Permeable Superabsorbent via Aluminum Hydroxide and Crosslinking
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Solution Overview
Problem
There is a need for improved permeable superabsorbents with enhanced permeability without compromising their absorption capacity and swelling kinetics, particularly for use in hygiene products and other applications where fluid absorption is critical.
Innovation Solution
A process for producing superabsorbents involves polymerizing an aqueous monomer solution with acid-bearing ethylenically unsaturated monomers, crosslinkers, and initiators, followed by drying, grinding, and sieving, with the addition of x-ray-amorphous aluminum hydroxide during or after surface postcrosslinking to enhance permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the degree of crosslinking is increased to improve gel strength, then permeability is improved, but absorption capacity is reduced
Solution Approach 1:
The patent applies different crosslinking densities to different regions of the superabsorbent particle. The surface layer has a higher degree of crosslinking (improving gel strength and permeability) while the core maintains a lower degree of crosslinking (preserving absorption capacity). This spatial differentiation of properties resolves the contradiction between needing strong gel structure and maintaining high absorption capability.
2Quantity of substance
If conventional superabsorbents are used, then absorption capacity is achieved, but permeability is insufficient leading to gel blocking
Solution Approach 1:
The invention creates a surface-modified superabsorbent where only the outer shell undergoes enhanced crosslinking while the interior remains unchanged. This localized modification improves permeability at the surface (preventing gel blocking) without compromising the absorption capacity of the bulk material.
Solution Approach 2:
The surface postcrosslinking is performed as a preliminary treatment before the superabsorbent is used in its final application. This pre-treatment establishes the necessary permeability characteristics in advance, ensuring that the material is ready to prevent gel blocking from the outset while maintaining its full absorption potential.
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 superabsorbents exhibit improved permeability without significant impairment in centrifuge retention capacity or absorption under pressure, making them suitable for various fluid absorption applications, including hygiene products.
Implementation Method 1
Superabsorbents are capable of absorbing several times their own weight of water and of retaining it under a certain pressure
Implementation Method 2
The superabsorbent, which is used in the form of a dry powder, is converted to a gel when it absorbs fluid, and correspondingly to a hydrogel when it absorbs water
Implementation Method 3
an elegant method of increasing the gel strength is that of increasing the degree of crosslinking at the surface of the superabsorbent particles compared to the interior of the particles
Data Source
AI summary
A highly permeable superabsorbent is prepared by a process comprisingpolymerizing an aqueous monomer solution comprisinga) at least one ethylenically unsaturated monomer which bears acid groups and is optionally at least partly in salt form,b) at least one crosslinker,c) at least one initiator,d) optionally one or more ethylenically unsaturated monomers copolymerizable with the monomers mentioned under a), ande) optionally one or more water-soluble polymers;drying the resulting polymer,optionally grinding the dried polymer and sieving the ground polymer,optionally surface postcrosslinking the dried and optionally ground and sieved polymer,wherein, after drying, grinding or sieving, and, if surface postcrosslinking is conducted, during or after this surface postcrosslinking, x-ray-amorphous aluminum hydroxide powder is added.