JP2013018917A - Method for manufacturing polyuronic acid or its salt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently manufacturing a polyuronic acid or its salt by a method with a less environmental load, suppressing the decrease in degrees of polymerization, and a method for manufacturing a water-absorbing resin by crosslinking the polyuronic acid or its salt.SOLUTION: [1] The method for manufacturing the polyuronic acid or its salt has (1) a process for grinding a cellulose-containing raw material in the coexistence of an oxidized sugar having a polymerization degree of 1-10 to obtain a low-crystallinity cellulose-containing raw material, and (2) a process for oxidizing the obtained low-crystallinity cellulose-containing raw material under a neutral or acidic condition to manufacture the polyuronic acid or its salt, and [2] the method for manufacturing the water-absorbing resin includes adding a crosslinking agent to the polyuronic acid or its salt manufactured by the method to induce a crosslinking reaction.

Description

  The present invention relates to a method for producing polyuronic acid or a salt thereof, and a method for producing a water-absorbent resin obtained by crosslinking polyuronic acid or a salt thereof.

The water-soluble polymer material has functions such as particle dispersion / stabilization, aggregation, viscosity adjustment, and adhesion, and is applied to various fields. In particular, since polycarboxylic acids can often be produced at low cost, many varieties are produced and used.
In addition, as environmental awareness increases, materials with less environmental impact are strongly demanded, and polymer materials manufactured from renewable natural raw materials have been developed. One of these is water-soluble polysaccharides and derivatives thereof. Among them, polyuronic acid is expected to be applied to water-absorbing resins and dispersants.

As a method for producing polyuronic acid, a polysaccharide is prepared by using an N-oxyl compound catalyst such as 2,2,6,6-tetramethyl-1-piperidine-1-oxyl (hereinafter referred to as “TEMPO”) and a pyranose ring. There is known a method of oxidizing the primary hydroxyl group at the C6 position.
For example, Patent Document 1 discloses a method of oxidizing starch or the like using an alkali metal bromide and an oxidizing agent in the presence of an N-oxyl compound. Patent Document 2 discloses that a polysaccharide is dispersed or dissolved in an aqueous system, oxidized using a co-oxidant in the presence of an N-oxyl compound, then precipitated by adding a polyvalent cation, washed with water, and desalted. Has been. Patent Document 3 describes a method for modifying cellulose having a step of oxidizing alkali-treated cellulose or regenerated cellulose in a neutral or acidic reaction solution containing an N-oxyl compound and an oxidizing agent that oxidizes an aldehyde group. Has been.
However, in the methods of Patent Documents 1 to 3, (i) when regenerated cellulose is used as the polysaccharide, it is necessary to perform a regeneration treatment after dissolving or derivatizing the cellulose in a copper-ammonia solution, (ii) There are problems that the oxidation reaction does not proceed sufficiently, (iii) metal waste is discharged due to the use of metal, and the burden on the environment is high due to complicated processes.

Patent Document 4 discloses a method of selectively and efficiently oxidizing a C6-position primary hydroxyl group by oxidizing a low crystalline cellulose derivative having a crystallinity of 30% or less in the presence of an N-oxyl compound. Have been described.
On the other hand, in Patent Document 5, a cellulose-containing raw material having a cellulose I-type crystallinity of more than 33% is pulverized together with a pulverization aid to reduce the crystallization degree, and low crystalline cellulose having an average particle size of 10 to 200 μm. The manufacturing method is described.

JP 2004-189924 A JP 2006-124598 A JP 2009-209217 A JP 2009-263641 A JP 2010-37526 A

It is known that when the primary hydroxyl group at the C6 position of the pyranose ring is oxidized by the polysaccharide oxidation method described in Patent Documents 1 to 4 using an N-oxyl compound catalyst, the degree of polymerization is greatly reduced. Maintaining molecular weight has been difficult.
In addition, when a polyuronic acid is chemically modified to produce a biodegradable high-performance material or the like, it is often inevitable that the molecular weight is lowered by a modification reaction. On the other hand, when it is used as a water-absorbing resin or combined with a polymer material, polyuronic acid preferably has a high molecular weight. However, the methods described in Patent Documents 1 to 4 can produce only polyuronic acid having a weight average molecular weight of about several tens of thousands, and development of a method capable of producing polyuronic acid having a weight average molecular weight of 100,000 or more is desired.
The present invention relates to a method for efficiently producing polyuronic acid or a salt thereof by a method that suppresses a decrease in the degree of polymerization and has a low environmental load, and a method for producing a water-absorbent resin obtained by crosslinking polyuronic acid or a salt thereof. The issue is to provide.

The present inventors pulverize cellulose-containing raw materials in the presence of oxidized sugars having a polymerization degree of 1 to 10, and then oxidize them under neutral or acidic conditions, thereby efficiently converting high molecular weight polyuronic acid or a salt thereof. It was found that it can be manufactured.
That is, the present invention provides the following [1] and [2].
[1] A process for producing polyuronic acid or a salt thereof having the following steps (1) and (2).
Step (1): A step of obtaining a low crystalline cellulose-containing raw material by pulverizing a cellulose-containing raw material in the presence of oxidized sugar having a polymerization degree of 1 to 10 Step (2): Low crystal obtained in step (1) A step of producing a polyuronic acid or a salt thereof by oxidizing a raw material containing cellulose in a neutral or acidic condition [2] adding a cross-linking agent to the polyuronic acid or a salt thereof produced by the method of [1], A method for producing a water-absorbent resin that undergoes a crosslinking reaction.

  According to the present invention, a method for efficiently producing polyuronic acid or a salt thereof by suppressing the decrease in the degree of polymerization and a method having a low environmental load, and a production of a water-absorbing resin obtained by crosslinking polyuronic acid or a salt thereof. A method can be provided.

The manufacturing method of the polyuronic acid or its salt of this invention has the following process (1) and (2).
Step (1): A step of obtaining a low crystalline cellulose-containing raw material by pulverizing a cellulose-containing raw material in the presence of oxidized sugar having a polymerization degree of 1 to 10 Step (2): Low crystal obtained in step (1) A process for producing a polyuronic acid or a salt thereof (hereinafter collectively referred to simply as “polyuronic acid salt”) by oxidizing a raw material containing a functional cellulose under neutral or acidic conditions. Each component used will be described sequentially.

[Step (1)] (Low crystallization treatment step)
In the step (1), the cellulose-containing raw material is pulverized in the presence of oxidized sugar having a polymerization degree of 1 to 10 to obtain a low crystalline cellulose-containing raw material.

<Cellulose-containing raw material>
The cellulose-containing raw material used in the step (1) of the present invention means a raw material containing cellulose that is generally used. Several crystal structures are known for cellulose, and the degree of crystallinity is calculated from the ratio of the crystal part to the total amount of the amorphous part and the crystal part.
There is no limitation in particular in the crystallinity degree of the cellulose contained in the cellulose containing raw material used at a process (1). However, usually, the treatment for reducing the crystallinity of cellulose is accompanied by a decrease in the degree of polymerization due to cleavage of the cellulose chain. In the present invention, since a decrease in the degree of polymerization during production is suppressed, it is possible to obtain a high molecular weight polyuronic acid salt as compared with the conventional method, and the production method of the present invention comprises a high molecular weight polyuronic acid salt. Higher value when applied for the purpose of obtaining. From this point of view, in the present invention, it is preferable to use a cellulose-containing raw material containing cellulose having a low degree of polymerization, that is, a crystallinity higher. On the other hand, it is difficult to obtain a cellulose-containing raw material having a crystallinity exceeding 95% and a very high crystallinity. Therefore, the crystallinity of cellulose contained in the cellulose-containing raw material is preferably 33 to 95%, more preferably 50 to 90%, and still more preferably 60 to 80%.
Here, “crystallinity” means the type I crystallinity derived from the crystal structure of natural cellulose, and from the diffraction intensity value obtained by applying the powder X-ray crystal diffraction spectrum method to the cellulose-containing raw material. It is calculated by the Segal method and is defined by the following formula (1). In the present specification, this cellulose type I crystallinity may be simply referred to as “crystallinity”.
Cellulose type I crystallinity (%) = [(I _22.6 -I _18.5 ) / I _22.6 ] × 100 (1)
[Wherein I _22.6 is the diffraction intensity of the grating plane (002 plane) (diffraction angle 2θ = 22.6 °) in X-ray diffraction, and I _18.5 is the amorphous portion (diffraction angle 2θ = 18.5 °). The diffraction intensity is shown. ]

There is no restriction | limiting in particular in the said cellulose containing raw material, Various wood chips; Pulp, such as wood pulp manufactured from wood, the cotton linter pulp obtained from the fiber around cotton seeds; Newspaper, corrugated cardboard, magazine, fine paper, etc. Paper stalks; plant stems and leaves such as rice straw and corn stalks; plant shells such as rice husks, palm husks and coconut husks.
The cellulose-containing raw material preferably has a cellulose content of 20% by weight or more, more preferably 40% by weight or more, and still more preferably 60% by weight or more in the remaining components obtained by removing water from the raw material. Here, the cellulose content means the total amount of cellulose and hemicellulose. In the case of a commercially available pulp, lignin is contained in addition to cellulose in the remaining components excluding water, but the content is very small, and the residue obtained by removing water from the pulp can be treated as substantially the same as cellulose.
The water content in the cellulose-containing raw material is preferably 20% by weight or less, more preferably 15% by weight or less, and still more preferably 10% by weight or less based on the cellulose in the cellulose-containing raw material. If the water content in the cellulose-containing raw material is 20% by weight or less, it can be easily pulverized and the crystallinity can be easily reduced by pulverization.

  There is no particular limitation on the shape of the cellulose-containing raw material, but the degree of polymerization of cellulose in the cellulose-containing raw material is also reduced by a treatment such as pulverization. Therefore, the shape of the cellulose-containing raw material is preferably a chip from the viewpoint of obtaining a high molecular weight polyuronic acid and from the viewpoint of operability during pulverization. To make the shape of the cellulose-containing raw material into chips, a shredder (for example, manufactured by Meiko Shokai Co., Ltd., trade name: “MSX2000-IVP440F”), a sheet pelletizer (for example, manufactured by Horai Co., Ltd., trade name: “SGG-220”). -3X3 ") or a rotary cutter. When using a rotary cutter, the magnitude | size of the chip-shaped cellulose containing raw material obtained can be controlled by changing the opening of a screen. The size of the chip is preferably 0.6 to 50 mm square, more preferably 0.8 to 30 mm square, and still more preferably 1 to 10 mm square from the viewpoint of operability.

<Low crystalline cellulose>
In the step (1) of the present invention, a low crystalline cellulose-containing raw material is obtained and used as the raw material in the step (2). Here, “low crystallinity” indicates a state in which the ratio of the amorphous part is large in the crystal structure of cellulose contained in the low crystalline cellulose-containing raw material, and specifically, cellulose I calculated from the above formula (1). This means that the crystallinity of the mold is 33% or less, including the case where the crystallinity is 0%.

  The degree of crystallinity is also related to the physical and chemical properties of cellulose, and the larger the value, the higher the crystallinity of cellulose and the less non-crystalline parts, so the hardness, density, etc. increase, but elongation, flexibility, Solubility and chemical reactivity in water and solvent decrease. If the crystallinity is 33% or less, the chemical reactivity of cellulose is good, and the oxidation reaction proceeds efficiently in step (2). In this respect, the crystallinity of cellulose in the low crystalline cellulose-containing raw material is preferably 25% or less, more preferably 15% or less, and preferably 0%. The cellulose I type crystallinity defined by the formula (1) may be a negative value in calculation, but in the case of a negative value, the cellulose I type crystallinity is 0%.

<Oxidized sugar with a polymerization degree of 1 to 10>
“Oxidized sugar having a degree of polymerization of 1 to 10” (hereinafter, also simply referred to as “oxidized sugar”) used in step (1) of the present invention is a simple substance having a carboxy group from the viewpoint of the reaction rate during oxidation described later. A monosaccharide having a degree of polymerization of 1 to 10, containing at least 10 to 100 mol%, preferably 30 to 100 mol%, more preferably 50 to 100 mol% of a saccharide, an oligosaccharide, a mixture of these saccharides and oligosaccharides, or a salt thereof. means.
Examples of the monosaccharide having a carboxy group include aldonic acid (for example, D-gluconic acid), uronic acid (for example, D-glucuronic acid), aldaric acid (for example, galactaric acid), ketoaldonic acid (for example, pent-2-uroson). Acid), sialic acid (for example, N-acetylneuraminic acid), and muramic acid (for example, N-acetylmuramic acid).
If the degree of polymerization of oxidized sugar is 1 to 10, the effect of suppressing the decrease in the degree of polymerization of cellulose in step (1) is high, but in the oxidized sugar of degree of polymerization 1 to 10, from the viewpoint of availability, Oxidized sugars having a polymerization degree of 1 to 5 are preferable, oxidized sugars having a polymerization degree of 1 to 3 are more preferable, uronic acids such as D-glucuronic acid, aldonic acids such as gluconic acid are more preferable, and uronic acid is particularly preferable. As such an oxidized sugar, it is also possible to reuse a low molecular weight polyuronic acid component generated during the synthesis of the polyuronic acid salt.
The oxidized sugar is preferably a salt from the viewpoint of chemical stability of the oxidized sugar and cellulose and the viewpoint of availability. As a salt, an alkali metal salt is preferable from the viewpoint of availability, and a sodium salt and a potassium salt are particularly preferable.
The amount of oxidized sugar used during the pulverization treatment is preferably 5 to 50% by weight based on the cellulose in the cellulose-containing raw material from the viewpoint of efficiency and operability for reducing the crystallinity of cellulose in the cellulose-containing raw material, and 6 to 40 % By weight is more preferable, and 7 to 30% by weight is even more preferable.

<Production of raw material containing low crystalline cellulose>
(Preprocessing)
In the present invention, when a cellulose-containing raw material having a bulk density of less than 100 kg / m ³ is used, a pretreatment is performed to make the bulk density 100 to 500 kg / m ³ , and then a raw material for producing a low crystalline cellulose-containing raw material is used. It is preferable.
As the pretreatment, if necessary, a coarse pulverization treatment and an extruder treatment can be performed to make the cellulose-containing raw material into a powder having an appropriate bulk density.
The coarse pulverization process is a process of coarsely pulverizing the cellulose-containing raw material into chips before putting it into the extruder. By performing this rough pulverization process in advance, the extruder process can be performed more efficiently. The size of the cellulose-containing raw material supplied to the extruder is preferably 1 to 50 mm square, more preferably 1 to 30 mm square.
Examples of the method for roughly pulverizing the cellulose-containing raw material into chips include a method using the shredder, a rotary cutter, or the like.

(Crushing process (low crystallization process))
By pulverizing the cellulose-containing raw material together with oxidized sugar with a pulverizer, the cellulose in the cellulose-containing raw material can be efficiently low-crystallized to obtain a low-crystalline cellulose-containing raw material.
As the pulverizer, a medium pulverizer can be preferably used. The medium type pulverizer includes a container driven pulverizer and a medium stirring pulverizer.
Examples of the container-driven pulverizer include a rolling mill, a vibration mill, a planetary mill, a centrifugal fluid mill, and the like. From the viewpoint of pulverization efficiency and productivity, a vibration mill is preferable.
As the medium agitating pulverizer, a tower-type pulverizer such as a tower mill; an agitator-type pulverizer such as an attritor, an aquamizer, and a sand grinder; And the like, and a continuous dynamic type pulverizer are preferable. From the viewpoint of pulverization efficiency and productivity, a stirred tank pulverizer is preferable. In the case of using a medium stirring pulverizer, the peripheral speed of the tip of the stirring blade is preferably 0.5 to 20 m / s, more preferably 1 to 15 m / s.
Regarding the pulverizer, reference can be made to “Progress of Chemical Engineering, No. 30, Fine Particle Control” (Chemical Engineering Society, Tokai Branch, issued October 10, 1996, Sakai Shoten).
The treatment method may be either batch type or continuous type.

There is no restriction | limiting in particular as a material of the medium with which a grinder is filled, For example, iron, stainless steel, an alumina, a zirconia, a titania, a silicon carbide, silicon nitride, glass etc. are mentioned.
When the pulverizer is a container-driven pulverizer such as a vibration mill and the medium is a ball, the outer diameter of the ball is preferably 0.1 to 100 mm from the viewpoint of efficiently reducing the crystallinity of cellulose. Preferably it is 0.5-50 mm. As the shape of the medium, a ball, a rod, a tube, or the like can be used.
The medium filling rate varies depending on the model of the medium type pulverizer, but is preferably in the range of 10 to 97%, more preferably 15 to 95%. When the filling rate is within this range, the contact frequency between the cellulose-containing raw material and a medium such as a ball or a rod can be improved, and the pulverization efficiency can be improved without hindering the movement of the medium. Here, the filling rate refers to the ratio of the apparent volume of the medium to the volume of the stirring section of the medium type pulverizer.
In addition, as a vibration mill, a vibration mill manufactured by Chuo Kakki Co., Ltd., a vibro mill manufactured by Eurus Techno Co., Ltd., a small vibration rod mill manufactured by Yoshida Manufacturing Co., Ltd., a vibration cup mill manufactured by Fritsch, Germany, and manufactured by Nikko Ceramics Co., Ltd. And a small vibration mill.

The pulverization time can be appropriately adjusted according to the type of pulverizer, the type, size, and filling rate of the medium filled in the pulverizer, but preferably from 0.01 to 50 hr from the viewpoint of reducing the crystallinity. More preferably, it is 0.05-20 hr, More preferably, it is 0.1-10 hr, More preferably, it is 0.1-5 hr, Most preferably, it is 0.1-3.5 hr. The pulverization temperature is not particularly limited, but is preferably 5 to 250 ° C, more preferably 10 to 200 ° C, and still more preferably 15 to 150 ° C from the viewpoint of preventing thermal deterioration.
The amount of water in the system at the time of pulverization is preferably 20% by weight or less with respect to cellulose in the cellulose-containing raw material from the viewpoint of low crystallization efficiency. On the other hand, from the viewpoint of eliminating local bias in the effect of addition of oxidized sugars having a polymerization degree of 1 to 10, the water content in the system during pulverization is 0.1% by weight or more based on cellulose in the cellulose-containing raw material. preferable.
From the above viewpoint, the amount of water in the system at the time of pulverization is preferably 0.1 to 20% by weight with respect to cellulose in the cellulose-containing raw material, and from the viewpoint of efficiency of reducing crystallization, 1 to 10% by weight is more preferable. 2 to 8% by weight is preferable.
The order of oxidized sugar and water added during pulverization is not particularly limited, but it is preferable to add them simultaneously.
By the above-described treatment method, a cellulose-containing raw material is used as a starting material, and a low-crystalline cellulose-containing raw material having a cellulose I-type crystallinity of 33% or less is efficiently obtained while suppressing a decrease in the degree of polymerization. In addition, the cellulose-containing raw material does not adhere to the inside of the pulverizer during the pulverizer treatment, and can be processed in a dry manner.

[Step (2)] (Oxidation reaction)
In step (2), the low crystalline cellulose-containing raw material obtained in step (1) is oxidized under neutral or acidic conditions to produce polyuronic acid or a salt thereof.
The oxidation reaction in the step (2) is a reaction that selectively oxidizes the C6 primary hydroxyl group of the glucose unit in cellulose to generate a carboxy group.
Examples of the selective oxidation reaction of the primary hydroxyl group include (i) an oxidation reaction using oxygen using a platinum catalyst, (ii) an oxidation reaction using nitrogen oxides, and specific examples of (ii) include nitric acid or nitroxyl radical compounds. An oxidation reaction by a catalyst is mentioned. Among these, from the viewpoint of high selectivity of the reaction, homogeneity, and smooth progress of the oxidation reaction under milder conditions, a nitroxyl radical compound is used as a catalyst, and an oxidant, and optionally a co-oxidant or It is preferable to carry out the oxidation reaction using a cocatalyst.

<Nitroxyl radical compound>
The nitroxyl radical compound used as a catalyst in the step (2) of the present invention is a hindered amine N-oxide, and has in its molecule a nitroxyl radical represented by the following structural formula (1), It does not have a hydrogen atom at the α-position of the nitrogen atom in the structure.

As the nitroxyl radical compound, those having a bulky group at the α-position of the nitrogen atom are preferable, piperidineoxyl compounds having an alkyl group having 1 or 2 carbon atoms are more preferable, and di-tert-alkylnitroxyl compounds are more preferable. .
Examples of the di-tert-alkylnitroxyl compound include 2,2,6,6-tetraalkylpiperidine-1-oxyl such as 2,2,6,6-tetramethylpiperidine-1-oxyl; 2,2,5,5-tetraalkylpiperidine-1-oxyl such as 5,5-tetramethylpyrrolidine-1-oxyl; 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4 -Ethoxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-acetoxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-propionyloxy-2,2,6 4-alkoxy-2,2,6,6-tetraalkylpiperidine-1-oxyl such as 6-tetramethylpiperidine-1-oxyl; 4-hydroxy-2,2,6 6-tetraalkylpiperidine-1-oxyl, 4-benzyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1- Oxyl, 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-acetamido-2,2, Examples include 6,6-tetramethylpiperidine-1-oxyl.

Among these, 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxyl and 2,2,6,6-tetramethylpiperidine-1-oxyl are preferred from the viewpoint of nitroxyl radical compound reactivity. preferable.
In the oxidation reaction using a nitroxyl radical compound as a catalyst, it is considered that an oxoammonium ion, which is a one-electron oxidant of the nitroxyl radical, is generated by an oxidant described later and functions as a catalytically active species.
The amount of the nitroxyl radical compound used in step (2) is 0.00001 to 1 mol of primary hydroxyl group of cellulose in the low crystalline cellulose-containing raw material from the viewpoint of reaction rate and oxidation efficiency in step (2). 0.2 mol is preferable, 0.0001 to 0.1 mol is more preferable, and 0.001 to 0.05 mol is still more preferable.

As the nitroxyl radical compound, a commercially available product can be used, and a known method, for example, (a) a method of oxidizing a secondary amine using an organic peroxide (European Patent Application Publication No. 157738), ( b) A method of oxidizing with hydrogen peroxide in the presence of tungstate (British Patent No. 1199351), (c) A method of oxidizing with hydrogen peroxide in the presence of carbonates, silicates and the like (JP 2002-145861 A). No.) etc. may be used.
Further, the nitroxyl radical compound can be added as it is, or may be added after being dissolved or suspended in a solvent.
The solvent for dissolving or suspending the nitroxyl radical compound is not particularly limited as long as it is inert to the oxidation reaction. For example, aromatic hydrocarbons such as toluene, xylene and mesitylene, halogenated hydrocarbons such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane, ethers such as diethyl ether, diisopropyl ether and methyl tert-butyl ether, methyl isobutyl Examples include ketones, ketones such as methyl tert-butyl ketone, water alone, and mixed solvents. The amount of such solvent used is not particularly limited.

<Oxidizing agent>
Examples of the oxidizing agent used in the oxidation reaction in step (2) include halogens such as chlorine, bromine, and iodine; hypochlorous acid, sodium hypochlorite, potassium hypochlorite, lithium hypochlorite, hypochlorous acid, and the like. Hypohalous acid such as bromic acid and hypoiodous acid or a salt thereof; Chlorous acid, sodium chlorite, potassium chlorite, lithium chlorite, bromic acid, iodic acid, etc. Perhalogen acids such as perchloric acid, perbromic acid and periodic acid or salts thereof; halogen oxides such as ClO, ClO ₂ , Cl ₂ O ₆ , BrO ₂ , Br ₃ O ₇ , NO, NO ₂ , Nitrogen oxides such as N ₂ O ₃ ; hydrogen peroxide; perorganic acids such as peracetic acid or salts thereof, oxygen, and the like. These oxidizing agents can be used alone or in combination of two or more.
Among these oxidizing agents, at least one selected from hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogenic acid or a salt thereof, hydrogen peroxide, and a perorganic acid or a salt thereof is preferable. More preferred is at least one selected from hypohalous acid or a salt thereof, and halous acid or a salt thereof, more preferred is at least one selected from hypochlorous acid or a salt thereof, and chlorous acid or a salt thereof, Sodium hypochlorite and / or sodium chlorite is even more preferred.
The amount of the oxidizing agent used can be appropriately adjusted according to the desired degree of oxidation, and is not particularly limited. However, from the viewpoint of the oxidation reaction rate and the efficiency of adding the oxidizing agent, the low-crystalline cellulose used for the raw material is contained. 0.1-20 mol is preferable with respect to 1 mol of primary hydroxyl groups in a raw material, 0.5-10 mol is more preferable, and 1.4-3 mol is still more preferable.
The form of the oxidizing agent at the time of addition may be any of gas, liquid, and solid, and may be used in a state dissolved in water or an organic solvent. The oxidizing agent may be added all at once at the beginning of the reaction, or may be added in a divided manner in the oxidation reaction step.

<Co-oxidizer or promoter>
In the oxidation step of step (2), a co-oxidant or a cocatalyst can coexist with the oxidant from the viewpoint of smoothly proceeding the oxidation reaction even under milder conditions.
Examples of the co-oxidant or co-catalyst include bromide or ammonium iodide; bromide or alkali metal iodide such as lithium bromide, potassium bromide, sodium bromide, lithium iodide, potassium iodide, sodium iodide. An alkaline earth metal bromide such as calcium bromide, magnesium bromide, strontium bromide, calcium iodide, magnesium iodide, strontium iodide or an alkaline earth metal iodide; These bromide salts and iodide salts can be used alone or in combination of two or more. Of these, sodium bromide is preferred.
The amount of the co-oxidant or cocatalyst used is 0.0001 to 1 mol with respect to 1 mol of the primary hydroxyl group of cellulose in the low crystalline cellulose-containing raw material used as the raw material from the viewpoint of the oxidation reaction rate and the efficiency of adding the oxidizing agent. Is preferable, 0.001-0.5 mol is more preferable, and 0.01-0.3 mol is still more preferable.

<Oxidation reaction conditions>
In the present invention, the pH of the reaction system is maintained neutral or acidic. Under these conditions, the beta glucooxide elimination reaction of cellulose is suppressed. Specifically, the pH is preferably 4 to 7, and more preferably 4.5 to 6.5. In particular, care should be taken so that the pH does not exceed 8.
The pH of the reaction system of the present invention is a pH value at 25 ° C. of a sample obtained by diluting the reaction mixture with pure water to 5 times weight.
The reaction is preferably carried out under a condition that suppresses the pH change of the reaction system using a buffer. By using a buffering agent, the addition of acid or alkali for maintaining pH can be suppressed. Examples of the buffer include phosphate, acetate, citrate, borate, tartrate, and tris salt.
The temperature of the oxidation reaction is preferably 100 ° C. or less, more preferably 80 ° C. or less, still more preferably 70 ° C. or less, from the viewpoint of reaction selectivity and side reaction suppression, and the lower limit is from the viewpoint of reaction rate. The temperature is preferably 20 ° C. or higher.
The reaction time of the oxidation reaction can be appropriately adjusted according to the progress rate of the oxidation reaction and the desired degree of oxidation, and is not particularly limited, but is usually 0.1 to 168 hours. From the viewpoint of productivity, it is preferably 72 hours or shorter, and preferably 36 hours or shorter. On the other hand, from the viewpoint of sufficiently proceeding the reaction, it is preferably 1 hour or longer, more preferably 5 hours or longer, and further preferably 12 hours or longer.

<Solvent>
The oxidation reaction is preferably performed by dispersing a low crystalline cellulose-containing raw material in a solvent. Examples of the solvent include water, secondary alcohols having 3 to 6 carbon atoms such as isopropanol and t-butanol, and tertiary alcohols, ketones having 1 to 6 carbon atoms such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, linear or Branched saturated or unsaturated hydrocarbons having 1 to 6 carbon atoms, aromatic hydrocarbons such as benzene and toluene, halogenated hydrocarbons such as methylene chloride and chloroform, lower alkyl ethers, N, N-dimethylformamide, Examples include polar solvents such as dimethyl sulfoxide. The above solvents can be used alone or in admixture of two or more. From the viewpoint of reactivity, water, a secondary alcohol having 3 to 6 carbon atoms, a ketone having 3 to 6 carbon atoms and a polar solvent are preferable. From the viewpoint of reducing environmental burden, water is preferable.
The amount of the solvent used is not particularly limited as long as it is an effective amount capable of dispersing the low crystalline cellulose, but it is preferably used in an amount of 1 to 500 times by weight based on the low crystalline cellulose-containing raw material, and 2 to 100 wt. It is more preferable to use twice, and it is more preferable to use 10 to 80 times by weight.

<Purification>
In the production of polyuronic acid salt by the above oxidation reaction, the remaining of a catalyst such as a nitroxyl radical compound or a salt by-product tends to occur. Therefore, purification can be performed as necessary in order to obtain a highly pure polyuronate. The purification method is not limited, and an optimum method can be adopted in consideration of the type of solvent in the oxidation reaction, the degree of oxidation of the product, and the degree of purification. For example, reprecipitation using water as a good solvent, methanol, ethanol, acetone or the like as a poor solvent, extraction of a catalyst or the like into a solvent that is phase-separated from water such as hexane, purification by ion exchange of salts, dialysis, etc. Can be mentioned.

<Polyuronic acid salt>
The polyuronic acid salt obtained by the method of the present invention is a polymer in which D-glucuronic acid and glucose are linked by a glycosidic bond, or a salt thereof, and is typically represented by the following structural formula (2).
The weight average molecular weight of the polyuronic acid salt obtained in the present invention is not particularly limited, but from the viewpoint of imparting water solubility and biodegradability, it is preferably 1,000,000 or less, more preferably 500,000 or less, and still more preferably. 200,000 or less.
According to the method of the present invention, a high molecular weight polyuronic acid salt, which has been difficult to produce by the conventional method, can be efficiently produced by a method with less environmental burden. From this viewpoint, the weight average molecular weight of the polyuronic acid salt obtained in the present invention is preferably 50,000 or more, more preferably 100,000 or more, still more preferably 120,000 or more, and even more preferably 150,000 or more. In the present invention, the weight average molecular weight of the polyuronic acid salt is a pullulan equivalent molecular weight in gel permeation chromatography (GPC). Specifically, it can be measured by the method described in the examples.

In the structural formula (2), X represents a cation. Specific examples include hydrogen ions, alkali metal ions, alkaline earth metal ions, various amines, and protonated products of amino acids. Here, when the valence (a) of the cation is 2 or more, the number of X per carboxy group is 1 / a. X is preferably an alkali metal ion, more preferably a sodium ion, from the viewpoint of the water solubility of the produced polyuronic acid salt.
M in the structural formula (2) represents the molar fraction of anhydroglucuronic acid units in the monosaccharide units constituting the polyuronic acid salts. The molar fraction m is preferably from 0.1 to 0.99, more preferably from 0.3 to 0.90, still more preferably from 0.3 to 0.80, from the viewpoint of water solubility of the polyuronic acid salt to be produced. . In Structural Formula (2), when X is an alkali metal, if m exceeds 0.6, the polyuronic acid salt exhibits high water solubility.
N in the structural formula (2) indicates the molar fraction of anhydroglucose units in the monosaccharide units constituting the polyuronic acid salt, and from the viewpoint of water solubility of the generated polyuronic acid salt, n is 0.01 to 0.9 is preferable, 0.01 to 0.7 is more preferable, and 0.2 to 0.7 is still more preferable.
From these viewpoints, the molar fraction ratio (n / m) between the molar fraction n of the anhydroglucose unit and the molar fraction m of the anhydroglucuronic acid unit is preferably 0 to 0.7, more preferably 0-0.5.

In the present invention, the degree of carboxylic acid substitution of the polyuronic acid salt is preferably from 0.1 to 0.99, more preferably from 0.3 to 0.9, from 0.3 to 0.9, from the viewpoint of surface activity and water solubility. 8 is more preferable. Here, the degree of carboxylic acid substitution of polyuronic acid salt is the number obtained by dividing the number of carboxy groups per molecule of polyuronic acid by the number of monosaccharide units constituting the main chain of polyuronic acid salt. It is calculated using the equivalent number of basic compounds required for the neutralization titration. Specifically, it is a value obtained by the following calculation formula (2) from the amount of carboxylic acid per unit weight of polyuronic acid salt measured by the neutralization titration method described in the examples.
Carboxylic acid substitution degree = 162.1 × A / (1-14.0 × A) (2)
Here, A is the amount of carboxylic acid (mol / g) determined by neutralization titration.
Examples of the basic compound used for neutralization include alkali metal or alkaline earth metal hydroxides such as sodium hydroxide, potassium hydroxide, and magnesium hydroxide, ammonia, and amine compounds.
The polyuronic acid salt obtained by the production method of the present invention can be used as a biodegradable water-soluble polymer material for various uses such as a water-absorbing resin and a dispersant.

[Method for producing water-absorbing resin]
The method for producing a water-absorbent resin of the present invention is characterized in that a crosslinking agent is added to the polyuronic acid salt produced by the method of the present invention to cause a crosslinking reaction.
<Crosslinking agent>
The cross-linking agent is not particularly limited as long as it can be crosslinked with the polyuronic acid salt as necessary, and is preferably a water-soluble cross-linking agent.
As the water-soluble crosslinking agent, known compounds such as methylene bisacrylamide, epichlorohydrin, polyglycidyl compound, aldehyde compound, polycarboxylic acid, methylol compound, polyisocyanate, polyoxazoline compound can be used.
Preferred examples of the water-soluble crosslinking agent include (a) a compound having two or more hydroxyl groups in the molecule, (b) a compound having two or more (meth) acryloyl groups, and (c) a compound having two or more epoxy groups. Etc.

(A) As a compound having two or more hydroxyl groups in the molecule, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, diethanolamine, polyoxypropylene, sorbitan fatty acid ester, trimethylolpropane, Examples include pentaerythritol, 1,3-propanediol, and sorbitol.
(B) Examples of the compound having two or more (meth) acryloyl groups in the molecule include bis (meth) acrylamide, di- or polyester of (meth) acrylic acid by polyol (for example, diethylene glycol diacrylate, trimethylolpropane triacrylate, Polyethylene glycol diacrylate, etc.), di- or (meth) acrylic acid with polyols derived from the reaction of C ₁ -C ₁₀ polyhydric alcohols with 2 to 8 C ₂ -C ₄ alkylene oxides per hydroxyl group Examples thereof include polyester (for example, ethoxylated trimethylolpropane triacrylate and the like).

(C) Compounds having two or more epoxy groups in the molecule include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane poly Examples thereof include polyglycidyl ether compounds such as glycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, and hydrogenated bisphenol A type diglycidyl ether.
Among these, from the viewpoint of reactivity and water absorption performance of the resulting polymer, (b) a compound having two or more (meth) acryloyl groups in the molecule, and (c) two or more epoxy groups in the molecule. Compounds are preferred, (c) compounds having two or more epoxy groups in the molecule are more preferred, and ethylene glycol diglycidyl ether is still more preferred.

  The use ratio of the polyuronic acid salt and the crosslinking agent is arbitrary, but the ratio of the crosslinking agent is preferably 100% by weight or less, more preferably 50% by weight or less, still more preferably 30% by weight or less based on the polyuronic acid salt. It is. If the use ratio is in the above range, a water-absorbing resin having a large water absorption amount and a high water absorption rate can be obtained. On the other hand, from the viewpoint of imparting sufficient gel strength to the water-absorbent resin and obtaining a water-absorbent resin excellent in water-absorbing performance such as a centrifugal holding amount, the ratio of the crosslinking agent used is 0. It is preferably 01% by weight or more, more preferably 1% by weight or more, and still more preferably 10% by weight or more.

<Solvent>
In the crosslinking reaction of the present invention, a solvent can also be used. The types of solvents that can be used and preferred modes thereof are the same as the types of solvents described in [Step (2)] and preferred modes thereof.
The amount of the solvent used is preferably 1 to 500 times by weight, more preferably 2 to 100 times by weight, and still more preferably 10 to 50 times by weight based on the polyuronic acid salt.

<Reaction conditions>
The reaction temperature varies depending on the reactivity of the crosslinking agent used and the freezing point of the solvent used, and is not generally determined, but is usually in the range of −20 to 100 ° C., and −10 from the viewpoint of reaction rate and side reaction suppression. -60 degreeC is preferable and 0-40 degreeC is more preferable.
The reaction time varies depending on the speed of the crosslinking reaction and cannot be determined unconditionally, but is usually 0.1 to 10 hours. From the viewpoint of sufficiently allowing the reaction to proceed and from the viewpoint of productivity, the reaction time is 0.2 to 5 hours. Time is preferable, and 0.5 to 3 hours is more preferable.
The reaction can be carried out with stirring as necessary.

<Post-processing>
The water-absorbent resin obtained by the crosslinking reaction can be purified as necessary. The purification method is not limited, and an optimum method can be adopted in consideration of the type of solvent in the crosslinking reaction, the degree of swelling of the product into various solvents, and the degree of purification.
The water-absorbent resin obtained by the cross-linking reaction can be subjected to solvent removal as necessary, and can be pulverized in consideration of the optimum size, operability, etc. during application. The method for removing the solvent is not particularly limited. For example, the solvent can be removed by heating under reduced pressure. There is no particular limitation on the pulverization method, and for example, the pulverizer described in [Step (1)] can be used.
Since the water-absorbent resin of the present invention is excellent in water absorption, it is useful for sanitary materials such as sanitary napkins, disposable diapers, adult sheets, tampons, and sanitary cotton. In addition, since the raw material of this water-absorbent resin is derived from plants, the amount of CO ₂ emitted during production and disposal is small, and the burden on the global environment is small. Furthermore, this water-absorbent resin is also expected to be applied to cosmetics where importance is attached to the production of natural products.

  In the following Examples, measurement of crystallinity of cellulose in cellulose-containing raw materials, measurement of water content, measurement of cellulose content, weight average molecular weight of polyuronic acid salt, degree of carboxylic acid substitution, measurement of infrared absorption spectrum, water absorption The measurement of the centrifugal retention amount of the functional resin and the measurement of the water absorption time of the water absorbent resin were performed by the following methods. In Examples, “%” means “% by weight” unless otherwise specified.

(1) Measuring method of crystallinity of cellulose in cellulose-containing raw material and low-crystalline cellulose-containing raw material Using “Rigaku RINT 2500VC X-RAY diffractometer” manufactured by Rigaku Corporation, the measurement was performed under the following conditions.
X-ray light source: Cu / Kα-radiation, tube voltage: 40 kV, tube current: 120 mA
Measurement range: 2θ = 5-45 °,
Measurement sample: created by compressing pellets of area 320 mm ² × thickness 1 mm X-ray scanning speed: 10 ° / min
(2) A method for measuring the water content of a cellulose-containing raw material.
An infrared moisture meter (manufactured by Kett Science Laboratory, product name “FD-610”) was used to measure the moisture content of the cellulose-containing raw material. The measurement was performed at 120 ° C., and the point at which the rate of change in weight for 30 seconds was 0.1% or less was taken as the end point of measurement. The value of the measured water content was converted to mass% with respect to the cellulose-containing raw material, and was used as the water content.
(3) The amount of cellulose in the cellulose-containing raw material.
The residue obtained by removing the water content from the cellulose powder was regarded as cellulose.

(4) Measurement of the weight average molecular weight of the polyuronic acid salt The weight average molecular weight (Mw) of the polyuronic acid obtained in the examples or comparative examples is L-6000 type high performance liquid chromatography manufactured by Hitachi, Ltd. It measured on the following conditions by the gel permeation chromatography (GPC).
Detector: Shodex RI SE-61 differential refractive index detector Column: Tosoh Corporation make, G4000PWXL, G2500PWXL were used in series.
Eluent: 0.2 M phosphate buffer / acetonitrile = 90/10 (volume ratio) was adjusted to a concentration of 0.5 g / 100 mL, and 20 μL was used.
Column temperature: 40 ° C
Flow rate: 1.0 mL / min Standard polymer: Pullulan

(5) Measurement of carboxylic acid substitution degree 50 g of 2% aqueous solution of polyuronic acid salt obtained in Examples or Comparative Examples was adjusted, and the pH was adjusted to 1 or less with 6N hydrochloric acid. This acidic solution was poured into 500 mL of ethanol, and the resulting precipitate was collected, washed several times with ethanol, and dried. 0.1 g of the resulting polyuronic acid is precisely weighed, dissolved or dispersed in 30 mL of ion exchange water, titrated with 0.1N aqueous sodium hydroxide solution using phenolphthalein as an indicator, and the amount of carboxylic acid per unit weight of polyuronic acid salt From this amount of carboxylic acid, the degree of carboxylic acid substitution was calculated by the above formula (2).
(6) Measurement of infrared absorption spectrum The infrared absorption spectrum was measured by the ATRP method using an infrared spectrophotometer, FT-710, manufactured by Horiba, Ltd.

(7) Measurement of centrifugal retention amount of water-absorbing resin The centrifugal retention amount was measured according to JIS K 7223 (1996) by the following method.
Nylon woven fabric (mesh opening 25, sold by Sanriki Co., Ltd., product name: nylon net, standard: 250 x mesh width x 30 m) is cut into a 10 cm wide and 40 cm long rectangle and folded in the middle in the longitudinal direction. Then, both ends were heat-sealed to prepare a nylon bag having a width of 10 cm (inner dimension: 9 cm) and a length of 20 cm. 1.0 g of the water-absorbent resin obtained in the examples or comparative examples was precisely weighed and placed uniformly at the bottom of the produced nylon bag. The nylon bag containing the sample was immersed in physiological saline (0.9% sodium chloride water) prepared at 25 ° C. After 30 minutes from the start of immersion, the nylon bag was taken out from the physiological saline, suspended in water for 1 hour and drained, and then dehydrated using a centrifugal dehydrator (manufactured by Kokusan Co., Ltd., model H-130C). The dehydration condition is 800 rpm for 10 minutes. After dehydration, the weight of the sample was measured, and the target centrifugal retention amount was calculated according to the following formula.
Centrifugal retention amount (g / g) = (abc) / c
(a: Total weight (g) of sample after centrifugal dehydration and nylon bag, b: Weight (g) before water absorption (when dried) of nylon bag, c: Weight (g) before water absorption (when dried) of sample )

(8) Measurement of water absorption time of water-absorbing resin The water absorption time was measured in accordance with JIS K 72240 (1996).
In a 100 mL glass beaker, put 50 mL of physiological saline (0.9% sodium chloride solution) and a magnetic stirrer chip, and stir at 600 ± 60 rpm. 2.0 g of the water-absorbing resin as a measurement sample was put into the center of the vortex of physiological saline being stirred, and the time until the vortex disappeared and the liquid surface became flat was measured.

Example 1
(1) producing cellulose powder polyuronic acid salt (KC Flock W-400G Nippon Paper Chemicals Co., sintering crystallization degree 60%, 1.2% moisture content, cellulose content 98.8%) 20 g, sodium glucuronate After mixing 6.0 g of monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) and 1.0 g of ion-exchanged water, pulverization with a planetary mill (manufactured by Fritsch) for 10 minutes (rotation speed: 400 rpm), 10 The operation of standing still for 4 minutes was repeated 4 times to obtain a low crystalline cellulose powder (low crystalline cellulose-containing raw material, crystallinity 0%) [Step (1)].
4-acetamido-2,2,6,6-tetramethyl-1-piperidine-N-oxyl (4-acetamido TEMPO, manufactured by Wako Pure Chemical Industries, Ltd.) in a 2 L flask equipped with a pH meter, thermometer and stirrer 1.92 g, 20 mL of 0.1 M acetic acid aqueous solution, 30 mL of 0.1 M sodium acetate aqueous solution, 1 L of ion-exchanged water, and stirred at a rotation speed of 200 rpm. Maintaining the temperature at 25 ° C., 20 g of the low crystalline cellulose powder obtained in step (1), 34 g of sodium chlorite (manufactured by Wako Pure Chemical Industries, Ltd.), 11% sodium hypochlorite aqueous solution (Wako Pure Chemical Industries, Ltd.) After adding 20 mL), the mixture was stirred for 24 hours at 60 ° C. and a pH of 5.0 to carry out an oxidation reaction [step (2)].
After completion of the reaction, the reaction product in step (2) was poured into 5 L of ethanol to precipitate a white solid. The precipitate was collected, washed with acetone, and then dried at 40 ° C. to obtain 22 g of white sodium polyuronic acid salt (1).
The obtained sodium polyuronic acid (1) had a weight average molecular weight of 170,000 and a carboxylic acid substitution degree of 0.80. The ¹ H-NMR spectrum of the obtained sodium polyuronate (1) showed a peak derived from the sugar skeleton in the vicinity of 3.0 to 4.5 ppm. In addition, in the IR spectrum, a peak corresponding to a carboxylate ion is observed in the vicinity of 1600 cm ⁻¹ , and from these results, the primary hydroxyl group at the 6-position of anhydroglucose constituting cellulose in the cellulose powder is oxidized. It was confirmed that

(2) Production of water-absorbing resin 10 g of sodium polyuronic acid (1) obtained in (1) above, ethylene glycol diglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-810, epoxy equivalent: 113) 0 g and 200 g of ion-exchanged water were added and the mixture was stirred at 25 ° C. for 1 hour to carry out a crosslinking reaction. The obtained aqueous solution was dried under reduced pressure at 70 ° C. and then pulverized with a pulverizer (analytical pulverizer R-8, manufactured by Nihon Riken Kikai Co., Ltd.) to obtain a water absorbent resin.
The centrifugal retention amount of this water absorbent resin was 14 g / g, and the water absorption time was 40 seconds.

Example 2
Except that the amount of sodium glucuronate monohydrate (Wako Pure Chemical Industries, Ltd.) used was changed to 2.2 g, the same operation as in Example 1 was performed, and white sodium polyuronic acid (2) 20 g Got. The crystallinity of the low crystalline cellulose powder obtained during the pulverization process in the step [1] was 0%.
The obtained sodium polyuronic acid (2) had a weight average molecular weight of 170,000 and a carboxylic acid substitution degree of 0.80. The ¹ H-NMR spectrum of the obtained sodium polyuronic acid (2) showed a peak derived from the sugar skeleton in the vicinity of 3.0 to 4.5 ppm. In the IR spectrum, a peak corresponding to a carboxylate ion was observed in the vicinity of 1600 cm ⁻¹ .
Except for the point using the obtained sodium polyuronic acid (2), the centrifugal retention amount of the water absorbent resin produced by performing the same operation as that of the water absorbent resin of Example 1 was 18.0 g / g, the water absorption time. Was 45 seconds.

Example 3
The same operation as in Example 1 was carried out except that the oxidized saccharide used was changed to potassium gluconate (manufactured by Wako Pure Chemical Industries, Ltd.) to obtain 23 g of white sodium polyuronic acid (3). The crystallinity of the low crystalline cellulose powder obtained during pulverization in the step [1] was 4.9%.
The obtained sodium polyuronate (3) had a weight average molecular weight of 100,000 and a carboxylic acid substitution degree of 0.85. The ¹ H-NMR spectrum of the obtained sodium polyuronate (3) showed a peak derived from the sugar skeleton in the vicinity of 3.0 to 4.5 ppm. In the IR spectrum, a peak corresponding to a carboxylate ion was observed in the vicinity of 1600 cm ⁻¹ .
Except for using the obtained sodium polyuronic acid (3), the centrifugal retention amount of the water absorbent resin produced by performing the same operation as that of the water absorbent resin of Example 1 was 14.0 g / g, the water absorption time. Was 55 seconds.

Comparative Example 1
As a low crystalline cellulose powder, 20 g of cellulose powder (KC Flock W-400G, manufactured by Nippon Paper Chemicals Co., Ltd.) used in Example 1 and 1.0 g of ion-exchanged water were mixed, and then a planetary mill (manufactured by Fritsch). ) For 10 minutes (rotation speed: 400 rpm), and synthesis was performed in the same manner as in Example 1 except that the operation (crystallinity: 0%) obtained by repeating the operation of standing for 10 minutes was repeated 4 times. Sodium polyuronate (4) was obtained.
The obtained sodium polyuronate (4) had a weight average molecular weight of 38,000 and a carboxylic acid substitution degree of 0.75. The ¹ H-NMR spectrum of sodium polyuronate (4) showed a peak derived from the sugar skeleton in the vicinity of 3.0 to 4.5 ppm. In the IR spectrum, a peak corresponding to a carboxylate ion was observed in the vicinity of 1600 cm ⁻¹ .
Except for using the obtained sodium polyuronic acid (4), the centrifugal retention amount of the water absorbent resin produced by performing the same operation as that of the water absorbent resin of Example 1 was 3.0 g / g. . Since the water absorption time did not gel even after 3 minutes, the measurement was terminated there.

Comparative Example 2
Cellulose powder (KC Flock W-400G, manufactured by Nippon Paper Chemicals Co., Ltd.) 3.0 g used in Example 1, sodium glucuronate monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) 1.0 g, ion-exchanged water 0 After mixing 5 g, the operation of grinding with a planetary mill (manufactured by Fritsch) for 10 minutes (rotation speed: 400 rpm) and allowing to stand for 10 minutes was repeated 4 times to obtain a low crystalline cellulose powder (crystallinity 0) %). [Step (1)]
In a 1 L beaker equipped with a pH meter, 2,0,6,6-tetramethylpiperidine 1-oxyl (trade name: TEMPO, manufactured by Aldrich) 0.20 g, water 100 g, low crystalline obtained in step (1) 3 g of cellulose powder was added, and the mixture was stirred at a rotation speed of 200 rpm using a stirrer. While maintaining the temperature at 25 ° C., 29 g of sodium hypochlorite solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise. Since the pH decreased as the oxidation reaction progressed, a 0.5N aqueous NaOH solution was gradually added using a microtube pump to maintain the pH of the solution at 8.5. A substantially uniform and transparent solution was obtained at the stage where the dropwise addition of the sodium hypochlorite aqueous solution and the sodium hydroxide aqueous solution was completed.
After completion of the reaction, the reaction mixture after completion of the oxidation reaction was poured into 1 L of ethanol to precipitate a white solid. The precipitate was collected, washed with acetone, and then dried at 40 ° C. to obtain 3 g of white polyuronic acid (5).
The resulting polyuronic acid (5) had a weight average molecular weight of 25,000 and a carboxylic acid substitution degree of 0.80. The 1H-NMR spectrum of polyuronic acid (5) showed a peak derived from the sugar skeleton in the vicinity of 3.0 to 4.5 ppm. Further, in the IR spectrum, a peak corresponding to a carboxylate ion was observed in the vicinity of 1600 cm-1.
The centrifugal retention produced using the resulting polyuronic acid (5) was 4.0 g / g. Since the water absorption time did not gel even after 3 minutes, the measurement was terminated there.

Claims (8)

The manufacturing method of the polyuronic acid or its salt which has the following process (1) and (2).
Step (1): A step of obtaining a low crystalline cellulose-containing raw material by pulverizing a cellulose-containing raw material in the presence of oxidized sugar having a polymerization degree of 1 to 10 Step (2): Low crystal obtained in step (1) A process for producing polyuronic acid or a salt thereof by oxidizing a raw material containing functional cellulose under neutral or acidic conditions   The method for producing polyuronic acid according to claim 1, wherein the oxidized sugar having a polymerization degree of 1 to 10 is at least one selected from aldonic acid, uronic acid, aldaric acid, ketoaldonic acid, sialic acid, and muramic acid.   The manufacturing method of the polyuronic acid or its salt of Claim 1 or 2 which performs a grinding | pulverization process with a medium type grinder.   The method for producing polyuronic acid or a salt thereof according to any one of claims 1 to 3, wherein in step (2), an oxidation reaction is performed in the presence of a nitroxyl radical compound.   In step (2), polyuronic acid or a salt thereof according to any one of claims 1 to 4, wherein at least one selected from hypohalous acid or a salt thereof, and halogenous acid or a salt thereof is used as an oxidizing agent. Manufacturing method.   The amount of oxidized sugar having a degree of polymerization of 1 to 10 coexisting during the pulverization treatment in step (1) is 5 to 50% by weight with respect to cellulose in the cellulose-containing raw material. A method for producing polyuronic acid or a salt thereof.   The method for producing polyuronic acid according to any one of claims 1 to 6, wherein the polyuronic acid or a salt thereof has a weight average molecular weight of 100,000 or more.   The manufacturing method of the water absorbing resin which adds a crosslinking agent to the polyuronic acid manufactured by the method in any one of Claims 1-7, or its salt, and carries out a crosslinking reaction.