JP2019163390A - Carboxyalkylated cellulose, and manufacturing method of carboxyalkylated cellulose nanofiber - Google Patents

Abstract

To provide a manufacturing method of carboxyalkylated cellulose capable of economically obtaining a cellulose nanofiber dispersion high in transparency.SOLUTION: In carboxyalkylation of cellulose, mercerization is conducted under a solvent containing water of 15 mass% or more under a temperature of less than 50°C, then carboxyalkylation is conducted under a mixed solvent of water and an organic solvent. The resulting carboxyalkylated cellulose is fibrillated, then a nanofiber dispersion of carboxyalkylated cellulose high in transparency can be economically obtained.SELECTED DRAWING: None

Description

  The present invention relates to a novel method for producing carboxyalkylated cellulose and carboxyalkylated cellulose nanofibers.

  Carboxyalkylated cellulose is a cellulose derivative in which a carboxyalkyl group is ether-bonded to a part of a hydroxyl group in a glucose residue constituting the skeleton of cellulose. As the amount of carboxyalkyl groups increases (ie, the degree of carboxyalkyl substitution increases), the carboxyalkylated cellulose becomes soluble in water. On the other hand, by adjusting the degree of carboxyalkyl substitution to an appropriate range, the fibrous shape of carboxyalkylated cellulose can be maintained even in water. A carboxyalkylated cellulose having a fibrous shape, such as carboxymethylated cellulose, can be converted into nanofibers having a nanoscale fiber diameter by mechanically defibrating (Patent Document 1).

  As a method for producing carboxyalkylated cellulose, generally, cellulose is treated with alkali (mercelization) and then treated with an etherifying agent (also referred to as carboxyalkylating agent) (carboxyalkylation, also referred to as etherification). A method is known, in which both mercerization and carboxyalkylation are performed using water as a solvent, and both mercerization and carboxyalkylation are performed in a solvent mainly composed of an organic solvent (Patent Document 2). The former is called the “water medium method” and the latter is called the “solvent method”.

  As a method for producing cellulose nanofibers having nanoscale fiber diameters, not only mechanical defibration of carboxyalkylated cellulose but also mechanical defibration of cellulose introduced with carboxyl groups is known (Patent Document 3). . It is known that the aqueous dispersion of cellulose nanofibers obtained by fibrillation of cellulose introduced with such a carboxyl group has high transparency, but it is obtained by fibrillation of carboxyalkylated cellulose obtained by a solvent method. The aqueous dispersion of cellulose nanofibers was lower in transparency than the aqueous dispersion of cellulose nanofibers obtained by defibrating cellulose introduced with carboxyl groups. In addition, the aqueous dispersion of cellulose nanofibers obtained by defibration of carboxyalkyl cellulose obtained by the aqueous medium method uses a large amount of drugs such as mercerizing agents and carboxyalkylating agents in order to increase transparency. It was necessary, and the production and economic problems were great. Since transparent materials are suitable for various applications, it is necessary to make cellulose nanofibers transparent.In particular, carboxyalkylated cellulose is a highly safe material, and therefore carboxyalkylated cellulose is used to provide transparency. There is a need to obtain high cellulose nanofibers in an economical manner.

International Publication No. 2014/088072 JP 2017-149901 A JP 2008-1728 A

  An object of this invention is to provide the manufacturing method of the carboxyalkylation cellulose which can obtain a transparent cellulose nanofiber dispersion.

  As a result of intensive studies on the above-mentioned object, the present inventors have conducted mercerization (cellulose alkali treatment) in a solvent containing 15% by mass or more of water at a reaction temperature of less than 50 ° C. in carboxyalkylation of cellulose. Thereafter, carboxyalkylation (also referred to as etherification) is carried out in a mixed solvent of water and an organic solvent, whereby a conventional aqueous medium method (a method in which both mercerization and carboxyalkylation are carried out using water as a solvent). Compared to carboxyalkylated cellulose obtained by the solvent method (both mercerization and carboxyalkylation in a solvent mainly composed of organic solvents), cellulose nanofiber dispersion with high transparency when defibrated Has been found to be economically produced with a high effective utilization rate of the carboxyalkylating agent.

The present invention includes, but is not limited to, the following.
(1) A step of treating cellulose with a mercerizing agent to obtain mercerized cellulose, and a step of reacting mercerized cellulose with a carboxyalkylating agent to obtain carboxyalkylated cellulose,
And the step of obtaining mercerized cellulose is carried out under a temperature condition of less than 50 ° C. under a solvent containing 15% by mass or more of water, and the step of obtaining carboxyalkylated cellulose is carried out under a mixed solvent of water and an organic solvent. A process for producing carboxyalkylated cellulose, as described in 1).
(2) The method according to (1), wherein the carboxyalkylated cellulose is carboxymethylated cellulose, and the degree of carboxyalkyl substitution per anhydroglucose unit in the carboxymethylated cellulose is less than 0.50.
(3) The method according to (1) or (2), wherein the crystallinity of cellulose type I of carboxyalkylated cellulose is 50% or more.
(4) The method according to any one of (1) to (3), wherein the mercerizing agent is sodium hydroxide, lithium hydroxide, potassium hydroxide, or a combination of two or more thereof.
(5) The method according to any one of (1) to (4), wherein the carboxyalkylating agent is monochloroacetic acid or sodium monochloroacetate.
(6) The method according to any one of (1) to (5), wherein the mixed solvent in the step of obtaining carboxyalkylated cellulose is a solvent containing 20 to 99% by mass of an organic solvent.
(7) The method according to any one of (1) to (6), wherein the organic solvent is isopropanol, methanol, ethanol, acetone, or a combination of two or more thereof.
(8) A method for producing nanofibers of carboxyalkylated cellulose, comprising defibrating the carboxyalkylated cellulose obtained by the method according to any one of (1) to (7).

  According to the method of the present invention, a carboxyalkylated cellulose capable of obtaining a highly transparent cellulose nanofiber dispersion upon defibration can be produced with a high effective utilization rate of a carboxyalkylating agent.

  The present invention is a method for producing carboxyalkylated cellulose. Carboxyalkylated cellulose has a structure in which a part of hydroxyl groups in a glucose residue constituting cellulose is ether-bonded to a carboxyalkyl group. The carboxyalkylated cellulose may take the form of a salt, and examples of the salt of carboxyalkylated cellulose include metal salts such as sodium carboxyalkylcellulose.

  In general, carboxyalkylated cellulose is obtained by treating cellulose with alkali (mercelization), and then reacting the obtained mercerized cellulose (also referred to as alkali cellulose) with a carboxyalkylating agent (also referred to as etherifying agent). Can be manufactured. When carrying out mercerization and carboxyalkylation, a conventional method in which both of these are performed using water as a solvent (aqueous medium method) and a method in which both of these are performed using a solvent mainly composed of an organic solvent (solvent method) ) Was known. The water medium method is a method that consistently uses water as a single solvent, while the solvent method is a method that consistently uses a high concentration organic solvent. Usually, mercerization reaction and carboxyalkylation reaction are carried out in a consistent flow using solvents having almost the same composition, and the composition of the solvent is intentionally changed for each of these reactions. I did not come. It was thought that intentionally changing the composition of the solvent led to a complicated manufacturing process and increased costs, and there was no advantage. In contrast, the inventors of the present invention controlled the composition of the solvent in the mercerization reaction and the carboxyalkylation reaction, respectively, to give a highly transparent cellulose nanofiber dispersion when fibrillated. It has been found for the first time that cellulose can be produced.

<Cellulose>
In the present invention, cellulose means a polysaccharide having a structure in which D-glucopyranose (also simply referred to as “glucose residue” or “anhydroglucose”) is linked by β-1,4 bonds. Cellulose is generally classified into natural cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose excluding non-crystalline regions, and the like, based on the origin, production method, and the like. In the present invention, any of these celluloses can be used as a raw material for mercerized cellulose.

  Examples of natural cellulose include bleached pulp or unbleached pulp (bleached wood pulp or unbleached wood pulp); linters, refined linters; cellulose produced by microorganisms such as acetic acid bacteria, and the like. The raw material of bleached pulp or unbleached pulp is not particularly limited, and examples thereof include wood, cotton, straw, bamboo, hemp, jute, kenaf and the like. Moreover, the manufacturing method of a bleached pulp or an unbleached pulp is not specifically limited, either, a mechanical method, a chemical method, or the method which combined two in the middle may be sufficient. Examples of bleached or unbleached pulp classified according to the production method include mechanical pulp (thermomechanical pulp (TMP), groundwood pulp), chemical pulp (conifer unbleached sulfite pulp (NUSP), conifer bleach sulfite pulp (NBSP). ) And the like, and softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), and hardwood bleached kraft pulp (LBKP)). Furthermore, dissolving pulp may be used in addition to papermaking pulp. Dissolving pulp is chemically refined pulp, which is mainly used by dissolving in chemicals, and is a main raw material for artificial fibers, cellophane and the like.

Examples of the regenerated cellulose include those obtained by dissolving cellulose in some solvent such as a copper ammonia solution, a cellulose xanthate solution, and a morpholine derivative and spinning again.
The fine cellulose is obtained by depolymerizing a cellulose-based material such as the above natural cellulose or regenerated cellulose (for example, acid hydrolysis, alkali hydrolysis, enzyme decomposition, explosion treatment, vibration ball mill treatment, etc.). And those obtained by mechanically treating the cellulose-based material.

<Mercelization>
The cellulose described above is used as a raw material, and mercerized cellulose (also referred to as alkali cellulose) is obtained by adding a mercerizing agent (alkali). In the present invention, the solvent used in the mercerization reaction is a solvent containing water in a proportion of 15% by mass or more, and the mixture is defibrated by using a mixed solvent of an organic solvent and water in the next carboxyalkylation. In particular, a carboxyalkylated cellulose that can be made into a cellulose nanofiber dispersion having high transparency can be economically obtained.

  The solvent containing 15% by mass or more of water refers to a solvent having a mass of water of 15 parts or more when the total mass of the solvent is 100 parts. The remainder of the solvent other than water may be an organic solvent. The solvent in the mercerization reaction is a solvent containing water at a ratio of 15% by mass or more as described above, preferably the ratio of water is 20% by mass or more, more preferably 30% by mass or more. By containing 15% by mass or more of water at the time of mercerization, cellulose nanofibers that give a highly transparent aqueous dispersion can be obtained when the resulting carboxyalkylated cellulose is defibrated. The upper limit of the ratio of water is not limited, and may be 100% by mass (that is, the solvent is water). From the viewpoint of improving the effective utilization rate of the carboxyalkylating agent described later, the ratio of water is 50% by mass. % Or less is also preferable.

  Examples of the solvent other than water (used by mixing with water) in a solvent containing 15% by mass or more of water include organic solvents used as a solvent in the subsequent carboxyalkylation. For example, alcohols such as methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol and tertiary butanol, ketones such as acetone, diethyl ketone and methyl ethyl ketone, and dioxane, diethyl ether, benzene and dichloromethane These can be used alone or a mixture of two or more thereof can be added to water in an amount of 85% by mass or less and used as a solvent for mercerization. The organic solvent in the solvent in the mercerization reaction is preferably 80% by mass or less, and more preferably 70% by mass or less. The lower limit of the ratio of the organic solvent is not limited, and may be 0% by mass.

  Examples of mercerizing agents include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, and any one or two or more of these can be used in combination. The mercerizing agent is not limited to this, but these alkali metal hydroxides are added to the reactor as an aqueous solution of, for example, 1 to 60% by mass, preferably 2 to 45% by mass, more preferably 3 to 25% by mass. Can be added.

  The amount of the mercerizing agent used is not particularly limited as long as the desired crystallinity and carboxyalkyl substitution degree of the carboxyalkylated cellulose are achieved, but the crystallinity of cellulose I type described later is 50% or more. It is preferable to use such an amount that a carboxyalkylated cellulose having a degree of carboxyalkyl substitution of less than 0.50 can be produced. When the crystallinity of cellulose type I of the carboxyalkylated cellulose is 50% or more and the carboxyalkyl substitution degree is less than 0.50, the fibrous shape of the carboxyalkylated cellulose is maintained, and cellulose nanofibers are obtained. Easy to defibrate. In one embodiment, the mercerizing agent is preferably used in an amount of 0.1 mol to 2.5 mol, preferably 0.3 mol to 2.0 mol, per 100 g of cellulose (absolutely dry). More preferably, it is 0.4 mol or more and 1.5 mol or less.

  The amount of the solvent mainly composed of water at the time of mercerization is not particularly limited as long as it is an amount capable of stirring and mixing the raw materials, but is preferably 1.5 to 20 times by mass with respect to the cellulose raw material, and 2 to 10 It is more preferable that the mass is.

  The mercerization treatment is performed by mixing a bottoming raw material (cellulose) and a solvent containing 15% by mass or more of water and adjusting the temperature of the reactor to less than 50 ° C. By setting the temperature to less than 50 ° C., the reaction tends to be uniform, and cellulose nanofibers that give a highly transparent aqueous dispersion can be obtained when the resulting carboxyalkylated cellulose is fibrillated. Moreover, since side reaction can be suppressed, the effective utilization factor of the carboxyalkylating agent mentioned later can be improved. The temperature of the reactor is preferably 0 ° C. or higher and lower than 50 ° C., more preferably 10 ° C. or higher and lower than 50 ° C., and more preferably 10 ° C. or higher and 40 ° C. or lower.

  A bottoming raw material (cellulose) and a solvent are added, and an aqueous mercerizing agent solution is added to the reactor whose temperature is adjusted as described above, and is 15 to 8 hours, preferably 30 to 7 hours, more preferably 30 minutes. Mercerization is carried out by stirring for ~ 3 hours. Thereby, mercerized cellulose (alkali cellulose) is obtained.

  The pH during mercerization is preferably 9 or more, whereby the mercerization reaction can proceed. The pH is more preferably 11 or more, still more preferably 12 or more, and may be 13 or more. The upper limit of pH is not particularly limited.

  Mercerization can be performed using a reactor capable of mixing and stirring the above components while controlling the temperature, and various reactors conventionally used in mercerization reactions can be used. For example, a batch type stirring apparatus in which two shafts are stirred and the above components are mixed is preferable from the viewpoints of both uniform mixing and productivity.

<Carboxyalkylation>
A carboxyalkylated cellulose is obtained by adding a carboxyalkylating agent (also referred to as an etherifying agent) to mercerized cellulose. In the present invention, a mixed solvent of water and an organic solvent is used as a solvent in this carboxyalkylation reaction. Cellulose nanofiber dispersion having high transparency when fibrillated by using a solvent containing 15% by mass or more of water for mercerization and using a mixed solvent of water and an organic solvent for carboxyalkylation The carboxyalkylated cellulose can be obtained economically.

  As the carboxyalkylating agent, carboxymethylating agents such as monochloroacetic acid, sodium monochloroacetate, methyl monochloroacetate, ethyl monochloroacetate and isopropyl monochloroacetate are preferable. Of these, monochloroacetic acid or sodium monochloroacetate is more preferable from the viewpoint of easy availability of raw materials.

  The amount of the carboxyalkylating agent used is not particularly limited as long as the desired crystallinity and carboxyalkyl substitution degree of the carboxyalkylated cellulose are achieved, and the crystallinity of cellulose I type described later is 50%. It is preferable to use such an amount that carboxyalkylated cellulose having a degree of carboxyalkyl substitution of less than 0.50 can be produced. When the crystallinity of cellulose type I of the carboxyalkylated cellulose is 50% or more and the carboxyalkyl substitution degree is less than 0.50, the fibrous shape of the carboxyalkylated cellulose is maintained, and cellulose nanofibers are obtained. Easy to defibrate. In one embodiment, the amount of the carboxyalkylating agent used is preferably in the range of 0.5 to 1.5 mol per anhydroglucose unit of cellulose. The lower limit of the above range is more preferably 0.6 mol or more, still more preferably 0.7 mol or more, and the upper limit is more preferably 1.3 mol or less, still more preferably 1.1 mol or less. The carboxyalkylating agent is not limited to this. For example, the carboxyalkylating agent can be added to the reactor as an aqueous solution of 5 to 80% by mass, more preferably 30 to 60% by mass. You can also.

  The molar ratio of mercerizing agent to carboxyalkylating agent (mercelling agent / carboxyalkylating agent) is generally 0.9 to 2.45 when monochloroacetic acid or sodium monochloroacetate is used as the carboxyalkylating agent. Adopted. The reason is that if it is less than 0.9, the carboxyalkylation reaction may become insufficient, and unreacted monochloroacetic acid or sodium monochloroacetate may remain, resulting in waste, and 2.45. If it exceeds 1, the side reaction between the excess mercerizing agent and monochloroacetic acid or sodium monochloroacetate may proceed to produce an alkali metal glycolate, which may be uneconomical.

  In the present invention, the effective utilization rate of the carboxyalkylating agent is preferably 15% or more. More preferably, it is 20% or more, more preferably 25% or more, and particularly preferably 30% or more. The effective utilization rate of the carboxyalkylating agent refers to the ratio of the carboxyalkyl group introduced into cellulose among the carboxyalkyl groups in the carboxyalkylating agent. In the present invention, by using a solvent containing 15% by mass or more of water at the time of mercerization and using a mixed solvent of water and an organic solvent at the time of carboxyalkylation, the effective utilization rate of the carboxyalkylating agent is high ( That is, a carboxyalkylated cellulose capable of obtaining a cellulose nanofiber dispersion having high transparency when defibrated can be produced without economically increasing the amount of carboxyalkylating agent used. The upper limit of the effective utilization rate of the carboxyalkylating agent is not particularly limited, but in reality, the upper limit is about 80%. The effective utilization rate of the carboxyalkylating agent may be abbreviated as AM.

The calculation method of the effective utilization rate of the carboxyalkylating agent is as follows:
AM = (DS × number of moles of cellulose) / number of moles of carboxyalkylating agent DS: Degree of carboxyalkyl substitution (measurement method will be described later)
Number of moles of cellulose: Pulp mass (dry mass when dried at 100 ° C. for 60 minutes) / 162
(162 is the molecular weight of cellulose per glucose unit).

  Although the density | concentration of the cellulose raw material in a carboxyalkylation reaction is not specifically limited, From a viewpoint of raising the effective utilization factor of a carboxyalkylating agent, it is preferable that it is 1-40% (w / v).

  At the same time as the addition of the carboxyalkylating agent, or before or immediately after the addition of the carboxyalkylating agent, an organic solvent or an aqueous solution of the organic solvent is appropriately added to the reactor, or other than water during mercerization treatment by reducing the pressure, etc. The organic solvent is appropriately reduced to form a mixed solvent of water and the organic solvent. In the present invention, the carboxyalkylation reaction proceeds under a mixed solvent of water and an organic solvent. The timing of addition or reduction of the organic solvent is not particularly limited as long as it is from the end of the mercerization reaction to immediately after the addition of the carboxyalkylating agent. For example, 30 minutes before and after adding the carboxyalkylating agent Is preferred.

  Examples of organic solvents include alcohols such as methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol and tertiary butanol, ketones such as acetone, diethyl ketone and methyl ethyl ketone, and dioxane, diethyl ether, Benzene, dichloromethane and the like can be mentioned, and these alone or a mixture of two or more thereof can be added to water and used as a solvent for carboxyalkylation. Among these, a monohydric alcohol having 1 to 4 carbon atoms is preferable, and a monohydric alcohol having 1 to 3 carbon atoms is more preferable because of excellent compatibility with water.

  The ratio of the organic solvent in the mixed solvent in the carboxyalkylation is preferably 20% by mass or more, more preferably 30% by mass or more, based on the sum of water and the organic solvent, It is more preferably 40% by mass or more, further preferably 45% by mass or more, and particularly preferably 50% by mass or more. As the proportion of the organic solvent is higher, an advantage that the transparency when the cellulose nanofiber dispersion is obtained becomes higher. The upper limit of the ratio of the organic solvent is not limited, and may be 99% by mass or less, for example. Considering the cost of the organic solvent to be added, it is preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less, and further preferably 70% by mass or less.

  After forming a mixed solvent of water and an organic solvent and adding a carboxyalkylating agent to mercerized cellulose, the temperature is preferably kept constant in the range of 10 to 40 ° C. for 15 minutes to 4 hours, preferably 15 Stir for about 1 to 1 hour. The mixing of the mercerized cellulose-containing liquid and the carboxyalkylating agent is preferably performed in a plurality of times or by dropwise addition in order to prevent the reaction mixture from becoming high temperature. After adding a carboxyalkylating agent and stirring for a certain time, the temperature is raised if necessary, and the reaction temperature is 30 to 90 ° C, preferably 40 to 90 ° C, more preferably 60 to 80 ° C, and 30 minutes to The etherification (carboxyalkylation) reaction is performed for 10 hours, preferably 1 hour to 4 hours, to obtain carboxyalkylated cellulose.

  In the carboxyalkylation, the reactor used in the mercerization may be used as it is, or another reactor capable of mixing and stirring the above components while controlling the temperature may be used. .

  After completion of the reaction, the remaining alkali metal salt may be neutralized with a mineral acid or an organic acid. If necessary, by-product inorganic salts, organic acid salts and the like may be removed by washing with water-containing methanol, dried, pulverized, and classified to obtain carboxyalkylated cellulose or a salt thereof. Examples of the apparatus used in the dry pulverization include impact mills such as a hammer mill and a pin mill, medium mills such as a ball mill and a tower mill, and jet mills. Examples of the apparatus used in the wet pulverization include apparatuses such as a homogenizer, a mass collider, and a pearl mill.

<Carboxyalkylated cellulose>
Carboxyalkylated cellulose is one in which a carboxyalkyl group is ether-bonded to a part of the hydroxyl group of a glucose residue in cellulose. Examples of the carboxyalkyl group to be introduced into the carboxyalkylated cellulose of the present invention include a carboxymethyl group and a carboxyethyl group. However, it is easy to react uniformly and considering the economically advantageous point, the carboxymethyl group Is preferred.

  The carboxyalkylated cellulose produced in the present invention is preferably one in which at least a part of the fibrous shape is maintained even when dispersed in water. That is, when an aqueous dispersion of carboxyalkylated cellulose is observed with an electron microscope, fibrous substances can be observed, and the peak of cellulose I-type crystals is observed when carboxyalkylated cellulose is measured by X-ray diffraction. Those that can be used are preferred.

  The carboxyalkylated cellulose that maintains at least a part of the fibrous shape even when dispersed in water has a carboxyalkyl substitution degree per cellulose anhydroglucose unit of less than 0.50, preferably 0.40 or less. It is. When the degree of substitution is 0.50 or more, dissolution in water tends to occur, the fiber form cannot be maintained, and it becomes difficult to fibrillate into nanofibers. The lower limit of the degree of carboxyalkyl substitution is particularly preferably 0.02 or more considering the ease of fibrillation of carboxyalkylated cellulose into nanofibers, the transparency and dispersion stability of the nanofiber dispersion, and the like. Is more preferably 0.05 or more, further preferably 0.10 or more, and further preferably 0.20 or more. By introducing a carboxyalkyl group into cellulose, the celluloses repel each other electrically, so that they can be fibrillated into nanofibers, but if the degree of carboxyalkyl substitution is less than 0.02, nanofibers In some cases, the fiber cannot be sufficiently defibrated. In addition, there are cases where the effects (such as imparting water retention and imparting shape retention) obtained by introducing a carboxyalkyl group cannot be sufficiently obtained. The degree of carboxyalkyl substitution can be adjusted by controlling the amount of carboxyalkylating agent to be reacted, the amount of mercerizing agent, the composition ratio of water and organic solvent, and the like.

  In the present invention, the anhydroglucose unit means individual anhydroglucose (glucose residue) constituting cellulose. The degree of carboxyalkyl substitution (also called degree of etherification) is the ratio of the hydroxyl groups in the glucose residues constituting cellulose that are substituted with carboxyalkyl ether groups (carboxyalkyl per glucose residue). The number of ether groups). The degree of carboxyalkyl substitution may be abbreviated as DS.

The method for measuring the degree of carboxyalkyl substitution is as follows:
About 2.0 g of sample is precisely weighed and placed in a 300 mL conical flask with a stopper. A solution of 100 mL of special concentrated nitric acid added to 1000 mL of nitric acid methanol is added and shaken for 3 hours to convert the salt of carboxyalkylated cellulose (CMC) into H-CMC (hydrogen-type carboxyalkylated cellulose). The absolute dry H-CMC is accurately weighed in an amount of 1.5 to 2.0 g and put into an Erlenmeyer flask with a 300 mL stopper. Wet H-CMC with 15 mL of 80% methanol, add 100 mL of 0.1 N NaOH, and shake at room temperature for 3 hours. Using phenolphthalein as an indicator, excess NaOH is back titrated with 0.1N—H ₂ SO ₄ and the degree of carboxyalkyl substitution (DS value) is calculated according to the following formula.
A = [(100 × F′−0.1N—H ₂ SO ₄ (mL) × F) × 0.1] / (absolute dry mass of H-CMC (g))
Carboxyalkyl substitution degree = 0.162 × A / (1−0.058 × A)
F ′: Factor of 0.1 N—H ₂ SO ₄ F: Factor of 0.1 N—NaOH

  The crystallinity of the cellulose in the carboxyalkylated cellulose of the present invention is preferably 50% or more, and more preferably 60% or more for the crystal I type. When the crystallinity is adjusted to the above range, the transparency of the cellulose nanofiber dispersion obtained by defibration is improved. Moreover, since the crystallinity is high, the carboxyalkylated cellulose is excellent in shape retention and the like. The crystallinity of cellulose can be controlled by the concentration of mercerizing agent and the temperature during processing, as well as the degree of carboxyalkylation. Since a high concentration of alkali is used in mercerization and carboxyalkylation, cellulose type I crystals are likely to be converted to type II, but the amount of modification may be reduced by adjusting the amount of alkali (mercellizing agent) used. The desired crystallinity can be maintained by adjusting the degree. The upper limit of the crystallinity of cellulose type I is not particularly limited. In reality, it is considered that the upper limit is about 90%.

The method for measuring the crystallinity of cellulose type I of carboxyalkylated cellulose is as follows:
The sample is placed on a glass cell and measured using an X-ray diffractometer (LabX XRD-6000, manufactured by Shimadzu Corporation). The degree of crystallinity is calculated using a method such as Segal and the diffraction intensity of 2θ = 10 ° to 30 ° in the X-ray diffraction diagram is used as a baseline, and the diffraction intensity of the 002 plane of 2θ = 22.6 ° and 2θ = It is calculated by the following formula from the diffraction intensity of the amorphous part at 18.5 °.

Xc = (I002c−Ia) / I002c × 100
Xc = crystallinity of cellulose type I (%)
I002c: 2θ = 22.6 °, diffraction intensity of 002 plane Ia: 2θ = 18.5 °, diffraction intensity of amorphous part.

  In the conventional aqueous medium method, it is difficult to obtain a carboxyalkylated cellulose having a carboxyalkyl substitution degree of 0.20 or more and less than 0.50 and a cellulose I type crystallinity of 50% or more. there were. Specifically, when it was attempted to achieve a carboxyalkyl substitution degree of 0.20 or more using the aqueous medium method, the crystallinity of cellulose type I tended to decrease to less than 50%. According to the method of the present invention, it is possible to produce a carboxyalkylated cellulose having a carboxyalkyl substitution degree of 0.20 or more and less than 0.50 and a cellulose I type crystallinity of 50% or more, Moreover, the advantage that the cellulose nanofiber dispersion manufactured using the obtained carboxyalkylated cellulose has high transparency is acquired.

  The carboxyalkylated cellulose produced according to the present invention can be used in the form of a dispersion obtained after the reaction. However, it can be dried and redispersed in water as necessary. The drying method is not limited in any way, for example, freeze drying method, spray drying method, shelf drying method, drum drying method, belt drying method, method of thinly extending and drying on a glass plate, fluidized bed drying method, microwave drying And known methods such as a heating fan type vacuum drying method can be used. You may grind | pulverize with a cutter mill, a hammer mill, a pin mill, a jet mill etc. as needed after drying. Further, the method for redispersion in water is not particularly limited, and a known dispersion apparatus can be used.

<Manufacture of carboxyalkylated cellulose nanofibers>
By defibrillating the carboxyalkylated cellulose obtained by the method of the present invention, it can be converted into cellulose nanofibers having nanoscale fiber diameters. The carboxyalkylated cellulose nanofibers obtained by the method of the present invention can be produced more economically than the carboxyalkylated cellulose nanofibers obtained by the conventional aqueous medium method or solvent method. In this state, it has high transparency.

  At the time of defibration, a dispersion of carboxyalkylated cellulose obtained by the above method is prepared. The dispersion medium is preferably water from the viewpoint of ease of handling. The concentration of the carboxyalkylated cellulose is preferably 0.01 to 10% (w / v) in consideration of the efficiency of defibration and dispersion.

  The apparatus used for defibrating carboxyalkylated cellulose is not particularly limited, and apparatuses such as a high-speed rotation type, a colloid mill type, a high-pressure type, a roll mill type, and an ultrasonic type can be used. During defibration, it is preferable to apply a strong shearing force to the carboxyalkylated cellulose dispersion. In particular, for efficient defibration, it is preferable to use a wet high-pressure or ultrahigh-pressure homogenizer that can apply a pressure of 50 MPa or more to the dispersion and can apply a strong shearing force. The pressure is more preferably 100 MPa or more, and further preferably 140 MPa or more. Further, prior to defibration and dispersion treatment with a high-pressure homogenizer, if necessary, the dispersion may be pretreated using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer. .

  High-pressure homogenizer is emulsified and dispersed by total energy such as collision between particles and shear force due to pressure difference by pressurizing (high pressure) the fluid with a pump and ejecting it from a very delicate gap provided in the flow path. , A device that performs de-pulverization, pulverization, and ultra-miniaturization.

  By defibrating the above carboxyalkylated cellulose, carboxyalkylated cellulose nanofibers having an average fiber diameter of 3 to 500 nm and an aspect ratio of 50 or more can be obtained. The average fiber diameter is preferably 3 to 150 nm, more preferably 3 to 20 nm, further preferably 5 to 19 nm, and further preferably 5 to 15 nm.

The average fiber diameter and average fiber length of the carboxyalkyl cellulose or carboxyalkyl cellulose nanofibers are atomic force microscope (AFM) when the diameter is 20 nm or less, and field emission scanning electron microscope (FE) when the diameter is 20 nm or more. -SEM) can be measured by analyzing 200 randomly selected fibers and calculating the average. Also, the aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length / average fiber diameter.

  The degree of carboxyalkyl substitution in the nanofibers of carboxyalkylated cellulose is usually the same as the degree of carboxyalkyl substitution in the carboxyalkylated cellulose prior to nanofibers. Moreover, the ratio of the I-type crystal in the carboxyalkyl cellulose nanofiber is usually the same as that in the carboxyalkyl cellulose before the nanofiber.

  By defibrating the carboxyalkylated cellulose obtained by the method of the present invention into nanofibers, a highly transparent carboxyalkylated cellulose cellulose nanofiber dispersion can be obtained. The carboxyalkyl cellulose nanofibers obtained by the present invention have, for example, an aqueous dispersion having a solid content of 1% (w / v) and a transparency (660 nm light transmittance) of 50% or more. More preferably, it is 60% or more, More preferably, it is 70% or more, More preferably, it is 80% or more, More preferably, it is 90% or more. Such cellulose nanofibers can be optimally used for applications requiring transparency. In the present invention, such highly transparent cellulose nanofibers can be produced with a high effective utilization rate of the carboxyalkylating agent (that is, economically without greatly increasing the amount of the carboxyalkylating agent). it can.

  The reason why a highly transparent cellulose nanofiber can be obtained economically by the production method of the present invention is not clear, but the production method of the present invention can maintain a relatively high degree of crystallinity of cellulose type I. Therefore, the present inventors have confirmed that the fibrous shape of carboxyalkylated cellulose can be maintained even with a relatively high degree of carboxyalkyl substitution. The ability to increase the degree of carboxyalkyl substitution while maintaining the fibrous shape (that is, introducing a large number of carboxyalkyl groups) is thought to lead to an improvement in the fibrillation property of carboxyalkylated cellulose, which is a highly transparent nanometer. It is speculated that this is one of the reasons why a fiber dispersion is obtained. However, there may be other reasons.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to these. In addition, unless otherwise indicated, a part and% show a mass part and mass%.
(Example 1)
Add 267 parts of water, 1089 parts of isopropanol (IPA), and 31 parts of sodium hydroxide in 200 parts of water to a 5 L biaxial kneader whose rotation speed is adjusted to 100 rpm. 200 parts of LBKP (made by Co., Ltd.) was charged in a dry mass when dried at 100 ° C. for 60 minutes. Mercerized cellulose was prepared by stirring and mixing at 30 ° C. for 60 minutes. Further, 90 parts of sodium monochloroacetate was added with stirring, and the mixture was stirred at 30 ° C. for 30 minutes, then heated to 70 ° C. over 30 minutes, and subjected to carboxymethylation reaction at 70 ° C. for 60 minutes. The ratio of water in the reaction medium during the mercerization reaction and the carboxymethylation reaction is 30% by mass. After completion of the reaction, the solution is neutralized, washed with 65% water-containing methanol, drained, dried and pulverized to obtain a sodium salt of carboxymethylated cellulose having a carboxymethyl substitution degree of 0.28 and a cellulose I type crystallinity of 70% Got. The effective utilization rate of the carboxymethylating agent was 45%. In addition, the measuring method of the carboxymethyl substitution degree and the crystallinity degree of cellulose I type, and the calculation method of the effective utilization factor of a carboxymethylating agent are as above-mentioned.

  The obtained sodium salt of carboxymethylated cellulose was dispersed in water to give a 1% (w / v) aqueous dispersion. This was treated three times with a 150 MPa high-pressure homogenizer to obtain a nanofiber dispersion of carboxymethylated cellulose. The transparency of the obtained dispersion was measured by the following method.

<Measurement of transparency of cellulose nanofiber dispersion>
The transparency (660 nm light transmittance) of the cellulose nanofiber dispersion (solid content 1% (w / v), dispersion medium: water) was measured using a UV-VIS spectrophotometer UV-1800 (Shimadzu Corporation). did.

(Example 2)
First, 267 parts of water, 467 parts of IPA, and 40 parts of sodium hydroxide were dissolved in 200 parts of water to perform a mercerization reaction, and instead of 90 parts of sodium monochloroacetate. A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that 117 parts of sodium monochloroacetate was added to carry out a carboxymethylation reaction. The ratio of water in the reaction medium during the mercerization reaction and the carboxymethylation reaction is 50% by mass. The sodium salt of the obtained carboxymethylated cellulose had a carboxymethyl substitution degree of 0.31, a crystallinity of cellulose type I of 69%, and an effective utilization rate of the carboxymethylating agent was 38%. The obtained sodium salt of carboxymethylated cellulose was defibrated in the same manner as in Example 1 to obtain a dispersion of carboxymethylated cellulose nanofibers.

(Example 3)
First, 200 parts of IPA was added instead of 467 parts of IPA to the biaxial kneader to perform a mercerization reaction, and 267 parts of IPA was added together with 117 parts of sodium monochloroacetate during the carboxymethylation reaction. Thus, a sodium salt of carboxymethylated cellulose was obtained. The ratio of water in the solvent during the mercerization reaction is 70% by mass, and the ratio of water in the solvent during the carboxymethylation reaction is 50% by mass. The sodium salt of the obtained carboxymethylated cellulose had a carboxymethyl substitution degree of 0.28, a crystallinity of cellulose type I of 64%, and an effective utilization rate of the carboxymethylating agent of 34%. The obtained sodium salt of carboxymethylated cellulose was defibrated in the same manner as in Example 2 to obtain a dispersion of carboxymethylated cellulose nanofibers.

Example 4
First, a mercerization reaction was carried out by adding 52 parts of IPA instead of 467 parts of IPA to the biaxial kneader, and 415 parts of IPA was added together with 117 parts of sodium monochloroacetate during the carboxymethylation reaction. Thus, a sodium salt of carboxymethylated cellulose was obtained. The ratio of water in the solvent during the mercerization reaction is 90% by mass, and the ratio of water in the solvent during the carboxymethylation reaction is 50% by mass. The sodium salt of the obtained carboxymethylated cellulose had a carboxymethyl substitution degree of 0.28, a cellulose I type crystallinity of 69%, and an effective utilization rate of the carboxymethylating agent of 34%. The obtained sodium salt of carboxymethylated cellulose was defibrated in the same manner as in Example 1 to obtain a dispersion of carboxymethylated cellulose nanofibers.

(Example 5)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 2 except that 467 parts of IPA were not added during the mercerization reaction and 467 parts of IPA were added during the carboxymethylation reaction. The ratio of water in the solvent during the mercerization reaction is 100% by mass, and the ratio of water in the solvent during the carboxymethylation reaction is 50% by mass. The sodium salt of the obtained carboxymethylated cellulose had a carboxymethyl substitution degree of 0.28, a crystallinity of cellulose type I of 66%, and an effective utilization rate of the carboxymethylating agent of 34%. The obtained sodium salt of carboxymethylated cellulose was defibrated in the same manner as in Example 1 to obtain a dispersion of carboxymethylated cellulose nanofibers.

(Example 6)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 5 except that the amount of IPA added during the carboxymethylation reaction was changed to 80% by mass of the water during the carboxymethylation reaction. The degree of carboxymethyl substitution was 0.20, the crystallinity of cellulose type I was 74%, and the effective utilization rate of the carboxymethylating agent was 24%. The obtained sodium salt of carboxymethylated cellulose was defibrated in the same manner as in Example 1 to obtain a dispersion of carboxymethylated cellulose nanofibers.

(Example 7)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 5 except that the amount of IPA added during the carboxymethylation reaction was changed to 70% by mass of the water during the carboxymethylation reaction. The degree of carboxymethyl substitution was 0.24, the crystallinity of cellulose type I was 73%, and the effective utilization rate of the carboxymethylating agent was 29%. The obtained sodium salt of carboxymethylated cellulose was defibrated in the same manner as in Example 1 to obtain a dispersion of carboxymethylated cellulose nanofibers.

(Example 8)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 5 except that the amount of IPA added during the carboxymethylation reaction was changed to 10% by mass of the water during the carboxymethylation reaction. The degree of carboxymethyl substitution was 0.24, the crystallinity of cellulose type I was 73%, and the effective utilization rate of the carboxymethylating agent was 29%. The obtained sodium salt of carboxymethylated cellulose was defibrated in the same manner as in Example 1 to obtain a dispersion of carboxymethylated cellulose nanofibers.

(Comparative Example 1)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 2 except that the ratio of the solvent initially added to the biaxial kneader was 10% by mass of water and 90% by mass of IPA. The degree of carboxymethyl substitution was 0.27, the crystallinity of cellulose type I was 64%, and the effective utilization rate of the carboxymethylating agent was 32%. The obtained sodium salt of carboxymethylated cellulose was defibrated in the same manner as in Example 1 to obtain a dispersion of carboxymethylated cellulose nanofibers.

(Comparative Example 2)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 5 except that IPA was not added during the carboxymethylation reaction. The degree of carboxymethyl substitution was 0.11, the degree of crystallinity of cellulose type I was 72%, and the effective utilization rate of the carboxymethylating agent was 13%. The obtained sodium salt of carboxymethylated cellulose was defibrated in the same manner as in Example 1 to obtain a dispersion of carboxymethylated cellulose nanofibers.

(Comparative Example 3)
Sodium monochloroacetate was used as a carboxymethylating agent in the carboxymethylation reaction by using 90 parts of sodium hydroxide dissolved in 200 parts of water instead of 40 parts of sodium hydroxide dissolved in 200 parts of water during the mercerization reaction. A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Comparative Example 2 except that 293 parts of sodium monochloroacetate was used instead of 117 parts. The degree of carboxymethyl substitution was 0.28, the crystallinity of cellulose type I was 45%, and the effective utilization rate of the carboxymethylating agent was 13%. The obtained sodium salt of carboxymethylated cellulose was defibrated in the same manner as in Example 1 to obtain a dispersion of carboxymethylated cellulose nanofibers.

  From the results of Table 1, in Examples 1 to 8 in which mercerization was performed in a solvent containing 15% by mass or more of water and carboxymethylation was performed in a mixed solvent of water and an organic solvent, cellulose nanofibers having high transparency It can be seen that a dispersion can be produced. On the other hand, in Comparative Example 1 (conventional solvent method) in which both mercerization and carboxymethylation were performed in a high concentration organic solvent (IPA 90 mass%), the transparency when the cellulose nanofiber dispersion was obtained may be low. Recognize. Further, in Comparative Examples 2 and 3 (conventional aqueous medium method) in which both mercerization and carboxymethylation were performed using water as a solvent, the amounts of mercerizing agent and carboxymethylating agent were equivalent to those of the solvent method. Then, it turns out that the transparency of a cellulose nanofiber dispersion becomes low, and a carboxymethyl substitution degree also becomes low (comparative example 2). On the other hand, increasing the degree of carboxymethyl substitution by increasing the addition amount of mercerizing agent and carboxymethylating agent increases the transparency of the cellulose nanofiber dispersion, but the effective utilization rate of the carboxymethylating agent is It turns out that it becomes significantly low compared with 1-8, and the crystallinity degree of a cellulose I type becomes low (comparative example 3).

Claims (8)

Treating cellulose with mercerizing agent to obtain mercerized cellulose; and reacting mercerized cellulose with carboxyalkylating agent to obtain carboxyalkylated cellulose;
And the step of obtaining mercerized cellulose is carried out under a temperature condition of less than 50 ° C. under a solvent containing 15% by mass or more of water, and the step of obtaining carboxyalkylated cellulose is carried out under a mixed solvent of water and an organic solvent. A process for producing carboxyalkylated cellulose, as described in 1).   The method of claim 1, wherein the carboxyalkylated cellulose is carboxymethylated cellulose and the degree of carboxymethyl substitution per anhydroglucose unit in the carboxymethylated cellulose is less than 0.50.   The method according to claim 1 or 2, wherein the crystallinity of cellulose type I of the carboxyalkylated cellulose is 50% or more.   The method according to any one of claims 1 to 3, wherein the mercerizing agent is sodium hydroxide, lithium hydroxide, potassium hydroxide, or a combination of two or more thereof.   The method according to any one of claims 1 to 4, wherein the carboxyalkylating agent is monochloroacetic acid or sodium monochloroacetate.   The method according to any one of claims 1 to 5, wherein the mixed solvent in the step of obtaining carboxyalkylated cellulose is a solvent containing 20 to 99% by mass of an organic solvent.   The method according to any one of claims 1 to 6, wherein the organic solvent is isopropanol, methanol, ethanol, acetone, or a combination of two or more thereof. The manufacturing method of the nanofiber of a carboxyalkylated cellulose including defibrating the carboxyalkylated cellulose obtained by the method of any one of Claims 1-7.