JP2003321574A - Decomposer for water absorptive polymer and method for decomposing water absorptive polymer by using the decomposer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a decomposer for a water absorptive polymer, having excellent versatility and decomposing ability, and to provide a method for decomposing the polymer by using the decomposer. <P>SOLUTION: The decomposer is obtained by compounding an alkali compound to a persulfate oxidizer at a molar ratio of 0.1-10 and making the oxidizer concentration in an aqueous solution to be 0.002-10 wt.%, and the decomposing treatment of the water absorptive polymer is performed at 40-100°C by using the decomposer as an aqueous solution of pH 4 to pH 14. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The invention of the present application relates to a decomposing agent for a water-absorbing polymer and a method for decomposing a water-absorbing polymer using the same.

[0002]

2. Description of the Related Art Water-absorbing polymers used in various fields such as sanitary products and sanitary products such as disposable diapers absorb water by virtue of their three-dimensionally cross-linked water-soluble polymers. It has a characteristic that it swells but does not dissolve. Therefore, for example, paper diapers and the like using these water-absorbent polymers are currently treated as incineration or landfill after use, which is not preferable from the viewpoint of environmental protection.

In order to solve such problems, various methods for decomposing water-absorbing polymers have been proposed so far. For example, Japanese Unexamined Patent Publication No. 4-317784 discloses a disposal method of decomposing a water-absorbing polymer with hydrogen peroxide, but it requires a large amount of hydrogen peroxide and a long-term treatment. There is a point.

Japanese Patent Application Laid-Open No. 5-247126 discloses a method for decomposing a water-absorbing polymer by microorganisms, which requires various conditions such as constantly blowing air into the polymer and long-term reaction. There is a problem of doing.

Further, JP-A-6-313008 discloses a method of decomposing a water-absorbing polymer in a short time by heating it with an aqueous solution of persulfate.
The amount of water-absorbent polymer that can be treated is not more than 1/30 of the weight ratio of the aqueous solution of persulfate, and the entire water-absorbent polymer must be swollen with the aqueous solution. There is a problem that the amount of polymer that can be treated per hour is limited, a polymer that is not swollen in an aqueous solution is not decomposed, and a polymer that has been decomposed once again becomes a gel due to a crosslinking reaction.

Under such circumstances, the inventors of the present application have disclosed that the water-absorbing polymer is decomposed by Japanese Patent Laid-Open No. 2001-2001.
In Japanese Patent No. 316519, it is disclosed that a decomposition agent containing periodate and a decomposition method using the decomposition agent are superior to the case of using persulfate alone. However, since periodate is more expensive than persulfate, it has been desired to develop a more versatile oxidizing agent and a method for decomposing a water-absorbing polymer using the oxidizing agent.

Therefore, the invention of this application solves the problems of the prior art as described above, and is a new technical technique capable of efficiently decomposing a water-absorbing polymer with an inexpensive and highly versatile oxidizing agent. The challenge is to provide measures.

[0008]

Means for Solving the Problems To solve the above problems, the invention of the present application is as follows. First, a decomposing agent for decomposing a water-absorbing polymer, which comprises at least one alkali compound and an oxidizing agent. At least one of the persulfate compounds being
Disclosed is a water-absorbing polymer decomposing agent, which comprises a seed.

Secondly, a water-absorbing polymer characterized in that the alkali compound is water-soluble and dissociates in its aqueous solution into monovalent cations and monovalent anions to show alkalinity. A decomposing agent, thirdly, a decomposing agent for a water-absorbing polymer, which is an aqueous solution in which the concentration of the oxidizing agent is 0.002 to 10% by weight, and fourthly, the alkali compound is The molar ratio to the oxidant is 0.1 to 0.1.
Disclosed is a decomposing agent for a water-absorbent polymer, which is contained in an amount of 10 times.

A fifth aspect of the invention of this application is a method for decomposing a water-absorbing polymer in a water-absorbing polymer or a water-absorbing material containing the water-absorbing polymer. A method for decomposing a water-absorbent polymer, which comprises decomposing the water-absorbent polymer in the presence of water.

Sixth, the pH of the aqueous solution of the decomposing agent is set to 4
The decomposition method is characterized in that
The present invention provides a decomposition method, wherein the treatment temperature is in the range of 40 ° C to 100 ° C.

Further, eighthly, there is provided a decomposition method characterized in that the water-absorbing polymer is decomposed in a state of containing at least a part of the water-absorbing polymer. And a weight ratio to the weight of 5 to 1000 times.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The invention of this application has the characteristics as described above, and the embodiments thereof will be described in detail below.

In the invention of this application, the water-absorbent polymer to be decomposed by the decomposing agent is, for example, a sanitary article,
It refers to a high molecular weight polymer which is used in various fields including hygiene products such as paper diapers and which wets or swells by absorbing water.

The kind and composition of the water-absorbing polymer are not particularly limited, but examples thereof include acrylic acid cross-linked polymers, isobutylene-maleic acid cross-linked polymers, and acrylic acid ester-vinyl acetate copolymers. Examples include those containing a hydrophilic vinyl polymer such as a saponified product crosslinked product and a starch-acrylic acid salt graft copolymer in the structure. Among them, an acrylic acid crosslinked polymer and an isobutylene-maleic acid crosslinked polymer are included. Some are exemplified as suitable targets.

Further, the form (shape) of this water-absorbent polymer
The material is not particularly limited, and may be, for example, powder, granule, sheet, fibrous, woven fabric, non-woven fabric, or the like.

The water-absorbing polymer decomposing agent of the invention of this application contains persulfate as an oxidizing agent.

The inventor has conducted extensive studies on a decomposing agent capable of efficiently decomposing a water-absorbing polymer, and as a result, a mixed aqueous solution of a persulfate salt as an oxidant and an alkali compound is composed of only a persulfate salt. It has been found that the water-absorbing polymer is a decomposing agent having a remarkably excellent resolution as compared with an aqueous solution, and the invention of this application has been completed based on such knowledge.

That is, first, when persulfate is used alone (without a periodate or an alkali compound) to decompose a large amount of water-absorbing polymer at one time, for example, water and water-absorbing polymer are used. When the water absorption ratio is 30% or less, or even when the water absorption ratio is 30% or less, if the persulfate concentration is 3% or more, the water-absorbing polymer is added to and mixed with this aqueous solution, and the persulfate is heated. Hydroxy radicals generated from the reaction of salt decomposition products with water abstract hydrogen from the polyacrylic acid main chain, and radicals are generated in the main chain, between adjacent water-absorbing polymer chains or once decomposed and dissolved polymers Cross-linking / gelling reaction (side reaction) occurs between the chains. This basic reaction mechanism is the same as in the case of irradiation (S.Zhu et al., Eur. Polym. J., Vol. 34,
487 (1998)). On the other hand, like the invention of this application,
In the case of a mixed aqueous solution of a persulfate and an alkaline compound, even after the water-absorbing polymer is decomposed and dissolved in the solution,
Cross-linking and gelation, which are side reactions, do not occur, so that the water-absorbing polymer has excellent resolution.

In the above-mentioned crosslinking / gelation reaction, when the pH of the aqueous solution becomes lower than 4, the dissociation of the side chain carboxyl groups of the water-absorbing polymer is suppressed and the ionic repulsion between the side chains is reduced. As a result, the crosslinking reaction due to the recombination of radicals between the molecular chains takes precedence over the decomposition reaction and gels as a result. In an aqueous solution containing only persulfate, the pH is about 6 in the initial stage of the decomposition reaction, and the decomposition reaction occurs preferentially, but since the pH of the solution continues to decrease gradually with time, the water-absorbing polymer is once decomposed. However, even if it is a uniform aqueous solution, even in a weakly acidic region of pH 4 or higher, when the polymer molecular chains are partially close,
Since the crosslinking reaction may occur, a transparent gel may be formed from the homogeneous solution when the pH becomes lower than 6.

From the above knowledge, in the invention of this application, in order to prevent crosslinking and gelation due to persulfate,
The pH of the aqueous solution is in the range of 4 to 14, more preferably 5 to
It is a preferred embodiment to carry out only the decomposition reaction of the water-absorbent polymer under the condition of 14 range, more preferably 6-14.

In the decomposition reaction, under the condition that one molecule of persulfate is thermally decomposed in an aqueous solution to generate two molecules of radicals, that is, the reaction temperature is preferably 40 ° C to 100 ° C, and 50 ° C to 50 ° C. The range of 100 ° C. is more preferable, and 60
The range of 100 ° C to 100 ° C is more preferable.

As the persulfate, for example, a water-soluble oxidizing agent such as potassium persulfate or ammonium persulfate is preferably used.

On the other hand, as the alkali compound, those which are water-soluble and show alkalinity by being dissociated into a monovalent cation and a monovalent anion in the aqueous solution thereof are preferably used. For example, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, alkali metal carbonates such as lithium carbonate, sodium carbonate and potassium carbonate, alkali metal hydrogen carbonates such as sodium hydrogen carbonate and potassium hydrogen carbonate. Alkali metal acetates such as sodium acetate, potassium acetate and ammonium acetate, alkali metal oxalates such as sodium oxalate and potassium oxalate, alkali metal succinates such as sodium succinate-sodium, glycine, alanine and glutamic acid Alkali metal salts of amino acids and ammonia are preferred. Among them, it is more preferable to use sodium hydrogen carbonate or sodium hydroxide.

The molar ratio of the alkali compound to the persulfate in the aqueous solution of the decomposing agent is not particularly limited as long as the pH of the aqueous solution of the reaction does not fall below at least 4 in the process of decomposing the water-absorbing polymer. The molar ratio of the alkali compound to the persulfate that enables this is preferably 0.1 to 10, more preferably 1 to 5, and even more preferably 1.5 to 3. As a result, the effect of suppressing the crosslinking / gelling reaction, which is a side reaction described above, can be further enhanced, and the water-absorbing polymer can be decomposed in a wide range of water absorption capacity.

Such a decomposing agent is preferably used, for example, as a solid, an aqueous solution or the like.

When the decomposing agent is used as a solid, for example, the water-absorbing polymer is swollen with water, and then the persulfate which is a decomposing agent and an alkali compound are added to the swollen water-absorbing polymer, or the water-absorbing polymer is added. After mixing the water-soluble polymer and the decomposing agent, water may be added.

In this case, the form (shape) of the decomposing agent may be, for example, powder, granules, pellets or the like.

On the other hand, when the decomposer is used as an aqueous solution, for example, a persulfate and an alkali compound are dissolved in water,
After preparing an aqueous solution having a predetermined concentration, the water absorbing polymer may be added to this aqueous solution.

When the decomposing agent is used as an aqueous solution, the concentration of the oxidizing agent in the aqueous solution is not particularly limited.
It is preferably 0.002 to 10% by weight, and 0.1 to 10% by weight
It is more preferably 8% by weight, and even more preferably 0.5 to 5% by weight.

Further, such decomposition of the water-absorbent polymer is preferably carried out while at least a part of the water-absorbent polymer is hydrated. That is, it is preferably carried out in a state of being moistened or swollen with water or a decomposition agent aqueous solution.

When the persulfate is used alone, decomposition of the water-absorbent polymer does not proceed unless all the water-absorbent polymer is swollen. Further, even when the persulfate is used alone even in a sufficiently swollen state, the decomposition reaction does not proceed completely, and a trace amount of undecomposed particulate matter remains.

On the other hand, in the decomposing agent of the invention of this application, it is not always necessary that the entire water-absorbent polymer is swollen with water (decomposing agent aqueous solution). That is, if at least a part of the water-absorbent polymer is in a water-containing state, the decomposition reaction of the water-absorbent polymer proceeds from this part, and the decomposition region (decomposition site) gradually increases. And finally, the whole water-absorbent polymer will be decomposed. Therefore, a larger amount of the water-absorbent polymer can be decomposed with a small amount of the decomposing agent.

The water content is, for example, preferably 5 to 1000 times, more preferably 10 to 500 times, and more preferably 15 to 1000 times the weight of the water-absorbent polymer.
More preferably, it is 200 times.

The water-absorbent polymer is preferably decomposed by adding, for example, 0.2 times by weight or more, preferably 0.5 times or more, with respect to the weight of the persulfate which is an oxidizing agent. Is more preferable, and 1.0 times or more is further preferable. This can increase the amount of water-absorbent polymer that can be decomposed (treated) at one time. That is, a large amount of water-absorbing polymer can be decomposed with a small amount of decomposing agent. Therefore, it is possible to reduce the amount of the decomposing agent remaining in the decomposing solution after decomposing the water-absorbing polymer, which is advantageous from the viewpoint of reducing environmental pollution when the decomposing solution is discarded.

From the viewpoint of environmental protection, the aqueous solution of the decomposer containing the persulfate and the alkali compound according to the invention of the present application, after the persulfate which is the oxidizing agent reacts to form a sulfate ion and is neutralized by the alkali compound, For example, since sodium sulfate, potassium sulfate, or the like is formed, the aqueous solution after the decomposition reaction is neutral or alkaline and safe. In addition, the water-soluble polyacrylic acid that is a decomposition product,
Since it is a polymer widely used in mining, textiles, cosmetics, paper manufacturing, oil mining, reforming agricultural land, water purification, etc., it does not pollute the environment.

When a strong alkali compound such as sodium hydroxide is used, the solution exhibits strong alkalinity of pH 10 to 14 even at a low concentration, but when a weak alkali compound such as sodium hydrogen carbonate is used, the solution is p
Since H7 to 9 exhibit weak alkalinity, hydrogen carbonate is more preferable from the viewpoint of disposal of the aqueous solution of decomposed products.

Further, the water-absorbent polymer according to the invention of this application can be decomposed even in the presence of non-decomposable substances such as plastic cover sheets, non-woven fabrics and cellulose powder which are constituents of disposable diapers and sanitary products. Unaffected,
The decomposition reaction proceeds 100%. That is, after the decomposition reaction, only the cover sheet, the non-woven fabric, and the cellulose powder,
It will be dispersed in the aqueous solution.

Of course, the invention of this application is not limited to this, and the water-absorbent polymer in soil in the fields of agriculture and horticulture, the water-absorbent polymer as a freshness-keeping agent for fruits and vegetables in the field of food, civil engineering / construction It is also highly applicable to the decomposition of water-absorbing polymers used as sealing materials in the field.

As the time for decomposing the water-absorbent polymer (decomposition time), the weight ratio of water (decomposing agent aqueous solution) to the weight of the water-absorbing polymer (absorption capacity), the concentration of persulfate which is an oxidizing agent, the alkali It can be appropriately selected depending on the compound concentration, temperature and the like, and is not particularly limited, but usually 1
It is preferably 0 minutes to 50 hours, and 15 minutes to 30 hours.
Time is more preferable, and 20 minutes to 24 hours is even more preferable.

Therefore, an embodiment will be shown below and further detailed description will be given. Of course, the invention is not limited to the following examples.

[0042]

[Example] 1. Decomposition of water-absorbing polymer (Example 1) 0.3 g of potassium persulfate and 0.185 g of sodium hydrogencarbonate (2 in molar ratio to potassium persulfate)
0.06 g of an alkali acid salt cross-linked polymer (water-absorbing polymer / granular: used in "Merrys" manufactured by Kao Corporation) in 10 g of distilled water.
Was added (water absorption ratio of 156 times) and mixed, and the water-absorbent polymer was decomposed and the reaction system was observed at 80 ° C. Twenty minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a uniform solution. After that, gelation did not occur at all even after a long time, and the solution was uniform. In addition, HORIBA, Ltd. D-2
1 When the pH of the liquid phase was measured with a pH meter, it was pH 8.4 at the start of the reaction and pH 8.5 at 20 minutes after 100% decomposition of the water-absorbing polymer, showing a slight decrease in pH even after a long time. It was (Example 2) 0.6 g of potassium persulfate and 0.37 g of sodium hydrogencarbonate (twice the molar ratio to potassium persulfate) were dissolved in 20 g of distilled water, and the same water absorption as in Example 1 was applied to this solution. 0.2g of water-soluble polymer (water absorption capacity 1
00 times), mixed, and decomposed the water-absorbent polymer and observed the reaction system at 80 ° C. 15 minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a homogeneous solution. After that, gelation did not occur at all even after a long time, and the solution was uniform. When the pH of the liquid phase was measured, it was pH 7.7 at the start of the reaction and 100% of the water-absorbent polymer was decomposed.
After 5 minutes, the pH was 7.8, and even after a long time, the decrease in pH was slight. (Example 3) 0.6 g of potassium persulfate and 0.18 g of sodium hydroxide (twice the molar ratio with respect to potassium persulfate) were dissolved in 20 g of distilled water, and the same water absorption as in Example 1 was applied to this solution. 0.2g of water-soluble polymer (water absorption capacity 1
00 times), mixed, and decomposed the water-absorbent polymer and observed the reaction system at 80 ° C. Twenty minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a uniform solution. After that, gelation did not occur at all even after a long time, and the solution was uniform. When the pH of the liquid phase was measured, it was pH 13.5 at the start of the reaction and pH 12.7 20 minutes after 100% decomposition of the water-absorbent polymer, and then the pH gradually decreased, but after a long time. The pH of was constant at 8. (Example 4) 0.6 g of potassium persulfate and 0.6 g of sodium hydrogencarbonate (3.2 mol ratio to potassium persulfate)
20 g of distilled water, and 0.2 g of the same water-absorbing polymer as in Example 1 was added (water-absorption capacity 100 times) to the solution and mixed to decompose and react the water-absorbing polymer at 80 ° C. The system was observed. Forty-five minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a homogeneous solution. After that, gelation did not occur at all even after a long time, and the solution was uniform. When the pH of the liquid phase was measured, it was pH 8.4 at the start of the reaction and was pH 8.5 45 minutes after 100% decomposition of the water-absorbing polymer, and showed almost no change even after a long time. (Example 5) 0.6 g of potassium persulfate and 0.29 g of sodium hydroxide (the molar ratio to potassium persulfate is 3.3).
20 g of distilled water, and 0.2 g of the same water-absorbing polymer as in Example 1 was added (water-absorption capacity 100 times) to the solution and mixed to decompose and react the water-absorbing polymer at 80 ° C. The system was observed. 15 minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a homogeneous solution. After that, gelation did not occur at all even after a long time, and the solution was uniform. When the pH of the liquid phase was measured, it was pH 13.9 at the start of the reaction, pH 12.8 15 minutes after 100% decomposition of the water-absorbing polymer, and pH did not change even after a long time. (Example 6) 0.6 g of potassium persulfate and 0.06 g of sodium hydroxide (molar ratio to potassium persulfate: 0.6)
(8 times amount) was dissolved in 20 g of distilled water, and 0.2 g of the same water-absorbing polymer as in Example 1 was added to this solution (water-absorbing capacity 100 times) and mixed to decompose the water-absorbing polymer at 80 ° C. The reaction system was observed. 15 minutes after starting the reaction,
All the water-absorbent polymers decomposed and became a homogeneous solution.
After that, gelation did not occur at all even after a long time, and the solution was uniform. When the pH of the liquid phase was measured, it was pH 12.4 at the start of the reaction and pH 12.2 15 minutes after 100% of the water-absorbing polymer had decomposed. The pH was about 5. (Example 7) 0.3 g of potassium persulfate and 0.185 g of sodium hydrogen carbonate (2 in molar ratio to potassium persulfate)
(Double volume) was dissolved in 10 g of distilled water, and 0.67 g of the water-absorbing polymer similar to that used in Example 1 was added to this solution (water-absorption ratio: 15 times) to decompose the water-absorbing polymer at 80 ° C. Observed. 90 minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a homogeneous solution. afterwards,
Gelation did not occur at all even after a long time, and the solution was uniform. The decomposition reaction made it possible to measure the pH of the liquid phase 15 minutes after the start of the reaction. The pH at this time is 7.6,
90 minutes after 100% decomposition of the water-absorbent polymer, the pH was 7.
It was 6, and the decrease in pH was slight even after a long time. (Example 8) 0.3 g of potassium persulfate and 0.06 g of sodium hydroxide (1.3 mol ratio to potassium persulfate)
(Double volume) was dissolved in 10 g of distilled water, and 0.67 g of the water-absorbing polymer similar to that used in Example 1 was added to this solution (water-absorption ratio: 15 times) to decompose the water-absorbing polymer at 80 ° C. Observed. 720 minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a uniform solution. After that, gelation did not occur at all even after a long time, and the solution was uniform. It should be noted that 30 minutes after the start of the reaction, a liquid phase appeared due to decomposition, and the pH of this liquid phase was measured.
9, p after 720 minutes after 100% decomposition of the water-absorbent polymer
H was about 5. (Example 9) 0.3 g of potassium persulfate and 0.185 g of sodium hydrogen carbonate (2 in molar ratio to potassium persulfate)
(Double volume) is dissolved in 10 g of distilled water, and an isobutylene-maleate cross-linked polymer (water-absorbing polymer / granular: "KI-GEL 201K" manufactured by Kuraray Co., Ltd.) is added to this solution.
Add 0.064 g (water absorption capacity 15 times), mix, 80
The decomposition of the water-absorbent polymer and the observation of the reaction system were carried out at ℃. Thirty minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a uniform solution. After that, gelation did not occur at all even after a long time, and the solution was uniform. The liquid phase p
When H was measured, pH was 9.2 at the start of the reaction, pH was 9.0 after 30 minutes when the water-absorbing polymer was 100% decomposed, and the decrease in pH was slight even after a long time. (Example 10) 0.3 g of potassium persulfate and 0.185 g of sodium hydrogen carbonate (twice the molar ratio with respect to potassium persulfate) were dissolved in 10 g of distilled water, and the same water absorption as in Example 9 was applied to this solution. 0.67 g of a water-soluble polymer was added (water absorption capacity: 15 times), and the water-absorbent polymer was decomposed at 80 ° C. and the reaction system was observed. Thirty minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a uniform solution. After that, gelation did not occur at all even after a long time, and the solution was uniform. The decomposition reaction made it possible to measure the pH of the liquid phase 15 minutes after the start of the reaction. The pH at this time is 8.7.
Then, 30 minutes after 100% decomposition of the water-absorbent polymer, pH
It was 8.6, and the decrease in pH was slight even after a long time. (Example 11) 0.3 g of potassium persulfate and 0.06 g of sodium hydroxide (molar ratio to potassium persulfate: 1.
(3 times the amount) was dissolved in 10 g of distilled water, and 0.67 g of the water-absorbent polymer similar to that used in Example 9 was added to this solution (water-absorption ratio of 15 times) to decompose the water-absorbent polymer at 80 ° C. Was observed. Thirty minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a uniform solution. After that, gelation did not occur at all even after a long time, and the solution was uniform. 15 minutes after the start of the reaction, a liquid phase appeared due to decomposition, and the pH of this liquid phase was measured.
0, pH 30 minutes after 100% decomposition of water-absorbent polymer
Was 9.7. After a long period of time, the decrease in pH was slight. (Comparative Example 1) 0.3 g of potassium persulfate was dissolved in 10 g of distilled water, and 0.064 g of the same water-absorbing polymer as in Example 1 was added to this solution (water absorption capacity: 156 times) and mixed, and the mixture was heated to 80 ° C. The water-absorbent polymer was decomposed and the reaction system was observed. 15 minutes after the start of the reaction, the viscosity of the liquid phase decreased due to the decomposition of some of the water-absorbing polymer, but the water-absorbing polymer particles remained. After 60 minutes, gelation of the water-absorbent polymer particles occurred. The pH of the liquid phase was measured and found to be pH 6.3 at the start of the reaction and pH 5.7 60 minutes after gelation had occurred. (Comparative Example 2) 0.6 g of potassium persulfate was dissolved in 20 g of distilled water, and 0.2 g of the same water-absorbing polymer as in Example 1 was added to this solution (water absorption ratio 100 times) and mixed,
At 0 ° C., the water-absorbent polymer was decomposed and the reaction system was observed. 15 minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a homogeneous solution. However, after 45 minutes, regelation started, and after 90 minutes, the gel phase and the liquid phase separated.
After that, the gel did not disappear. The pH of the liquid phase was measured and found to be pH 6.1 at the start of the reaction and pH 5.6 45 minutes after regelation had occurred. (Comparative Example 3) 0.3 g of potassium persulfate was dissolved in 10 g of distilled water, and 0.67 g of the same water-absorbing polymer as that of Example 1 was added to this solution (water absorption ratio of 15 times), and water absorption at 80 ° C was carried out. Of the reactive polymer and the reaction system were observed.
Initially, the entire water-absorbent polymer was wet with the above aqueous solution, and the system gelled after 15 minutes without being dissolved over time. In addition, since the liquid phase was not generated,
The pH could not be measured. (Comparative Example 4) 0.3 g of potassium persulfate was dissolved in 10 g of distilled water, and 0.064 g of the same water-absorbing polymer as that of Example 9 was added to this solution (water absorption ratio of 156 times) and mixed, and the mixture was heated to 80 ° C. The water-absorbent polymer was decomposed and the reaction system was observed. Thirty minutes after the start of the reaction, all the water-absorbent polymers were decomposed and became a uniform solution. But after 60 minutes,
Gelation occurred again, and after 120 minutes, a gelled product was precipitated, and thereafter, the gel did not decompose and disappear. In addition, when the pH of the liquid phase was measured, the pH was
7.2, 60 minutes after gelation had occurred, the pH dropped to 3.3. 2. Evaluation In Examples 1 to 11 above, after elapse of a predetermined time,
The undegraded water-absorbent polymer was filtered with a filter paper, washed with water, dried at 80 ° C. for 24 hours, the weight of the dried product was measured, and the decomposition rate of the water-absorbent polymer was determined based on the measured value.
Further, in Comparative Examples 1 to 5, even if the water-absorbing polymer once decomposed and dissolved, re-gelation occurs or the water-absorbing polymer is partially decomposed after a predetermined period of time,
Since other water-absorbing polymer particles gelled while remaining, the object of the invention of this application is to develop a decomposing agent and a decomposition method for completely decomposing the water-absorbing polymer to form a stable homogeneous solution. Considering this, the decomposition rate was not determined by the method of Examples 1 to 11.

The results are shown in Table 1. In the column of the decomposition rate of Comparative Examples 1 to 5, regelation or gelation was described instead of the value of the decomposition rate, and it was shown that the decomposition did not proceed 100%.

[0044]

[Table 1]

As shown in Table 1, each of the decomposing agents of Examples 1 to 11 was excellent in the resolution of the water-absorbent polymer. On the other hand, each of the decomposing agents of Comparative Examples 1 to 5
All were inferior in the resolution of the water absorbing polymer.

Further, for example, in Comparative Examples 2 and 5 having a water absorption capacity of 100 times, by adding a slight amount of sodium hydrogencarbonate to potassium persulfate, the time until regelation occurs becomes longer. It was also found that when the molar ratio of sodium hydrogencarbonate to potassium persulfate was 2, as in Example 2, the regelation reaction was completely suppressed and only the decomposition reaction occurred.

[0047]

As described in detail above, according to the invention of this application, it is possible to provide a decomposing agent for a water-absorbing polymer, which has high versatility and excellent resolution, and a highly efficient decomposing method using the same. it can.

In particular, when a persulfate and an alkali compound are contained, a cross-linking reaction between the molecular chains of radicals produced on the molecular chains of the water-absorbing polymer caused by the thermal decomposition of the persulfate, that is, The alkali compound greatly suppresses the gelation reaction, and the synergistic effect of preferentially decomposing the decomposition reaction is exhibited, and further excellent resolution is exhibited, which is advantageous in that it can be easily and inexpensively produced.

Thus, the decomposing agent of the invention of this application is
Since it has excellent resolution, more water-absorbing polymers can be decomposed with a small amount, which is advantageous from the viewpoint of environmental protection.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Chiyuki Kikushima             2-6-11 Shiba Park, Minato-ku, Tokyo Japan             Sahi Kiko Sales Co., Ltd. F-term (reference) 4D004 AA06 AA48 CA34 CA35 CA36                       CC11 DA03 DA06 DA10 DA11                       DA20                 4F301 CA09 CA23 CA41 CA72

Claims (9)

[Claims] 1. A decomposing agent for decomposing a water-absorbing polymer, comprising at least one alkali compound and at least one persulfate compound which is an oxidizing agent. . 2. The decomposition according to claim 1, wherein the alkaline compound is water-soluble and shows alkalinity by dissociating into a monovalent cation and a monovalent anion in an aqueous solution thereof. Agent. 3. The decomposing agent according to claim 1, which is an aqueous solution in which the concentration of the oxidizing agent is 0.002 to 10% by weight. 4. The decomposing agent according to claim 1, wherein the alkali compound is contained in a molar ratio of 0.1 to 10 times that of the oxidizing agent. 5. A method for decomposing a water-absorbing polymer in a water-absorbing polymer or a water-absorbing material containing the same,
A method for decomposing a water-absorbent polymer, comprising adding the decomposing agent according to claim 1 to the water-absorbent polymer to decompose the water-absorbent polymer in the presence of water. 6. The decomposition method according to claim 5, wherein the pH of the aqueous solution of the decomposition agent is set in the range of 4 to 14. 7. The decomposition method according to claim 5, wherein the treatment temperature is in the range of 40 ° C. to 100 ° C. 8. The decomposition method according to claim 5, wherein the decomposition treatment is carried out in a state where at least a part of the water-absorbent polymer is contained in water. 9. The decomposition method according to claim 8, wherein the water content is 5-1000 times the weight ratio of the water-absorbent polymer.