Super Absorbent Polymer with Gradient Crosslinking for Load Retention
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Solution Overview
Problem
Super absorbent polymers face challenges in simultaneously achieving high centrifuge retention capacity and absorbency under load while preventing rewetting phenomena, especially in hygiene products like diapers and sanitary napkins, due to conflicting physical properties and external pressure issues.
Innovation Solution
A super absorbent polymer composition comprising porous particles, secondary granule particles, and non-porous particles with specific weight percentages and surface characteristics, optimized through a crosslinking polymerization process involving a foam-promoting agent and silicone-based surfactant, to enhance absorption rate and prevent rewetting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the overall crosslinking density of the super absorbent polymer is controlled to be low, then the centrifuge retention capacity can be relatively high, but the crosslinking structure may be loose, the gel strength may be low and thus the absorbency under load may be lowered
Solution Approach 1:
The patent applies local quality by creating particles with non-uniform crosslinking density - the surface layer has higher crosslinking density while the inner core has lower crosslinking density. This allows the surface to provide structural strength and gel stability while the inner core maintains high moisture absorption capacity, thereby simultaneously improving both gel strength and centrifuge retention capacity without the trade-off present in uniformly crosslinked structures.
2Strength
If controlling the crosslink density to a high level to improve the absorbency under load, then it becomes difficult for moisture to be absorbed between densely crosslinked structures, so that the basic centrifuge retention capacity may be lowered
Solution Approach 1:
The patent resolves this contradiction by implementing local quality through spatially differentiated crosslinking - the surface layer is highly crosslinked to provide structural integrity and load-bearing capacity, while the inner core remains less crosslinked to maintain open network structures that facilitate moisture absorption. This gradient structure enables both high absorbency under load and high centrifuge retention capacity to coexist.
3Quantity of substance
If super absorbent polymer absorbs liquid and then pressure is applied due to the weight of the user, then a rewetting phenomenon where some liquid absorbed in the super absorbent polymer again leak out can occur
Solution Approach 1:
The patent applies preliminary action by pre-forming a dense crosslinked surface layer on the particles before they are used in the absorbent structure. This surface layer acts as a preliminary barrier that prevents liquid from penetrating back into the particle interior when external pressure is applied, thereby suppressing the rewetting phenomenon before it can occur. The surface crosslinked layer is formed during the polymerization process, creating a protective shell that maintains absorption reliability under load.
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 optimized polymer exhibits excellent absorption capacity, absorbency under load, and liquid permeability, effectively preventing rewetting even under external pressure, ensuring improved performance in hygiene products.
Implementation Method 1
a super absorbent polymer comprising: porous particles in which a plurality of pores having an average pore diameter of 10 μm or more are formed on the surface
Implementation Method 2
Super absorbent polymer (SAP) is a synthetic polymer material capable of absorbing moisture from about 500 to about 1,000 times its own weight
Implementation Method 3
the crosslinking structure may be loose, the gel strength may be low and thus the absorbency under load may be lowered
Implementation Method 4
when the overall crosslinking density of the super absorbent polymer is controlled to be low
Data Source
AI summary
A method of preparing super absorbent polymer includes carrying out a crosslinking polymerization of a monomer mixture comprising a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups, a forming agent, a foam-promoting agent and a silicone-based surfactant in the presence of an internal crosslinking agent to form a hydrogel polymer; drying, pulverizing and classifying the hydrogel polymer to form a base polymer powder; and further crosslinking a surface of the base polymer powder in the presence of a surface crosslinking agent to form a surface crosslinked layer. The method produces super absorbent polymer having not only an excellent absorbent capacity and an absorbency under load but also the rewetting phenomenon can be effectively prevented.