The difference between TPU polyether type and polyester type

The difference between TPU polyether type and polyester type

TPU can be divided into two types: polyether type and polyester type. According to the different requirements of product applications, different types of TPUs need to be selected. For example, if the requirements for hydrolysis resistance are relatively high, polyether type TPU is more suitable than polyester type TPU.

So today, let’s talk about the differences between polyether type TPU and polyester type TPU, and how to distinguish them? The following will elaborate on four aspects: differences in raw materials, structural differences, performance comparisons, and identification methods.

1、 Differences in raw materials

I believe many people know the concept of thermoplastic elastomers, which have a structural feature of containing both soft and hard segments, respectively, to bring flexibility and rigidity to the material.

TPU also has both soft and hard chain segments, and the difference between polyether type TPU and polyester type TPU lies in the difference in soft chain segments. We can see the difference from the raw materials.

Polyether type TPU: 4-4 ‘- diphenylmethane diisocyanate (MDI), polytetrahydrofuran (PTMEG), 1,4-butanediol (BDO), with a dosage of approximately 40% for MDI, 40% for PTMEG, and 20% for BDO.

Polyester type TPU: 4-4 ‘- diphenylmethane diisocyanate (MDI), 1,4-butanediol (BDO), adipic acid (AA), with MDI accounting for about 40%, AA accounting for about 35%, and BDO accounting for about 25%.

We can see that the raw material for the polyether type TPU soft chain segment is polytetrahydrofuran (PTMEG); The raw material for polyester type TPU soft chain segments is adipic acid (AA), where adipic acid reacts with butanediol to form polybutylene adipate ester as the soft chain segment.

2、 Structural differences

The molecular chain of TPU has an (AB) n-type block linear structure, where A is a high molecular weight (1000-6000) polyester or polyether, B is generally butanediol, and the chemical structure between the AB chain segments is diisocyanate.

According to the different structures of A, TPU can be divided into polyester type, polyether type, polycaprolactone type, polycarbonate type, etc. The more common types are polyether type TPU and polyester type TPU.

From the above figure, we can see that the overall molecular chains of polyether type TPU and polyester type TPU are both linear structures, with the main difference being whether the soft chain segment is a polyether polyol or a polyester polyol.

3、 Performance comparison

Polyether polyols are alcohol polymers or oligomers with ether bonds and hydroxyl groups at the end groups on the molecular main chain structure. Due to its low cohesive energy of ether bonds in its structure and ease of rotation.

Therefore, polyether TPU has excellent low-temperature flexibility, hydrolysis resistance, mold resistance, UV resistance, etc. The product has a good hand feel, but the peel strength and fracture strength are relatively poor.

The ester groups with strong covalent bonding energy in polyester polyols can form hydrogen bonds with hard chain segments, serving as elastic crosslinking points. However, polyester is prone to breakage due to the invasion of water molecules, and the acid generated by hydrolysis can further catalyze the hydrolysis of polyester.

Therefore, polyester TPU has excellent mechanical properties, wear resistance, tear resistance, chemical corrosion resistance, high temperature resistance, and easy processing, but poor hydrolysis resistance.

4、 Identification method

As for which TPU is better to use, it can only be said that the selection should be based on the physical requirements of the product. To achieve good mechanical properties, use polyester TPU; If considering cost, density, and product usage environment, such as making water amusement products, polyether TPU is more suitable.

However, when choosing, or accidentally mixing up two types of TPUs, they do not have a significant difference in appearance. So how should we distinguish them?

There are actually many methods, such as chemical colorimetry, gas chromatography-mass spectrometry (GCMS), mid infrared spectroscopy, etc. However, these methods require high technical requirements and take a long time.

Is there a relatively simple and fast identification method? The answer is yes, for example, density comparison method.

This method only requires one density tester. Taking a high-precision rubber density meter as an example, the measurement steps are:

Place the product into the measuring table, display the weight of the product, and press the Enter key to remember.
Place the product in water to display the density value.
The entire measurement process takes about 5 seconds, and then it can be distinguished based on the principle that the density of polyester type TPU is higher than that of polyether type TPU. The specific density range is: polyether type TPU -1.13-1.18 g/cm3; Polyester TPU -1.18-1.22 g/cm3. This method can quickly distinguish between TPU polyester type and polyether type.