, are preferred from the viewpoint of modification properties and fibrillation properties; Saturated aliphatic dicarboxylic acid anhydrides having 4 to 6 carbon atoms are more preferred, and saturated aliphatic dicarboxylic acid anhydrides having 4 to 5 carbon atoms are most preferred. If the number of carbon atoms is too large, there is a risk that the permeability between microfibrils and the reactivity with cellulose hydroxyl groups will decrease.

The concentration (mass percentage) of the dibasic carboxylic acid anhydride in the reactive fibrillation solution is approximately 0.5 to 50% by mass from the viewpoint of achieving a good balance between permeability between microfibrils and reactivity to cellulose hydroxyl groups. The concentration of the dibasic carboxylic acid anhydride may be low, for example, from 1 to 30% by mass, preferably from 1.5 to 10% by mass, since the method of the present invention has excellent permeability to the reactive defibration liquid. % by weight, more preferably 2-5% by weight, most preferably 2.5-4% by weight.

The ratio of cellulose to dibasic carboxylic acid anhydride is the molar ratio in terms of anhydroglucose units (anhydroglucose units) of cellulose, and the former /latter=approximately 10/1 to 1/10, for example, 1/1 to 1/8, preferably 1/2 to 1/6, and more preferably 1/3 to 1/5. The mass ratio of both is, for example, cellulose/dibasic carboxylic acid anhydride=70/30 to 5/95, preferably 65/35 to 10/90, more preferably 60/40 to 20/80, more preferably 55 /45 to 30/70, most preferably 50/50 to 40/60.

(catalyst)
In the present invention, a catalyst containing a metal compound in addition to a dibasic carboxylic acid anhydride is used to promote esterification of cellulose. In the present invention, by using a catalyst containing a metal compound as the catalyst, the carboxyl groups introduced into the cellulose fine fibers form a metal salt, and the fibrillation efficiency can be improved.

Examples of the metal compound include alkali metal compounds and alkaline earth metal compounds. These metal compounds can be used alone or in combination of two or more.

Examples of alkali metal compounds include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; alkali metal carbonates such as lithium carbonate, sodium carbonate, and potassium carbonate; sodium hydrogen carbonate, potassium hydrogen carbonate, etc. alkali metal bicarbonates; alkali metal hydrides such as sodium hydride and potassium hydride; alkali metal carboxylates such as lithium acetate, sodium acetate, potassium acetate, sodium propionate, potassium propionate, and sodium butyrate; metaboric acid Alkali metal borates such as sodium, sodium tetraborate (borax); alkali metal phosphates such as trisodium phosphate; alkalis such as sodium dihydrogen phosphate, potassium dihydrogen phosphate, and disodium hydrogen phosphate Metal hydrogen phosphate; alkali metal C _1-4 alkoxides such as sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium t-butoxide, potassium t-butoxide, and the like.

Examples of alkaline earth metal compounds include alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide; alkaline earth metal carbonate salts such as magnesium carbonate; and alkaline earth metal hydrogen carbonate salts such as magnesium hydrogen carbonate. ; carboxylic acid alkaline earth metal salts such as calcium acetate; and alkaline earth metal C _1-4 alkoxides such as calcium di-t-butoxide.

Of these metal compounds, weakly basic base catalysts (especially weakly salt) is particularly preferred. Even if the metal compound is a basic catalyst, if the metal compound is strongly basic, the reaction will proceed on the surface of cellulose before the esterifying agent penetrates between the microfibrils, and there is a possibility that the fibrillation property will be reduced. The weakly basic metal compound may have a pH of about 7 to 11, preferably 7.5 to 10, more preferably 7.8 to 9 (especially 8 to 8.5) in a 1 mol/liter aqueous solution. good.

Such weakly basic metal compounds include alkali metal carbonates such as sodium carbonate; alkali metal hydrogen carbonates such as sodium hydrogen carbonate; alkali metal carboxylates such as lithium acetate and sodium acetate; sodium tetraborate ( Alkali metal borates such as borax; alkali metal phosphates such as trisodium phosphate; alkali metal hydrogen phosphates such as sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate; carbonic acid Examples include alkaline earth metal carbonates such as magnesium; alkaline earth metal hydrogen carbonates such as magnesium hydrogen carbonate; alkaline earth metal carboxylates such as calcium acetate. These metal compounds can be used alone or in combination of two or more. Among these, alkali metal hydrogen carbonates such as sodium hydrogen carbonate, alkali metal C _1-4 alkane monocarboxylate such as lithium acetate are preferred, and alkali metal Particularly preferred are hydrogen carbonates.

The metal compound (particularly the alkali metal compound) may be 50% by mass or more in the catalyst, for example 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass (metal compound alone). . If the proportion of the metal compound is too small, there is a risk that the fibrillation efficiency will decrease.

In addition to the metal compound, the catalyst may further contain another catalyst (catalyst not containing metal). Other catalysts include base catalysts, acid catalysts (protic acids, Lewis acids, etc.).

Examples of the base catalyst include ammonia, tertiary amines (for example, tri-C _1-4 alkylamines such as trimethylamine and triethylamine), heterocyclic amines (4-dimethylaminopyridine, morpholine, piperidine, etc.), Examples include quaternary ammonium salts (eg, tetraC _1-4 alkyl ammonium halides such as tetraethylammonium chloride and tetraethylammonium bromide; benzyltriC _1-4 alkyl ammonium halides such as benzyltrimethylammonium chloride), and the like.

Examples of acid catalysts include inorganic acids [for example, sulfuric acid, hydrogen chloride (or hydrochloric acid), nitric acid, phosphoric acid, etc.], organic acids [for example, sulfonic acids (such as methanesulfonic acid, ethanesulfonic acid, trifluoromethanesulfonic acid, etc.)] arenesulfonic acids such as alkanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid].

The proportion of the other catalyst may be 50 parts by mass or less (for example, 0.1 to 50 parts by mass), preferably 30 parts by mass or less, more preferably 10 parts by mass or less, based on 100 parts by mass of the metal compound. It is. If the proportion of other catalysts is too large, the fibrillation efficiency and transparency may decrease.

The proportion of the catalyst (particularly the metal compound) may be 10 to 1000 parts by mass, for example 30 to 500 parts by mass, preferably 50 to 1000 parts by mass, based on the entire reactive fibrillation liquid per 100 parts by mass of cellulose as a raw material. ~400 parts by weight, more preferably 80 to 300 parts by weight, more preferably 100 to 250 parts by weight, and most preferably 150 to 200 parts by weight. The proportion of the catalyst (particularly the metal compound) may be 0.5 to 50% by mass based on the entire reactive defibration liquid, for example 1 to 30% by mass, preferably 2 to 20% by mass, more preferably 2.5-15% by weight, more preferably 3-10% by weight, most preferably 5-8% by weight. If the proportion of the catalyst is too small, the modification rate of cellulose may decrease, and the effect of fibrillating cellulose may also decrease. On the other hand, if the proportion of the catalyst is too high, the modification rate is too high and there is a risk that cellulose will decompose, and the permeability of the reactive fibrillation liquid to cellulose will decrease, and the effect of fibrillating cellulose will also decrease. There is a possibility.

The proportion of the catalyst may be 30 parts by mass or more based on 100 parts by mass of the dibasic carboxylic acid anhydride, and can be selected from a range of about 50 to 1000 parts by mass, for example 50 to 500 parts by mass, preferably 80 to 100 parts by mass. The amount is 400 parts by weight, more preferably 100 to 300 parts by weight, and most preferably 150 to 200 parts by weight. If the proportion of the catalyst is too small, the modification rate of cellulose may decrease, and the effect of fibrillating cellulose may also decrease.

(solvent)
The solvent is not particularly limited as long as it does not impair the reactivity of the dibasic carboxylic anhydride and the fibrillation of cellulose, but it can promote the permeability of the dibasic carboxylic anhydride between microfibrils and is suitable for cellulose. A solvent containing an aprotic solvent having 25 or more donors is preferable because the reactivity toward hydroxyl groups can be adjusted appropriately. The donor number of such an aprotic solvent is, for example, 25 to 35, preferably 26 to 33, more preferably 28 to 33, and most preferably 29 to 31. If the number of donors is too low, there is a possibility that the effect of improving the permeability of the carboxylic acid anhydride between microfibrils will not be expressed. Regarding the number of donors, reference can be made to the document "Netsu Sokutei 28 (3) 135-143".

Examples of the aprotic solvent include alkyl sulfoxides, alkylamides, and pyrrolidones. These solvents can be used alone or in combination of two or more.

Examples of the alkyl sulfoxides include di-C _1-4 alkyl sulfoxides such as dimethyl sulfoxide (DMSO), methyl ethyl sulfoxide, and diethyl sulfoxide.

Examples of the alkylamides include N,N-diC _1-4 alkylformamides such as N,N-dimethylformamide (DMF) and N,N-diethylformamide; N,N-dimethylacetamide (DMAc), N, Examples include N,N-diC _1-4 alkyl acetamides such as N-diethylacetamide.

Examples of the pyrrolidones include pyrrolidones such as 2-pyrrolidone and 3-pyrrolidone; N-C _1-4 alkyl-pyrrolidones such as N-methyl-2-pyrrolidone (NMP).

These aprotic solvents can be used alone or in combination of two or more. Among these aprotic solvents (the number in parentheses is the number of donors), DMSO (29.8), DMF (26.6), DMAc (27.8), NMP (27.3), etc. are commonly used. .

Among these aprotic solvents, alkyl sulfoxides and/or alkyl acetamides (especially dicarbonate such as DMSO) can highly promote the permeability of dibasic carboxylic acid anhydrides between microfibrils. _1-2 alkyl sulfoxide) is preferred, DMSO is particularly preferred because it can improve the fibrillation effect of cellulose, and DMAc is particularly preferred because it can suppress discoloration. In particular, alkyl sulfoxides are preferred from the viewpoint of excellent chemical defibration properties, and di-C _1-2 alkyl sulfoxides such as DMSO are particularly preferred.

The solvent may contain, as other solvents, conventional solvents with a donor number of less than 25, such as methanol, acetonitrile, dioxane, acetone, dimethyl ether, tetrahydrofuran, etc., but is mainly an aprotic solvent with a donor number of 25 or more. Preferably, it is included as a solvent. The proportion of the aprotic solvent having 25 or more donors may be 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and 100% by mass (donors). (25 or more aprotic solvents alone) may be used. If there is too much solvent having a donor number of less than 25, the permeability of the reactive fibrillation liquid between cellulose microfibrils will decrease, and there is a possibility that the fibrillation rate of cellulose will decrease.

The proportion of the solvent may be 1 part by weight or more per 1 part by weight of cellulose, for example 1 to 1000 parts by weight, preferably 5 to 500 parts by weight, more preferably 10 to 100 parts by weight, most preferably 20 parts by weight. ~50 parts by mass. The mass ratio of catalyst (especially alkali metal hydrogen carbonate such as sodium hydrogen carbonate) and solvent (especially aprotic solvent such as alkyl sulfoxides and/or alkylamides) is catalyst/solvent = 100/0. ~0.1/99.9, for example, 50/50~0.5/99.5 from the viewpoint of improving the modification reaction rate and the permeation rate of the reactive defibration liquid between microfibrils. , preferably 20/80 to 2/98, more preferably 15/85 to 2.5/97.5, more preferably 10/90 to 3/97, most preferably 8/90 to 4/96. If the proportion of the solvent is too large, the modification rate of cellulose may decrease, and the effect of fibrillating cellulose may also decrease.

(Other esterifying agents)
In the modified defibration step, other esterifying agents may be used in addition to the dibasic carboxylic anhydride within a range that does not impair the effects of the present invention. Other esterifying agents include dibasic carboxylic acids (e.g., aliphatic dicarboxylic acids such as succinic acid, adipic acid, maleic acid, itaconic acid; 1-cyclohexene-1,2-dicarboxylic acid, hexahydrophthalic acid, methyl alicyclic dicarboxylic acids such as tetrahydrophthalic acid; aromatic dicarboxylic acids such as phthalic acid and naphthalic acid), monobasic carboxylic acids or their anhydrides [e.g. (anhydrous) acetic acid, (anhydrous) propionic acid, (anhydrous) (anhydrous) aliphatic monocarboxylic acid such as butyric acid, (anhydrous) isobutyric acid, (anhydrous) valeric acid, ethanoic acid propionic anhydride, (meth)acrylic acid (anhydrous), (anhydrous) crotonic acid, (anhydrous) oleic acid, etc. Acids; (anhydrous) alicyclic carboxylic acids such as (anhydrous) cyclohexanecarboxylic acid and (anhydrous) tetrahydrobenzoic acid; (anhydrous) aromatic monocarboxylic acids such as (anhydrous) benzoic acid and (anhydrous) 4-methylbenzoic acid; ], polybasic carboxylic acids [for example, (anhydrous) polycarboxylic acids such as trimellitic acid, trimellitic anhydride, and pyromellitic anhydride]. These esterifying agents can be used alone or in combination of two or more.

The proportion of other esterifying agents is 50 parts by weight or less, for example 0 to 30 parts by weight, preferably 0.01 to 10 parts by weight, more preferably 0.01 to 10 parts by weight, based on 100 parts by weight of the dibasic carboxylic anhydride. It is 1 to 5 parts by mass. If the proportion of other esterifying agents is too large, there is a possibility that the modification rate with the dibasic carboxylic anhydride may decrease or the fibrillating property may decrease.

(Reaction conditions)
In the modified fibrillation process, a reactive fibrillation liquid containing a catalyst containing a metal compound and a dibasic carboxylic acid anhydride is permeated into cellulose to cause an esterification reaction in the cellulose, thereby removing the hydroxyl groups on the surface of cellulose microfibrils. It is sufficient if the carboxyl group introduced into the cellulose forms a metal salt with the metal ion of the metal compound and the cellulose can be defibrated. Although such chemical defibration methods are not particularly limited, they are usually A method can be used in which a reactive fibrillation liquid containing a catalyst and a dibasic carboxylic acid anhydride (and a solvent if necessary) is prepared, and cellulose is added to and mixed with the prepared reactive fibrillation liquid.

The method for preparing the reactive fibrillation liquid is to mix the catalyst and dibasic carboxylic acid anhydride (with a solvent if necessary) in advance by stirring, etc., and mix the dibasic carboxylic acid anhydride in the catalyst (and solvent). It may be dissolved uniformly in

The obtained reactive defibration liquid has high permeability to cellulose. Therefore, by adding cellulose to the reactive defibration liquid and mixing it, the dibasic carboxylic acid anhydride and catalyst penetrate between the microfibrils and modify the hydroxyl groups present on the surface of the microfibrils. Cellulose modification and fibrillation can be performed simultaneously.

Specifically, the chemical defibration method may be a method in which cellulose is mixed with a reactive defibration liquid and left to stand for 2 hours or more to esterify, and after mixing, the cellulose is further maintained in a uniform state in the solution. Stirring and kneading to the extent possible (stirring and kneading to the extent that cellulose is not physically defibrated or crushed) may be performed. That is, in the method of the present invention, the permeability of the reactive fibrillation liquid is dramatically improved by the carboxyl groups modifying cellulose forming metal salts. Although cellulose can proceed simply by mixing and leaving it, in order to promote penetration or uniformity, stirring means that can stir the cellulose without crushing or defibrating it (such as in a low-concentration reactive defibrating solution) or Stirring and kneading may be performed using a kneading means (means using a high concentration reactive defibration liquid).

The stirring means is not a strong stirring that physically crushes or defibrates the cellulose, but a magnetic stirrer or stirring blade (for example, 10 to 2000 rpm, preferably 50 to 1500 rpm, more preferably 50 to 1500 rpm, more preferably Stirring at a rotational speed of 50 to 1000 rpm, particularly 50 to 500 rpm may be sufficient. Further, stirring may be performed continuously or intermittently.

On the other hand, the kneading means is not a strong kneading method of physically pulverizing or defibrating the cellulose, but a conventional kneading means (usually kneading means at room temperature), for example, from 10 to 2000 rpm, preferably from 20 to 1500 rpm, and The kneading may be carried out preferably at a rotational speed of about 30 to 1000 rpm, particularly about 50 to 500 rpm. Examples of conventional kneading methods include methods using mixing rollers, kneaders, Banbury mixers, extruders (such as single-screw or twin-screw extruders), and the like. The use of kneading means is advantageous in that the chemical defibration of cellulose and the subsequent step of promoting infiltration or uniformity can be carried out industrially and continuously.

In the present invention, the reaction temperature in chemical defibration does not need to be heated, and the reaction may be carried out at room temperature, but if the room temperature is lower than the melting point of the solvent, it is preferable to heat it to a temperature higher than the melting point of the solvent. By reacting at such a reaction temperature for 2 hours or more, cellulose can be chemically defibrated without using mechanical defibration means using shearing force. Therefore, in the present invention, cellulose can be defibrated without using extra energy. In order to promote the reaction, heating may be performed, and the heating temperature is, for example, 90° C. or lower (eg, about 40 to 90° C.), preferably 80° C. or lower, and more preferably about 70° C. or lower.

The reaction time can be selected depending on the type of dibasic carboxylic acid anhydride and catalyst, and the number of donors in the solvent, and is, for example, 3 to 72 hours, preferably 5 to 48 hours, more preferably 10 to 36 hours (especially 18 to 30 hours). time). If the reaction time is too short, the reactive fibrillation liquid may not sufficiently penetrate between the microfibrils, the reaction may become insufficient, and the degree of fibrillation may decrease. On the other hand, if the reaction time is too long, the yield of modified cellulose fine fibers may decrease.

Although the reaction may be carried out under an inert gas atmosphere (nitrogen, rare gas such as argon, etc.) or under reduced pressure, it is usually carried out in a closed reaction vessel in many cases. Such reaction conditions are preferable because moisture in the air is not sucked into the system.

After the reaction, the modified cellulose fine fibers obtained by chemical defibration are processed by a conventional method by adding a deactivating agent such as water to deactivate the dibasic carboxylic acid anhydride (esterifying agent). Separation and purification may be performed (for example, centrifugation, filtration, concentration, extraction, etc.). For example, a washing solvent capable of dissolving the deactivated esterifying agent, catalyst, and solvent is added to the reaction mixture, and the separation and purification (washing) is carried out by a separation method (commonly used) such as centrifugation, filtration, or extraction. Good too. Note that the separation operation can be performed multiple times (for example, about 2 to 5 times). Examples of the cleaning solvent include water, ketones such as acetone, and C _1-4 alkanols such as ethanol and isopropanol.

[Stirring process]
The obtained modified cellulose fine fibers have been chemically defibrated to nano-sized fibers, but some micron-sized fibers in which the fibers are loosely aggregated remain. Therefore, by stirring with a dispersion medium in the stirring step, nanofibers having a more uniform fiber diameter can be prepared.

The stirring method is not particularly limited as long as it can stir, and any conventional stirring method can be used, such as a stirrer with stirring blades (e.g., mixer, emulsifier, etc.), a grinder (e.g., mass colloider, etc.), and a high-pressure dispersion device. (For example, a method using starburst, etc.) can be used.

Among these, a preferred stirring method is a stirring method in which modified cellulose fine fibers are subjected to liquid-liquid shearing, since modified cellulose nanofibers with a uniform nanosize, less damage to the fiber shape, and a high aspect ratio can be obtained. Liquid-liquid shear differs from shear caused by external shear forces between the fluid and the contacting wall surface. Liquid-liquid shear generates a turbulent area and is caused by an internal shear force called Reynolds stress (the fluid itself) caused by irregular fluctuations in velocity. This is shearing that utilizes the intermolecular attraction of In the present invention, an emulsifying device that combines a screen (a conical body having a plurality of slit-like holes) and a rotor (stirring blades housed inside the screen) can be used as a stirrer for shearing liquid-liquid. . In this emulsification device, the modified cellulose fine fibers and the dispersion medium stirred by the rotor pass through a screen, thereby applying Reynolds stress to the modified cellulose fine fibers. As such an emulsifying device, a commercially available emulsifying device (for example, “Clearmix” manufactured by M Technique Co., Ltd.) can be used.

The rotational speed of stirring may be 2000 rpm or more, for example 2000 to 100000 rpm, preferably 3000 to 50000 rpm, more preferably 5000 to 30000 rpm, and most preferably 10000 to 25000 rpm. If the rotation speed is too low, there is a risk that the uniformity of the fiber diameter will decrease.

The stirring time can be appropriately selected depending on the rotation speed, and may be, for example, 30 seconds or more, for example, 30 seconds to 1 hour, preferably 1 to 30 minutes, and more preferably 2 to 10 minutes.

In the present invention, uniform nanofibers can be obtained without using external shearing force such as a media mill, colloid mill, roll mill, rotary type, or high-pressure homogenizer. Therefore, a stirring method that does not utilize external shearing force is preferred.

The dispersion medium may be water or an organic solvent. Examples of organic solvents include alcohols (C _1-4 alkanols such as methanol, ethanol, propanol, and isopropanol), ethers (cyclic ethers such as dioxane and tetrahydrofuran), ketones (acetone, etc.), and amides (such as dioxane and tetrahydrofuran). dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, etc.), sulfoxides (dimethylsulfoxide, etc.), alkanediols (e.g., C2-4 alkanediols such as ethylene glycol and propylene glycol), cellosolves (methyl cellosolve, ethyl cellosolve) , carbitols (such as ethyl carbitol), carbonates (cyclic carbonates such as ethylene carbonate and propylene carbonate; dimethyl carbonate, etc.). These dispersion media may be used alone or in combination of two or more. Note that the dispersion medium may be newly added in the stirring step, or the solvent used in the washing or the like in the modified defibration step may be used.

The higher the solubility parameter (SP value) of the dispersion medium, the more preferable it is, and the specific solubility parameter may be 10 or more, for example 10 to 30, preferably 12 to 28, more preferably 15 to 26, most preferably It is 20-25. If the solubility parameter is too low, the uniformity of fiber diameter may decrease. Note that the SP value in this specification and claims is Hildebrand's SP value.

Among these dispersion media, water and organic solvents with a solubility parameter of 10 or more (particularly C _1-4 alkanols) are preferred from the standpoint of improving the uniformity of fiber diameter. Further, the dispersion medium particularly preferably contains water, and may be water alone or a mixed solvent of water and a C _1-4 alkanol (such as ethanol).

The proportion of the dispersion medium is, for example, 10 to 1000 parts by mass, preferably 20 to 500 parts by mass, more preferably 30 to 300 parts by mass, and most preferably 50 to 200 parts by mass, per 1 part by mass of modified cellulose fine fibers. be. If the proportion of the dispersion medium is too small, it will be difficult to stir at high speed, and there is a risk that damage to the fibers will increase and the uniformity of the fiber diameter will decrease. On the other hand, if the proportion of the dispersion medium is too high, the efficiency may decrease and recovery of the modified cellulose nanofibers may become difficult.

[Modified cellulose nanofiber]
The modified cellulose nanofibers of the present invention are obtained through the above-mentioned stirring step, are modified with dibasic carboxylic acid anhydride, contain metal salts, are extremely fine nano-sized, and are dissolved into uniform fiber diameters. It is made of fiber. The average fiber diameter of the modified cellulose nanofibers may be 200 nm or less (preferably 150 nm or less, more preferably 120 nm or less, most preferably 100 nm or less), for example 1 to 200 nm, preferably 10 to 150 nm, more preferably 30 nm or less. ~120 nm, most preferably 50-100 nm. If the fiber diameter is too large, there is a risk that transparency, thixotropy, film formability, etc. in the state of a film or solution may be reduced, or the effect as a reinforcing material may be reduced. On the other hand, if the fiber diameter is too small, the handling properties and heat resistance of the fine fibers may also be reduced.

The modified cellulose nanofiber of the present invention has a carboxyl group modified with a dibasic carboxylic acid anhydride, and at least a part of this carboxyl group is in the form of a metal salt. The proportion of carboxyl groups in the form of metal salts may be 50 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more, based on the total carboxyl groups, Most preferably it is 100 mol%. If the proportion of the metal salt is too small, the fibrillation efficiency may decrease and it may be difficult to produce uniform nanofibers.

The modified cellulose nanofiber of the present invention has a uniform fiber diameter, and the number of fibers with a fiber diameter of 300 nm or more may be 10% or less (especially 5% or less) of the total number of fibers, and the number of fibers with a fiber diameter of 300 nm or more may be 10% or less (especially 5% or less), and Preferably, it contains substantially no (0%) fibers. Therefore, the maximum fiber diameter of the modified cellulose nanofiber of the present invention may be 500 nm or less (especially 300 nm or less), preferably 200 nm or less, and more preferably 100 nm or less. If the uniformity of the fiber diameter is too low, transparency, thixotropy, film formability, etc. may deteriorate, or a dense or uniform film may not be formed.

The modified cellulose nanofibers of the present invention are chemically defibrated into nano-sized fibers and then stirred without applying a strong external shearing force. The average fiber length may be 1 μm or more, for example, from a range of about 1 to 1000 μm, for example, 1 to 1000 μm, preferably 3 to 500 μm, and Preferably it is 5 to 200 μm. If the fiber length is too short, there is a risk that the reinforcing effect and film forming function will be reduced. Furthermore, if the length is too long, the fibers tend to become entangled, which may reduce the dispersibility in solvents and resins.

The ratio (aspect ratio) of the average fiber length to the average fiber diameter of the modified cellulose nanofibers can be adjusted depending on the application, and may be, for example, 10 or more, for example, 30 to 10,000, preferably 50 to 8,000, and more preferably 100. ~5000.

In this specification and claims, the average fiber diameter of the modified cellulose nanofibers is calculated by randomly selecting 50 fibers from SEM photographic images and averaging them, and the average fiber length is calculated by averaging The aspect ratio may be calculated by randomly selecting 50 fibers from the electron micrograph images and averaging them, and calculating the aspect ratio from the results.

In addition, each fiber or all of the modified cellulose nanofibers are evenly esterified and modified, so that they can be well dispersed in organic media such as organic solvents and resins. In order for the resin to effectively exhibit the properties of modified cellulose nanofibers (for example, low linear expansion properties, strength, heat resistance, etc.), highly crystalline modified cellulose nanofibers are preferred. The modified cellulose fine fibers of the present invention are chemically defibrated and can maintain the crystallinity of the raw material cellulose, so they have a high degree of crystallinity. The crystallinity of the modified cellulose nanofibers may be 50% or more (particularly 65% or more), for example 50-98%, preferably 65-95%, more preferably 70-92%, most preferably 75-98%. It is 90%. If the degree of crystallinity is too low, there is a risk that properties such as linear expansion properties and strength may be deteriorated.

In addition, in this specification and the claims, the crystallinity is measured by the XRD analysis method (Segal method) based on the reference literature: Textile Res. J. 29:786-794 (1959), and is calculated by the following formula. Calculated.

Crystallinity (%) = [(I ₂₀₀ - I _AM )/I ₂₀₀ ] x 100%
[In the formula, I ₂₀₀ is the diffraction intensity of the lattice plane (002 plane) (diffraction angle 2θ = 22.6°) in X-ray diffraction, I _AM is the amorphous part (lowest part between 002 plane and 110 plane, diffraction angle 2θ = 18.5°).

The average degree of substitution of the modified cellulose nanofibers depends on the diameter of the nanofibers and the type of esterifying agent, but is 2.0 or less (for example, 0.05 to 2.0), for example, 0.1 to 1.5, preferably is from 0.15 to 1.0, more preferably from 0.2 to 0.7, most preferably from 0.3 to 0.5. If the average degree of substitution is too large, the crystallinity or yield of the modified cellulose nanofibers may decrease. The average degree of substitution (DS) is the average number of substituted hydroxyl groups per glucose, which is the basic structural unit of cellulose, and is described in Biomacromolecules 2007, 8, 1973-1978, WO2012/124652A1 or WO2014/142166A1, etc. You can refer to it. Note that in this specification and claims, the average degree of substitution can be measured by the method described in Examples below, and is preferably measured by titration.

The present invention will be explained in more detail below based on Examples, but the present invention is not limited by these Examples. The details of the raw materials used are as follows, and the properties and evaluation of the obtained modified cellulose nanofibers were measured as follows.

(cellulose pulp)
As the cellulose pulp used as a raw material, eucalyptus-derived pulp (L-BKP) was cut into pieces to a size that could be placed in a sample bottle. Moreover, a SEM photograph of this pulp is shown in FIG. The average fiber diameter of the pulp was about 10 μm.

(other raw materials, catalysts and solvents)
As other raw materials, catalysts, and solvents, reagents manufactured by Nacalai Tesque Co., Ltd. were used.

(Observation of shape of modified cellulose nanofibers)
The shape of the modified cellulose nanofibers was observed using a scanning electron microscope SEM (JSM-6510 manufactured by JEOL Ltd., measurement conditions: 20 mA, 60 seconds). Note that the average fiber diameter and average fiber length were calculated by randomly selecting 50 fibers from the SEM photograph and averaging them.

(Average degree of substitution of modified cellulose nanofibers)
The modification rate of the modified cellulose nanofibers was expressed as an average degree of substitution, and was measured by the titration method (electrical conductivity titration method) shown below. Note that the average degree of substitution is the average value of the number of modified hydroxyl groups (number of substituents) per repeating unit of cellulose.

Prepare 60ml of 0.5% by mass slurry of modified cellulose nanofibers, add 0.1M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then dropwise add 0.05N sodium hydroxide aqueous solution to conduct electricity until the pH reaches 11. The degree of From the amount (a) of the aqueous sodium hydroxide solution consumed in the neutralization step of the weak acid where the electrical conductivity changes slowly, the number of moles Q of the substituents introduced by chemical modification is determined by the following formula.

Q (mol) = a [ml] x 0.05/1000

The relationship between the number of moles Q of this substituent and the average degree of substitution D is calculated by the following formula [cellulose = (glucose C ₆ O ₅ H ₁₀ ) _n = (162.14) _n , 1 repeating unit Number of hydroxyl groups per unit = 3, molecular weight of OH = 17].

D=162.14×Q/[sample amount-(T-17)×Q]
(where T is the molecular weight of the dibasic carboxylic acid anhydride that is the precursor of the esterification substituent).

Furthermore, when some of the samples were analyzed using a Fourier transform infrared spectrophotometer (FT-IR), an absorption band of ester bond at 1730 cm ^-1 was detected in all samples. Note that the measurement was performed using "Nicolet iS5" manufactured by Thermo Fisher Scientific, and analyzed by the ATR method (total reflection method).

Example 1
3.3 g of succinic anhydride and 5.6 g of sodium hydrogen carbonate were added to a beaker containing 90 g of dimethyl sulfoxide and dissolved with stirring. Next, after adding 3.0 g of cellulose pulp, the mixture was stirred with a stirrer (rotation speed: 400 rpm) at room temperature adjusted to 23° C. for 24 hours to obtain a dispersion containing cellulose fine fibers modified with succinic acid. This dispersion was centrifuged for 30 minutes to remove the supernatant solution, and then 400 mL of distilled water was added and washed three times by centrifugation to remove remaining dimethyl sulfoxide, succinic acid, and hydrogen carbonate. Sodium was removed. Distilled water was added to the defibrated solution after washing to adjust the total volume to 700 mL, and then the defibration solution was adjusted to a total volume of 700 mL, and then it was processed using an emulsifier ("Clearmix CLM-0.8S" manufactured by M Technique Co., Ltd.) at 15,000 rpm for 3 minutes. A defibration treatment was performed. The appearance of the obtained dispersion was transparent. The SEM image is shown in Figure 2. As is clear from FIG. 2, in the obtained modified cellulose nanofibers, almost no thick fibers exceeding 300 nm were observed, and the fibers were well defibrated. The average degree of substitution of the obtained modified cellulose nanofibers was 0.39, the average fiber diameter was 80 nm, and the average fiber length was 5 μm or more.

Example 2
The defibration operation was carried out in the same manner as in Example 1 except that the amount of sodium hydrogen carbonate used was 2.8 g. The appearance of the obtained dispersion was transparent. The SEM image is shown in Figure 3. The average degree of substitution of the obtained modified cellulose nanofibers was 0.47, the average fiber diameter was 100 nm, and the average fiber length was 5 μm or more as determined from the SEM image. For the same reason as in Example 1, the actual average fiber diameter is considered to be smaller than the average fiber diameter obtained from the SEM image.

Example 3
The defibration operation was carried out in the same manner as in Example 1 except that the amount of succinic anhydride used was 2.8 g. The appearance of the obtained dispersion was transparent. The SEM image is shown in Figure 4. The average degree of substitution of the obtained modified cellulose nanofibers was 0.29, the average fiber diameter was 90 nm, and the average fiber length was 5 μm or more as determined from the SEM image. For the same reason as in Example 1, the actual average fiber diameter is considered to be smaller than the average fiber diameter obtained from the SEM image.

Example 4
The defibration operation was carried out in the same manner as in Example 1 except that 3.3 g of maleic anhydride was used instead of succinic anhydride. The appearance of the resulting dispersion was almost transparent. Although some fibers that were slightly thicker than those of succinic anhydride remained, most of them were well defibrated to a fiber diameter of 100 nm or less. The SEM image is shown in FIG. The average degree of substitution of the obtained modified cellulose nanofibers was 0.18, the average fiber diameter was 90 nm, and the average fiber length was 5 μm or more as determined from the SEM image. For the same reason as in Example 1, the actual average fiber diameter is considered to be smaller than the average fiber diameter obtained from the SEM image.

Example 5
The defibration operation was carried out in the same manner as in Example 1 except that 5.6 g of potassium carbonate was used instead of sodium hydrogen carbonate. The appearance of the resulting dispersion was almost transparent. Although some fibers that were slightly thicker than those of sodium hydrogen carbonate remained, most of them were well defibrated to fiber diameters of 100 nm or less. The SEM image is shown in FIG. The average degree of substitution of the obtained modified cellulose nanofibers was 0.25, the average fiber diameter was 80 nm, and the average fiber length was 5 μm or more as determined from the SEM image. For the same reason as in Example 1, the actual average fiber diameter is considered to be smaller than the average fiber diameter obtained from the SEM image.

Example 6
The defibration operation was carried out in the same manner as in Example 1 except that 5.6 g of lithium acetate was used instead of sodium hydrogen carbonate. The appearance of the resulting dispersion was almost transparent. Although some fibers that were slightly thicker than those of sodium hydrogen carbonate remained, most of them were well defibrated to fiber diameters of 100 nm or less. The SEM image is shown in FIG. The average degree of substitution of the obtained modified cellulose nanofibers was 0.41, the average fiber diameter was 90 nm, and the average fiber length was 5 μm or more as determined from the SEM image. For the same reason as in Example 1, the actual average fiber diameter is considered to be smaller than the average fiber diameter obtained from the SEM image.

Example 7
The defibration operation was carried out in the same manner as in Example 1 except that 90 g of dimethyl formamide was used instead of dimethyl sulfoxide. The appearance of the resulting dispersion was almost transparent. Although some fibers that were slightly thicker than dimethyl sulfoxide remained, most of them were well defibrated to a fiber diameter of 100 nm or less. The SEM image is shown in FIG. The average degree of substitution of the obtained modified cellulose nanofibers was 0.20, the average fiber diameter was 70 nm, and the average fiber length was 5 μm or more as determined from the SEM image. For the same reason as in Example 1, the actual average fiber diameter is considered to be smaller than the average fiber diameter obtained from the SEM image.

Comparative example 1
The defibration operation was carried out in the same manner as in Example 1 except that succinic anhydride was not added. In the obtained liquid, some portions of the fiber surface were found to have become nanofibers, but the cellulose remained as a raw material with a size of approximately several μm. The SEM image is shown in FIG.

Comparative example 2
The defibration operation was carried out in the same manner as in Example 1 except that sodium hydrogen carbonate was not added. In the obtained liquid, some portions of the fiber surface were found to have become nanofibers, but the cellulose remained as a raw material with a size of approximately several μm. The SEM image is shown in FIG.

The modified cellulose nanofibers of the present invention can be used in various composite materials and coating agents, and can also be used by being formed into sheets and films.

Claims (11)

Cellulose is esterified and chemically defibrated by infiltrating cellulose with a reactive defibration liquid containing a catalyst made of a weakly basic metal compound and a dibasic carboxylic anhydride, and then the cellulose is esterified and chemically defibrated. Modified fibrillation step to obtain modified cellulose fine fibers formed from cellulose that is modified and contains a metal salt form, and a dispersion medium is added to the obtained modified cellulose fine fibers and stirred to obtain modified cellulose nanofibers. A method for producing modified cellulose nanofibers, comprising a stirring step. 2. The manufacturing method according to claim 1, wherein the weakly basic metal compound is an alkali metal compound. 3. The method according to claim 1, wherein the weakly basic metal compound is an alkali metal hydrogen carbonate. The manufacturing method according to any one of claims 1 to 3 , wherein the reactive fibrillation liquid further contains an aprotic solvent having 25 or more donors. 5. The production method according to claim 4 , wherein the aprotic solvent having 25 or more donors is at least one selected from the group consisting of alkyl sulfoxides, alkylamides, and pyrrolidones. 5. The production method according to claim 4, wherein the aprotic solvent having 25 or more donors is di-C _1-2 alkyl sulfoxide. Any one of claims 1 to 6 , wherein the dibasic carboxylic anhydride is at least one selected from the group consisting of aliphatic dicarboxylic anhydrides, alicyclic dicarboxylic anhydrides, and aromatic dicarboxylic anhydrides. The manufacturing method described in section. 8. The production method according to claim 1, wherein the dibasic carboxylic anhydride is a saturated aliphatic dicarboxylic anhydride having 4 to 6 carbon atoms. The production method according to any one of claims 1 to 8 , wherein the proportion of the catalyst is 100 parts by mass or more based on 100 parts by mass of the dibasic carboxylic acid anhydride. The production method according to any one of claims 1 to 9 , wherein the proportion of dibasic carboxylic acid anhydride is 60 parts by mass or more based on 100 parts by mass of cellulose. The manufacturing method according to any one of claims 1 to 10 , wherein in the stirring step, the modified cellulose fine fibers are subjected to liquid-liquid shearing.