JP7015201B2 - Modified chitin nanofibers and their manufacturing methods - Google Patents

Description

The present invention relates to modified chitin-based nanofibers that can be used as a transparent film raw material, a medical material, a cosmetic raw material, a resin strengthening agent, and the like, and a method for producing the same.

Chitin is a polysaccharide in which acetylglucosamine is linearly linked, and is the main component of the cell wall of fungi including crabs, shrimp, insect hulls, and basidiomycetes (mushrooms). , Has characteristics such as biocompatibility. Therefore, nanofibers obtained by defibrating chitin are expected to be used for transparent film raw materials, medical materials, cosmetic raw materials, resin strengthening agents, etc., and a simple method for producing chitin nanofibers is required. There is.

Japanese Patent Application Laid-Open No. 2003-155349 (Patent Document 1) applies a shearing force to a swelling medium such as methanol or ethanol by applying a shearing force to a swelling medium such as chitin / chitosan fiber at a sample concentration of 1 to 5%. Ultrafine fibers are manufactured by defibrating. In the examples, as natural organic fibers, cellulosic natural fibers, chitosan, collagen fibers, and recycled products are ultrafine.

However, with this method, hydrogen bonds between fibers cannot be sufficiently broken, and uniform nanofibers cannot be produced.

Japanese Patent No. 5186694 (Patent Document 2) describes a step of subjecting a chitin-containing material derived from shellfish to at least one deproteinization step and at least one decalcification step, and then treating the chitin-containing material with an acidic reagent. Then, a method for producing chitin nanofibers to be subjected to the defibration step is disclosed. This document describes that the defibration step is defibrated using a millstone grinder and / or a high pressure homogenizer.

However, this method requires strong mechanical processing to produce nanofibers.

JP-A-2003-155349 (Claim 1, Example) Japanese Patent No. 5186694 (Claims 1 and 3)

Therefore, an object of the present invention is to provide a modified chitin-based nanofiber having a uniform nanosize, less damage to the fiber shape, and a large aspect ratio, and a method for producing the same, which can be easily and efficiently produced.

Another object of the present invention is to provide modified chitin-based nanofibers which can be produced by an energy-saving method without strong mechanical shearing and a method for producing the same.

Still another object of the present invention is to provide a modified chitin-based nanofiber having excellent dispersibility in an organic solvent and a method for producing the same.

As a result of diligent studies to achieve the above-mentioned problems, the present inventors infiltrate the chitins with a reactive defibrating solution containing a base or an acid catalyst and a carboxylic acid anhydride, and esterify the chitins to chemically solve them. The present invention has been completed by finding that it is possible to easily and efficiently produce a specific modified chitin-based fine fiber, that is, a chitin-based nanofiber having a uniform nanosize, less damage to the fiber shape, and a large aspect ratio.

That is, in the method for producing modified chitin-based nanofibers of the present invention, a reactive defibrating solution containing a catalyst containing a base catalyst or an acid catalyst and a carboxylic acid anhydride is permeated into the chitins to esterify the chitins. It includes a modified defibration step of chemically defibrating to obtain modified chitin-based fine fibers, and a stirring step of adding a dispersion medium to the obtained modified chitin-based fine fibers and stirring to obtain modified chitin-based nanofibers. The reactive defibrating solution further comprises at least one selected from the group consisting of aprotic solvents having 25 or more donors, for example, alkyl sulfoxides, alkyl amides and pyrrolidones (particularly, di-C _1-2 alkyl). It may contain sulfoxide). The carboxylic acid anhydride is at least one selected from the group consisting of dibasic carboxylic acid anhydrides, for example, aliphatic dicarboxylic acid anhydrides, alicyclic dicarboxylic acid anhydrides and aromatic dicarboxylic acid anhydrides (particularly,). It may be a saturated aliphatic dicarboxylic acid anhydride having 4 to 6 carbon atoms). The catalyst may be an alkali metal bicarbonate. The ratio of the catalyst may be 100 parts by weight or more with respect to 100 parts by weight of the carboxylic acid anhydride. The ratio of the carboxylic acid anhydride may be 60 parts by weight or more with respect to 100 parts by weight of the chitins. In the stirring step, the modified chitin-based finely divided fiber may be liquid-liquid sheared.

The present invention also includes modified chitin-based nanofibers modified with alkanedioic anhydride, having an average fiber diameter of 100 nm or less and an average fiber length of 1 μm or more.

In the present invention, a reactive defibrating solution containing a base or acid catalyst and a carboxylic acid anhydride is permeated into chitins to esterify the chitins for chemical defibration. Can be defibrated without destroying. In particular, in the present invention, chitins can be swelled with the permeation of the reactive defibrating solution, and the defibration efficiency of chitins can be improved without strong mechanical shearing. Therefore, modified chitin-based fine fibers having a nano-sized size, less damage to the fiber shape, a large aspect ratio, and excellent dispersibility in an organic solvent can be easily and efficiently produced by an energy-saving method.

FIG. 1 is a scanning electron microscope (SEM) photograph (5000x) of the modified chitin nanofibers obtained in Example 1. FIG. 2 is a graph showing the measurement results of FT-IR of the modified chitin nanofibers obtained in Example 1. FIG. 3 is an SEM photograph (5000 times) of the modified chitin nanofiber obtained in Example 2. FIG. 4 is an SEM photograph (5000 times) of the modified chitin nanofiber obtained in Example 3. FIG. 5 is an SEM photograph (5000 times) of the modified chitin nanofiber obtained in Example 4. FIG. 6 is an SEM photograph (5000 times) of the modified chitin nanofiber obtained in Example 5. FIG. 7 is an SEM photograph (5000 times) of the modified chitin nanofiber obtained in Example 6. FIG. 8 is an SEM photograph (1000 times) of the chitin fiber obtained in Comparative Example 1. FIG. 9 is an SEM photograph (5000 times) of the chitin fiber obtained in Comparative Example 2.

[Modified defibration process]
In the method for producing modified chitin-based nanofibers of the present invention, a reactive defibrating solution (reactive defibrating solution or mixed solution) containing a catalyst containing a base catalyst or an acid catalyst and a carboxylic acid anhydride is impregnated into chitins. It includes a modified defibration step of esterifying chitins and chemically defibrating them to obtain modified chitin-based fine fibers. In the present invention, the reason why chitins are modified and defibrated at the same time by this step can be presumed as follows. That is, the reactive defibrating solution containing the catalyst and the carboxylic acid anhydride (particularly, further an aprotic solvent) is a solution having low solubility in chitins, and this solution permeates between the microfibrils of the chitins. It swells the chitin-based fibers and modifies the hydroxyl groups on the surface of the microfibrils. Furthermore, this modification breaks the hydrogen bonds between the microfibrils, and the microfibrils are easily separated from each other and defibrated. Further, since the solution does not penetrate into the crystal zone (domain) of the microfibril, the obtained modified chitin-based fine fiber has less damage and has a structure similar to that of a natural microfibril. At the same time, in this step, chitins can be defibrated without using mechanical defibration means by the action of a strong shearing force, so that there is little damage due to physical action. Therefore, it can be estimated that the obtained modified chitin-based fine fibers retain high strength.

(Chitins)
The raw materials for chitin are crustaceans such as crabs and shrimp, shells of natural organisms such as krill and insects, and chitin (β-1,4-poly-N-acetyl-D-glucosamine) derived from the outer skin or derivatives thereof. be. In the present specification and the scope of patent claims, a chitin derivative is a derivative of chitin, such as a part of N-acetyl group being deacetylated or a part of hydroxyl group being an alkyl group or an acyl group as long as the characteristics of chitin are not impaired. Means a derivative substituted with.

The crystal structure of chitin is not particularly limited and may be any of α-type, β-type and γ-type, but α-type is preferable because it has abundant resources and can improve strength.

The degree of N-acetylation of chitin (the ratio of N-acetylated glucosamine units to the total glucosamine units) is not particularly limited and is usually about 90% or more (for example, 90 to 100%), but defibration. From the viewpoint of excellent properties, a higher value is preferable, and purification of 100% acetylated chitin is difficult, for example, 91 to 99.9%, preferably 92 to 99%, and more preferably 93 to 98%. ..

Within the present specification and claims, the degree of N-acetylation of chitins can be calculated based on the nitrogen content, and can also be measured by an infrared absorption spectrum, an NMR spectrum, or the like.

The average degree of polymerization (viscosity average degree of polymerization) of chitins is, for example, 100 to 100,000, preferably 500 to 50,000, and more preferably 1,000 to 30,000 (particularly 2000 to 20,000).

The shape of the chitins used as a raw material is not particularly limited, and is usually granular or fibrous. The average particle size of chitins (in the case of an anisotropic shape such as a fiber shape, the average value of the major axis and the minor axis is calculated as the particle size) is usually 0.1 μm or more, for example, 1 to 5000 μm, preferably 3 to 3. It may be about 1000 μm, more preferably about 5 to 100 μm (particularly 10 to 50 μm). In the present specification and claims, the average particle size of the raw material chitins may be calculated by randomly selecting 50 fibers from the image of the SEM photograph and adding and averaging them.

The weight ratio of the chitins and the reactive defibrating solution can be selected from the range of the former / the 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 10/90 (particularly 2/98 to 5/95). If the proportion of chitins is too small, the production amount of modified chitin-based fine fibers will be low, and if it is too large, the reaction time will be long, and in any case, the productivity may decrease. Furthermore, if the proportion of chitins is too large, the size of the obtained fine fibers and the uniformity of the modification rate may decrease.

(Carboxylic acid anhydride)
The carboxylic acid anhydride (esterifying agent) includes a monobasic carboxylic acid (monocarboxylic acid) anhydride, a dibasic carboxylic acid (dicarboxylic acid) anhydride, and a polybasic carboxylic acid anhydride.

Examples of the monobasic carboxylic acid anhydride include anhydrous saturated aliphatic monocarboxylic acids such as anhydrous acetic acid, anhydrous propionic acid, anhydrous butyric acid, anhydrous isobutyric acid, anhydrous valeric acid, and ethanoic acid propionic anhydride; anhydrous (meth) acrylic. Anhydrous unsaturated aliphatic monocarboxylic acid such as acid and crotonic anhydride; Anhydrous alicyclic monocarboxylic acid such as cyclohexanecarboxylic acid anhydride and tetrahydrobenzoic acid anhydride; Anhydrous aromatic acid such as benzoic acid anhydride and 4-methylbenzoic acid anhydride. Examples include monocarboxylic acid.

Examples of the dibasic carboxylic acid anhydride include anhydrous saturated aliphatic dicarboxylic acid such as succinic anhydride; anhydrous unsaturated aliphatic dicarboxylic acid such as maleic anhydride and itaconic anhydride; 1-cyclohexene-1,2-dicarboxylic acid. Anhydrous alicyclic dicarboxylic acids such as anhydrous, hexahydroanhydride phthalic acid and methyltetrahydrohydride phthalic acid; anhydrous aromatic dicarboxylic acids such as phthalic acid anhydride and naphthalic acid anhydride can be mentioned.

Examples of the polybasic carboxylic acid anhydride include anhydrous polycarboxylic acids such as trimellitic anhydride and pyromellitic anhydride.

These carboxylic acid anhydrides can be used alone or in combination of two or more. Of these carboxylic acid anhydrides, at least one selected from the group consisting of aliphatic dicarboxylic acid anhydrides, alicyclic dicarboxylic acid anhydrides and aromatic dicarboxylic acid anhydrides from the viewpoint of modifying property and defibration. The dibasic carboxylic acid anhydride of is preferable, a saturated or unsaturated aliphatic dicarboxylic acid anhydride having 4 to 8 carbon atoms is more preferable, and a saturated aliphatic dicarboxylic acid anhydride (alkane) having 4 to 6 carbon atoms such as succinic anhydride is preferable. Diacid anhydride) is most preferable. If the number of carbon atoms is too large, the permeability between microfibrils and the reactivity of chitins with hydroxyl groups may decrease.

The concentration (weight ratio) of the carboxylic acid anhydride in the reactive defibrating solution is 1 to 50% by weight (for example, 1.) from the viewpoint of excellent balance between the permeability between microfibrils and the reactivity of chitins with hydroxyl groups. It can be selected from the range of about 5 to 40% by weight), and is, for example, 2 to 30% by weight, preferably 2.5 to 10% by weight, and more preferably about 3 to 5% by weight.

The ratio of chitins and carboxylic acid anhydrides is converted into a glucosamine unit (N-acetyl-D-glucosamine unit) of chitins because it has an excellent balance between permeability between microfibrils and reactivity of chitins with hydroxyl groups. The molar ratio of the former / the latter can be selected from the range of about 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. It is about / 5. The weight ratio of the two is, for example, chitin / carboxylic acid anhydride = 70/30 to 5/95, preferably 60/40 to 10/90, and more preferably about 50/50 to 30/70. From the viewpoint of chemical defibration, the ratio of the carboxylic acid anhydride may be 20 parts by weight or more (for example, 20 to 500 parts by weight) with respect to 100 parts by weight of the chitins, for example, 50 to 300 parts by weight, preferably 50 parts by weight. May be about 80 to 200 parts by weight, more preferably 90 to 150 parts by weight (particularly 100 to 130 parts by weight).

(catalyst)
In the present invention, a catalyst is used in addition to the carboxylic acid anhydride to promote the esterification of chitins. The catalyst includes a base catalyst and an acid catalyst (protonic acid, Lewis acid, etc.).

Examples of the base catalyst include tertiary amines (eg, tri-C _1-4 alkylamines such as trimethylamine and triethylamine), heterocyclic amines (4-dimethylaminopyridine, morpholin, piperidine, etc.), and fourth. Secondary ammonium salts (eg, tetraalkylammonium halides such as tetraethylammonium chloride, tetraethylammonium bromide; benzyltrialkylammonium halides such as benzyltrimethylammonium chloride, etc.), alkali metal compounds (eg, sodium hydroxide, potassium hydroxide, etc.) Alkaline metal hydroxides; Alkaline metal carbonates such as sodium carbonate and potassium carbonate; Alkaline metal hydrogen carbonates such as sodium hydrogen carbonate and potassium hydrogen carbonate; Alkaline metal hydrides such as sodium hydride and potassium hydride; Sodium acetate, Alkali metal carboxylates such as potassium acetate, sodium propionate, potassium propionate, sodium butyrate; alkali metal borates such as sodium metaborate, sodium tetraborate (hosand); alkali phosphates such as trisodium phosphate Metal salts; Alkaline metal hydrogen phosphates such as sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate; sodium methoxyd, potassium methoxyd, sodium ethoxydo, potassium ethoxydo, sodium t-butoxide, Alkaline metal alkoxides such as potassium t-butoxide), alkaline earth metal compounds (eg, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide; alkaline earth metal carbonates such as magnesium carbonate; hydrogen carbonate Alkaline earth metal hydrogen carbonates such as magnesium; carboxylic acid alkaline earth metal salts such as calcium acetate; alkaline earth metal alkoxides such as calcium t-butoxide) and the like. These base catalysts can be used alone or in combination of two or more.

Examples of the acid catalyst include inorganic acids [eg, sulfuric acid, hydrogen chloride (or hydrochloric acid), nitrate, phosphoric acid, etc.] and organic acids [eg, sulfonic acids (methane sulfonic acid, ethane sulfonic acid, trifluoromethane sulfonic acid, etc.). Alcan sulfonic acid, benzene sulfonic acid, p-toluene sulfonic acid, allene sulfonic acid such as naphthalene sulfonic acid), etc.] can be mentioned. These acid catalysts can be used alone or in combination of two or more.

Of these catalysts, a base catalyst is preferable, and a weakly basic base catalyst (particularly, a weak base) is preferable because it can promote not only the catalytic action in the esterification reaction but also the permeability of the carboxylic acid anhydride between microfibrils. Sexual salt) is particularly preferred. Even if it is a base catalyst, if it is strongly basic, the reaction on the surface of chitins may proceed before the esterifying agent permeates between the microfibrils, and the defibration property may decrease. The weakly basic base catalyst has a pH of 7.3 to 10, preferably 7.5 to 9.5, and more preferably 7.8 to 9 (particularly 8 to 8.5) in a 1 mol / liter aqueous solution. May be.

As such a weakly basic base catalyst, an alkali metal carbonate such as sodium carbonate; an alkali metal hydrogen carbonate such as sodium hydrogen carbonate; a carboxylate alkali metal salt such as sodium acetate; sodium tetraborate (hosago). Alkaline metal borates such as; Alkali metal phosphates such as trisodium phosphate; Alkaline metal phosphates such as sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate; magnesium carbonate, etc. Alkaline earth metal carbonates; alkaline earth metal hydrogen carbonates such as magnesium hydrogen carbonate; alkaline earth metal carboxylates such as calcium acetate, and the like. These base catalysts can be used alone or in combination of two or more. Of these, alkali metal bicarbonates such as sodium hydrogencarbonate, alkali metal C _1-4 alcan-monocarboxylates such as sodium acetate are preferred, and alkali metal bicarbonates are particularly preferred.

The ratio of the catalyst may be 0.5 to 50% by weight, preferably 1 to 30% by weight, preferably 2 to 20% by weight, and more preferably 3 to 15% by weight (more preferably 3 to 15% by weight) with respect to the entire reactive defibrating solution. In particular, it is about 5 to 10% by weight). If the proportion of the catalyst is too small, the modification rate of chitins may decrease, and the action of defibrating chitins may also decrease. On the other hand, if the proportion of the catalyst is too large, the modification rate is too high and the chitins may be decomposed, and the permeability of the reactive defibrating solution to the chitins is lowered, so that the chitins are defibrated. May also decrease.

The ratio of the catalyst may be 50 parts by weight or more with respect to 100 parts by weight of the carboxylic acid anhydride, and can be selected from the range of, for example, about 50 to 1000 parts by weight, for example, 50 to 500 parts by weight, preferably 80 to 400 parts by weight. Parts, more preferably about 100 to 300 parts by weight (particularly about 150 to 200 parts by weight). From the viewpoint of chemical defibration, the ratio of the catalyst may be 10 parts by weight or more with respect to 100 parts by weight of the carboxylic acid anhydride, for example, 10 to 500 parts by weight, preferably 50 to 400 parts by weight (for example, 100 parts by weight). It may be about 350 parts by weight), more preferably about 130 to 300 parts by weight (particularly about 150 to 250 parts by weight). If the proportion of the catalyst is too small, the modification rate of chitins may decrease, and the action of defibrating chitins may also decrease.

(solvent)
The solvent is not particularly limited as long as it is a solvent that does not impair the reactivity of the carboxylic acid anhydride and the defibration of the chitins, but can promote the permeability of the carboxylic acid anhydride between the microfibrils and the hydroxyl group of the chitins. A solvent containing an aprotic solvent having 25 or more donors is preferable because the reactivity with respect to the solvent can be appropriately adjusted. The number of donors of such an aprotic solvent is, for example, 25 to 35, preferably 26 to 33, and more preferably about 28 to 30. If the number of donors is too low, the effect of improving the permeability of the carboxylic acid anhydride between microfibrils may not be exhibited. For the number of donors, refer to the document "Netsu Sokutei 28 (3) 135-143".

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

Examples of the alkyl sulfoxides include diC _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 thereof include N, N-diC _1-4 alkylacetamide such as N-diethylacetamide.

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

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

Of these, among the aprotic solvents, alkylsulfoxides and / or alkylacetamides (particularly, diC _1- such as DMSO) are capable of highly promoting the permeability of carboxylic acid anhydrides between microfibrils. ₂ Alkyl sulfoxide) is preferable, DMSO is particularly preferable because it can improve the defibrating effect of chitins, and DMAc is particularly preferable because it can suppress discoloration. In particular, alkyl sulfoxides are preferable from the viewpoint of excellent chemical defibration, and diC _1-2 alkyl sulfoxide such as DMSO is particularly preferable.

The solvent may contain, as another solvent, a conventional solvent having less than 25 donors, for example, methanol, acetonitrile, dioxane, acetone, dimethyl ether, tetrahydrofuran and the like, but mainly an aprotic solvent having 25 or more donors. It is preferably contained as a solvent. The proportion of the aprotic solvent having 25 or more donors may be 50% by weight or more, preferably 80% by weight, more preferably 90% by weight or more, and 100% by weight (number of donors) with respect to the total solvent. It may be 25 or more aprotic solvents alone). If there are too many solvents with less than 25 donors, the permeability of the reactive defibrating solution between the microfibrils of the chitins will decrease, and the defibration rate of the chitins may decrease.

The weight ratio of the catalyst (particularly alkali metal bicarbonate such as sodium hydrogen carbonate) to the solvent (particularly an aprotic solvent such as alkylsulfoxides and / or alkylamides) is the former / latter = 100/0 to 0. It can be selected from a range of about 1 / 99.9, and from the viewpoint of improving the modification reaction rate and the permeation rate of the reactive defibrated solution between microfibrils, for example, 50/50 to 1/99, preferably 30/70 to It is about 2/98, more preferably 20/80 to 3/97 (particularly 10/90 to 4/96). If the proportion of the solvent is too large, the modification rate and defibration rate of chitins may decrease, and the action of defibrating chitins may also decrease.

(Other esterifying agents)
In the modified defibration step, another esterifying agent may be used as long as the effect of the present invention is not impaired. Examples of other esterifying agents include carboxylic acids corresponding to the carboxylic acid anhydride (for example, aliphatic dicarboxylic acids such as succinic acid) and the like. Other esterifying agents can be used alone or in combination of two or more. The ratio of the other esterifying agent is 50 parts by weight or less with respect to 100 parts by weight of the carboxylic acid anhydride, for example, 0 to 30 parts by weight, preferably 0.01 to 10 parts by weight, and more preferably 0.1 to 10 parts by weight. It is about 5 parts by weight. If the proportion of the other esterifying agent is too large, the modification rate may decrease or the reactivity of the obtained modified chitin-based fine fibers may decrease.

(Reaction condition)
In the modified defibration step, a reactive defibrating solution containing a catalyst containing a base catalyst or an acid catalyst and a carboxylic acid anhydride is permeated into the chitins, and the chitins are subjected to an esterification reaction to form microfibrils of the chitins. It suffices if the hydroxyl group on the surface can be esterified and modified, and the chitins can be defibrated. Such a chemical defibration method is not particularly limited, but usually a catalyst and a carboxylic acid anhydride (and a solvent if necessary) are used. A method can be used in which a reactive defibrating solution containing the mixture is prepared, and chitins are added to the prepared reactive defibrating solution and mixed.

The method for preparing the reactive defibrating solution is to mix the catalyst, the carboxylic acid anhydride (with a solvent if necessary) in advance by stirring, or the like, and uniformly dissolve the carboxylic acid anhydride in the catalyst (and the solvent). May be good.

Since the obtained reactive defibrating solution has high permeability to chitins, the carboxylic acid anhydride and the catalyst penetrate between the microfibrils by adding the chitins to the reactive defibrating solution and mixing them. Therefore, by modifying the hydroxyl group existing on the surface of the microfibril, the modification of chitins and the defibration can be performed at the same time.

Specifically, the chemical defibration method may be a method in which chitins are mixed with a reactive defibrating solution and left for 2 hours or more for esterification, and after mixing, the chitins are further in a uniform state in the solution. You may perform stirring and kneading to the extent that the above can be maintained (stirring and kneading to the extent that the chitins are not physically defibrated or crushed). That is, the reaction proceeds even if the chitins are mixed with the reactive defibrating solution and left to stand, but in order to promote permeation or uniformity, the stirring means capable of stirring without crushing or defibrating the chitins. Stirring or kneading may be performed using (means for a low-concentration reactive defibrating solution) or kneading means (means for a high-concentration reactive defibrating solution).

The stirring means is not a strong stirring that physically grinds or defibrates chitins, but is usually a magnetic stirrer or a stirring blade (for example, 10 to 2000 rpm, preferably 50 to 1500 rpm, more preferably 50 to 1500 rpm, which is widely used in chemical reactions. Is agitation at a rotation speed of about 50 to 1000 rpm, particularly about 50 to 500 rpm). Further, the stirring may be continuous or intermittent.

On the other hand, the kneading means is not a strong kneading method for physically crushing or defibrating chitins, but a conventional kneading means (usually a kneading means at room temperature), for example, 10 to 2000 rpm, preferably 20 to 1500 rpm. More preferably, kneading may be performed at a rotation speed of about 30 to 1000 rpm, particularly about 50 to 500 rpm. Examples of the conventional kneading method include a method using a mixing roller, a kneader, a Banbury mixer, an extruder (such as a single-screw or twin-screw extruder) and the like. The use of kneading means is advantageous in that the chemical defibration of chitins and the subsequent permeation or homogenization promotion steps can be carried out industrially and continuously.

In the present invention, the reaction temperature in chemical defibration does not need to be heated, the reaction may be carried out at room temperature, and the reaction is carried out for 2 hours or more without using mechanical defibration means by the action of shearing force. Can be chemically defibrated. Therefore, in the present invention, chitins can be defibrated without using extra energy. In addition, in order to promote the reaction, heating may be performed, and the heating temperature is, for example, 90 ° C. or lower (for example, about 40 to 90 ° C.), preferably 80 ° C. or lower, and more preferably 70 ° C. or lower.

The reaction time can be selected depending on the type of carboxylic acid anhydride and catalyst and the number of donors of the solvent, for example, 3 to 72 hours, preferably 5 to 48 hours, more preferably 10 to 36 hours (particularly 18 to 30 hours). Degree. If the reaction time is too short, the reactive defibrating solution does not sufficiently permeate between the microfibrils, the reaction becomes insufficient, and the degree of defibration may decrease. On the other hand, if the reaction time is too long, the yield of chitin-based fine fibers may decrease.

The reaction may be carried out under an atmosphere of an inert gas (noble gas such as nitrogen or argon) or under reduced pressure, but it is usually carried out in a closed reaction vessel. These reaction conditions are preferable because the water generated by the esterification reaction is not discharged to the outside of the system and the water in the air is not inhaled into the system.

After the reaction is completed, the modified chitin-based fine fibers obtained by chemically defibrating are added with a deactivating agent such as water to deactivate the carboxylic acid anhydride (esterifying agent), and then the conventional method ( For example, it may be separated and purified by centrifugation, filtration, concentration, extraction, etc.). For example, an inactivated esterifying agent, a catalyst, and a solvent capable of dissolving the solvent may be added to the reaction mixture, and the mixture may be separated and purified (washed) by a separation method (conventional method) such as centrifugation, filtration, or extraction. good. The separation operation can be performed a plurality of times (for example, about 2 to 5 times). Examples of the solvent include water, ketones such as acetone, C _1-4 alkanol such as ethanol and isopropanol, and the like.

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

The stirring method is not particularly limited as long as it can be stirred, and a conventional stirring method can be used. For example, a method using a stirrer having a stirring blade (for example, a mixer, an emulsifying device, etc.) can be used.

Among them, as a stirring method, a stirring method in which modified chitin-based fine fibers are liquid-liquid sheared is used because it is possible to obtain modified chitin-based nanofibers having a uniform nanosize, less damage to the fiber shape, and a large aspect ratio. preferable. Liquid-liquid shear is different from shearing due to the external shearing force between the fluid and the contact wall surface, which creates a turbulent flow zone and causes an internal shearing force called Reynolds stress (fluid itself) caused by irregular fluctuations in velocity. Shearing using the intermolecular attractive force of. In the present invention, as such a liquid-liquid shearing stirrer, an emulsifying device combining a screen (a cone having a plurality of slit-shaped holes) and a rotor (a stirring blade housed inside the screen) can be used. .. In this emulsifying device, Reynolds stress can be applied to the modified chitin-based fine fibers by passing the modified chitin-based fine fibers and the dispersion medium agitated by the rotor through the screen. As such an emulsifying device, a commercially available emulsifying device (for example, "Clairemix" manufactured by M-Technique Co., Ltd.) can be used.

The rotation speed of stirring may be 2000 rpm or more, for example, 2000 to 100,000 rpm, preferably 3000 to 50000 rpm, and more preferably 5000 to 30000 rpm (particularly 10000 to 25000 rpm). If the rotation speed is too low, the uniformity of the fiber diameter may 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 utilizing an external shearing force such as a media mill, a colloid mill, a roll mill, a rotary type, or a high pressure homogenizer. Therefore, a stirring method that does not utilize an external shearing force is preferable.

The dispersion medium may be water or an organic solvent. Examples of the organic solvent include alcohols (C _1-4 alkanol such as methanol, ethanol, propanol and isopropanol), ethers (cyclic ethers such as dioxane and tetrahydrofuran), ketones (acetone and the like), and amides (acetone and the like). Dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, etc.), sulfoxides (dimethylsulfoxide, etc.), alkanediol (eg, C _2-4 alkanediol such as ethylene glycol, propylene glycol), cellosolves (methylcellosolve, ethylserosolve, etc.) ), Carbitols (ethylcarbitol, etc.), carbonates (cyclic carbonates such as ethylene carbonate and propylene carbonate; dimethyl carbonate, etc.) and the like. These dispersion media may be used alone or in combination of two or more. The dispersion medium may be newly added in the stirring step, or the solvent used in washing in the modified defibration step may be used.

The solubility parameter (SP value) of the dispersion medium is preferably high, and the specific solubility parameter may be 10 or more, for example, 10 to 30, preferably 12 to 28, and more preferably 15 to 26 [particularly 20 to 20 to 20]. 25]. If the solubility parameter is too low, the uniformity of the fiber diameter may decrease. The SP value in the present specification and claims is the SP value of Hildebrand.

Of these dispersion media, water and an organic solvent having a solubility parameter of 10 or more (particularly C _1-4 alkanol) are preferable from the viewpoint of improving the uniformity of the fiber diameter. Further, the dispersion medium is particularly preferably containing water, and may be water alone or a mixed solvent of water and C _1-4 alkanol (ethanol or the like).

The ratio of the dispersion medium is, for example, about 10 to 1000 parts by weight, preferably 20 to 500 parts by weight, more preferably 30 to 300 parts by weight (particularly 50 to 150 parts by weight) with respect to 1 part by weight of the modified chitin-based fine fiber. Is. If the proportion of the dispersion medium is too small, it becomes difficult to stir at high speed, damage to the fibers increases, and the uniformity of the fiber diameter may decrease. On the other hand, if the proportion of the dispersion medium is too large, the efficiency may decrease and it may be difficult to recover the chitin-based nanofibers.

[Modified chitin nanofibers]
The modified chitin-based nanofibers of the present invention are obtained through the above-mentioned stirring step, are modified with a carboxylic acid anhydride (particularly alkandidiic acid anhydride), and have an ultrafine nanosize and a uniform fiber diameter. It has been defibrated. The average fiber diameter of the modified chitin-based nanofibers may be 100 nm or less (preferably 80 nm or less, more preferably 50 nm or less), for example, 1 to 100 nm, preferably 3 to 80 nm, still more preferably 5 to 60 nm (particularly 10). ~ 50 nm). If the fiber diameter is too large, the transparency, thixotropic property, film forming property, etc. in the state of the film or solution may be deteriorated, or the effect as a reinforcing material may be deteriorated. On the other hand, if the fiber diameter is too small, the handleability and heat resistance of the fine fibers may deteriorate.

The modified chitin-based nanofiber of the present invention has a uniform fiber diameter, and the number of fibers having a fiber diameter of 300 nm or more may be 10% or less (particularly 5% or less) with respect to the total number of fibers, and is 300 nm. It is preferable that the above fibers are not substantially contained (0%). Therefore, the maximum fiber diameter of the modified chitin-based nanofiber of the present invention may be 500 nm or less (particularly 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, the transparency, thixotropic property, film forming property and the like may be deteriorated, or a dense or uniform film may not be formed.

Since the modified chitin-based nanofibers of the present invention are chemically defibrated, defibrated to nanosize, and then stirred without applying a strong external external shearing force, the conventional powerful mechanical defibration method can be used. It has a fiber length longer than that of the obtained nanofibers, and the average fiber length may be 1 μm or more, and can be selected from the range of, for example, about 1 to 1000 μm, for example, 1 to 1000 μm, preferably 3 to 500 μm. More preferably, it may be about 5 to 200 μm. If the fiber length is too short, the reinforcing effect and the film forming function may be deteriorated if the fiber length is too short. On the other hand, if it is too long, the fibers are likely to be entangled, so that the dispersibility in the solvent or the resin may decrease.

The ratio (aspect ratio) of the average fiber length to the average fiber diameter of the modified chitin-based nanofibers can be adjusted according to the application, and may be, for example, 10 or more, for example, 30 to 10000, preferably 50 to 8000, and more preferably 50 to 8000. It may be about 100 to 5000.

In the present specification and claims, the average fiber diameter, average fiber length and aspect ratio of the modified chitin-based nanofibers are averaged by randomly selecting 50 fibers from the images of the scanning electron micrograph. It may be calculated by

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The details of the raw materials used are as follows, and the characteristics and evaluation of the obtained modified chitin nanofibers were measured as follows.

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

(Presence / absence of modification of modified chitin nanofibers)
The obtained modified chitin nanofibers were dried under reduced pressure at 80 ° C. for 5 hours and analyzed by a Fourier transform infrared spectrophotometer (FT-IR). The measurement was performed using "NICOLET iS5" manufactured by NICOLET, and the analysis was performed in the reflection mode.

Example 1
To 90 g of dimethyl sulfoxide, 3 g of chitin (manufactured by Tokyo Chemical Industry Co., Ltd.), 3.3 g of succinic anhydride, and 5.6 g of sodium hydrogen carbonate were added, and the mixture was stirred with a stirrer for 24 hours in a room at 25 ° C. The reaction was filtered, washed 3 times with 90 g of water and centrifuged to remove unmodified raw materials and catalyst. Distilled water was added to the obtained solid to make a total volume of 700 ml, and the mixture was stirred with an emulsifying device (“Clearmix CLM-0.8S” manufactured by M-Technique Co., Ltd.) for 5 minutes to obtain a chitin nanofiber dispersion. FIG. 1 shows the results of SEM observation of the shape of the chitin nanofibers in the obtained dispersion. As is clear from FIG. 1, nanofibers are produced in the dispersion liquid. Further, the dispersion liquid was dried, and the results measured by FTIR are shown in FIG. As shown in FIG. 2, the absorption band of the ester bond at 1730 cm ^-1 was detected, and it was confirmed that it was modified with succinic anhydride.

Example 2
A chitin nanofiber dispersion was obtained in the same manner as in Example 1 except that 90 g of dimethyl sulfoxide was changed to 90 g of dimethylacetamide. The results of SEM observation of the shape of the obtained chitin nanofibers are shown in FIG.

Example 3
A chitin nanofiber dispersion was obtained in the same manner as in Example 1 except that 3.3 g of succinic anhydride was changed to 3.2 g of maleic anhydride. The results of SEM observation of the shape of the obtained chitin nanofibers are shown in FIG.

Example 4
A chitin nanofiber dispersion was obtained in the same manner as in Example 1 except that 3.3 g of succinic anhydride was changed to 3.3 g of phthalic anhydride. The results of SEM observation of the shape of the obtained chitin nanofibers are shown in FIG.

Example 5
A chitin nanofiber dispersion was obtained in the same manner as in Example 1 except that 5.6 g of sodium hydrogen carbonate was changed to 2.8 g. The results of SEM observation of the shape of the obtained chitin nanofibers are shown in FIG.

Example 6
A chitin nanofiber dispersion was obtained in the same manner as in Example 1 except that 3.3 g of succinic anhydride was changed to 1.7 g. The results of SEM observation of the shape of the obtained chitin nanofibers are shown in FIG.

Comparative Example 1
Distilled water was added to the raw material chitin without chemical defibration treatment to make a total volume of 700 ml, and the mixture was stirred with an emulsifying device for 5 minutes to obtain a dispersion. FIG. 8 shows the results of SEM observation of the shape of the chitin nanofibers in the obtained dispersion. As is clear from the results of FIG. 8, a part of the surface of chitin was made into nanofibers, but most of the particles were several μm or more.

Comparative Example 2
A chitin nanofiber dispersion was obtained in the same manner as in Example 1 except that sodium hydrogen carbonate was not added. The results of SEM observation of the shape of the obtained chitin nanofibers are shown in FIG. As is clear from the results of FIG. 9, defibration progressed in some parts, but uniform nanofibers could not be obtained, and many undefibrated parts remained.

The chitin-based nanofiber of the present invention can be used as a transparent film raw material, a medical material, a cosmetic raw material, a resin strengthening agent, and the like.

Claims (11)

A modified defibration step of permeating a reactive defibrating solution containing a catalyst and a dibasic carboxylic acid anhydride into chitins to esterify the chitins and chemically defibrating them to obtain modified chitin-based fine fibers. A method for producing modified chitin-based nanofibers, which comprises a stirring step of adding a dispersion medium to the modified chitin-based fine fibers and stirring to obtain modified chitin-based nanofibers.
The catalyst is alkali metal carbonate, alkali metal hydrogen carbonate, carboxylic acid alkali metal salt, alkali metal borate, alkali metal phosphate, alkali metal hydrogen phosphate, alkaline earth metal carbonate, alkaline earth metal. A production method that is at least one selected from bicarbonate and alkaline earth metal carboxylates . The production method according to claim 1, wherein the reactive defibrating solution further contains an aprotic solvent having 25 or more donors. The production method according to claim 2, wherein the aprotic solvent having 25 or more donors is at least one selected from the group consisting of alkyl sulfoxides, alkyl amides and pyrrolidones. The production method according to claim 3, wherein the aprotic solvent having 25 or more donors is diC _1-2 alkyl sulfoxide. One of claims 1 to 4, wherein the dibasic carboxylic acid anhydride is at least one selected from the group consisting of an aliphatic dicarboxylic acid anhydride, an alicyclic dicarboxylic acid anhydride and an aromatic dicarboxylic acid anhydride. The manufacturing method described. The production method according to any one of claims 1 to 5, wherein the dibasic carboxylic acid anhydride is a saturated aliphatic dicarboxylic acid anhydride having 4 to 6 carbon atoms. The production method according to any one of claims 1 to 6 , wherein the catalyst is an alkali metal bicarbonate. The production method according to any one of claims 1 to 7 , wherein the ratio of the catalyst is 100 parts by weight or more with respect to 100 parts by weight of the dibasic carboxylic acid anhydride. The production method according to any one of claims 1 to 8 , wherein the ratio of the dibasic carboxylic acid anhydride is 60 parts by weight or more with respect to 100 parts by weight of chitins. The production method according to any one of claims 1 to 9 , wherein the modified chitin-based fine fibers are liquid-liquid sheared in the stirring step. A modified chitin-based nanofiber modified with alkandidiic anhydride, having an average fiber diameter of 100 nm or less and an average fiber length of 1 μm or more.

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