Water-absorbing polymer particles surface crosslinking
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Solution Overview
Problem
Current methods for producing water-absorbing polymer particles struggle to achieve a high swell rate combined with high retention capacity while maintaining favorable permeability of the swollen gel bed, often resulting in a trade-off between these properties.
Innovation Solution
A process involving polymerization of ethylenically unsaturated monomers with acid groups and crosslinkers, followed by pelletization through a die plate under controlled conditions, drying, grinding, classifying, and surface crosslinking, which enhances the surface area and flow conductivity of the polymer particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of crosslinker is increased to improve retention capacity, then the centrifuge retention capacity falls and the absorption under load passes through a maximum
Solution Approach 1:
The patent applies surface crosslinking to create a crosslinked skin layer on the particle surface while maintaining a different crosslinking density in the particle core. This local differentiation allows the surface to provide retention capacity while the core maintains absorption capacity, resolving the contradiction between these two properties.
Solution Approach 2:
The patent divides the polymer particle into functionally distinct regions: a crosslinked surface layer for retention and an uncrosslinked or lightly crosslinked core for absorption. This segmentation allows each region to optimize its function independently, achieving both high retention capacity and high absorption under load.
2Speed
If the swell rate is increased to improve absorption rate, then the retention capacity is lowered with comparable permeability
Solution Approach 1:
The surface crosslinked structure creates a porous skin layer that facilitates rapid liquid penetration (high swell rate) while the crosslinked network at the surface maintains retention capacity. The local porous structure at the surface resolves the contradiction between fast absorption and retention.
Solution Approach 2:
The patent creates a microporous structure on the particle surface through surface crosslinking, which allows rapid liquid uptake while maintaining structural integrity for retention. The porous surface layer enables high swell rate without sacrificing retention capacity.
3Quantity of substance
If the superabsorbent content is increased to improve absorption capacity, then the permeability of the swollen gel bed is reduced due to gel blocking
Solution Approach 1:
The surface crosslinked porous structure prevents gel blocking by maintaining open channels at the particle surface even at high superabsorbent loading. This local porous architecture allows liquid to penetrate through the particle surface without being blocked by the swollen gel, enabling high superabsorbent content while maintaining permeability.
4Productivity
If surface crosslinking is applied to improve permeability and absorption under load, then the retention capacity may be affected
Solution Approach 1:
Surface crosslinking creates a localized crosslinked layer at the particle surface that provides both permeability enhancement and retention capacity. The crosslinked surface structure prevents particle disintegration while maintaining porosity for liquid flow, achieving both improved absorption under load and retained centrifuge retention capacity.
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 process results in water-absorbing polymer particles with improved free swell rate, centrifuge retention capacity, and a favorable ratio of permeability to retention capacity, optimizing their performance in hygiene articles.
Implementation Method 1
The polymer chains of the water-absorbing polymer particles are crosslinked with one another. One effect of this is that the polymer particles are water-insoluble.
Implementation Method 2
water-absorbing polymer particles having a high swell rate and a high retention capacity
Implementation Method 3
the ability of the hydrogel to conduct liquid (permeability) and distribute it
Data Source
AI summary
A process for producing water-absorbing polymer particles is provided, comprising a) a polymerization step in which an aqueous monomer solution comprising at least one ethylenically unsaturated monomer M which bears acid groups and may have been at least partly neutralized and at least one crosslinker is polymerized to obtain an aqueous polymer gel; b) a pelletization step in which the aqueous polymer gel having a solids content of 35 to 70% by weight and a temperature of 75 to 125° C. is forced from a high-pressure zone through a die plate into a low-pressure zone and pellets are obtained, the pressure differential between the high-pressure zone and the low-pressure zone being 4 to less than 14 bar and the orifice ratio of the die plate being 30 to 80%; c) a drying step in which the pellets are dried to a moisture content of less than 10% by weight; d) a grinding step and a classifying step to obtain water-absorbing polymer particles; and e) surface crosslinking of the water-absorbing polymer particles. The water-absorbing polymer particles have a high swell rate and a high retention capacity combined with a favorable ratio of permeability of the swollen gel bed SFC to centrifuge retention capacity CRC.