Water-Absorbing Polymer Permeability and Absorption Balance

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Solution Overview

Problem

Water-absorbing polymers typically face a trade-off between absorption capacity and permeability, with post-crosslinking reducing absorption capacity while improving permeability, and existing methods struggle to achieve high levels of both properties simultaneously.

Innovation Solution

A process involving the polymerization of a monomer solution with specific ethylenically unsaturated acid group-bearing monomers, controlled use of crosslinkers and post-crosslinkers, and treatment with polyvalent cations to enhance permeability without significantly reducing absorption capacity, using smaller amounts of crosslinkers and post-crosslinkers to achieve additive behavior between absorption capacity and permeability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If post-crosslinking is performed to improve permeability, then permeability is improved, but absorption capacity decreases

Engineering Contradiction:

ImprovepermeabilityVSAvoidabsorption capacity

Core Design Contradiction:

Use of energy by moving objectVSQuantity of substance

Solution Approach 1:

The patent applies parameter changes by precisely controlling the amounts of crosslinker (0.01 to 0.5% by weight) and post-crosslinker (0.05 to 0.25% by weight, specifically excluding polyols) to achieve optimal balance between permeability and absorption capacity. The exclusion of polyols as post-crosslinkers and the specific concentration ranges represent parameter optimization to resolve the contradiction.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite structure by combining the base polymer with specific crosslinking agents and post-crosslinking agents in controlled amounts. This composite approach allows the material to exhibit both high absorption capacity (through the polymer network) and high permeability (through controlled crosslinking density), resolving the contradiction between these two properties.

Inventive Principle:

Principle #40Composite materials

2Use of energy by moving object

If crosslinker amount is increased to improve permeability, then permeability is improved, but absorption capacity drops significantly

Engineering Contradiction:

ImprovepermeabilityVSAvoidabsorption capacity

Core Design Contradiction:

Use of energy by moving objectVSQuantity of substance

Solution Approach 1:

The patent applies partial action by using small, controlled amounts of crosslinker (0.01 to 0.5% by weight) and post-crosslinker (0.05 to 0.25% by weight) rather than large amounts. This partial crosslinking approach is sufficient to improve permeability while minimizing the negative impact on absorption capacity, thus resolving the contradiction.

Inventive Principle:

Principle #16Partial or excessive action

3Use of energy by moving object

If polyol post-crosslinkers are used to improve permeability, then permeability is improved, but absorption capacity decreases undesirably

Engineering Contradiction:

ImprovepermeabilityVSAvoidabsorption capacity

Core Design Contradiction:

Use of energy by moving objectVSQuantity of substance

Solution Approach 1:

The patent specifically excludes polyols as post-crosslinkers because they cause undesirably large drops in absorption capacity. By eliminating this class of crosslinking agents and using alternative post-crosslinkers in controlled amounts (0.05 to 0.25% by weight), the patent achieves permeability improvement while preserving absorption capacity.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 produces water-absorbing polymers with high centrifuge retention capacity and permeability, maintaining absorption capacity while increasing permeability, suitable for use in hygiene products and agricultural applications.

Implementation Method 1

whereby the monomer solution polymerizes

Methodology Applied

Scientific EffectPolymerization: Photopolymerisation

Implementation Method 2

Crosslinkers suitable for this are compounds which contain at least two groups which can form covalent bonds with the carboxylate groups of the hydrophilic polymer

Methodology Applied

Scientific EffectCovalent bonding: Chemical Bonding

Implementation Method 3

0.05 to 0.5% by weight of at least one polyvalent cation, based on the polymer, is treated afterwards

Methodology Applied

Scientific EffectIonic interaction: Ion Repulsion/Attraction

Data Source

PatentEP1960440B1Process for preparing water-absorbing polymers with high absorption capacity and high permeability

Publication Date: 2017.01.11 BASF SE

AI summary

A process for preparing water-absorbing polymers by polymerizing a monomer solution comprising at least one ethylenically unsaturated monomer which bears acid groups and may be at least partly neutralized, from 0.01 to 0.5% by weight of at least one crosslinker, based on the monomer, wherein the monomer solution is polymerized and the resulting polymer is aftertreated with from 0.05 to 0.25% by weight of at least one postcrosslinker, based on the polymer, where the postcrosslinker is not a polyol, and from 0.05 to 0.5% by weight of at least one polyvalent cation, based on the polymer.