Super Absorbent Polymer Crosslinking for Rewetting and Pressure Absorption

Solution Overview

Problem

Super absorbent polymers face challenges in simultaneously enhancing water retention capacity and absorption ability under pressure, while also preventing rewetting and urine leakage phenomena, especially in hygiene products like diapers and sanitary napkins.

Innovation Solution

A preparation method involving the cross-linking of acrylic acid-based monomers with a specific combination of internal and surface cross-linking agents, including poly(meth)acrylate of polyols and polyglycidyl ether of polyols, and the use of a polyvalent metal salt to optimize the cross-linking structure and gel strength, resulting in a super absorbent polymer with improved rewetting properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If the overall crosslink density of the super absorbent polymer is controlled to be low, then the water retention capacity (CRC) may relatively increase, but the absorption ability under pressure (AUP) may decrease because the cross-linked structure becomes loose and the gel strength is reduced

Engineering Contradiction:

Improvewater retention capacityVSAvoidabsorption ability under pressure

Core Design Contradiction:

Quantity of substanceVSStrength

Solution Approach 1:

The patent applies local quality by creating different crosslinking densities in different regions of the polymer structure. The internal crosslinking agent (poly(meth)acrylate of polyols) provides a loose crosslinked structure in the interior for high water retention capacity, while the surface crosslinking agent (polyglycidyl ether of polyols) creates a dense crosslinked shell for high absorption ability under pressure and gel strength. This spatial differentiation of structure allows simultaneous optimization of both contradictory properties.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent uses composite materials by combining two different crosslinking agents with distinct chemical structures and functions. The internal crosslinking agent (poly(meth)acrylate of polyols) and surface crosslinking agent (polyglycidyl ether of polyols) form a composite crosslinked network where each component contributes its unique properties. The epoxy groups of the surface crosslinking agent form strong crosslinks at the particle surface, while the internal crosslinking agent provides a more open network structure for water absorption.

Inventive Principle:

Principle #40Composite materials

2Strength

If the cross-linking density is controlled to be high for improving the absorption ability under pressure (AUP), then the basic water retention capacity (CRC) may decrease because moisture is hardly absorbed through the dense cross-linked structure

Engineering Contradiction:

Improveabsorption ability under pressureVSAvoidwater retention capacity

Core Design Contradiction:

StrengthVSQuantity of substance

Solution Approach 1:

The patent applies local quality by creating different crosslinking densities in different regions of the polymer structure. The internal crosslinking agent (poly(meth)acrylate of polyols) provides a loose crosslinked structure in the interior for high water retention capacity, while the surface crosslinking agent (polyglycidyl ether of polyols) creates a dense crosslinked shell for high absorption ability under pressure and gel strength. This spatial differentiation of structure allows simultaneous optimization of both contradictory properties.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent uses composite materials by combining two different crosslinking agents with distinct chemical structures and functions. The internal crosslinking agent (poly(meth)acrylate of polyols) and surface crosslinking agent (polyglycidyl ether of polyols) form a composite crosslinked network where each component contributes its unique properties. The epoxy groups of the surface crosslinking agent form strong crosslinks at the particle surface, while the internal crosslinking agent provides a more open network structure for water absorption.

Inventive Principle:

Principle #40Composite materials

3Quantity of substance

If the super absorbent polymer is made thinner to meet hygiene product requirements, then higher absorption performance is required, but it becomes more difficult to maintain shape and prevent rewetting in expanded state

Engineering Contradiction:

Improveabsorption performanceVSAvoidshape maintenance in expanded state

Core Design Contradiction:

Quantity of substanceVSShape

Solution Approach 1:

The patent applies the principle of flexible shells by forming a surface crosslinked layer that acts as a flexible skin on the polymer particles. This surface layer, created by the polyglycidyl ether of polyols crosslinking agent, provides mechanical strength and shape maintenance to the particles even when they are highly swollen with water. The flexible shell prevents particle collapse and maintains the expanded structure necessary for liquid permeability while preventing rewetting.

Inventive Principle:

Principle #30Flexible shells and thin films

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 method effectively enhances the absorption properties of super absorbent polymers, including water retention, absorption under pressure, and liquid permeability, while significantly reducing rewetting and urine leakage phenomena.

Implementation Method 1

an acrylic acid-based monomer having at least partially neutralized acidic groups and an internal cross-linking agent are cross-linked and polymerized

Methodology Applied

Scientific EffectCross-linking: Chemical Bonding

Implementation Method 2

an acrylic acid-based monomer having at least partially neutralized acidic groups and an internal cross-linking agent are cross-linked and polymerized

Methodology Applied

Scientific EffectPolymerization: Photopolymerisation

Implementation Method 3

heating the base resin in the presence of a surface cross-linking agent and a polyvalent metal salt to carry out surface modification

Methodology Applied

Scientific EffectSurface cross-linking: Chemical Bonding

Implementation Method 4

heating the base resin in the presence of a surface cross-linking agent and a polyvalent metal salt to carry out surface modification

Methodology Applied

Scientific EffectHeating: Heating

Implementation Method 5

A super absorbent polymer (SAP) is a type of synthetic polymeric material capable of absorbing 500 to 1000 times its own weight of moisture

Methodology Applied

Scientific EffectAbsorption: Absorption (physical)

Data Source

PatentEP3521343B1Absorbent polymer and preparation method therefor

Publication Date: 2024.03.27 LG CHEM LTD

AI summary

The present disclosure relates to a super absorbent polymer exhibiting improved rewetting property and excellent absorption property, and a preparation method of the same. This preparation method of a super absorbent polymer includes the steps of: preparing a base resin in which an acrylic acid-based monomer having at least partially neutralized acidic groups and an internal cross-linking agent are cross-linked and polymerized; and heating the base resin in the presence of a surface cross-linking agent to carry out surface modification, wherein the internal cross-linking agent includes a poly(meth)acrylate of polyols-based first internal cross-linking agent and a polyglycidyl ether of polyols-based second internal cross-linking agent in a specific weight ratio.