Water-Absorbing Polymer Particles with Ionic Surfactants
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Solution Overview
Problem
Existing methods for producing water-absorbing polymer particles struggle to achieve high free swell rates while maintaining optimal centrifuge retention capacity and permeability, particularly under pressure, in hygiene products like diapers and tampons.
Innovation Solution
A process involving the polymerization of a monomer solution containing ethylenically unsaturated monomers with acid groups, crosslinkers, initiators, and ethylenically unsaturated ionic surfactants, which increases the free swell rate by modifying the surface tension and polymer network structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the amount of crosslinker is increased to improve absorption under pressure, then the centrifuge retention capacity falls
Solution Approach 1:
The patent applies different crosslinking densities to different parts of the polymer particle - the surface is heavily crosslinked while the core maintains lower crosslinking. This is achieved by performing surface postcrosslinking after bulk polymerization, allowing the particle surface to have high crosslink density for pressure resistance while the core retains porosity for fluid retention
Solution Approach 2:
The patent performs bulk polymerization and crosslinking first to establish the core structure with appropriate porosity and absorption capacity, then subsequently applies surface postcrosslinking to modify only the particle surface. This sequential approach allows optimization of both core and surface properties independently
2Productivity
If surface postcrosslinking is performed to improve permeability and absorption under pressure, then the centrifuge retention capacity is decoupled but requires additional processing steps
Solution Approach 1:
The patent combines bulk polymerization, bulk crosslinking, and surface postcrosslinking into a unified multi-stage process using the same reactor system. The surface postcrosslinking is performed by adding crosslinker solution to the already polymerized particles in the same reactor, eliminating the need for separate coating equipment
Solution Approach 2:
The patent uses the same reactor system to perform multiple functions - bulk polymerization, bulk crosslinking, and surface postcrosslinking. The reactor serves as both the polymerization vessel and the surface treatment vessel, reducing equipment complexity
3Quantity of substance
If conventional monomers are used to achieve high absorption capacity, then the free swell rate remains insufficient for optimal hygiene product performance
Solution Approach 1:
The patent modifies the chemical composition parameters of the monomer mixture by incorporating specific comonomers with different functional groups and hydrophilicities. This changes the polymer network structure to achieve both high absorption capacity and rapid swelling by optimizing the balance between crosslinking density and hydrophilic pathways
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 enhances the free swell rate, centrifuge retention capacity, and permeability of water-absorbing polymer particles, improving their performance in hygiene products by incorporating ethylenically unsaturated ionic surfactants that enhance the polymer network's properties.
Implementation Method 1
The ethylenically unsaturated ionic surfactants for use in accordance with the invention are interface-active compounds which lower the surface tension of water, preferably below 70 mN/m, more preferably below 68 mN/m, most preferably below 67 mN/m
Implementation Method 2
a process for producing water-absorbing polymer particles by polymerizing a monomer solution or suspension comprising an ethylenically unsaturated monomer which bears acid groups and may be at least partly neutralized, at least one crosslinker, at least one initiator
Implementation Method 3
Crosslinkers suitable for that purpose are compounds which can form covalent bonds to at least two carboxylate groups of the water-absorbing polymer particles
Data Source
AI summary
A process for producing water-absorbing polymer particles with high free swell rate by polymerizing a monomer solution or suspension comprising an ethylenically unsaturated monomer bearing acid groups, a crosslinker, an initiator and an ethylenically unsaturated ionic surfactant.