Carboxymethyl cellulose

Abstract

A carboxymethylated cellulose, wherein the degree of carboxymethyl substitution is 0.50 or less, and the crystallinity of cellulose type I is 50% or more. Preferably, the degree of anionization is 0.00 meq / g to 1.00 meq / g. Furthermore, the Schubert-Regler free degree is preferably 60.0°SR or more. Additionally, the proportion of filter residue is preferably 0 to 30% by mass. Furthermore, the viscosity (30 rpm, 25°C) when prepared as an aqueous dispersion with 1% (w / v) solids is preferably 10.0 mPa·s or less.

Description

Technical Field

[0001] This invention relates to carboxymethylated cellulose. Background Technology

[0002] Carboxymethyl cellulose is a derivative of cellulose, formed by the addition of carboxymethyl groups to a portion of the hydroxyl groups in the glucose residues that form the backbone of cellulose via ether bonds. When the amount of carboxymethyl groups increases (i.e., when the degree of carboxymethyl substitution increases), carboxymethyl cellulose dissolves in water. On the other hand, by adjusting the degree of carboxymethyl substitution to an appropriate range, carboxymethyl cellulose can maintain its fibrous shape even in water.

[0003] As a method for manufacturing carboxymethyl cellulose, it is generally known to treat cellulose with alkali (alkalization) and then treat it with an etherifying agent (also called a carboxymethylating agent) (carboxymethylation, also called etherification). There are known methods that use water as a solvent for alkalization and carboxymethylation, as well as methods that use organic solvents as the main solvent for alkalization and carboxymethylation (Patent Documents 1-4). The former is called the "water-based method", and the latter is called the "solvent method".

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2017-149901

[0007] Patent Document 2: Japanese Patent Application Publication No. 2008-222859

[0008] Patent Document 3: Japanese Patent Application Publication No. 2007-191558

[0009] Patent document 4: Japanese Patent Application Publication No. 2002-194001. Summary of the Invention

[0010] Carboxymethyl cellulose is used as an additive in various fields such as food and beverage, cosmetics, and water-based coatings due to its thickening, water absorption, and water retention properties. These common carboxymethyl celluloses are typically water-soluble polymers with a carboxymethyl substitution degree (also known as etherification degree) of 0.55 or higher. On the other hand, in recent years, research has been conducted on carboxymethyl cellulose with a carboxymethyl substitution degree of 0.50 or lower, maintaining the crystallinity of cellulose and partially retaining its fibrous shape while being incompletely dissolved in water, exploring new applications utilizing its shape, crystallinity, and other characteristics. The object of this invention is to provide a carboxymethyl cellulose, particularly with a low carboxymethyl substitution degree (below 0.50) and high crystallinity (above 50%) of cellulose type I.

[0011] The inventors have studied carboxymethylated cellulose with low carboxymethyl substitution (below 0.50) and high crystallinity of cellulose type I (above 50%). However, carboxymethylated cellulose with both carboxymethyl substitution and cellulose type I crystallinity within the aforementioned ranges tends to be heterogeneous, exhibiting problems such as unstable dispersion. Furthermore, it tends to maintain a fibrous shape in the dispersion medium and easily forms clumps (agglomerates). This is presumably because the local introduction of carboxymethyl groups into cellulose results in partially dissolved and insoluble portions within the carboxymethylated cellulose, leading to quality differences and dispersion instability due to the state of carboxymethyl introduction. This phenomenon is particularly pronounced with low carboxymethyl substitution. This is believed to be because it is difficult to uniformly introduce small amounts of carboxymethyl groups into cellulose (not in a dense form at one or multiple locations). Additionally, when partially dissolved and insoluble portions are formed in carboxymethylated cellulose, there is a tendency for the insoluble portions to remain in clumps.

[0012] Furthermore, maintaining a crystallinity of over 50% in cellulose type I is inherently difficult, for example, within a carboxymethyl substitution range of 0.20–0.50. This is presumably because by locally introducing carboxymethyl groups into cellulose, dissolution in water begins from the areas where the substituents are concentrated, thus reducing the overall crystallinity of carboxymethylated cellulose.

[0013] In order to manufacture carboxymethylated cellulose with more stable quality (uniform dispersion), the inventors conducted in-depth research on carboxymethylated cellulose with low carboxyl substitution degree (below 0.50) and high crystallinity of cellulose type I (above 50%). The results showed that by performing alkalization (alkali treatment of cellulose) in a water-based solvent followed by carboxymethylation (also known as etherification) in a mixed solvent of water and organic solvent during cellulose carboxylation, compared with conventional methods such as aqueous methods (using water as a solvent for both alkalization and carboxymethylation) and solvent methods (using organic solvents as a primary solvent for both alkalization and carboxymethylation), it is possible to produce carboxymethylated cellulose with low carboxyl substitution degree (below 0.50) and high crystallinity of cellulose type I (above 50%). The carboxymethylated cellulose exhibits stable quality (uniform dispersion), high water retention, and is less prone to clumping when dispersed in water.

[0014] As part of the present invention, the following methods may be cited, but are not limited to.

[0015] (1) A carboxymethylated cellulose, wherein the degree of carboxymethyl substitution is less than 0.50 and the crystallinity of cellulose type I is more than 50%.

[0016] (2) The carboxymethyl cellulose according to (1), wherein the degree of anionization is 0.00 meq / g to 1.00 meq / g.

[0017] (3) The carboxymethyl cellulose according to (1), wherein the Schubert-Regler free degree is 60.0°SR or higher.

[0018] (4) The carboxymethyl cellulose according to (3), wherein the free concentration according to Canadian standards is less than 150 ml.

[0019] (5) According to (1), the dry mass of the filter residue on the filter when the carboxymethyl cellulose is added to 500g of water and stirred at 400rpm for 5 seconds is 0 to 30% of the dry mass of the carboxymethyl cellulose added to the water.

[0020] (6) The carboxymethyl cellulose according to (1), wherein the viscosity (30 rpm, 25 °C) of an aqueous dispersion with a solid content of 1% (w / v) is less than 10.0 mPa·s.

[0021] (7) The carboxymethyl cellulose according to any one of (1) to (6), wherein the carboxymethyl group is bonded to a portion of the hydroxyl group of the glucose residue constituting the cellulose via an ether bond.

[0022] The carboxymethylated cellulose of the present invention has a carboxymethyl substitution degree of 0.50 or less and a crystallinity of cellulose type I of 50% or more. It has a moderate degree of carboxymethyl substitution and maintains crystallinity, and can stably obtain the effects unique to carboxymethylated cellulose, such as high performance in terms of shape retention and water absorption.

[0023] Carboxymethylated cellulose (CMC) improves its dispersibility in water by introducing carboxyl groups into cellulose, causing electrorepulsion between the cellulose molecules. However, if carboxyl groups are introduced locally, there will be locally dissolved and undissolved portions, resulting in unstable dispersion. CMC considered to have a viscosity (30 rpm, 25°C) of less than 10.0 mPa·s when prepared as an aqueous dispersion with a solid content of 1% (w / v) indicates that the carboxyl groups are uniformly introduced into the cellulose matrix (not locally), preventing localized dissolution and resulting in uniform dispersion with low viscosity.

[0024] Furthermore, it is believed that if carboxymethyl groups are locally introduced into carboxymethyl cellulose, the hydrophilicity of the cellulose is locally higher, resulting in a portion that is locally soluble in water. As the amount of water-soluble portion increases, the absolute value of the anionization degree measured using a galvanometer becomes larger. On the other hand, it can be said that the closer the anionization degree is to 0, the less water-soluble portion (i.e., the less carboxymethyl group is locally introduced). It is considered that carboxymethyl cellulose with an anionization degree of 0.00 meq / g to 1.00 meq / g has carboxymethyl groups uniformly (not locally) introduced into the cellulose as a whole. "Anionization degree" will be explained in detail below, referring to the charge equivalent per unit mass of carboxymethyl cellulose, a value determined by titration using a galvanometer (unit: meq / g).

[0025] The closer the Schubert-Regler free degree is to 100°SR, the higher the water retention. Carboxymethylated cellulose with a Schubert-Regler free degree of 60.0°SR or higher, when added to food and cosmetics, further improves their water retention, for example, by achieving a moist texture, but not limited to these benefits. Furthermore, carboxymethylated cellulose with a carboxylation substitution degree of 0.50 or less, a cellulose type I crystallinity of 50% or more, and a Schubert-Regler free degree of 60.0°SR or higher maintains fiber shape and crystallinity. Therefore, when added to food and cosmetics, it also improves their formability and shape retention.

[0026] For carboxymethyl cellulose with a degree of carboxymethyl substitution of 0.50 or less, a crystallinity of cellulose type I of 50% or more, and a ratio of the dry mass of the filter residue after natural filtration to the dry mass of the carboxymethyl cellulose added to water (the ratio of filter residue) of 0 to 30%, even if the degree of carboxymethyl substitution and crystallinity are within the above range, it is not easy to clump when it is made into a dispersion. Moreover, it has a moderate degree of carboxymethyl substitution and maintains crystallinity. Therefore, it can exhibit the unique effects of carboxymethyl cellulose. For example, when used as an additive that utilizes shape retention and imparts water absorption, it exhibits these high effects and can obtain the advantages of not easily clumping in the dispersion medium and being easy to use. Detailed Implementation

[0027] <Carboxymethylated cellulose>

[0028] This invention relates to carboxymethylated cellulose. Carboxymethylated cellulose has a structure in which a portion of the hydroxyl group in the glucose residues constituting the cellulose pair is ether-bonded to the carboxymethyl group. Carboxymethylated cellulose is sometimes produced in the form of salts, and the carboxymethylated cellulose of this invention also includes salts of carboxymethylated cellulose. Examples of salts of carboxymethylated cellulose include, for example, metal salts such as sodium carboxymethyl cellulose.

[0029] The carboxymethylated cellulose of the present invention preferably retains at least a portion of its fibrous shape even when dispersed in water. That is, it is preferable that the fibrous material can be observed when the aqueous dispersion of carboxymethylated cellulose is observed using an electron microscope or the like. Furthermore, if the carboxymethylated cellulose of the present invention is measured using X-ray diffraction, peaks of cellulose type I crystals can be observed.

[0030] <Degree of carboxymethyl substitution>

[0031] In the carboxymethylated cellulose of the present invention, the degree of carboxymethyl substitution per glucosinolate unit of cellulose is 0.50 or less, preferably 0.40 or less. When the degree of substitution exceeds 0.50, it is easy to dissolve in water, and even in water, the fiber shape can be maintained, and the shape-preserving effect may be reduced. In order to obtain the shape-preserving and water-absorbing effects of carboxymethylated cellulose, a certain degree of carboxymethyl substitution is necessary. For example, if the degree of carboxymethyl substitution is less than 0.02, the advantages of introducing carboxymethyl may not be obtained depending on the application. Therefore, the degree of carboxymethyl substitution is preferably 0.02 or more, more preferably 0.05 or more, further preferably 0.10 or more, even more preferably 0.15 or more, even more preferably 0.20 or more, and even more preferably 0.25 or more. It should be noted that, particularly in the range of 0.20 to 0.50 carboxymethyl substitution, obtaining carboxymethylated cellulose with a crystallinity of 50% or more of cellulose type I (described later) is particularly difficult using conventional aqueous methods. The inventors, for example, have been able to produce carboxymethylated cellulose with a carboxymethyl substitution degree of 0.20 to 0.50, a crystallinity of cellulose type I of 50% or more, stable quality (producing a low-viscosity dispersion and / or a small absolute value of anionization), and resistance to clumping, through the method described later. The degree of carboxymethyl substitution can be adjusted by controlling the amount of carboxymethylating agent added in the reaction, the amount of alkalizing agent, and the composition ratio of water to organic solvent.

[0032] In this invention, the glucosamine unit refers to each glucosamine (glucose residue) that constitutes cellulose. Additionally, the degree of carboxymethyl substitution (also known as the degree of etherification) indicates the proportion of hydroxyl groups in the glucose residues constituting cellulose that are replaced by carboxymethyl ether groups (the number of carboxymethyl ether groups per glucose residue). It should be noted that the degree of carboxymethyl substitution is sometimes abbreviated as DS.

[0033] The method for determining the degree of carboxymethyl substitution is as follows:

[0034] Accurately weigh approximately 2.0 g of the sample and add it to a 300 mL Erlenmeyer flask with a stopper. Add 100 mL of a solution obtained by adding 100 mL of super-concentrated nitric acid to 1000 mL of nitric acid methanol, and shake for 3 hours to convert the carboxymethyl cellulose salt (CMC) to H-CMC (hydrogen-form carboxymethyl cellulose). Accurately weigh 1.5–2.0 g of absolutely dry H-CMC and add it to a 300 mL Erlenmeyer flask with a stopper. Moisten the H-CMC with 15 mL of 80% methanol, add 100 mL of 0.1N-NaOH, and shake at room temperature for 3 hours. Use phenolphthalein as an indicator, back-titrate the excess NaOH with 0.1N-H₂SO₄, and calculate the degree of carboxymethyl substitution (DS value) using the following formula.

[0035] A = [(100 × F' - 0.1 N - H2SO4 (mL) × F) × 0.1] / (absolute dry mass of H - CMC (g))

[0036] Degree of carboxymethyl substitution = 0.162 × A / (1 - 0.058 × A)

[0037] F': Factor of 0.1N-H2SO4

[0038] F: The factor of 0.1N-NaOH.

[0039] <Crystallinity of Cellulose Type I>

[0040] The crystallinity of the carboxymethylated cellulose fiber of the present invention is 50% or more, more preferably 60% or more, of type I crystals. By adjusting the crystallinity to the above range, the shape-preserving effect imparted by carboxymethylated cellulose is highly obtained. The crystallinity of cellulose can be controlled by the concentration of the alkalizing agent, the temperature during treatment, and the degree of carboxymethylation. Since a high concentration of alkali is used in alkalization and carboxymethylation, type I cellulose crystals are easily converted to type II crystals, but by adjusting the amount of alkali (alkalizing agent) used, the degree of modification can be adjusted to maintain the desired crystallinity. There is no particular upper limit to the crystallinity of type I cellulose. It is considered that approximately 90% is actually the upper limit.

[0041] The method for determining the crystallinity of cellulose type I carboxymethyl cellulose is as follows:

[0042] The sample was placed in a glass bath and measured using an X-ray diffraction apparatus (LabX XRD-6000, manufactured by Shimadzu Corporation). Crystallinity was calculated using methods such as Segal, with the diffraction intensity at 2θ = 10°–30° of the X-ray diffraction pattern as a baseline. The crystallinity was calculated using the following formula, based on the diffraction intensity of the 002 plane at 2θ = 22.6° and the diffraction intensity of the amorphous portion at 2θ = 18.5°.

[0043] Xc=(I002c―Ia) / I002c×100

[0044] Xc = Crystallinity of type I cellulose (%)

[0045] I002c: Diffraction intensity of the 002 plane at 2θ = 22.6°

[0046] Ia: 2θ = 18.5°, diffraction intensity of the amorphous portion.

[0047] Carboxymethyl cellulose is typically manufactured by treating cellulose with alkali (alkalization), followed by reacting the resulting alkalized cellulose (also known as alkali cellulose) with a carboxymethylating agent (also known as an etherifying agent).

[0048] <Anionization>

[0049] The anionization degree (also known as anion charge density) of carboxymethyl cellulose is preferably 0.00 meq / g to 1.00 meq / g. In this invention, the method for determining the anionization degree is as follows:

[0050] Carboxymethyl cellulose was dispersed in water to prepare an aqueous dispersion with a solid content of 10 g / L. The dispersion was stirred at 1000 rpm for 24 hours using a magnetic stirrer. The resulting slurry was diluted to 0.1 g / L, and 10 ml was taken and titrated with diallyl dimethyl ammonium chloride (DADMAC) at a concentration of 1 / 1000 using a flow current detector (Mutek Particle Charge Detector 03). The degree of anionization was calculated using the amount of DADMAC added until the flow current became zero, according to the following formula:

[0051] q=(V×c) / m

[0052] q: Degree of anionization (meq / g)

[0053] V: Amount of DADMAC added until the current reaches zero (L)

[0054] c: Concentration of DADMAC (meq / L)

[0055] m: Determine the mass (g) of carboxymethyl cellulose in the sample.

[0056] As can be seen from the above-described determination method, in this specification, "degree of anionization" is the equivalent of DADMAC required to neutralize anionic groups per unit mass of carboxymethyl cellulose, and is equivalent to the anionic equivalent per unit mass of carboxymethyl cellulose.

[0057] The anionization degree of carboxymethylated cellulose is preferably 0.00 meq / g to 1.00 meq / g, more preferably 0.00 meq / g to 0.80 meq / g, and even more preferably 0.00 meq / g to 0.60 meq / g. It is believed that carboxymethylated cellulose with this range of anionization degree, compared to carboxymethylated cellulose with anionization degree higher than 1.00 meq / g, has its carboxyl groups uniformly introduced into the entire cellulose structure rather than locally, thus stably achieving the unique effects of carboxymethylated cellulose, such as shape retention and water absorption.

[0058] <Schöber-Regler Freeness>

[0059] The Schubert-Regler free degree of carboxymethylated cellulose is preferably 60.0°SR or higher. In this invention, the method for determining the Schubert-Regler free degree is based on JIS P 82121-1:2012, specifically as follows:

[0060] Carboxymethyl cellulose was dispersed in water to prepare an aqueous dispersion with a solid content of 10 g / L. The dispersion was stirred at 1000 rpm for 24 hours using a magnetic stirrer. The resulting slurry was diluted to 1 g / L. A 60-mesh sieve (0.17 mm wire diameter) was set on a MEWTEC DFR-04 sieve, and the volume of liquid passing through the sieve from 1000 ml of test solution was measured for 60 seconds. The Schubert-Regler free fraction was calculated according to the method based on JISP 8121-1:2012.

[0061] Schubert-Regler freeness is a measure of the degree of water filtration in a fiber suspension. The lower limit is 0°SR and the upper limit is 100°SR. The closer the Schubert-Regler freeness is to 100°SR, the less water filtration (water loss), which means that the fiber has high water retention.

[0062] The Schubert-Regler free degree of carboxymethyl cellulose is preferably 60.0°SR or higher, more preferably 65.0°SR or higher. There is no particular upper limit, but it is 100.0°SR or lower, preferably 90.0°SR or lower. Carboxymethyl cellulose with a Schubert-Regler free degree of 60.0°SR or higher has high water retention and can be used as a water-retaining agent in various compositions, such as, but not limited to, food, cosmetics, and pharmaceuticals.

[0063] <Canadian Standard Freeness>

[0064] The Canadian standard freeness (Canadian standard filtration density) of carboxymethyl cellulose is preferably below 150 ml, more preferably below 120 ml, and even more preferably below 110 ml. The Canadian standard freeness measure determines the degree of filtration of the fiber suspension; a lower value indicates less filtration (water loss), meaning higher water retention of the fiber. The method for determining the Canadian standard freeness is as follows:

[0065] The sample was prepared using the same method as the aforementioned Schubert-Regler free fraction. A 60-mesh sieve (0.17 mm wire) was set on a MEWTEC DFR-04. The amount of liquid passing through the sieve from 1000 ml of test solution was measured for 60 seconds. The Canadian standard free fraction was calculated according to the method based on JISP 8121-2:2012.

[0066] <Filtration capacity>

[0067] The filtration volume of the carboxymethylated cellulose of the present invention is preferably 400 ml or less, more preferably 380 ml or less, and even more preferably 370 ml or less. Filtration volume is a measure of the degree of water filtration in the fiber suspension; a smaller value indicates less water filtration (drainage), i.e., higher water retention capacity of the fiber. The method for measuring filtration volume is as follows:

[0068] The sample was prepared using the same method as the aforementioned Schubert-Regler free fraction determination. A 60-mesh sieve (0.17 mm wire diameter) was set on a MEWTEC DFR-04. The amount of liquid passing through the sieve from 1000 ml of test solution was measured for 60 seconds, and the amount of water filtered was calculated.

[0069] <Proportion of Filter Residue>

[0070] When carboxymethyl cellulose is prepared into a dispersion (aqueous dispersion) using water as the dispersion medium, it is preferable to have a low amount of lumps formed (i.e., a low proportion of filter residue). Specifically, when carboxymethyl cellulose is added to 500g of water and stirred at 400rpm for 5 seconds, the dry mass of the filter residue on the filter after natural filtration using a 20-mesh filter is preferably 0-30% by mass relative to the dry mass of carboxymethyl cellulose added to the water (in this specification, the ratio of the dry mass of the filter residue after natural filtration calculated by the above method to the dry mass of carboxymethyl cellulose added to the water is referred to as the "filter residue ratio"). In this invention, the method for determining the filter residue ratio is as follows:

[0071] (1) Determination of the amount of filter residue

[0072] Take 500g of water and place it in a 1L beaker. Take 5g of carboxymethyl cellulose and record its mass. Install the stirring blades on an IKA (registered trademark) EUROSTAR P CV S1 (manufactured by IKA Corporation) and pre-stir the water at 400rpm. Add the recorded mass of carboxymethyl cellulose all at once to the stirred water and stir for 5 seconds. After stirring, disconnect the power to the stirrer. After stirring, quickly perform natural filtration using a pre-measured 20-mesh filter. After natural filtration, dry the filter and the residue together on a flat plate at 100°C for 2 hours. Measure the mass of the filter and the residue, subtract the mass of the filter, and calculate the absolute dry mass (g) of the residue.

[0073] (2) Calculation of moisture content of carboxymethyl cellulose

[0074] Heat the weighing bottle at 100°C for 2 hours, cool it in a silica gel desiccator, and accurately weigh the absolute dry mass of the weighing bottle (absolute dry weighing bottle mass). Measure approximately 1.5g of carboxymethyl cellulose into the weighing bottle and accurately weigh it (CMC mass before drying). Open the lid of the weighing bottle and heat it at 105°C for 2 hours. Close the lid of the weighing bottle and cool it in the silica gel desiccator for 15 minutes. Accurately weigh the mass of the dried weighing bottle (including the dried carboxymethyl cellulose) (mass of the dried weighing bottle containing CMC). Calculate the moisture content of the carboxymethyl cellulose using the following formula:

[0075] Moisture content of carboxymethyl cellulose (%) = [{mass of CMC before drying (g) - (mass of weighing bottle containing CMC after drying (g) - mass of weighing bottle that is absolutely dry (g))} / mass of CMC before drying (g)] × 100.

[0076] (3) Calculation of the proportion of filter residue

[0077] Using the mass (g) of carboxymethyl cellulose determined in (1) and the mass (g) of the absolutely dry residue, and the moisture content (%) of carboxymethyl cellulose calculated in (2), the proportion of the filter residue of carboxymethyl cellulose is calculated using the following formula:

[0078] The percentage of carboxymethyl cellulose filter residue (%) = [absolutely dry residue mass (g) / {mass of carboxymethyl cellulose (g) × (100 - moisture content of carboxymethyl cellulose (%)) / 100}] × 100.

[0079] The proportion of filter residue in carboxymethyl cellulose is preferably 0-30%, more preferably 0-20%, and even more preferably 0-10%. Carboxymethyl cellulose with a low proportion of filter residue is easy to disperse and has excellent operability.

[0080] <Viscosity of aqueous dispersion>

[0081] When carboxymethyl cellulose is prepared into a dispersion (aqueous dispersion) using water as the dispersion medium, it preferably exhibits low viscosity. In this invention, the viscosity is measured using the following method:

[0082] Carboxymethyl cellulose was weighed into a 1000 ml glass beaker and dispersed in 900 ml of distilled water to prepare an aqueous dispersion with a solid content of 1% (w / v). The aqueous dispersion was stirred at 600 rpm for 3 hours at 25°C. Subsequently, the viscosity was measured after 3 minutes using a Type B viscometer (manufactured by Toki Kogyo Co., Ltd.) with rotor No. 1 and a rotation speed of 30 rpm, according to JIS-Z-8803.

[0083] The viscosity of carboxymethylated cellulose is preferably below 10.0 mPa·s, more preferably below 8.0 mPa·s, and even more preferably below 7.0 mPa·s. It is believed that such low-viscosity carboxymethylated cellulose, with carboxyl groups uniformly introduced throughout the cellulose rather than locally, can more stably achieve the unique effects of carboxymethylated cellulose, such as shape retention and water absorption. The lower limit of the above viscosity is not particularly limited. It is considered that approximately 1.0 mPa·s is practically the lower limit.

[0084] <Other>

[0085] Carboxymethyl cellulose can be in the form of a dispersion obtained after manufacturing, and can be dried as needed, or redispersed in water. There are no limitations on the drying method; for example, known methods such as freeze drying, spray drying, tray drying, drum drying, belt drying, thin-layer drying on glass plates, fluidized bed drying, microwave drying, and heated fan vacuum drying can be used. After drying, it can also be pulverized as needed using a cutter, hammer mill, pin mill, jet mill, etc. Furthermore, there are no particular limitations on the redispersibility method in water; known dispersion devices can be used.

[0086] Carboxymethyl cellulose is nanofiberized by defibrillation, but nanofiberization is costly, so it can be used without nanofiberization unless there is a specific need for it.

[0087] The uses of carboxymethyl cellulose are not particularly limited. The carboxymethyl cellulose of the present invention has a degree of carboxymethyl substitution of 0.50 or less and a crystallinity of cellulose type I of 50% or more, exhibiting excellent shape retention and water absorption, and is therefore particularly suitable for applications requiring shape retention and water absorption. However, it can be used for other applications as well. The application areas of carboxymethyl cellulose are not limited, and it can be used in various fields where additives are commonly used, such as food, beverages, cosmetics, pharmaceuticals, papermaking, various chemicals, coatings, sprays, pesticides, civil engineering, construction, electronic materials, flame retardants, household products, adhesives, cleaning agents, fragrances, lubricating compositions, etc., as a thickener, gelling agent, paste, food additive, excipient, coating additive, adhesive additive, papermaking additive, abrasive, compounding material for rubber or plastics, water retainer, shape retainer, mud conditioner, filter aid, mud overflow preventer, etc.

[0088] <Method for manufacturing carboxymethyl cellulose>

[0089] Carboxymethyl cellulose is generally manufactured by treating cellulose with alkali (alkalization), and then reacting the resulting alkalized cellulose (also known as unalkalized cellulose) with a carboxymethylating agent (also known as an etherifying agent).

[0090] The carboxymethylated cellulose of the present invention has a degree of carboxymethyl substitution of 0.50 or less and a crystallinity of cellulose type I of 50% or more. For example, it can be manufactured by alkalization (alkali treatment of cellulose) in a water-based solvent, followed by carboxymethylation (also called etherification) in a mixed solvent of water and an organic solvent, but is not limited thereto. Compared with carboxymethylated cellulose obtained by conventional aqueous methods (methods involving both alkalization and carboxymethylation using water as a solvent) and solvent methods (methods involving both alkalization and carboxymethylation in a solvent primarily composed of an organic solvent), the carboxymethylated cellulose obtained in this way exhibits lower viscosity when formed into an aqueous dispersion, a smaller absolute value of anionization (closer to 0), higher Schöber-Regler freeness, and is less prone to clumping when formed into an aqueous dispersion. Furthermore, the above method has the advantage of high utilization rate of the carboxymethylating agent. The above method can be used to manufacture carboxymethylated cellulose with a carboxymethyl substitution degree of 0.50 or less, a cellulose I crystallinity of 50% or more, and a viscosity (30 rpm, 25°C) of 10.0 mPa·s or less when forming an aqueous dispersion with a solid content of 1% (w / v). Furthermore, the above method can be used to manufacture carboxymethylated cellulose with a carboxymethyl substitution degree of 0.50 or less, a cellulose I crystallinity of 50% or more, and an anionization degree of 0.00 meq / g to 1.00 meq / g. Additionally, the above method can be used to manufacture carboxymethylated cellulose with a carboxymethyl substitution degree of 0.50 or less, a cellulose I crystallinity of 50% or more, and a Schubert-Regler free degree of 60.0°SR or more. Finally, the above method can be used to manufacture carboxymethylated cellulose with a carboxymethyl substitution degree of 0.50 or less, a cellulose I crystallinity of 50% or more, and a filter residue ratio of 0% to 30%.

[0091] <Cellulose>

[0092] In this invention, cellulose refers to a polysaccharide composed of D-glucanopyranose (also simply referred to as "glucose residues" or "glucose anhydride") linked by β-1,4 bonds. Cellulose is typically classified according to its origin, preparation method, etc., into natural cellulose, regenerated cellulose, microcellulose, and microcrystalline cellulose excluding amorphous regions. In this invention, all of these types of cellulose can be used as raw materials for alkalized cellulose; however, to maintain a crystallinity of cellulose type I of more than 50% in carboxymethylated cellulose, it is preferable to use cellulose with high crystallinity of cellulose type I as the raw material. The crystallinity of cellulose type I used as the raw material is preferably 70% or more, more preferably 80% or more. The method for determining the crystallinity of cellulose type I is as follows.

[0093] Examples of natural cellulose include bleached or unbleached pulp (bleached or unbleached wood pulp); cotton linters, refined cotton linters; and cellulose produced by microorganisms such as acetic acid bacteria. The raw materials for bleached or unbleached pulp are not particularly limited; examples include wood, kapok, wheat straw, bamboo, hemp, jute, and kenaf. Furthermore, the manufacturing method for bleached or unbleached pulp is not particularly limited; it can be a mechanical method, a chemical method, or a combination of both. Bleached or unbleached pulps are classified by manufacturing method, including, for example, mechanical pulp (thermomechanical pulp (TMP), wood chip pulp), chemical pulp (unbleached coniferous sulfite pulp (NUSP), bleached coniferous sulfite pulp (NBSP), etc., unbleached coniferous kraft pulp (NUKP), bleached coniferous kraft pulp (NBKP), unbleached broadleaf kraft pulp (LUKP), bleached broadleaf kraft pulp (LBKP), etc.). Furthermore, in addition to pulps used for papermaking, dissolving pulp can also be used. Dissolving pulp refers to pulp obtained through chemical refining, primarily dissolved in pharmaceuticals, and used as a main raw material for synthetic fibers, cellophane, etc.

[0094] Examples of regenerated cellulose include cellulose obtained by dissolving cellulose in solvents such as copper ammonia solution, cellulose xanthate solution, and morpholine derivatives, and then re-spinning it. Examples of microcellulose include cellulose obtained by depolymerizing cellulose-based materials (e.g., acid hydrolysis, alkaline hydrolysis, enzymatic decomposition, bursting treatment, vibratory ball milling treatment, etc.), as represented by the above-mentioned natural cellulose and regenerated cellulose, and cellulose obtained by mechanically treating the above-mentioned cellulose-based materials.

[0095] <Alkalization>

[0096] By using the aforementioned cellulose as a raw material and adding an alkalizing agent (alkali), alkalized cellulose (also known as alkali cellulose) is obtained. According to the method described in this specification, the solvent for this alkalization reaction is primarily water, and a mixture of organic solvent and water is used in the subsequent carboxymethylation process, thus economically obtaining the carboxymethylated cellulose of the present invention. The carboxymethylated cellulose thus obtained exhibits low viscosity when formulated into an aqueous dispersion. Furthermore, the absolute value of the degree of anionization of the carboxymethylated cellulose thus obtained is small. Additionally, the Schubert-Regler free degree of the carboxymethylated cellulose thus obtained is high. Furthermore, when formulated into an aqueous dispersion, the carboxymethylated cellulose thus obtained exhibits less lumps (i.e., a smaller proportion of filter residue).

[0097] The solvent primarily using water (a water-based solvent) refers to a solvent containing water at a proportion of more than 50% by mass. The water content in the water-based solvent is preferably 55% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, further preferably 80% by mass or more, further preferably 90% by mass or more, and even more preferably 95% by mass or more. A particularly preferred water-based solvent is one where the water content is 100% by mass (i.e., water). The higher the proportion of water during alkalization, the more uniformly the carboxymethyl groups are introduced into the cellulose. Examples of solvents other than water (used in mixture with water) in the water-based solvent include organic solvents used as solvents in the subsequent carboxymethylation stage. Examples include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and tert-butanol, ketones such as acetone, diethyl ketone, and methyl ethyl ketone, and diethyl ketone. Alkane, diethyl ether, benzene, dichloromethane, etc., can be added alone or in mixtures of two or more in an amount of less than 50% by mass to water as a solvent for alkalization. The organic solvent in the water-based solvent is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, and even more preferably 0% by mass.

[0098] Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide, which can be used in one or more combinations. The alkali metal hydroxides are not limited to these; they can be added to the reactor in the form of an aqueous solution, for example, 1-60% by mass, preferably 2-45% by mass, and more preferably 3-25% by mass.

[0099] The amount of alkalizing agent used is not particularly limited, as long as it is sufficient to achieve both a carboxymethyl substitution degree of less than 0.50 for carboxymethylated cellulose and a crystallinity of more than 50% for cellulose type I. In one embodiment, the amount is preferably 0.1 mol to 2.5 mol relative to 100 g (absolutely dry) of cellulose, more preferably 0.3 mol to 2.0 mol, and even more preferably 0.4 mol to 1.5 mol.

[0100] The amount of water-based solvent used during alkalization is not particularly limited, as long as it is sufficient to mix the raw materials. It is preferably 1.5 to 20 parts by weight relative to the cellulose raw material, and more preferably 2 to 10 parts by weight.

[0101] The alkalization treatment is carried out as follows: the starting material (cellulose) is mixed with a water-based solvent; the temperature of the reactor is adjusted to 0–70°C, preferably 10–60°C, more preferably 10–40°C; an aqueous solution of an alkalizing 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. This yields alkalized cellulose (alkali cellulose).

[0102] The pH during alkalization is preferably 9 or higher, thereby allowing the alkalization reaction to proceed. More preferably, the pH is 11 or higher, even more preferably 12 or higher, and may also be 13 or higher. There is no particular upper limit to the pH.

[0103] Alkalization can be carried out in a reactor that mixes and stirs the above-mentioned components while controlling the temperature. Various reactors that have been used for alkalization reactions can be used. For example, from the viewpoints of uniform mixing and productivity, a batch stirring device with two shafts for stirring and mixing the above-mentioned components is preferred.

[0104] <Carboxymethylation>

[0105] Carboxymethylated cellulose is obtained by adding a carboxymethylating agent (also called an etherifying agent) to alkalized cellulose. According to the method described in this specification, water is used as the main solvent during alkalization, and a mixture of water and an organic solvent is used during carboxymethylation, thus economically obtaining the carboxymethylated cellulose of the present invention. The carboxymethylated cellulose obtained in this way exhibits low viscosity when formed into an aqueous dispersion. Furthermore, the absolute value of the degree of anionization of the carboxymethylated cellulose obtained in this way is small. Additionally, the Schöber-Regler free degree of the carboxymethylated cellulose obtained in this way is high. Furthermore, the carboxymethylated cellulose obtained in this way exhibits less lumps when formed into an aqueous dispersion (i.e., a smaller proportion of filter residue).

[0106] Examples of carboxymethylating agents include monochloroacetic acid, sodium monochloroacetate, methyl monochloroacetate, ethyl monochloroacetate, and isopropyl monochloroacetate. Among these, monochloroacetic acid or sodium monochloroacetate are preferred due to the ease of obtaining the raw materials.

[0107] The amount of carboxymethylating agent used is not particularly limited, as long as it achieves a carboxymethyl substitution degree of 0.50 or less in carboxymethylated cellulose and a crystallinity of 50% or more in cellulose type I. In one embodiment, it is preferable to add it in the range of 0.5 to 1.5 mol per glucosinolate unit of cellulose. The lower limit of the above range is more preferably 0.6 mol or more, further preferably 0.7 mol or more, and the upper limit is more preferably 1.3 mol or less, further preferably 1.1 mol or less. The carboxymethylating agent can be added to the reactor, for example, in the form of an aqueous solution of 5 to 80% by mass, more preferably 30 to 60% by mass, but is not limited thereto. Alternatively, it can be added in powder form without dissolution.

[0108] When using monochloroacetic acid or sodium monochloroacetate as a carboxylating agent, the molar ratio of alkalizing agent to carboxylating agent (alkalizing agent / carboxylating agent) is generally between 0.90 and 2.45. This is because if the ratio is less than 0.90, the carboxylation reaction may be incomplete, resulting in unreacted monochloroacetic acid or sodium monochloroacetate residue and waste. Furthermore, if the ratio exceeds 2.45, excess alkalizing agent and monochloroacetic acid or sodium monochloroacetate may undergo side reactions to form alkali metal glycolates, which is uneconomical.

[0109] The effective utilization rate of the carboxymethylating agent in carboxymethylation 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 proportion of carboxymethyl groups in the carboxymethylating agent that are introduced into cellulose. By using a water-based solvent during alkalization and a mixed solvent of water and organic solvents during carboxymethylation, the carboxymethylated cellulose of the present invention can be obtained with a high effective utilization rate of the carboxymethylating agent (i.e., without significantly increasing the amount of carboxymethylating agent used, which is more economical). There is no particular upper limit to the effective utilization rate of the carboxymethylating agent, but in practice, the upper limit is about 80%. It should be noted that the effective utilization rate of the carboxymethylating agent is sometimes abbreviated as AM.

[0110] The effective utilization rate of carboxymethylating agents is calculated as follows:

[0111] AM = (DS × number of moles of cellulose) / number of moles of carboxymethylating agent

[0112] DS: Degree of carboxymethyl substitution (the determination method will be described later).

[0113] Moles of cellulose: Pulp mass (drying mass at 100°C for 60 minutes) / 162

[0114] (162 is the molecular weight of cellulose per glucose unit).

[0115] There is no particular limitation on the concentration of cellulose raw material in the carboxymethylation reaction, but from the viewpoint of improving the effective utilization rate of the carboxymethylating agent, it is preferably 1 to 40% (w / v).

[0116] Simultaneously with, or before or after the addition of the carboxymethylating agent, an organic solvent or an aqueous solution of an organic solvent is appropriately added to the reactor, or the organic solvent other than water used in the alkalization treatment is appropriately reduced by means of reduced pressure, to form a mixed solvent of water and organic solvent. The carboxymethylation reaction is carried out in this mixed solvent. The timing of adding or removing the organic solvent can be from the end of the alkalization reaction to the time after the addition of the carboxymethylating agent, and is not particularly limited. For example, it is preferred to be within 30 minutes before or after the addition of the carboxymethylating agent.

[0117] Examples of organic solvents include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, acetone, diethyl ketone, methyl ethyl ketone, and diethyl ketone. Alkanes, diethyl ethers, benzene, dichloromethane, etc., can be added to water alone or in mixtures of two or more to be used as solvents for carboxymethylation. Among these, monohydric alcohols with 1 to 4 carbon atoms are preferred, and monohydric alcohols with 1 to 3 carbon atoms are even more preferred, considering their excellent compatibility with water.

[0118] Regarding the proportion of organic solvent in the mixed solvent during carboxymethylation, relative to the sum of water and organic solvent, organic solvent 2 is preferably 0% by mass or more, more preferably 0% by mass or more, further preferably 40% by mass or more, even more preferably 45% by mass or more, and particularly preferably 50% by mass or more. A higher proportion of organic solvent facilitates uniform carboxymethyl substitution, resulting in carboxymethylated cellulose with stable quality. There is no upper limit to the proportion of organic solvent; for example, it can be 99% by mass or less. Considering the cost of the added organic solvent, it is preferably 90% by mass or less, more preferably 85% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0119] The preferred reaction medium for carboxymethylation (a mixture of water and organic solvents, etc., without cellulose) has a lower proportion of water (in other words, a higher proportion of organic solvents) compared to the reaction medium for alkalization. By satisfying this range, it is easier 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 for carboxymethylation has a lower proportion of water (a higher proportion of organic solvents) compared to the reaction medium for alkalization, the following advantages are obtained: when shifting from the alkalization reaction to the carboxymethylation reaction, a mixed solvent for the carboxymethylation reaction can be easily formed by adding the desired amount of organic solvent to the reaction system after the alkalization reaction has ended.

[0120] A mixed solvent of water and organic solvent is formed. After adding a carboxymethylating agent to alkalized cellulose, the mixture is stirred for 15 minutes to 4 hours, preferably 15 minutes to 1 hour, while maintaining a constant temperature within the preferred range of 10–40°C. To prevent the reaction mixture from reaching high temperatures, the mixing of the alkalized cellulose solution and the carboxymethylating agent is preferably carried out in multiple stages or titrated. After adding the carboxymethylating agent and stirring for a certain period, the temperature is raised if necessary, and an etherification (carboxymethylation) reaction is carried out at a reaction temperature of 30–90°C, preferably 40–90°C, more preferably 60–80°C, for 30 minutes to 10 hours, preferably 1 hour to 4 hours, to obtain carboxymethylated cellulose. By raising the temperature during the carboxymethylation reaction, the advantage of conducting the etherification reaction in a short time and with high efficiency is achieved.

[0121] During carboxymethylation, the reactor used for alkalization can be used directly, or other reactors that can simultaneously control the temperature and mix the above components can be used.

[0122] After the reaction is complete, the remaining alkali metal salts can be neutralized with inorganic or organic acids. Alternatively, byproduct inorganic salts and organic acid salts can be removed by washing with aqueous methanol, followed by drying, pulverizing, and classifying to produce carboxymethyl cellulose or its salts. Examples of dry pulverizing apparatus include impact mills such as hammer mills and pin mills, media mills such as ball mills and tower mills, and jet mills. Examples of wet pulverizing apparatus include homogenizers, mass colloiders, and bead mills.

[0123] Using the above method, it is possible to obtain carboxymethylated cellulose that forms a low-viscosity dispersion even when the degree of carboxymethyl substitution is 0.50 or less and the crystallinity of cellulose type I is 50% or more; it is also possible to obtain carboxymethylated cellulose with a small absolute value of anionization when the degree of carboxymethyl substitution is 0.50 or less and the crystallinity of cellulose type I is 50% or more; it is also possible to obtain carboxymethylated cellulose with a high degree of Schubert-Regler freeness; and it is possible to obtain carboxymethylated cellulose with a degree of carboxymethyl substitution of 0.50 or less and a crystallinity of cellulose type I of 50%... The reasons for the low proportion of filter residue in carboxymethylated cellulose obtained above are not yet clear, but the inventors speculate as follows: It is believed that by using a water-based solvent for the alkalization reaction, the alkalizing agent can be easily and uniformly mixed, resulting in a more uniform alkalization reaction. Furthermore, the presence of an organic solvent in the carboxymethylation process increases the effective utilization rate of the carboxymethylating agent, thus reducing the likelihood of side reactions caused by excess carboxymethylating agent (e.g., the formation of alkali metal salts of glycolate), leading to stable quality, reduced viscosity, and a smaller absolute value of anionization. Additionally, it is believed that uniform carboxymethylation results in higher water retention and less filtration water. Furthermore, it is believed that because carboxymethylation occurs uniformly, carboxymethylated cellulose is easily and uniformly dispersed, reducing the proportion of filter residue. However, theories other than these are not excluded.

[0124] Example

[0125] The present invention will now be specifically described by way of examples and comparative examples, but the present invention is not limited thereto. It should be noted that, unless otherwise specified, parts and % refer to parts by mass and percentage by mass.

[0126] (Example 1)

[0127] In a twin-shaft kneader set to 100 rpm, a solution of 130 parts water and 20 parts sodium hydroxide dissolved in 100 parts water was added. Then, 100 parts of hardwood pulp (manufactured by Nippon Paper Corporation, LBKP) was added, based on the dry weight after drying at 100°C for 60 minutes. The mixture was stirred at 30°C for 90 minutes to prepare alkalized cellulose. While stirring, 100 parts isopropanol (IPA) and 60 parts sodium monochloroacetate were added. After stirring for 30 minutes, the temperature was raised to 70°C for a carboxymethylation reaction for 90 minutes. The concentration of IPA in the reaction medium during the carboxymethylation reaction was 30%. After the reaction, the solution was neutralized to approximately pH 7 with acetic acid, followed by dehydration, drying, and pulverization to obtain sodium salt of carboxymethylated cellulose with a carboxymethyl substitution degree of 0.24 and a crystallinity of 73% (cellulose type I). The effective utilization rate of the carboxymethylating agent was 29%. It should be noted that the methods for determining the degree of carboxymethyl substitution and the crystallinity of cellulose type I, as well as the methods for calculating the effective utilization rate of the carboxymethylating agent, are as described above.

[0128] The obtained sodium salt of carboxymethyl cellulose was dispersed in water to prepare a 1% (w / v) aqueous dispersion. Its viscosity was determined using the method described above, and the result was 5.6 mPa·s.

[0129] (Example 2)

[0130] By varying the amount of IPA added to achieve a IPA concentration of 50% in the reaction solution during the carboxymethylation reaction, the process was carried out in the same manner as in Example 1, yielding a sodium salt of carboxymethylated cellulose. 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 prepared into an aqueous dispersion with a solid content of 1% (w / v), and the viscosity was measured in the same manner as in Example 1, yielding a result of 5.6 mPa·s.

[0131] (Comparative Example 1)

[0132] The solvent used in the alkalization reaction was 10% water and 90% IPA. The same solvent composition was used in the carboxymethylation reaction, except that the process was the same as in Example 1, to obtain a sodium salt of carboxymethylated cellulose. The degree of carboxymethyl substitution was 0.29, the crystallinity of cellulose type I was 66%, and the effective utilization rate of the carboxymethylating agent was 35%. The obtained sodium salt of carboxymethylated cellulose was prepared into an aqueous dispersion with a solid content of 1% (w / v), and the viscosity was measured in the same manner as in Example 1, resulting in 14.4 mPa·s.

[0133] [Table 1]

[0134]

[0135] As shown in Table 1, Examples 1 and 2, which involved alkalization in a water-based solvent and carboxymethylation in a mixed solvent of water and organic solvents, produced dispersions exhibiting low viscosity compared to Comparative Example 1 (solvent method), which involved both alkalization and carboxymethylation in a solvent primarily composed of organic solvents, a conventional method. Furthermore, the carboxymethylated cellulose obtained in Comparative Example 1 exhibited a localized swelling due to water content, while the carboxymethylated cellulose obtained in Examples 1 and 2 formed more homogeneous dispersions.

[0136] (Example 3)

[0137] In a twin-shaft kneader with the speed adjusted to 100 rpm, a solution of 130 parts water and 20 parts sodium hydroxide in 100 parts dissolved water was added, along with 100 parts of hardwood pulp (manufactured by Nippon Paper Corporation, LBKP) based on its dry mass after drying at 100°C for 60 minutes. The mixture was stirred at 30°C for 90 minutes to prepare alkalized cellulose. Then, while stirring, 100 parts isopropanol (IPA) and 60 parts sodium monochloroacetate were added, and after stirring for 30 minutes, the temperature was raised to 70°C for a carboxymethylation reaction for 90 minutes. The concentration of IPA in the reaction medium during the carboxymethylation reaction was 30%. After the reaction, the solution was neutralized to approximately pH 7 with acetic acid, followed by dehydration, drying, and pulverization to obtain sodium salt of carboxymethylated cellulose with a carboxymethyl substitution degree of 0.24 and a crystallinity of 73% (cellulose type I). The effective utilization rate of the carboxymethylating agent was 29%. It should be noted that the methods for determining the degree of carboxymethyl substitution and the crystallinity of cellulose type I, as well as the methods for calculating the effective utilization rate of the carboxymethylating agent, are as described above.

[0138] The anionization degree of the obtained sodium salt of carboxymethyl cellulose was determined using the method described above, and the result was 0.32 meq / g.

[0139] (Example 4)

[0140] By varying the amount of IPA added to achieve a IPA concentration of 50% in the reaction solution during the carboxymethylation reaction, the process was carried out in the same manner as in Example 3, yielding a sodium salt of carboxymethylated cellulose. 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 anionization degree of the obtained sodium salt of carboxymethylated cellulose was measured in the same manner as in Example 3, and the result was 0.53 meq / g.

[0141] (Comparative Example 2)

[0142] The solvent used in the alkalization reaction was 10% water and 90% IPA. The same solvent composition was used in the carboxymethylation reaction, except that the process was the same as in Example 3, to obtain sodium salt of carboxymethylated cellulose. The degree of carboxymethyl substitution was 0.29, the crystallinity of cellulose type I was 66%, and the effective utilization rate of the carboxymethylating agent was 35%. The anionization degree of the obtained sodium salt of carboxymethylated cellulose was determined in the same manner as in Example 3, and the result was 1.10 meq / g.

[0143] [Table 2]

[0144]

[0145] As shown in Table 2, in Examples 3 and 4, where alkalization was performed in a water-based solvent and carboxymethylation was performed in a mixed solvent of water and organic solvent, compared to Comparative Example 2 (solvent method), which involved both alkalization and carboxymethylation in a solvent primarily composed of organic solvent, a conventional method, carboxymethylated cellulose with a smaller absolute value of anionization was produced. Furthermore, the carboxymethylated cellulose obtained in Comparative Example 2 exhibited a state of localized swelling due to water content, while the carboxymethylated cellulose obtained in Examples 3 and 4 formed a more homogeneous dispersion.

[0146] (Example 5)

[0147] In a biaxial kneader with the speed adjusted to 100 rpm, a solution of 130 parts water and 20 parts sodium hydroxide in 100 parts dissolved water was added. Then, 100 parts of hardwood pulp (manufactured by Nippon Paper Corporation, LBKP) based on the dry mass after drying at 100°C for 60 minutes was added. The mixture was stirred at 30°C for 90 minutes to prepare alkalized cellulose. While stirring, 100 parts isopropanol (IPA) and 60 parts sodium monochloroacetate were added. After stirring for 30 minutes, the temperature was raised to 70°C for a carboxymethylation reaction for 90 minutes. The concentration of IPA in the reaction medium during the carboxymethylation reaction was 30%. After the reaction, the solution was neutralized to approximately pH 7 with acetic acid, followed by dehydration, drying, and pulverization to obtain sodium salt of carboxymethylated cellulose with a carboxymethyl substitution degree of 0.24, a cellulose type I crystallinity of 73%, a Schubert-Regler free degree of 66.7°SR, a Canadian standard free degree of 106 ml, and a filtration rate of 369 ml / 10 seconds. The effective utilization rate of the carboxymethylating agent was 29%. It should be noted that the methods for determining the degree of carboxymethyl substitution, the crystallinity of cellulose type I, the Schubert-Regler free degree, the Canadian standard free degree, and the filtration rate, as well as the calculation method for the effective utilization rate of the carboxymethylating agent, are as described above.

[0148] (Example 6)

[0149] By varying the amount of IPA added to achieve a 50% concentration of IPA in the reaction solution during the carboxymethylation reaction, the process was carried out in the same manner as in Example 5 to obtain the sodium salt of carboxymethylated cellulose. The degree of carboxymethyl substitution was 0.31, the crystallinity of cellulose type I was 66%, the Schubert-Regler free degree was 71.3°SR, the Canadian standard free degree was 85 ml, the filtration rate was 302 ml / 10 seconds, and the effective utilization rate of the carboxymethylating agent was 37%.

[0150] (Comparative Example 3)

[0151] The solvent used in the alkalization reaction was 10% water and 90% IPA. The same solvent composition was used in the carboxymethylation reaction. Otherwise, the process was carried out in the same manner as in Example 5 to obtain the sodium salt of carboxymethylated cellulose. The degree of carboxymethyl substitution was 0.29, the crystallinity of cellulose type I was 66%, the Schubert-Regler free degree was 57.7°SR, the Canadian standard free degree was 157 ml, the filtration rate was 447 ml / 10 seconds, and the effective utilization rate of the carboxymethylating agent was 35%.

[0152] [Table 3]

[0153]

[0154] According to the results in Table 3, in Examples 5 and 6, alkalization was performed in a water-based solvent, and carboxymethylation was performed in a mixed solvent of water and organic solvents. Compared with Comparative Example 3 (solvent method), which involved alkalization and carboxymethylation in a solvent primarily composed of organic solvents, the latter produced carboxymethylated cellulose with high Schubert-Regler freeness, Canadian standard freeness, and low water content. Furthermore, the carboxymethylated cellulose obtained in Comparative Example 3 exhibited a state of localized swelling due to water content, while the carboxymethylated cellulose obtained in Examples 5 and 6 formed a more homogeneous dispersion.

[0155] (Example 7)

[0156] In a twin-shaft kneader with a speed adjusted to 100 rpm, a solution of 130 parts water and 20 parts sodium hydroxide dissolved in 100 parts water was added, along with 100 parts of hardwood pulp (manufactured by Nippon Paper Corporation, LBKP) based on its dry weight after drying at 100°C for 60 minutes. The mixture was stirred at 30°C for 90 minutes to prepare alkalized cellulose. Then, while stirring, 100 parts isopropanol (IPA) and 60 parts sodium monochloroacetate were added, and after stirring for 30 minutes, the temperature was raised to 70°C for a carboxymethylation reaction for 90 minutes. The concentration of IPA in the reaction medium during the carboxymethylation reaction was 30%. After the reaction, the solution was neutralized to approximately pH 7 with acetic acid, followed by dehydration, drying, and pulverization to obtain sodium salt of carboxymethylated cellulose with a carboxymethyl substitution degree of 0.24 and a crystallinity of 73% (cellulose type I). The effective utilization rate of the carboxymethylating agent was 29%, and the proportion of filter residue was 7%. It should be noted that the methods for determining the degree of carboxymethyl substitution and the crystallinity of cellulose type I, as well as the methods for calculating the effective utilization rate of the carboxymethylating agent and the proportion of filter residue, are as described above.

[0157] (Example 8)

[0158] By varying the amount of IPA added to achieve a IPA concentration of 50% in the reaction solution during the carboxymethylation reaction, the process was carried out in the same manner as in Example 7, yielding a sodium salt of carboxymethylated cellulose. The degree of carboxymethyl substitution was 0.31, the crystallinity of cellulose type I was 66%, the effective utilization rate of the carboxymethylating agent was 37%, and the proportion of filter residue was 2%.

[0159] (Example 9)

[0160] By varying the amount of IPA added, the concentration of IPA in the reaction solution during the carboxymethylation reaction was adjusted to 65%. Otherwise, the process was carried out in the same manner as in Example 7 to obtain the sodium salt of carboxymethylated cellulose. The degree of carboxymethyl substitution was 0.20, the crystallinity of cellulose type I was 74%, the effective utilization rate of the carboxymethylating agent was 25%, and the proportion of filter residue was 3%.

[0161] (Comparative Example 4)

[0162] The solvent used in the alkalization reaction was 10% water and 90% IPA. The same solvent composition was used in the carboxymethylation reaction. Otherwise, the process was carried out in the same manner as in Example 7, yielding a sodium salt of carboxymethylated cellulose. The degree of carboxymethyl substitution was 0.29, the crystallinity of cellulose type I was 66%, the effective utilization rate of the carboxymethylating agent was 35%, and the proportion of filter residue was 48%.

[0163] (Comparative Example 5)

[0164] The solvent used in the alkalization reaction was 19% water and 81% IPA. The same solvent composition was used in the carboxymethylation reaction. Otherwise, the process was carried out in the same manner as in Example 7, yielding a sodium salt of carboxymethylated cellulose. The degree of carboxymethyl substitution was 0.60, the crystallinity of cellulose type I was 0%, the effective utilization rate of the carboxymethylating agent was 67%, and the proportion of filter residue was 91%.

[0165] [Table 4]

[0166]

[0167] As shown in Table 4, the carboxymethylated cellulose of Examples 7-9, obtained by alkalization in a water-based solvent and carboxymethylation in a mixed solvent of water and organic solvent, exhibited significantly less filtration residue (i.e., less agglomeration when dispersed in water) compared to the carboxymethylated cellulose of Comparative Examples 4 and 5 (solvent method), which were obtained by conventional methods involving both alkalization and carboxymethylation in an organic solvent-based solvent. Furthermore, while the carboxymethylated cellulose obtained in Comparative Examples 4 and 5 showed localized swelling due to water content, the carboxymethylated cellulose obtained in Examples 7-9 formed a more homogeneous dispersion.

Claims

1. A carboxymethylated cellulose, wherein the degree of carboxymethyl substitution is less than 0.50, and the crystallinity of cellulose type I is more than 50%. Add carboxymethyl cellulose to 500g of water, stir at 400rpm for 5 seconds, and then filter naturally through a 20-mesh filter. The dry mass of the filter residue on the filter is 0-30% by mass relative to the dry mass of the carboxymethyl cellulose added to the water. Furthermore, the carboxymethylated cellulose is manufactured by a method comprising alkalizing the cellulose in a solvent containing more than 50% by mass of water, followed by carboxymethylating the alkalized cellulose in a mixed solvent of water and organic solvent, wherein the amount of solvent during alkalization is 2 to 10 times by mass relative to the cellulose, and the proportion of organic solvent in the mixed solvent during carboxymethylation is more than 50% by mass relative to the sum of water and organic solvent.

2. The carboxymethylated cellulose according to claim 1, wherein, The degree of anionization is 0.00 meq / g to 1.00 meq / g.

3. The carboxymethylated cellulose according to claim 1, wherein, The freeness of the Schubert-Regler is above 60.0°SR.

4. The carboxymethylated cellulose according to claim 3, wherein, The Canadian standard for free volume is below 150ml.

5. The carboxymethyl cellulose according to claim 1, wherein, The viscosity (30 rpm, 25 °C) of an aqueous dispersion with 1% (w / v) solid content is less than 10.0 mPa·s.

6. The carboxymethylated cellulose according to any one of claims 1 to 5, wherein, It has a structure in which the carboxymethyl group is partially bonded to the hydroxyl group of the glucose residues that make up cellulose via an ether bond.

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