JPH10251402A - Biodegradable water-absorbing resin and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a biodegradable water-absorbing resin which has a high gelation ratio, absorbs water even from an aq. or salt soln., and absorbs ethanol by forming a cross-linked poly-γ-glutamic acid having a specified gelation ratio. SOLUTION: This water-absorbing resin, a crosslinked poly-γ-glutamic acid, is obtd. by dissolving poly-γ-glutamic acid in a solvent (e.g. water) to give a soln. with a concn. of 2-15wt.%, exposing the soln. to a radiation, and separating and purifying the resultant cross-linked polymer. Poly-γ-glutamic acid used as the raw material is obtd. e.g. by culturing with Bacillus subtilis, by culturing with gene recombination microorganisms, or by chemical synthesis. The polymn. of poly-γ-glutamic acid is pref. conducted by free-radical polymn. with a radiation. Pref. the dose rate is 1.0-20kGy/hr, and the dosage is pref. 30kGy or higher. After the exposure to radiation, water is removed to obtain a solid biodegradable resin, a crosslinked poly-γ-glutamic acid, having a gelation ratio of 91-100%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biodegradable water-absorbent resin and a method for producing the same. More specifically, the present invention relates to a water-absorbent resin having excellent water-absorbing ability and having biodegradability, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, water-absorbent resins have been used not only in applications such as disposable diapers, but also in medical fields such as body fluid absorbers, construction fields, food fields such as freshness preserving agents, and agricultural and horticultural fields such as greening. Used in the field. As the water absorbing resin, various kinds of water absorbing resins according to various fields are known.
Among these various water-absorbing resins, acrylic acid-based water-absorbing resins are widely used because they have a certain level of water absorbing ability and are inexpensive. However, since it has almost no biodegradability, it is known that it is not decomposed by bacteria or the like in the soil and causes environmental problems such as environmental pollution. In addition, the acrylic acid-based water-absorbing resin has a remarkably low water supply rate with respect to a salt solution and an absorptivity with respect to ethanol, and is not practically satisfactory. In order to solve this problem, starch-based water-absorbent resins, hyaluronic acid-based water-absorbent resins, and the like are known as biodegradable water-absorbent resins. As these water-absorbing resins, in particular, poly-γ-glutamic acid-based crosslinked products and the like are known as biodegradable water-absorbing resins (for example, JP-A-6-322358 and JP-A-7-300563). However, poly-γ-
The gelation ratio of glutamic acid and the like was up to 90%. Further, it has been desired to improve the water supply rate for salt solutions and the absorption rate for ethanol.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a biodegradable bioabsorbable resin comprising a crosslinked poly-γ-glutamic acid having a higher gelation ratio. Another object of the present invention is to provide a biodegradable bioabsorbent resin comprising a crosslinked poly-γ-glutamic acid having a water absorbing property for water or a salt solution and having a high absorbing property for ethanol. Another object of the present invention is to provide a method for producing a biodegradable water-absorbent resin comprising a crosslinked poly-γ-glutamic acid having a higher gelation ratio.

[0004]

The present inventors have conducted various studies to develop a water-absorbent resin comprising a crosslinked product of poly-γ-glutamic acid having biodegradability, and as a result, it has a higher gelation ratio. Succeeded in obtaining a water-absorbent resin comprising a cross-linked poly-γ-glutamic acid, and found that this cross-linked body has water absorbability without losing biodegradability,
Based on this finding, the present invention has been completed. Further, when the concentration of poly-γ-glutamic acid and the radiation dose rate are within a specific range, it is possible to obtain a water-absorbent resin comprising a crosslinked poly-γ-glutamic acid having a gelation rate of 91 to 100%. The present inventors have completed the present invention based on this finding.

That is, the present invention provides the following biodegradable water-absorbent resin and a method for producing the same. (1) A biodegradable water-absorbent resin comprising a crosslinked poly-γ-glutamic acid having a gelation ratio of 91 to 100%. (2) A biodegradable water-absorbing resin comprising a crosslinked poly-γ-glutamic acid having a gelation ratio of 94 to 100%. (3) In a method for producing a biodegradable water-absorbent resin comprising a cross-linked poly-γ-glutamic acid, radiation is irradiated after dissolving poly-γ-glutamic acid so that its concentration becomes 2 to 15% by weight. A method for producing a biodegradable water-absorbent resin, which comprises irradiating at least 30 kGy to obtain a crosslinked poly-γ-glutamic acid having a gelation ratio of 91 to 100%. (4) In a method for producing a biodegradable absorbent resin comprising a cross-linked poly-γ-glutamic acid, poly-γ-glutamic acid is dissolved so that its concentration becomes 2 to 8% by weight, and then radiation is dosed. A method for producing a biodegradable water-absorbent resin, which comprises irradiating at 1.0 to 1.4 kGy / hour to obtain a crosslinked poly-γ-glutamic acid having a gelation ratio of 91 to 100%. (5) In a method for producing a biodegradable absorbent resin comprising a cross-linked poly-γ-glutamic acid, poly-γ-glutamic acid is dissolved so that its concentration becomes 4 to 7% by weight, and then radiation is dosed. A method for producing a biodegradable water-absorbent resin, which comprises irradiating at 1.0 to 1.4 kGy / hour to obtain a crosslinked poly-γ-glutamic acid having a gelation ratio of 94 to 100%. (6) The method for producing a biodegradable water-absorbent resin according to any one of the above (3) to (5), wherein the radiation is gamma rays.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The water-absorbent resin comprising a crosslinked poly-γ-glutamic acid of the present invention has a poly-γ-glutamic acid concentration of 2 to 15% by weight, preferably 2 to 8% by weight, more preferably It can be obtained by dissolving it in a solvent such as water so as to have a concentration of 4 to 7% by weight, and then irradiating the solution with radiation, and then separating and producing the resulting crosslinked product. If it is 2% by weight or less, the water absorption is low,
If it is 15% by weight or more, the gelation rate is low, which is not preferable in terms of yield.

[0007] The poly-γ-glutamic acid used in the present invention is not particularly limited, and those produced by various production methods are used. For example, various methods such as a culture method using a microorganism, for example, Bacillus subtilis, a culture method using a genetically modified microorganism, a method using natto, or a chemical synthesis method are considered. In the case of producing poly-γ-glutamic acid by a culture method using a microorganism, any strain can be used as long as it produces poly-γ-glutamic acid outside the cells, but a Bacillus species is particularly desirable. Specific examples include Bacillus subtilis, Bacillus anthracis, and Bacillus natto. In particular, those having a molecular weight of several millions or more produced by a microorganism such as Bacillus subtilis are preferable. (Japanese Unexamined Patent Publication No. 1-174397)
When the polymerization reaction is not affected, a derivative in which a carboxyl group or the like of poly-γ-glutamic acid is modified with an alkyl group or the like can be used.

[0008] In the method for culturing microorganisms used in the present invention, any strain, medium, etc. may be used as long as poly-γ-glutamic acid is produced. For example, any of a synthetic medium and a natural medium may be used as long as the medium appropriately contains a carbon source, a nitrogen source, inorganic substances, and other nutrients. As the added amino acid, L-glutamic acid, aspartic acid, alanine, leucine, phenylalanine, histidine or the like or a salt thereof can be used, and preferably L-glutamic acid,
It is 12%, preferably 3 to 10%.

As a carbon source, glucose, sucrose,
, Citric acid or xylose can be used, but preferably citric acid or glucose. As a nitrogen source, an organic nutrient such as peptone or yeast extract, an inorganic nutrient such as ammonium sulfate, or the like can be used. The culture is performed under aerobic conditions such as shaking culture or stirring culture, and the culture temperature is 25 to 45 ° C, preferably 30 to 40 ° C. The pH during the culture is 5 to 9, preferably 6 to 8, and the pH during the culture is adjusted with sodium hydroxide, potassium hydroxide or the like.

The cultivation time is usually 48 to 72 hours and the poly-γ
-Glutamic acid is accumulated extracellularly. The poly-γ-glutamic acid in the culture solution after completion of the culture can be recovered by a conventional method. That is, the cells are removed by centrifugation, filtration aid or filter filtration having micropores, and poly-γ is obtained by ultrafiltration.
-Glutamic acid can be recovered. Also, 3-4
A double amount of ethanol or the like is added to precipitate poly-γ-glutamic acid. Dissolve the precipitate in water to remove insolubles, remove low molecular weight substances such as dialysis or ultrafiltration,
Poly-γ-glutamic acid can be recovered by repeating reprecipitation with ethanol or the like.

In the present invention, the method for polymerizing poly-γ-glutamic acid is by free radical polymerization. At this time, the type of free radical reaction varies, and the initiator of the reaction may be a peroxide, an azo compound or the like. Although not particularly limited in the case of the present invention, free radical polymerization by radiation is preferred. In the case of radiation, the dissolution of poly-γ-glutamic acid is not particularly limited as long as poly-γ-glutamic acid can be dissolved, and examples thereof include water, a methyl alcohol aqueous solution, and an ethyl alcohol aqueous solution.
Water is particularly preferred.

The solution in which the poly-γ-glutamic acid is dissolved is used in a radiolucent container such as a glass vial. The radiation is not particularly limited, and includes, for example, α-rays, β-rays, γ-rays, electron beams, neutron rays, X-rays, etc., and preferably γ-rays. The γ-rays are not particularly limited, but, for example, those generated by an irradiation device using cobalt 60 as a radiation source are used. In this case, the dose rate is preferably 1.0 to 20 kGy / hour. More preferably, the dose rate is 1.0 to 1.4 kGy / hour. The irradiation time is not particularly limited, but is preferably set to an irradiation dose of 30 kGy or more.

Thereafter, water is removed to obtain a solid water-absorbing resin. This water-absorbent resin is colorless and transparent, has excellent water absorbability, and has biodegradability. The water-absorbent resin obtained by the above method may be granulated into a predetermined shape, or may be irregularly crushed, spherical, or the like. This water-absorbent resin can be used not only in the hygiene field but also in various fields. For example, by adding the water-absorbent resin of the present invention to a microorganism culture solution, gelling the culture solution, and then appropriately processing such as addition of microorganisms, efficient composting can be achieved. In addition, the water-absorbent resin of the present invention is edible, and various edible containers can be manufactured by molding to solve environmental problems such as dust. Further, by utilizing the adhesiveness of the water-absorbent resin of the present invention, the water-absorbent resin can be used as an adhesive which does not require a moisture absorbent.

The gelation ratio used in the present invention is a value obtained by dividing the dry weight of the water-absorbent resin composed of the crosslinked poly-γ-glutamic acid by the amount of poly-γ-glutamic acid using the dry weight.
That is, it means the percentage of the dry weight of the water-absorbent resin composed of the crosslinked poly-γ-glutamic acid to the amount of the charged poly-γ-glutamic acid.

[0015]

The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. Examples 1 to 3 Meiji γ-PGA (poly-γ-glutamic acid manufactured by Meiji Seika Co., Ltd.) was dissolved in water to a concentration of 4% by weight, bubbled with nitrogen, and then 2 ml each in a 10 ml sample bottle with a lid. Put in and close the lid. In this sample bottle,
With a gamma irradiation device using cobalt 60 as a radiation source,
Irradiation was performed at room temperature at a dose rate of 1.2 kGy / hour at a dose rate of 20 kGy, 50 kGy, and 110 kGy. The treated product was taken out of a 10 ml sample bottle with a lid, immersed in water at 4 ° C. for one week, and the uncrosslinked poly-
γ-glutamic acid was removed. The poly-γ-glutamic acid hydrogel swollen by absorbing water was filtered through an 80-mesh wire gauze and freeze-dried to obtain a cross-linked poly-γ-glutamic acid. The gelation rate and the water absorption rate of the water-absorbent resin of this crosslinked body were measured, and the results are shown in Table 1. The gelation ratio was determined as a percentage of the dry weight of the water-absorbent resin composed of the crosslinked poly-γ-glutamic acid based on the amount of the charged poly-γ-glutamic acid. The water absorption was determined by immersing a water-absorbent resin composed of a cross-linked poly-γ-glutamic acid in a large excess of distilled water to sufficiently swell, and then measuring the weight (wet weight) after draining with a 80-mesh wire gauze. The weight (the amount obtained by subtracting the dry weight from the wet weight) was divided by the dry weight to obtain a numerical value.

[0016]

[Table 1]

Examples 4 to 7 Meiji γ-PGA (Meiji Seika Co., Ltd.) was prepared using 2, 5, 7, 8
After dissolving in water to a concentration of weight% and bubbling with nitrogen, 2 ml was put into a 10 ml sample bottle with a lid, and the lid was closed. The sample bottle was irradiated with γ-rays at a dose rate of 1.
Irradiation was performed at room temperature at 2 kGy / hour so that the irradiation dose was 20 kGy. The treated product was taken out of a 10 ml sample bottle with a lid and immersed in water at 4 ° C. for one week to remove uncrosslinked poly-γ-glutamic acid. The poly-γ-glutamic acid hydrogel swollen by absorbing water was filtered through an 80-mesh wire gauze and freeze-dried to obtain a cross-linked poly-γ-glutamic acid. The gelation rate and the water absorption rate of the water-absorbent resin of this crosslinked body were measured, and the results are shown in Table 2. The gelation ratio and the water absorption were measured in the same manner as in Example 1.

[0018]

[Table 2]

Examples 8 to 13 Bacillus subtilis IFO3335 strain was used as a strain to be used, and the medium shown in Table 3 was placed in a 3 ml test tube and shake-cultured at 37 ° C. overnight to prepare a preculture solution. Next, 100 ml of the medium shown in Table 2 was placed in a 500 ml Sakaguchi flask, and the preculture liquid 1 was added.
The resulting mixture was shake-cultured at 37 ° C., and the culture solution was recovered after 72 hours. Four times the amount of water is added to the collected culture solution, and p
H was adjusted to 2.5. This culture was incubated at 4 ° C. for 12,000 hours.
0r. p. After centrifugation for 30 minutes, the culture supernatant after centrifugation was ultrafiltered, and the concentrated poly-γ-glutamic acid solution was lyophilized. By this operation, 1.5 g / 100
Thus, poly-γ-glutamic acid in the ml culture solution was obtained.

The poly-γ-glutamic acid obtained by performing the above-mentioned production method several times is 2,5,7,8,10,
After dissolving in water to a concentration of 15% by weight and bubbling with nitrogen, 2 ml was placed in a 10 ml sample bottle with a lid.
Put in and close the lid. The sample bottle was irradiated with gamma rays using cobalt 60 as a radiation source at a dose rate of 10 kGy / hour at room temperature so as to have an irradiation dose of 30 kGy. Take out the obtained processed product from the 10 ml sample bottle with a lid,
It was immersed in water at 4 ° C. for one week to remove uncrosslinked poly-γ-glutamic acid. After filtering the water-swollen poly-γ-glutamic acid hydrogel through an 80 mesh wire mesh,
It was freeze-dried to obtain a cross-linked poly-γ-glutamic acid. The gelation rate and water absorption rate of the water-absorbent resin of this crosslinked body were measured, and the results are shown in Table 4. The gelation ratio and the water absorption were measured in the same manner as in Example 1.

[0021]

[Table 3]

[0022]

[Table 4]

Example 14 With respect to the water-absorbent resin of the crosslinked product obtained in Example 12, the absorptance of each salt solution was measured.
It was shown to. Absorbance was measured by immersing a water-absorbent resin composed of cross-linked poly-γ-glutamic acid in a large excess of each salt solution to sufficiently swell, then draining with a 80-mesh wire net, and measuring the weight (wet weight). It was determined by dividing the absorbed weight (wet weight minus dry weight) by dry weight.

[0024]

[Table 5]

Example 15 The water-absorbent resin of the crosslinked product obtained in Example 12 was measured for the absorptivity to various alcohol aqueous solutions, and the results are shown in Table 6. Absorbance was measured by immersing a water-absorbent resin composed of a cross-linked poly-γ-glutamic acid in a large excess of various alcohol aqueous solutions to sufficiently swell, then draining with a 80-mesh wire net, and measuring the weight (wet weight). It was determined by dividing the absorbed weight (wet weight minus dry weight) by dry weight.

The crosslinked water-absorbent resin obtained in the examples swells even in a 20% aqueous solution and a 40% aqueous solution of 2-propanol, 3-methyl-1-butanol, and 1-butanol, and has an absorbing ability. It was confirmed.

[0027]

[Table 6]

Example 16 The water-absorbent resin of the crosslinked product obtained in Example 12 was examined for its absorption capacity in various solutions, and the results are shown in Table 7. For the absorption capacity, various solutions 20
Add 0.05 g of water-absorbent resin to the solution containing
The state of various solutions was examined.

[0029]

[Table 7]

Reference Examples 1 to 5 Meiji γ-PGA (poly-γ-glutamic acid manufactured by Meiji Seika Co., Ltd.) was dissolved in water so as to have a concentration of 5, 9, 15, 20, or 25% by weight, and bubbling was performed with nitrogen. After that, 2 ml each was placed in a 10 ml sample bottle with a lid, and the lid was closed. The sample bottle was irradiated with γ-rays at a dose rate of 1.2 kGy / hour at room temperature to give an irradiation dose of 20 kGy by a γ-ray irradiator using cobalt 60 as a radiation source. The treated product was taken out of a 10 ml sample bottle with a lid, immersed in water at 4 ° C. for one week, and subjected to uncrosslinked poly-γ-
Glutamic acid was removed. Poly swelled by absorbing water
The γ-glutamic acid hydrogel was filtered through an 80-mesh wire gauze and freeze-dried to obtain a cross-linked poly-γ-glutamic acid. The gelation rate and the water absorption rate of the water-absorbent resin of this crosslinked body were measured, and the results are shown in Table 8. The gelation ratio and the water absorption were measured in the same manner as in Example 1.

[0031]

[Table 8]

Reference Example 6 Meiji γ-PGA (poly-γ-glutamic acid manufactured by Meiji Seika Co., Ltd.) was dissolved in water to a concentration of 10% by weight, bubbled with nitrogen, and placed in a 10 ml sample bottle with a lid. 2 ml was put and the lid was closed. The sample bottle was irradiated with γ-rays at a dose rate of 1.2 kGy / hour at room temperature to give an irradiation dose of 20 kGy by a γ-ray irradiator using cobalt 60 as a radiation source. The obtained processed product was taken out of a 10 ml sample bottle with a lid and kept at 4 ° C for one week.
In water to remove uncrosslinked poly-γ-glutamic acid. The poly-γ-glutamic acid hydrogel swollen by absorbing water was filtered through an 80-mesh wire gauze and freeze-dried to obtain a cross-linked poly-γ-glutamic acid. The gelation rate and the water absorption rate of this crosslinked water-absorbent resin were measured in the same manner as in Example 1, and the gelation rate was 86%.
The water absorption was 5000.

The crosslinked water-absorbent resin is
The absorption rate of each salt solution was measured in the same manner as in Example 14, and the results are shown in Table 9.

[0034]

[Table 9]

Reference Examples 7 to 10 Bacillus subtilis IFO3335 strain was used as a strain to be used, and the medium shown in Table 2 was placed in a 3 ml test tube and shake-cultured at 37 ° C. overnight to obtain a preculture solution. Next, 100 ml of the medium of Table 2 was placed in a 500 ml Sakaguchi flask, and 1 m of the preculture liquid was added.
and shaking culture was performed at 37 ° C., and a culture solution was collected after 72 hours. The recovered culture solution was 12,000 r.
p. m, centrifugation for 30 minutes, and adding a three-fold amount of ethyl alcohol to the culture supernatant after centrifugation, collects the precipitate by centrifugation, and freeze-drys to obtain a precipitate.
g / 100 ml of the culture solution was able to obtain poly-γ-glutamic acid.

The poly-γ-glutamic acid obtained by performing the above-mentioned production method several times is dissolved in water so as to have a concentration of 9, 15, 20, and 25% by weight, bubbled with nitrogen, and then 10 ml with a lid. Put 2 ml in the sample bottle,
The lid was closed. In this sample bottle, cobalt 6 was used as a radiation source.
Irradiation was carried out at room temperature at a dose rate of 1.2 kGy / hour using γ-rays using 0 at an irradiation dose of 20 kGy. The treated product was taken out of a 10 ml sample bottle with a lid and immersed in water at 4 ° C. for one week to remove uncrosslinked poly-γ-glutamic acid. The poly-γ-glutamic acid hydrogel swollen by absorbing water was filtered through an 80-mesh wire gauze and freeze-dried to obtain a cross-linked poly-γ-glutamic acid.
The gelation rate and water absorption rate of the water-absorbent resin of this crosslinked body were measured in the same manner as in Example 1, and the results are shown in Table 10.

[0037]

[Table 10]

[0038]

EFFECT OF THE INVENTION The water-absorbent resin of the crosslinked poly-γ-glutamic acid of the present invention can achieve a higher gelation rate and has excellent water absorption performance (not only can be advantageously produced in production). It also has biodegradability. The above water absorbent resin,
It can be applied not only to sanitary fields such as disposable diapers, but also to a wide range of fields such as the medical field, the construction field, the food field, and the agriculture and horticulture fields. In addition, because of its excellent biodegradability, it has the effect that disposal is safe and simple. Further, according to the production method of the present invention, it is possible to produce water absorption performance having a higher gelation rate and excellent water absorption performance.

Claims (6)

[Claims] 1. A biodegradable water-absorbing resin comprising a crosslinked poly-γ-glutamic acid having a gelation ratio of 91 to 100%. 2. A biodegradable water-absorbent resin comprising a crosslinked poly-γ-glutamic acid having a gelation ratio of 94 to 100%. 3. A method for producing a biodegradable water-absorbent resin comprising a cross-linked poly-γ-glutamic acid, comprising the steps of:
-Dissolving glutamic acid so that its concentration becomes 2 to 15% by weight, and then irradiating it with an irradiation dose of 30 kGy or more to obtain a crosslinked poly-γ-glutamic acid having a gelation ratio of 91 to 100%. Method for producing biodegradable water absorbent resin 4. A method for producing a biodegradable absorbent resin comprising a cross-linked poly-γ-glutamic acid, comprising the steps of:
After dissolving glutamic acid so that its concentration becomes 2 to 8% by weight, irradiation with radiation is performed at a dose rate of 1.0 to 1.4 kGy / hour to crosslink poly-γ-glutamic acid having a gelation rate of 91 to 100%. A method for producing a biodegradable water-absorbent resin, comprising obtaining a body. 5. A method for producing a biodegradable absorbent resin comprising a cross-linked poly-γ-glutamic acid, comprising the steps of:
-Dissolving glutamic acid to a concentration of 4 to 7% by weight, and then irradiating with radiation at a dose rate of 1.0 to 1.4 kGy / hour to crosslink poly-γ-glutamic acid having a gelation rate of 94 to 100%. A method for producing a biodegradable water-absorbent resin, comprising obtaining a body. 6. The method for producing a biodegradable water-absorbent resin according to claim 3, wherein the radiation is gamma rays.