Method of Preparing Superabsorbent Polymer

Abstract

Provided is a method of preparing a superabsorbent polymer, in which an interpenetrating polymer network (IPN) is formed on the surface of the superabsorbent polymer during formation of a surface-crosslinked layer of the superabsorbent polymer, thereby improving physical properties of the superabsorbent polymer.

Claims

1. A method of preparing a superabsorbent polymer, the method comprising: 1) carrying out a crosslinking polymerization of a water-soluble ethylene-based unsaturated monomer having acidic groups which are at least partially neutralized, in the presence of an internal crosslinking agent, to form a water-containing gel polymer including a first crosslinked polymer; 2) coarsely pulverizing the water-containing gel polymer; 3) drying, pulverizing, and size-sorting the water-containing gel polymer to form a base polymer powder; and 4) reacting the base polymer powder with a surface crosslinking solution to form an interpenetrating polymer network on a surface of the base polymer powder, wherein the surface crosslinking solution includes a monomer having an amine group and a compound represented by the following Chemical Formula 1: ##STR00002## in Chemical Formula 1, n is an integer of 1 to 10.

2. The method of claim 1, wherein a solvent of the surface crosslinking solution is water.

3. The method of claim 1, wherein a pH of the surface crosslinking solution is 1 to 3.

4. The method of claim 1, wherein the monomer having an amine group is chitosan or cyclodextrin.

5. The method of claim 1, wherein a concentration of the monomer having an amine group in the surface crosslinking solution is 1 N to 10 N.

6. The method of claim 1, wherein a concentration of the compound represented by Chemical Formula 1 in the surface crosslinking solution is 1 N to 10 N.

7. The method of claim 1, wherein a weight ratio of the chitosan and the compound represented by Chemical Formula 1 in the surface crosslinking solution is 1:1 to 5:1.

8. The method of claim 1, wherein n of Chemical Formula 1 is an integer of 2 to 4.

9. The method of claim 1, wherein the compound represented by Chemical Formula 1 is glutaraldehyde.

10. The method of claim 1, wherein the reacting the base polymer powder with a surface crosslinking solution is carried out at a temperature of 20° C. to 90° C.

11. The method of claim 1, wherein a CRC of the superabsorbent polymer is 30 g/g to 40 g/g.

12. The method of claim 1, wherein a gel strength of the superabsorbent polymer is 1.50 N to 3.00 N.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0084] Hereinafter, preferred exemplary embodiments are provided for better understanding of the present technology. However, the following exemplary embodiments are only for illustrating the present technology, and the present technology is not limited thereto.

Preparation Example: Preparation of Base Polymer

[0085] 20.5 g (80 ppm) of 0.21% IRGACURE 819 initiator diluted with 500 g of acrylic acid was mixed, and 21 g of a 10% polyethylene glycol diacrylate (PEGDA, Mw=400) solution diluted with acrylic acid was injected to the mixed solution, and 12 g of a 2% SDS(Sodium dodecyl sulfate) solution was mixed therewith, and 800 g of a 24% caustic soda solution was slowly added dropwise thereto, followed by mixing. As a water-soluble ethylene-based unsaturated monomer thus obtained, acrylic acid had a degree of neutralization of 70 mole % in sodium acrylate.

[0086] After confirming that the temperature of the mixture increased to 72° C. or higher by neutralization heat generated upon mixing the two solutions, when the temperature was cooled to 43° C., 13.4 g of 4% sodium bicarbonate was mixed, and 16 g of 4% sodium persulfate solution diluted with water was injected at the same time.

[0087] The solution was poured in a tray (15 cm in width×15 cm in length) installed in a square polymerizer which had a UV irradiation device installed at the top and was preheated to 80° C., and polymerization was initiated by UV irradiation. A sheet-type polymer thus prepared was cut in a size of 5 cm×5 cm, and then injected to a meat chopper to pulverize the polymer. Thus, water-containing particles having a size of 1 mm to 10 mm were obtained.

[0088] The crumbs were dried in an oven capable of shifting airflow up and down. The crumbs were uniformly dried by flowing hot air at 180° C. or higher from the bottom to the top for 15 minutes and from the top to the bottom for 15 minutes. After drying, the dried product had a water content of 2% or less. After drying, the product was pulverized using a pulverizer and sorted by size, and a size of about 150 to about 850 um was selected to prepare a base polymer.

Example 1

[0089] Chitosan (0.05 g) and glutaraldehyde (0.025 mL) were added to a 0.1 N HCl aqueous solution (10 ml), and stirred to prepare a surface crosslinking solution.

[0090] The surface crosslinking solution was sprayed onto 100 g of the base polymer prepared in Preparation Example, and uniformly mixed, and then a reaction was allowed at 25° C. for 40 minutes to prepare a superabsorbent polymer.

Examples 2 to 4 and Comparative Examples 1 and 2

[0091] Each superabsorbent polymer was prepared in the same manner as in Example 1, except that the composition of the surface crosslinking solution was changed as in Table 1, below.

Experimental Example

[0092] Physical properties of the superabsorbent polymers prepared in Examples and Comparative Examples were measured by the following methods, respectively.

[0093] 1) CRC

[0094] Centrifuge retention capacity by absorbency under no load was measured for each polymer according to EDANA WSP 241.3.

[0095] In detail, from the polymers of Examples and Comparative Examples, each polymer size-sorted using #30-50 sieve was obtained. Each polymer W.sub.0(g) (about 2.0 g) was uniformly placed into a nonwoven-fabric-made bag, followed by sealing. Then, the bag was immersed in a physiological saline solution (0.9% by weight) at room temperature. After 30 minutes, the bag was drained at 250 G for 3 minutes with a centrifuge, and the weight W.sub.2(g) of the bag was then measured. Further, the same procedure was carried out using no polymer, and the resultant weight W.sub.1(g) was measured. Thus, CRC (g/g) was calculated from the obtained weights according to the following Equation:

CRC(g/g)={[W.sub.2(g)−W.sub.1(g)]/W.sub.0(g)}−1  [Equation 1]

[0096] 2) Gel Strength

[0097] From the polymers of Examples and Comparative Examples, each polymer size-sorted using #30-50 sieve was obtained, and 1 g thereof was weighed. The weighed samples were sufficiently immersed and swelled in 100 g of a physiological saline solution for 1 hour. Thereafter, the solvent not absorbed therein was removed by using an aspirator for 4 minutes, and the solvent left on the surface of the same was evenly distributed and wiped once with a filter paper.

[0098] 2.5 g of the swelled superabsorbent polymer was positioned between two plates (a diameter of 25 mm, with a wall of about 2 mm at the bottom for preventing the sample from leaking) of a rheometer, and the gap between the two plates was adjusted to 1 mm (At this time, when the sample is hard and thus it is difficult to adjust the gap to 1 mm, the gap between the plates was properly adjusted by pressing the plates with a force of about 3 N such that the swelled superabsorbent polymer sample was contacted evenly at the face of the plates).

[0099] Subsequently, the superabsorbent polymer sample between the plates was stabilized for about 5 minutes.

[0100] Thereafter, a linear viscoelastic regime section of strain where the storage modulus (G′) and the loss modulus (G″) are steady was found by using the rheometer while increasing the strain at frequency of 10 rad/s. Generally, in the case of a swollen superabsorbent polymer, a strain of 0.1% was imparted in the linear regime section, and viscoelastic properties (G′, G″) of the swollen polymer are measured using the strain value of the linear regime section at a constant frequency of 10 rad/s for 60 seconds. The obtained G′ values were averaged to obtain the gel strength.

[0101] The measurement results are shown in Tables 1 and 2 below.

TABLE-US-00001 TABLE 1 0.1N HCl CRC Gel strength solution Chitosan Glutaraldehyde (g/g) (N) Ex. 1 10 mL 0.05 g 0.025 mL 35.9 1.73 Ex. 2 30 mL 0.10 g 0.050 mL 34.4 1.96 Ex. 3 30 mL 0.05 g 0.025 mL 35.2 1.77 Ex. 4 10 mL 0.10 g 0.050 mL 34.3 1.84

TABLE-US-00002 TABLE 2 Gel Ethylene Propylene Polycarboxylate Aluminum CRC strength Water carbonate carbonate salt sulfate (g/g) (N) Comparative 4.4 mL 0.3 g (none) 0.07 g 0.3 g 39.9 0.56 Ex. 1 Comparative 5.4 mL 0.9 g 0.9 g (none) 0.2 g 36.4 1.68 Ex. 2

[0102] As shown in Tables 1 and 2, the superabsorbent polymers of Examples 1 to 4 according to the present technology showed the similar levels of CRC, but showed the increased gel strength, as compared with the superabsorbent polymers of Comparative Examples 1 and 2. The superabsorbent polymers of Comparative Examples 1 and 2 also had the surface-crosslinked layer of a network structure by surface crosslinking, but the superabsorbent polymers of Examples 1 to 4 according to the present technology had a structure in which, in addition to the network structure, additional crosslinking occurred, and thus another network structure was formed, thereby having the improved gel strength.