Super absorbent polymer and method for preparing same
The present disclosure relates to: a super absorbent polymer having a rapid absorption rate and maintaining elasticity even in a condition of being pressed multiple times, thereby having excellent dryness characteristic; and a preparation method therefor. The super absorbent polymer of the present disclosure exhibits excellent performance for use in hygiene materials such as diapers.
1. A method for preparing a super absorbent polymer comprising:
polymerizing a monomer composition including an acrylic acid-based monomer having at least partially neutralized acidic groups, a foaming agent, an internal crosslinking agent, and a polymerization initiator to form a hydrogel polymer;
chopping the hydrogel polymer through a chopper containing two or more hole plates arranged in series with a screw therethrough;
drying, pulverizing and classifying the chopped hydrogel polymer to form a base polymer; and
further crosslinking a surface of the base polymer powder in the presence of a surface crosslinking agent to form a surface crosslinked layer,
wherein each of the two or more hole plates comprises a plurality of holes,
wherein an average diameter of the plurality of holes of each successive hole plate becomes smaller with each successive hole plate in a direction away from an inlet to the screw;
wherein the hydrogel polymer is pulverized while being pushed out of each hole plate by the screw while being continuously pushed out by the screw in subsequent hole plates in decreasing particle size, and
wherein the super absorbent polymer has an absorption rate (vortex) of 40 seconds or less calculated by measuring in seconds an amount of time required for a vortex to disappear after adding 2 g of a super absorbent polymer to 50 mL of physiological saline solution at 23° C. to 24° C. and then stirring at 600 rpms.
2. The method for preparing the super absorbent polymer according to claim 1 , wherein the foaming agent comprises one or more of sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium carbonate, magnesium bicarbonate or magnesium carbonate.
3. The method for preparing the super absorbent polymer according to claim 1 , wherein the foaming agent is contained in an amount of 500 ppmw or less based on the weight of a acrylic acid-based monomer.
4. The method for preparing the super absorbent polymer according to claim 1 , wherein the monomer composition further comprises a surfactant.
5. The method for preparing the super absorbent polymer according to claim 4 , wherein the surfactant comprises one or more of sodium dodecyl sulfate, ammonium lauryl sulfate, sodium laureth sulfate, dioctyl sodium sulfosuccinate, perfluorooctane sulfonate, perfluorobutane sulfonate, alkyl-aryl ether phosphate, alkyl ether phosphate, sodium myreth sulfate or carboxylate salt.
6. The method for preparing the super absorbent polymer according to claim 1 , wherein the chopping is performed by further adding a polycarboxylic acid-based copolymer.
7. The method for preparing the super absorbent polymer according to claim 6 , wherein the polycarboxylic acid-based copolymer comprises one or more of alkoxy polyalkylene glycol mono(meth)acrylic acid ester-based monomers or (meth)acrylic acid ester-based monomers.
8. The super adsorbent polymer prepared according to the method of claim 1 in which a recovery rate of the super adsorbent polymer calculated by the following Equation 1 is 85% or more:
Recovery rate (%)=Fourth resilience value/first resilience value*100; [Equation 1]
wherein in Equation 1, the first resilience value is a modulus (unit: Kpa) of the super adsorbent polymer which is measured after 2 g of the super adsorbent polymer is swollen in 200 mL of physiological saline (0.9 wt % NaCl) for 1 hour under no pressure, loaded into a DMA (Dynamic Mechanical Analysis) measuring device, pressed at room temperature (25° C.) under 0.72 psi for 5 minutes, and then released from pressure and allowed to stand for 10 minutes, and
the fourth resilience value is the modulus (unit: Kpa) of the super adsorbent polymer, which is measured for the fourth time after the process of measuring the first resilience value and then pressing again to measure a resilience value, which is repeated three times in the same manner.
9. The super absorbent polymer according to claim 8 , wherein the first resilience value is 90 Kpa or more.