KR102447886B1 - Super absorbent polymer and preparation method of super absorbent polymer - Google Patents

Abstract

The present invention relates to a super absorbent polymer and a method for preparing the same. By adding cellulose in the surface crosslinking step, a superabsorbent polymer with significantly improved biodegradability can be prepared.

Description

Super absorbent polymer and manufacturing method thereof

The present invention relates to a superabsorbent polymer having a cross-linked surface layer to which cellulose is added and a method for preparing the same.

The superabsorbent polymer is a polymer material capable of absorbing about 500 to 1,000 times its own weight in water. The composition of the superabsorbent polymer is composed of a monomer, an internal crosslinking agent, a thermal initiator, a surface crosslinking agent, and various additives. In order to improve the absorption characteristics of the superabsorbent polymer, a technique for improving the absorption characteristics by adding various additives including a surface crosslinking agent to additionally crosslink the surface of the superabsorbent polymer is widely used.

The superabsorbent polymer as described above started to be used as a hygiene product, and now, in addition to diapers for children and adults, it is used in a variety of fields, from horticultural maintenance agents, civil engineering and construction water-retaining materials, food distribution fields to moisture retention agents, and electrical insulation fields. is being used Superabsorbent polymers are most widely used in disposable hygiene products such as diapers for children and adults. Due to the characteristics of disposable products, they are used once and thrown away.

The composition of a general superabsorbent polymer is composed of a non-biodegradable monomer, an internal crosslinking agent, a surface crosslinking agent, a thermal initiator, and an additive. show characteristics. Superabsorbent polymers exhibiting these characteristics have a very harmful problem in terms of the environment due to the characteristics of the material widely used in disposable products.

As a result of intensive research efforts by the present inventors to solve the environmental problem due to the low biodegradability of the superabsorbent polymer, a superabsorbent polymer with significantly improved biodegradability was completed by mixing a biodegradable monomer and an additive to improve the biodegradability during surface crosslinking. .

One object of the present invention is to provide a superabsorbent polymer in which a surface crosslinking agent and cellulose are mixed.

Another object of the present invention is to provide a method for preparing a superabsorbent polymer in which a surface crosslinking agent and cellulose are mixed.

This will be described in detail as follows. Meanwhile, each description and embodiment disclosed in the present invention may be applied to each other description and embodiment. That is, all combinations of the various elements disclosed herein fall within the scope of the present invention. In addition, it cannot be considered that the scope of the present invention is limited by the specific descriptions described below.

A first aspect of the present invention is a base resin powder having water absorption; and a surface crosslinking layer provided on the base resin powder, wherein the base resin powder contains a polymer of an internal crosslinking agent including an unsaturated carboxylic acid monomer and an ethylenic monomer, and the surface crosslinking layer is the unsaturated carboxylic acid monomer. To provide a superabsorbent polymer comprising a mixture of a monomer, a surface crosslinking agent comprising at least one selected from the group consisting of a diepoxy crosslinking agent and a polyol based crosslinking agent, and cellulose.

The unsaturated carboxylic acid monomer of the present invention may mean a monomer having an unsaturated dicarboxylic acid. Specifically, it may be an unsaturated carboxylic acid monomer having about 3 to 10 carbon atoms, and more specifically, acrylic acid, itaconic acid, maleic acid, fumaric acid, cis-aconic acid, crotonic acid, (meth)acrylic acid, maleic anhydride, and the like. not limited This may mean that an unsaturated carboxylic acid monomer is used among hydrophilic monomers in order to improve the biodegradability of the superabsorbent polymer.

The unsaturated carboxylic acid monomer may be included in an amount of about 20 to about 80 parts by weight based on the total weight of the superabsorbent polymer. When the proportion of the unsaturated carboxylic acid monomer is less than about 20 parts by weight, there is a problem of poor biodegradability, and when the proportion of the unsaturated carboxylic acid monomer is greater than about 80 parts by weight, the degree of internal crosslinking decreases and the yield of the superabsorbent polymer decreases.

The internal crosslinking agent of the present invention may mean mixing to introduce a basic crosslinking structure to the base resin powder. The superabsorbent polymer may be crosslinked by being included in an amount of about 0.1 to about 1.0 parts by weight based on the total weight of the superabsorbent polymer. When it is less than about 0.1 parts by weight, sufficient crosslinking does not occur, and when it exceeds about 1.0 parts by weight, there is a problem in economical efficiency.

The surface crosslinking agent of the present invention may mean crosslinking the internally crosslinked surface of the base resin powder. When surface crosslinking in the presence of cellulose, it provides a superabsorbent polymer with significantly improved biodegradability while having the same or higher functions as the conventional superabsorbent polymer under pressure (AUL), centrifugal separation capacity (CRC), and liquid permeability (Perm). can do.

The surface crosslinking agent may be included in an amount of about 0.1 to about 2.0 parts by weight based on the total weight of the superabsorbent polymer. When the content of the surface crosslinking agent is too small, the surface crosslinking reaction hardly occurs, and when it exceeds about 2.0 parts by weight, the physical properties of the superabsorbent polymer may be rather deteriorated due to the excessive surface crosslinking reaction.

The cellulose of the present invention may be in an amount of about 5 to about 18 parts by weight based on 100 parts by weight of the base resin. When the amount of the cellulose is less than 5 parts by weight, the effect of improving biodegradability may be insignificant, and when it is more than about 18 parts by weight, there is a problem in that the physical properties of the superabsorbent polymer are deteriorated. In an embodiment of the present invention, as a result of testing the degree of biodegradability according to the ISO 14851 standard, it was confirmed that the biodegradability was 100% within about 60 days to about 80 days.

Specifically, examples of the cellulose may be at least one or more from the group consisting of carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose.

Among the superabsorbent polymers of the present invention, the absorbency under pressure (AUL) of 0.3 psi for physiological saline based on the superabsorbent polymer having a particle diameter of about 300 um to about 600 um is about 22 g/g to about 26 g/g , the centrifugation retention capacity (CRC) may be about 33 g/g to about 36 g/g, and the permeability (perm) may be about 14 ml to about 23 ml. The higher the absorbency under pressure, the better, but the absorbency under pressure is a physical property opposite to the water holding capacity. Therefore, it is an important technical factor to simultaneously improve the absorbency under pressure and the water holding capacity. Through a comparative experiment on physical properties of the superabsorbent polymer before and after the addition of cellulose according to an embodiment of the present invention, it was confirmed that the superabsorbent polymer had physical properties equal to or higher than that of the superabsorbent polymer even when cellulose was added.

A second aspect of the present invention comprises a first step of mixing an unsaturated carboxylic acid monomer and an acrylate-based monomer as an internal crosslinking agent to form a polymer; a second step of drying, freezing and pulverizing the polymer to prepare a base resin powder; and a third step of adding a solvent, a surface crosslinking agent, an inorganic material, and cellulose to the base resin powder to form a surface crosslinking layer provided on the base resin powder.

The first step of the present invention may refer to a step of further polymerization by adding an internal crosslinking agent after polymerization of the unsaturated carboxylic acid monomer. At this time, a thermal polymerization initiator is used, whereby the temperature may be increased from about 60° C. to about 80° C. during the polymerization reaction.

The acrylate-based monomer, which is the internal crosslinking agent of the present invention, is a part of the water-soluble ethylene-based monomer and may mean that it has a crosslinkable functional group used in the preparation of the superabsorbent polymer. Specifically, the group consisting of polyethylene glycol diacrylate (PEGDA), glycerin diacrylate, glycerin triacrylate, trimethylolpropane triacrylate (TMPTA), hexanediol diacrylate (HDODA), and triethylene glycol diacrylate It may be at least one or more.

The thermal polymerization initiator of the present invention may be one or more selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide and ascorbic acid. Specifically, examples of the persulfate-based initiator include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), ammonium persulfate ((NH4)2S2O8), and the like, and azo-based Examples of initiators include 2,2-azobis-(2-amidinopropane) dihydrochloride (2,2-azobis(2-amidinopropane) dihydrochloride), 2,2-azobis-(N,N-dimethylene)isobu Tyramide dihydrochloride (2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoylazo)isobutyronitrile (2-(carbamoylazo)isobutylonitril), 2,2-azobis [2-(2-imidazolin-2-yl)propane]dihydrochloride (2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride), 4,4-azobis-( 4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)) and the like.

The second step of the present invention is a step of preparing a base resin powder, and may refer to a step of preparing a base resin powder by drying, freezing and pulverizing the polymer prepared in the first step. The drying, freezing, and pulverizing methods will be described in more detail as follows. After drying at about 50° C. to about 70° C., it can be pulverized through a step of freezing in a freezer at about 5° C. to about 15° C.

The drying method may be hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation, but is not limited thereto. Specifically, the pulverizer is a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a disc pulverizer ( Disc mill), a shredder (shred crusher), crusher (Crusher), chopper (chopper), and may include any one selected from the group consisting of a disc cutter (Disc cutter), but is not limited thereto.

Meanwhile, the drying time may be about 8 hours to about 16 hours in consideration of process efficiency, but is not limited thereto. The freezing time may be about 15 minutes to about 30 minutes, but is not limited now.

The third step of the present invention is a step of forming a surface crosslinking layer, and may refer to a step of adding a solvent, a surface crosslinking agent, an inorganic material, and cellulose to the base resin powder.

The surface crosslinking agent may be a polyol crosslinking agent or a diepoxy crosslinking agent. Specifically, examples of the polyol crosslinking agent include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2-methyl-1,3-propanediol , 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol and at least one polyol selected from the group consisting of glycerol, but limited thereto doesn't happen Specifically, examples of the diepoxy crosslinking agent include 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, Neopentyl glycol diglycidyl ether, polyglycerol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, trimethylpropane polyglycidyl ether, 1,2-(bis(2,3) )-epoxypropoxy)ethylene, pentaerythritol polyglycidyl ether, and sorbitol polyglycidyl ether may be at least one diepoxy-based crosslinking agent selected from the group consisting of, but not limited thereto.

The inorganic material may be at least one or more from the group consisting of silica, clay, alumina, silica-alumina composite, titania, zinc oxide, and aluminum sulfate, but is not limited thereto. The superabsorbent polymer prepared by adding an inorganic material may have improved liquid permeability and absorption rate without deterioration of absorbency under pressure.

The solvent is a solvent capable of dissolving the above-mentioned substances, such as water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol. Monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cello It may be sorbacetate and N,N-dimethylacetamide.

In the third step, the surface crosslinking reaction may be performed by heating the base resin powder to which the surface crosslinking agent and cellulose are added at a temperature of about 150°C to about 200°C. Specifically, it may be heated to a temperature of about 150° C. to about 200° C. and from about 20 minutes to about 1 hour or less. When the temperature is less than about 150° C., the surface cross-linking is not sufficient, and when the temperature is more than about 200° C., there is a problem of deterioration of the physical properties of the superabsorbent polymer due to side reactions. The heat source for the heating may include, but is not limited to, heating through electricity and heating through gas.

The method may further include re-grinding the superabsorbent polymer with the surface cross-linked layer formed in the third step of the present invention. As the re-grinding device, any one selected from the above-mentioned pulverizing device group may be used, and a surface-crosslinked superabsorbent polymer having a particle diameter of about 150 μm to about 850 μm may be manufactured through re-grinding.

The present invention relates to an environmentally friendly superabsorbent polymer with significantly improved biodegradability by adding cellulose in the surface crosslinking step and a method for preparing the same. As an eco-friendly material, it can be widely used in household products such as disposable products.

1 is a graph showing the results of measuring the biodegradability of the superabsorbent polymer prepared in an embodiment of the present invention based on the KS M ISO 14851 standard.

Hereinafter, the present invention will be described in more detail by way of Examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Comparative Example 1. Preparation of cellulose-free super absorbent polymer

About 40 g of itaconic acid, about 50 g of acrylic acid, and about 10 g of sulfonic acid were added to a glass reactor with a capacity of 500 mL in a four-neck flask prepared in advance at room temperature. Then, to the glass reactor, about 80 g of a 50% caustic soda solution was slowly added dropwise and mixed. At this time, the stirring speed was about 250 rpm. It was confirmed that the temperature of the mixed solution increased to about 70° C. or higher by the heat of neutralization. The degree of neutralization of the mixed solution was about 70 mol%. After confirming that the temperature was cooled to about 60° C., about 0.1 g of PEGDA and HDODA were added each. After adding about 0.5 g of sodium persulfate, the mixture was stirred at about 250 rpm for about 3 minutes, transferred to a plastic tray, and further polymerized in a convection oven at about 50° C. for about 24 hours.

Then, the polymerized sheet was further dried at about 60° C. for about 12 hours, then frozen in a freezer at about -10° C. for about 20 minutes, and then coarsely pulverized. Then, the pulverized powder was dried in a convection oven at about 60° C. for about 24 hours. Thereafter, the powder was dried so that the moisture content of the powder was about 2% or less, and then the dried powder was pulverized with a grinder and classified to obtain a base resin having a size of about 150 μm to 850 μm. The thus-prepared base resin had a water holding capacity of about 60.1 g/g and an absorbency under pressure of about 8.8 g/g. The water holding capacity and absorbency under pressure were measured according to the following experimental examples.

Then, about 10 g of the base resin prepared in the previous step was added to a solvent in which about 10 g of water and about 20 g of methanol were mixed, about 3.5 g of butanediol as a surface crosslinking agent, about 0.1 g of aluminum sulfate as an inorganic material, and silica About 0.1 g was added to the solvent and then swelled for about 10 minutes. Then, the surface crosslinking reaction was carried out at about 170° C. for about 30 minutes. Then, the obtained product was pulverized and classified to obtain a surface-crosslinked superabsorbent polymer having a particle size of about 150 to 850 μm.

Examples 1 to 3 and Comparative Example 2. Preparation of superabsorbent polymer containing cellulose

In the surface crosslinking step of Comparative Example 1, Examples 1 to 3 and Comparative Example 2 were prepared by changing cellulose in addition to about 3.5 g of butanediol as a surface crosslinking agent as shown in Table 1 below.

Example 1 Example 2 Example 3 Comparative Example 2 cellulose
(g) 0.5 1.0 1.5 2.0

Experimental Example 1. Evaluation of biodegradability

1 shows the results of measuring the biodegradability of Examples 1 to 3 and Comparative Examples 1 and 2 based on the KS M ISO 14851 standard. The degree of biodegradation may mean a value obtained by measuring the degree of biodegradation of the superabsorbent polymer based on the degree of biodegradation of the added cellulose. As shown in FIG. 1 , Comparative Examples 1 and 2 and Examples 1 to 3 all showed a tendency to increase relative biodegradability over time. However, in the case of Examples 1 to 3 and Comparative Example 2 in which cellulose was added, the time taken to show a relative degree of biodegradation of 100% was 60 to 80 days, whereas Comparative Example 1 took 160 days or more, whereas biodegradation was achieved in a very short time. could see what was happening. Through this, it was found that the biodegradability of the superabsorbent polymer to which cellulose was added was remarkably improved.

Experimental Example 2. Evaluation of physical properties of super absorbent polymer: pressure absorption capacity, centrifugation water retention capacity, liquid permeability evaluation

(1) The absorbency under pressure (AUL) of 0.3 psi of the superabsorbent polymers of Examples 1 to 3 and Comparative Examples 1 and 2 with respect to physiological saline was measured according to the method of WSP 242.2 of the EDANA method. Among the superabsorbent polymers to be measured, the AUL was measured for the superabsorbent polymer having a particle diameter of 300 to 600 μm.

Specifically, a stainless steel screen of 400 mesh was attached to the bottom of a plastic cylindrical cylinder having an inner diameter of 25 mm. Then, the super absorbent polymer W0 (g, about 0.16 g) to measure the absorbency under pressure was uniformly sprayed. Then, a piston capable of uniformly applying a load of 0.3 psi was added on the superabsorbent polymer. At this time, the outer diameter of the piston is slightly smaller than 25 mm, there is no gap with the inner wall of the cylinder, and the one manufactured so that it can move freely up and down was used. Then, the weight W1 (g) of the device thus prepared was measured.

Next, a glass filter having a diameter of 90 mm and a thickness of 5 mm was placed inside a petro dish having a diameter of 150 mm, and 0.9% by weight of physiological saline was poured into the Petro dish. At this time, the physiological saline was poured until the water level of the physiological saline was level with the upper surface of the glass filter. Then, one sheet of filter paper having a diameter of 100 mm was placed on the glass filter.

Then, the prepared device was placed on the filter paper so that the superabsorbent polymer in the device was swollen with physiological saline under a load. After 1 hour, the weight W2 (g) of the device containing the swollen superabsorbent polymer was measured.

Using the thus measured weight, the absorbency under pressure was calculated according to Equation 1 below.

[Formula 1]

AUL(g/g) = [W2(g) - W1(g)]/W0

(2) For the superabsorbent polymers of Examples 1 to 3 and Comparative Examples 1 and 2, centrifugal separation retention capacity (CRC) was measured by absorption magnification under no load. Among the superabsorbent polymers to be measured, a superabsorbent polymer having a particle diameter of 300 μm to 600 μm was selected, and CRC was measured.

Specifically, the polymer W0 (g, about 0.2 g) of Examples 1 to 3 and Comparative Examples 1 and 2 was uniformly put into a non-woven tea bag and sealed, and then immersed in 0.9 wt% physiological saline at room temperature. After 30 minutes, the tea bag was dried at 300 G for 3 minutes using a centrifugal separator, and then the mass W3 (g) of the bag was measured. Further, after the same operation was performed without using the superabsorbent polymer, the tea bag mass W4 (g) at that time was measured.

Centrifugation retention capacity (CRC) was calculated according to Equation 2 below using each mass thus obtained.

[Formula 2]

CRC(g/g) = {[W3(g) - W4(g) - W0(g)]/W0(g)}

(3) The liquid permeability of the superabsorbent polymers of Examples 1 to 3 and Comparative Examples 1 and 2 to physiological saline was measured under a pressure of 0.3 psi. Among the superabsorbent polymers to be measured, a superabsorbent polymer having a particle diameter of 300 to 600 μm was selected, and perm was measured.

Specifically, 0.5 g of each of the superabsorbent polymers of Examples and Comparative Examples are put into a cylinder with an inner diameter of 20 mm and a glass filter installed at the bottom, and 100 mL of physiological saline is poured so that the superabsorbent polymer is completely submerged in the superabsorbent polymer. Swell for 30 minutes. Thereafter, the time T1 (seconds) taken for 20 mL of physiological saline to pass through the swollen superabsorbent polymer under a pressure of 0.3 psi was measured.

For the super absorbent polymers of Examples 1 to 3 and Comparative Examples 1 and 2, liquid permeability was measured through Equation 3.

[Formula 3]

Perm = [20 mL / T1 (sec)] * 60 sec

The results of evaluation of physical properties according to (1) to (3) are shown in Table 3 below.

AUL [g/g]
(0.3 psi) CRC [g/g] Perm [mL] Comparative Example 1 24.7 33.7 17 Example 1 24.5 33.8 19 Example 2 25.9 34.5 22 Example 3 23.4 35.1 14 Comparative Example 2 22.1 34.8 12

Accordingly, it was confirmed that Examples 1 to 3 had the same or higher absorbency under pressure, centrifugation retention capacity, and liquid permeability as compared to the super absorbent polymer of Comparative Examples 1 and 2. This indicates that the addition of cellulose does not degrade essential physical properties that the superabsorbent polymer should have. However, when the amount of cellulose added was 2.0 g or more (Comparative Example 2), the absorbency under pressure and the liquid permeability tended to significantly decrease. Through this, it was possible to infer the amount of added cellulose having excellent biodegradability without reducing physical properties.

Experimental Example 3. Yellowness evaluation

Yellowness was measured according to ASTM D 1925 standard. As a result, the yellowness (YI) and (dYI) indicating the degree of change in yellowness compared to Comparative Example 1 are shown in Table 3 below.

YI dYI Comparative Example 1 9.82 - Example 1 10.33 0.51 Example 2 10.61 0.78 Example 3 10.73 0.91 Comparative Example 2 11.42 1.59

In Examples 1 to 3, the increase in yellowness was insignificant compared to Comparative Example 1.

appeared to have ceased. However, as in Comparative Example 2, when 2.0 g of cellulose was added, it was confirmed that the yellowness of the superabsorbent polymer was significantly increased. Through this, it was possible to determine the addition amount of cellulose having excellent biodegradability without reducing the physical properties as in Experimental Example 2.

Claims (13)

base resin powder having water absorption; and
A surface crosslinking layer provided on the base resin powder,
The base resin powder includes a polymer of an internal crosslinking agent including an unsaturated carboxylic acid monomer and an ethylenic monomer,
The surface crosslinking layer includes a mixture of a surface crosslinking agent including a polyol-based crosslinking agent, and cellulose,
The cellulose is mixed in a ratio of 0.5 g to 1.5 g with respect to 10 g of the base resin powder, the superabsorbent polymer. delete According to claim 1,
The cellulose is at least one or more from the group consisting of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl methyl cellulose. According to claim 1,
The unsaturated carboxylic acid monomer is included in an amount of 20 to 80 parts by weight based on the total weight of the superabsorbent polymer. According to claim 1,
wherein the internal crosslinking agent is included in an amount of 0.1 to 1.0 parts by weight based on the total weight of the superabsorbent polymer. According to claim 1,
The surface crosslinking agent is included in an amount of 0.1 to 2.0 parts by weight based on the total weight of the superabsorbent polymer. According to claim 1,
The superabsorbent polymer having a particle size of 300 um to 600 um has an absorbency under pressure (AUL) of 0.3 psi with respect to physiological saline of 22 g/g to 26 g/g, and a centrifugation retention capacity (CRC) of 33 g/g to 36 g/g, and the liquid permeability (perm) is 14 ml to 23 ml, the superabsorbent polymer. A first step of forming a polymer by mixing an unsaturated carboxylic acid monomer and an acrylate-based monomer as an internal crosslinking agent;
a second step of drying, freezing and pulverizing the polymer to prepare a base resin powder; and
A third step of forming a surface crosslinking layer provided on the base resin powder by adding a solvent, a surface crosslinking agent including a polyol-based crosslinking agent, an inorganic material, and cellulose to the base resin powder;
The method for producing a superabsorbent polymer, wherein the cellulose is mixed in a ratio of 0.5 g to 1.5 g with respect to 10 g of the base resin powder. 9. The method of claim 8,
The acrylate-based monomer as the internal crosslinking agent is polyethylene glycol diacrylate (PEGDA), glycerin diacrylate, glycerin triacrylate, trimethylolpropane triacrylate (TMPTA), hexanediol diacrylate (HDODA), and triethylene At least one selected from the group consisting of glycol diacrylate, the method for producing a super absorbent polymer. 9. The method of claim 8,
The method for producing a super absorbent polymer, wherein the inorganic material is at least one selected from the group consisting of silica, clay, alumina, silica-alumina composite, titania, zinc oxide and aluminum sulfate. delete 9. The method of claim 8,
The third step is a method for producing a super absorbent polymer, which is carried out at a temperature of 150 ℃ to 200 ℃. 9. The method of claim 8,
The method for producing a superabsorbent polymer, further comprising the step of re-grinding the superabsorbent polymer having the surface cross-linked layer formed in the third step.

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