Super Absorbent Polymer and Preparation Method Thereof

Abstract

Provided are a superabsorbent polymer and a method of preparing the same, more particularly, a superabsorbent polymer capable of exhibiting an improved bacterial growth-inhibitory property without deterioration in a water retention capacity of the superabsorbent polymer, and a method of preparing the same.

Claims

1. A superabsorbent polymer comprising a base polymer comprising a crosslinked polymer which is obtained by polymerizing an acrylic acid-based monomer including acidic groups of which at least part is neutralized, a polymerizable antibacterial monomer represented by Chemical Formula 1, and a first crosslinking agent, wherein at least part of the base polymer is surface-treated by a second crosslinking agent: ##STR00006## in Chemical Formula 1, R.sub.1 to R.sub.3 are each independently hydrogen or methyl, R.sub.4 is hydrogen or a substituted or unsubstituted alkyl having 1 to 20 carbon atoms, and L.sub.1 is a substituted or unsubstituted alkylene having 1 to 10 carbon atoms.

2. The superabsorbent polymer of claim 1, wherein R.sub.1 and R.sub.2 are each hydrogen, and R.sub.3 is methyl.

3. The superabsorbent polymer of claim 1, wherein R.sub.4 is tert-butyl.

4. The superabsorbent polymer of claim 1, wherein L.sub.1 is ethylene.

5. The superabsorbent polymer of claim 1, wherein the polymerizable antibacterial monomer is a compound represented by Chemical Formula 1-1: ##STR00007##

6. The superabsorbent polymer of claim 1, wherein the polymerizable antibacterial monomer is used in an amount of 5 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the acrylic acid-based monomer.

7. The superabsorbent polymer of claim 1, wherein the superabsorbent polymer exhibits an antibacterial property against the Gram-negative bacterium.

8. The superabsorbent polymer of claim 7, wherein the Gram-negative bacterium is Escherichia coli or Proteus mirabilis.

9. The superabsorbent polymer of claim 1, wherein the superabsorbent polymer exhibits a 30-min centrifuge retention capacity (CRC) of g/g or more and 45 g/g or less for physiological saline (0.9 wt % aqueous sodium chloride solution), as measured according to the EDANA method WSP 241.3.

10. A method of preparing a superabsorbent polymer, the method comprising the steps of: forming a water-containing gel polymer by performing a crosslinking polymerization of an acrylic acid-based monomer including acidic groups of which at least part is neutralized, and a polymerizable antibacterial monomer represented by Chemical Formula 1 in the presence of a first crosslinking agent and a polymerization initiator; forming a base polymer comprising a crosslinked polymer by drying, pulverizing, and classifying the water-containing gel polymer; and surface-crosslinking the base polymer by heat treatment in the presence of a second crosslinking agent: ##STR00008## in Chemical Formula 1, R.sub.1 to R.sub.3 are each independently hydrogen or methyl, R.sub.4 is hydrogen or a substituted or unsubstituted alkyl having 1 to 20 carbon atoms, and Li is a substituted or unsubstituted alkylene having 1 to 10 carbon atoms.

11. The method of claim 10, wherein the polymerizable antibacterial monomer is used in an amount of 5 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the acrylic acid-based monomer.

12. A hygiene product comprising the superabsorbent polymer of claim 1.

13. The superabsorbent polymer of claim 1, wherein the superabsorbent polymer comprises particles having a particle size of about 150 m to about 850 m.

14. The method of claim 10, wherein the first crosslinking agent is used in an amount of 0.01 part by weight to 1 part by weight with respect to 100 parts by weight of the acrylic acid-based monomer, and the second crosslinking agent is used in an amount of about 0.001 part by weight to about 5 parts by weight with respect to 100 parts by weight of the water-containing gel polymer.

15. The method of claim 10, Wherein a water content of the water-containing gel polymer is about 40% by weight to about 80% by weight with respect to the total weight of the water-containing gel polymer.

Description

EXAMPLE: PREPARATION OF SUPERABSORBENT POLYMER

Example 1

[0124] In a 3 L glass container equipped with a stirrer, a nitrogen feeder, and a thermometer, 100 parts by weight of acrylic acid, 0.35 parts by weight of polyethylene glycol diacrylate (PEGDA, Mn=575) as a first crosslinking agent, 0.008 parts by weight of bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide as a photoinitiator, 0.12 parts by weight of sodium persulfate (SPS) as a thermal initiator, 123.5 parts by weight of a sodium hydroxide solution with purity of 31.5%, 54.9 parts by weight of water, and 5 parts by weight of 2-(tert-butylamino)ethyl methacrylate (Sigma-Aldrich, product no. 444332) were added to prepare an aqueous solution of water-soluble unsaturated monomer while feeding nitrogen continuously.

[0125] The aqueous solution of water-soluble unsaturated monomer was transferred to a stainless steel container having a width of 250 mm, a length of 250 mm, and a height of 30 mm, and then subjected to ultraviolet irradiation (dose: 10 mV/cm.sup.2) in a UV chamber at 80 C. for 2 minutes and aged for 2 minutes to obtain a water-containing gel polymer.

[0126] The obtained water-containing gel polymer was pulverized into a size of 3 mm*3 mm, and then the obtained gel-type polymer was spread on a stainless wire gauze having a hole size of 600 m at a thickness of about 30 mm, and dried in a hot air oven at 120 C. for 11 hours. The dried polymer thus obtained was pulverized using a pulverizer, and classified with a standard sieve according to ASTM to obtain a base polymer having a particle size of 150 m to 850 m.

[0127] Meanwhile, for surface crosslinking (additional crosslinking) of the base polymer, a surface crosslinking solution was prepared by mixing 5.4 parts by weight of water, 1.2 parts by weight of ethylene carbonate, and 0.2 parts by weight of propylene glycol, 0.2 parts by weight of a polycarboxylic acid surfactant, and 0.2 parts by weight of aluminum sulfate, based on 100 parts by weight of the base polymer. The surface crosslinking agent was sprayed onto 100 parts by weight of the base polymer using a paddle type mixer at 1000 rpm. Then, surface crosslinking was performed by heat treatment at the maximum temperature of 184 C. for 40 minutes to prepare a superabsorbent polymer of Example 1.

Example 2

[0128] A superabsorbent polymer was prepared in the same manner as in Example 1, except that 10 parts by weight of 2-(tert-butylamino)ethyl methacrylate was used and the surface crosslinking was performed at the maximum temperature of 178 C. for 30 minutes in Example 1.

Comparative Example 1

[0129] A superabsorbent polymer was prepared in the same manner as in Example 1, except that 2-(tert-butylamino)ethyl methacrylate was not used in Example 1.

Comparative Example 2

[0130] 2-(tert-butyl amino)ethyl methacrylate (18.5 g) and ethanol (30 mL) were added to a 2-neck round bottom flask capable of maintaining a nitrogen environment, followed by stirring for 10 minutes. Thereafter, azobisisobutyronitrile (AIBN (493 mg)) was added, followed by stirring at 80 C. for 16 hours. The temperature of the reaction mixture was decreased to room temperature, and then a small amount of ethanol was added to dilute the solution. The diluted solution was slowly added dropwise to distilled water. The produced solid was filtered, washed with a small amount of distilled water, and dried to obtain 2-(tert-butyl amino)ethyl methacrylate polymer (Mw=32856, Mn=21055, Mp=49340, PD=1.6).

[0131] A superabsorbent polymer mixture was prepared by mixing 5 parts by weight of 2-(tert-butylamino)ethyl methacrylate polymer with 100 parts by weight of the superabsorbent polymer prepared in the same manner as in Comparative Example 1.

Comparative Example 3

[0132] 2-(tert-butyl amino)ethyl methacrylate (18.5 g) and ethanol (30 mL) were added to a 2-neck round bottom flask capable of maintaining a nitrogen environment, followed by stirring for 10 minutes. Thereafter, azobisisobutyronitrile (AIBN (493 mg)) was added, followed by stirring at 80 C. for 16 hours. The temperature of the reaction mixture was decreased to room temperature, and then a small amount of ethanol was added to dilute the solution. The diluted solution was slowly added dropwise to distilled water. The produced solid was filtered, washed with a small amount of distilled water, and dried to obtain 2-(tert-butyl amino)ethyl methacrylate polymer (Mw=32856, Mn=21055, Mp=49340, PD=1.6).

[0133] A superabsorbent polymer mixture was prepared by mixing 10 parts by weight of 2-(tert-butylamino)ethyl methacrylate polymer with 100 parts by weight of the superabsorbent polymer prepared in the same manner as in Comparative Example 1.

[0134] Mw, Mn, Mp and PD of 2-(tert-butyl amino)ethyl methacrylate polymers of Comparative Example 2 and Comparative Example 3 were measured by the following methods. The molecular weight distribution (PD=Mw/Mn) was determined by measuring Mw and Mn using gel permeation chromatography (GPC). The test was performed using a Waters E2695, 2414 RI instrument using a Polymer Laboratories's PLgel MIX-C/D 300 mm-length column. The test temperature was N,N-dimethylformamide (DMF) was used as a solvent, and measurement was performed at a flow rate of 1 mL/min. Samples were prepared at a concentration of mg/1mL and then supplied in an amount of 100 L. The values of Mw and Mn were derived using a calibration curve formed using polymethyl methacrylate (PMMA) standards. 9 kinds of polymethyl methacrylate standards having a molecular weight of 1,980/13,630/32,340/72,800/156,200/273,600/538,500/1,020,000/1,591,000 were used.

Experimental Example

[0135] (1) Evaluation of Antibacterial Property of Polymerizable Antibacterial Monomer Against E. coli

[0136] Antibacterial properties of the monomer 2-(tert-butylamino)ethyl methacrylate included in Examples and the following monomer 2-(dimethylamino)ethyl methacrylate were evaluated by the following methods.

[0137] The antibacterial property of 2-(tert-butylamino)ethyl methacrylate was shown in Experimental Examples 1-1 to 1-3, and the antibacterial property of 2-(dimethylamino)ethyl methacrylate was shown in Comparative Experimental Examples 1-1 to 1-4.

##STR00005##

[0138] The monomer was put in a 50 ml conical tube according to the content of Table 1 below, and then 25 ml of a nutrient broth (Becton Dickinson) solution, to which 3000300 CFU/ml of E. coli (ATCC 25922) standard strain was inoculated, was injected. After culturing for 18 hours in a shaking incubator (Vision Scientific, VS-37SIF) at 35 C., the culture solution was diluted to concentration using 1 PBS (Gibco). The absorbance of the diluted solution was measured at a wavelength of 600 nm using a UV-Vis spectrophotometer. At this time, the absorbance measured after culturing the nutrient broth solution to which the bacteria was inoculated without the addition of the monomer was compared to the absorbance of the sample to which the monomer was added, and the degree of growth of the bacteria was examined. The bacterial growth-inhibitory rate was calculated according to the following Equation 1, and the results are shown in Table 1 below.

Bacterial growth-inhibitory rate(%)=[(OD.sub.ReferenceOD.sub.sample)/OD.sub.Reference]*100 [Equation 1]

in Equation, OD.sub.Reference represents absorbance of the culture medium of Comparative Experimental Example 1-1 without the antibacterial material, and OD.sub.sample represents absorbance of the culture medium with the antibacterial material.

TABLE-US-00001 TABLE 1 Content of Optical Bacterial growth- Kind of monomer monomer (g) density inhibitory rate (%) Experimental Example 1-1 2-(tert-butylamino)ethyl 0.03 0.185 5.61 methacrylate Experimental Example 1-2 2-(tert-butylamino)ethyl 0.05 0.070 64.29 methacrylate Experimental Example 1-3 2-(tert-butylamino)ethyl 0.07 0.009 95.41 methacrylate Comparative Experimental 2-(tert-butylamino)ethyl 0 0.196 0 Example 1-1 methacrylate Comparative Experimental 2-(dimethylamino)ethyl 0.03 0.196 0.00 Example 1-2 methacrylate Comparative Experimental 2-(dimethylamino)ethyl 0.05 0.189 3.67 Example 1-3 methacrylate Comparative Experimental 2-(dimethylamino)ethyl 0.07 0.149 23.98 Example 1-4 methacrylate

[0139] According to Table 1, when the polymerizable antibacterial monomer of the present invention was included, the bacteriostatic reduction rate was superior to that of the case where the different monomer 2-(dimethylamino)ethyl methacrylate of Comparative Experimental Example was used in the same amount, of which the terminal substituent was a tertiary amine group.

(2) Evaluation of Antibacterial Property of Polymerizable Antibacterial Monomer Against Proteus mirabilis (P. mirabilis)

[0140] To examine the antibacterial properties of the monomer 2-(tert-butylamino)ethyl methacrylate included in Examples and the monomer 2-(dimethylamino)ethyl methacrylate against Proteus mirabilis, the bacterial growth-inhibitory rate (%) against Proteus mirabilis (P. mirabilis) was calculated in the same manner as in the antibacterial property evaluation for E. coli, except that a nutrient broth solution, to which 3000300 CFU/ml of Proteus mirabilis (P. mirabilis, ATCC 29906) standard strain was inoculated instead of E. coli (ATCC 25922), was used. The results are shown in Table 2 below.

[0141] In calculating the bacteriostatic reduction rate using Equation 1, C.sub.Reference represents CFU of bacteria after culturing with the monomer of Comparative Experimental Example 2-1 without the antibacterial material.

TABLE-US-00002 TABLE 2 Content of Optical Bacterial growth- Kind of monomer monomer (g) density inhibitory rate (%) Experimental Example 2-1 2-(tert-butylamino)ethyl 0.03 0.144 19.10 methacrylate Experimental Example 2-2 2-(tert-butylamino)ethyl 0.05 0.100 43.82 methacrylate Experimental Example 2-3 2-(tert-butylamino)ethyl 0.07 0.009 94.94 methacrylate Comparative Experimental 2-(tert-butylamino)ethyl 0 0.178 0 Example 2-1 methacrylate Comparative Experimental 2-(dimethylamino)ethyl 0.03 0.172 3.37 Example 2-2 methacrylate Comparative Experimental 2-(dimethylamino)ethyl 0.05 0.142 20.22 Example 2-3 methacrylate Comparative Experimental 2-(dimethylamino)ethyl 0.07 0.057 67.98 Example 2-4 methacrylate

[0142] According to Table 2, when the polymerizable antibacterial monomer of the present invention was included, the bacteriostatic reduction rate was superior to that of the case where the different monomer 2-(dimethylamino)ethyl methacrylate of Comparative Experimental Example was used in the same amount, of which the terminal substituent was a tertiary amine group.

(3) Evaluation of Absorption Properties of Superabsorbent Polymer

[0143] Centrifuge retention capacity (CRC) of the superabsorbent polymers of Examples and Comparative Examples was evaluated by the following method, and shown in Table 3.

[0144] The centrifuge retention capacity by absorption capacity under no load was measured for each of the superabsorbent polymers and base polymers of Examples and Comparative Examples in accordance with the European Disposables and

[0145] Nonwovens Association (EDANA) WSP 241.3.

[0146] In detail, after uniformly introducing W.sub.0(g) (about 0.2 g) of the superabsorbent polymer in a nonwoven fabric-made bag and sealing the same, it was immersed in physiological saline (0.9 wt % aqueous sodium chloride solution) at room temperature. After 30 minutes, the bag was drained using a centrifuge at 250 G for 3 minutes, and then the weight W2(g) of the bag was measured. Further, after carrying out the same operation without using the polymer, the weight W.sub.1(g) of the bag was measured. CRC (g/g) was calculated using each obtained weight according to the following Equation:

CRC(g/g)={[W.sub.2(g)W.sub.1(g)]/W.sub.0(g)}1 [Equation 3]

in Equation 3,

[0147] W.sub.0(g) is the initial weight (g) of the superabsorbent polymer,

[0148] W.sub.1(g) is the weight of the bag, which was measured after the bag without the superabsorbent polymer was immersed in physiological saline for 30 minutes, and then drained using a centrifuge at 250 G for 3 minutes, and

[0149] W.sub.2(g) is the weight of the bag including the superabsorbent polymer, which was measured after the superabsorbent polymer was immersed in physiological saline at room temperature for 30 minutes, and then drained using a centrifuge at 250 G for 3 minutes.

(4) Evaluation of Antibacterial Property of Superabsorbent Polymer Against Escherichia coli (E. coli)

[0150] 2 g of each superabsorbent polymer prepared in Examples and Comparative Examples was put in a 250 ml cell culture flask, and 50 ml of artificial urine, to which a test bacterium, Escherichia coli (E. coli, ATCC 25922) standard strain was inoculated at 3000300 CFU/ml, was injected thereto. Thereafter, to allow the superabsorbent polymer to sufficiently absorb the artificial urine solution, they were mixed for about 1 minute. When the polymer sufficiently absorbed the solution, it exhibited a gel form, which was incubated in an incubator (JEIO TECH) at for 12 hours. To the sample, of which incubation was completed, 150 ml of 0.9 wt % NaCl solution was added, followed by shaking for about 1 minute. This dilution was spread on an agar medium plate. Thereafter, serial dilution was performed for colony counting, and in this procedure, 0.9 wt % NaCl solution was used. Antibacterial performance was determined by calculating a bacteriostatic reduction rate (%) against E. coli (ATCC 25922) according to the following Equation 1 after calculating the initial concentration of the bacteria (Co, CFU/ml) based on the dilution concentrations. The results are shown in Table 3 below.

Bacteriostatic reduction rate(%)=(1C.sub.sample/C.sub.Reference)*100 [Equation 2]

[0151] In calculating the bacteriostatic reduction rate using Equation 1, C.sub.sample represents CFU of bacteria after incubation of the superabsorbent polymer with the antibacterial material, and C.sub.Reference represents CFU of bacteria after incubation of the superabsorbent polymer of Comparative Example 1 without the antibacterial material.

(5) Evaluation of Antibacterial Property of Superabsorbent Polymer Against Proteus mirabilis (P. mirabilis)

[0152] To examine antibacterial properties of the superabsorbent polymers prepared in Examples and Comparative Examples against Proteus mirabilis (P. mirabilis), the bacteriostatic reduction rate (%) against Proteus mirabilis was calculated in the same manner as in (4) evaluating the antibacterial property of the superabsorbent polymer against Escherichia coli (E. coli), except that Proteus mirabilis (P. mirabilis) was used instead of Escherichia coli (E. coli, ATCC 25922) standard strain. The results are shown in Table 3 below.

(6) Evaluation of Ammonia Deodorization

[0153] Deodorization evaluation was performed on the superabsorbent polymers of Examples and Comparative Examples by the following method.

[0154] In detail, each of the superabsorbent polymers prepared in Examples and Comparative Examples was injected, at a concentration of 0.04 g/ml per 1 ml of solvent, into 50 ml of artificial urine, to which Proteus Mirabilis (ATCC 29906) was inoculated at 10,000 CFU/ml, followed by incubation in an incubator (JEIO TECH) at 35 C. for 12 hours. After connecting an ammonia detection tube (Gastech, ammonia 3M) and a suitable pump (Gastech, GV-100) to the incubated vessel, 50 ml was extracted using a syringe needle. The color of the detection tube was changed by ammonia, and the scale was examined and compared. The composition of the artificial urine used at this time was prepared using a method described in J Wound Ostomy Continence Nurs. 2017; 44(1) 78-83. The results are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Comparative Comparative Comparative Example 1 Example 2 Example 1 Example 2 Example 3 CRC (g/g) of base polymer 43.7 40.4 44.6 43.7 43.7 CRC (g/g) of final superabsorbent 35.6 37.4 36.7 35.6 35.6 polymer Surface crosslinking time (min) 40 30 40 40 40 Surface crosslinking temperature ( C.) 184 178 184 184 184 Bacteriostatic reduction rate(%) 47.05 95.49 0 4.05 against E. coli Bacteriostatic reduction rate(%) 87.85 99.99 0 9.40 against P. mirabilis Ammonia (ppm) <10 <10 >500 >500 >500

[0155] The results of Table 3 showed that the superabsorbent polymers of Examples 1 and 2 and Comparative Example 1 had the equivalent level of CRC by controlling the surface crosslinking time and temperature, whereas the bacteriostatic reduction rate against Escherichia coli and Proteus mirabilis was high, indicating antibacterial properties. In Comparative Examples 2 and 3, the superabsorbent polymer of Example 1 was used, and thus they had the same absorption properties as that of Example 1. However, it was confirmed that the antibacterial properties against Escherichia coli and Proteus mirabilis were significantly reduced only by simple mixing.

[0156] In addition, Proteus mirabilis, which is a microorganism having an enzyme such as urease, decomposes urea contained in artificial urine into the form of ammonia. Thus, as Proteus mirabilis proliferated, the amount of ammonia increased, and thus the odor of urine was greatly increased. As shown in Table 3, the generation of ammonia was greatly reduced in Examples, as compared to Comparative Examples, indicating the excellent deodorizing effect by antibacterial action.