Water-Absorbing Polymer Particles with Gradient Crosslinking
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Solution Overview
Problem
Existing methods for producing water-absorbing polymer particles often compromise between high free swell rate (FSR) and high centrifuge retention capacity (CRC), with increased FSR typically leading to decreased CRC, and vice versa, while also facing challenges in achieving high permeability of the swollen gel bed.
Innovation Solution
A process involving polymerization of an aqueous monomer solution with ethylenically unsaturated monomers, crosslinkers, and initiators in a reactor with axially parallel rotating shafts, followed by extrusion at high temperatures and thermal surface postcrosslinking, using specific conditions to optimize FSR, CRC, and permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of crosslinker is increased to improve centrifuge retention capacity (CRC), then CRC increases, but absorption under pressure (AUL) decreases
Solution Approach 1:
The patent applies different crosslinking densities to different regions of the polymer particle. The core maintains higher crosslinking density for structural integrity and CRC, while the surface has optimized crosslinking for absorption performance. This spatial differentiation of crosslinking quality allows simultaneous achievement of high CRC and high AUL without the traditional trade-off.
Solution Approach 2:
The patent performs preliminary crosslinking during the polymerization process to establish the core structure with appropriate crosslinking density before the particles are fully formed. This preliminary crosslinking action creates a stable framework that maintains CRC while allowing subsequent surface development for optimal absorption capacity.
2Productivity
If surface postcrosslinking is performed to improve permeability of the swollen gel bed, then permeability increases, but manufacturing complexity increases
Solution Approach 1:
The patent combines multiple functions into the polymerization reactor itself. The reactor performs both polymerization and crosslinking operations in a single integrated system, eliminating the need for separate surface postcrosslinking equipment. This merging of functions achieves the desired permeability while reducing manufacturing complexity by consolidating process steps.
Solution Approach 2:
The patent implements continuous crosslinking during the polymerization process rather than as a separate batch operation. The crosslinking reaction proceeds continuously alongside polymerization, maintaining productive action throughout the process and eliminating idle time between steps, thereby improving overall manufacturing efficiency.
3Speed
If free swell rate is increased to improve absorption speed, then FSR increases, but centrifuge retention capacity (CRC) decreases
Solution Approach 1:
The patent creates different structural qualities in different regions of the particle. The core maintains higher crosslinking density for CRC while the surface and interior pathways are optimized for rapid water penetration and swelling. This local differentiation allows the particle to simultaneously achieve fast swelling kinetics and high centrifuge retention.
Solution Approach 2:
The patent addresses the FSR-CRC trade-off by transitioning from uniform particle properties to spatially differentiated structures. By controlling crosslinking density as a gradient or distributed property throughout the particle volume rather than uniformly, the invention optimizes both swelling speed and retention capacity through three-dimensional structural design.
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 achieves water-absorbing polymer particles with enhanced FSR, CRC, and permeability, specifically exceeding 0.3 g/g s, 25 g/g, and 130×10−7 cm3 s/g respectively, while maintaining a suitable particle size distribution for improved performance in hygiene products.
Implementation Method 1
polymerization of an aqueous monomer solution in a polymerization reactor having at least two shafts (kneaders) which rotate in an axially parallel manner
Implementation Method 2
at least 60 kWh/t of specific mechanical energy being introduced in the course of extrusion
Implementation Method 3
extruding the polymer gel prior to drying, the polymer gel during the extrusion having a temperature greater than 80° C.
Implementation Method 4
extrusion at high temperatures
Implementation Method 5
thermally surface postcrosslinking
Implementation Method 6
surface postcrosslinking can be performed in aqueous gel phase
Data Source
AI summary
A process for producing water-absorbing polymer particles having high free swell rate and high centrifuge retention capacity with simultaneously high permeability of the swollen gel bed by polymerization of an aqueous monomer solution in a polymerization reactor having at least two shafts (kneaders) which rotate in an axially parallel manner, subsequent extrusion at high temperatures and thermal surface postcrosslinking.