Recycled Thermoplastic Polyurethane Process
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Solution Overview
Problem
Recycling of thermoplastic polyurethanes (TPUs) faces challenges in maintaining mechanical properties due to molecular weight reduction and phase mixing issues when recycling single-variety or mixed-grade wastes, leading to suboptimal product quality and increased stiffness from isocyanate reactions with moisture.
Innovation Solution
A two-stage process involving the reaction of TPU with a compound having two hydroxyl groups to reduce molecular weight, followed by synthesis with an isocyanate composition matched to the hard segment content of the original TPU, allowing for controlled molecular weight adjustment and phase separation to achieve desired mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If thermoplastic polyurethane is recycled through melting and reprocessing, then recycling cost-effectiveness is improved, but molecular weight reduces and mechanical properties deteriorate
Solution Approach 1:
The patent applies parameter changes by controlling the NCO-OH index (isocyanate to hydroxyl group ratio) within specific ranges (0.8-1.2) and adjusting polyol molecular weight (500-5000 g/mol) and hard segment content (10-40 wt%) to optimize the balance between recyclability and mechanical properties. This controlled parameter adjustment allows repeated melting while maintaining adequate molecular weight and mechanical performance.
Solution Approach 2:
The patent utilizes phase transitions of thermoplastic polyurethane between crystalline and amorphous states during melting and cooling cycles. By controlling the hard segment content and its distribution, the material maintains reversible phase transitions that enable thermoplastic processing without irreversible degradation, allowing mechanical recycling while preserving structural integrity.
2Adaptability or versatility
If different grades of thermoplastic polyurethane waste are mixed for recycling, then recycling versatility is improved, but phase mixing occurs and mechanical properties worsen
Solution Approach 1:
The patent applies local quality by ensuring homogeneous distribution of hard segments within the polymer matrix through controlled synthesis parameters. By maintaining uniform local composition and hard segment dispersion, the material achieves consistent phase separation even when recycling mixed-grade wastes, preventing macroscopic phase mixing while preserving mechanical properties.
Solution Approach 2:
The patent uses parameter changes in hard segment content (10-40 wt%) and polyol characteristics to control phase behavior. By adjusting these parameters, the material maintains stable microphase separation that can accommodate variations in waste composition, enabling versatile recycling while preserving composition stability through self-organizing phase structures.
3Strength
If isocyanate is added to increase molecular weight during recycling, then molecular weight is improved, but stiffness increases and crosslinking occurs
Solution Approach 1:
The patent applies parameter changes by precisely controlling the NCO-OH index within the range of 0.8-1.2, preventing excessive isocyanate addition. This controlled stoichiometry allows molecular weight recovery through chain extension while avoiding crosslinking reactions. The patent also controls reaction temperature and time parameters to favor linear chain growth over crosslinking, maintaining thermoplastic processability.
Solution Approach 2:
The patent applies partial action by adding only the necessary amount of isocyanate and polyol components to achieve adequate molecular weight without excessive chain extension. This controlled partial addition prevents over-crosslinking and excessive stiffness while still recovering sufficient molecular weight for mechanical property restoration, balancing chain extension benefits against crosslinking risks.
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 process produces TPUs with mechanical properties comparable to freshly produced materials, enabling cost-effective recycling of TPUs with adjustable hardness independently of the mixture's initial hardness, maintaining polymer chain integrity and phase separation.
Implementation Method 1
Chemical processes such as hydrolysis, hydrogenation, pyrolysis and glycolysis are suitable for the recovery of polyurethanes
Implementation Method 2
reacting the mixture (G-a) with a mixture (G-b) comprising an isocyanate composition (ZI) comprising at least one diisocyanate and optionally a polyol composition (ZP) comprising at least one polyol (P2) to obtain a thermoplastic polyurethane (TPU target)
Data Source
AI summary
The present invention relates to a process for producing a thermoplastic polyurethane reacting at least one thermoplastic polyurethane (TPU-1) or a polyurethane mixture comprising a thermoplastic polyurethane (TPU-1) with at least one compound (V1) comprising two hydroxyl groups to obtain a mixture (G-a) comprising a thermoplastic polyurethane (TPU-2) and the reaction of the mixture (G-a) with a mixture (G-b) comprising an isocyanate composition (ZI) comprising at least one diisocyanate and optionally and a polyol composition (ZP) comprising at least one polyol (P2) to obtain a thermoplastic polyurethane (TPU target), wherein the proportion of the employed components (ZI) and (ZP) is matched to the hard segment content of the employed thermoplastic polyurethane (TPU-1), (V1) and the hard segment content of the thermoplastic polyurethane (TPU target). The invention further relates to a thermoplastic polyurethane obtained or obtainable by such a process and to the use thereof for producing extruded, injection molded and pressed articles as well as foams, cable sheathings, hoses, profiles, drive belts, fibers, nonwovens, films, moldings, soles, sporting goods, shoes, plugs, housings, damping elements for the electricals industry, automotive industry, mechanical engineering, 3D printing, medicine and consumer goods.