Absorbent Structure Wet Strength via Cationic Polymers
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Solution Overview
Problem
Existing methods for producing wet laid disposable absorbent structures, such as paper towels and facial tissues, often compromise on wet strength, absorbency, and softness, with mechanical refining and the use of carboxymethylcellulose (CMC) leading to stiffness and surface roughness.
Innovation Solution
The use of cationic wet strength resins in combination with anionic polyacrylamides and cellulase enzymes during the stock preparation stage of the wet laid manufacturing process, which allows for the removal of CMC and limits mechanical refining, enhancing wet strength and absorbency while maintaining softness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If mechanical refining and CMC are used to produce wet laid absorbent structures, then manufacturing process is simplified, but wet strength, absorbency, and softness deteriorate
Solution Approach 1:
The patent changes the chemical parameters of the fiber suspension by introducing cationic polymers (polyethyleneimine and polyaminoamide-epichlorohydrin resin) with specific molecular weights and charge densities. These chemical parameter changes enable wet strength enhancement without mechanical refining or CMC, resolving the contradiction between manufacturing simplicity and wet strength
Solution Approach 2:
The patent creates a composite system by combining cationic polymers with anionic polyacrylamide in the fiber suspension. This composite material approach provides both wet strength and absorbency enhancement while avoiding the need for mechanical refining and CMC, thus maintaining manufacturing simplicity while improving wet strength
2Strength
If mechanical refining is increased to improve web strength, then wet strength improves, but softness and absorbency deteriorate
Solution Approach 1:
The patent replaces the mechanical refining system with a chemical bonding system using cationic polymers. The cationic polymers form chemical bridges between fibers through electrostatic interactions, providing wet strength without the mechanical damage that reduces softness and absorbency
Solution Approach 2:
The patent changes the chemical composition parameters by adding cationic polymers with controlled molecular weights (10,000-1,000,000 for polyethyleneimine and 100,000-10,000,000 for polyaminoamide-epichlorohydrin resin). These parameter changes enable strength enhancement through chemical rather than mechanical means, preserving softness
3Strength
If CMC is used as a strength component, then wet strength improves, but surface roughness and stiffness increase
Solution Approach 1:
The patent extracts CMC from the formulation entirely and replaces it with cationic polymers (polyethyleneimine and polyaminoamide-epichlorohydrin resin). This extraction eliminates the surface roughness and stiffness problems associated with CMC while maintaining wet strength through the cationic polymer-fiber interactions
Solution Approach 2:
The patent changes the chemical parameter from anionic CMC to cationic polymers with specific molecular weights and charge densities. This parameter change fundamentally alters the interaction mechanism with fibers, providing wet strength without the adverse surface properties caused by CMC
4Productivity
If web compaction is increased during pressing, then production efficiency improves, but absorbency and thickness deteriorate
Solution Approach 1:
The patent applies partial pressing action rather than excessive compaction. The cationic polymers provide adequate wet strength at lower pressing levels, allowing the web to retain its thickness and porosity structure, thus maintaining absorbency while still achieving production efficiency
Solution Approach 2:
The patent changes the chemical bonding parameters by introducing cationic polymers that form strength bonds at lower compression levels. This parameter change allows the pressing operation to be less intensive, preserving the web's three-dimensional structure and absorbency while maintaining productivity
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 approach results in absorbent structures with improved wet tensile strength, absorbency, and softness, with CD wet tensile strength at least 35% of the dry tensile strength and HF softness of at least 46, while minimizing the need for mechanical refining and reducing bulk and stiffness.
Implementation Method 1
cationic wet strength resin(s) with anionic polyacrylamide(s) and cellulase enzyme(s) in the stock preparation stage
Implementation Method 2
cellulase enzyme(s) in the stock preparation stage
Data Source
AI summary
A method of making an absorbent structure including forming a stock mixture of fibers, a cationic wet strength resin, an anionic polyacrylamide and a cellulase enzyme, and at least partially drying the stock mixture to form a web.