JP2001181387A - Water absorptive polymer and manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel water absorptive polymer obtained by crosslinking a polyglutamic acid with a metal. SOLUTION: The water absorptive polymer is constituted by crosslinking a polyglutamic acid and/or a polyglutamic acid salt with a trivalent metal. Use of aluminum, particularly its double salt which is alum as this metal can provide an edible water absorptive polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a water-absorbing polymer containing polyglutamic acid or the like as a main component and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, various kinds of polymer materials have been developed, and one of them is a water-absorbing polymer. This water-absorbing polymer has the ability to absorb water tens to hundreds of times its own weight. Utilizing such properties, it can be used as a sanitary article such as a disposable diaper or a body fluid absorbent, in the medical field, fresh fish, etc. It is widely used as a preservative in the food field, agricultural and horticultural fields such as desert greening, and the like.

An acrylic water-absorbing polymer obtained by copolymerizing starch, cellulose or the like with acrylonitrile or the like is widely used as the water-absorbing polymer. Although this acrylic water-absorbing polymer is inexpensive, it lacks biodegradability and has a problem that it is not decomposed by bacteria in the soil. The biodegradability of such a polymer is a property required to solve the problem of waste disposal of a polymer material. Therefore, the development of a biodegradable water-absorbing polymer is also required.

[0004] In order to meet such demands, biodegradable water-absorbing polymers have been developed. As biodegradable water-absorbing polymers, there are starch-based water-absorbing resins and hyaluronic acid-based water-absorbing resins, and polyglutamic acid-based crosslinked products have been proposed. For example, JP
-251402 discloses a polyglutamic acid-based crosslinked product obtained by irradiating poly-γ-glutamic acid with radiation and crosslinking by radical polymerization.

[0005]

However, a crosslinked polyglutamic acid has been proposed as a water-absorbing polymer. However, since a conventional crosslinked polyglutamic acid is produced by irradiation with radiation, equipment and the like are required for the production. It was restricted and it was difficult to manufacture easily.

[0006] The conventional polyglutamic acid-based crosslinked product may be limited in its use. For example, polyglutamic acid is included as an ingredient in foods such as Bacillus natto (B. subtilis) gum and can be edible, but a crosslinked polyglutamic acid produced by irradiation with radiation cannot be used for food. Limited.

On the other hand, konjac mannan is a water-absorbing polymer commonly used for food. However, although konjak mannan has water absorbency, its water absorption rate is low. Therefore, in addition to konjac mannan, development of an edible and highly water-absorbing polymer has been desired.

Accordingly, the present invention has been made in view of the above-mentioned problems, and has as its object to provide a biodegradable polyglutamic acid-based water-absorbing polymer which can be easily produced, and a highly edible polymer. It is to provide a water-absorbing polymer.

[0009]

In order to achieve the above object, the water-absorbing polymer of the present invention comprises polyglutamic acid and / or polyglutamate (hereinafter referred to as "polyglutamic acid and / or polyglutamate"). Etc.) are crosslinked with a metal.

By cross-linking polyglutamic acid or the like with a metal as described above, a water-absorbing polymer can be produced from polyglutamic acid or the like without using conventional radiation or the like.

The metal in the water-absorbing polymer may be divalent or higher in order to form a crosslink, but preferably trivalent or higher.

The polyglutamic acid or the like is preferably poly-γ-glutamic acid and / or poly-γ-glutamate. The polyglutamic acid or the like, if it is polyglutamic acid or the like, may be a synthesized product, for example, a product obtained by purifying a biological product such as Bacillus natto, or a product contained in a culture supernatant such as Bacillus natto. included.

[0013] The present invention also includes a method for producing a water-absorbing polymer in which polyglutamic acid or the like is crosslinked with a metal. In this method, polyglutamic acid or the like and a composition containing a metal are mixed in an aqueous solution. Process.

By mixing polyglutamic acid and the like and the composition containing a metal in an aqueous solution, crosslinking of the polyglutamic acid and the like with the metal is started, and a gel which is a polymer of polyglutamic acid and the like is formed. .

When polyglutamic acid and the like and a composition containing a metal are mixed in an aqueous solution, when both the composition containing the polyglutamic acid and the like and the composition containing a metal are mixed as an aqueous solution, the polyglutamic acid and the like remain powdered. In the case of mixing with an aqueous solution of a composition containing a metal in the case where the composition containing a metal is mixed with an aqueous solution of polyglutamic acid or the like as a powder, further, both are added and mixed in an appropriate aqueous solution while the powder remains There are cases.

The composition containing a metal is a metal compound,
And its resalts.

In the above method, the aqueous solution is preferably acidic. For example, when the pH of the aqueous solution is 3 to 6
Can be adjusted.

In the present invention, the term "water-absorbing" means a substance capable of simply absorbing water, and is a substance capable of absorbing several hundred to several thousand times as much as a general water-absorbing polymer. It is not limited, and includes, for example, those capable of absorbing about tens of times more moisture than its own weight.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The water-absorbing polymer of this embodiment and a method for producing the same will be described.

1. Water-absorbing polymer The water-absorbing polymer in this embodiment is formed by crosslinking polyglutamic acid and / or polyglutamate with a metal. Hereinafter, each of these components will be described in detail.

The polyglutamic acid is preferably poly-γ-glutamic acid. The poly-γ-glutamic acid is not particularly limited, and those produced by various production methods can be used. For example, a culture method using a microorganism, a chemical synthesis method, and an oxygen synthesis method can be considered. In particular, it is preferable to use polyglutamic acid having a molecular weight of several millions or more, which is produced by a microorganism such as Bacillus subtilis (JP-A-1-17439). In the case of products produced by microorganisms,
It may be poly-γ-glutamic acid existing in the culture supernatant, or may be purified from the culture supernatant.

The above-mentioned polyglutamic acid salt is a poly-glutamic acid salt.
It is preferably γ-glutamate. This poly
γ-glutamic acid salt can be obtained by reacting poly-γ-glutamic acid with a basic compound.

Here, the basic compound is not particularly limited, and alkali metals such as lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, barium hydroxide, magnesium hydroxide, etc. Organic basic compounds such as oxides and amines are preferably used.

When poly-γ-glutamic acid is produced from poly-γ-glutamic acid and a basic compound,
The ratio of γ-glutamic acid to the basic compound is determined by poly-γ
-0.5 to 1. relative to one equivalent of carboxylic acid of glutamic acid.
It is preferable to use 0 equivalent of the basic compound. More preferably, the ratio of the basic compound is 0.7 to 0.95 with respect to one equivalent of the carboxylic acid of poly-γ-glutamic acid.

When poly-γ-glutamic acid is reacted with a basic compound, the pH of the reaction system can be acidic, for example, in the range of 3 to 6, and preferably 3.5 to 6.
5.0.

Further, poly-γ-glutamic acid or poly-γ-glutamic acid
The metal that crosslinks γ-glutamate may be a divalent or higher-valent metal so that it can react with a plurality of carboxyl groups of glutamic acid, but in order to form a polymer having high water absorption, trivalent or higher is necessary. Is preferably used. For example, examples of the trivalent metal include aluminum, chromium (III), and iron (III).

In the case of forming a crosslink, a crosslink can be formed using a metal compound containing these metals. The metal compound is not particularly limited, but an aluminum compound is preferable, and a double salt thereof can also be suitably used. There is no particular limitation as long as the compound is an aluminum compound or a double salt thereof.
Dodecahydrate (also known as alum), potassium aluminum sulfate (anhydride), ammonium ammonium sulfate 1
Examples include dihydrate (also known as ammonium alum), ammonium ammonium sulfate (anhydride), dihydroxyaluminum aminoacetate, and the like.

In addition to aluminum, chromium (II
I) A compound or a salt thereof can also be suitably used, and for example, potassium chromium (III) sulfate or the like can be used.

The above-mentioned metals include trivalent or higher valent metals such as aluminum, chromium (III) and iron (III). However, in order to form edible water-absorbing polymers, they are recognized as edible. It is preferable to use aluminum, specifically, alum, which is a salt thereof.

By using alum for cross-linking polyglutamic acid, both polyglutamic acid and alum are recognized as edible, and the resulting water-absorbing polymer is expected to have edibility. Therefore, it can be a novel water-absorbing polymer replacing konjac mannan.

As described above, the water-absorbing polymer of the present embodiment is used for conventional cosmetics, general-purpose products, pharmaceuticals, sanitary articles such as disposable diapers, civil engineering materials used in landfills, agricultural chemicals, and other conventional water-absorbing polymers. In addition, those using alum have uses as foods.

2. Method for producing water-absorbing polymer The method for producing a water-absorbing polymer comprises three main steps: addition of raw materials in an aqueous solution, mixing and stirring, and recovery of the product.

(1) Step of adding polyglutamic acid or the like and the above-mentioned metal compound or its salt to an aqueous solution In this addition step, these raw materials may be added to the aqueous solution. Glutamic acid or the like may be added in a solid state, or an aqueous solution of a polyglutamic acid or the like may be added to the aqueous solution of the metal compound.
However, in order to form a homogeneous polymer having high water absorption, it is preferable that the metal compound be an aqueous solution and polyglutamic acid or the like is added to the aqueous solution as it is.

The solution used here is not particularly limited as long as it can dissolve polyglutamic acid or the like and a metal compound or a double salt thereof, and examples thereof include water and dimethyl sulfoxide. Water can be suitably used.

The mixing ratio of polyglutamic acid and the like to the metal compound and the like in these aqueous solutions is 1
The metal compound or its salt can be mixed in an amount of 1 to 20 parts by weight with respect to 00 parts by weight. For example, when alum is used as the metal compound or the like, if less than 1 part by weight, the crosslinking reaction does not sufficiently proceed, and a crosslinked product having high water absorption cannot be obtained. On the other hand, when the amount exceeds 20 parts by weight, a high water absorption rate is not exhibited and an undesirable result is obtained.

However, this ratio may vary slightly depending on the type of metal and the like, and can be appropriately changed depending on the type of metal.

As the reaction mode, either a homogeneous system or a suspension system can be suitably used. Here, the homogeneous system will be exemplified. Therefore, when polyglutamic acid is used in the above, a basic compound is added to the aqueous solution to which the metal compound and polyglutamic acid have been added, so that the polyglutamic acid is uniformly dissolved in the reaction solution.

As the basic compound that can be used here, as described above, an alkali metal compound and an alkaline earth metal compound such as sodium hydroxide, potassium hydroxide, lithium hydroxide, and calcium hydroxide are used. Can be. Of these, it is preferable to use sodium hydroxide in order to form a polymer having a high water absorption. The basic compound is preferably added as an aqueous solution in order to easily adjust the amount of the basic compound.

The amount of the basic aqueous solution to be added can be determined based on the carboxylic acid in polyglutamic acid. For example, the amount of the basic aqueous solution to be added is 0.5 to 1.0 equivalent of the basic compound with respect to 1 equivalent of the carboxylic acid, and more preferably 0.7 to 0.95. can do.

When the ratio of the basic compound is less than 0.5, a water-absorbing polymer can be produced, but the solubility of polyglutamate in water is reduced, and high water-absorbing property is not obtained. It is in.

The amount of the basic compound to be added can also be determined based on the pH of the aqueous solution. For example, after polyglutamic acid and a metal compound are added, a basic compound is added, and the pH of the aqueous solution is 3.0 to 6.0, preferably,
It can be added until pH 3.5-5.0.

The reaction temperature is preferably from 10 ° C. to 100 ° C., particularly preferably from 15 ° C. to 40 ° C. If the temperature is lower than 10 ° C., an extremely long time is required for the reaction to proceed. Therefore, the aqueous solution is maintained at this suitable temperature, and the process proceeds to the following stirring step.

(2) Stirring Step The aqueous solution is stirred, and polyglutamic acid and the like and a metal compound are mixed to progress the polymer formation.

First, the first stirring step for mixing the polyglutamic acid and the metal compound in the aqueous solution is started after these raw materials are added, and is performed until the raw materials are sufficiently homogeneously mixed in the aqueous solution. . Therefore, in this step, as long as the raw materials are sufficiently homogeneously mixed, there is no limitation on the stirring time and stirring conditions.

Next, the second stirring step is also a step which affects the formation of the finally obtained gel and its water absorption. The stirring conditions in this step are to monitor the final water absorption and the like. However, it is desirable to determine appropriate conditions.

For example, the second stirring step can be performed simultaneously with the addition of the basic compound for dissolving the polyglutamic acid in the aqueous solution of the metal compound as described above. Specifically, an aqueous solution of a basic compound is added dropwise, and the mixture is stirred at a speed of 50 to 350 rpm. However, in order to form a polymer having a high water absorption, 15
The stirring speed is preferably about 0 to 250 rpm, and more preferably about 150 rpm. This second stirring step is further divided into the first half and the second half, and the first half is divided into three.
Stir at a relatively high speed such as 50 rpm, 50
By stirring at a relatively slow speed of about 100 rpm to about 100 rpm, the entire stroke of the second stirring step can be reduced by 15 minutes.
It is possible to produce a water-absorbing polymer having a high water absorption close to that when stirring at 0 rpm.

Note that this value corresponds to the polyglutamic acid 20
g, 0.2 M alum aqueous solution 35 ml, distilled water 55 m
and a 14N aqueous sodium hydroxide solution 1
Since the results are based on the results when 0 ml is dropped in 1 ml portions, it is not appropriate to change the stirring speed appropriately while monitoring the water absorption of the finally obtained polymer when the volume, material, etc. are changed. It is easy for a trader.

After the second stirring step, as a third stirring step, stirring is performed slowly for 1 to 2 hours, and the stirring operation is completed.

(3) Step of recovering water-absorbing polymer After completion of the stirring step, the reaction solution is left as it is to obtain a gel-like crosslinked product. Unreacted raw materials and the like are removed from the gel-like crosslinked product, and water is further removed, whereby a water-absorbing polymer having a water absorption rate of several tens to several hundreds of its own weight is recovered.

3. Apparatus for producing water-absorbing polymer The apparatus for producing the above-mentioned water-absorbing polymer is not particularly limited, and the reaction can be carried out in a separable flask or a water bath equipped with a stirring device. The device having the configuration described above can be suitably used.

For example, the apparatus for producing a water-absorbing polymer needs to be provided with a reaction bath for performing a crosslinking reaction. Further, it is preferable that a temperature control unit for controlling the temperature of the reaction system accommodated in the reaction bath is provided.

Further, it is preferable that a stirring means for stirring the solution or the like in the reaction bath is provided. The stirring means may be provided with a control section or the like, and may be configured to automatically adjust the stirring speed set in accordance with the above-described first, second, and third stirring steps.

Further, if necessary, a washing means for washing and removing unreacted raw materials from the crosslinked product formed after the completion of the crosslinking reaction, and a drying means for removing water from the crosslinked product after washing, etc. It can also be provided.

According to such an apparatus, a water-absorbing polymer can be easily produced from polyglutamic acid and a metal compound.

[0055]

Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 Production of Crosslinked Polyglutamic Acid by Purified Poly-γ-Glutamic Acid and Kali alum Potassium aluminum sulfate dodecahydrate (Kali alum) was dissolved in distilled water to prepare a 0.2 M aqueous solution. A mixed aqueous solution of 35 ml of this aqueous solution and 55 ml of distilled water was added to 20 g of polyglutamic acid and mixed. While lowering the aqueous solution of sodium hydroxide adjusted to 14N, the mixture was stirred until the polyglutamic acid was dissolved. When the dissolution was completed, the stirring was stopped, and the mixture was allowed to stand for 2 days. As a result, 115 g of a gel (crosslinked polyglutamic acid) was obtained.

In order to measure the water absorption of the formed gel, the gel was allowed to stand in a large amount of distilled water for 2 days. After that, unreacted substances and the like were removed by filtration, and the weight (g) of the swollen gel was measured. Next, after freeze-drying the gel, the weight (b) was measured again, and the water absorption (a / b) was measured.
I asked. As a result, the water absorption of the crosslinked polyglutamic acid produced here was about 150 times.

Example 2 Influence of Capacity of Aqueous Solution The amount of distilled water to be mixed with the 0.2 M aqueous solution of potassium aluminum sulfate (or called alum solution) in Example 1 was changed from 55 ml to 35 ml. A crosslinked product was produced in the same manner as in Example 1, and the water absorption was measured.

That is, 20 g of polyglutamic acid was added to and mixed with 35 ml of a 0.2 M aqueous solution of potassium aluminum sulfate and 35 ml of distilled water, and an aqueous solution of sodium hydroxide adjusted to 14N was added to the mixture.
With stirring, the polyglutamic acid dissolved. After the dissolution was completed, the mixture was allowed to stand for 2 days to obtain a crosslinked polyglutamic acid.

Next, in order to measure the water absorption, the crosslinked product was allowed to stand in a large amount of distilled water for 2 days, unreacted substances and the like were filtered, and then the weight (g) of the swollen gel was measured. Thereafter, the gel was freeze-dried, and its weight (b) was measured again.
The water absorption (a / b) was determined. As a result, the water absorption of the crosslinked polyglutamic acid in this example was about 250 times.

As described above, it was shown that the water absorption varies depending on the volume of the aqueous solution when dissolving polyglutamic acid. Therefore, by adjusting the volume of the aqueous solution, a water-absorbing polymer having a desired water absorption can be produced.

Example 3 Crosslinking with Various Metal Compounds A crosslinking reaction was carried out using various metal compounds other than potassium aluminum sulfate dodecahydrate, and the presence or absence of a water-absorbing polymer due to crosslinking and the measurement of the water absorption were measured. Was done.

The metal compounds studied in this example are:
(1) potassium aluminum sulfate 12 hydrate, (2) aluminum ammonium sulfate 12 hydrate, (3) aluminum sulfate 14-18 hydrate, (4) potassium chromium (III) sulfate 12 hydrate, (5 ) Iron (III) sulfate n-hydrate,
(6) cobalt acetate, (7) nickel acetate, (8) magnesium sulfate, and (9) calcium chloride.

The crosslinking reaction was carried out as follows. First, as shown in Table 1, mixed aqueous solutions were prepared. Using these mixed aqueous solutions, the same operation as in Example 1 was performed to determine whether or not a crosslinked product was formed, and for those in which the crosslinked product was formed, the presence or absence of water absorption and the measurement of the water absorption were measured. Table 2 shows the results.

[0065]

[Table 1]

[Table 2] As shown in Table 2, (1) aluminum potassium sulfate 12
Using the metal compounds (2) to (4) other than the hydrate, a crosslinked polyglutamic acid having water absorbency could be produced.

Among these, (3) aluminum sulfate 14
In the case where １８18 hydrate was used, a crosslinked product having a high water absorption of over 250 times as high as (1) potassium aluminum sulfate dodecahydrate was produced. When (2) aluminum ammonium sulfate dodecahydrate and (4) potassium chromium (III) sulfate dodecahydrate were used, a crosslinked product having a water absorption of more than 160 times was formed.

When iron (III) sulfate n-hydrate was used, gelation was caused by crosslinking with polyglutamic acid, but no water absorption was exhibited.

As described above, the formation of a crosslinked body was examined using various metal compounds. As a result, formation of a crosslinked body was observed in a trivalent metal.

Example 4 Examination of Mixing Ratio of Poly-γ-Glutamic Acid and Metal Compound The presence or absence of gel formation was determined by variously changing the amounts of polyglutamic acid (PGA) and a 0.2 M aqueous solution of potassium aluminum sulfate. The water absorption at the time was examined. The amount of the mixed aqueous solution of the aqueous solution of potassium aluminum sulfate and distilled water was fixed at 90 ml.

Table 3 shows the amount of polyglutamic acid, the amount of 0.2 M aqueous solution of potassium aluminum sulfate in a mixed aqueous solution (90 ml), the presence or absence of gelation when a crosslinked product was formed using this mixed aqueous solution, and the transparency of the gel. (PGA solubility) is shown.

[0071]

[Table 3] As shown in Table 3, when the amount of the 0.2 M aqueous solution of potassium aluminum sulfate was smaller than that of PGA, gelation was not likely to occur. This indicated that gelation requires a certain amount of 0.2 M aqueous solution of aluminum potassium sulfate, that is, an amount of metal ions such as aluminum ions. Conversely, when the amount of the 0.2 M aqueous solution of potassium aluminum sulfate was large, the transparency of the gel tended to decrease.

Accordingly, it was shown that an appropriate amount of a 0.2 M aqueous solution of potassium aluminum sulfate was required to form a gel (a crosslinked PGA) without leaving undissolved PGA.

In the present embodiment, a 0.2 M aqueous solution of potassium aluminum sulfate was used, but other aluminum sulfate 14 to 18 hydrates, aluminum ammonium sulfate 12 hydrate, potassium chromium (III) sulfate 12 For an aqueous solution such as a hydrate, an appropriate amount for forming a crosslinked body can be determined by similar experiments.

Example 5 Examination of Mixing Operation In the above examples, a metal compound such as alum was dissolved to form an aqueous solution, and polyglutamic acid powder was mixed and dissolved in this aqueous solution. In the examples, this mixing operation was performed in the following three ways. Then, the gelation due to the formation of the crosslinked body and the influence on the water absorption of the gel were examined by the difference of these operations.

The three operations include (1) mixing an aqueous solution of polyglutamic acid with an aqueous alum solution, (2) mixing an alum solid with an aqueous solution of polyglutamic acid, and (3) dissolving the solid polyglutamic acid in an alum aqueous solution. Is mixed.

More specifically, in the first operation, a 10% aqueous 15% (W / V) polyglutamic acid solution finally adjusted to pH 5.0 using an aqueous sodium hydroxide solution was used.
Was prepared. 0.2 M alum aqueous solution 5
The mixture was vigorously stirred while dropping ml, to form crosslinks.

In the second operation, similarly to the first operation, a 15% (W / V) aqueous solution of polyglutamic acid finally adjusted to pH 5.0 using an aqueous sodium hydroxide solution was used.
0 ml was prepared. To this aqueous solution, alum 0.474
After adding 4 g, stirring was attempted to form a crosslink.

The third operation is as shown in the second embodiment.
20 g of polyglutamic acid was mixed with a mixed aqueous solution of 35 ml of a 0.2M alum aqueous solution and 55 ml of distilled water, and the mixture was stirred while dropping a 14N aqueous sodium hydroxide solution until the polyglutamic acid was dissolved to form a crosslink. Table 4 shows the results.

[0079]

[Table 4] As shown in Table 4, in the first and third operations, a crosslinked body was formed and gelation was observed, but no gelation occurred in the second operation. This indicates that in order to form a crosslinked product, it is necessary to prepare at least a metal compound such as alum as an aqueous solution and mix it with PGA.

In the first operation, a gel was produced, but the produced gel was inferior in homogeneity. Therefore, it was shown that it is preferable to add a polyglutamic acid solid to the aqueous metal compound solution in order to form a homogeneous crosslinked gel.

Example 6 Examination of pH Final in Reaction System In this example, the pH of the aqueous solution of polyglutamic acid was adjusted.
However, it was examined whether or not this had an effect on gelation. For this study, the amount of the 14N aqueous sodium hydroxide solution added to dissolve polyglutamic acid was changed,
An acidic or alkaline aqueous solution of polyglutamic acid was prepared.

The gel was purified using these aqueous solutions of polyglutamic acid having different pH values. As a result, the gel was purified in the acidic aqueous solution of polyglutamic acid. However, gelation did not occur in the alkaline aqueous solution of polyglutamic acid.

Example 7 Examination of Stirring Speed It was examined whether the stirring speed at the time of dissolving polyglutamic acid affects the physical properties of the finally obtained gel.

Here, 20 g of polyglutamic acid, 0.1 g of polyglutamic acid were used.
35 ml of 2M alum aqueous solution and 55 ml of distilled water are mixed and stirred for 30 minutes to 1 hour. Thereafter, a 1N aqueous solution of 14N sodium hydroxide was added thereto in an amount of 1 ml each, and the mixture was added dropwise until the total amount of the final mixture became 10 ml. At this time, the first 5m
The process of dropping 1 was defined as “process A”, and the process of dropping the remaining 5 ml was defined as “process B”.

A gel was formed by changing the stirring speed in the steps A and B variously. The water absorption of each gel finally obtained was measured, and the measurement results are shown in Table 5. The water absorption was measured in the same manner as in Example 1.

[0086]

[Table 5] As shown in Table 5, the condition showing the highest water absorption was the case where stirring was performed at 150 rpm in both processes A and B shown as condition 6. Next, conditions 5, 4, and 3, that is, process A is 350 rpm and process B is 50, 75,
This was followed by stirring at 100 rpm. Thus, it has been shown that there is an optimal stirring speed for producing a gel having a high water absorption.

Example 8 Influence of the Type of Polyglutamic Acid Dissolving Salt on the Water Absorption of the Gel In Example 1 described above, a 14N aqueous sodium hydroxide solution was used for dissolving polyglutamic acid. A gel was formed by adding the salt as powder, and the water absorption of the formed gel was measured. Table 6 shows the results. Except for the above points, the conditions for gel formation were the same as in Example 1.

[0088]

[Table 6] As shown in Table 6, a water-absorbing gel could be produced using any powder of sodium hydroxide, potassium hydroxide, lithium hydroxide, and calcium hydroxide. However, the water absorption of each gel was different, and sodium hydroxide showed the highest water absorption among these. Next, the water absorption decreased in the order of potassium hydroxide, lithium hydroxide, and calcium hydroxide.

[0089]

As described above, according to the present invention, a polymer having water absorbency can be produced from polyglutamic acid, which is a natto fungus gum, and a polyvalent metal ion such as aluminum. This water-absorbing polymer has a use as a food in addition to the conventional use, by selecting a metal ion that is approved for use in foods such as alum.

Claims (7)

[Claims] 1. A water-absorbing polymer in which polyglutamic acid and / or polyglutamate is crosslinked with a metal. 2. The water-absorbing polymer according to claim 1, wherein the metal is a trivalent or higher valent metal. 3. The method of claim 1, wherein the polyglutamic acid and / or polyglutamic acid salt is poly-γ-glutamic acid and / or poly-glutamic acid.
The water-absorbing polymer according to claim 1, which is a γ-glutamate. 4. A method for producing a water-absorbing polymer in which polyglutamic acid and / or polyglutamate is crosslinked with a metal, wherein the polyglutamic acid and / or polyglutamate and a composition containing the metal are mixed in an aqueous solution. A method for producing a water-absorbing polymer, comprising mixing. 5. The method for producing a water-absorbing polymer according to claim 4, wherein the metal is trivalent. 6. The aqueous solution according to claim 4, wherein 100 parts by weight of the polyglutamic acid and / or polyglutamate and 1 to 20 parts by weight of the composition containing the metal are mixed in the aqueous solution. 3. The method for producing a water-absorbing polymer according to 1.). 7. The method for producing a water-absorbing polymer according to claim 4, wherein the aqueous solution is acidic.