Processing method of water absorbing polymer

Abstract

To provide a technique of efficiently processing water absorbing polymer.SOLUTION: A processing method of water absorbing polymer according to an aspect of the present invention is a processing method of water absorbing polymer contained in an object to be treated. The processing method includes: a thermal decomposition step of subjecting the water absorbing polymer contained in the object to be treated to thermal decomposition to generate water-soluble polymer; and a melting step of melting the water-soluble polymer into water.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for treating a water-absorbing polymer to solubilize the water-absorbing polymer. [Background technology]

[0002] From the viewpoint of efficient use of resources and reduction of greenhouse gas emissions, it is desirable to recycle used absorbent articles such as disposable diapers and sanitary napkins. However, water-absorbent polymers used in absorbent articles remain in a swollen state even after use and are difficult to separate from other materials in the absorbent article. For this reason, water-absorbent polymers that have absorbed water can hinder the recycling of each material in the used absorbent article.

[0003] In this regard, a technique is known in which absorbed water-absorbing polymers are chemically decomposed by a treatment agent. Patent Document 1 discloses a technique for decomposing and solubilizing absorbent polymers using an oxidizing agent. Patent Document 2 discloses a technique for decomposing water-absorbing polymers using an acid or alkali. Patent Document 3 discloses a technique for immersing used sanitary products in an ozone-containing aqueous solution to decompose superabsorbent polymers. Patent Document 4 discloses a technique for immersing used sanitary product constituent materials in an acid-containing aqueous solution, and then adding a chlorine dioxide generating material to generate chlorine dioxide and decompose the superabsorbent polymer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-317784 [Patent Document 2] Japanese Patent Application Publication No. 9-249711 [Patent Document 3] JP 2016-79525 A [Patent Document 4] JP 2019-108639 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, treatments that mainly involve chemical reactions using a treatment agent can cause the following problems. First, when treating a large amount of material, the cost of the treatment agent becomes high. In addition, the combined volume of the material and treatment liquid becomes large, requiring a large device. Furthermore, the disposal of waste liquid after treatment is time-consuming and costly. Therefore, there is a demand for technology that can more efficiently treat water-absorbent polymers.

[0006] The present invention relates to a technique for efficiently treating water-absorbing polymers. [Means for solving the problem]

[0007] A method for treating a water-absorbent polymer according to one embodiment of the present invention is a method for treating a water-absorbent polymer contained in a treatment target, comprising the steps of: A pyrolysis step of generating a water-soluble polymer by pyrolyzing the water-absorbing polymer in the object to be treated; A dissolving step of dissolving the water-soluble polymer in water. Effect of the Invention

[0008] According to the present invention, it is possible to efficiently treat a water-absorbing polymer. [Brief description of the drawings]

[0009]

Figure 1

Figure 2

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Figure 4

[0010] <Summary of the Invention> The present invention relates to a method for treating a water-absorbent polymer, which comprises thermally decomposing the water-absorbent polymer to solubilize it in water. According to one embodiment of the present invention, the water-absorbent polymer can be decomposed mainly by dry processing to generate a water-soluble polymer. This makes it possible to efficiently separate the water-absorbent polymer from other materials constituting an absorbent article and to efficiently recycle these materials.

[0011] Water-absorbent polymers generally have a three-dimensional network structure in which the main chains having hydrophilic groups are crosslinked. Water-absorbent polymers can retain moisture in the network formed by the main chains and crosslinked chains by bonding the hydrophilic groups to water molecules through hydrogen bonds or the like. Specifically, the water-absorbent polymer includes at least one water-absorbent polymer selected from, for example, polyacrylic acid, polyacrylic acid salts, partially crosslinked polymers of polymer compounds having a carboxyl group or a salt thereof, partially crosslinked polysaccharides, etc. The partially crosslinked polymers of polymer compounds having a carboxyl group or a salt thereof include crosslinked polyacrylates, poly(vinyl alcohol / acrylate) copolymers (crosslinked), starch-acrylate graft copolymers (crosslinked), and polyvinyl alcohol-polymaleic anhydride graft copolymers (crosslinked), etc. The partially crosslinked polysaccharides include crosslinked carboxymethyl cellulose salts, etc. The "salt" constituting the water-absorbing polymer includes at least one salt selected from, for example, alkali metal salts (sodium salts, potassium salts, lithium salts, etc.), alkaline earth metal salts (calcium salts, magnesium salts, barium salts, etc.), ammonium salts (quaternary ammonium salts, quaternary alkyl ammonium salts, etc.), etc. The water-absorbent polymer of the present invention preferably contains, for example, a polyacrylate-based polymer, and more preferably contains a crosslinked sodium polyacrylate.

[0012] In the present invention, the absorbent article means an article that has a water-absorbing polymer and can absorb water. Examples of the absorbent article include disposable diapers, sanitary napkins, urine pads, panty liners, pet toilet sheets, drip sheets, moisture absorbents, deodorants, etc. The "drip sheet" means a water-absorbing sheet that absorbs excess water (body fluids, etc.) from food ingredients such as meat and fish. In the present invention, a used absorbent article means an absorbent article in a state in which it has absorbed moisture after use. Furthermore, in the present invention, the absorbent article is preferably an absorbent sanitary product that absorbs body fluids such as urine and menstrual blood. Examples of absorbent sanitary products include disposable diapers, sanitary napkins, urine pads, panty liners, etc. Such absorbent sanitary products include, for example, an absorbent body containing a water-absorbent polymer and a sheet material covering the front and back of the absorbent body, and each component is bonded by an adhesive or the like.

[0013] First Embodiment [Method of treating water-absorbent polymer] As shown in FIG. 1, the method for treating a water-absorbing polymer according to the first embodiment of the present invention includes, for example, a thermal decomposition step S11 and a dissolution step S12.

[0014] (Pyrolysis step S11) In the thermal decomposition step S11, the water-absorbing polymer in the object to be treated is thermally decomposed to generate a water-soluble polymer. The term "thermal decomposition" used here means that the molecules of the water-absorbing polymer are decomposed by a dry heating process. The thermal decomposition process according to this embodiment is carried out, for example, under low-oxygen or oxygen-free conditions. In addition, the process is preferably a process that does not use an additive that chemically decomposes the water-absorbing polymer, such as an acid, an alkali, or an oxidizing agent.

[0015] In this embodiment, the object to be treated is a treatment target containing a water-absorbent polymer, and preferably includes, for example, a used absorbent article or a material derived therefrom. In addition, the object to be treated may include waste or auxiliary materials that do not contain a water-absorbent polymer, in addition to the material containing the water-absorbent polymer.

[0016] As a specific heating means for heating the object to be treated in this step, for example, a heating device for heating an open or closed space in which the object to be treated can be used, and from the viewpoint of efficiently heating the object to be treated, it is preferable to use a heating device such as a heating furnace for heating a closed space. From the viewpoint of efficiently heating the object to be treated in this step, it is preferable to heat the object to be treated while stirring it. The atmosphere during heating in this step can be appropriately selected from an air atmosphere, a low-oxygen atmosphere, an inert gas atmosphere, a water vapor atmosphere, etc., but from the viewpoint of controlling the decomposition of the water-absorbing polymer molecules, a low-oxygen atmosphere is preferable. Note that a low-oxygen atmosphere refers to an atmosphere with an oxygen partial pressure of 10 kPa or less, preferably 8 kPa or less. Furthermore, even if the low-oxygen atmosphere is used, it is more preferable that the low-oxygen atmosphere is an inert gas atmosphere or a water vapor atmosphere in which there is almost no oxygen. Examples of the inert gas include nitrogen gas and argon gas.

[0017] The water-absorbent polymer to be thermally decomposed forms a three-dimensional network structure in which multiple main chains are crosslinked by crosslinking chains including hydrogen bonds and ester bonds. When the water-absorbent polymer is heated at a certain temperature range, radicals are generated, and it is considered that the molecules forming the three-dimensional network structure are cleaved. At this time, it is considered that relatively weak bonds such as hydrogen bonds and ester bonds become thermally unstable and are easily cleaved. In addition, when the water-absorbent polymer is a copolymer of multiple types of monomers, it is also considered that the structural units resulting from the thermally unstable monomers are preferentially cleaved. Thus, in this step, by utilizing the fact that the water-absorbent polymer has a thermally unstable site, the three-dimensional network structure is thermally decomposed while leaving the hydrophilic groups of the water-absorbent polymer, and a water-soluble polymer is generated.

[0018] Here, the relationship between the heating temperature and the structural change of the water-absorbing polymer will be described based on the findings obtained from the tests of the present inventors. FIG. 2 is a graph showing a thermogravimetric (TG) curve obtained by performing a thermogravimetric (TG) analysis on a treated object made of a water-absorbing polymer, with the horizontal axis showing temperature and the vertical axis showing the mass loss of the treated object. In this test, 1 mg of crosslinked sodium polyacrylate as the water-absorbing polymer was placed in an aluminum pan, which was then set in a thermogravimetric analyzer (TG-DTA) (manufactured by Hitachi High-Tech Science Corporation, product name: STA7200RV). This water-absorbing polymer was heated in a nitrogen atmosphere from 30° C. to 600° C. at a rate of 10° C. / min.

[0019] The TG curve shown in FIG. 2 had three gradient change points. The first change point P1 occurs at temperature T1. The second change point P2 occurs at temperature T2, which is higher than temperature T1. The third change point P3 occurs at temperature T3, which is higher than temperature T2. In the following description, the temperature zone from the start of heating to temperature T1 corresponding to the first change point P1 is referred to as the first temperature zone R1. The temperature zone from temperature T1 to temperature T2 corresponding to the second change point P2 is referred to as the second temperature zone R2. The temperature zone from temperature T2 to temperature T3 corresponding to the third change point P3 is referred to as the third temperature zone R3. The temperature zone above temperature T3 is referred to as the fourth temperature zone R4.

[0020] In the TG curve shown in Fig. 2, the gradient is gentle in the first temperature zone R1. In this first temperature zone R1, the structure of the water-absorbing polymer does not change, and the evaporation of water from the object to be treated proceeds. The gradient of the TG curve in the second temperature zone R2 is steeper than that in the first temperature zone R1. In the second temperature zone R2, the three-dimensional network structure of the water-absorbent polymer is cleaved to produce a water-soluble polymer. The gradient of the TG curve in the third temperature zone R3 is steeper than that in the second temperature zone R2. 2 The thermal decomposition of the workpiece progresses while the mass of the workpiece decreases rapidly due to the vaporization of gases such as volatile organic compounds. Furthermore, in the fourth temperature zone R4, the mass of the workpiece hardly changes and the thermal decomposition is almost complete.

[0021] The thermal decomposition temperature zone in this step, i.e., the temperature at which the object to be treated containing the water-absorbing polymer is heated, can be set to the second temperature zone R2 at which the water-soluble polymer is produced. For example, when the water-absorbing polymer contains a polyacrylate-based polymer as a main component, the thermal decomposition temperature zone can be set to 350°C or more and 450°C or less, more preferably 350°C or more and 430°C or less, with reference to Figure 2. In other words, it is preferable that this step includes a step of thermally decomposing under heating at 350°C or more and 450°C or less, further 350°C or more and 430°C or less.

[0022] In the above test, sodium polyacrylate was used as the treated material, but due to the above-mentioned molecular structure characteristics common to water-absorbing polymers, TG curves with the same characteristics as those in FIG. 2 can be obtained for other water-absorbing polymers. As a specific method for setting the thermal decomposition temperature zone for other water-absorbing polymers, an element containing a water-absorbing polymer is taken out as a sample from the treated material, and the above-mentioned TG analysis is performed on the sample. In the obtained TG curve, the temperature zone (e.g., the second temperature zone R2 in FIG. 2) adjacent to the low-temperature side of the temperature zone with the steepest gradient (e.g., the third temperature zone R3 in FIG. 2) can be set as the thermal decomposition temperature zone. Depending on the moisture content of the sample, the first change point P1 may not be clearly obtained. In this case, the temperature zone between the temperature corresponding to the gradient change point on the low-temperature side of the temperature zone with the steepest gradient (the temperature corresponding to the temperature T2 in FIG. 2) and a temperature 100° C. lower than that temperature can be set as the thermal decomposition temperature zone.

[0023] The heating temperature in this step may vary within the pyrolysis temperature range or may be maintained approximately constant. The workpiece may be heated by a heating device preheated to a heating temperature in the temperature range. Alternatively, the workpiece may be heated so that the maximum temperature reached is included in the temperature range. When the temperature is increased, the rate of temperature increase is preferably 0.001° C. / min to 20° C. / min, more preferably 0.01° C. / min to 15° C. / min, more preferably 0.1° C. / min to 12° C. / min, and even more preferably 1° C. / min to 10° C. / min.

[0024] The water-soluble polymer produced in this step is a polymer derived from a water-absorbent polymer and is soluble in water. The water solubility of the polymer can be confirmed by mixing the polymer with a sufficient amount of water (for example, 100 times or more by mass relative to the mass of the polymer) and stirring, and measuring the amount of the polymer filtered through a filter paper. For example, if the water-absorbent polymer is not water-soluble, it will remain on the filter paper, and the weight of the dried residue on the filter paper will be equal to the weight of the stirred polymer.

[0025] (Dissolving step S12) In the dissolving step of this embodiment, the produced water-soluble polymer is dissolved in water. This produces an aqueous solution containing the water-soluble polymer as a solute. In this step, for example, it is preferable to dissolve the water-soluble polymer in water by mixing the entire object to be treated obtained in the pyrolysis step S11 with water. This makes it easy to separate insoluble substances (e.g., plastics and cellulose materials other than the water-absorbent polymer) from the water-soluble polymer derived from the water-absorbent polymer after heating.

[0026] The water used in this step is preferably purified water (pure water, ion-exchanged water, etc.), but may be ordinary water such as tap water. However, from the viewpoint of suppressing gelation of the water-soluble polymer solution, soft water with a low concentration of metal ions is preferable. Furthermore, from the viewpoint of suppressing an increase in the viscosity of the water-soluble polymer solution, the amount of water-soluble polymer to be dissolved is preferably 0.0001 g or more and 100 g or less, and more preferably 0.001 g or more and 50 g or less, per 1 L of water.

[0027] [Effects of this embodiment] In the method for treating a water-absorbent polymer according to the present embodiment, the produced water-soluble polymer is dissolved in water, so that the polymer derived from the water-absorbent polymer can be easily removed from the material to be treated. This makes it possible to separate the water-absorbent polymer from other materials, and promotes the recycling of the material to be treated.

[0028] In addition, in the treatment method of this embodiment, the water-absorbing polymer can be decomposed into a water-soluble polymer by pyrolysis without adding an additive, so that the cost of the additive can be reduced. In addition, by not adding additives or water to the object to be treated, the mass of the object to be heated can be reduced, and the energy required for heating can be reduced. This can reduce the cost and environmental load of heating. Furthermore, since no waste liquid is generated after the pyrolysis step S11, the environmental load and treatment cost due to the waste liquid can also be reduced. Therefore, the treatment method of this embodiment can efficiently treat the water-absorbing polymer while suppressing the environmental load.

[0029] Furthermore, by pyrolyzing the water-absorbing polymer into a water-soluble polymer, the recycling efficiency of the water-absorbing polymer can be increased compared to when the water-absorbing polymer is pyrolyzed into a monomer. For example, if the water-absorbing polymer is pyrolyzed into a monomer, it is necessary to polymerize the monomer in order to regenerate the water-absorbing polymer from these monomers, which increases the burden. In contrast, in this embodiment, since a water-soluble polymer is generated from the water-absorbing polymer, the burden of regenerating the water-absorbing polymer is reduced compared to when the water-absorbing polymer is decomposed into a monomer. In addition, there is a possibility that the water-soluble polymer itself can be utilized. Therefore, a compound with high utility value can be obtained from the water-absorbing polymer, and resources can be effectively utilized.

[0030] <Second embodiment> The method for treating a water-absorbing polymer according to the present invention may include other steps in addition to the steps described in the above embodiment 1. Hereinafter, other embodiments of the method for treating a polymer according to the present invention will be described.

[0031] The polymer processing method according to the second embodiment of the present invention may include, for example, a drying step S21, a pyrolysis step S22, and a dissolving step S23, as shown in Fig. 3. Note that the pyrolysis step S22 and the dissolving step S23 are similar to the pyrolysis step S11 and the dissolving step S12 of the first embodiment, and therefore detailed description thereof will be omitted.

[0032] In the drying step S21, the object to be processed is dried before the pyrolysis step S22. In this step, the object to be processed can be dried by heating and / or air-drying the object to be processed. For example, in this step, the object to be processed may be heated without blowing air, or air may be blown while heating the object to be processed. Also, warm air may be sent to the object to be processed. Further, in this step, from the viewpoint of efficiently drying the object to be processed, it is preferable to dry the object to be processed while stirring. In this step, a heating device or a drying device corresponding to the drying mode can be used.

[0033] When this step involves heating, the same heating device as in the pyrolysis step S22 can be used, or a different device can be used. The drying temperature in this step is less than the pyrolysis temperature of the water-absorbing polymer, and preferably can be 40°C or higher. The drying temperature may be maintained substantially constant, but from the viewpoint of smoothly transitioning to the pyrolysis step S22, it is preferably set to rise continuously or stepwise. The heating rate when raising the temperature is preferably 0.001°C / min or more and 20°C / min or less, more preferably 0.01°C / min or more and 15°C / min or less, still more preferably 0.1°C / min or more and 12°C / min or less, and even more preferably 1°C / min or more and 10°C / min or less. When raising the temperature in this step, it is preferable that this step and the pyrolysis step S22 are continuously performed in the same device.

[0034] In this embodiment, by performing the drying step S21, the moisture content of the object to be processed can be reduced, and the time required for the pyrolysis step S22 can be shortened. Therefore, the amount of energy required for the treatment can be reduced, and the treatment cost and environmental load can be suppressed.

[0035] <Third Embodiment> The water-absorbing polymer processing method according to the third embodiment of the present invention may include, for example, a processing object preparation step S31, a pyrolysis step S32, and a dissolution step S33, as shown in Fig. 4. Note that the pyrolysis step S32 and the dissolution step S33 are similar to the pyrolysis step S11 and the dissolution step S12 of the first embodiment, and therefore detailed description thereof will be omitted.

[0036] In the step S31 of preparing the object to be treated, an object to be treated derived from a used absorbent article is prepared before the step S32 of pyrolysis. That is, in this embodiment, the object to be treated is an object to be treated derived from a used absorbent article. In this step, there is no particular limitation as long as an object to be treated to be subjected to the pyrolysis step S32 can be obtained from the used absorbent article. For example, the collected used absorbent article itself may be prepared as the object to be treated, or the collected used absorbent article may be subjected to pretreatment. For example, the pretreatment may be a treatment that exerts at least one of a physical action or a chemical action on the used absorbent article.

[0037] The treatment of exerting a physical action on the used absorbent article may be at least one treatment selected from, for example, stirring, crushing, cutting, vibration, drying, freezing, pressurization, decompression, irradiation with energy rays (laser, etc.), or squeezing. Such treatments can be performed by known devices capable of performing each of the above treatments on the object to be treated. The treatment of exerting a physical action can expose elements containing a water-absorbent polymer from the used absorbent article, and can increase the heating efficiency of the water-absorbent polymer. The treatment of exerting a physical action can also reduce the moisture content of the object to be treated, and can shorten the time required for the pyrolysis step S22. Therefore, the amount of energy required for the treatment can be reduced, and the treatment cost and environmental load can be suppressed.

[0038] The treatment that exerts a chemical effect on the used absorbent article may include, for example, a treatment of separating each element of the used absorbent article using an acid, an alkali, an oxidizing agent, a salt, etc. Further, the treatment may include a treatment of dehydrating the used absorbent article using an aqueous solution or solid containing polyvalent metal ions, an acidic aqueous solution, electrolysis, etc. By the treatment that exerts a chemical effect, the moisture content of the object to be treated can be reduced, and the time required for the pyrolysis step S22 can be shortened. Therefore, the amount of energy required for the treatment can be reduced, and the treatment cost and environmental load can be suppressed.

[0039] Further, from the viewpoint of promoting the separation of the used absorbent article without involving waste liquid treatment, etc., the treatment that exerts a chemical effect on the used absorbent article may include a heat treatment for modifying a thermoplastic polymer other than the water-absorbing polymer. In this case, the heating temperature is preferably below the thermal decomposition temperature range of the absorbent polymer and above the glass transition point of the thermoplastic polymer used in the used absorbent article. By modifying a thermoplastic polymer other than the water-absorbing polymer, etc., each element of the used absorbent article can be easily separated, and the heating efficiency of the water-absorbing polymer can be increased. In addition, when the drying of the used absorbent article proceeds by this heat treatment, this step can also serve as the above-mentioned drying step S21.

[0040] Further, in this step, a treatment that exerts both a chemical action and a physical action on the used absorbent article may be performed. As an example of such a treatment, a treatment of heating the used absorbent article while stirring it can be mentioned. Thereby, the separation between the element containing the water-absorbing polymer and the element containing other polymers can be further promoted. Alternatively, a treatment that exerts a physical action may be performed while adding additives such as an acid, an alkali, an oxidizing agent, and a salt to the used absorbent article.

[0041] Furthermore, in this step, after the used absorbent article is decomposed into each element, elements that do not contain a water-absorbing polymer can also be removed by separation treatment or precipitation treatment using a separator (such as a sieve, classifier, screen separator, cyclone separator, centrifuge, etc.). Thereby, the content ratio of the water-absorbing polymer in the object to be treated can be increased, and the treatment efficiency of the water-absorbing polymer can be further enhanced.

[0042] In this embodiment, an object to be treated derived from a used absorbent article can be obtained by the preparation step S31, and the treatment of the water-absorbing polymer contained in the used absorbent article can be efficiently performed. Further, by performing a treatment that exerts at least one of a physical action or a chemical action on the used absorbent article in the preparation step S31, an object to be treated suitable for the thermal decomposition step S32 can be obtained from the used absorbent article, and the heating efficiency in the thermal decomposition step S32 can be increased.

[0043] <Other Embodiments> As described above, the embodiments of the present invention have been described. However, the present invention is not limited only to the above-described embodiments, and it goes without saying that various changes can be made without departing from the gist of the present invention. For example, the method for treating a water-absorbing polymer according to another embodiment may include both the drying step S21 described in the second embodiment and the preparation step S31 of the object to be treated described in the third embodiment.

Examples

[0044] 5 g of a water-absorbing polymer (crosslinked sodium polyacrylate) was put into a tubular furnace, heated from 30 °C at a rate of 10 °C / min, and heat-treated. The maximum temperature reached in Comparative Example 1 was 300 °C. The maximum temperature reached in Example 1 was 350 °C. The maximum temperature reached in Example 2 was 375 °C. The maximum temperature reached in Example 3 was 400 °C. The maximum temperature reached in Example 4 was 425 °C. The maximum temperature reached in Example 5 was 450 °C. The maximum temperature reached in Comparative Example 2 was 500 °C. The maximum temperature reached in Comparative Example 3 was 600 °C. In each example, the atmosphere in the furnace was a 100% nitrogen atmosphere, and the flow rate of nitrogen gas was 1.0 L / min.

[0045] After holding the workpiece in each of the examples and comparative examples at the maximum temperature reached for 5 minutes, it was cooled to room temperature. 1 g of the cooled workpiece was taken, mixed with 100 mL of pure water and stirred, and the mixture was filtered through a hydrophilic PTFE membrane filter (pore size 0.45 μm). The dry weight of the filtrate dried at 60 °C for 1 day was measured as the dissolved matter.

[0046] In Comparative Example 1 heated to 300 °C, solids remained on the filter. On the other hand, since the dry weight of the dissolved matter was 0.01 g, it is considered that the water-absorbing polymer was not solubilized in Comparative Example 1. In Example 1 heated to 350 °C, solids remained on the filter. On the other hand, since the dry weight of the dissolved matter was 0.5 g, it is considered that a water-soluble polymer was produced in Example 1. In Example 2 heated to 375 °C, Example 3 heated to 400 °C, and Example 4 heated to 425 °C, no residue was observed on the filter, and the filtrate became transparent brown. On the other hand, since the dry weight of the dissolved matter was 1.0 g, it is considered that a water-soluble polymer was produced in Examples 2, 3, and 4. In Example 5 heated to 450 °C, solids were observed on the filter. On the other hand, since the dry weight of the dissolved matter was 0.3 g, it is considered that a water-soluble polymer was produced in Example 5. In Comparative Example 2 heated to 500°C and Comparative Example 3 heated to 600°C, solids remained on the filter. On the other hand, since the dry weight of the dissolved matter was 0.01 g, it is considered that in Examples 3 and 4, the water-absorbing polymer was not solubilized.

Claims

1. A method for treating a water-absorbing polymer contained in an object to be treated, comprising: a thermal decomposition step of generating a water-soluble polymer by thermally decomposing the water-absorbing polymer in the object to be treated; and a dissolution step of dissolving the water-soluble polymer in water. A method for treating a water-absorbing polymer.

2. The method for treating a water-absorbing polymer according to claim 1, further comprising a drying step of drying the object to be treated before the thermal decomposition step. The method for treating a water-absorbing polymer according to claim 1.

3. The method for treating a water-absorbing polymer according to claim 1 or 2, wherein the object to be treated is an object to be treated derived from a used absorbent article. The method for treating a water-absorbing polymer according to claim 1 or 2.

4. The method for treating a water-absorbing polymer according to any one of claims 1 to 3, wherein the water-absorbing polymer contains a polyacrylate-based polymer. The method for treating a water-absorbing polymer according to any one of claims 1 to 3.

5. The method for treating a water-absorbing polymer according to claim 4, wherein the thermal decomposition step includes a step of performing thermal decomposition under heating at 350°C or higher and 450°C or lower. The method for treating a water-absorbing polymer according to claim 4.

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