Method of Preparing Superabsorbent Polymer

A method of preparing a superabsorbent polymer, the method comprising:

• carrying out a crosslinking polymerization of a water-soluble ethylene-based unsaturated monomer having acidic groups which are at least partially neutralized, in the presence of an internal crosslinking agent including a compound of Chemical Formula 1, to form a water-containing gel polymer;
• gel-pulverizing the water-containing gel polymer;
• drying, pulverizing, and size-sorting the gel-pulverized water-containing gel polymer to form a base polymer powder;
• and
• carrying out a surface crosslinking of the base polymer powder by heat treatment in the presence of a surface crosslinking agent,
• wherein the gel-pulverizing is carried out by extruding the water-containing gel polymer through a porous plate having a plurality of holes using a screw extruder mounted inside a cylindrical pulverizer under a condition that a chopping index according to following Equation 1 is 28 (/s) or more:
• wherein in Chemical Formula 1, R1 is a divalent organic group derived from alkane having 1 to 10 carbon atoms, and R2 is hydrogen or a methyl group,
• Chopping index(C.I.)=ω×(TSC/A)×number of times of chopping(T) [Equation 1]
• wherein in Equation 1,
• ω represents angular velocity (2π×N/60 s) of screw in the screw extruder, wherein in angular velocity (2π×N/60 s), N represents a number of rotation (rpm) of the screw,
• TSC represents a solid content (%) of the water-containing gel polymer fed into the pulverizer, and
• A represents porosity (πr2×n/πR2) of the porous plate, wherein in porosity (πr2×n/πR2), r represents a radius (mm) of the holes formed in the porous plate, n represents the number of holes formed in the porous plate, and R represents a radius (mm) of the porous plate.