Thermoplastic polyurethane (TPU) is a class of polyurethane that can be plasticized upon heating and dissolved in solvents. Compared with both compound-type and cast-type polyurethanes, thermoplastic polyurethanes have virtually no or very few chemical crosslinks in their chemical structure; their molecular chains are essentially linear, yet they do exhibit a certain degree of physical entanglement.

Now that we know what TPU is, what are its different classifications? Depending on the criteria used for classification, TPU can be categorized in many different ways.

For example, based on the soft segment structure, polyesters, polyethers, and polybutadienes can be distinguished, each containing an ester group, an ether group, or a butene group, respectively. Based on the hard segment structure, they are classified into urethane-type and urethane-urea-type, which are obtained using diol chain extenders or diamine chain extenders, respectively.

The commonly used classification divides them into polyester-type and polyether-type.

Although TPU has many different classifications, from a molecular structural perspective, it all belongs to the polyurethane family. So, how exactly is it polymerized?

In bulk polymerization, the process can further be classified into two methods—prepolymerization and one-step method—depending on whether a pre-reaction is involved: In the prepolymerization method, the diisocyanate is first reacted with a macromolecular diol for a certain period of time before chain extender is added to produce TPU; in the one-step method, the macromolecular diol, diisocyanate, and chain extender are simultaneously mixed and reacted to form TPU.

Solution polymerization involves first dissolving the diisocyanate in a solvent, then adding a macromolecular diol and allowing the reaction to proceed for a specified period. Finally, an chain extender is added to produce TPU.

Melt processing is a commonly used technique in the plastics industry, including processes such as compounding, calendering, extrusion, blow molding, and molding (including injection, compression, transfer, and centrifugal molding, among others). Solution processing involves dissolving pellets in a solvent or directly polymerizing them in a solvent to form a solution, which is then used for coating, spinning, and other similar operations.

A material is widely used precisely because it boasts exceptionally excellent performance—and TPU is no exception.

Like cast polyurethane (liquid) and compound polyurethane (solid), TPU boasts high modulus, high strength, high elongation, and high elasticity, as well as excellent resistance to abrasion, oil, low temperatures, and aging. Among these properties, TPU’s outstanding advantages include high tensile strength, large elongation, and low long-term compression set.

Next, we will primarily discuss the mechanical properties of TPU from the perspectives of tensile strength and elongation at break, resilience, and hardness.

① High tensile strength and high elongation.

TPU exhibits exceptionally high tensile strength and elongation at break. As shown in the data below, polyether-based TPU significantly outperforms polyvinyl chloride plastics and rubber in both tensile strength and elongation at break.

Moreover, TPU requires little or no additives during the processing, meeting the stringent requirements of the food industry—something that other materials such as PVC and rubber find it difficult to achieve.

② Elasticity is highly sensitive to temperature.

The resilience of TPU refers to the degree to which it rapidly returns to its original shape after the removal of deforming stress. It is quantified by the recovery energy, which is the ratio of the work required to reverse the deformation to the work needed to induce the deformation in the first place. Resilience is a function of the dynamic modulus and internal friction of the elastomer and is highly sensitive to temperature.

The soft segments of the TPU are PTMG, PCL, and PBA, with relative molecular weights of 1000 and 2000, respectively. The hard segments are MDI-BDO, with hard-segment contents of 48.2% (42.7% for PCL-1250) and 31.7%, respectively. The pre-polymerization method was carried out using an r0 value of 1.05.

As expected, the resilience decreases as the temperature drops, until a certain temperature at which elasticity suddenly increases again. This temperature is the crystallization temperature of the soft segment, which depends on the structure of the macromolecular diol; polyether-based TPU has a lower crystallization temperature than polyester-based TPU. Below the crystallization temperature, the elastomer becomes very rigid and loses its elasticity. Consequently, resilience at these temperatures resembles the rebound experienced when leaving a hard metal surface.

③ , with a hardness range of 60 Shore. 0A--80D

TPU hardness is typically measured using Shore A and Shore D durometers. Shore A is used for softer TPUs, while Shore D is used for harder TPUs.

Because the hardness of TPU can be adjusted by varying the ratio of soft and hard segments, TPU boasts a relatively wide hardness range—from 60A to 80D on the Shore scale—spanning the hardness levels of both rubber and plastic. Moreover, TPU exhibits high elasticity across its entire hardness range.

Currently, the major global manufacturers of TPU raw materials include BASF, Covestro, Lubrizol, Huntsman, Megasun, Gao Ding, and others.

As a high-performance elastomer, TPU has a wide range of downstream applications and is extensively used in fields such as daily consumer goods, sporting goods, toys, and decorative materials. Here are a few examples:

① Shoe materials

TPU is primarily used in footwear materials due to its excellent elasticity and wear resistance. Footwear products containing TPU offer significantly greater comfort than conventional footwear, making them widely favored in high-end shoe categories—particularly sports shoes and casual shoes.

② hose

Due to their flexibility, excellent tensile strength, impact resistance, and ability to withstand both high and low temperatures, TPU hoses are widely used in China as air- and oil-conveying hoses for mechanical equipment such as aircraft, tanks, automobiles, motorcycles, machine tools, and more.

③ Cable

TPU offers tear resistance, abrasion resistance, and flexibility; its ability to withstand both high and low temperatures is particularly critical for cable performance. Consequently, in the Chinese market, high-end cables—such as control cables and power cables—are increasingly using TPU as a jacket material to protect cables with complex designs, and its applications are becoming ever more widespread.

④ Medical devices

TPU is a safe, durable, and high-quality alternative to PVC that contains no harmful chemicals such as phthalates, which could migrate into blood or other fluids within medical catheters or bags and cause adverse side effects. Specifically developed TPU grades—both extrusion-grade and injection-grade—can be easily used with only minor adjustments to existing PVC equipment.