JP2019163437A - Carboxymethylated cellulose - Google Patents

Abstract

To provide novel carboxymethylated cellulose showing a low viscosity when formed into an aqueous dispersion.SOLUTION: There is provided carboxymethylated cellulose having a carboxymethyl substitution degree of 0.50 or less, a cellulose I-type crystallinity index of 50% or more and a viscosity (30 rpm, 25°C) of 30.0 mPa s or less when formed into an aqueous dispersion having a solid content of 1% (W/v).SELECTED DRAWING: None

Description

  The present invention relates to carboxymethylated cellulose. In detail, it is related with the carboxymethylated cellulose which shows a low viscosity when it is set as an aqueous dispersion.

  Carboxymethylated cellulose is a derivative of cellulose, and is obtained by ether-bonding a carboxymethyl group to a part of hydroxyl groups in a glucose residue constituting the skeleton of cellulose. As the amount of carboxymethyl groups increases (ie, the degree of carboxymethyl substitution increases), the carboxymethylated cellulose becomes soluble in water. On the other hand, by adjusting the degree of carboxymethyl substitution within an appropriate range, the fibrous shape of carboxymethylated cellulose can be maintained even in water.

  As a method for producing carboxymethylated cellulose, generally, cellulose is treated with alkali (mercelization) and then treated with an etherifying agent (also referred to as carboxymethylating agent) (carboxymethylated, also referred to as etherification). A method is known, and a method in which both mercerization and carboxymethylation are carried out using water as a solvent, and a method in which both mercerization and carboxymethylation are carried out in a solvent mainly composed of an organic solvent (Patent Documents 1 to 4). The former is called the “water medium method” and the latter is called the “solvent method”.

JP 2017-149901 A JP 2008-222859 A JP 2007-191558 A JP 2002-194001 A

  Carboxymethylated cellulose is used as an additive in various fields such as foods and drinks, cosmetics, and water-based paints due to its properties such as thickening, water absorption, and water retention. These widely used carboxymethylated celluloses are usually water-soluble polymers having a carboxymethyl substitution degree (also referred to as etherification degree) of 0.55 or more. On the other hand, research on carboxymethylated cellulose has been recently conducted in which the degree of carboxymethyl substitution is 0.50 or less, the crystallinity of cellulose remains, and a part of the fibrous shape is maintained without being completely dissolved in water. Searches for new uses that utilize features such as shape and crystallinity are being conducted. In particular, the present invention provides a carboxymethylated cellulose having novel characteristics in a carboxymethylated cellulose having a low degree of carboxymethyl substitution (0.50 or less) and a high degree of crystallinity of cellulose type I (50% or more). The purpose is to do.

  The present inventors examined carboxymethylated cellulose having a low degree of carboxymethyl substitution (0.50 or less) and a high degree of crystallinity of cellulose type I (50% or more). However, carboxymethylated cellulose in which both the degree of carboxymethyl substitution and the degree of crystallinity of cellulose type I are within this range is likely to be heterogeneous, for example, causing problems such as unstable dispersion. This is because the carboxymethyl group is locally introduced into the cellulose, so that a part of the carboxymethylated cellulose that locally dissolves in water and a part that does not dissolve in water are produced. It was estimated that dispersion was unstable depending on the state of introduction. Such a phenomenon was particularly remarkable when the degree of carboxymethyl substitution was low. This was thought to be because it was difficult to introduce a small amount of carboxymethyl groups uniformly into cellulose (in a form that was not concentrated in one place or several places). In addition, for example, in the range of the carboxymethyl substitution degree of 0.20 or more and 0.50 or less, it was difficult to maintain the crystallinity of cellulose I type at 50% or more. This is presumed to be due to the fact that the carboxymethyl group is locally introduced into the cellulose, so that it is dissolved in water from the portion where the substituents are concentrated and the crystallinity of the carboxymethylated cellulose as a whole is lowered. .

  In order to produce a carboxymethylated cellulose having a low degree of carboxymethyl substitution (0.50 or less) and a high degree of crystallinity of cellulose type I (50% or more), a more stable quality is produced. We conducted an intensive study. At that time, attention was paid to the viscosity of the dispersion of carboxymethylated cellulose as an indicator of the stable quality (uniform dispersion) of carboxymethylated cellulose. By introducing a carboxymethyl group into cellulose, the celluloses become electrically repelled and the dispersibility of carboxymethylated cellulose in water is improved, but at this time, the carboxymethyl group is locally introduced. If this is the case, a portion that dissolves locally in water and a portion that does not dissolve in water appear, so that dispersion becomes unstable and the viscosity increases. On the other hand, if carboxymethyl groups are introduced more uniformly (not locally) throughout the cellulose, local dissolution of the carboxymethylated cellulose is less likely to occur, and it will be uniformly dispersed and show a low viscosity. It is done.

  In the carboxymethylation of cellulose, the present inventors perform mercerization (alkali treatment of cellulose) in a solvent mainly composed of water, and then perform carboxymethylation (also referred to as etherification) with water and an organic solvent. The conventional aqueous medium method (method in which both mercerization and carboxymethylation are performed using water as a solvent) and the solvent method (both mercerization and carboxymethylation are mainly organic solvents) In the carboxymethylated cellulose having a low degree of carboxymethyl substitution (0.50 or less) and a high degree of crystallinity of cellulose type I (50% or more), compared to the carboxymethylated cellulose obtained by the method performed in a solvent) It has been found that carboxymethylated cellulose having an unprecedented low viscosity can be produced when an aqueous dispersion is obtained.

The present invention includes, but is not limited to, the following.
(1) Viscosity when a carboxymethyl substitution degree is 0.50 or less, a crystallinity of cellulose type I is 50% or more, and an aqueous dispersion having a solid content of 1% (w / v) (30 rpm, Carboxymethylated cellulose having a temperature of 25 ° C. or less of 30.0 mPa · s or less.
(2) The carboxymethylated cellulose according to (1), wherein the viscosity is 10.0 mPa · s or less.
(3) The carboxymethylated cellulose according to (1) or (2), wherein the carboxymethyl group has a structure in which a carboxymethyl group is ether-bonded to a part of a hydroxyl group in a glucose residue constituting cellulose.

  Viscosity (30 rpm, 30%) when the carboxymethyl substitution degree of the present invention is 0.50 or less, the crystallinity of cellulose type I is 50% or more, and an aqueous dispersion having a solid content of 1% (w / v) The carboxymethylated cellulose having a temperature of 25 ° C. or less of 30.0 mPa · s remains crystallizable while having an appropriate degree of carboxymethyl substitution, and the degree of carboxymethyl substitution and the degree of crystallinity are within the above ranges. Nonetheless, by exhibiting a low viscosity (more uniform introduction of carboxymethyl groups) in the dispersion, a high effect can be stably obtained with respect to the effects specific to carboxymethylated cellulose, such as shape retention and water absorption. It is considered possible.

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

  The carboxymethylated cellulose of 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 carboxymethylated cellulose is observed with an electron microscope or the like, those capable of observing a fibrous substance are preferable. Moreover, when the carboxymethylated cellulose of the present invention is measured by X-ray diffraction, the peak of cellulose I-type crystal can be observed.

<Carboxymethyl substitution degree>
In the carboxymethylated cellulose of the present invention, the degree of carboxymethyl substitution per anhydroglucose unit of cellulose is 0.50 or less, preferably 0.40 or less. If the degree of substitution exceeds 0.50, dissolution in water tends to occur, the fiber form cannot be maintained in water, and effects such as imparting shape retention may be reduced. In order to obtain effects such as shape retention and water absorption by carboxymethylated cellulose, it is necessary to have a certain degree of carboxymethyl substitution. For example, when the degree of carboxymethyl substitution is less than 0.02, Depending on the application, there may be no advantage obtained by introducing a carboxymethyl group. Accordingly, the degree of carboxymethyl substitution is preferably 0.02 or more, more preferably 0.05 or more, further preferably 0.10 or more, and further preferably 0.15 or more. 0.20 or more, more preferably 0.25 or more. In particular, when the degree of carboxymethyl substitution is in the range of 0.20 to 0.50, obtaining a carboxymethylated cellulose having a cellulose I-type crystallinity of 50% or more, which will be described later, is a conventional aqueous medium. Although it was difficult by the method, the present inventors, for example, have a carboxymethyl substitution degree of 0.20 or more and 0.50 or less, a cellulose I crystallinity of 50% or more by the production method described later, It was found that a stable carboxymethylated cellulose (which gives a low viscosity dispersion) can be produced. The degree of carboxymethyl substitution can be adjusted by controlling the amount of carboxymethylating 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 carboxymethyl substitution (also referred to as etherification degree) is the proportion of hydroxyl groups in the glucose residues constituting cellulose that are substituted with carboxymethyl ether groups (carboxymethyl per glucose residue). The number of ether groups). The degree of carboxymethyl substitution may be abbreviated as DS.

The method for measuring the degree of carboxymethyl 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 carboxymethylated cellulose (CMC) into H-CMC (hydrogen-type carboxymethylated 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 carboxymethyl 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))
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

<Crystallinity of cellulose type I>
The crystallinity of cellulose in the carboxymethylated cellulose fiber of the present invention is preferably 50% or more, and more preferably 60% or more for crystal I type. By adjusting the crystallinity to the above range, effects such as imparting shape retention by carboxymethylated cellulose can be obtained. The crystallinity of cellulose can be controlled by the concentration of mercerizing agent and the temperature during processing, as well as the degree of carboxymethylation. In mercerization and carboxymethylation, a high concentration of alkali is used, so cellulose type I crystals are likely to be converted to type II. However, modification by adjusting the amount of alkali (mercellizing agent) used, etc. 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 carboxymethylated 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 general, carboxymethylated cellulose is obtained by treating cellulose with an alkali (mercelization), and then reacting the obtained mercerized cellulose (also referred to as alkali cellulose) with a carboxymethylating agent (also referred to as an etherifying agent). Can be manufactured.

<Viscosity in water dispersion>
The carboxymethylated cellulose of the present invention is characterized in that it exhibits a low viscosity when it is made into a dispersion using water as a dispersion medium (aqueous dispersion). In the present invention, the viscosity is measured as follows:
Carboxymethylated cellulose is measured in a 1000 ml glass beaker, dispersed in 900 ml of distilled water, and an aqueous dispersion is prepared so as to have a solid content of 1% (w / v). The aqueous dispersion is stirred at 25 ° C. with a stirrer at 600 rpm for 3 hours. Then, according to the method of JIS-Z-8803, using a B-type viscometer (made by Toki Sangyo Co., Ltd.), No. The viscosity after 3 minutes is measured at 1 rotor / rotation speed of 30 rpm.

  The viscosity of the carboxymethylated cellulose of the present invention is 30.0 mPa · s or less. More preferably, it is 25.0 mPa · s or less, More preferably, it is 20.0 mPa · s or less, More preferably, it is 15.0 mPa · s or less, More preferably, it is 10.0 mPa · s or less, More preferably Is 8.0 mPa · s or less, more preferably 7.0 mPa · s or less. Such low-viscosity carboxymethylated cellulose is considered to have carboxymethyl groups introduced uniformly throughout the cellulose rather than locally, and has the effects unique to carboxymethylated cellulose, such as shape retention, It is considered that water absorption can be obtained more stably. The lower limit of the viscosity is not particularly limited. Actually, the lower limit is considered to be about 1.0 mPa · s.

<Others>
The carboxymethylated cellulose may be in the form of a dispersion obtained after production, but may be dried or 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.

  Carboxymethylated cellulose can be made into nanofibers by defibration. However, since nanofiberization is costly, it may be used without being made into nanofibers unless particularly necessary.

  The use of carboxymethylated cellulose is not particularly limited, but the carboxymethylated cellulose of the present invention has a carboxymethyl substitution degree of 0.50 or less and a cellulose I type crystallinity of 50% or more, It is considered that it can be optimally used for applications requiring shape retention and water absorption because of its excellent water absorption and low viscosity and high stability. However, it may be used for other purposes. The field in which carboxymethylated cellulose is used is not limited, and various fields in which additives are generally used, such as food, beverages, cosmetics, pharmaceuticals, papermaking, various chemicals, paints, sprays, agricultural chemicals, civil engineering, and architecture. , Electronic materials, flame retardants, household goods, adhesives, cleaning agents, fragrances, lubricating compositions, thickeners, gelling agents, glues, food additives, excipients, paint additives, It can be used as an adhesive additive, paper additive, abrasive, rubber / plastic compounding material, water retention agent, shape retention agent, mud adjuster, filter aid, anti-sludge agent, etc. .

<Method for producing carboxymethylated cellulose>
In general, carboxymethylated cellulose is obtained by treating cellulose with an alkali (mercelization), and then reacting the obtained mercerized cellulose (also referred to as alkali cellulose) with a carboxymethylating agent (also referred to as an etherifying agent). Can be manufactured.

  Viscosity (30 rpm, 30%) when the carboxymethyl substitution degree of the present invention is 0.50 or less, the crystallinity of cellulose type I is 50% or more, and an aqueous dispersion having a solid content of 1% (w / v) The carboxymethylated cellulose having a temperature of 25 ° C. or less of 30.0 mPa · s is not limited to this. For example, mercerization (alkali treatment of cellulose) is performed in a solvent mainly containing water, and then carboxymethyl (Also referred to as etherification) can be produced by carrying out in a mixed solvent of water and an organic solvent. The carboxymethylated cellulose thus obtained can be obtained by using a conventional aqueous medium method (a method in which both mercerization and carboxymethylation are performed using water as a solvent) and a solvent method (in which both mercerization and carboxymethylation are performed using an organic solvent). Compared to the carboxymethylated cellulose obtained in the main solvent), it has a characteristic that it shows a low viscosity when it is made into an aqueous dispersion. Moreover, said method has the advantage that the effective utilization factor of a carboxymethylating agent is high.

<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. In order to maintain a cellulose I type crystallinity of 50% or more in carboxymethylated cellulose, cellulose I type It is preferable to use cellulose having a high crystallinity as a raw material. The cellulose I type crystallinity of the raw material cellulose is preferably 70% or more, and more preferably 80% or more. The method for measuring the crystallinity of cellulose type I is as described above.

  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). According to the method described in the present specification, when water is mainly used as a solvent in the mercerization reaction, and a mixed solvent of an organic solvent and water is used in the next carboxymethylation to form an aqueous dispersion. Carboxymethylated cellulose having a low viscosity can be obtained economically.

  The main use of water as a solvent (a solvent mainly containing water) refers to a solvent containing water in a proportion higher than 50% by mass. Water in the solvent mainly composed of 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, Preferably it is 90 mass% or more, More preferably, it is 95 mass% or more. Particularly preferably, the solvent mainly composed of water is 100% by mass of water (that is, water). The greater the proportion of water during mercerization, the more advantageous is that carboxymethyl groups are introduced more uniformly by cellulose. Examples of the solvent other than water (used by mixing with water) in the solvent mainly containing 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 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 less than 50% by mass and used as a solvent for mercerization. The organic solvent in the solvent mainly composed of water is preferably 45% by mass or less, more preferably 40% by mass or less, further 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 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 it is an amount that can achieve both a carboxymethyl substitution degree of 0.50 or less in carboxymethylated cellulose and a crystallinity of cellulose I type of 50% or more, but in one embodiment, It 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, and more preferably 0.4 mol or more and 1.5 mol or less with respect to 100 g (absolutely dry) of cellulose. More preferably, it is less than or equal to mol.

  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.

  In the mercerization treatment, the bottoming material (cellulose) and a solvent mainly composed of water are mixed, 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 the mixture is stirred for 15 minutes to 8 hours, preferably 30 minutes to 7 hours, more preferably 30 minutes to 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.

<Carboxymethylation>
Carboxymethylated cellulose is obtained by adding a carboxymethylating agent (also referred to as an etherifying agent) to mercerized cellulose. According to the method described in this specification, water is used as a main solvent in mercerization, and a mixed solvent of water and an organic solvent is used in carboxymethylation to form an aqueous dispersion. Carboxymethylated cellulose having a low viscosity can be obtained economically.

  Examples of the carboxymethylating agent include monochloroacetic acid, sodium monochloroacetate, methyl monochloroacetate, ethyl monochloroacetate, isopropyl monochloroacetate and the like. Of these, monochloroacetic acid or sodium monochloroacetate is preferable from the viewpoint of easy availability of raw materials.

  The amount of the carboxymethylating agent is not particularly limited as long as the amount of carboxymethyl substitution in the carboxymethylated cellulose is 0.50 or less and the crystallinity of cellulose I type is 50% or more, but is not particularly limited. It is preferable to add 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 carboxymethylating agent is not limited to this, but for example, it can be added to the reactor as an aqueous solution of 5 to 80% by mass, more preferably 30 to 60% by mass, does not dissolve, and is added in a powder state. You can also.

  The molar ratio of mercerizing agent to carboxymethylating agent (mercelling agent / carboxymethylating agent) is generally 0.90 to 2.45 when monochloroacetic acid or sodium monochloroacetate is used as the carboxymethylating agent. Adopted. The reason is that if it is less than 0.90, the carboxymethylation 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 carboxymethylation, the effective utilization rate of the carboxymethylating 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 a carboxymethylating agent refers to the proportion of carboxymethyl groups introduced into cellulose among carboxymethyl groups in the carboxymethylating agent. By using a solvent mainly composed of water at the time of mercerization and using a mixed solvent of water and an organic solvent at the time of carboxymethylation, the effective utilization rate of the carboxymethylating agent is high (ie, the carboxymethylating agent). The carboxymethylated cellulose according to the present invention can be obtained economically without greatly increasing the amount of the styrene. The upper limit of the effective utilization rate of the carboxymethylating agent is not particularly limited, but in reality, 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 × number of moles of cellulose) / number of moles of carboxymethylating agent DS: degree of carboxymethyl 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 carboxymethylation reaction is not specifically limited, From a viewpoint of raising the effective utilization factor of a carboxymethylating agent, it is preferable that it is 1-40% (w / v).

  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 the water used in the mercerization process by reducing the pressure. The organic solvent is appropriately reduced to form a mixed solvent of water and the organic solvent, and the carboxymethylation reaction proceeds under the mixed solvent of the water and the 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 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, etc. can be mentioned, These alone or a mixture of two or more thereof can be added to water and used as a solvent for carboxymethylation. 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 carboxymethylation 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, there is an advantage that a carboxymethylated cellulose having a stable quality can be obtained, for example, uniform carboxymethyl group substitution is likely to occur. 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.

  The reaction medium at the time of carboxymethylation (a mixed solvent of water and an organic solvent, which does not contain cellulose) has a smaller proportion of water than the reaction medium at the time of mercerization (in other words, the proportion of the organic solvent is lower). Many). By satisfying this range, it becomes easy to maintain the crystallinity of the obtained carboxymethylated cellulose, and the carboxymethylated cellulose of the present invention can be obtained more efficiently. In addition, when the reaction medium at the time of carboxymethylation is less than the reaction medium at the time of mercerization (the ratio of the organic solvent is large), when shifting from the mercerization reaction to the carboxymethylation reaction, There is also an advantage that a mixed solvent for the carboxymethylation reaction can be formed by a simple means of adding a desired amount of an organic solvent to the reaction system after completion of the mercerization reaction.

  After forming a mixed solvent of water and an organic solvent and adding a carboxymethylating 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 carboxymethylating agent is preferably performed in a plurality of times or by dropping in order to prevent the reaction mixture from becoming high temperature. After adding a carboxymethylating agent and stirring for a certain 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, and 30 minutes to The etherification (carboxymethylation) reaction is performed for 10 hours, preferably 1 hour to 4 hours, to obtain carboxymethylated cellulose. By raising the temperature during the carboxymethylation reaction, there is an advantage that the etherification reaction can be efficiently performed in a short time.

  In the carboxymethylation, 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 carboxymethylated 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.

  The reason why carboxymethylated cellulose capable of forming a low-viscosity dispersion despite the carboxymethyl substitution degree of 0.50 or less and the cellulose I type crystallinity of 50% or more by the above-mentioned production method is clear. However, the present inventors speculate as follows: by performing the mercerization reaction using a solvent mainly containing water, the mercerizing agent is easily mixed uniformly, and the mercerization reaction is further improved. In addition, the presence of the organic solvent in the carboxymethylation improves the effective utilization of the carboxymethylating agent, and as a result, side reactions (for example, alkali glycolate) by the excess carboxymethylating agent. This is presumed to be because the production of metal salts, etc.) is less likely to occur and the quality is stabilized. However, it is not limited to this.

  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)
130 parts of water and 20 parts of sodium hydroxide dissolved in 100 parts of water are added to a biaxial kneader whose rotational speed is adjusted to 100 rpm, and hardwood pulp (manufactured by Nippon Paper Industries Co., Ltd., LBKP) is added at 100 ° C. 60 100 parts were charged in a dry mass when dried for a minute. Mercerized cellulose was prepared by stirring and mixing at 30 ° C. for 90 minutes. Further, with stirring, 100 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 cause carboxymethylation reaction for 90 minutes. The concentration of IPA in the reaction medium during the carboxymethylation reaction is 30%. After completion of the reaction, the reaction solution is neutralized with acetic acid so that the pH is about 7, drained, dried and pulverized to obtain a sodium salt of carboxymethylated cellulose having a carboxymethyl substitution degree of 0.24 and cellulose I type crystallinity of 73%. Obtained. The effective utilization rate of the carboxymethylating agent was 29%. 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. About this, when the viscosity was measured by the above-mentioned method, it was 5.6 mPa * s.

(Example 2)
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 during the carboxymethylation reaction was changed to 50% by changing the amount of IPA added. The degree of carboxymethyl substitution was 0.31, the crystallinity of cellulose type I was 66%, and the effective utilization rate of the carboxymethylating agent was 37%. The obtained sodium salt of carboxymethylated cellulose was used as an aqueous dispersion having a solid content of 1% (w / v), and the viscosity was measured in the same manner as in Example 1. The result was 5.6 mPa · s.

(Comparative Example 1)
A sodium salt of carboxymethylated cellulose was obtained in the same manner as in Example 1, except that the solvent during the mercerization reaction was 6% water and 94% IPA, and the solvent having the same composition was used during the carboxymethylation reaction. The degree of carboxymethyl substitution was 0.29, the crystallinity of cellulose type I was 51%, and the effective utilization rate of the carboxymethylating agent was 35%. The obtained sodium salt of carboxymethylated cellulose was used as an aqueous dispersion having a solid content of 1% (w / v), and the viscosity was measured in the same manner as in Example 1. As a result, it was 40.0 mPa · s.

  From the results of Table 1, in Examples 1 and 2 in which mercerization was performed in a solvent mainly containing water and carboxymethylation was performed in a mixed solvent of water and an organic solvent, It can be seen that a dispersion having a low viscosity can be produced as compared with Comparative Example 1 (solvent method) in which both carboxymethylation was performed in a solvent mainly composed of an organic solvent. The carboxymethylated cellulose obtained in Comparative Example 1 was locally swollen with water, but the carboxymethylated cellulose obtained in Examples 1 and 2 was A more homogeneous dispersion was formed.

Claims (3)

  Viscosity (30 rpm, 25 ° C.) when an aqueous dispersion having a carboxymethyl substitution degree of 0.50 or less, a cellulose I crystallinity of 50% or more, and a solid content of 1% (w / v) Is 30.0 mPa · s or less, carboxymethylated cellulose.   The carboxymethylated cellulose according to claim 1, wherein the viscosity is 10.0 mPa · s or less. The carboxymethylated cellulose according to claim 1 or 2, wherein the carboxymethylated cellulose has a structure in which a carboxymethyl group is ether-bonded to a part of a hydroxyl group in a glucose residue constituting cellulose.