Auxetic Polyurethane and Melamine Foams via Triaxial Compression
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Solution Overview
Problem
Existing processes for preparing auxetic foams with negative Poisson's ratio are inefficient and require additional steps, as they start from reticulated polymer foams, making the process less efficient and less scalable.
Innovation Solution
A process involving providing a foam with a specific flow resistance range, subjected to thermoforming with triaxial compression without prior reticulation, resulting in foams with a Poisson's ratio between -0.8 and 0.3, utilizing foams based on melamine-formaldehyde or polyurethane with controlled density and composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reticulation is performed before thermoforming, then auxetic foam structure can be achieved, but process complexity and production time increase
Solution Approach 1:
The invention extracts and eliminates the reticulation step from the conventional two-step process. By using foams with specific flow resistance characteristics (3000-8000 Pas/m2) as starting material, the auxetic structure is achieved directly through triaxial compression without requiring prior reticulation, thus simplifying the overall process while maintaining manufacturing precision
Solution Approach 2:
The invention changes the key parameter from reticulation degree to flow resistance. By selecting foams within the specific flow resistance range of 3000-8000 Pas/m2, the material becomes directly suitable for triaxial compression to produce auxetic structures, eliminating the need for reticulation and simplifying the manufacturing process
2Manufacturing precision
If reticulation is performed before thermoforming, then auxetic foam structure can be achieved, but production efficiency decreases
Solution Approach 1:
The invention removes the reticulation step entirely from the production process. By selecting pre-formed foams with appropriate flow resistance (3000-8000 Pas/m2) as starting material, the process is reduced to a single triaxial compression step, significantly improving production efficiency while maintaining the required auxetic foam structure
Solution Approach 2:
The invention performs the reticulation action in advance during foam production rather than as a separate preprocessing step. The starting foam is manufactured with specific flow resistance characteristics that inherently provide the necessary structure for auxetic behavior, eliminating the need for a dedicated reticulation step and improving overall 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
This method efficiently produces foams with desired auxetic behavior, suitable for energy absorption and various applications, such as protective gear and acoustic materials, by eliminating the need for prior reticulation and simplifying the process.
Implementation Method 1
subjecting the foam (F1) to thermoforming comprising triaxial compression
Implementation Method 2
thermoforming comprising triaxial compression
Data Source
AI summary
Described herein is a process for preparing a foam (FA) with a Poisson's ratio in the range of from −0.5 to 0.3, the method including the steps of providing a foam (F1) with a flow resistance in the range of from 3000 to 8000 Pas/m, determined according to DIN EN 29053, and subjecting the foam (F1) to thermoforming including triaxial compression, wherein the foam (F1) is not reticulated prior to step (ii). Also described herein is the foam obtained or obtainable according to the process and the use of the foam as, for example, an energy absorbing device, preferably in protective gear, furniture, cushions, in cleaning devices with improved rinse-out behavior, in shoe soles, or as sealing, insulating or anchorage providing material for example used in earphones, ear plugs or dowels, or as acoustic material.