JP5722556B2 - Method for producing polyuronic acid salt - Google Patents

Description

  The present invention relates to a method for producing a polyuronic acid salt.

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, various biodegradable water-soluble polymers that are reproducible and manufactured from natural raw materials with low environmental impact and excellent in biodegradability have been proposed and developed. One of them is a water-soluble polysaccharide or a derivative thereof. Specific examples include xanthan gum, alginic acid, pectic acid, hyaluronic acid, carboxymethylcellulose, hydroxyethylcellulose, polyuronic acid, and the like. Among them, polyuronic acid is expected to be applied to builders, dispersants, stabilizers, flocculants, viscosity modifiers, adhesives, film forming agents, and the like.

Various methods are known as methods for producing polyuronic acid, but there are problems such as a large amount of waste discharged and high production costs.
For example, Patent Document 1 discloses that amylose or starch is converted to an alkali metal bromide and an oxidizing agent in the presence of an N-oxyl compound such as 2,2,6,6-tetramethyl-1-piperidine-1-oxyl (TEMPO). A method for producing a water-soluble polyuronic acid that oxidizes is disclosed.
Patent Document 2 discloses an aqueous solution in which 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. A method for producing a soluble polyuronic acid is disclosed.
However, the methods of Patent Documents 1 and 2 have a problem that a large amount of waste is generated.
Patent Document 3 discloses a method for producing a polyuronic acid salt in which low crystalline powdery cellulose having a crystallinity of 30% or less is oxidized in the presence of an N-oxyl compound. The method of Patent Literature 3 requires a stoichiometric amount of hypochlorous acid with respect to a desired oxidation amount. In particular, in order to produce water-soluble polyuronic acid, 1.2 times mol or more of hypochlorite is required with respect to the anhydroglucose unit of the raw material cellulose, and after the reaction, the amount of hypochlorite used is reduced. Corresponding by-product salt is formed.

Non-Patent Document 1 discloses a product having a high amount of carboxylic acid (high oxidation degree) by performing a selective oxidation method of the C6 hydroxyl group of potato starch (starch) by electrolytic oxidation using TEMPO as a mediator (electron mediator). Have been reported. Since this method does not require a stoichiometric amount of oxidant, it is excellent in terms of waste reduction.
However, in the method of Non-Patent Document 1, the reaction does not proceed sufficiently with a raw material that does not dissolve in water such as cellulose, and it has been difficult to produce polyuronic acid with a high degree of water solubility and high oxidation degree.

JP 2004-189924 A JP 2006-124598 A JP 2009-263641 A

Karsten Schnatbaum, Hans J. Schafer, Synthesis, 5, p.864-872, 1999

  An object of the present invention is to provide a method for efficiently producing polyuronic acid salts by efficiently oxidizing cellulose, reducing wastes and the like.

By using low crystalline cellulose as a raw material, the present inventors efficiently produce polyuronic acid salt by using electrolytic oxidation in the presence of a mediator without using a special solvent or an oxidizing agent in a stoichiometric amount or more. I found out that I can do it.
That is, the present invention is a low crystal having a crystallinity of 0 to 30% in the presence of one or more mediators selected from N-oxyl compounds, oxime compounds, N-hydroxy compounds, nitroso compounds, and N-oxy compounds. It is a manufacturing method of the polyuronic acid salt which electrolytically oxidizes water-soluble cellulose.

  According to the present invention, it is possible to efficiently oxidize low crystalline cellulose, and to provide a method for efficiently producing polyuronic acid salts with little waste.

The method for producing a water-soluble polyuronic acid salt of the present invention comprises a crystallinity in the presence of one or more mediators selected from N-oxyl compounds, oxime compounds, N-hydroxy compounds, nitroso compounds, and N-oxy compounds. Is characterized by electrolytically oxidizing 0 to 30% of low crystalline cellulose.
Hereinafter, each component used for this invention, manufacturing conditions, etc. are demonstrated.

In the present invention, low crystalline cellulose is used as a raw material.
(Low crystalline cellulose)
In general, some crystal structures are known for cellulose, and it is known that an amorphous part and a crystal part coexist. Generally known cellulose also has an extremely small amount of amorphous part. The degree of crystallization can be quantified as the degree of crystallinity by putting the numerical value obtained from the X-ray crystal diffraction spectrum into the following formula (1).
Crystallinity (%) = [(I _22.6 −I _18.5 ) / I _22.6 ] × 100 (1)
[I _22.6 indicates the diffraction intensity of the lattice plane (002 plane) (diffraction angle 2θ = 22.6 °) in X-ray diffraction, and I _18.5 indicates the diffraction of the amorphous part (diffraction angle 2θ = 18.5 °). Indicates strength. ]
This index uses the change in the X-ray diffraction intensity on the 002 plane of the cellulose I-type crystal accompanying the change from crystal to amorphous as its index. Therefore, if the crystal form contained in cellulose is only type I, the crystallinity is theoretically a value of 0 to 100%. Actually, since there are a plurality of crystal forms in cellulose, a negative value can also be taken when crystals other than type I are sufficiently destroyed and amorphized, but in the present application, the above calculation formula (1 ) Is considered to be 0 when a negative value is obtained.

The “low crystallinity” of the low crystalline cellulose in the present invention indicates a state where the ratio of the amorphous part is large in the crystal structure of the cellulose, specifically, the crystallinity defined in the present invention is 0 to 30%. It means that.
Even if the crystallinity of cellulose is in the range of 0 to 30%, it does not dissolve in a reaction solvent such as water, but if this crystallinity is 30% or less, the electrolytic oxidation reaction of cellulose is very good. A polyuronic acid salt that progresses and has a high degree of oxidation can be efficiently obtained. In this respect, the crystallinity of cellulose is preferably 25% or less, more preferably 20% or less, and still more preferably 10% or less. Particularly in the present invention, it is most preferable to use cellulose having a crystallinity of 0% according to the above formula (1).
Since generally known cellulose also has an extremely small amount of amorphous part, the crystallinity thereof is generally included in the range of 60 to 90% according to the above formula (1) used in the present invention. Even if the electrolytic oxidation conditions of the present invention are applied to these crystalline celluloses, the oxidation proceeds only on the crystal surface, and a highly oxidized polyuronic acid salt is efficiently obtained. It is difficult.

In the present invention, the degree of oxidation of polyuronic acid salt refers to the number obtained by dividing the number of carboxy groups per molecule of polyuronic acid salt by the number of sugar units constituting the main chain of polyuronic acid salt, and neutralization of polyuronic acid. It is calculated using the number of equivalents of the basic compound used in. Specifically, it is a value obtained by the following calculation formula (2) from the amount of carboxylic acid per unit weight of polyuronic acid measured by the neutralization titration method described in the examples.
Oxidation degree (%) = [(162.1 × A) / (1-14.0 × A)] × 100 (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.

(Production of low crystalline cellulose)
Although there is no restriction | limiting in particular in the manufacturing method of the low crystalline cellulose used for this invention, The method of grind | pulverizing a cellulose containing raw material with a grinder is preferable. The cellulose-containing raw material is preferably obtained by processing with an extruder, and can be obtained, for example, by processing chip-like pulp obtained by roughly pulverizing sheet pulp with an extruder.
Examples of the extruder used in this method include a single-screw or twin-screw extruder, preferably a twin-screw extruder. From the viewpoint of applying a strong compressive shear force, a so-called kneading is applied to any part of the screw. A thing provided with a disk part is preferred.
The kneading disc portion is composed of a plurality of kneading discs, which are combined while being shifted at a constant phase. For example, a combination of 3 to 20 kneading disks, preferably 6 to 16 kneading disks, which are staggered at a phase of 90 °. The kneading disk portion can be continuously processed while applying a very strong shearing force by forcibly passing chip-like pulp through the narrow gap as the screw rotates. As a shear rate in an extruder process, 600-3000 sec < ^-1 > is preferable and 6000-2000 sec < ^-1 > is more preferable.
Although there is no restriction | limiting in particular as a processing method using an extruder, The method of throwing a chip-form pulp into an extruder and processing continuously is preferable.

As a pulverizer used in the method for producing low crystalline cellulose, a medium pulverizer is preferable. The medium type pulverizer includes a container driven pulverizer and a medium stirring pulverizer. Examples of the container-driven crusher include a rolling mill, a vibration mill, a planetary mill, and a centrifugal fluid mill. Among these, a vibration mill is preferable from the viewpoint of high grinding efficiency and productivity. As a medium agitation pulverizer, a tower-type pulverizer such as a tower mill; an agitator-type pulverizer such as an attritor, an aquamizer, and a sand grinder; a distribution tank-type pulverizer such as a visco mill and a pearl mill; For example, a continuous dynamic type pulverizer. Among these, a stirring tank type pulverizer is preferable from the viewpoint of high pulverization efficiency and productivity. When using a medium stirring pulverizer, the peripheral speed at the tip of the stirring blade is preferably 0.5 to 20 m / s, more preferably 1 to 15 m / s.
For the type of pulverizer, refer to “Progress of Chemical Engineering, Vol. 30, Fine Particle Control” (Chemical Engineering Society, Tokai Branch, issued October 10, 1996, Sakai Shoten).
The processing method may be either a batch type or a continuous type.

There is no restriction | limiting in particular as a material of the medium of a grinder, For example, iron, stainless steel, an alumina, a zirconia, silicon carbide, a silicon nitride, glass etc. are mentioned.
When the medium of the pulverizer is a ball, the outer diameter of the ball is preferably 0.1 to 100 mm, more preferably 0.5 to 50 mm. If the size of the balls is in the above range, the desired pulverization force can be obtained, and the cellulose can be efficiently amorphized without contaminating the cellulose-containing raw material by mixing pieces of balls and the like. . As the medium, a medium such as a rod or a tube can be used in addition to the ball.
The filling rate of balls varies depending on the type of pulverizer, but is preferably 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 the ball is improved, and the grinding efficiency can be improved without hindering the movement of the medium. Here, the filling rate refers to the apparent volume of the ball relative to the volume of the stirring unit of the pulverizer.

Although there is no restriction | limiting in particular in the magnitude | size of the cellulose containing raw material processed with a grinder, 1 micrometer-50 mm are preferable from an operational viewpoint, 5 micrometers-20 mm are more preferable, and 7 micrometers-10 mm are especially preferable.
The treatment time cannot be determined unconditionally depending on the type of pulverizer, the type of ball, the size, the filling rate, etc., but from the viewpoint of reducing the crystallinity, it is preferably 0.01 to 50 hr, more preferably 0.05. -20 hr, more preferably 0.1-10 hr. Although processing temperature does not have a restriction | limiting in particular, From a viewpoint of preventing deterioration by a heat | fever, Preferably it is 5-250 degreeC, More preferably, it is 10-200 degreeC.
If the method as described above is used, it is possible to control the molecular weight of the obtained low crystalline cellulose. That is, it is possible to easily produce cellulose having a high degree of polymerization and low crystallinity that is generally difficult to obtain. In the present invention, the degree of polymerization of cellulose refers to the viscosity average degree of polymerization of cellulose obtained by the copper-ammonia method described in the Examples. The degree of polymerization of the low crystalline cellulose is preferably 10 to 1000, more preferably 20 to 500, and more preferably 30 to 200.
The average particle size of the obtained low crystalline cellulose can be obtained by laser diffraction / scattering particle size distribution measurement. The average particle diameter (median diameter) of the low crystalline cellulose is not particularly limited, but is preferably 300 μm or less, more preferably 150 μm, and even more preferably 50 μm or less from the viewpoint of allowing the electrolytic oxidation reaction to proceed in a slurry state. . However, from the viewpoint of operability when carried out industrially, it is preferably 20 μm or more, more preferably 25 μm or more.

(Production of polyuronic acid salt by electrolytic oxidation method)
In the present invention, the crystallinity obtained above is 0 to 30 in the presence of one or more mediators selected from N-oxyl compounds, oxime compounds, N-hydroxy compounds, nitroso compounds, and N-oxy compounds. % Of low crystalline cellulose by electrolytic oxidation. Preferably, the polyuronic acid salt can be obtained by dispersing the low crystalline cellulose in a solvent containing the mediator and the supporting electrolyte, and performing electrolytic oxidation by a conventional method.
In the electrolytic oxidation method, anode and cathode electrodes are inserted into a reaction solution, electricity is supplied from a power source such as a potentiostat or a galvanostat, and electricity is allowed to flow between the anode and the cathode, thereby releasing electrons on the anode side. This is a reaction method for oxidizing low crystalline cellulose as a raw material.
In the present invention, in order to suppress side reactions and increase the reaction efficiency, a small amount of a mediator having a low oxidation potential is added, and after the oxidation reaction between the anode and the mediator, the mediator is oxidized and becomes highly active. And a low crystalline cellulose (indirect reaction).

(Mediator)
In the electrolytic oxidation reaction of the present invention, N-oxyl compounds, oxime compounds, N-hydroxy compounds, nitroso compounds are used as mediators from the viewpoint of selectively oxidizing the hydroxyl group at the C6 position of the anhydroglucose unit of low crystalline cellulose. And one or more compounds selected from N-oxy compounds. Among these, N-oxyl compounds, oxime compounds, and N-hydroxy compounds are preferable, and N-oxyl compounds are more preferable.
The N-oxyl compound is a hindered amine N-oxide, and more preferably a heterocyclic N-oxyl compound having a bulky group at the α-position of the amino group.

(N-oxyl compound)
The heterocyclic N-oxyl compound is preferably at least one selected from piperidine oxyl compounds having 1 or 2 carbon atoms, pyrrolidine oxyl compounds, imidazoline oxyl compounds, and azaadamantane compounds.
Specific examples of the piperidineoxyl compound having an alkyl group having 1 or 2 carbon atoms include 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO), 4-hydroxy-2,2,6,6 -Tetramethyl-piperidine-1-oxyl, 4-amino-2,2,6,6-tetramethyl-piperidine-1-oxyl, 4-oxo-2,2,6,6-tetramethyl-piperidine-1- Oxyl, 4-methoxy-2,2,6,6-tetramethyl-piperidine-1-oxyl, 4-acetoxy-2,2,6,6-tetramethyl-piperidine-1-oxyl, 4-acetamido-2, 2,6,6-tetramethyl-piperidine-1-oxyl, 4- (isothiocyanato) -2,2,6,6-tetramethyl-piperidine-1-oxyl, 4-maleimide 2,2,6,6-tetramethyl-piperidine-1-oxyl, 4-benzoyloxy-2,2,6,6-tetramethyl-piperidine-1-oxyl, 4- (4-nitrobenzoyloxy) -2 , 2,6,6-tetramethyl-piperidine-1-oxyl, 4- (phosphonooxy) -2,2,6,6-tetramethyl-piperidine-1-oxyl, 4-cyano-2,2,6,6 - tetramethyl - piperidine-1-oxyl, PIPO (polymer-bound piperidinyloxy Le), SiO ₂ supported TEMPO, polystyrene - and polyacrylic acid-supported TEMPO, and the like.
Examples of the pyrrolidineoxyl compound having an alkyl group having 1 or 2 carbon atoms include 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolidine-1-oxyl.
Examples of the imidazoline oxyl compound having an alkyl group having 1 or 2 carbon atoms include 4-phenyl-2,2,5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyl, 4-carbamoyl-2,2 , 5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyl, 4-phenacridene-2,2,5,5-tetramethyl-imidazolidine-1-oxyl, and the like.
Examples of the azaadamantane compound include 2-azaadamantane-N-oxyl and 1-methyl-2-azaadamantane-N-oxyl.

Among these, from the viewpoints of solubility in solvents and reactivity, piperidine oxyl compounds having a methyl group or azaadamantane compounds are preferred, and 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) is preferred. ), 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl, 4-amino-2,2,6,6-tetramethyl-piperidine-1-oxyl, 4-methoxy-2, 2,6,6-tetramethyl-piperidine-1-oxyl, 4-acetoxy-2,2,6,6-tetramethyl-piperidine-1-oxyl, 4-benzoyloxy-2,2,6,6-tetra More preferred is methyl-piperidine-1-oxyl, 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO), 4-hydroxy-2, , 6,6-tetramethyl-piperidine-1-oxyl, 4-methoxy-2,2,6,6-tetramethyl-piperidine-1-oxyl, 2-azaadamantane-N-oxyl, 1-methyl-2- Azaadamantane-N-oxyl is more preferred, and 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) is particularly preferred.
The amount of the mediator in the present invention may be a catalytic amount, and is preferably 0.001 to 5% by mass, more preferably 0.1 to 4% by mass, and particularly preferably 0.1% by mass with respect to the low crystalline cellulose. It is 5 to 3% by mass.

(Oxidizer, etc.)
In the present invention, an oxidizing agent having the ability to oxidize a reduced form of the N-oxyl compound can also be used. As the oxidizing agent, considering the solubility and reaction rate when the solvent is adjusted to an alkaline range, alkali metal hypohalites, alkaline earth metal hypohalites, alkali metal hypohalites, halogen halides, and the like. Acid alkaline earth metal salts, halogen acid alkali metal salts, halogen acid alkaline earth metal salts and the like can be mentioned.
In order to perform the oxidation reaction more efficiently, a halogen-containing salt can be added to the reaction system. Examples of the halogen-containing salt include halogenated alkali metal salts, halogenated alkaline earth metal salts, halogenated ammonium salts, and halogenated tetraalkylammonium salts.
The amount of the oxidizing agent used varies depending on the degree of oxidation desired for the produced polyuronic acid salt, but from the viewpoint of the load during purification, it is 0 to 0 per mole of anhydroglucose unit of the low-crystalline cellulose as the raw material. 0.5 mol is preferable, 0 to 0.1 mol is preferable, and it is particularly preferable not to use it.

(electrode)
There is no restriction | limiting in particular in the material and shape of the electrode used for the electrolytic oxidation reaction of this invention, The electrode used for a normal electrolytic reaction can be utilized widely. For example, the anode material includes platinum, gold, titanium, platinized titanium, stainless steel, nickel, ruthenium, lead oxide, iron oxide, carbon, etc., and the cathode material includes platinum, gold, titanium, platinized titanium, Tin, aluminum, stainless steel, zinc, lead, copper, carbon, etc. are mentioned. Among these, from the viewpoint of corrosion resistance and reactivity, a combination of platinum, platinum-plated titanium, graphite, and glassy carbon is more preferable as the anode and cathode materials.
As the electrolysis apparatus, a single tank electrolysis apparatus with two electrodes (anode and cathode) is used, but a filter press type electrolysis apparatus and the like can also be used.
The electrode interval is not particularly limited as long as a necessary current can be applied, but it is usually installed at intervals of 5 mm to 10 cm.

(solvent)
The electrolytic oxidation reaction in the present invention is preferably carried out by dispersing low crystalline cellulose in a solvent. Examples of the solvent include water, alcohols having 1 to 3 carbon atoms such as methanol, ethanol, and propanol, ketones having 1 to 6 carbon atoms such as acetone and methyl isobutyl ketone, n-pentane, n-hexane, and 2-pentene. Linear or branched saturated hydrocarbons having 1 to 6 carbon atoms such as 1-hexene, linear or branched unsaturated hydrocarbons having 1 to 6 carbon atoms such as 2-pentene and 1-hexene, benzene, Examples include aromatic hydrocarbons such as toluene, halogenated hydrocarbons such as methylene chloride and chloroform, polar solvents such as esters, lower alkyl ethers, cyclic ethers, N, N-dimethylformamide, and dimethyl sulfoxide. In these, water, a C1-C6 alcohol, a C1-C6 ketone, and a polar solvent are preferable from a reactive viewpoint, and water is preferable from a viewpoint of environmental impact reduction.
The said solvent can be used individually or in mixture of 2 or more types.

(Supporting electrolyte)
The supporting electrolyte used in the electrolytic oxidation of the present invention is not particularly limited as long as it is a salt that is soluble in a solvent and in which the solution after dissolution can be energized, and various supporting electrolytes used in general electrolytic reactions should be used. Can do. Above all, from the viewpoint of solubility in a solvent and electrolytic oxidation reactivity, alkali metal carbonate, alkaline earth metal carbonate, alkali metal phosphate, alkaline earth metal phosphate, alkali metal halide, alkali halide In addition to earth metal salts, there may be mentioned alkali metal hydroxides, alkaline earth metal hydroxides, various amines, pH buffers such as amino acids, and the like.
Examples of the alkali metal carbonate include lithium carbonate, sodium carbonate, and potassium carbonate, and examples of the alkaline earth metal carbonate include magnesium carbonate and calcium carbonate. Examples of the alkali metal phosphate include sodium dihydrogen phosphate, disodium phosphate, potassium dihydrogen phosphate, and dipotassium phosphate. Examples of the alkaline earth metal phosphate include magnesium phosphate and calcium phosphate. Is mentioned.
Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide, and examples of the alkaline earth metal hydroxide include barium hydroxide and calcium hydroxide.
Among these, from the viewpoints of electrolytic oxidation reactivity and product yield, alkali metal hydroxides or alkaline earth metal hydroxides are preferable as the supporting electrolyte, and alkali metal hydroxides are more preferable.
These supporting electrolytes can be used alone or in combination of two or more.
The amount of the solvent used in the electrolytic reaction is not particularly limited and may be appropriately selected depending on the reaction conditions and the like, but is usually about 2 to 2000 liters, preferably about 5 to 100 liters per kg of low crystalline cellulose as a raw material. And it is sufficient.

Although there is no restriction | limiting in particular about the usage-amount of a supporting electrolyte, When using a buffer, it is preferable to use it in the quantity used as 0.05-2 mol / L with respect to the solvent to be used, 0.1-1 mol / L L is more preferable. The buffer solution is not particularly limited as long as it is a buffer aqueous solution having a pH in the range of 6 to 10, and a sodium carbonate / sodium bicarbonate buffer aqueous solution or the like can be used.
When using an alkali metal hydroxide or an alkaline earth metal hydroxide as the supporting electrolyte, it is preferable to use 0.5 to 10 times mol of 1 mol of anhydroglucose unit of the raw material low crystalline cellulose, 1-3 moles are more preferred.
When alkali metal hydroxide or alkaline earth metal hydroxide is used for the supporting electrolyte, the alkali metal hydroxide or alkaline earth metal hydroxide is neutralized with the formation of carboxylic acid as the reaction proceeds, and the reaction Since the pH of the system is lowered, it is preferable to sequentially add alkali metal hydroxide or alkaline earth metal hydroxide in order to maintain the pH.

(Electrolytic reaction conditions)
The temperature of the electrolytic reaction is preferably 50 ° C. or lower from the viewpoint of reaction selectivity and suppression of side reactions. More preferably, it is 40 degrees C or less, More preferably, it is 30 degrees C or less. The lower limit is preferably −5 ° C. or higher from the viewpoint of reactivity.
Moreover, since the pH of the reaction system has a great influence on the reactivity of the electrolytic oxidation reaction, it is preferably carried out in the range of pH 4 to pH 14. More preferably, it is pH 6-pH 14, More preferably, it is pH 7-pH 13, Especially preferably, it is pH 10-13.
In the electrooxidation reaction, it is preferable to stir during the reaction.

(potential)
The potential in the electrolytic oxidation reaction is a potential between electrodes measured by a reference electrode (SCE) inserted from the outside. The preferred potential varies depending on the mediator used and the supporting electrolyte, but is 0.1 to 2.0 V vs. SCE. Is preferable from the viewpoint of the selectivity of the reaction. More preferably, it is 0.2-1.5V vs SCE, Most preferably, it is 0.3-1.0V vs SCE.
The reaction time varies depending on the electric potential, and also varies depending on the desired amount of oxidation, but the amount of electricity calculated from the current value and time passed is 3 to 50 F / mol per mole of anhydroglucose unit of cellulose used as a raw material. The reaction time is preferably More preferably, it is 5 to 40 F / mol.
Electrolytic oxidation can be performed under potential regulation conditions or applied voltage regulation conditions, but is preferably performed under current density regulation conditions that are easy to operate. The current density is usually 1 to 5000 mA / cm ² , preferably 10 to 500 mA / cm ² .

(Purification)
In the production of polyuronic acid salts, mediators remain or salts are by-produced, and therefore purification operations are performed as necessary. Examples of the purification method include reprecipitation using water as a good solvent and methanol, ethanol, acetone or the like as a poor solvent, extraction of a mediator into a solvent that is phase-separated with water, ion exchange of salts, purification by dialysis, and the like. However, an optimum method can be adopted in consideration of the type of solvent in the electrolytic oxidation reaction, the degree of oxidation of the product, the degree of purification desired, and the like.

(Polyuronic acid salt)
The polyuronic acid salt obtained by the above method 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 (1).
The weight average molecular weight of the polyuronic acid salt is not particularly limited, but is preferably in the range of 500 to 500,000, more preferably 1,000 to 200,000, from the viewpoint of imparting water solubility and biodegradability. In addition, a weight average molecular weight is a pullulan conversion molecular weight in gel permeation chromatography (GPC).

In the structural formula (1), 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 (1) indicates the molar fraction of anhydroglucuronic acid units in the polyuronic acid salt and is synonymous with the degree of oxidation of polyuronic acid. The molar fraction m, that is, the degree of oxidation of the polyuronic acid salt, is preferably from 60 to 100%, more preferably from 70 to 100%, from the viewpoint of the water solubility of the polyuronic acid salt produced. In the structural formula (1), when X is an alkali metal, the polyuronic acid salt exhibits high water solubility if m exceeds 60%.
N in the structural formula (1) indicates the molar fraction of anhydroglucose units in the polyuronic acid salt, and n is preferably 0 to 40%, more preferably from the viewpoint of the water solubility of the resulting polyuronic acid salt. 0-30%.
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 following examples, the crystallinity, polymerization degree, and average particle size of cellulose, and the weight average molecular weight and oxidation degree of polyuronic acid salt were measured by the following methods.
(1) Calculation of crystallinity of cellulose The crystallinity of cellulose is calculated from the peak intensity of the diffraction spectrum measured under the following conditions using “Rigaku RINT 2500VC X-RAY diffractometer” manufactured by Rigaku Corporation. It was calculated by the formula (1).
X-ray light source: Cu / Kα-radiation,
Tube voltage: 40 kV, tube current: 120 mA, measurement range: 2θ = 5-45 °,
Measurement sample: compressed by pellets with an area of 320 mm ² × 1 mm thickness X-ray scanning speed: 10 ° / min

(2) Measurement of degree of polymerization of powdered cellulose The degree of polymerization of powdered cellulose was calculated from the results of kinematic viscosity measurement by the copper-ammonia method described in ISO-4312 method.
(3) Measurement of average particle diameter of powdered cellulose The average particle diameter of powdered cellulose was measured using a laser diffraction / scattering particle size distribution measuring device “LA-920” (manufactured by Horiba, Ltd.). The measurement conditions were that the sample was dispersed in water and then treated with ultrasonic waves for 1 minute before the particle size measurement, and the volume-based median diameter was measured at a temperature of 25 ° C.

(4) Measurement of weight average molecular weight of polyuronic acid salt The weight average molecular weight of polyuronic acid salt was measured under the following conditions using gel permeation chromatography (GPC).
Column: Tosoh Corporation G4000PWXL + G2500PWXL
Eluent: 0.2M phosphate buffer / acetonitrile = 9/1 (volume ratio)
Measurement temperature: 40 ° C., flow rate: 1.0 mL / min, detector: UV or RI
Standard polymer: Pullulan

(5) Measurement of degree of oxidation of polyuronic acid salt Sodium polyuronic acid obtained in Examples was prepared as a 2% aqueous solution, and the pH was adjusted to 1 or less with 6N hydrochloric acid. This acidic aqueous solution was poured into ethanol, and the resulting precipitate was collected and washed several times with ethanol. 0.05 g of the obtained polyuronic acid is precisely weighed and dissolved in 30 mL of ion exchange water, and titrated with 0.1N sodium hydroxide aqueous solution using phenolphthalein as an indicator to determine the amount of carboxylic acid per unit weight of polyuronic acid salt. It was. Furthermore, from this amount of carboxylic acid, the degree of oxidation of polyuronic acid [mole fraction of uronic acid (m in structural formula (1)]) was determined by the above formula (2).
Further, the molar fraction of glucose units that are not uronic acid units (n in the structural formula (1)) was determined by the following formula (3).
Mole fraction of glucose units (n) = 100−m (3)

Production Example 1 (Production of Amorphized Powdered Cellulose)
A wood pulp sheet (Bolleguard's pulp sheet, crystallinity 74%) was shredded (manufactured by Meiko Shokai Co., Ltd., “MSX2000-IVP440F”) into a chip shape.
Next, the obtained chip-like pulp was charged at 2 kg / hr into a twin-screw extruder (manufactured by Suehiro EPM, "EA-20") equipped with a kneading disk at the center of the screw, and a shear rate was obtained. Under the conditions of 660 sec ⁻¹ and a screw rotation speed of 300 rpm, one pass treatment was performed while flowing cooling water from the outside to form powder.
Next, the powdered cellulose thus obtained is mixed into a batch-type medium stirring ball mill (Nihon Coke Kogyo Co., Ltd., “Attritor”: container volume 800 mL, 6 mmφ steel ball 1400 g filled, stirring blade diameter 65 mm) 100 g of cellulose was added. While cooling water was passed through the container jacket, pulverization was performed at a stirring rotation speed of 600 rpm to obtain powdered cellulose (crystallinity 0%, polymerization degree 72, average particle size 40 μm).

Example 1
A 200 mL beaker containing a magnetic stir bar was charged with 100 g of ion exchange water, and 0.16 g of 2,2,6,6-tetramethyl-1-piperidine-1-oxyl (TEMPO) was dissolved therein. Thereto was added 0.81 g of the amorphous cellulose powder obtained in Production Example 1, and the mixture was stirred and dispersed. After 1.7 mL of 1M sodium hydroxide was added to adjust the pH to 12, an electrode (area 40 × 45 mm) in which platinum foil (manufactured by Katani Sangyo Co., Ltd.) was attached to a plastic sheet as an anode, and glassy carbon (B The electrode which attached AMS Co., Ltd. area (25x25mm) with the caterpillar clip was immersed in the reaction liquid so that it might become a 1-cm space | interval. Moreover, the calomel electrode (made by BAS Co., Ltd.) was inserted in the reaction solution as a reference electrode, and each electrode was attached to the terminal of potentiostat (Hokuto Denko Co., Ltd. HA-151).
The electrolytic oxidation reaction was performed such that the set potential was 0.53 V vs SCE and the potential was constant. During the electrolytic oxidation reaction, the pH was appropriately measured. When the pH was lower than 12, 1M sodium hydroxide was added. After 81.4 hours, the electrolytic oxidation reaction was stopped. During the electrolytic oxidation, the initial current value was 36 mA, but when the electrolytic oxidation reaction was terminated, it decreased to 0.7 mA. 8.8 mL of 1M sodium hydroxide was added. The reaction-terminated liquid was filtered with a filter paper (manufactured by Advantech, No. 2), the filtrate was reprecipitated with ethanol, washed with ethanol three times, then washed with acetone, and the precipitate was dried under reduced pressure. The obtained product was 0.61 g of sodium polyuronic acid having an oxidation degree of 71%, and its weight average molecular weight was 1,770.

Reference example 2
Carbonate buffer solution 105.94 g (sodium hydrogen carbonate: 5.64 g, sodium carbonate: 0.3 g, ion-exchanged water 100 g, pH 8.5) was used as a reaction solvent, and the anode was made of glassy carbon (BSS Corporation). The reaction was carried out under the same reaction conditions as in Example 1 except that the cathode was platinum-plated titanium (Denbo Kogyo Co., Ltd., 40 × 45 mm). Since a buffer solution was used here, post-addition of sodium hydroxide was not performed as in Example 1. After electrolytic oxidation for 112.5 hours, the reaction solution was filtered (manufactured by Advantech, No. 2). The filtrate was adjusted to pH 5 or less with 6M hydrochloric acid, and then reprecipitated with ethanol. The precipitated product was washed with ethanol three times, then with acetone, and dried under reduced pressure. The obtained product was 0.12 g, sodium polyuronic acid having an oxidation degree of 63%, and its weight average molecular weight was 1640.

  The polyuronic acid salt obtained by the production method of the present invention is suitable as a biodegradable water-soluble polymer material for a wide range of uses such as a dispersion / stabilizer, a flocculant, a viscosity modifier, an adhesive, and a film-forming agent. Can be used.

Claims (5)

In the presence of one or more mediators selected from a heterocyclic N-oxyl compound, a piperidine oxyl compound having a C 1 or C 2 alkyl group, a pyrrolidine oxyl compound, an imidazoline oxyl compound, and an azaadamantane compound , Production of polyuronic acid salt by electrolytic oxidation by dispersing low crystalline cellulose having a crystallinity of 0 to 30% in a solvent containing alkali metal hydroxide and / or alkaline earth metal hydroxide as supporting electrolyte Method. The method for producing a polyuronic acid salt according to claim 1, wherein the mediator is a piperidine oxyl compound having an alkyl group having 1 or 2 carbon atoms . The production of a polyuronic acid salt according to claim 1 or 2, wherein the piperidineoxyl compound having an alkyl group having 1 or 2 carbon atoms is 2,2,6,6-tetramethyl-piperidine-1-oxyl. Method. A piperidine oxyl compound having an alkyl group having 1 or 2 carbon atoms, which is a heterocyclic N-oxyl compound after obtaining a low crystalline cellulose having a crystallinity of 0 to 30% by pulverizing with a pulverizer In the presence of one or more mediators selected from pyrrolidine oxyl compounds, imidazoline oxyl compounds, and azaadamantane compounds , the cellulose is treated with an alkali metal hydroxide and / or alkaline earth metal hydroxide as a supporting electrolyte. A method for producing a polyuronic acid salt, which is dispersed in a solvent and electrolytically oxidized. The method for producing a polyuronic acid salt according to claim 4, wherein the mediator is a piperidine oxyl compound having an alkyl group having 1 or 2 carbon atoms.