JP2008111027A - Water-absorbing gel of biodegradable polymer and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an absorbing gel of a biodegradable polymer having excellent absorbing rate and absorbing performance to various components such as water, saline water and blood and to provide a method for producing the gel. <P>SOLUTION: The method for producing an absorbing gel of a biodegradable polymer comprises a step to thoroughly knead a cellulose derivative and/or a starch derivative with water to form a paste, a step to irradiate the paste with radiation and obtain a hydrogel and a step to remove the water-soluble component sol of the hydrogel. The production method enables the removal of a sol of a water-soluble component from a self-crosslinking biodegradable hydrogel derived from a cellulose derivative and/or a starch derivative. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention can be suitably used for applications such as disposable diapers, cloth diapers, sanitary products and the like that can absorb a large amount of water and is biodegradable polymer water-absorbing gel that is biodegradable by microorganisms in the soil. And a manufacturing method thereof.

  Gels that absorb water can be obtained by crosslinking reaction with poly (sodium acrylate), starch grafted with acrylic acid, or polyethylene oxide, polyvinyl alcohol, acrylamide or polyvinylpyrrolide aqueous solution with ionizing radiation. There is a water-absorbing gel. There are also water-absorbing gels obtained by crosslinking by chemical treatment with formalin, glutaraldehyde and the like. Water-absorbing gels are used in large quantities in the fields of agriculture, medical care, and hygiene products, and it is predicted that the production volume will continue to increase in the future.

  A water-absorbing gel obtained by crosslinking a water-soluble polymer such as sodium polyacrylate is widely used in sanitary products such as disposable diapers. However, disposable diapers used in infants and hospitals are mainly disposed of by incineration. When wet diapers are placed in an incinerator, the combustion temperature decreases, leading to the generation of dioxins and an increase in carbon gas. When it is buried in the soil, it does not decompose and stays for a long time, giving a load to the environment.

  On the other hand, there is a method of synthesizing a water-absorbing agent by chemical crosslinking using a reagent such as formalin, glutaraldehyde, epichlorohydrin or the like on a derivative such as starch or cellulose. However, these chemical substances are highly toxic and have problems such as environmental pollution at the work site and residual in the water-absorbing agent.

  For this reason, the water absorption material by the material which does not give load to an environment is calculated | required. Biodegradable polymers that are decomposed and digested by microorganisms in the soil and can be easily treated after use are attracting attention as environmentally friendly materials.

  A self-crosslinking type biodegradable cellulose water-absorbing agent that does not use a crosslinking agent can be disposed of by composting as a fertilizer and can be used as a resource if a recovery system after use can be constructed. As a water-absorbing agent using a self-crosslinking type biodegradable cellulose derivative, for example, water is added to carboxymethylcellulose (CMC) and kneaded well so as to form a paste having a concentration of 10% or more. There is a dry gel obtained by drying a hydrogel obtained by irradiation (see Patent Document 1).

Moreover, as an absorbent using a self-crosslinking type biodegradable starch derivative, for example, carboxymethyl starch (CMS) and starch are blended and obtained by irradiation with ionizing radiation in a paste-like paste well kneaded with water. There is a superabsorbent starch gel (see Patent Document 2).
JP 2001-2703 A JP 2003-48997 A

  However, the gels described in Patent Documents 1 and 2 cannot be said to have sufficient water absorption speed and water absorption performance for components such as water, salt water, blood, etc., and these properties are required for practical use in hygiene products. Improvement of this was strongly desired.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is a biodegradable polymer absorbent gel excellent in water absorption speed and water absorption performance for components such as water, salt water, blood and the like, and a method for producing the same. Is to provide.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have added water to carboxymethylcellulose sodium (CMC) and carboxymethyl starch sodium (CMS), respectively, and a paste having a concentration of 10% or more ( Paste well, and after irradiation with ionizing radiation such as γ-rays or electron beams, the dried gel is immersed in a large amount of water immediately after irradiation and then cross-linked. The present inventors have found that a gel exhibiting excellent water absorption speed and water absorption performance can be obtained by dissolving and removing a component called no sol on the water side, and the present invention has been completed based on such knowledge.

  That is, the biodegradable polymer water-absorbing gel of the present invention is characterized in that the sol of a water-soluble component in a self-crosslinking biodegradable hydrogel using a cellulose derivative and / or a starch derivative is removed.

  The cellulose derivative is preferably carboxyalkyl cellulose, hydroxyalkyl cellulose, alkyl cellulose, a mixture thereof, or an alkali metal salt thereof, and more preferably carboxymethyl cellulose sodium (CMC).

  The starch derivative is preferably carboxyalkyl starch, hydroxyalkyl starch, alkyl starch, or a mixture thereof, or an alkali metal salt thereof, more preferably carboxymethyl starch sodium (CMS).

  In addition, the biodegradable polymer absorbent gel can absorb 300 grams or more of pure water per gram of gel.

  In addition, the method for producing the biodegradable polymer water-absorbing gel of the present invention includes a step of kneading a cellulose derivative and / or starch derivative well with water to form a paste, and a step of obtaining a hydrogel by irradiating radiation in the paste state. And a step of removing the sol of the water-soluble component of the hydrogel.

  In the step of removing the sol, the hydrogel immediately after the irradiation and / or the dried gel from which the water of the hydrogel has been removed can be removed by immersing in 100 times or more of a large amount of water.

  In the step of obtaining the hydrogel by irradiating the radiation, the radiation dose can be 0.1 to 500 kGy.

  In the paste-like step, carboxymethylcellulose sodium (CMC) and carboxymethyl starch sodium (CMS), both having a substitution degree of 0.01 to 2.5, are kneaded well with water, and the concentration is 10% or more. It can be made into a paste form.

  According to the biodegradable polymer water-absorbing gel of the present invention, the water-absorbing speed and water-absorbing performance with respect to components such as water, salt water, blood, etc. are excellent, and a large amount of water such as disposable diapers, cloth diapers, sanitary products, etc. Since it can be suitably used for absorbing applications and biodegraded by microorganisms in the soil, it can be made into an environmentally friendly product.

  Further, according to the method for producing a biodegradable polymer water-absorbing gel of the present invention, it is possible to efficiently and reliably obtain a biodegradable polymer water-absorbing gel excellent in water absorption speed and water absorption performance for components such as water, salt water and blood. Can do.

(Cellulose derivative)
In the present invention, examples of the cellulose derivative used as a raw material include carboxyalkyl cellulose (A), hydroxyalkyl cellulose (B), alkyl cellulose (C), or a mixture thereof.

(Carboxyalkyl cellulose (A))
Examples of the carboxyalkyl cellulose (A) include those in which the hydrogen of the hydroxyl group of cellulose is substituted with a carboxymethyl group, a carboxyethyl group, or a carboxypropyl group. Preferred carboxyalkyl cellulose (A) is carboxymethyl cellulose or carboxyethyl cellulose. In particular, those having a substitution degree of carboxymethyl of 0.01 to 2.5 can be suitably used. In the carboxyalkyl cellulose, 20% or more, preferably 40% or more of the carboxyl groups can be alkali metal salt, ammonium salt or amine salt. Examples of the alkali metal salt include sodium salt, potassium salt, lithium salt and the like, preferably sodium salt. When the ratio of forming the salt is less than the above range, it becomes difficult to form a uniform mixture or aqueous solution with water. There is no particular upper limit on the ratio of salt formation, and 100% salt may be formed.

(Hydroxyalkyl cellulose (B))
The hydroxyalkyl cellulose (B) is preferably hydroxyethyl cellulose or hydroxypropyl cellulose. In the hydroxyalkyl cellulose (B), 20% or more, preferably 40% or more, more preferably 50% or more of the hydroxyl group can be used as an alkali metal salt. Examples of the alkali metal salt include sodium salt, potassium salt, lithium salt and the like, preferably sodium salt. When the ratio of forming the salt is less than the above range, it becomes difficult to form a uniform mixture or aqueous solution with water. There is no particular upper limit on the ratio of salt formation, and 100% salt may be formed.

(Alkylcellulose (C))
Alkyl cellulose (C) is one in which hydrogen of hydroxyl group of cellulose is partially substituted with methyl group, ethyl group, and propyl group, and preferable alkyl cellulose (C) is methyl cellulose and ethyl cellulose. In the alkyl cellulose (C), 40% or more, preferably 50% or more of the remaining hydroxyl groups can be used as an alkali metal salt. Examples of the alkali metal salt include sodium salt, potassium salt, lithium salt and the like, preferably sodium salt. When the ratio of forming the salt is less than the above range, it becomes difficult to form a uniform mixture or aqueous solution with water. There is no particular upper limit on the ratio of salt formation, and 100% salt may be formed.

(Starch derivative)
In the present invention, the starch derivative used as a raw material includes carboxyalkyl starch (D), hydroxyalkyl starch (E), alkyl starch (F), or a mixture thereof.

(Carboxyalkyl starch (D))
Carboxyalkyl starch (D) is obtained by carboxymethylating, carboxyethylating, or carboxypropylating starch made from corn, rice, potato, tapioca, sweet potato, or the like. A preferred carboxyalkyl starch (D) is carboxymethyl starch. In particular, those having a substitution degree of carboxymethyl of 0.01 to 2.5 can be suitably used. Moreover, the alkali metal salt, ammonium salt, or amine salt of the said carboxyalkyl starch may be sufficient, As an alkali metal salt, sodium salt, potassium salt, lithium salt etc. are mentioned, Preferably it is sodium salt. There is no particular upper limit on the ratio of salt formation, and 100% salt may be formed.

(Hydroxyalkyl starch (E))
The hydroxyalkyl starch (E) is preferably hydroxyethyl starch or hydroxypropyl cell starch. Moreover, the alkali metal salt of the said hydroxyalkyl starch (E) may be sufficient, and a sodium salt, potassium salt, lithium salt etc. are mentioned as an alkali metal salt, Preferably it is a sodium salt. There is no particular upper limit on the ratio of salt formation, and 100% salt may be formed.

(Alkyl starch (F))
The alkyl starch (F) is preferably methyl starch or ethyl starch. Moreover, the alkali metal salt of the said alkyl starch (F) may be sufficient, and a sodium salt, potassium salt, lithium salt etc. are mentioned as an alkali metal salt, Preferably it is a sodium salt. There is no particular upper limit on the ratio of salt formation, and 100% salt may be formed.

(water)
Examples of water used to make a paste in the production method of the present invention include city water, industrial water, deaerated water, deionized water, gel filtered water, distilled water, and the like, preferably oxygen, ions, etc. Is not included.

(radiation)
Next, a crosslinking reaction occurs by irradiating the paste sample of the cellulose derivative and / or starch derivative with high-energy ionizing radiation to obtain a hydrogel. Here, as a radiation source used in the radiation irradiation treatment, α rays, β rays, γ rays, X rays, electron beams, ultraviolet rays, and the like can be used, but γ rays from cobalt 60, electron beams, X-rays are more preferred. In particular, electron beam irradiation treatment using the γ-ray or electron accelerator is convenient for introducing a bridge structure.

  The electron accelerator is most preferably a medium energy to high energy electron accelerator capable of irradiating a thick material with an acceleration voltage of 1 MeV or higher. If pressure is applied to the sample before irradiation and it is processed into a film, an electron beam can be transmitted even with a low energy electron accelerator of 1 MeV or less, so that a hydrogel can be obtained by radiation crosslinking. Although there is almost no effect on crosslinking due to oxygen during irradiation, it is desirable to cover the upper surface with a plastic film such as polyester in order to prevent evaporation of moisture during irradiation and suppress a decrease in crosslinking density. .

  The amount of radiation irradiated in the present invention is 0.1 to 500 kGy, preferably 0.5 to 100 kGy, and more preferably 5 to 50 kGy. When the irradiation amount of the radiation is less than the above range, crosslinking does not occur and water absorption becomes insufficient, and when it exceeds the above range, crosslinking proceeds too much and water absorption becomes insufficient.

  In paste-like irradiation of carboxymethylcellulose sodium (CMC), a crosslinking reaction occurs in a range of substitution degree of 0.01 to 2.5 and polymer concentration of 10 to 60%. For CMC with a degree of substitution around 1.0, the preferred polymer concentration for crosslinking is 20% to 40%. On the other hand, the preferred polymer concentration when the substitution degree is around 2.0 is 40% to 60%.

(Use)
When a conventional polymer absorbent contains a salt like urine, the amount of absorption is remarkably reduced, so that improvement is required. As in the present invention, the absorption gel excluding the sol is easy to absorb water, physiological saline and blood, and has a high water absorption rate. Therefore, it can be expected to be applied to sanitary goods such as disposable diapers. Moreover, if the amount of absorption increases, the amount of use decreases, and the sanitary goods can be thinned, leading to cost reduction.

  In addition, most of the polymer absorbers that have been commercialized so far are made from petroleum, and incineration increases carbon dioxide, which is also the cause of global warming. Since the plant-derived material of the present invention is a resource circulation type that can produce and regenerate the same amount of plants with the carbon dioxide gas generated even after burning, future demand expansion can be expected as an environmental conservation product.

(Measurement of water absorption)
First, carboxymethylcellulose sodium (CMC) powder having a substitution degree of 1.3 is dissolved in water to a concentration of 20%, processed into a paste, irradiated with 5 kGy of γ rays, and then dried to remove water. A dry gel was obtained. Table 1 shows the maximum water absorption when this dried gel is immersed in pure water, physiological saline and human blood for 24 hours as a comparative example.
In addition, the amount of water absorption was represented by how many times the amount of pure water, physiological saline, and human blood could be absorbed by the dry gel with respect to 1 g of the dry gel.

  Next, the hydrogel dried gel obtained by irradiation in the comparative example was immersed in a large amount (1000 times) of water for 24 hours to remove the sol, and a gel having an insoluble component as a whole was obtained. Table 2 shows the water absorption when this gel was immersed in water, physiological saline and human blood for 24 hours as Example 1.

  From the results of Tables 1 and 2, the gel composed of insoluble components excluding the sol content absorbs pure water and blood more than 3 times more easily than the gel without the sol content. It was found that it was easy to absorb about 3 times.

(Measurement of water absorption rate)
First, carboxymethylcellulose sodium (CMC) powder having a substitution degree of 1.3 is dissolved in water to a concentration of 20%, processed into a paste, irradiated with 5 kGy of γ rays, and then dried to remove water. A dry gel was obtained. Table 3 shows the water absorption when the dried gel was immersed in pure water and physiological saline for 30, 60 and 90 minutes as a comparative example.

  Next, the hydrogel dried gel obtained by irradiation in the comparative example was immersed in a large amount (1000 times) of water for 24 hours to remove the sol, and a gel having an insoluble component as a whole was obtained. Table 4 shows the water absorption when this gel was soaked in water and physiological saline.

  From the results of Tables 3 and 4, it can be seen that the gel composed of insoluble components excluding the sol content has an absorption of pure water four times or more in 60 minutes as compared with the gel not excluding the sol content. Further, it was found that the physiological saline has a high absorption rate and reaches a nearly saturated state in 30 minutes.

Industrial applicability

  As described above, the absorption gel excluding the sol component can easily absorb water, physiological saline and blood, and has a high water absorption rate. Therefore, it can be expected to be applied to sanitary goods such as disposable diapers.

Claims (10)

  A biodegradable polymer absorbent gel, wherein a sol of a water-soluble component in a self-crosslinking biodegradable hydrogel using a cellulose derivative and / or a starch derivative is removed.   The biodegradable polymer absorbent gel according to claim 1, wherein the cellulose derivative is carboxyalkyl cellulose, hydroxyalkyl cellulose, alkyl cellulose, a mixture thereof, or an alkali metal salt thereof.   The biodegradable polymer absorbent gel according to claim 1, wherein the cellulose derivative is carboxymethylcellulose sodium (CMC).   The biodegradable polymer absorbent gel according to claim 1, wherein the starch derivative is carboxyalkyl starch, hydroxyalkyl starch, alkyl starch, a mixture thereof, or an alkali metal salt thereof.   The biodegradable polymer absorbent gel according to claim 1, wherein the starch derivative is carboxymethyl starch sodium (CMS).   The biodegradable polymer absorbent gel according to any one of claims 1 to 4, which absorbs 300 g or more of pure water per gram of gel.   A step of kneading a cellulose derivative and / or starch derivative well with water to form a paste, a step of irradiating radiation in the paste state to obtain a hydrogel, and a step of removing the sol of the water-soluble component of the hydrogel A method for producing a biodegradable polymer absorbent gel, comprising:   The step of removing the sol is performed by immersing the hydrogel immediately after the irradiation and / or the dried gel from which the water of the hydrogel has been removed by immersing it in a large amount of water of 100 times or more. A method for producing a biodegradable polymer absorbent gel.   The method for producing a biodegradable polymer absorbent gel according to claim 7, wherein the step of irradiating the radiation to obtain a hydrogel has a radiation irradiation dose of 0.1 to 500 kGy.   The step of making the paste is well kneaded with water using carboxymethylcellulose sodium (CMC) and carboxymethyl starch sodium (CMS) both having a substitution degree of 0.01 to 2.5, and the concentration is 10% or more. The method for producing a biodegradable polymer absorbent gel according to claim 7, wherein the biodegradable polymer absorbent gel is formed into a paste form.