JPH06322358A - New biodedgradable high water absorbent and its production - Google Patents

Abstract

PURPOSE:To obtain a biodegradable water absorbent, excellent in biocompatibility and useful as a soil improving agent, a material, etc., for artificial skin by dissolving a specific amount of poly(gamma-glutamic acid) in water, etc., exposing the resultant solution to radiation and then separating the produced cross-linked material. CONSTITUTION:The objective water absorbent having 40-90% gelatinization ratio is obtained by dissolving poly(gamma-glutamic acid) produced by a microorganism in water or a mixed solvent of the water with a water-soluble solvent such as methyl alcohol so as to provide 1.5-6wt.% concentration thereof, exposing the resultant solution to radiation such as-rays preferably at 1.0-50Mrad and then separating the produced cross-linked material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel biodegradable highly water absorbent body and a method for producing the same. The biodegradable superabsorbent of the present invention undergoes biodegradation in nature, and therefore, for example, a modifier in the field of civil engineering, a soil improver in the field of agriculture and horticulture, a seed coating agent, a water retention agent for plant cultivation, in the field of makeup and toiletries. It can be used for disposable diapers, sanitary products, and mechanochemical materials.

[0002]

2. Description of the Related Art It is known that a super absorbent body is formed by using graft polymerization, radiation crosslinking, ionic crosslinking, crosslinking with a crosslinking agent, molecular crosslinking by repeating freezing and melting on a water-soluble polymer. There is. Unlike water absorbents such as cloth and cotton, these compounds take advantage of the property that they do not release water even when pressure is applied, and after absorbing water-based dirt, products that can hold it, such as disposable diapers and It is often used for sanitary products.

As such a water-absorbing material, a starch-based high water-absorbing material obtained by graft-polymerizing a synthetic monomer such as acrylic acid into starch as a raw material and three-dimensionally crosslinking it, or a biological hydrogel Examples of the hyaluronic acid-based superabsorbent, chemically synthesized polyvinyl alcohol-based superabsorbent, acrylate-based superabsorbent, and acrylamide-based superabsorbent.

[0004] When used in the natural world like a soil conditioner, these superabsorbents remain without being decomposed in the natural world after use. Also, it is very difficult to collect these. Therefore, from the viewpoint of environmental protection, there is an urgent need to develop a highly water-absorbing body having biodegradability that is decomposed by microorganisms living in the natural world after use and taken into the natural carbon cycle.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a biodegradable superabsorbent body which overcomes the drawbacks of the conventional superabsorbent body and can be used in the natural world. It was made as.

[0006]

Means for Solving the Problems As a result of various researches conducted to develop a biodegradable highly water-absorbing body, the present inventors have found that poly (γ-glutamic acid), which is a biodegradable water-soluble polymer.
Based on this finding, it was found that a cross-linked product having a predetermined gelation rate obtained by irradiating a predetermined concentration of an aqueous solution or an aqueous solution with a predetermined irradiation dose of radiation has excellent water absorption without losing biodegradability. The present invention has been completed.

That is, according to the present invention, the gelation rate is 40 to 90.
% Of poly (γ-glutamic acid) radiation-crosslinked product.

In the present invention, the gelation rate means the percentage of the dry weight of the crosslinked poly (γ-glutamic acid) radiation to the amount of charged poly (γ-glutamic acid).

The biodegradable superabsorbent material of the present invention comprises poly (γ-
Glutamic acid) is dissolved in water or a mixed solvent of water and a water-soluble solvent so that the concentration thereof is 1.5 to 6% by weight, preferably 2 to 5% by weight, and then the resulting solution is irradiated with radiation. Can be produced by separating the crosslinked product thus produced.

The poly (γ-glutamic acid) used in the present invention is not particularly limited and may be produced by any production method such as a production method using a microorganism or a chemical synthesis method. However, those produced by a microorganism such as Bacillus Those produced by microorganisms such as Bacillus spp. Such as Subtilis [eg Biosci. Biotech.
Biochem. , 56, 1031 to 1035 (199
2), JP-A-1-174397]. Among them, those having a molecular weight of several hundreds of thousands to several hundreds of thousands are preferable.

In the present invention, the water-soluble solvent used as a mixed solvent with water for dissolving poly (γ-glutamic acid) is not particularly limited, but poly (γ-glutamic acid) may be dissolved in It is preferable that the ratio of water is sufficient and the ratio of water-soluble solvent is appropriately adjusted. Examples of the water-soluble solvent include methyl alcohol, ethyl alcohol, acetone, methyl acetate, ethyl acetate and the like.

The solution in which poly (γ-glutamic acid) is dissolved is preferably placed in a radiation permeable container such as a glass vial and sealed before use. There is no particular limitation on the radiation applied to this solution. For example, α rays, β
Rays, γ rays, electron rays, neutron rays, X rays, charged particle rays and the like can be mentioned, but γ rays are preferably used, and β rays, electron rays and α rays have a small penetrating power, so that the object is a film. Allows you to get in the shape.

When γ-rays are used for such a radiation irradiation treatment, the γ-rays are preferably used in an irradiation dose of 1.0 to 50 Mra.
d, preferably 1.5 to 40 Mrad, more preferably 2 to 30 Mrad, and the crosslinking usually proceeds at room temperature.

The γ-ray is not particularly limited, but for example, the one generated by an irradiation device using cobalt 60 as a radiation source or the like is used. In the cross-linking, the temperature is not particularly important, and the cross-linking usually proceeds at room temperature.

The crude product thus obtained is subjected to a purification treatment with an aqueous medium, preferably water such as distilled water, to remove uncrosslinked polymers and decomposed products, thereby forming a desired highly pure crosslinked product. A biodegradable super absorbent body can be prepared. This purification treatment is usually performed by dipping, dialysis or the like.

The biodegradable highly water-absorbent material thus obtained is a colorless and transparent gel, has excellent water absorbability, and swells in a mixed solvent of water and alcohol or a mixed solvent of acetone and water. , Methyl alcohol, ethyl alcohol, acetone, tetrahydrofuran, chloroform, benzene, n
-Does not swell in hexane or n-heptane.

The characteristics of the biodegradable highly water-absorbing material of the present invention differ depending on the radiation dose and the concentration of the solution. At low doses and low concentrations, the degree of cross-linking is small and the water absorption rate is high. When the concentration is high, the crosslinking is saturated and the water absorption is relatively low, but sufficient water absorption can be maintained even in this case.

The biodegradable highly water-absorbent material of the present invention can be repeatedly used. There is no change in the water absorption performance even if the crosslinked body that has absorbed water is lyophilized to be dried and swollen again in water. Even if this was repeated several times, there was almost no change in the water absorption performance.

The biodegradable highly water-absorbent material of the present invention has a pH value of
As a result, the water absorption performance changes, and the water absorption rate is low in the acidic pH range and high in the alkaline pH range. This indicates that the volume changes depending on the environment in which the crosslinked product is placed, and can be expected to be used for mechanochemical materials.

[0020]

EFFECTS OF THE INVENTION The biodegradable highly water-absorbent body of the present invention is excellent in biodegradability because it is decomposed by microorganisms living therein even if left in the natural environment.

Therefore, the biodegradable highly water-absorbent material of the present invention can be suitably used as a soil improving agent, a seed coating agent, a material for a water retaining agent for plant cultivation, which is left in the natural environment after use. Since it can be easily treated after use, it can be used for sanitary products, materials for disposable diapers, etc., respectively.

The superabsorbent material of the present invention has good compatibility with living organisms, and thus can be used as a material for artificial skin, and also as a material for mechanochemical elements by utilizing volume change due to the surrounding environment.

[0023]

The present invention will be described in more detail with reference to Examples.

Examples 1 to 12 The conditions for forming a crosslinked product by changing the irradiation dose were examined. Poly (γ-glutamic acid) produced by a microorganism was dissolved in water so as to have a concentration of 5% by weight, 0.5 ml was dispensed into each 1 ml vial and the lid was closed. Each of these samples was irradiated with γ rays at various irradiation doses as shown in Table 1 by a γ ray irradiation device equipped with cobalt 60 (110 TBq) as a radiation source. Each of the obtained sample treated products was taken out of each vial and immersed in distilled water to remove uncrosslinked polymers and decomposition products. In this way, highly crosslinked products were obtained. With respect to each of these crosslinked products, the gelation rate [gel dry weight / percentage ratio of charged poly (γ-glutamic acid)] and water absorption rate (water content maximally retained in crosslinked product / gel dry weight) were measured. The results are shown in Table 1.

[0025]

[Table 1]

The crosslinked body formed at an irradiation dose of 1.92 Mrad was fragile, but had a water absorption rate of 3550, that is, it was able to absorb about 3500 times as much water as its own weight. The gelation rate tends to increase as the irradiation dose increases, and the water absorption rate increases when the irradiation dose is low,
Moreover, it decreases with the increase of the irradiation dose, and when the irradiation dose is high, it becomes almost the same because the crosslinking is saturated, and in any case, the water absorption rate exceeds 100 and it can be seen that sufficient water absorption performance is exhibited.

The infrared absorption spectrum of the crosslinked product obtained in Example 5 with the irradiation dose of 10.24 Mrad is shown in FIG. From this, it was confirmed that this crosslinked product was a crosslinked product of poly (γ-glutamic acid). The crosslinked product was a water-insoluble gel.

The biodegradability of the obtained crosslinked product was examined as follows. That is, when each crosslinked product was buried in soil (field) and left to stand, it was decomposed until it halved after 2 months and completely decomposed after 4 months.

Examples 13 to 16 The conditions for forming crosslinked products when the concentration of the aqueous poly (γ-glutamic acid) solution subjected to γ-ray irradiation was changed were examined. Poly (γ-glutamic acid) was dissolved at 2 to 5% by weight, 0.5 ml was dispensed into each 1 ml vial, and the vial was capped. For each of these samples, cobalt 60 (110 TB
γ-ray irradiation device equipped with q) as a radiation source
Irradiation treatment was performed at each irradiation dose of rad and 10 Mrad. Each of the obtained sample treated products was taken out of each vial and immersed in distilled water to remove uncrosslinked polymers and decomposition products. In this way, highly crosslinked products were obtained. The water absorption rate of each of these crosslinked products was measured. The results are shown in Table 2.

[0030]

[Table 2]

Comparative Example A γ-ray-irradiated product was obtained in the same manner as in Example 13 except that the concentration of poly (γ-glutamic acid) was changed to 1% by weight. This product showed formation of a crosslinked product and gelation. I couldn't do it.

Example 17 It was examined whether the desired crosslinked product can withstand repeated use. The crosslinked product of Example 16 produced at an irradiation dose of 10 Mrad was immersed in distilled water for 1 week and freeze-dried. The amount of water retained at this time was measured to determine the water absorption rate. I repeated this several times. The results are shown in Table 3.

[0033]

[Table 3]

From the above, it can be seen that the crosslinked product retains its properties when first used even after repeated use and can withstand repeated use.

[Brief description of drawings]

FIG. 1 is an infrared absorption spectrum diagram of a crosslinked product produced at an irradiation dose of 10.24 Mrad in Example 5.

Claims (4)

[Claims] 1. A biodegradable highly water-absorbing material comprising a radiation-crosslinked poly (γ-glutamic acid) having a gelation rate of 40 to 90%. 2. Poly (γ-glutamic acid) is dissolved in water or a mixed solvent of water and a water-soluble solvent so that the concentration thereof is 1.5 to 6% by weight, and then the resulting solution is irradiated with radiation. After that, a method for producing a biodegradable highly water-absorbing body, which comprises separating the produced crosslinked body. 3. The irradiation of radiation is a γ-ray irradiation dose of 1.0.
The method according to claim 2, wherein the irradiation is performed at -50 Mrad. 4. The method according to claim 3, wherein the poly (γ-glutamic acid) is produced by a microorganism.