Preparation method for superabsorbent polymer
A method of preparing a superabsorbent polymer and the superabsorbent polymer maintaining excellent basic absorption performances such as centrifuge retention capacity, while exhibiting improved gel strength and absorption rate are provided. The nanocellulose fiber is introduced during the preparation of the superabsorbent polymer to improve mechanical strength, to form a porous structure, and to rapidly absorb the surrounding water through capillary action and delivering the water to the inside of the superabsorbent polymer.
1 . A method of preparing a superabsorbent polymer, comprising:
a) mixing a water-soluble ethylene-based unsaturated monomer, an internal crosslinking agent, and a solvent to prepare a first monomer mixture;
b) introducing a nanocellulose fiber having a width of 3 nm to 50 nm, a length of 1 μm to 5 μm, and a tensile strength of 2,000 MPa or more, and a surfactant while shear mixing the first monomer mixture to prepare a second monomer mixture;
c) introducing a polymerization initiator to the second monomer mixture to prepare a third monomer mixture;
d) polymerizing the third monomer mixture to prepare a water-containing gel polymer;
e) chopping the water-containing gel polymer;
f) drying, pulverizing, and size-sorting the water-containing gel polymer to prepare a base polymer; and
g) carrying out an additional crosslinking of the surface of the base polymer in the presence of a surface crosslinking agent to form a surface-crosslinked layer and thereby produce the superabsorbent polymer,
wherein the shear mixing of the first monomer mixture to prepare the second monomer mixture is performed at a shear rate of 6 s −1 or more.
2 . The method of claim 1 , wherein the nanocellulose fiber has a tensile strength of 3,000 MPa to 20,000 MPa.
3 . The method of claim 1 , wherein the nanocellulose fiber is included in an amount of 0.001 part by weight to 10 parts by weight, based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer.
4 . The method of claim 1 , wherein the surfactant is fatty acid sodium, sulfonate, or sorbitan ester having 10 to 30 carbon atoms.
5 . The method of claim 1 , wherein the surfactant is included in an amount of 0.01 part by weight to 1 part by weight, based on 100 parts by weight of the water-soluble ethylene-based unsaturated monomer.
6 . A superabsorbent polymer having a gel strength of 10,000 Pa or more, comprising:
base polymer particles including a crosslinked polymer which is obtained by crosslinking polymerization of a water-soluble ethylene-based unsaturated monomer in the presence of an internal crosslinking agent;
a surface-crosslinked layer which is formed on the surface of the base polymer particles and is obtained by additional crosslinking of the crosslinked polymer via a surface crosslinking agent; and
a nanocellulose fiber having a width of 3 nm to 50 nm, a length of 1 μm to 5 μm, and a tensile strength of 2,000 MPa or more, which is incorporated with the base polymer.
7 . The superabsorbent polymer of claim 6 , wherein a content of the nanocellulose fiber is 0.0001% by weight to 10% by weight, based on 100% by weight of the superabsorbent polymer.
8 . The superabsorbent polymer of claim 6 , wherein a centrifuge retention capacity (CRC) is 24 g/g to 45 g/g, as measured according to EDANA WSP 241.3.
9 . The superabsorbent polymer of claim 6 , wherein absorbency under load (AUL) of 0.7 psi is 23 g/g to 40 g/g, as measured according to EDANA WSP 242.3.
10 . The superabsorbent polymer of claim 6 , wherein an absorption rate (vortex time) is 55 seconds or less, as measured according to JIS K 7224.
11 . The superabsorbent polymer of claim 6 , wherein an absorption capacity of 0.3 psi is 18 g/g or more.
12 . The method of claim 1 , wherein the shear rate is from 6 s 1 to 20 s −1 .
13 . The superabsorbent polymer of claim 6 , wherein the gel strength of the superabsorbent polymer is from 10,000 Pa to 20,000 Pa.
14 . The superabsorbent polymer of claim 6 , wherein the tensile strength of the nanocellulose fiber is from 2,000 MPa to 20,000 MPa.
15 . The superabsorbent polymer of claim 6 , wherein the absorption rate (vortex time) is from 10 seconds to 55 seconds, as measured according to JIS K 7224.
16 . The superabsorbent polymer of claim 6 , wherein the absorption capacity of 0.3 psi is from 18 g/g or more 30 g/g or less.