Super Absorbent Polymer Surface Cross-Linking for Permeability
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Solution Overview
Problem
Existing super absorbent polymers face a trade-off between improving liquid permeability and absorption rate, which often results in compromised basic absorption performance, particularly in sanitary products like diapers, where increased gel strength and surface cross-linking can lead to reduced absorbency under pressure and external forces.
Innovation Solution
A super absorbent polymer is developed with a base polymer powder and a surface cross-linked layer formed using alkylene carbonate, incorporating specific silica particles and surface cross-linking agents, optimizing centrifuge retention capacity, absorbency under pressure, saline flow conductivity, and particle strength to enhance liquid permeability and absorption rate while maintaining excellent absorption performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If gel strength is increased to improve liquid permeability and absorption rate, then liquid permeability and absorption rate are improved, but basic absorption performance (absorbency under pressure) is greatly lowered
Solution Approach 1:
The patent applies surface cross-linking to create a hardened shell layer on the outer surface of the polymer particles, while the internal structure remains soft and highly absorbent. This local differentiation allows the surface to provide mechanical strength for liquid permeability while the interior maintains high absorption capacity under pressure.
Solution Approach 2:
The patent creates a composite structure with two distinct phases: a cross-linked surface layer providing structural integrity and a non-cross-linked or lightly cross-linked core providing absorption capacity. This composite architecture resolves the contradiction between surface strength requirements and bulk absorption performance.
2Strength
If surface cross-linking is increased to harden the surface and improve liquid permeability, then liquid permeability is improved, but absorption performance is compromised
Solution Approach 1:
The patent applies surface cross-linking to create a hardened shell layer on the outer surface of the polymer particles, while the internal structure remains soft and highly absorbent. This local differentiation allows the surface to provide mechanical strength for liquid permeability while the interior maintains high absorption capacity under pressure.
Solution Approach 2:
The patent applies cross-linking selectively only to the surface region of the particles rather than throughout the entire particle volume. This partial cross-linking approach provides sufficient surface hardening for liquid permeability without excessively restricting the absorption capacity of the particle interior.
3Strength
If particle strength is increased to maintain shape in expanded state, then shape retention is improved, but liquid permeability may be reduced
Solution Approach 1:
The patent applies surface cross-linking to create a hardened shell layer on the outer surface of the polymer particles, while the internal structure remains soft and highly absorbent. This local differentiation allows the surface to provide mechanical strength for liquid permeability while the interior maintains high absorption capacity under pressure.
Solution Approach 2:
The cross-linked surface layer acts as a flexible shell that maintains particle shape during swelling while still allowing liquid penetration. The shell provides structural integrity without being so rigid as to prevent liquid access to the absorbent interior.
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 optimized super absorbent polymer exhibits improved liquid permeability and absorption rate with maintained absorption performance, suitable for use in sanitary materials, particularly ultra-thin diapers with reduced pulp content, by forming a uniform and strong surface cross-linked layer that enhances particle and gel strength.
Implementation Method 1
a surface cross-linked layer formed on the base polymer powder and including a second cross-linked polymer in which the first cross-linked polymer is further cross-linked via an alkylene carbonate having 2 to 5 carbon atoms
Implementation Method 2
a centrifuge retention capacity (CRC) for a physiological saline solution (0.9 wt % sodium chloride aqueous solution) for 30 minutes is 25 to 35 g/g, an absorbency under pressure (AUP) under 0.7 psi for a physiological saline solution (0.9 wt % sodium chloride aqueous solution) for 1 hour is 23.5 to 30 g/g
Data Source
AI summary
The present invention relates to a super absorbent polymer exhibiting more improved liquid permeability and/or absorption rate while maintaining excellent absorption performance. Such super absorbent polymer comprises a base polymer powder including a first cross-linked polymer of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups; and a surface cross-linked layer formed on the base polymer powder and including a second cross-linked polymer in which the first cross-linked polymer is further cross-linked through an alkylene carbonate having 2 to 5 carbon atoms, and satisfies predetermined physical properties.