Water-absorbent resin gel-shape stability
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Solution Overview
Problem
Water-absorbent resins used in hygienic materials like disposable diapers face challenges with gel-shape stability and water-absorption capacity, particularly when the amount of resin increases and hydrophilic fibers decrease, leading to deformation and reduced liquid absorption.
Innovation Solution
A water-absorbent resin with specific properties, including a disintegration amount at 20-fold swelling of 30% or less and solubility in physiological saline of 25% or less, is developed, which improves gel-shape stability and water-absorption capacity when used in combination with hydrophilic fibers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the amount of water-absorbent resin is increased to increase liquid absorption amount, then the water-absorption capacity is improved, but the gel-shape stability deteriorates causing deformation and cracking under compression
Solution Approach 1:
The invention changes the chemical composition parameters of the water-absorbent resin by specifying a copolymer structure containing acrylic acid units and carboxyl groups, with controlled neutralization degree (30-70%). This parameter optimization allows the resin to achieve both high liquid absorption capacity and maintained gel-shape stability, resolving the contradiction between absorption amount and shape stability.
Solution Approach 2:
The invention creates a composite structure within the water-absorbent resin by forming a copolymer of acrylic acid with specific functional groups (carboxyl groups) at controlled ratios. This composite molecular structure combines the swelling capacity of hydrophilic segments with the structural stability provided by crosslinked carboxyl groups, enabling simultaneous achievement of high absorption and shape retention.
2Quantity of substance
If the amount of hydrophilic fibers is reduced to increase water-absorbent resin content, then the water-absorption capacity is improved, but the intertwinement decreases leading to poor structural integrity
Solution Approach 1:
The invention optimizes the chemical parameters of the water-absorbent resin by controlling the neutralization degree (30-70%) and specifying the presence of carboxyl groups, which provide both absorption capacity and structural strength. This allows the resin to maintain strong intertwinement with hydrophilic fibers even at higher resin content, resolving the contradiction between resin quantity and bonding strength.
3Stability of the object's composition
If thermally fused fibers are incorporated to improve gel-shape stability, then the deformation resistance is improved, but the liquid permeation rate and absorption amount decrease due to hydrophobicity
Solution Approach 1:
The invention changes the chemical nature of the water-absorbent resin by specifying a copolymer structure with high acrylic acid content and controlled neutralization, creating a highly hydrophilic material that improves liquid permeation rate. Simultaneously, the controlled crosslinking through carboxyl groups maintains gel-shape stability, resolving the contradiction between hydrophobicity and absorption performance.
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 resin enhances the stability and absorption capacity of absorbent materials, preventing deformation and liquid re-wet, even under compression or shearing forces, while maintaining effective water absorption.
Implementation Method 1
when the absorbent material has absorbed a liquid, the volume of the absorbent material increases due to swelling of the water-absorbent resin
Implementation Method 2
crosslinked products of partially neutralized polymers of acrylic acid
Data Source
AI summary
Provided is a water-absorbent resin which is capable of giving an absorbent material improved gel-shape stability and which has excellent water-absorption capacity. A water-absorbent resin of the present invention is a polymer of a water-soluble ethylenically unsaturated monomer, and has the following properties (1) and (2): (1) A disintegration amount at 20-fold swelling is 30% by mass or less; and (2) a solubility in physiological saline is 25% by mass or less. (Determination Method for Disintegration Amount at 20-Fold Swelling) 5 g of the water-absorbent resin is added to 100 g of physiological saline to allow the water-absorbent resin to absorb the physiological saline, thereby obtaining a gel. The obtained gel is divided approximately equally into five portions, and these portions are introduced respectively into cylindrical molds having a length of 3.6 cm and a radius of 2.8 cm and molded. The masses of the five molded cylindrical gels are measured. The heaviest and the lightest of the five gels are removed, and the remaining three gels are used as samples. A mass Wa (g) of each sample is measured. Each weighed sample is placed on the uppermost sieve of a combination of JIS standard sieves having a mesh size of 5.6 mm and a receptacle in this order and shaken for 10 minutes using a Ro-Tap shaker (rotation speed, 290 rpm; number of taps, 165 rpm). A mass Wb (g) of the gel which has passed through the sieves is measured. The disintegration amount of each sample is calculated using the following equation: Disintegration amount of sample (%)=Wb (g)/Wa (g)×100. An average of the disintegration amounts for three samples to be measured is regarded as the disintegration amount at 20-fold swelling of the water-absorbent resin.