Super absorbent polymer and preparation method thereof

Abstract

The present disclosure relates to a super absorbent polymer, including: a base resin powder comprising a first cross-linked polymer of a water soluble ethylene-based unsaturated monomer containing acidic groups which are at least partially neutralized; and a surface cross-linked layer comprising a second cross-linked polymer further cross-linked from the first cross-linked polymer and formed on the base resin powder, wherein the first cross-linked polymer is bound to a porous zeolite in which a mesopore having a BET surface area of at least 100 m.sup.2/g and a porosity of at least 0.2 cm.sup.3/g is formed, and a preparation method thereof.

Claims

1. A super absorbent polymer, comprising: a base resin powder comprising a first cross-linked polymer of a water soluble ethylene-based unsaturated monomer containing acidic groups which are at least partially neutralized; and a surface cross-linked layer comprising a second cross-linked polymer further cross-linked from the first cross-linked polymer and formed on the base resin powder, wherein the first cross-linked polymer is bound to a porous zeolite in which a mesopore having a BET surface area of at least 100 m.sup.2/g and a porosity of at least 0.2 cm.sup.3/g is formed.

2. The super absorbent polymer of claim 1, wherein the mesopore formed in the porous zeolite has a porosity of 0.2 cm.sup.3/g to 0.8 cm.sup.3/g, and a BET surface area of 100 m.sup.2/g to 250 m.sup.2/g.

3. The super absorbent polymer of claim 1, wherein a total porosity of the porous zeolite is 0.5 cm.sup.3/g to 1.0 cm.sup.3/g, and a BET surface area of entire pores formed in the porous zeolite is 500 m.sup.2/g to 1500 m.sup.2/g.

4. The super absorbent polymer of claim 1, wherein the porous zeolite further comprises a micropore having a BET surface area of 300 to 900 m.sup.2/g and a porosity of 0.1 to 0.5 cm.sup.3/g.

5. The super absorbent polymer of claim 1, wherein the soluble ethylene-based unsaturated monomer comprises at least one selected from the group consisting of: 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, and a salt thereof; a nonionic hydrophilic monomer of (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, methoxypolyethyleneglycol(meth)acrylate, or polyethyleneglycol(meth)acrylate; and an amino-containing unsaturated monomer of (N,N)-dimethylaminoethyl(meth)acrylate or (N,N)-dimethylaminopropyl(meth)acrylamid, and a quaternary compound thereof.

6. The super absorbent polymer of claim 1, wherein the first cross-linked polymer comprises a cross-linked polymer obtained by polymerizing the water soluble ethylene-based unsaturated monomer in the presence of an internal cross-linking agent including a polyfunctional acrylate-based compound containing a plurality of ethylene oxide groups.

7. The super absorbent polymer of claim 6, 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 super absorbent polymer of claim 1, further comprising an inorganic particle chemically bonded to the first cross-linked polymer by a medium of a cross-linking bond, an oxygen-containing bond (O), or a nitrogen-containing bond (NR; wherein R is hydrogen, a C1 to C3 alkyl group, or an amide bond).

9. The super absorbent polymer of claim 8, wherein the inorganic particle is a silica nanoparticle, or an alumina nanoparticle surface-modified with a cross-linkable or hydrophilic functional group containing at least one functional group selected from the group consisting of a (meth)acrylate-based functional group, an allyl group, a vinyl group, an epoxy group, a hydroxyl group, an isocyanate group and an amine group.

10. The super absorbent polymer of claim 1, wherein the second cross-linked polymer comprises a polymer that the first cross-linked polymer is further cross-linked by a surface cross-linking agent.

11. The super absorbent polymer of claim 10, wherein the surface cross-linking agent comprises at least one selected from the group consisting of ethylene glycol, 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.

12. The super absorbent polymer of claim 1, wherein the porous zeolite is included in an amount of 0.01 to 30 parts by weight based on 100 parts by weight of the base resin powder.

13. The super absorbent polymer of claim 1, which has a particle diameter of 150 to 850 jim.

14. A method of preparing the super absorbent polymer of claim 1, comprising the steps of: preparing a monomer neutralized solution by adding an internal cross-linking agent and a porous zeolite containing a mesopore having a BET surface area of at least 100 m.sup.2/g and a porosity of at least 0.2 cm.sup.3/g to a neutralized solution in which at least 20 mol % of a water soluble ethylene-based unsaturated monomer containing acidic groups is neutralized, preparing a hydrogel polymer from the monomer neutralized solution by thermal polymerization or photopolymerization; preparing a base resin powder by drying, pulverizing, and classifying the hydrogel polymer; and 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.

15. The method of preparing the super absorbent polymer of claim 14, further comprising a step of adding a basic compound to the water soluble ethylene-based unsaturated monomer containing acidic groups to form a neutralized solution which is at least 20 mol % neutralized.

16. The method of preparing the super absorbent polymer of claim 14, wherein the monomer neutralized solution further comprises a thermal polymerization initiator or a photopolymerization initiator.

17. The method of preparing the super absorbent polymer of claim 14, wherein the water soluble ethylene-based unsaturated compound is included in an amount of 20 to 60 wt % in the monomer neutralized solution.

18. The method of preparing the super absorbent polymer of claim 14, wherein the mesopore formed in the porous zeolite has a porosity of 0.2 cm.sup.3/g to 0.8 cm.sup.3/g, and a BET surface area of 100 m.sup.2/g to 250 m.sup.2/g.

19. The method of preparing the super absorbent polymer of claim 14, wherein a total porosity of the porous zeolite is 0.5 cm.sup.3/g to 1.0 cm.sup.3/g, and a BET surface area of entire pores formed in the porous zeolite is 500 m.sup.2/g to 1500 m.sup.2/g.

20. The method of preparing the super absorbent polymer of claim 14, wherein the porous zeolite further comprises a micropore having a BET surface area of 300 to 900 m.sup.2/g and a porosity of 0.1 to 0.5 cm.sup.3/g.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) 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

(2) 537.45 g of acrylic acid, 0.8 g (0.15 parts by weight based on 100 parts by weight of the monomer) of a porous zeolite containing a mesopore of Table 1, 0.86 g of polyethyleneglycol diacrylate (Mw=598) as a cross-linking agent, 653.17 g of 30% sodium hydroxide (NaOH), 0.04 g of 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide as an UV initiator, 1.07 g of sodium persulfate, and 206.41 g of water were mixed to prepare a monomer composition with the concentration of acrylic acid monomer of 36.7 wt % (the neutralization degree of acrylic acid: 70 mol %).

(3) Thereafter, the monomer composition was stirred for 25 seconds at 300 rpm for foaming. Subsequently, the monomer composition was added through a feeder consisting of a movable conveyor belt of a polymerization reactor, irradiated with ultraviolet rays (irradiation amount: 2 mW/cm.sup.2) using a UV irradiation device, and subjected to UV polymerization for 1 min and thermal polymerization for 2 min to prepare a hydrogel polymer. 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 %.

(4) 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 38/1 sieve.

(5) 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.

(6) Thereafter, the surface cross-linking solution was sprayed on the prepared base resin powder, and stirred at room temperature so that the surface cross-linking solution was evenly distributed on the base resin powder. The base resin powder mixed with the cross-linking solution was then added into a surface cross-linking reactor, followed by surface cross-linking reaction. 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.

(7) After the surface cross-linking reaction, a 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.

Example 2

(8) A super absorbent polymer having a particle size of 150 m to 850 m was prepared in the same manner as in Example 1 except that 2.68 g (0.5 parts by weight based on 100 parts by weight of the monomer) of the porous zeolite containing a mesopore as shown in Table 1 was used and the foaming time was changed to 22 seconds.

Comparative Example 1

(9) A super absorbent polymer having a particle size of 150 m to 850 m was prepared in the same manner as in Example 1 except that 0.8 g of the porous zeolite containing a mesopore (the porosity of the mesopore is 0.2 or less as shown in Table 1) was used.

Comparative Example 2

(10) A super absorbent polymer of Example 2 having a particle size of 150 m to 850 m was prepared in the same manner as in Example 1 except that the porous zeolite containing a mesopore was not used.

(11) TABLE-US-00001 TABLE 1 Specific Specific surface surface Specific Specific Porosity Porosity area of area of surface surface Total of of entire other area of area of Porous porosity micropore mesopore pores pores micropore mesopore zeolite (cm.sup.3/g) (cm.sup.3/g) (cm.sup.3/g) (m.sup.2/g) (m.sup.2/g) (m.sup.2/g) (m.sup.2/g) Example 1 0.7 0.3 0.3 822.6 129.6 671.4 134.6 Example 2 0.9 0.2 0.6 650.6 165.9 484.7 133.9 Comp. 0.37 0.25 0.12 697.0 Example 1

Experimental Examples

(12) 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.

(13) (1) Centrifuge Retention Capacity (CRC)

(14) 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.

(15) 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.

(16) 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]

(17) In Calculation Equation 1,

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

(19) 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

(20) 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.

(21) (2) Absorbency Under Pressure (AUP)

(22) For the super absorbent polymers of Examples and Comparative Examples, the absorbency under pressure (AUP) was measured according to the EDANA (European Disposables and Nonwovens Association) method WSP 242.3.

(23) First, a 400 mesh stainless steel net was installed in a cylindrical bottom of a plastic having an internal diameter of 60 mm. W.sub.0(g, 0.90 g) of the absorbent polymers prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were uniformly scattered on the steel net under conditions of temperature of 232 C. and relative humidity of 45%, and a piston which can provide a load of 4.83 kPa (0.7 psi) uniformly was put thereon. The external diameter of the piston was slightly smaller than 60 mm, there was no gap between the cylindrical internal wall and the piston, and the jig-jog of the cylinder was not interrupted. At this time, the weight W.sub.3(g) of the device was measured.

(24) After putting a glass filter having a diameter of 125 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 wt % 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 120 mm was put thereon. The measuring device was put on the filter paper and the solution was absorbed under a load for about 1 hour. After 1 hour, the weight W.sub.4(g) was measured after lifting the measuring device up.

(25) AUP (g/g) was calculated by using the obtained weight values according to the following Calculation Equation 2, and the absorbency under pressure was confirmed.
AUP(g/g)=[W.sub.4(g)W.sub.3(g)]/W.sub.0(g)[Calculation Equation 2]

(26) In Calculation Equation 2,

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

(28) W.sub.3(g) is a sum of a weight of the super absorbent polymer and a weight of the apparatus providing a load to the polymer, and

(29) W.sub.4(g) is a sum of a weight of the super absorbent polymer and a weight of the apparatus providing a load to the polymer measured after making the super absorbent polymer absorb the saline solution for 1 h under a load (0.7 psi).

(30) (3) BPI(Base Polymer Index) Measurement

(31) For the super absorbent polymers of Examples and Comparative Examples, the centrifuge retention capacity (CRC, unit: g/g), the water-soluble component content (unit: wt %), and the absorbency under pressure of 0.7 psi (AUP, unit: g/g) were measured according to the EDANA method 441.2-02, 270.2, and 242.3, respectively. And then, the BPI was calculated according to the following Equation 1.

(32) $\begin{array}{cc}BPI=\frac{CRC+8.7585}{\ln \left(\mathrm{the}\mathrm{water}\text{-}\mathrm{soluble}\mathrm{component}\mathrm{content}\right)}& \left[\mathrm{Equation}1\right]\end{array}$

(33) The properties of the super absorbent polymers of Examples and Comparative Examples measured by the above methods are listed in Table 2.

(34) TABLE-US-00002 TABLE 2 Centrifuge Retention Capacity of the base Centrifuge resin without surface Retention AUP cross-linked layer Capacity (CRC) [unit: g/g] (CRC) [unit: g/g] [unit: g/g] BPI Example 1 25.7 52.7 38.8 18.9 Example 2 22.5 54.3 41.1 19.3 Comp. 18.5 51.1 40.7 18.1 Example 1 Comp. 20.6 49.3 35.6 18.0 Example 2

(35) As shown in Table 2, Comparative Example 1 showed an inverse relationship between the water retention capacity and the absorption ability under pressure, since it uses the porous zeolite in which a mesopore having a porosity of less than 0.2 is formed. However, the super absorbent polymers of Examples 1 and 2 showed the water retention capacity which was maintained almost as it was or rather increased, and more improved absorption performance compared with the Comparative Examples, in spite of the increase of the content of the porous zeolite in which a mesopore having a BET surface area of at least 100 m.sup.2/g and a porosity of at least 0.2 cm.sup.3/g is formed. That is, it is confirmed that the super absorbent polymer exhibiting an excellent characteristics in which both of the water retention capacity and the absorption ability under pressure are improved together can be provided.