JP2008094951A - Process for producing radiation crosslinked hydrogel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable low cost production of a carboxymethylcellulose (CMC) hydrogel with the use of a low concentration CMC aqueous solution by a low irradiation dose. <P>SOLUTION: The hydrogel is produced by irradiating an aqueous solution of CMC having a low concentration of 5 pts.wt. or less and a metal salt such as calcium chloride with γ rays of 3 kGy or more to allow the CMC to gel and dipping the obtained gel in water to eliminate the metal salt. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for producing a radiation-crosslinked CMC hydrogel (hereinafter simply referred to as CMC hydrogel) in which carboxymethylcellulose (CMC) is gelled by irradiation. In particular, the present invention relates to a method for producing a CMC hydrogel that requires only a very small amount of radiation for the gelation of CMC.

CMC is the most commonly used water-soluble polymer at present. By irradiating the CMC aqueous solution with radiation such as γ-rays and cross-linking the CMC molecules, a cellulose molecule has a three-dimensional network structure, and a gel is obtained in which water is firmly captured inside the network structure. It is known. Since the gel thus obtained is an environmentally-conserved and highly safe gel, it is widely used in foods, pharmaceuticals, water retaining materials and the like.

As described above, a method for preparing a CMC hydrogel by irradiating a CMC aqueous solution with radiation such as γ rays is disclosed in, for example, JP-A-2001-2703 (Patent Document 1).

JP2001-2703

As apparent from FIGS. 1 and 3 of Patent Document 1, generally, as the CMC concentration increases and the irradiation dose of γ rays increases, the gel fraction increases and the degree of swelling decreases. Therefore, in the conventional method as described above, in order to obtain a large amount of CMC hydrogel, it is necessary to use a large amount of CMC, and further, it is necessary to increase the irradiation dose of γ-rays, resulting in a production cost. There was a problem of high.

Accordingly, an object of the present invention is to provide a method for producing a hydrogel that can produce a polysaccharide hydrogel at low cost by using a low concentration polysaccharide aqueous solution such as a low concentration CMC aqueous solution and with a low irradiation dose. There is.

The present invention basically adds a metal salt such as calcium chloride, magnesium chloride, magnesium sulfate to a low-concentration polysaccharide aqueous solution of 5 parts by weight or less, and shortens the distance between the molecular chains of the polysaccharide. The purpose is to bridge the radiation by irradiating with ionizing radiation. In the present invention, polysaccharides can be crosslinked with a lower irradiation dose than in the conventional example by reducing the distance between molecular chains by the action of metal ions.

A more specific and preferable method for producing a gel of the present invention is to irradiate a low-concentration aqueous solution of a metal salt and a carboxymethylated polysaccharide with ionizing radiation to cause the polysaccharide to undergo radiation crosslinking. Then, the gel is immersed in water to desorb the metal salt to obtain a radiation-crosslinked hydrogel.

Gelation is promoted by adding a metal salt to an aqueous solution of polysaccharides (CM-chitin, CM-chitosan, CM-starch) that is not limited to CMC aqueous solution but is carboxymethylated. Most preferably, the low concentration polysaccharide is 5 parts by weight or less of carboxymethylcellulose.

In order to increase the gel generation efficiency, the metal salt is preferably calcium chloride, but may be potassium chloride or sodium chloride. A metal salt having a higher valence tends to be gelled at a lower metal salt concentration, but a trivalent metal salt is likely to form a physical gel and difficult to control gelation. Divalent metal salts, particularly calcium chloride, are suitable for controlling gelation.

Furthermore, the radiation used in the above-described manufacturing method is γ-ray, and the radiation dose is preferably 3 kGy or more. However, in addition to γ rays, radiation that can give energy to cause bridging, such as electron beams, may be used.

Furthermore, in a more preferable production method, an aqueous solution of carboxymethyl cellulose having a low concentration of 5 parts by weight or less and a metal salt of calcium chloride, potassium chloride or sodium chloride is irradiated with γ-rays of 3 kGy or more, and the carboxy Methyl cellulose is gelled and the gel is immersed in water to release the metal salt to obtain a hydrogel.

According to the present invention, a sufficient gel fraction was not obtained even when a high irradiation dose of 30 kGy or 40 kGy was given, but even by a polysaccharide having a low concentration of 5 parts by weight or less, by adding a metal salt By reducing the distance between the molecular chains of the polysaccharide, a large gel fraction can be obtained simply by giving a low irradiation dose. That is, since the amount of polysaccharide used is small and the dose of ionizing radiation is low, the production cost of the gel can be greatly reduced.

Hereinafter, the production method of the radiation-crosslinked hydrogel of the present invention will be described in detail with reference to the drawings. All these experiments were performed at room temperature under atmospheric pressure.
First, to help understanding of the present invention, the principle of the present invention will be described with reference to FIG. FIG. 1 is a flowchart showing a schematic configuration of a method for producing a radiation-crosslinked hydrogel of the present invention. In FIG. 1, specific substances such as calcium chloride and CMC and their concentrations are described. However, this is merely an example and is not limited to these substances and their concentrations as described later. Absent.

First, calcium chloride powder is prepared to make metal ions (step 101). Ultrapure water is added to the calcium chloride powder and mixed with a stirrer such as a magnetic stirrer to prepare a uniform 1 part by weight calcium chloride aqueous solution (step 102). Thereafter, CMC2.2 (where 2.2 indicates the degree of substitution) is added to the prepared 1 part by weight calcium chloride aqueous solution and stirred, and the aqueous solution contains 5 parts by weight CMC2.2 and 1 part by weight calcium chloride. Is prepared (step 103). This aqueous solution is irradiated with an appropriate amount of γ rays to cause radiation crosslinking in CMC and gel (step 104). Finally, the prepared gel is immersed in water to elute the sol and metal salt to obtain a CMC hydrogel containing no metal ions (step 105). In the above examples, an aqueous calcium chloride solution is prepared and CMC2.2 is added to the aqueous solution, but there is no major problem even if this procedure is reversed. In the final step, the time for immersing in water to elute the sol and the metal salt is approximately 48 hours, although it varies depending on the metal ions to be added.

The hydrogel according to the present invention thus prepared contains a harmful metal ion in the prepared gel, unlike the conventional physical gel in which a metal salt is added to a CMC aqueous solution and a metal group that interacts with a CM group. There is no feature. Further, the effect of adding a metal salt makes it possible to gel CMC even when the CMC concentration is low and the irradiation dose of ionizing radiation is small.

These features will be described more specifically with reference to FIG. FIG. 2 is a graph showing the difference in gel fraction according to the prior art and the present invention. Each graph shows the difference in CMC concentration, the horizontal axis of the graph shows the radiation dose (kGy), and the vertical axis shows the gel fraction (%). The dotted line graph is for explaining the prior art, and the solid line is for explaining the present invention. First, as is clear from the graph on the lower left, in the conventional technique in which no metal salt is added, gelation starts only when the dose of radiation reaches 30 kGy, and 40 kGy is irradiated with a low concentration of CMC2.2 of 5 parts by weight. Even so, the gel fraction is limited to about 30%. Further, it can be seen from the central graph that in order to obtain a gel fraction of 80% or more even when the CMC concentration is increased to 40 parts by weight, it is necessary to irradiate with radiation of 20 kGy or more. On the other hand, according to the production method of the present invention in which a metal salt is added, gelation starts from an irradiation dose of about 3 kGy, even at a low concentration of CMC2.2 of 5 parts by weight, and the irradiation dose is 5 kGy. It can be seen that the gel fraction reaches 80%.

Hereinafter, several examples performed by the present inventors will be described with respect to the method for producing the radiation-crosslinked hydrogel of the present invention. The raw material CMC used in the following examples is manufactured by Daicel Chemical Industries, Ltd., and details thereof are as follows.
CMC A: viscosity of 1 part by weight aqueous solution at 25 ° C 142 (mPa · s) Degree of substitution 2.2
CMC B: Viscosity 1610 (mPa · s) at 25 ° C of 1 part by weight aqueous solution Degree of substitution 0.65
CMC C: Viscosity of 1 part by weight aqueous solution at 25 ° C 126 (mPa · s) Degree of substitution 0.89
CMC D: Viscosity at 25 ° C of 1 part by weight aqueous solution 387 (mPa · s) Degree of substitution 0.95
CMC E: Viscosity of 1 part by weight aqueous solution at 25 ° C 1728 (mPa · s) Degree of substitution 0.95
CMC F: viscosity of 1640 parts by weight aqueous solution at 25 ° C 1640 (mPa · s) degree of substitution 1.34
CMC G: Viscosity 3410 (mPa · s) of 1 part by weight aqueous solution at 25 ° C Substitution degree 1.1
CMC H: Viscosity 5710 (mPa · s) at 25 ° C of 1 part by weight aqueous solution Degree of substitution 0.86
Example 1 (Dependence of calcium chloride concentration on gel fraction and swelling degree of CMC aqueous solution)

5 parts by weight of CMC A is added to a metal salt aqueous solution in which 100 parts by weight of ultrapure water is added to calcium chloride so that the salt concentration becomes 0.001 to 1 part by weight (0.000068 to 0.068 mol / L). Thus, a CMC aqueous solution containing a metal salt was prepared. This sample was irradiated with γ-ray 20 kGy, and then the irradiated sample was immersed in ultrapure water to desorb and swell the sol and the metal salt component.

The results are shown in FIGS. FIG. 3 shows the relationship between the calcium chloride concentration in the CMC aqueous solution and the gel fraction. In FIG. 3, the horizontal axis indicates the calcium chloride concentration (mol / L), and the vertical axis indicates the gel fraction (%). As can be seen from FIG. 3, as the calcium chloride concentration increases from 0.01 parts by weight (0.00068 mol / L) to 1 part by weight (0.068 mol / L), the gel fraction increases from about 20% to 99%. Rose. FIG. 4 shows the relationship between the calcium chloride concentration in the CMC aqueous solution and the degree of swelling. Depending on the concentration of calcium chloride added, the swelling degree of 1 g of the dried gel was about 90 to 7,000.
Example 2 (Dose dependence on gel fraction and swelling degree of CMC / CaCl ₂ aqueous solution)

CMC aqueous solution added with metal salt by adding 5 parts by weight of CMC A to a metal salt aqueous solution in which 100 parts by weight of ultrapure water is added to calcium chloride so that the salt concentration becomes 1 part by weight (0.068 mol / L). It was. This sample was irradiated with γ rays of 0 to 40 kGy, and then the irradiated sample was immersed in ultrapure water to desorb and swell the sol and the metal salt component.

The measurement results are shown in FIGS. FIG. 5 shows the relationship between the dose of CMC / calcium chloride aqueous solution and the gel fraction. The horizontal axis in FIG. 5 indicates the dose (kGy), and the vertical axis indicates the gel fraction (%). In this example, gelation started from 3 kGy and reached a gel fraction of 80% at 5 kGy. FIG. 6 shows the relationship between the dose of CMC / calcium chloride aqueous solution and the degree of swelling. The horizontal axis in FIG. 6 indicates the dose (kGy), and the vertical axis indicates the degree of swelling. In this example, the swelling degree of 1 g of the dried gel was about 45 to 2500.
Example 3 (Effect of substitution degree and molecular weight on the gel fraction of CMC)

(1) Influence of degree of substitution (DS = Degree of Substitution) Sample 1 in which 5 parts by weight of CMC B, E and F were added to 100 parts by weight of water to form a CMC aqueous solution, and 1 part by weight of calcium chloride (= 0.068 mol) / L) 100 parts by weight of water was added to form a metal salt aqueous solution, and CMC was further added to form a metal salt-added CMC aqueous solution. Sample 2 was irradiated with 20 kGy of γ rays. Thereafter, the irradiated sample was immersed in ultrapure water to desorb the sol and the metal salt component.
FIG. 7 shows the relationship between the degree of CMC substitution and the gel fraction. The horizontal axis in FIG. 7 indicates the degree of substitution, and the vertical axis indicates the gel fraction (%). In this example, gelation started from a substitution degree of 1.34, and the effect of adding a metal salt was observed.

(2) Influence of molecular weight (absolute viscosity = AV = Absolute Viscosity) Sample 1 with 5 parts by weight of CMC C, D, E, G, H added to 100 parts by weight of water and 1 part by weight of calcium chloride 100 parts by weight of water was added to (= 0.068 mol / L) to form a metal salt aqueous solution, and CMC was further added to form a metal salt-added CMC aqueous solution. Sample 2 was irradiated with γ rays of 20 kGy. Thereafter, the irradiated sample was immersed in ultrapure water to desorb the sol and the metal salt component.

FIG. 8 shows the relationship between the absolute viscosity of the CMC aqueous solution and the gel fraction. The horizontal axis in FIG. 8 indicates absolute viscosity (mPa · s), and the vertical axis indicates gel fraction (%). In Sample 2 to which the metal salt was added, gelation started to occur in the CMC aqueous solution to which the absolute viscosity of 3410 mPa · s or more was added. However, gelation could not be confirmed in the metal salt-free sample 1.

From the above results (1) and (2), it was found that CMC having a degree of substitution of 1 or more and a molecular weight of about 3410 or more in absolute viscosity is preferable for radiation crosslinking of an aqueous CMC solution containing a metal salt.
Example 4 (Dependence of various metal salt concentrations on gel fraction and swelling degree of CMC aqueous solution)

100 parts by weight of water is added to calcium chloride, magnesium chloride, magnesium sulfate, strontium chloride, barium chloride, zinc chloride, aluminum nitrate, and aluminum sulfate, and the metal salt concentration is 0.01 to 1 part by weight (0.0000267 to 0.005). 073 mol / L), 5 parts by weight of CMC A was added to the aqueous metal salt solution and irradiated with 5, 10, 20, and 40 kGy of γ rays.

FIG. 9 shows the relationship between various metal salt concentrations in the CMC aqueous solution and the gel fraction. The horizontal axis in FIG. 9 indicates the metal salt concentration (mol / L), and the vertical axis indicates the gel fraction (%). In this example, 10 to 100% gel was obtained from a sample to which a metal salt was added. Gelation could not be confirmed in the CMC aqueous solution without addition of metal. FIG. 10 shows the relationship between the various metal salt concentrations in the CMC aqueous solution and the degree of swelling. The horizontal axis in FIG. 10 indicates the metal salt concentration (mol / L), and the vertical axis indicates the degree of swelling. In this example, the water absorption of 1 g of the dried gel was about 75-5500.
Example 5 (CMC / Dose dependency on gel fraction of various metal salt aqueous solutions)

FIG. 11 shows the relationship between the dose of CMC / various metal salt aqueous solutions and the gel fraction. The horizontal axis in FIG. 11 indicates the dose (kGy), and the vertical axis indicates the gel fraction (%). In this example, gelation started with 3 kGy irradiation. And it reached the gel fraction of 80% or more by 20 kGy irradiation.
Example 6 (Sodium chloride concentration dependence on gel fraction and swelling degree of CMC aqueous solution)

100 parts by weight of water is added to sodium chloride, and the concentrations are 0.1, 0.5, 1.0, and 35.8 parts by weight (0.017, 0.086, 0.17, and 6.12 mol / L, respectively). A metal salt-added CMC aqueous solution was prepared by adding 5 parts by weight of CMC A to the metal salt aqueous solution. This sample was irradiated with 20 kGy of gamma rays. Thereafter, the irradiated sample was immersed in ultrapure water to detach and swell the sol and the metal salt component. FIG. 12 shows the relationship between the sodium chloride concentration in the CMC aqueous solution and the gel fraction. In FIG. 12, the horizontal axis indicates the sodium chloride concentration (mol / L), and the vertical axis indicates the gel fraction (%). In this example, gelation did not occur at a sodium chloride concentration of 0.1 part by weight (0.017 mol / L). A gel fraction of about 50% was reached at 0.5 part by weight (0.086 mol / L) and about 70% at 35.8 parts by weight (6.12 mol / L) saturated with sodium chloride. Formation of a physical gel was not observed with a monovalent metal salt.

FIG. 13 shows the relationship between the sodium chloride concentration in the CMC aqueous solution and the degree of swelling in this example. The horizontal axis in FIG. 13 indicates the sodium chloride concentration (mol / L), and the vertical axis indicates the degree of swelling. In this example, the water absorption amount per 1 g of the dried gel was about 85 to 2000 g.
Example 7 (Dose dependence on gel fraction and swelling degree of CMC / monovalent metal salt aqueous solution)

Add 100 parts by weight of water to potassium chloride, sodium chloride, sodium sulfate, and sodium acetate to obtain a metal salt aqueous solution with a sodium ion concentration of 0.50 M, and then add 5 parts by weight of CMC A to obtain a CMC aqueous solution. Irradiated with 10, 20, and 40 kGy of gamma rays.
The results are shown in FIGS. FIG. 14 shows the relationship between the dose of the CMC / monovalent metal salt aqueous solution and the gel fraction. The horizontal axis in FIG. 14 indicates the radiation dose (kGy), and the vertical axis indicates the gel fraction (%). In this example, the gel fraction of the CMC aqueous solution to which the metal salt was added reached 20 to 100%, and in particular with potassium chloride and sodium chloride, the gel fraction was high even at 5 kGy.

FIG. 15 shows the relationship between the dose of CMC / monovalent metal salt aqueous solution and the degree of swelling. The horizontal axis in FIG. 15 indicates the radiation dose (kGy), and the vertical axis indicates the degree of swelling. In this example, the water absorption per 1 g of the dried gel was about 80 to 750 g. In the CMC aqueous solution without addition of metal salt, gel could not be obtained by irradiation with 5, 10, 20 kGy.
Example 8 (effect of adding metal salt to other polysaccharide aqueous solution)

(1) Carboxymethylchitin (CM-chitin) DS = 0.81 Deacetylation degree (DDA) = 24.6%
A sample of CM-chitin solution containing 5, 7 or 10 parts by weight of CM-chitin added to 100 parts by weight of water, and 100 parts by weight of water and CM-chitin powder added to 1 part by weight of calcium chloride. The sample made into CM-chitin aqueous solution was irradiated with 20 kGy of γ rays.
Table 1 shows the results of irradiation with CM-chitin. With 5 parts by weight of CM-chitin, no gelation was observed after γ-irradiation with or without addition of a metal salt, but gelation occurred when irradiated to a sample with 7 parts by weight of metal salt added.

(2) Carboxymethyl chitosan (CM-chitosan) DS = 0.54 DDA = 61.8%
CM-chitosan aqueous solution sample 1 in which 5, 6 and 10 parts by weight of CM-chitosan was added to 100 parts by weight of water, and 100 parts by weight of water and CM-chitosan powder were added to 1 part by weight of calcium chloride and a metal salt was added. Sample 2 prepared as a CM-chitosan aqueous solution was irradiated with 20 kGy of γ rays.
Table 2 shows the results of irradiation with CM-chitosan. In 5 parts by weight of CM-chitosan, no gelation was observed after γ-irradiation with or without addition of a metal salt, but gelation occurred when the sample was added with 6 parts by weight of metal salt.

(3) Carboxymethyl starch (CMS) DS = 0.15
CMS aqueous solution sample 1 in which 5 or 10 parts by weight of CMS is added to 100 parts by weight of water, and sample 2 in which 100 parts by weight of water and CMS are added to 0.1 part by weight of calcium chloride to form a CMS aqueous solution to which a metal salt is added Each was irradiated with 5 kGy of γ rays.
Table 3 shows the results of CMS irradiation. Gelation was not observed in the 7 parts by weight CMS aqueous solution, but gelation occurred in the CMS aqueous solution to which the metal salt was added.

The gel produced as described above can be used in a wide range of fields such as industry, agriculture, medicine and food. Examples thereof are given below, but are not limited thereto.
The CMC hydrogel according to the present invention is an environmentally friendly material having biodegradability, excellent water absorption and water retention. Currently, water-absorbing agents used in disposable diapers and sanitary products are acrylamide-based materials that are not biodegradable and are incinerated. However, by using the CMC hydrogel according to the present invention having biodegradability, it is possible to directly dispose of it in the soil without incineration. It is also expected to be used as a water-retaining agent for gardening and desertified soil, as a water-absorbing material during drilling operations such as oil field development and landfill development, for food use, and as a purification agent for industrial wastewater. it can.

It is a flowchart which shows schematic structure of the manufacturing method of the gel which concerns on this invention. It is a graph which shows the difference of the gel fraction by a prior art and this invention. The relationship between the calcium chloride concentration in CMC aqueous solution and a gel fraction is shown. The relationship between the calcium chloride concentration in CMC aqueous solution and a swelling degree is shown. The relationship between the dose of CMC / calcium chloride aqueous solution and a gel fraction is shown. The relationship between the dose of CMC / calcium chloride aqueous solution and the degree of swelling is shown. The relationship between the substitution degree of CMC and the gel fraction is shown. The relationship between the absolute viscosity of CMC aqueous solution and a gel fraction is shown. The relationship between the various metal salt concentration in CMC aqueous solution and a gel fraction is shown. The relationship between the various metal salt concentration in CMC aqueous solution and swelling degree is shown. The relationship between the dose of CMC / various metal salt aqueous solutions and the gel fraction is shown. The relationship between the sodium chloride concentration in CMC aqueous solution and a gel fraction is shown. The relationship between the sodium chloride concentration in CMC aqueous solution and swelling degree is shown. The relationship between the dose of CMC / monovalent metal salt aqueous solution and the gel fraction is shown. The relationship between the dose of CMC / monovalent metal salt aqueous solution and the degree of swelling is shown.

Explanation of symbols

CMC Carboxymethylcellulose DS Substitution degree AV Absolute viscosity CM Carboxymethyl CMS Carboxymethyl starch

Claims (8)

  After irradiating a low-concentration aqueous solution of a metal salt and a carboxymethylated polysaccharide with radiation, the polysaccharide is subjected to radiation cross-linking to gel, and then the gel is immersed in water to desorb the metal salt. A method for producing a radiation-crosslinked hydrogel, characterized in that a hydrogel is obtained.   2. The method for producing a radiation-crosslinked hydrogel according to claim 1, wherein the carboxylated polysaccharide is 5 parts by weight or less of carboxymethylcellulose. .   3. The method for producing a radiation-crosslinking hydrogel according to claim 1 or 2, wherein the metal salt is calcium chloride.   The method for producing a radiation-crosslinked hydrogel according to any one of claims 1 to 3, wherein the radiation is γ-ray, and the radiation dose is 3 kGy or more. Type hydrogel production method.   An aqueous solution of 5 parts by weight or less of low concentration carboxymethyl cellulose and a metal salt is irradiated with 3 kGy or more of γ-rays to gel the carboxymethyl cellulose, and the gel is immersed in water to release the metal salt. A method for producing a radiation-crosslinking hydrogel characterized by obtaining a gel.   6. The method for producing a radiation-crosslinked hydrogel according to claim 5, wherein the metal salt is calcium chloride.   6. The method for producing a radiation-crosslinking hydrogel according to claim 5, wherein the metal salt is potassium chloride.   6. The method for producing a radiation-crosslinked hydrogel according to claim 5, wherein the metal salt is sodium chloride.

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