Engineered Thermoplastic Polyurethane (ETPU): What do You Need to Know About This Material?
Learn about the material's properties, uses, advantages, and toxicity.
This article will go into more detail about what Thermoplastic Polyurethane, Engineering (ETPU) is, how it is made, its properties, use cases, advantages, disadvantages, and its potential health effects on humans.
What is Engineered Thermoplastic Polyurethane (ETPU)?
On a chemical level, ETPU is a block copolymer that consists of alternating hard and soft segments. Changing the proportion of each of these segments will result in different hardnesses, allowing for significant customization. This methodology stands in contrast to other softening techniques such as adding plasticizers to normal thermoplastics (which tends to weaken the material). The type of hard and soft segments in the ETPU will define the thermoplastic polyurethane properties, including the level of opacity.
- Hard segments - These can consist of either aliphatic or aromatic isocyanates. These segments make the material tougher and stronger.
- Soft segments - These consist of a reacted polyol, either as a polyether or a polyester. These segments give the material its characteristic flexibility.
How is Engineered Thermoplastic Polyurethane Made?
Engineered Thermoplastic Polyurethane (ETPU) plastic is produced by reacting a diisocyanate with one or more diols (long-chain or short-chain diols). The ratios of these constituents can be varied to create a wide range of physical properties.
This material is used as a standard thermoplastic and can be injection molded, blow-molded, compression-molded, 3D printed, or extrusion molded. Additionally, foaming agents can be added to create closed-cell foams for use in shock-absorbing applications.
What Are the Properties of Engineered Thermoplastic Polyurethane, (ETPU)?
The properties of engineered thermoplastic polyurethane (ETPU) are shown in the table below. The values listed represent the typical or average ETPU properties of the material. There are many different grades on the market, so note that some specialized formulations may fall outside the range of the properties listed below.
| Property | Range |
|---|---|
Property Tensile Strength (MPa) | Range 20 to 60 |
Property Elongation at Yield (%) | Range 350 to 800 |
Property Elastic Modulus (GPa) | Range 0.03 to 0.7 |
Property Melting Point (degrees C) | Range 120 to 220 |
Property Density (g/cm3) | Range 1.05 to 1.34 |
Property Max Operating temperature - Long Exposure (C) | Range 90 to 90 |
Property Max Operating temperature - Short Exposure (C) | Range 120 to 135 |
Property Thermal Conductivity W/(mK) | Range 0.014 to 0.5 |
Property Hardness (Shore Scale) | Range 70A to 88D |
Table 1. ETPU Properties
What Are the Uses of Engineered Thermoplastic Polyurethane?
ETPU is used in many different applications primarily due to its flexibility and toughness. Listed below are some of the more common uses for engineered thermoplastic polyurethane.
- Medical devices: ETPU is ideal for catheters, infusion tubes, medical instrument cables, anesthesia masks, and oxygen masks. These components are often transparent for monitoring purposes and are typically not manufactured with any additives.
- Automotive TPU applications: ETPU has excellent scratch resistance making it an ideal material for heavy-use items such as gear knobs and instrument buttons.
- Sporting goods: ETPU materials lend themselves well to shoe cushions and shock absorbers, thanks to the material's flexibility and weather resistance.
- Industrial tools: ETPU is ideal for ergonomic grips on tools such as drills or other hand tools. The flexible ETPU is often overmolded onto more rigid thermoplastic materials.
- Laminates: ETPU is used as a laminate between glass panels due to its excellent optical properties.
What Are the Advantages of Using Engineered Thermoplastic Polyurethane?
The key advantages of thermoplastic polyurethane are:
- ETPUs are ideal for medical applications as they are biocompatible (provided no additives are used).
- Aliphatic ETPUs can be made optically clear and will maintain the same transparency even when exposed to UV radiation.
- ETPU remains flexible and impact-resistant even at low temperatures.
- ETPU is chemically resistant to many solvents and greases.
What Are the Disadvantages of Using Engineered Thermoplastic Polyurethane?
The disadvantages and limitations of Engineered Thermoplastic Polyurethane are:
- ETPUs are generally more costly than other commodity thermoplastics.
- ETPUs are more difficult to process; they must be processed within a narrow temperature range and in very dry conditions.
- Polyester-based ETPUs easily absorb moisture, causing the materials to decompose over time.
- Aromatic ETPUs tend to decompose when exposed to UV radiation or heat. If made transparent, this grade of thermoplastic polyurethane also tends to yellow when exposed to UV radiation.
How Does Engineered Thermoplastic Polyurethane Affect Human Health?
ETPU is extensively used in the medical field. However, it must be noted that not all ETPUs are created equal. Among the main sources of potentially harmful chemicals are the various additives used to improve or enhance the properties of ETPUs. As such, medical applications where ETPU products will come in direct contact with tissue typically have no additives. By eliminating these additives, the potential for skin irritation or dermatitis during long-term skin contact is mitigated. At normal temperatures, ETPU does not give off any gasses that can be inhaled. However, if the material is burned, it can produce hazardous gasses.
Is Engineered Thermoplastic Polyurethane Toxic?
If processed correctly, ETPU poses no toxicity risk. It contains no BPA, BPS, or BPF and has not demonstrated any effects on the endocrine or hormonal systems. However, improperly processed ETPU materials may have leftover reactive elements from the polymerization process such as toxic monomers or catalysts. As mentioned previously, some additives may also pose toxicity risks. If burnt, ETPUs can release extremely toxic gasses that contain cyanide compounds. For this reason, ETPUs should not be used in conditions that can cause combustion. The best practice when considering any material is to review the relevant safety data sheet prior to use so that you understand all of the potential safety hazards involved.
What is the Difference Between Engineered Thermoplastic Polyurethane and Thermoplastic Elastomer?
A thermoplastic elastomer is any thermoplastic material that exhibits elastomeric or rubber-like behavior. As such, ETPU is simply a subset under broader thermoplastic elastomer classification.
For more information, see our guide on thermoplastic elastomer.
Summary
This article summarized the properties, uses, advantages, and toxicity of Engineered Thermoplastic Polyurethane (ETPU).
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