Heterogeneous Absorbent Structure Breaking Capillarity-Permeability Trade-off
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Solution Overview
Problem
Conventional absorbent structures for hygiene products face a trade-off between capillarity and permeability, where high capillarity results in low permeability and vice versa, limiting their ability to efficiently absorb and retain fluids.
Innovation Solution
A heterogeneous absorbent structure comprising creped cellulose wadding, fluffed cellulose fibers, and open-cell foam pieces, specifically High Internal Phase Emulsion (HIPE) foam, which breaks the capillarity-permeability trade-off by integrating enrobeable elements and discrete open-cell foam pieces to enhance both capillary suction and fluid flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the surface-to-volume ratio is increased to enhance capillary suction, then the capillary pressure increases, but the permeability decreases due to more tortuous flow paths
Solution Approach 1:
The absorbent structure is divided into multiple strata with different surface-to-volume ratios. The first stratum has a higher surface-to-volume ratio to provide high capillary suction, while the second stratum has a lower surface-to-volume ratio to provide high permeability. This segmentation allows each layer to optimize for its specific function without compromising the other.
Solution Approach 2:
Different regions of the absorbent structure have different properties tailored to their functional requirements. The first stratum is designed with high surface-to-volume ratio characteristics for capillary action, while the second stratum is designed with low surface-to-volume ratio characteristics for fluid transport. This local differentiation resolves the contradiction by assigning optimal properties to specific locations.
2Speed
If the capillary radius is increased to speed up capillary rise, then the acquisition speed increases, but the driving force (capillary pressure) decreases resulting in lower rewet pressure
Solution Approach 1:
The absorbent structure segments the capillary rise process across two strata. The first stratum with higher surface-to-volume ratio provides the driving capillary pressure, while the second stratum with lower surface-to-volume ratio provides the high-speed transport pathway. This segmentation allows the system to achieve both high speed and high driving force that cannot be achieved in a single homogeneous structure.
Solution Approach 2:
The solution moves from optimizing a single capillary dimension to optimizing a multi-dimensional stratified structure. By introducing the vertical dimension of multiple layers with different properties, the system can simultaneously achieve high capillary pressure (in the first stratum) and high rise speed (in the second stratum), effectively resolving the trade-off through dimensional expansion.
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 absorbent structure achieves a Capillary Work Potential greater than the trade-off boundary, allowing for high permeability and capillarity, effectively absorbing and retaining fluids without compromising on either property.
Implementation Method 1
Conventional Porous Media (PM) structures and super absorbent polymers (SAP) utilized as acquisition and storage layers in the hygiene product industry show a known trade-off between driving force for fluid acquisition (capillary suction) and resistance to the flow
Implementation Method 2
whenever the ratio surface to volume is low in a porous material, then the resistance to flow is reduced (high permeability)
Implementation Method 3
Absorbent structures for the absorption of fluids aim to rapidly absorb fluids so that they are not left in contact with the user
Data Source
Figure 1
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AI summary
An absorbent structure comprising a single stratum exhibiting a Capillarity Work Potential greater than the Capillarity Work Potential trade-off Boundary.