Super Absorbent Polymer Metal Cation Cross-Linking
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Solution Overview
Problem
Super absorbent polymers face a challenge in maintaining high absorption performance while increasing gel strength, as improving gel strength through surface cross-linking density leads to decreased moisture absorption and retention capacity.
Innovation Solution
A method involving the formation of a hydrogel polymer by cross-linking and polymerizing a water-soluble ethylene-based unsaturated monomer, followed by surface cross-linking and the addition of a monovalent to trivalent metal cation at controlled temperatures and aging, to optimize ionic functional groups and maintain gel strength while enhancing absorption performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If surface cross-linking density is increased to improve gel strength, then gel strength is improved, but absorption performance deteriorates
Solution Approach 1:
The patent applies preliminary action by adding a metal cation before the surface cross-linking step. This metal cation addition modifies the polymer structure in advance, creating ionic cross-links that provide initial gel strength. When surface cross-linking is subsequently applied, the absorption performance deterioration is mitigated because the metal cation already established a cross-linking network that prevents excessive densification of the surface structure.
Solution Approach 2:
The patent utilizes parameter changes by introducing metal cations (such as Ca2+, Mg2+, or Zn2+) that change the ionic state of the polymer. This parameter change creates ionic cross-links with different bonding characteristics than conventional covalent cross-links, allowing the polymer to maintain gel strength while preserving more open structure for absorption. The metal cation concentration and type can be adjusted to optimize the balance between gel strength and absorption performance.
2Strength
If surface cross-linking is performed at high temperature to increase gel strength, then gel strength is improved, but moisture absorption capacity decreases
Solution Approach 1:
The metal cation addition is performed as a preliminary action before high-temperature surface cross-linking. This preliminary modification allows the polymer to withstand the high-temperature cross-linking process better, as the metal cation-ionic cross-links provide structural support that prevents excessive collapse of the polymer network during thermal treatment.
Solution Approach 2:
The patent creates a composite structure by combining metal cation-ionic cross-links with covalent cross-links from surface cross-linking. This composite cross-linking system leverages the strengths of both bonding types: ionic bonds provide reversible, water-soluble cross-links that maintain gel strength while allowing water penetration, while covalent bonds provide stable structural support.
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 results in a super absorbent polymer with improved water retention capacity and absorbency under pressure, maintaining excellent gel strength and liquid permeability, suitable for thin sanitary products with reduced pulp content.
Implementation Method 1
forming a hydrogel polymer by cross-linking and polymerizing a water-soluble ethylene-based unsaturated monomer
Implementation Method 2
forming a hydrogel polymer by cross-linking and polymerizing a water-soluble ethylene-based unsaturated monomer
Implementation Method 3
forming a surface cross-linked layer by further cross-linking a surface of the base resin powder
Implementation Method 4
adding a monovalent to trivalent metal cation on the surface cross-linked base resin powder
Implementation Method 5
the super absorbent polymer should exhibit high moisture absorbency, it should not release the absorbed water
Data Source
AI summary
The present disclosure relates to a preparation method of a super absorbent polymer capable of improving absorption performance of the super absorbent polymer by adding a simple additive later. The preparation method includes the steps of: forming a hydrogel polymer by cross-linking and polymerizing a water-soluble ethylene-based unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal cross-linking agent; drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; forming a surface cross-linked layer by further cross-linking a surface of the base resin powder in the presence of a surface cross-linking agent, adding a monovalent to trivalent metal cation on the surface cross-linked base resin powder at a temperature of 25° C. to 80° C., and maintaining and aging the resulting metal cation-added product at a temperature of 40° C. to 60° C. for 10 to 30 minutes.