What is thermoplastic polyurethane (TPU)?
What is thermoplastic polyurethane (TPU)?
Thermoplastic polyurethane (TPU) is a melt-processable thermoplastic elastomer with high durability and flexibility. It provides several physical and chemical property combinations for demanding applications. Some examples include:
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automotive,
- wires and cables,
- breathable films for leisure, sports, and textile coatings,
- weatherable, non-yellowing films, etc.
It has properties between the characteristics of plastic and rubber. Thanks to its thermoplastic nature, it has several benefits over other elastomers are unable to match, such as:
The discovery of TPU occurred in 1937 by Otto Bayer and his coworkers. It took place at the laboratories of I.G. Farben in Leverkusen, Germany.
How TPU is produced?
How TPU is produced?
When a polyaddition reaction occurs between a diisocyanate and one or more diols in a specific way, it produces TPU. The three basic raw materials required to produce a TPU are:
- A polyol or long-chain diol
- A chain extender or short-chain diol
- A diisocyanate
It is a linear segmented block copolymer composed of soft and hard segments.
- Soft Segment (polyether or polyester): It is built out of a polyol and an isocyanate. Provides flexibility and the elastomeric character of a TPU.
- Hard Segment (aromatic or aliphatic): It is constructed from a chain extender and isocyanate. This gives TPU its toughness and physical performance properties.
- Aromatic TPUs - based on isocyanates such as MDI
- Aliphatic TPUs - based on isocyanates like H12 MDI, HDI, and IPDI
Molecular Structure of Thermoplastic Polyurethanes
What are the properties of TPU?
What are the properties of TPU?
TPUs allow industries to mainly benefit from the following combination of properties :
Abrasion/Scratch Resistance
High abrasion and scratch resistance ensure durability and aesthetic value
TPU is the material of choice in applications where abrasion resistance is critical. These include automotive interior parts, sports and leisure, technical parts, and specialty cables. It shows excellent results when compared to other thermoplastic materials.
The abrasion resistance of materials is usually determined by measuring the weight loss of a specimen in a standardized wear test. This is shown in the chart below:
Comparative results of such a test as depicted in the figure above. This clearly shows the superior abrasion resistance of TPU when compared to other materials, such as PVC and rubbers.
Soft Touch/High Comfort of Use for Ergonomic Applications
Recent developments have made it possible to produce plasticizer-free TPU. These solutions have a hardness range of 55 to 80 Shore A, and offer:
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high-quality surface finish,
- excellent adhesion to engineering plastics such as ABS and Nylon,
- unequal scratch and abrasion resistance.
UV Resistance
Aliphatic TPUs ensure color fastness to your aesthetic parts. They show superior stability to ultraviolet radiation and thus superior color stability. Along with these features they also maintain good mechanical properties.
Aliphatic TPU has exactly the right property profile and versatility to make it the material of choice for electronic applications. For both light & dark color parts, OEMs can rely on TPU's high scratch resistance & UV performance. View TPU Grades for Electronic Components »
Highly Breathable TPU Ensures Optimum Comfort
Comfort is the utmost priority when you design sportswear or building and construction products. Highly breathable TPUs are available to ensure optimum comfort.
Traditional TPU has a vapor transmission below 1,500 g/m2/day. While highly breathable grades have values as high as 10,000 g/m2/day (+560%). Traditional TPUs can be blended with breathable ones. This fine-tunes the breathability according to your application requirements.
Combination of High Transparency with Abrasion Resistance
Crystal-clear TPUs are available with very good hardness. This characteristic allows the use of TPU in the:
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extrusion of transparent films & tubes and hoses, or
- injection molding of technical, aesthetic parts, where transparency at a thickness as high as 6mm can be achieved.
Other Benefits of TPU
- High elasticity across the entire hardness range
- Excellent low-temperature and impact strength
- Resilience to oils, greases, and numerous solvents
- Good flexibility over a wide temperature range
- Robust weather and high-energy radiation resistance
Thermoplastic polyurethanes are elastic and melt-processable. Aromatic TPUs are strong, general-purpose resins that resist attack by microbes. They stand up well to chemicals. A drawback is that they degrade by free radical pathways induced by exposure to heat or UV. This degradation leads to product discoloration and loss of physical properties.
Aliphatic TPUs, on the other hand, are inherently light-stable. They resist discoloration from UV exposure. They are also optically clear. This makes them suitable laminates for encapsulating glass and security glazing.
How additives impact the properties of TPU?
How additives impact the properties of TPU?
Additives can improve the dimensional stability, heat and fungal resistance of TPUs. They also reduce friction, increase flame retardancy, and weatherability. Some examples of additives include antioxidants, UV absorbers, and hindered amine stabilizers. They protect polyurethanes from UV light-induced oxidation. This makes TPUs suitable for a wide range of applications that may require both thermal and/or light stability.
Other specialty grades include:
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Reinforced TPU – When mixed with glass or mineral fillers/fibers, it becomes a structural engineering polymer with desirable properties of abrasion resistance, high impact strength, good fuel resistance, and high flow characteristics.
- Flame Retardancy – Flame retardant TPU grades are widely used to provide tear resistance and toughness for cable jacketing.
How is TPU processed?
How is TPU processed?
Thermoplastic Polyurethane can be processed easily via conventional processing methods. These include injection molding, extrusion, blow, and compression molding. It can also be:
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compounded to create robust plastic moldings, or
- processed using organic solvents to form laminated textiles, protective coatings, or functional adhesives.
They are easily molded into shapes to produce grips, gaskets, caps, prosthetics, and several other applications.
Drying is a critical step in ensuring TPU’s process effectively and that a good part is obtained upon molding. Remove the moisture effectively before processing. This will allow effective drying of molded parts. This in turn leads to a loss in properties and brittleness.
Recommended residual moisture content
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For injection molding ≤ 0.05%
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For extrusion 0.02%
What are the main types of TPU films?
What are the main types of TPU films?
Polyester, Polyether and Polycaprolactone are the three main chemical classes of TPU films.
Credit: Huntsman
Polycarbonate Diols (PCDs)
Another interesting class of polyols used for thermoplastic polyurethane production is Polycarbonate diols. Generally used to produce polyurethanes that incorporate the carbonate linkages for superior performance. Polycarbonate-polyurethanes can also be produced through the use of polycarbonate-based polyurethane prepolymers.
A polycarbonate-based polyurethane prepolymer is a derivative of the corresponding polycarbonate diol in which all the polyol hydroxyl (OH) end groups have been reacted with an isocyanate leaving isocyanate groups (NCO) at the termini instead of hydroxyls.
When compared to polycaprolactone and PTMEG-based polyurethanes, PU elastomers based on PC-PU prepolymers exhibit:
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Extreme durability
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Higher chemical resistance
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Improved hydrolytic stability
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Greater thermal resistance
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Better abrasion resistance, and
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Superior mechanical properties
What are the environmental benefits of TPU?
What are the environmental benefits of TPU?
TPU is biodegradable & can be recycled. Other benefits offered by TPU over PVC include:
- Environmental protection
- TPU is abrasion resistant while PVC can crack over time
- More elastic and lighter than PVC
- In medical devices, it is accepted as a safe alternative to PVC. This is because TPU healthcare grades do not use rubber accelerators and plasticizers that can cause skin irritation or dermatitis.
Polyurethanes used as insulators in buildings, transportation and appliances effectively improve energy efficiency and lower carbon emissions. In vehicles, TPU products enhance fuel efficiency, because they are lighter than alternative metals.
What are the limitations of TPUs?
What are the limitations of TPUs?
- Some grades of TPU have relatively short shelf life
- Drying time is required before processing can begin
- Not as cost-effective as other alternatives
- Narrower hardness range than other thermoplastic elastomers
- Narrow temperature range for processing
- Tendency to be hydrolyzed especially in case of polyester-based TPU
What are the commercially available TPUs?
What are the commercially available TPUs?
View a wide range of thermoplastic polyurethane grades available today, analyze technical data of each product, get technical assistance or request samples.