JP2019099758A - Production method of carboxymethylated cellulose nanofiber - Google Patents

Abstract

To provide a novel production method of carboxymethylated cellulose capable of economically obtaining a cellulose nanofiber dispersion with high transparency.SOLUTION: In carboxymethylation of cellulose, mercerization is performed under a solvent mainly made of water, thereafter, the carboxymethylation is performed under a mixed solvent of water and an organic solvent. When the obtained carboxymethylated cellulose is fibrillated, a nanofiber dispersion of the carboxymethylated cellulose having high transparency can be economically obtained.SELECTED DRAWING: None

Description

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

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

  Generally as a manufacturing method of a carboxymethylated cellulose, after processing a cellulose (merization) with an alkali, it processes (it is called carboxymethylation also called etherification) with an etherifying agent (it is also called a carboxymethylation agent). Methods are known, wherein both mercerization and carboxymethylation are carried out with water as a solvent, and both mercerization and carboxymethylation are carried out under organic solvent or mixed solvent of organic solvent and water ( Patent Document 2) is known, the former being called the "water medium method" and the latter being called the "solvent method".

  As a method for producing cellulose nanofibers having a nanoscale fiber diameter, not only mechanical disintegration of carboxymethylated cellulose, but also mechanical disintegration of cellulose having a carboxyl group introduced (Patent Document 3) . It is known that the aqueous dispersion of cellulose nanofibers obtained by disentanglement of such carboxyl group-introduced cellulose is highly transparent, but obtained by disentanglement of carboxymethylated cellulose obtained by the solvent method The aqueous dispersion of cellulose nanofibers was lower in transparency than the aqueous dispersion of cellulose nanofibers obtained by defibration of cellulose having a carboxyl group introduced. In addition, an aqueous dispersion of cellulose nanofibers obtained by disaggregation of carboxymethylated cellulose obtained by the water medium method uses a large amount of a drug such as a mercerizing agent or a carboxymethylating agent to enhance transparency. Needs, and there are major manufacturing and economic issues. Since transparent materials are suitable for various applications, it is required to make cellulose nanofibers transparent. Especially, carboxymethylated cellulose is a material with high safety, so transparency using carboxymethylated cellulose is required. 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 the present invention is to provide a novel method for producing carboxymethylated cellulose which can obtain a transparent cellulose nanofiber dispersion.

  As a result of intensive investigations for the above object, the present inventors conducted mercerization (alkali treatment of cellulose) in the carboxymethylation of cellulose under a solvent mainly composed of water and then carboxylation (etherification). ) In a mixed solvent of water and an organic solvent, the conventional water medium method (a method in which both mercerization and carboxylation are performed using water as a solvent) or a solvent method (mercelization and carboxylation) Method of carrying out both under the organic solvent or the mixed solvent of water and the organic solvent), the cellulose nanofiber dispersion having a very high transparency when disintegrated as compared to the carboxymethylated cellulose obtained by It has been found that it can be economically produced at a high effective utilization rate of the agent.

The present invention includes, but is not limited to, the following.
(1) treating cellulose with a mercerizing agent to obtain mercerized cellulose, and reacting mercerized cellulose with a carboxymethylating agent to obtain carboxymethylated cellulose,
A method for producing carboxymethylated cellulose, comprising the steps of: obtaining a mercerized cellulose under a solvent mainly comprising water; and obtaining the carboxymethylated cellulose under a mixed solvent of water and an organic solvent.
(2) The method according to (1), wherein the solvent mainly comprising water in the step of obtaining mercerized cellulose is a solvent containing water at a ratio higher than 50% by mass.
(3) The method according to (2), wherein the water-based solvent in the step of obtaining mercerized cellulose is water.
(4) The method according to any one of (1) to (3), wherein the effective utilization rate of the carboxymethylating agent is 15% or more.
(5) The method according to any one of (1) to (4), wherein the mercerizing agent is sodium hydroxide, lithium hydroxide, potassium hydroxide, or a combination of two or more thereof.
(6) The method according to any one of (1) to (5), wherein the carboxymethylating agent is monochloroacetic acid or sodium monochloroacetate.
(7) The method according to any one of (1) to (6), wherein the mixed solvent in the step of obtaining carboxymethylated cellulose is a solvent containing 20 to 99% by mass of an organic solvent.
(8) The method according to any one of (1) to (7), wherein the organic solvent is isopropanol, methanol, ethanol, acetone, or a combination of two or more thereof.
(9) The method according to any one of (1) to (8), wherein the degree of carboxymethyl substitution per anhydroglucose unit in carboxymethylated cellulose is less than 0.50.
(10) The method according to any one of (1) to (9), wherein the crystallinity of cellulose type I of carboxymethylated cellulose is 50% or more.
The manufacturing method of the nanofiber of carboxymethylated cellulose including disentanglement of the carboxymethylated cellulose obtained by the method as described in any one of (11) (1)-(10).

  According to the method of the present invention, carboxymethylated cellulose capable of obtaining a dispersion of cellulose nanofibers having high transparency when defibrated can be produced at a high effective utilization rate of a carboxymethylating agent.

  The present invention is a method of producing carboxymethylated cellulose. Carboxymethylated cellulose has a structure in which a part of the hydroxyl groups in the glucose residue constituting the cellulose is ether-bonded to a carboxymethyl group. The carboxymethylated cellulose may be in the form of a salt, and examples of the carboxymethylated cellulose salt include metal salts such as carboxymethylcellulose sodium salt and the like.

  In general, after carboxymethylated cellulose is treated (mercified) with alkali, the resulting mercerized cellulose (also referred to as alkali cellulose) is reacted with a carboxymethylating agent (also referred to as an etherifying agent). Can be manufactured by

<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 from which non-crystalline regions are removed, and the like from the origin, production method and the like. In the present invention, any of these celluloses can be used as a raw material of 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. Also, the method for producing the bleached pulp or the unbleached pulp is not particularly limited, and a mechanical method, a chemical method, or a method combining two in between may be used. Examples of bleached pulp or unbleached pulp classified according to the production method include mechanical pulp (thermomechanical pulp (TMP), ground pulp), chemical pulp (softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP) Etc., softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), kraft pulp such as hardwood bleached kraft pulp (LBKP), and the like. Furthermore, dissolving pulp may be used besides paper pulp. The dissolved pulp is a chemically refined pulp, which is mainly used dissolved in chemicals, and is a main raw material for man-made fibers, cellophane and the like.

As regenerated cellulose, what melt | dissolved cellulose in some solvent, such as a copper ammonia solution, a cellulose xanthate solution, and a morpholine derivative, and was spun again is illustrated.
Fine cellulose can be obtained by depolymerizing (for example, acid hydrolysis, alkali hydrolysis, enzymatic decomposition, explosion treatment, vibration ball milling, etc.) of a cellulose-based material including the above natural cellulose and regenerated cellulose. And those obtained by mechanically processing the cellulose-based material are exemplified.

Mercerization
The cellulose described above is used as a raw material, and a mercerizing agent (alkali) is added to obtain mercerized cellulose (also referred to as alkali cellulose). In the present invention, cellulose is used as a solvent in this mercerization reaction, and cellulose having very high transparency when disintegrated by using a mixed solvent of an organic solvent and water in the subsequent carboxymethylation. Carboxymethylated cellulose that can be made into a nanofiber dispersion can be obtained economically.

  The term “water mainly used as a solvent (water-based solvent)” refers to a solvent containing water at a ratio higher than 50% by mass. The water content in the solvent mainly containing water is preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more, and further Preferably it is 90 mass% or more, More preferably, it is 95 mass% or more. Particularly preferably, the solvent mainly comprising water is 100% by weight of water (that is, water). As the proportion of water at the time of mercerization increases, the transparency of the cellulose nanofiber dispersion obtained by disaggregating carboxymethylated cellulose increases. Examples of solvents other than water (used in combination with water) in a solvent mainly composed of water include organic solvents used as a solvent in the subsequent carboxymethylation. For example, alcohols such as methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, ketones such as acetone, diethyl ketone and methyl ethyl ketone, and dioxane, diethyl ether, benzene, dichloromethane These can be used alone or as a mixture of two or more thereof in water in an amount of less than 50% by mass and used as a solvent for mercerization. The organic solvent in the solvent mainly containing water is preferably 45% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, and further preferably 20% by mass or less. More preferably, it is 10 mass% or less, More preferably, it is 5 mass% or less, More preferably, it is 0 mass%.

  Examples of the mercerizing agent include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide, and any one or two or more of them can be used in combination. The mercerizing agents are not limited to these, but, for example, 1 to 60% by mass, preferably 2 to 45% by mass, more preferably 3 to 25% by mass of these alkali metal hydroxides are added to the reactor as an aqueous solution. It can be added. In one embodiment, the amount of the mercerizing agent used is preferably 0.1 mol or more and 2.5 mol or less, more preferably 0.3 mol or more and 2.0 mol or less, with respect to 100 g of cellulose (absolutely dry) It is more preferable that it is 0.4 mol or more and 1.5 mol or less.

  The amount of the solvent mainly containing water at the time of mercerization is not particularly limited as long as it allows stirring and mixing of the raw material, but 1.5 to 20 times by mass is preferable with respect to the cellulose raw material, and 2 to 10 More preferably, it is mass-folded.

  In the mercerization treatment, the base material (cellulose) is mixed with a solvent mainly containing water, and the temperature of the reactor is adjusted to 0 to 70 ° C., preferably 10 to 60 ° C., more preferably 10 to 40 ° C. Then, an aqueous solution of mercerizing agent is added, and stirring is performed for 15 minutes to 8 hours, preferably 30 minutes to 7 hours, more preferably 30 minutes to 3 hours. This gives mercerized cellulose (alkali cellulose).

  The pH for mercerization is preferably 9 or more, which allows the mercerization reaction to proceed. The pH is more preferably 11 or more, further preferably 12 or more, and may be 13 or more. The upper limit of pH is not particularly limited.

  The mercerization can be carried out using a reactor capable of mixing and stirring the above-mentioned components while controlling the temperature, and various reactors conventionally used for the mercerization reaction can be used. For example, a batch-type stirring apparatus in which two shafts are stirred and the above-described components are mixed is preferable from the viewpoints of uniform mixing and productivity.

<Carboxymethylation>
Carboxymethylated cellulose is obtained by adding a carboxymethylating 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 carboxymethylation reaction. Cellulose nanofiber dispersion having very high transparency when disintegrated by using as a solvent mainly composed of water in mercerization and using a mixed solvent of water and an organic solvent in carboxymethylation It is possible to economically obtain carboxymethylated cellulose which can be

  Examples of the carboxymethylating agent include monochloroacetic acid, sodium monochloroacetate, methyl monochloroacetate, ethyl monochloroacetate, isopropyl monochloroacetate and the like. Among these, monochloroacetic acid or sodium monochloroacetate is preferable in terms of availability of raw materials. The carboxymethylating agent is preferably added in the range of 0.5 to 1.5 moles 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 carboxymethylating agent can be added to the reactor as an aqueous solution of, for example, 5 to 80% by mass, more preferably 30 to 60% by mass, but is not limited thereto, does not dissolve, and is added in powder form It can also be done.

  The molar ratio of the mercerizing agent to the carboxymethylating agent (merceling agent / carboxymethylating agent) is generally 0.9 to 2.45 when monochloroacetic acid or sodium monochloroacetate is used as the carboxymethylating agent. Will be adopted. The reason is that if it is less than 0.9, the carboxymethylation reaction may be insufficient, and unreacted monochloroacetic acid or sodium monochloroacetate may be left to waste, and 2.45. If the ratio is more than that, the side reaction by the excess mercerizing agent and monochloroacetic acid or sodium monochloroacetate may proceed to form an alkali metal glycolate, which may be uneconomical.

  In the present invention, the effective utilization rate of the carboxymethylating agent is preferably 15% or more. More preferably, it is 20% or more, further preferably 25% or more, and particularly preferably 30% or more. The effective utilization rate of the carboxymethylating agent refers to the ratio of the carboxymethyl group introduced to the cellulose to the carboxymethyl group in the carboxymethylating agent. In the present invention, a solvent mainly containing water is used in mercerization, and a mixed solvent of water and an organic solvent is used in carboxymethylation, so that the effective utilization rate of the carboxymethylating agent can be achieved (ie, It is possible to produce carboxymethylated cellulose which can be obtained economically and cellulose nanofiber dispersion having high transparency when defibrated, without significantly increasing the amount of the carboxymethylating agent used. The upper limit of the effective utilization rate of the carboxymethylating agent is not particularly limited, but practically the upper limit is about 80%. The effective utilization rate of the carboxymethylating agent may be abbreviated as AM.

The calculation method of the effective utilization rate of the carboxymethylating agent is as follows:
AM = (DS x number of moles of cellulose) / number of moles of carboxymethylating agent DS: Degree of substitution of carboxymethyl (the method of measurement 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 per glucose unit of cellulose).

  The concentration of the cellulose raw material in the carboxymethylation reaction is not particularly limited, but is preferably 1 to 40% (w / v) from the viewpoint of enhancing the effective utilization rate of the carboxymethylating agent.

  Simultaneously with the addition of the carboxymethylating agent, or before or immediately after the addition of the carboxymethylating agent, an organic solvent or an aqueous solution of the organic solvent is appropriately added to the reactor, or water other than water at the mercerization treatment by reduced pressure or the like. The organic solvent and the like are appropriately reduced to form a mixed solvent of water and the organic solvent. In the present invention, the carboxymethylation reaction is allowed to proceed in the mixed solvent of water and an organic solvent. The timing of addition or reduction of the organic solvent may be from the end of the mercerization reaction to immediately after the addition of the carboxymethylating agent, and is not particularly limited. For example, 30 minutes before and after adding the carboxymethylating agent Within is preferable.

  As the organic solvent, alcohols such as methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, ketones such as acetone, diethyl ketone, methyl ethyl ketone and the like, dioxane, diethyl ether, Benzene, dichloromethane, etc. can be mentioned, and these single or 2 or more types of mixtures can be added to water, and can be used as a solvent in carboxymethylation. Among these, C1-C4 monohydric alcohol is preferable, and C1-C3 monohydric alcohol is more preferable, since compatibility with water is excellent.

  The proportion of the organic solvent in the mixed solvent at the time of carboxymethylation is preferably 20 to 99% by mass with respect to the total of water and the organic solvent, and more preferably 30 to 99% by mass. The content is preferably 40 to 99% by mass, and more preferably 45 to 99% by mass.

  The reaction medium for carboxymethylation (a mixed solvent of water and an organic solvent, etc. not containing cellulose) has a lower proportion of water than the reaction medium for mercerization (in other words, the proportion of organic solvent is Many) is preferable. By satisfying this range, it becomes easy to increase the degree of carboxymethyl substitution while maintaining the crystallinity of the resulting carboxymethylated cellulose, and the carboxymethylated cellulose which becomes a highly transparent cellulose nanofiber dispersion when disintegrated Can be obtained more efficiently. When the reaction medium in the case of carboxymethylation has a lower proportion of water (the proportion of the organic solvent is larger) than the reaction medium in the case of mercerization, when transitioning from the mercerization reaction to the carboxymethylation reaction, The advantage is also obtained that the mixed solvent for the carboxymethylation reaction can be formed by a simple means of adding a desired amount of organic solvent to the reaction system after completion of the mercerization reaction.

  After a mixed solvent of water and an organic solvent is formed and a carboxymethylating agent is added to the 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 minute to 1 hour. The mixing of the liquid containing mercerized cellulose and the carboxymethylating agent is preferably carried out in multiple times or by dropwise addition to prevent the reaction mixture from becoming hot. After adding a carboxymethylating agent and stirring for a fixed time, the temperature is raised if necessary, and the reaction temperature is set to 30 to 90 ° C., preferably 40 to 90 ° C., more preferably 60 to 80 ° C., for 30 minutes to The etherification (carboxymethylation) reaction is carried out for 10 hours, preferably 1 to 4 hours to obtain carboxymethylated cellulose.

  In the case of carboxymethylation, the reactor used in mercerization may be used as it is, or another reactor capable of mixing and stirring the above-mentioned 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. In addition, if necessary, by-produced inorganic salts, organic acid salts and the like may be washed and removed with water-containing methanol, dried, pulverized and classified to give carboxymethylated cellulose or a salt thereof. As an apparatus used for dry grinding, an impact type mill such as a hammer mill and a pin mill, a medium mill such as a ball mill and a tower mill, and a jet mill are exemplified. As an apparatus used by wet grinding, apparatuses, such as a homogenizer, a mass colloider, and a pearl mill, are illustrated.

<Carboxymethylated cellulose>
The carboxymethylated cellulose produced in the present invention is preferably one in which at least a part of the fibrous form is maintained even when dispersed in water. That is, when an aqueous dispersion of carboxymethylated cellulose is observed with an electron microscope, fibrous substances can be observed, and when carboxymethylated cellulose is measured by X-ray diffraction, peaks of cellulose type I crystals are observed. What can be done is preferred.

  Carboxymethylated cellulose, which retains at least a part of its fibrous form when dispersed in water, has a degree of carboxymethyl substitution of less than 0.50 per anhydroglucose unit of cellulose. When the degree of substitution is 0.50 or more, dissolution in water is likely to occur, and the fiber form can not be maintained. In consideration of operability, the substitution degree is particularly preferably 0.02 to 0.50, more preferably 0.05 to 0.50, and still more preferably 0.10 to 0.40. And 0.20 to 0.40. By introducing a carboxymethyl group into cellulose, the celluloses are electrically repelled to be able to disintegrate into nanofibers, but the degree of carboxymethyl substitution per anhydroglucose unit is 0.02 or more If the size is small, disintegration into nanofibers may not be sufficient. The degree of carboxymethyl substitution can be adjusted by controlling the amount of the carboxymethylating agent to be reacted, the amount of the mercerizing agent, the composition ratio of water to the organic solvent, and the like.

  In the present invention, the anhydroglucose unit means individual anhydroglucose (glucose residue) constituting cellulose. In addition, the degree of carboxymethyl substitution (also referred to as the degree of etherification) means the ratio of the hydroxyl groups in the glucose residues constituting the cellulose to those substituted with a carboxymethyl ether group (carboxymethyl per glucose residue) The number of ether groups is shown. The carboxymethyl substitution degree may be abbreviated as DS.

The method for measuring the degree of carboxymethyl substitution is as follows:
Approximately 2.0 g of the sample is precisely weighed and placed in a 300 mL stoppered Erlenmeyer flask. 100 mL of a solution obtained by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol nitrate is added, and shaken for 3 hours to convert a salt of carboxymethylated cellulose (CMC) into H-CMC (hydrogenated carboxymethylated cellulose). The 1.5 to 2.0 g of the absolute-dried H-CMC is precisely weighed and placed in a 300 mL stoppered Erlenmeyer flask. 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. The excess NaOH is back titrated with 0.1 N H ₂ SO ₄ using phenolphthalein as an indicator, and the degree of carboxymethyl substitution (DS value) is calculated by the following formula.
A = [(100 x F '-0.1 N H ₂ SO ₄ (mL) x F) x 0.1] / (absolute dry mass of H-CMC (g))
Carboxymethyl 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 carboxymethylated cellulose fiber of the present invention is preferably 50% or more, more preferably 60% or more of crystalline Form I. When the crystallinity is adjusted to the above range, the transparency of the cellulose nanofiber dispersion obtained by defibration is improved. The crystallinity of the cellulose can be controlled by the concentration of mercerizing agent and the temperature at the time of treatment, as well as the degree of carboxymethylation. Because mercerization and carboxymethylation use a high concentration of alkali, type I crystals of cellulose are easily converted to type II, but modification of the cellulose by modifying the amount of alkali (merceling agent) used, etc. By adjusting the degree, desired crystallinity can be maintained.

The method of measuring the crystallinity of cellulose type I of carboxymethylated cellulose is as follows:
The sample is placed on a glass cell, and measurement is performed using an X-ray diffraction measurement apparatus (LabX XRD-6000, manufactured by Shimadzu Corporation). Calculation of the degree of crystallinity is carried out using the method of Segal et al. With the diffraction intensity at 2θ = 10 ° to 30 ° of the X-ray diffraction pattern as a baseline, the diffraction intensity of the 002 plane at 2θ = 22.6 ° and 2θ = It is calculated by the following equation from the diffraction intensity of the amorphous part at 18.5 °.

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

  Although the carboxymethylated cellulose produced according to the present invention can be used in the form of a dispersion obtained after the reaction, it can also be used after being dried and redispersed in water, if necessary. The drying method is not limited at all, but, for example, freeze drying method, spray drying method, tray type drying method, drum drying method, belt drying method, a method of thinly extending and drying on a glass plate, fluid bed drying method, microwave drying A known method such as a method, a heating fan type reduced pressure drying method can be used. After drying, if necessary, it may be crushed by a cutter mill, a hammer mill, a pin mill, a jet mill or the like. Also, the method of redispersion in water is not particularly limited, and known dispersion devices can be used.

<Production of Carboxymethylated Cellulose Nanofibers>
By disentanglement of the carboxymethylated cellulose obtained by the method of the present invention, it can be converted to cellulose nanofibers having a nanoscale fiber diameter. The nanofibers of carboxymethylated cellulose obtained by the method of the present invention can be economically produced as compared to the nanofibers of carboxymethylated cellulose obtained by the conventional aqueous medium method or solvent method, and an aqueous dispersion In the state of, it has high transparency.

  At the time of disintegration, a dispersion of carboxymethylated cellulose obtained by the above method is prepared. The dispersion medium is preferably water because of easy handling. The concentration of carboxymethylated cellulose is preferably 0.01 to 10% (w / v) in consideration of the efficiency of disintegration and dispersion.

  The device used for defibrillation of carboxymethylated cellulose is not particularly limited, but devices such as high-speed rotation type, colloid mill type, high pressure type, roll mill type and ultrasonic type can be used. It is preferable to apply strong shearing force to the dispersion of carboxymethylated cellulose at the time of disintegration. In particular, in order to disintegrate efficiently, it is preferable to use a wet high pressure or ultra high pressure homogenizer capable of applying a pressure of 50 MPa or more to the dispersion and applying a strong shearing force. The pressure is more preferably 100 MPa or more, still more preferably 140 MPa or more. In addition, prior to disintegration and dispersion treatment with a high-pressure homogenizer, the dispersion may be subjected to pretreatment, if necessary, using a known mixing, stirring, emulsifying, and dispersing apparatus such as a high-speed shear mixer. .

  A high-pressure homogenizer is a pump that pressurizes a fluid (high pressure) and ejects it from a very fine gap provided in the flow path to emulsify and disperse it by integrated energy such as collision between particles and shear force due to pressure difference. , Defibrillation, pulverization, and ultra-refining.

  By disentanglement of the above-mentioned carboxymethylated cellulose, nanofibers of carboxymethylated cellulose 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 still more preferably 5 to 15 nm.

The average fiber diameter and average fiber length of carboxymethylated cellulose or carboxymethylated cellulose nanofibers are atomic force microscopy (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 used to analyze 200 randomly selected fibers and calculate the average. Also, the aspect ratio can be calculated by the following equation:
Aspect ratio = average fiber length / average fiber diameter.

  The degree of carboxymethyl substitution in the nanofibers of carboxymethylated cellulose is generally the same as the degree of carboxymethyl substitution in carboxymethylated cellulose prior to the nanofibers. Also, the proportion of type I crystals in carboxymethylated cellulose nanofibers is usually the same as in carboxymethylated cellulose before being made into nanofibers.

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

  Although the reason why the process of the present invention can obtain highly transparent cellulose nanofibers by an economical method is not clear, according to the process of the present invention, it is possible to maintain relatively high crystallinity of cellulose type I Therefore, the present inventors have confirmed that the fibrous shape of carboxymethylated cellulose can be maintained even if the degree of carboxymethyl substitution is relatively high. Being able to increase the degree of carboxymethyl substitution (that is, introduce a large amount of carboxymethyl groups) while maintaining the fibrous shape is considered to lead to the improvement of the disaggregation properties of carboxymethylated cellulose, which is a highly transparent nano It is presumed to be one of the reasons for obtaining a fiber dispersion. However, there may be other reasons.

Hereinafter, the present invention will be more specifically described by way of examples and comparative examples, but the present invention is not limited to these. In addition, unless otherwise indicated, part and% show a mass part and mass%.
Example 1
In a twin-screw kneader whose rotational speed was adjusted to 100 rpm, 130 parts of water and 20 parts of sodium hydroxide dissolved in 100 parts of water were added, and hardwood pulp (manufactured by Nippon Paper Industries Co., Ltd., LBKP) at 100.degree. 100 parts by dry weight when dried for a minute were charged. The mixture was stirred at 30 ° C. for 90 minutes and mixed to prepare mercerized cellulose. Further, while stirring, 230 parts of isopropanol (IPA) and 60 parts of sodium monochloroacetate were added and stirred for 30 minutes, and then the temperature was raised to 70 ° C. to perform a carboxymethylation reaction for 90 minutes. The concentration of IPA in the reaction medium at the time of the carboxymethylation reaction is 50%. After completion of the reaction, the reaction solution was neutralized, drained, dried and pulverized to obtain a carboxymethylated cellulose sodium salt having a degree of carboxymethyl substitution of 0.31 and a degree of crystallinity of cellulose type I of 67%. The effective utilization rate of the carboxymethylating agent was 37%. The methods for measuring the degree of carboxymethyl substitution and the degree of crystallinity of cellulose type I, and the method for calculating the effective utilization of a carboxymethylating agent are as described above.

  The sodium salt of carboxymethyl cellulose thus obtained 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 dispersion of carboxymethylated cellulose nanofibers. The transparency and the viscosity of the obtained dispersion were measured by the following method.

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

<Measurement of viscosity>
A cellulose nanofiber dispersion (solid content 1% (w / v), dispersion medium: water) is allowed to stand for 16 hours and then stirred at 3000 rpm for 1 minute using a stirrer to make a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) No. The viscosity after 3 minutes was measured at 4 rotors / rotation speed 60 rpm or 6 rpm.

(Example 2)
The sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the concentration of IPA in the reaction solution at the time of the carboxymethylation reaction was changed to 90% by changing the addition amount of IPA. The degree of carboxymethyl substitution was 0.47, the degree of crystallinity of cellulose type I was 63%, and the effective utilization of the carboxymethylating agent was 56%.

The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.
(Example 3)
The solvent for the mercerization reaction was 90% water and IPA 10%, and the IPA concentration in the mixed solvent for carboxymethyl reaction was adjusted to 50% in the same manner as in Example 1 by changing the addition amount of IPA. Analogously to 1, the sodium salt of carboxymethylated cellulose was obtained. The degree of carboxymethyl substitution was 0.28, the degree of crystallinity of cellulose type I was 69%, and the effective utilization of the carboxymethylating agent was 34%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 4)
The experiment was conducted except that the solvent in the mercerization reaction was 70% water and IPA 30%, and the IPA concentration in the mixed solvent in the carboxymethylation reaction was adjusted to 50% as in Example 1 by changing the addition amount of IPA. The sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1. The degree of carboxymethyl substitution was 0.28, the degree of crystallinity of cellulose type I was 64%, and the effective utilization of the carboxymethylating agent was 34%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.
(Example 5)
The experiment was conducted except that the solvent in the mercerization reaction was 55% water and 45% IPA, and the IPA concentration in the mixed solvent in the carboxymethylation reaction was adjusted to 50% as in Example 1 by changing the addition amount of IPA. The sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1. The degree of carboxymethyl substitution was 0.28, the degree of crystallinity of cellulose type I was 66%, and the effective utilization of the carboxymethylating agent was 34%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 6)
A lithium salt of carboxymethyl cellulose was obtained in the same manner as in Example 1 except that lithium hydroxide was used in place of sodium hydroxide as the mercerizing agent. The degree of carboxymethyl substitution was 0.25, the degree of crystallinity of cellulose type I was 62%, and the effective utilization of the carboxymethylating agent was 30%. The obtained lithium salt of carboxymethylated cellulose was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethylated cellulose.

(Example 7)
A potassium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that potassium hydroxide was used in place of sodium hydroxide as the mercerizing agent. The degree of carboxymethyl substitution was 0.25, the degree of crystallinity of cellulose type I was 61%, and the effective utilization of the carboxymethylating agent was 30%. The potassium salt of carboxymethylated cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethylated cellulose.

(Example 8)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the organic solvent added at the time of the carboxymethylation reaction was changed from IPA to methanol. The degree of carboxymethyl substitution was 0.29, the degree of crystallinity of cellulose type I was 66%, and the effective utilization of the carboxymethylating agent was 35%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 9)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the organic solvent added during the carboxymethylation reaction was changed from IPA to ethanol. The degree of carboxymethyl substitution was 0.30, the degree of crystallinity of cellulose type I was 67%, and the effective utilization of the carboxymethylating agent was 36%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 10)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the organic solvent added during the carboxymethylation reaction was changed from IPA to acetone. The degree of carboxymethyl substitution was 0.26, the degree of crystallinity of cellulose type I was 63%, and the effective utilization of the carboxymethylating agent was 31%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 11)
Instead of dissolving 20 parts of sodium hydroxide in 100 parts of water in the mercerization reaction, using 40 parts of sodium hydroxide dissolved in 100 parts of water, sodium monochloroacetate as a carboxymethylating agent in the carboxymethylation reaction A sodium salt of carboxymethyl cellulose was obtained in the same manner as in Example 1 except that 50 parts of monochloroacetic acid was used instead of 60 parts. The degree of carboxymethyl substitution was 0.31, the degree of crystallinity of cellulose type I was 60%, and the effective utilization of the carboxymethylating agent was 36%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 12)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the concentration of IPA in the reaction solution at the time of the carboxymethylation reaction was changed to 30% by changing the addition amount of IPA. The degree of carboxymethyl substitution was 0.24, the degree of crystallinity of cellulose type I was 73%, and the effective utilization of the carboxymethylating agent was 29%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 13)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the concentration of IPA in the reaction solution at the time of the carboxymethylation reaction was changed to 20% by changing the addition amount of IPA. The degree of carboxymethyl substitution was 0.20, the degree of crystallinity of cellulose type I was 74%, and the effective utilization of the carboxymethylating agent was 24%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Comparative example 1)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the solvent in the carboxymethylation reaction was changed to 100% of water. The degree of carboxymethyl substitution was 0.11, the degree of crystallinity of cellulose type I was 72%, and the effective utilization of the carboxymethylating agent was 13%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Comparative example 2)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the solvent for the mercerization reaction was 10% of water and IPA 90%, and the solvent having the same composition was used also for the carboxymethylation reaction. The degree of carboxymethyl substitution was 0.27, the degree of crystallinity of cellulose type I was 64%, and the effective utilization of the carboxymethylating agent was 32%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Comparative example 3)
Instead of dissolving 20 parts of sodium hydroxide in 100 parts of water at the time of mercerization reaction, using 45 parts of sodium hydroxide dissolved in 100 parts of water, sodium monochloroacetate as a carboxymethylating agent at the time of carboxymethylation reaction A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Comparative Example 1 except that 150 parts of sodium monochloroacetate was used instead of 60 parts. The degree of carboxymethyl substitution was 0.28, the degree of crystallinity of cellulose type I was 45%, and the effective utilization of the carboxymethylating agent was 13%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

  From the results of Table 1, in Examples 1 to 13 in which mercerization was carried out in a solvent mainly composed of water and carboxymethylation was carried out in a mixed solvent of water and an organic solvent, the mercerization which is the conventional method is It can be seen that a cellulose nanofiber dispersion having a very high transparency can be produced as compared to Comparative Example 2 (solvent method) in which both carboxymethylation is performed in a solvent mainly containing an organic solvent. In addition, compared to Comparative Examples 1 and 3 in which both mercerization and carboxymethylation are performed using water as a solvent, a cellulose nanofiber dispersion having high transparency is produced at an effective utilization rate of a high carboxymethylation agent. It can be seen that

(Example 4)
The experiment was conducted except that the solvent in the mercerization reaction was 70% water and IPA 30%, and the IPA concentration in the mixed solvent in the carboxymethylation reaction was adjusted to 50% as in Example 1 by changing the addition amount of IPA. The sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1. The degree of carboxymethyl substitution was 0.28, the degree of crystallinity of cellulose type I was 64%, and the effective utilization of the carboxymethylating agent was 34%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose .

(Example 5 )
A lithium salt of carboxymethyl cellulose was obtained in the same manner as in Example 1 except that lithium hydroxide was used in place of sodium hydroxide as the mercerizing agent. The degree of carboxymethyl substitution was 0.25, the degree of crystallinity of cellulose type I was 62%, and the effective utilization of the carboxymethylating agent was 30%. The obtained lithium salt of carboxymethylated cellulose was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethylated cellulose.

(Example 6 )
A potassium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that potassium hydroxide was used in place of sodium hydroxide as the mercerizing agent. The degree of carboxymethyl substitution was 0.25, the degree of crystallinity of cellulose type I was 61%, and the effective utilization of the carboxymethylating agent was 30%. The potassium salt of carboxymethylated cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethylated cellulose.

(Example 7 )
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the organic solvent added at the time of the carboxymethylation reaction was changed from IPA to methanol. The degree of carboxymethyl substitution was 0.29, the degree of crystallinity of cellulose type I was 66%, and the effective utilization of the carboxymethylating agent was 35%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 8 )
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the organic solvent added during the carboxymethylation reaction was changed from IPA to ethanol. The degree of carboxymethyl substitution was 0.30, the degree of crystallinity of cellulose type I was 67%, and the effective utilization of the carboxymethylating agent was 36%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 9 )
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the organic solvent added during the carboxymethylation reaction was changed from IPA to acetone. The degree of carboxymethyl substitution was 0.26, the degree of crystallinity of cellulose type I was 63%, and the effective utilization of the carboxymethylating agent was 31%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 10 )
Instead of dissolving 20 parts of sodium hydroxide in 100 parts of water in the mercerization reaction, using 40 parts of sodium hydroxide dissolved in 100 parts of water, sodium monochloroacetate as a carboxymethylating agent in the carboxymethylation reaction A sodium salt of carboxymethyl cellulose was obtained in the same manner as in Example 1 except that 50 parts of monochloroacetic acid was used instead of 60 parts. The degree of carboxymethyl substitution was 0.31, the degree of crystallinity of cellulose type I was 60%, and the effective utilization of the carboxymethylating agent was 36%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 11 )
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the concentration of IPA in the reaction solution at the time of the carboxymethylation reaction was changed to 30% by changing the addition amount of IPA. The degree of carboxymethyl substitution was 0.24, the degree of crystallinity of cellulose type I was 73%, and the effective utilization of the carboxymethylating agent was 29%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

(Example 12 )
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1 except that the concentration of IPA in the reaction solution at the time of the carboxymethylation reaction was changed to 20% by changing the addition amount of IPA. The degree of carboxymethyl substitution was 0.20, the degree of crystallinity of cellulose type I was 74%, and the effective utilization of the carboxymethylating agent was 24%. The sodium salt of carboxymethyl cellulose thus obtained was disintegrated in the same manner as in Example 1 to obtain a dispersion of nanofibers of carboxymethyl cellulose.

From the results of Table 1, in Examples 1 to 12 in which mercerization was carried out in a solvent mainly composed of water and carboxymethylation was carried out in a mixed solvent of water and an organic solvent, the mercerization which is the conventional method is It can be seen that a cellulose nanofiber dispersion having a very high transparency can be produced as compared to Comparative Example 2 (solvent method) in which both carboxymethylation is performed in a solvent mainly containing an organic solvent. In addition, compared to Comparative Examples 1 and 3 in which both mercerization and carboxymethylation are performed using water as a solvent, a cellulose nanofiber dispersion having high transparency is produced at an effective utilization rate of a high carboxymethylation agent. It can be seen that

The present inventors have result of intensive studies with respect to the object, in the carboxymethylation of cellulose is performed mercerization (the alkali treatment of the cellulose) under solvent composed mainly of water, then, carboxy methylation ( also referred to as etherification.) by the carried out in a solvent mixture of water and an organic solvent, a method conventional water medium method (both mercerized and carboxy methylation performed using water as a solvent) or solvent method (mercerized and both carboxy methylation compared to carboxymethyl cellulose, obtained by the method) carried out in a solvent mixture of an organic solvent or under water and an organic solvent, when defibrating, highly transparent cellulose nanofibers It has been found that the dispersion can be manufactured economically with high utilization of carboxymethylating agents.

Claims (11)

Treating the cellulose with a mercerizing agent to obtain a mercerized cellulose, and reacting the mercerized cellulose with a carboxymethylating agent to obtain a carboxymethylated cellulose,
A method for producing carboxymethylated cellulose, comprising the steps of: obtaining a mercerized cellulose under a solvent mainly comprising water; and obtaining the carboxymethylated cellulose under a mixed solvent of water and an organic solvent.   The method according to claim 1, wherein the water-based solvent in the step of obtaining mercerized cellulose is a solvent containing water at a ratio higher than 50% by mass.   The method according to claim 2, wherein the water-based solvent in the step of obtaining mercerized cellulose is water.   The method according to any one of claims 1 to 3, wherein the effective utilization rate of the carboxymethylating agent is 15% or more.   The method according to any one of claims 1 to 4, 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 5, wherein the carboxymethylating agent is monochloroacetic acid or sodium monochloroacetate.   The method according to any one of claims 1 to 6, wherein the mixed solvent in the step of obtaining carboxymethylated cellulose is a solvent containing 20 to 99% by mass of an organic solvent.   The method according to any one of claims 1 to 7, wherein the organic solvent is isopropanol, methanol, ethanol, acetone, or a combination of two or more thereof.   The method according to any one of claims 1 to 8, wherein the degree of carboxymethyl substitution per anhydroglucose unit in the carboxymethylated cellulose is less than 0.50.   The method according to any one of claims 1 to 9, wherein the crystallinity of cellulose type I of carboxymethylated cellulose is 50% or more. The manufacturing method of the nanofiber of carboxymethylated cellulose including disentangling carboxymethylated cellulose obtained by the method of any one of Claims 1-10.