Superabsorbent Polymer Surface Crosslinking for Rewet Prevention
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Solution Overview
Problem
Superabsorbent polymers used in hygienic goods like diapers and sanitary pads face challenges in simultaneously improving centrifuge retention capacity and absorption under pressure, leading to rewet phenomena and urine leakage due to conflicting properties and pressure applications.
Innovation Solution
A method involving the preparation of superabsorbent polymers through crosslinking acrylic acid-based monomers with internal and epoxy-based surface crosslinking agents, followed by surface modification with hydrophobic materials, to enhance absorption properties and prevent rewet and urine leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the whole crosslinking density of superabsorbent polymer is controlled low, then centrifuge retention capacity becomes relatively high, but the crosslink structure becomes loose and gel strength decreases, thus deteriorating absorption under pressure
Solution Approach 1:
The patent applies local quality by introducing a surface crosslinking layer with high crosslinking density on the outer surface of the polymer particles, while maintaining low crosslinking density in the inner core. This creates a gradient structure where the surface layer provides strength and pressure resistance, while the inner core maintains high moisture absorption capacity. The surface crosslinking layer acts as a protective barrier that prevents structural collapse under pressure without restricting the swelling capability of the inner core.
Solution Approach 2:
The patent segments the polymer structure into two distinct regions: an inner core with low crosslinking density for absorption and an outer surface layer with high crosslinking density for strength. This segmentation allows each region to perform its specific function optimally - the core absorbs moisture while the surface maintains structural integrity and prevents deformation under external pressure.
2Strength
If the crosslinking density is controlled high to improve absorption under pressure, then gel strength increases, but it becomes difficult to absorb moisture between the dense crosslink structures, thus deteriorating centrifuge retention capacity
Solution Approach 1:
The patent implements local quality by creating a spatial variation in crosslinking density - high crosslinking density at the surface for strength and low crosslinking density in the core for absorption. This prevents the uniform high crosslinking that would block moisture absorption while still providing the necessary structural strength through the surface layer.
Solution Approach 2:
The patent divides the polymer into functional segments - an inner absorption core and an outer strength layer. The inner core with low crosslinking density maintains open structure for moisture penetration, while the outer layer with high crosslinking density provides mechanical strength and pressure resistance, thus resolving the contradiction between absorption and strength.
3Quantity of substance
If superabsorbent polymer absorbs liquid and then pressure is applied by the weight of a user, then rewet phenomenon occurs wherein a part of the liquid absorbed in the superabsorbent polymer exudes again
Solution Approach 1:
The patent applies local quality by creating a surface crosslinking layer that acts as a pressure-resistant barrier. This surface layer maintains its structural integrity under external pressure from the user's weight, preventing the collapsed structure that would otherwise cause liquid exudation. The surface crosslinks provide a stable network that holds absorbed liquid even when compressed.
Solution Approach 2:
The patent applies preliminary action by pre-forming a surface crosslinking layer before the polymer encounters usage conditions. This preliminary surface strengthening prevents structural collapse during actual use, thereby preventing rewet phenomenon and urine leakage that would occur with untreated polymers under pressure.
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 resulting superabsorbent polymers exhibit improved centrifuge retention capacity, absorption under pressure, and permeability, effectively preventing rewet and urine leakage while maintaining dryness and absorption performance.
Implementation Method 1
preparing base resin in which acrylic acid-based monomers having acid groups, of which at least a part are neutralized, and an internal crosslinking agent are crosslinked
Implementation Method 2
mixing hydrophobic material having HLB of 0 or more and 6 or less, and an epoxy-based surface crosslinking agent with the base resin
Implementation Method 3
increasing the temperature of the mixture of step 2 to conduct surface modification of the base resin
Data Source
AI summary
The present invention relates to superabsorbent polymer and a method for preparing the same. According to the method for preparing superabsorbent polymer of the present invention, superabsorbent polymer having improved rewet property and absorption speed can be provided.