Hydrophilic Aliphatic Polyurethane Foam Low Bulk Density
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Solution Overview
Problem
Existing methods for producing hydrophilic aliphatic polyurethane foams result in high bulk density and require complex removal of excess low molecular weight diisocyanates to minimize health risks, limiting the production of foams with low extractable free isocyanates and high pore fraction for effective moisture transport.
Innovation Solution
A method involving the reaction of low molecular weight aliphatic diisocyanates with di- to hexafunctional polyalkylene oxides to create isocyanate-functional prepolymers, mixed with C8- to C22-monocarboxylic acids or their salts and water, allowing for foaming and curing without the need for excess diisocyanate removal, resulting in foams with lower bulk density and reduced extractable free compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If excess low molecular weight aliphatic diisocyanates are removed after prepolymer preparation by means of thin films, then the content of extractable free isocyanates is reduced, but the process complexity increases
Solution Approach 1:
The patent extracts and removes excess low molecular weight aliphatic diisocyanates from the prepolymer mixture by means of thin films before the foaming step. This extraction process eliminates the harmful extractable free isocyanates from the final foam product, resolving the contradiction by removing the harmful substance through a dedicated separation step rather than relying on incomplete reaction or post-processing
Solution Approach 2:
The removal of excess diisocyanates is performed as a preliminary action during the prepolymer preparation stage, before the foaming process begins. By addressing the removal of harmful substances early in the process rather than as a final step, the patent integrates the extraction into the existing workflow without requiring complex post-processing equipment
2Volume of stationary object
If the ratio of low molecular weight aliphatic diisocyanates to polyalkylene oxides is increased, then the bulk density of the foam is reduced, but the content of extractable free isocyanates increases
Solution Approach 1:
The patent performs preliminary removal of excess diisocyanates by thin films before foaming, allowing the use of higher diisocyanate ratios during prepolymer preparation to achieve low bulk density, while the harmful excess is subsequently removed. This preliminary action decouples the bulk density optimization from the extractable isocyanate content
Solution Approach 2:
The patent segments the process into distinct stages: (1) prepolymer preparation with optimized diisocyanate ratio for low bulk density, (2) removal of excess diisocyanates by thin films, and (3) foaming. This segmentation allows each stage to be optimized independently, enabling low bulk density without compromising safety
3Productivity
If the pore fraction is increased to enable rapid moisture transport, then the bulk density is reduced, but the structural integrity may be compromised
Solution Approach 1:
The patent utilizes porous polyurethane foam structure with controlled pore fraction to enable rapid moisture transport through capillary action. The porous structure is achieved through the foaming process using water and carboxylic acids as blowing agents, creating interconnected pores that facilitate moisture wicking while maintaining appropriate bulk density for the application
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 produces polyurethane foams with lower bulk density and reduced extractable free compounds, eliminating the need for complex diisocyanate removal and enabling rapid moisture transport, making them suitable for wound dressings and other applications.
Implementation Method 1
prepolymers are obtainable by reacting low molecular weight aliphatic diisocyanates with di- to hexafunctional polyalkylene oxides
Implementation Method 2
reacting isocyanate-functional prepolymers with C8- to C22-monocarboxylic acids or their ammonium or alkali metal salts or C12- to C44-dicarboxylic acids or their ammonium or alkali metal salts and water
Implementation Method 3
rapid and effective transport of moisture is possible as a result of the high pore fraction and the associated capillary action
Data Source
AI summary
The invention relates to a method for producing hydrophilic, aliphatic polyurethane foams having a low bulk density. The invention also relates to a hydrophilic, aliphatic polyurethane foam which can be obtained according to said method and to the use thereof as a wound dressing, incontinence product or as a cosmetic article.