If you’re looking for a material that’s resistant to water absorption, then ThermoPlastic Urethane (TPU) may be a great option for you.
TPU is a versatile material used in various industries because of its unique properties. One of the questions that come up often is whether TPU is hygroscopic. In this article, we will explore what hygroscopic means, why it matters, and whether TPU is hygroscopic.
Quick Answer: Is TPU Hygroscopic?
Yes, thermoplastic polyurethane (TPU) is hygroscopic. It absorbs moisture from the air, but its water absorption rate is significantly lower than materials such as nylon. Proper drying before processing is recommended to maintain optimal mechanical properties and surface quality.
What Does Hygroscopic Mean?
Hygroscopicity is a material’s ability to absorb moisture from the air. This moisture can come from the surrounding environment, like the air or water. When a material is hygroscopic, it can absorb water vapor from the air and retain it. This characteristic can affect the material’s properties, including its strength and durability.
Why is Hygroscopicity Important?
The hygroscopicity of a material is important because it can affect its physical properties. The ability to absorb moisture can lead to changes in a material’s dimensions, weight, and overall performance. This can be especially important in industries where consistent performance is necessary, such as in aerospace, automotive, and medical applications.
Is TPU Hygroscopic?
Now let’s answer the question you’re here for: is TPU hygroscopic? The answer is yes, TPU is hygroscopic. However, it’s not as hygroscopic as some other materials like nylon. TPU has a low water absorption rate compared to other polymers, and this is one of the reasons why it’s often used in applications where water resistance is important.
The amount of moisture that TPU absorbs can depend on the type of TPU, the environment it’s in, and the time it’s exposed to that environment. For example, TPU may absorb more moisture in a humid environment than a dry one. However, even in a humid environment, TPU’s water absorption rate is relatively low compared to other materials.
How Much Moisture Does TPU Absorb?
TPU typically has a water absorption rate of approximately 0.2% to 0.5% (24 hours at room temperature), depending on the formulation.
In comparison:
- Nylon (PA) can absorb 2%–3% or more.
- ABS absorbs significantly less than TPU.
This relatively low moisture absorption makes TPU more dimensionally stable than many other engineering polymers.
What Are The Benefits of TPU’s Low Hygroscopicity?
TPU’s low hygroscopicity has several benefits for its users. One of the most significant advantages is that it allows TPU to maintain its physical properties even when exposed to moisture. This means that TPU can be used in applications where exposure to moisture is unavoidable, like outdoor gear or medical applications.
Another benefit of TPU’s low hygroscopicity is that it can improve the material’s durability. Moisture absorption can cause materials to swell or crack, but TPU’s resistance to moisture can prevent these issues from occurring. This can result in a longer lifespan for products made with TPU.
Does TPU Need to Be Dried Before Processing?
Yes. Although TPU has relatively low hygroscopicity, it should be properly dried before injection molding or extrusion.
Excess moisture can cause:
- Surface bubbles
- Reduced mechanical strength
- Poor transparency
- Hydrolytic degradation
Typical drying recommendations:
- Temperature: 80–110°C
- Drying time: 2–4 hours
Proper drying ensures consistent product quality and mechanical performance.
How Can You Mitigate TPU’s Hygroscopicity?
If you’re concerned about TPU’s hygroscopicity, there are several ways to mitigate its effects. One way is to use a TPU formulation that has been specifically designed to resist moisture absorption. Another way is to limit the TPU’s exposure to moisture by keeping it in a dry environment. Finally, you can also use a coating or finish on the TPU to protect it from moisture.
Hydrolysis Resistance of Different TPU Grades
Certain polyester-based TPU grades may be sensitive to long-term exposure to moisture and heat, potentially leading to hydrolytic degradation.
However, polyether-based TPU generally provides superior hydrolysis resistance and is preferred in humid or water-exposed environments.
This distinction is important when selecting TPU for outdoor or high-moisture applications.
Conclusion
Thermoplastic Urethane is a versatile material that has low hygroscopicity compared to other materials. Its resistance to moisture absorption makes it an excellent choice for applications where exposure to moisture is unavoidable.
If you’re using TPU in a high-moisture environment, there are ways to mitigate its hygroscopicity and maintain its properties. Overall, TPU’s low hygroscopicity is a significant benefit for its users and makes it an excellent choice for a wide range of applications.
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Founded in 2008 in Foshan, China, PENGDE started to research rubber and plastic products, especially in the production of polyurethane (PU) products.
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