Superabsorbent Polymer Surface Crosslinking Rewetting
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Solution Overview
Problem
Superabsorbent polymers face challenges in simultaneously enhancing centrifuge retention capacity and absorbency under load while preventing the rewetting phenomenon, which affects their performance in hygienic materials like diapers and sanitary napkins.
Innovation Solution
A superabsorbent polymer with a crosslinked polymer structure and a surface-crosslinked layer is developed, using water-soluble ethylene-based unsaturated monomers and internal and surface crosslinking agents, achieving a low saline extraction rate from empty spaces between swollen gel particles, thereby preventing rewetting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the overall crosslinking density of the superabsorbent polymer is controlled to be low, then centrifuge retention capacity becomes relatively high, but a crosslinking structure becomes loose and gel strength becomes low, leading to a reduction in absorbency under load
Solution Approach 1:
The patent applies local quality by creating a surface-crosslinked layer on the base resin powder, where only the surface region has high crosslinking density while the interior maintains lower crosslinking density. This is achieved by treating the base resin powder with a crosslinking agent under controlled conditions to form a shell-like crosslinked structure, allowing the surface to provide strength while the interior provides absorption capacity.
Solution Approach 2:
The patent segments the superabsorbent polymer into two distinct structural regions: a base resin powder core and a surface-crosslinked layer shell. This segmentation allows each region to fulfill different functions - the core provides centrifuge retention capacity through low crosslinking density, while the shell provides absorbency under load through high crosslinking density.
2Strength
If the crosslinking density is controlled to be high, then absorbency under load is improved, but water is hardly absorbed between compact crosslinking structures, leading to a reduction in basic centrifuge retention capacity
Solution Approach 1:
The patent implements local quality by concentrating high crosslinking density only in the surface layer while maintaining low crosslinking density in the interior. The surface-crosslinked layer is formed by exposing the base resin powder to a crosslinking agent, creating a gradient structure where crosslinking intensity decreases from the surface toward the core, enabling both high strength and high absorption capacity.
Solution Approach 2:
The patent divides the polymer structure into functional segments: an outer shell with high crosslinking density for mechanical strength, and an inner core with low crosslinking density for maximum water absorption. This segmentation resolves the contradiction by assigning different crosslinking densities to different spatial regions.
3Reliability
If absorbency under load is enhanced to prevent rewetting phenomenon, then liquid retention is improved, but the structure may become too compact affecting liquid permeability
Solution Approach 1:
The patent applies local quality by creating a surface-crosslinked layer that provides the necessary mechanical strength and liquid retention properties to prevent rewetting, while the interior base resin maintains high porosity and low crosslinking density to ensure rapid liquid permeability. The surface layer acts as a barrier that holds liquid without becoming overly compact.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The polymer exhibits improved centrifuge retention capacity, absorbency under load, and liquid permeability, maintaining a fluffy texture in hygienic materials even after fluid discharge by minimizing saline retention in empty spaces, effectively preventing rewetting.
Implementation Method 1
A superabsorbent polymer (SAP) is a synthetic polymeric material capable of absorbing moisture from about 500 to 1000 times its own weight
Implementation Method 2
centrifuge retention capacity (CRC), which is a basic physical property of showing water absorption and retention capacities of the superabsorbent polymer
Implementation Method 3
a surface-crosslinked layer formed on the base resin powder, in which the surface-crosslinked layer is obtained by additionally crosslinking the crosslinked polymer in the presence of a surface crosslinking agent
Data Source
Figure 1~2
Figure 3~4
AI summary
Provided are a superabsorbent polymer and a preparation method thereof. The superabsorbent polymer may effectively avoid a rewetting phenomenon after absorbing liquid, because a saline solution hardly remains in the empty spaces between swollen gel particles. Accordingly, the superabsorbent polymer may be used to provide hygienic materials, such as diapers, sanitary napkins, etc., which have a fluffy texture even after body fluid is discharged thereto.