Porous super absorbent polymer and preparation method thereof

Abstract

The present disclosure relates to a preparation method of a porous super absorbent polymer exhibiting excellent absorption performance and improved absorption rate due to a novel pore structure, and a porous super absorbent polymer prepared therefrom. The porous super absorbent polymer includes a base resin powder including a cross-linked polymer of a water soluble ethylene-based unsaturated monomer containing acidic groups which are at least partially neutralized, and an inorganic filler contained in the cross-linked structure of the cross-linked polymer, wherein the base resin powder includes a plurality of pores having a diameter of a sub-micron (sub-m) scale in the cross-linked structure, and an interconnected pore structure in the form of an open channel in which 90% or more of the pores are connected to each other.

Claims

1. A preparation method of a porous super absorbent polymer, comprising the steps of: preparing a monomer composition comprising a water soluble ethylene-based unsaturated monomer containing acidic groups which are at least partially neutralized, an internal cross-linking agent, an initiator, an inorganic filler, and an anionic surfactant; stirring the monomer composition under a shear force at a rate of 3000 to 20,000 rpm to generate bubbles in the monomer composition; preparing a hydrogel polymer by cross-linking the monomer composition; and preparing a base resin powder by drying, pulverizing, and classifying the hydrogel polymer, wherein the monomer has acidic groups which are at least 80 mol % neutralized, and the anionic surfactant has 10 or more carbon atoms or HLB of 15 or more, and includes a compound in the form of a sulfate salt, a carboxylate salt or a phosphate salt.

2. The preparation method of a porous super absorbent polymer of claim 1, wherein the anionic surfactant is used in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the monomer.

3. The preparation method of a porous super absorbent polymer of claim 1, wherein the anionic surfactant comprises sodium dodecyl sulfate, sodium dodecanoate, alkyl phosphate having a C10 to C30 alkyl group, alkyl sulfate having a C10 to C30 alkyl group, or alkyl carboxylate having a C10 to C30 alkyl group.

4. The preparation method of a porous super absorbent polymer of claim 1, wherein the anionic surfactant has a number average molecular weight of 220 to 800.

5. The preparation method of a porous super absorbent polymer of claim 1, wherein the step of stirring is carried out for 1 min to 100 min.

6. The preparation method of a porous super absorbent polymer of claim 1, wherein the water soluble ethylene-based unsaturated monomer comprises an anionic monomer of acrylic acid, methacrylic acid, maleic anhydride, fumalic acid, crotonic acid, itaconic acid, 2-acryloylethane sulfonic acid, 2-methacryloylethane sulfonic acid, 2-(meth)acryloylpropane sulfonic acid, or 2-(meth)acrylamide-2-methyl propane sulfonic acid, or a salt thereof.

7. The preparation method of a porous super absorbent polymer of claim 1, wherein the internal cross-linking agent comprises at least one selected from the group consisting of polyethylene glycol diacrylate (PEGDA), glycerine diacrylate, glycerine triacrylate, unmodified or ethoxylated trimethylol triacrylate (TMPTA), hexanediol diacrylate, and triethylene glycol diacrylate.

8. The preparation method of a porous super absorbent polymer of claim 1, wherein the inorganic filler comprises a silica nanoparticle or an alumina nanoparticle.

9. The preparation method of a porous super absorbent polymer of claim 1, further comprising a step of further cross-linking the surface of the base resin powder in the presence of a surface cross-linking agent to form a surface cross-linked layer.

10. The preparation method of a porous super absorbent polymer of claim 9, wherein the surface cross-linking agent comprises at least one selected from the group consisting of ethylene glycol, 1,3-propandiol, 1,4-butanediol, 1,6-hexanediol, propylene glycol, 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, glycerol, ethylene carbonate and propylene carbonate.

11. A porous super absorbent polymer, comprising a base resin powder comprising a cross-linked polymer of a water soluble ethylene-based unsaturated monomer containing acidic groups which are at least partially neutralized, and an inorganic filler contained in the cross-linked structure of the cross-linked polymer, wherein the base resin powder comprises a plurality of pores having a diameter of a sub-micron (sub-m) scale in the cross-linked structure, and an interconnected pore structure in the form of an open channel in which 90% or more of the pores are connected to each other.

12. The porous super absorbent polymer of claim 11, wherein each of the pores has a maximum diameter of 5 to 500 m.

13. The porous super absorbent polymer of claim 11, wherein the base resin powder has a pore volume fraction of 0.74 or more, defined as a ratio of the volume of the plurality of pores to the total volume.

14. The porous super absorbent polymer of claim 11, wherein centrifuge retention capacity (CRC) to a saline solution (0.9 wt % aqueous solution of sodium chloride) for 30 min is 26 to 35 g/g, and absorption rate to a saline solution (0.9 wt % aqueous solution of sodium chloride) is less than 55 sec.

15. The porous super absorbent polymer of claim 11, further comprising a surface cross-linked layer, which is formed on a surface of the base resin powder and further cross-linked from the cross-linked polymer by a medium of a surface cross-linking agent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a SEM image showing the pore structure of the porous super absorbent polymer prepared in Example 1.

(2) FIG. 2 is a SEM image showing the pore structure of the porous super absorbent polymer prepared in Example 4.

(3) FIG. 3 is a SEM image showing the pore structure of the porous super absorbent polymer prepared in Comparative Example 1.

(4) FIG. 4 is a SEM image showing the pore structure of the porous super absorbent polymer prepared in Comparative Example 2.

(5) FIG. 5 is a SEM image showing the pore structure of the super absorbent polymer prepared in Comparative Example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only, and the invention is not intended to be limited by these examples.

EXAMPLE 1

Preparation of Super Absorbent Polymer

(7) 35.83 g of acrylic acid, 1.07 g (1 part by weight based on 100 parts by weight of the monomer) of sodium dodecyl sulfate (HLB: 40, number average molecular weight: 288) as an anionic surfactant, 0.06 g (1600 ppm) of polyethylene glycol diacrylate (Mw=598) as a cross-linking agent, 57.94 g of 30% sodium hydroxide (NaOH), 2.2 g (10 parts by weight based on 100 parts by weight of the monomer) of a silica nano particle (30 wt % dispersion) having a diameter of 12 nm, 1.42 g of sodium persulfate (10 wt % solution), and 7.76 g of water were mixed to prepare a monomer composition having an acrylic acid monomer concentration of 33.7 wt % and a neutralization degree of 90 mol %.

(8) Thereafter, the monomer composition was stirred with applying a shear force at 5000 rpm for 60 min using a mechanical mixer to perform foaming.

(9) Subsequently, the monomer composition was added through a feeder consisting of a movable conveyor belt of a polymerization reactor, and subjected to thermal polymerization for 20 min to prepare a hydrogel polymer.

(10) The hydrogel polymer was transferred to a cutter and cut to 0.2 cm. Here, the moisture content of the cut hydrogel polymer was 50 wt %.

(11) Subsequently, the hydrogel polymer was dried with a hot air drier at 185 C. for 40 min, and the dried hydrogel polymer was pulverized with a pin mill pulverizer. And then, the polymer having a diameter less than about 150 m and the polymer having a diameter of about 150 m to 850 m were classified by using a sieve.

(12) After proceeding up to the above classification, a base resin powder was obtained. Then, 0.67 g of 1,3-propanediol as a surface cross-linking agent was added to 2.8 g of water and 3.5 g of methanol, and mixed to prepare a surface cross-linking solution. Thereafter, the surface cross-linking solution was sprayed onto the base resin powder, and stirred at room temperature so that the surface cross-linking solution was evenly distributed on the base resin powder. Subsequently, the base resin powder mixed with the surface cross-linking solution was put into the surface cross-linking reactor and subjected to the surface cross-linking reaction.

(13) In this surface cross-linking reactor, the base resin powder was surface cross-linked at 185 C. for 90 min to prepare a super absorbent polymer of Example 1. After the surface cross-linking reaction, a porous super absorbent polymer of Example 1 having a particle size of 150 m to 850 m was prepared

(14) The pore structure of the porous super absorbent polymer of Example 1 was confirmed using a scanning electron microscope as shown in FIG. 1. For reference, the right image is an enlarged image of the left image. As shown in FIG. 1, it was confirmed that the porous super absorbent polymer of Example 1 includes a plurality of pores having a maximum diameter of 5 to 400 m, and an interconnected pore structure in the form of an open channel in which 90% or more of the pores are connected to each other.

EXAMPLE 2

Preparation of Super Absorbent Polymer

(15) A porous super absorbent polymer of Example 2 was prepared in the same manner as in Example 1 except that 1.07 g (3 parts by weight based on 100 parts by weight of the monomer) of sodium dodecanoate (HLB: 21, number average molecular weight: 222) was used as the anionic surfactant.

(16) By observing the pore structure using a scanning electron microscope in the same manner as in Example 1, it was confirmed that the porous super absorbent polymer of Example 2 includes a plurality of pores having a maximum diameter of 5 to 500 m, and an interconnected pore structure in the form of an open channel in which 90% or more of the pores are connected to each other.

EXAMPLE 3

Preparation of Super Absorbent Polymer

(17) A porous super absorbent polymer of Example 3 was prepared in the same manner as in Example 1 except that 1.07 g of Hannong COP-140 (oleyl phosphate-based surfactant, number average molecular weight: 460) was used as the anionic surfactant.

(18) By observing the pore structure using a scanning electron microscope in the same manner as in Example 1, it was confirmed that the porous super absorbent polymer of Example 3 includes a plurality of pores having a maximum diameter of 5 to 400 m, and an interconnected pore structure in the form of an open channel in which 90% or more of the pores are connected to each other.

EXAMPLE 4

Preparation of Super Absorbent Polymer

(19) 35.83 g of acrylic acid, 1.07 g (1 part by weight based on 100 parts by weight of the monomer) of sodium dodecyl sulfate (HLB: 40, number average molecular weight: 288) as an anionic surfactant, 0.06 g (1600 ppm) of polyethylene glycol diacrylate (Mw=598) as a cross-linking agent, 50.84 g of 30% sodium hydroxide (NaOH), 2.2 g (10 parts by weight based on 100 parts by weight of the monomer) of a silica nano particle (30 wt % dispersion) having a diameter of 12 nm, 1.42 g of sodium persulfate (10 wt % solution), and 7.76 g of water were mixed to prepare a monomer composition having an acrylic acid monomer concentration of 36.1 wt % and a neutralization degree of 80 mol %.

(20) A porous super absorbent polymer of Example 4 was prepared in the same manner as in Example 1 except that the above monomer composition was used.

(21) The pore structure of the porous super absorbent polymer of Example 4 was confirmed using a scanning electron microscope as shown in FIG. 2. For reference, the right image is an enlarged image of the left image. As shown in FIG. 2, it was confirmed that the porous super absorbent polymer of Example 4 includes a plurality of pores having a maximum diameter of 5 to 400 m, and an interconnected pore structure in the form of an open channel in which 90% or more of the pores are connected to each other.

COMPARATIVE EXAMPLE 1

Preparation of Super Absorbent Polymer

(22) 35.83 g of acrylic acid, 1.07 g (1 part by weight based on 100 parts by weight of the monomer) of sodium dodecyl sulfate (HLB: 40, number average molecular weight: 288) as an anionic surfactant, 0.06 g (1600 ppm) of polyethylene glycol diacrylate (Mw=598) as a cross-linking agent, 46.54 g of 30% sodium hydroxide (NaOH), 2.2 g (10 parts by weight based on 100 parts by weight of the monomer) of a silica nano particle (30 wt % dispersion) having a diameter of 12 nm, 1.42 g of sodium persulfate (10 wt % solution), and 7.76 g of water were mixed to prepare a monomer composition having an acrylic acid monomer concentration of 37.8 wt % and a neutralization degree of 75 mol %.

(23) Thereafter, the monomer composition was stirred with applying a shear force at 5000 rpm for 60 min using a mechanical mixer to perform foaming.

(24) Subsequently, the monomer composition was added through a feeder consisting of a movable conveyor belt of a polymerization reactor, and subjected to thermal polymerization for 20 min to prepare a hydrogel polymer.

(25) The hydrogel polymer was transferred to a cutter and cut to 0.2 cm. Here, the moisture content of the cut hydrogel polymer was 50 wt %.

(26) Subsequently, the hydrogel polymer was dried with a hot air drier at 185 C. for 40 min, and the dried hydrogel polymer was pulverized with a pin mill pulverizer. And then, the polymer having a diameter less than about 150 m and the polymer having a diameter of about 150 m to 850 m were classified by using a sieve.

(27) After proceeding up to the above classification, a base resin powder was obtained. Then, 0.67 g of 1,3-propanediol as a surface cross-linking agent was added to 2.8 g of water and 3.5 g of methanol, and mixed to prepare a surface cross-linking solution. Thereafter, the surface cross-linking solution was sprayed onto the base resin powder, and stirred at room temperature so that the surface cross-linking solution was evenly distributed on the base resin powder. Subsequently, the base resin powder mixed with the surface cross-linking solution was put into the surface cross-linking reactor and subjected to the surface cross-linking reaction.

(28) In this surface cross-linking reactor, the base resin powder was surface cross-linked at 185 C. for 90 min to prepare a super absorbent polymer of Example 1. After the surface cross-linking reaction, a porous super absorbent polymer of Example 1 having a particle size of 150 m to 850 m was prepared by classifying with a standard mesh of ASTM standard.

(29) The pore structure of the porous super absorbent polymer of Comparative Example 1 was confirmed using a scanning electron microscope as shown in FIG. 3. Referring to FIG. 3, it was confirmed that the porous super absorbent polymer of Comparative Example 1 has a plurality of pores, but these pores are formed in an independent form that they are not connected to each other, so that the polymer has a pore structure different from that of Examples.

COMPARATIVE EXAMPLE 2

Preparation of Super Absorbent Polymer

(30) A porous super absorbent polymer of Comparative Example 2 was prepared in the same manner as in Comparative Example 1 except that 1.07 g of dioctyl sulfosuccinate sodium salt (HLB: 11) as the anionic surfactant and a monomer composition with a neutralization degree of 90 mol % were used.

(31) The pore structure of the porous super absorbent polymer of Comparative Example 2 was confirmed using a scanning electron microscope as shown in FIG. 4. Referring to FIG. 4, it was confirmed that the porous super absorbent polymer of Comparative Example 2 has a plurality of pores, but these pores are formed in an independent form that they are not connected to each other, so that the polymer has a pore structure different from that of Examples.

COMPARATIVE EXAMPLE 3

Preparation of Super Absorbent Polymer

(32) A super absorbent polymer of Comparative Example 3 was prepared in the same manner as in Example 1 except that the monomer composition was stirred with applying a shear force at 2000 rpm for 60 min using a mechanical mixer to perform foaming.

(33) The pore structure of the super absorbent polymer of Comparative Example 3 was confirmed using a scanning electron microscope as shown in FIG. 5. Referring to FIG. 5, it was confirmed that the super absorbent polymer of Comparative Example 3 has a non-porous structure in which pores are hardly observed.

EXPERIMENTAL EXAMPLES

(34) The properties of the super absorbent polymers of Examples and Comparative Examples were evaluated according to the following methods, and the measured property values are shown in the following Table 1.

(35) (1) Pore Volume and Pore Volume Fraction

(36) 2.5 g of the base resin powder before surface cross-linking was filled in a 4 ml cylindrical column, and the internal pore volume was defined based on the volume occupied by isopropyl alcohol (IPA). The porosity (pore volume fraction) was confirmed by the result of the pore volume and the result of an electron microscope (50) analysis.

(37) (2) Centrifuge Retention Capacity (CRC)

(38) For the super absorbent polymers of Examples and Comparative Examples, the centrifuge retention capacity (CRC) by absorption ratio under a non-loading condition was measured according to the EDANA (European Disposables and Nonwovens Association) method WSP 241.2.

(39) That is, after inserting W.sub.0 (g, about 0.2 g) of each polymer obtained in Examples and Comparative Examples uniformly in a nonwoven fabric envelope and sealing the same, it was soaked in a 0.9 wt % saline solution at room temperature. After 30 min, it was dehydrated by using a centrifuge at 250 G for 3 min, and the weight W.sub.2 (g) of each envelope was measured. Further, after carrying out the same operation without using the polymer, the weight W.sub.1 (g) of each envelope was measured.

(40) CRC (g/g) was calculated by using the obtained weight values according to the following Calculation Equation 1, and the water retention capacity was confirmed.
CRC (g/g)={[W.sub.2 (g)W.sub.1 (g)]/W.sub.0 (g)}1[Calculation Equation 1]

(41) In Calculation Equation 1,

(42) W.sub.0 (g) is an initial weight (g) of the super absorbent polymer,

(43) W.sub.1 (g) is a weight of the apparatus measured after dehydrating the same by using a centrifuge at 250 G for 3 min without using the super absorbent polymer, and

(44) W.sub.2 (g) is a weight of the apparatus with the superabsorbent polymer measured after soaking the super absorbent polymer in a 0.9 wt % saline solution for 30 min at room temperature and dehydrating the same by using a centrifuge at 250 G for 3 min.

(45) (3) Content of Water Soluble Component

(46) 1.0 g of a sample having a diameter of 300 m to 500 m of the super absorbent polymer prepared in Examples and Comparative Examples was placed in a 250 mL erlenmeyer flask, and free swollen in a 200 mL saline solution which is 0.9 wt % aqueous solution of sodium chloride while stirring at 250 rpm for 1 hour. Thereafter, the aqueous solution was filtered by a filter paper. The filtrate was primarily titrated to pH 10 with 0.1 N sodium hydroxide solution, and then back-titrated to pH 2.7 with 0.1 N hydrogen chloride solution. The content (wt %) of water soluble component in the super absorbent polymer was calculated from the obtained titration amount in accordance with EDANA WSP 270.3.

(47) (4) Absorption Rate (s)

(48) 2.0 g of a sample having a diameter of 300 m to 500 m of the super absorbent polymer prepared in Examples and Comparative Examples was placed in a 100 mL flask. And then, it was added to 50 mL of a saline solution which is 0.9 wt % aqueous solution of sodium chloride, and free swollen while stirring at 600 rpm. Thereafter, the time was measured until the vortex of the liquid generated by the stirring disappeared and a smooth surface was formed.

(49) The properties measured by the above methods are listed in Table 1.

(50) TABLE-US-00001 TABLE 1 Pore volume fraction Content of Pore (whether it water volume is 0.74 or soluble (IPA, more; SEM CRC component Absorption ml) X50) (g/g) (wt %) rate (s) Example 1 2.3 31.5 15.9 39 Example 2 2.5 26.0 7.9 41 Example 3 2.3 30.3 11.5 49 Example 4 2.4 32.4 8.2 50 Comp. Ex. 1 1.8 X 28.2 3.0 60 Comp. Ex. 2 2.0 X 25.0 16.4 58 Comp. Ex. 3 1.0 X 21.1 12.6 88

(51) Referring to Table 1, it was confirmed that the super absorbent polymer of Examples exhibited the absorption performance (water retention capacity) at least equal to or higher than that of Comparative Examples and the absorption rate superior to that of Comparative Examples.