A preparation method of a superabsorbent polymer, and a superabsorbent polymer prepared thereby are provided. The preparation method of the superabsorbent polymer according to the present disclosure prevents polymer particles from being broken or the surface thereof from being damaged during preparation and handling of the superabsorbent polymer, thereby providing a superabsorbent polymer having excellent absorption properties and permeability.

Claims

1. A preparation method of a superabsorbent polymer, the method comprising: forming a water-containing gel polymer by performing thermal polymerization or photopolymerization of a monomer composition including water-soluble ethylene-based unsaturated monomers and a polymerization initiator; drying the water-containing gel polymer; pulverizing the dried polymer; surface-crosslinking the pulverized polymer; and treating the surface-crosslinked polymer with a polycarboxylic acid-based copolymer having repeating units represented by the following Chemical Formula 1-a and Chemical Formula 1-b: ##STR00004## wherein, in Chemical Formula 1-a and 1-b, R.sup.1, R.sup.2, and R.sup.3 are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, RO is an oxyalkylene group having 2 to 4 carbon atoms, M.sup.1 is hydrogen or a monovalent metal or non-metal ion, X is COO, an alkyloxy group having 1 to 5 carbon atoms, or an alkyldioxy group having 1 to 5 carbon atoms, m is an integer of 1 to 100, n is an integer of 1 to 1000, and p is an integer of 1 to 150, and provided that there are two or more of p, two or more repeating (RO)s are the same as or different from each other.

2. The preparation method of the superabsorbent polymer of claim 1, wherein the polycarboxylic acid-based copolymer is mixed in an amount of 0.001 parts by weight to 5 parts by weight, based on 100 parts by weight of the surface-crosslinked polymer.

3. The preparation method of the superabsorbent polymer of claim 1, wherein the polycarboxylic acid-based copolymer has a weight average molecular weight of 500 to 1,000,000.

4. The preparation method of the superabsorbent polymer of claim 1, wherein the drying of the water-containing gel polymer is performed at a temperature of 120 C. to 250 C.

5. The preparation method of the superabsorbent polymer of claim 1, further comprising pulverizing the water-containing gel polymer to have a particle size of 1 mm to 10 mm, before drying the water-containing gel polymer.

6. The preparation method of the superabsorbent polymer of claim 1, wherein the pulverizing of the dried polymer is performed such that the pulverized polymer has a particle size of 150 m to 850 m.

7. The preparation method of the superabsorbent polymer of claim 1, wherein the surface crosslinking of the pulverized polymer is performed at a temperature of 100 C. to 250 C.

8. The preparation method of the superabsorbent polymer of claim 1, wherein the surface crosslinking is performed by reacting one or more surface crosslinking agents selected from the group consisting of ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, ethylene carbonate, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, propanediol, dipropylene glycol, polypropylene glycol, glycerin, polyglycerin, butanediol, heptanediol, hexanediol trimethylol propane, pentaerythritol, sorbitol, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, iron hydroxide, calcium chloride, magnesium chloride, aluminum chloride, and iron chloride.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) Hereinafter, the preferred examples are provided for better understanding. However, these examples are for illustrative purposes only, and the present invention is not intended to be limited by these examples.

PREPARATION EXAMPLE 1

(2) To a 3 L, 4-necked flask reactor equipped with a stirrer, a thermometer, a nitrogen inlet, and a circulation condenser, 400 parts by weight of ion exchanged water was fed, and the interior of the reactor was replaced by nitrogen under stirring, followed by heating to 75 C. under a nitrogen atmosphere.

(3) 2 parts by weight of ammonium persulfate was fed to the reactor, and dissolved completely. Then, a monomer aqueous solution including a mixture of 600 parts by weight of methoxy polyethylene glycol monomethacrylate (average addition molar number of ethylene oxide (EO): about 50 mol), 99.6 parts by weight of methacrylic acid, and 190 parts by weight of water, and a solution mixture of 5 parts by weight of 3-mercaptopropionic acid and 60 parts by weight of water, and 150 parts by weight of a 3 wt % ammonium persulfate aqueous solution, were continuously fed at a constant speed for 4 h. After completion of the feeding, 5 parts by weight of a 3 wt % ammonium persulfate aqueous solution was fed at once.

(4) Thereafter, the internal temperature of the reactor was raised to 85 C., and maintained at 85 C. for 1 h to complete the polymerization reaction.

(5) The polycarboxylic acid-based copolymer thus prepared was found to have a weight average molecular weight of 40,000, as measured by GPC (gel permeation chromatography).

PREPARATION EXAMPLE 2

(6) A polycarboxylic acid-based copolymer (weight average molecular weight of 40,000) was obtained in the same manner as in Preparation Example 1, except that neutralization was performed using a 30 wt % triethanolamine aqueous solution for about 1 h after completion of the polymerization reaction, as in Preparation Example 1.

PREPARATION EXAMPLE 3

(7) A polycarboxylic acid-based copolymer (weight average molecular weight of 40,000) was obtained in the same manner as in Preparation Example 2, except that neutralization was performed using a sodium hydroxide aqueous solution, instead of the triethanolamine aqueous solution.

PREPARATION EXAMPLE 4

(8) To a 3 L, 4-necked flask reactor equipped with a stirrer, a thermometer, a nitrogen inlet, and a circulation condenser, 300 parts by weight of ion exchanged water was fed, and the interior of the reactor was replaced by nitrogen under stirring, followed by heating to 75 C. under a nitrogen atmosphere.

(9) 2 parts by weight of ammonium persulfate was fed to the reactor, and dissolved completely. Then, a monomer aqueous solution including a mixture of 300 parts by weight of methoxy polyethylene glycol monomethacrylate (average addition molar number of ethylene oxide (EO): about 50 mol), 49.8 parts by weight of methacrylic acid, and 50 parts by weight of water, and a solution mixture of 5 parts by weight of 3-mercaptopropionic acid and 30 parts by weight of water, and 80 parts by weight of a 3 wt % ammonium persulfate aqueous solution, were continuously fed at a constant speed for 4 h. After completion of the feeding, 5 parts by weight of a 3 wt % ammonium persulfate aqueous solution was fed at once.

(10) Thereafter, the internal temperature of the reactor was raised to 85 C., and maintained at 85 C. for 1 h to complete the polymerization reaction.

(11) The polycarboxylic acid-based copolymer thus prepared was found to have a weight average molecular weight of 45,000, as measured by GPC (gel permeation chromatography).

PREPARATION EXAMPLE 5

(12) A polycarboxylic acid-based copolymer (weight average molecular weight of 45,000) was obtained in the same manner as in Preparation Example 4, except that neutralization was performed using the 30 wt % triethanolamine aqueous solution for about 1 h after completion of the polymerization reaction, as in Preparation Example 4.

PREPARATION EXAMPLE 6

(13) A polycarboxylic acid-based copolymer (weight average molecular weight of 45,000) was obtained in the same manner as in Preparation Example 5, except that neutralization was performed using the sodium hydroxide aqueous solution, instead of the triethanolamine aqueous solution.

EXAMPLE 1

(14) About 5.0 g of N,N-methylenebisacrylamide as an internal crosslinking agent was added to and mixed with about 500 g of acrylic acid, and then about 971.4 g of a 20% sodium hydroxide aqueous solution was added to prepare a monomer composition (degree of neutralization of acrylic acid-based monomer: 70 mol %).

(15) The monomer composition was fed into a 5 L twin-armed kneader equipped with a sigma-type axis, maintained at 65 C., and purged with nitrogen gas for 30 min to eliminate oxygen dissolved in the aqueous solution. About 30.0 g of 0.2 wt % L-ascorbic acid, about 50.5 g of a sodium persulfate aqueous solution, and about 30.0 g of a 2.0 wt % hydrogen peroxide aqueous solution were fed under stirring. The polymerization reaction was initiated in 5 min, and the gel produced was finely divided by way of shear force for 3 min. The divided water-containing crosslinked polymer was taken from the kneader, and put in a meat chopper (manufactured by SL Corporation; the discharge port with a mesh hole diameter of 10 mm) and divided to have a diameter of about 5 mm or less.

(16) The finely divided gel was spread as thick as about 30 mm on a stainless wire gauze having a hole size of 600 m and dried in a hot air oven at 150 C. for 4 h. The dry polymer thus obtained was ground with a grinder and then size-sorted through an ASTM standard sieve to obtain an absorbent polymer powder having a particle size of 150 m to 850 m.

(17) 100 g of the polymer powder was uniformly blended with a surface crosslinking solution containing 0.3 g of ethylene glycol diglycidyl ether (surface crosslinking agent), 3 g of methanol, and 3 g of water, and then dried in a hot air oven at 140 C. for 30 min to obtain a surface-crosslinked polymer powder.

(18) Subsequently, a solution containing about 0.2 g of the polycarboxylic acid-based copolymer according to Preparation Example 1 and 2 g of water was added to and uniformly mixed with 100 g of the surface-crosslinked polymer powder, and dried in a hot air oven at 80 C. for 10 min.

(19) The dry polymer was size-sorted through an ASTM standard sieve to obtain a superabsorbent polymer having a particle size of 150 m to 850 m.

EXAMPLE 2

(20) A superabsorbent polymer was obtained in the same manner as in Example 1, except that the polycarboxylic acid-based copolymer according to Preparation Example 2 instead of Preparation Example 1 was used.

EXAMPLE 3

(21) A superabsorbent polymer was obtained in the same manner as in Example 1, except that the polycarboxylic acid-based copolymer according to Preparation Example 3 instead of Preparation Example 1 was used.

EXAMPLE 4

(22) A superabsorbent polymer was obtained in the same manner as in Example 1, except that the polycarboxylic acid-based copolymer according to Preparation Example 4 instead of Preparation Example 1 was used.

EXAMPLE 5

(23) A superabsorbent polymer was obtained in the same manner as in Example 1, except that the polycarboxylic acid-based copolymer according to Preparation Example 5 instead of Preparation Example 1 was used.

EXAMPLE 6

(24) A superabsorbent polymer was obtained in the same manner as in Example 1, except that the polycarboxylic acid-based copolymer according to Preparation Example 6 instead of Preparation Example 1 was used.

COMPARATIVE EXAMPLE 1

(25) A superabsorbent polymer was obtained in the same manner as in Example 1, except that the polycarboxylic acid-based copolymer according to Preparation Example 1 was not added.

COMPARATIVE EXAMPLE 2

(26) A superabsorbent polymer was obtained in the same manner as in Example 1, except that an equal amount of polyethylene glycol (Sigma-Aldrich, PEG-200) was used, instead of the polycarboxylic acid-based copolymer according to Preparation Example 1.

COMPARATIVE EXAMPLE 3

(27) A superabsorbent polymer was obtained in the same manner as in Example 1, except that an equal amount of polyoxyethylene sorbitan monooleate was used, instead of the polycarboxylic acid-based copolymer according to Preparation Example 1.

EXPERIMENTAL EXAMPLE 1

(28) Centrifuge retention capacity (CRC) was measured in accordance with EDANA WSP 241.2 for each polymer of the examples and comparative examples.

(29) In detail, each polymer W (g) (about 0.2 g) obtained in the examples and comparative examples 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 min, the bag was drained at 250 G for 3 min 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 these weights thus obtained according to the following Equation 1.
CRC(g/g)={(W.sub.2W.sub.1)/(W1)}[Equation 1]

EXPERIMENTAL EXAMPLE 2

(30) Absorbency under pressure (AUP) was measured in accordance with EDANA WSP 242.3 for each polymer of the examples and comparative examples.

(31) In detail, a 400 mesh stainless steel net was installed in the bottom of a plastic cylinder having an internal diameter of 60 mm. The superabsorbent polymer W (g) (about 0.90 g) was uniformly scattered on the steel net at room temperature and humidity of 50%, and a piston which may provide a load of 4.83 kPa (0.7 psi) was uniformly put thereon, in which the external diameter of the piston was slightly smaller than 60 mm, there was no appreciable gap between the internal wall of the cylinder and the piston, and the jig-jog of the cylinder was not interrupted. At this time, the weight W.sub.a (g) of the device was measured.

(32) After putting a glass filter having a diameter of 90 mm and a thickness of 5 mm in a petri dish having a diameter of 150 mm, a physiological saline solution composed of 0.90% by weight of sodium chloride was poured in the dish until the surface level became equal to the upper surface of the glass filter. A sheet of filter paper having a diameter of 90 mm was put thereon. The measuring device was put on the filter paper and the solution was absorbed for 1 h under the load. After 1 h, the weight W.sub.b (g) was measured after lifting up the measuring device.

(33) W.sub.a and W.sub.b thus obtained were used to calculate absorbency under pressure (g/g) according to the following Equation 2.
AUP(g/g)={W.sub.bW.sub.a}/W[Equation 2]

EXPERIMENTAL EXAMPLE 3

(34) Liquid permeability (saline flow conductivity, SFC) was measured according to a method disclosed in [0184] to [0189] of column 16 of US Patent Publication No. 2009-0131255.

(35) TABLE-US-00001 TABLE 1 CRC AUP SFC (g/g) (g/g) (cm.sup.3*s*10.sup.7/g) Example 1 30.7 24.6 51 Example 2 30.7 24.8 50 Example 3 30.6 24.7 52 Example 4 30.7 24.6 50 Example 5 30.5 24.6 49 Example 6 30.4 24.7 50 Comparative 30.2 24.2 44 Example 1 Comparative 30.1 24.3 45 Example 2 Comparative 29.5 24.7 38 Example 3

(36) Referring to Table 1, it was found that the superabsorbent polymers according to the examples have excellent centrifuge retention capacity (CRC) and absorbency under pressure (AUP), thereby having excellent absorption properties and permeability, as compared with the superabsorbent polymer according to Comparative Example 1.

(37) When no polyethylene glycol or no surfactant was used as in Comparative Example 2 and Comparative Example 3, it is difficult to obtain superabsorbent polymers having physical properties which are the same as those of the superabsorbent polymers of the examples.

EXPERIMENTAL EXAMPLE 4

(38) 100 g of the surface-crosslinked absorbent polymer was put into a turbulizer mixer (custom-made by UTO engineering), which was operated at 1000 rpm for 1 min. Then, the entire absorbent polymer was recovered. The recovered absorbent polymer was subjected to an attrition test by measuring the amount (wt %) of fine particles of 100 mesh or less (150 m or less) using a sieve shaker (Retsch AS 200 model, amplitude: 1.5 mm/g, size-sorted for 10 min).

(39) After the attrition test, physical properties according to Experimental Examples 1 to 3 were measured again, and the results are shown in the following Table 2.

(40) TABLE-US-00002 TABLE 2 CRC AUP SFC Fine particles (g/g) (g/g) (cm.sup.3*s*10.sup.7/g) (wt %) Example 1 30.6 24.4 48 0.1 Example 2 30.6 24.6 47 0.1 Example 3 30.5 24.5 49 0.1 Example 4 30.6 24.4 47 0.1 Example 5 30.4 24.4 46 0.1 Example 6 30.3 24.5 47 0.1 Comparative 30.1 23.6 35 0.3 Example 1 Comparative 30.0 23.8 39 0.2 Example 2 Comparative 29.4 23.3 32 0.2 Example 3

(41) As confirmed in Table 2, the superabsorbent polymers according to the examples showed generation of a small amount of fine particles in the attrition test and low deterioration in absorbency under pressure and permeability after the attrition test, as compared with those of the comparative examples.

(42) When the commercial polymer (polyethylene glycol) was used as in Comparative Example 2, deterioration of physical properties was higher than those of the polymers of the examples. When the surfactant was used as in Comparative Example 3, there was no effect of preventing deterioration of physical properties.

(43) In particular, the superabsorbent polymers according to the examples generated a small amount of fine particles, indicating that the superabsorbent polymer particles are hardly broken or the surface thereof is hardly damaged due to external force.

(44) Accordingly, the preparation method of the superabsorbent polymer according to the present disclosure prevents polymer particles from being broken or the surface thereof from being damaged during preparation and handling of the superabsorbent polymer, thereby providing a superabsorbent polymer having excellent absorption properties and permeability.