Super absorbent polymer
A polyacrylic acid (salt)-based super absorbent polymer may be analyzed by a time-domain nuclear magnetic resonance spectroscopy (TD-NMR) analysis. The results of the TD-NMR analysis may satisfy Equation 1. In Equation 1, N t=0.1 is a normalized intensity measured at a signal acquisition time of 0.1 ms. 2.5 ( % ) ≤ N t = 0.1 ( % ) ≤ 3.5 ( % ) [ Equation 1 ]
1 . A polyacrylic acid (salt)-based super absorbent polymer,
wherein a TD-NMR analysis result satisfies Equation 1, and
wherein the polyacrylic acid (salt)-based super absorbent polymer has an average convexity value of 0.93 or less and 0.87 or more for all particles, calculated using Equation 2:
2.5
(
%
)
≤
N
t
=
0.1
(
%
)
≤
3
.
5
(
%
)
[
Equation
1
]
M
c
=
L
s
/
L
[
Equation
2
]
wherein in Equation 1 and Equation 2,
N t=0.1 is a normalized intensity measured at a signal acquisition time of 0.1 ms,
M c is convexity,
L s is a length of a perimeter of a polygon of minimal perimeter that surrounds a two-dimensional (2D) image of a three-dimensional (3D) particle to be measured, and
L is an actual perimeter length of the 2D image of the 3D particle to be measured.
2 . The polyacrylic acid (salt)-based super absorbent polymer of claim 1 , wherein the polyacrylic acid (salt)-based super absorbent polymer has an extractable component content of 10 wt % or less based on a total weight of the polyacrylic acid (salt)-based super absorbent polymer, measured after free swelling in water having an electrical conductivity of 100 to 130 μS/cm for 30 minutes.
3 . The polyacrylic acid (salt)-based super absorbent polymer of claim 1 , wherein the polyacrylic acid (salt)-based super absorbent polymer has an extractable component content of 17 wt % or less based on a total weight of the polyacrylic acid (salt)-based super absorbent polymer, measured after free swelling in water having an electrical conductivity of 100 to 130 μS/cm for 3 hours.
4 . The polyacrylic acid (salt)-based super absorbent polymer of claim 1 , wherein the polyacrylic acid (salt)-based super absorbent polymer has an absorbency under pressure (AUP) of 28 g/g or more, measured under 0.3 psi according to EDANA method WSP 242.3.
5 . The polyacrylic acid (salt)-based super absorbent polymer of claim 1 , wherein the polyacrylic acid (salt)-based super absorbent polymer has a centrifuge retention capacity (CRC) of 33 g/g or more, measured according to EDANA method WSP 241.3.
6 . The polyacrylic acid (salt)-based super absorbent polymer of claim 1 , wherein the polyacrylic acid (salt)-based super absorbent polymer has an effective absorption capacity (EFFC) of 30 g/g or more, calculated by the Equation 3:
EFFC
=
(
C
R
C
+
A
UP
)
/
2
[
Equation
3
]
wherein in Equation 3,
CRC is a centrifuge retention capacity (units: g/g) measured according to EDANA method WSP 241.3, and
AUP is an absorbency under pressure (units: g/g) measured under 0.3 psi according to EDANA method WSP 242.3.
7 . The polyacrylic acid (salt)-based super absorbent polymer of claim 1 , wherein the polyacrylic acid (salt)-based super absorbent polymer has an absorption rate (vortex time) of 40 seconds or less measured by a vortex measurement method at 24.0° C.
8 . The polyacrylic acid (salt)-based super absorbent polymer of claim 1 , wherein when the polyacrylic acid (salt)-based super absorbent polymer is swelled in water having an electrical conductivity of 100 to 130 μS/cm for 1 minute, a maximum capacity of water that the polyacrylic acid (salt)-based super absorbent polymer is able to hold (free swelling capacity) is 170 g/g or more.
9 . The polyacrylic acid (salt)-based super absorbent polymer of claim 1 , wherein the polyacrylic acid (salt)-based super absorbent polymer has a liquid permeability of 65 ml or more, calculated by Equation 4:
Perm
=
[
20
mL
/
T
1
(
sec
)
]
×
60
sec
[
Equation
4
]
wherein in Equation 4,
Perm is liquid permeability, and
T1 is a time (seconds) taken for 20 mL of saline to pass through the polyacrylic acid (salt)-based super absorbent polymer under a pressure of 0.3 psi after placing 0.2 g of the polyacrylic acid (salt)-based super absorbent polymer in a cylinder, pouring saline (0.9 wt % sodium chloride aqueous solution) so that the polyacrylic acid (salt)-based super absorbent polymer is completely submerged, and allowing the polyacrylic acid (salt)-based super absorbent polymer to swell for 30 minutes.
10 . The polyacrylic acid (salt)-based super absorbent polymer of claim 1 , wherein the polyacrylic acid (salt)-based super absorbent polymer comprises pores of 100 μm or less.