Thermoplastic Open-Cell Flexible Polyurethane Foam for Recycling
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Solution Overview
Problem
Conventional polyurethane flexible foams are not recyclable by thermoplastic processing due to crosslinking and high melting temperatures, leading to unsuitability for extrusion or injection molding, and existing methods for producing flexible open-cell foams face issues with high density, shrinkage, and environmental emissions.
Innovation Solution
A method involving the production of thermoplastic polyurethane flexible foam with specific polyol and diisocyanate ratios, minimal water content, and gas mixing to form a pre-foam, followed by vacuum expansion and curing, achieving a density of 15 to 100 g/dm³ and high open cell content, allowing recyclability without virgin thermoplastic addition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional polyurethane flexible foams are produced with crosslinked polyol phase and urea hard phase, then the foam structure and mechanical properties are improved, but the material cannot be melted or has extremely low melt flow making it unsuitable for extrusion or injection molding
Solution Approach 1:
The patent changes the chemical composition parameters by using polyols with functionality of 2.0-2.4 (lower than conventional 2.4-4.0) and limiting crosslinking density to 1.5-2.0 mol/m³ (lower than conventional levels). This parameter adjustment reduces crosslinking while maintaining foam structure, enabling the material to achieve both structural stability and melt processability for recycling.
2Ease of manufacture
If water content and urea content are reduced to improve melt flow, then processibility is enhanced, but the foam density and mechanical properties deteriorate
Solution Approach 1:
The patent optimizes water content to 0.5-2.0 parts by weight (lower than conventional levels) and controls urea content through limited crosslinking, achieving a balance where melt flow is sufficient for processing while foam density and mechanical properties remain within acceptable ranges for flexible foam applications.
3Strength
If polyols with higher functionality (2.4-4.0) are used to improve crosslinking and foam structure, then the mechanical properties are enhanced, but the melt viscosity increases and processibility is lost
Solution Approach 1:
The patent selects polyols with functionality of 2.0-2.4, which is lower than the conventional 2.4-4.0 range. This parameter change reduces the number of crosslinking sites per polyol molecule, thereby decreasing crosslinking density and melt viscosity while still achieving adequate foam structure and mechanical properties through optimized formulation and processing.
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 results in a foam with high melt flow index, homogeneous density, low emissions, and excellent mechanical properties, enabling recyclability and suitability for various applications without the need for virgin materials.
Implementation Method 1
mixed with a gas to form a pre-foam, followed by vacuum expansion and curing
Implementation Method 2
Conventional polyurethane flexible foams are produced by reaction of polyisocyanates with polyols having an average functionality of 2.4 to about 4 and water as blowing agent. This results in a crosslinked polyurethane wherein the higher functional polyols form chemical crosslinks and urea groups form physical crosslinks.
Implementation Method 3
mixed with a gas to form a pre-foam, followed by vacuum expansion and curing
Data Source
Figure 1
AI summary
The present invention relates to a method for the production of a thermoplastic molded polyurethane flexible foam having a foam density of 15 to 100 g/dm3 comprising mixing of (a) Diisocyanate, (b) Polyol having an OH number of less than 280 mg KOH/g and an average functionality of 1.9 – 2.2 (c) 3 to 20 wt.-% based on the total weight of components a) to c), of one or more chain extenders, (d) optionally catalyst and (e) optionally fillers and/or polyurethane additives at an isocyanate index of 80 to 110 to form a reaction mixture, wherein the amount of water added to the reaction mixture is less than 0.1 % by weight, based on the total weight of components a) to e), mixing the reaction mixture with a gas at an isocyanate content of the reaction mixture of more than 0.05 % by weight, based on the total weight of the mixture, to form a pre-foam having a density of 110 to 800 g/dm3 injecting the pre-foam into a mold, applying vacuum to the mold to further expand the pre-foam and curing the expanded pre-foam. The invention is further directed to a thermoplastic flexible polyurethane foam, obtainable from such a method, a composite, comprising such a thermoplastic flexible polyurethane foam and a method of recycling such a composite.