TPU stands for Thermoplastic Polyurethanes, a type of thermoplastic elastomer rubber. It is not a traditional textile or leather. TPU overcomes many of the shortcomings of PVC, PU leather, and PU coatings, making significant breakthroughs in waterproof and breathable fabric applications. TPU not only possesses most of the characteristics of rubber and conventional plastics but also boasts excellent comprehensive physical and chemical properties. It is a new type of environmentally friendly polymer material that lies between rubber and plastic, offering both the softness of rubber and the hardness of rigid plastic.
TPU is mainly divided into polyester-based and polyether-based types. It has a wide hardness range (60HA-85HD), is wear-resistant, oil-resistant, transparent, and has good elasticity. It is widely used in daily necessities, sports goods, toys, decorative materials, and other fields. Halogen-free flame-retardant TPU can also replace soft PVC to meet the environmental requirements of more and more fields.
An elastomer is defined as a polymer material with a glass transition temperature below room temperature, a break elongation rate of >50%, and good recovery after the removal of external forces. Polyurethane elastomers are a special category of elastomers with a wide range of hardness and performance, making them a type of polymer material that lies between rubber and plastic.
TPU can be heated and plasticized, has little to no chemical cross-linking, and its molecules are mostly linear, although there is some physical cross-linking. This type of polyurethane is known as TPU.
Wide Hardness Range: By changing the ratio of the reactive components in TPU, products with different hardness levels can be obtained. As hardness increases, the products still maintain good elasticity and wear resistance. The rigidity of TPU can be measured by its elastic modulus. The elastic modulus of rubber is usually between 1-10 MPa, TPU is between 10-1000 MPa, and plastics like nylon, ABS, PC, and POM are between 1000-10000 MPa. TPU has a wide hardness range from Shore A 60 to Shore D 85 and maintains high elasticity across this range.
High Mechanical Strength: TPU products have outstanding load-bearing capacity, impact resistance, and shock absorption performance.
Excellent Cold Resistance: TPU has a low glass transition temperature and maintains good elasticity, flexibility, and other physical properties at temperatures as low as -35°C. TPU remains flexible over a wide temperature range of -40 to 120°C without the need for plasticizers.
Good Processing Performance: TPU can be processed using common thermoplastic methods such as injection molding, extrusion, and calendering. TPU can also be co-processed with certain polymers to create polymer alloys with complementary properties.
Oil, Water, and Mold Resistance: TPU has good resistance to oils (mineral oils, animal and vegetable fats, and lubricants) and many solvents.
Recyclability: TPU can be recycled and reused.
Weather Resistance and Radiation Resistance: TPU has good weather resistance and excellent resistance to high-energy radiation.
Wear Resistance, Tear Resistance, and Flexural Strength: TPU is known for its excellent wear resistance, tear resistance, and flexural strength. It also has high tensile strength, large elongation, and low long-term compression set.
Mechanical Properties: The mechanical properties of TPU elastomers include hardness, tensile strength, compression performance, tear strength, resilience, wear resistance, and flexural resistance. TPU elastomers also have high shear strength and impact energy.
Hardness: Hardness is an indicator of a material’s ability to resist deformation, indentation, and scratching. TPU hardness is usually measured using Shore A (for softer TPU) and Shore D (for harder TPU) durometers. Hardness is mainly determined by the hard segment content in the TPU structure. As the hard segment content increases, the hardness of TPU increases, which also affects other properties such as tensile modulus, tear strength, rigidity, and compressive stress. The relationship between TPU hardness and temperature shows that from room temperature down to the transition temperature (-4 to -12°C), hardness does not change significantly. At the transition temperature, TPU hardness suddenly increases, becoming very hard and losing elasticity due to the crystallization of the soft segments.
Relationship Between Hardness, Tensile Stress, and Elongation: As TPU hardness increases, the 100% and 300% tensile stress rapidly increase, while elongation decreases. This is mainly due to the increase in hard segment content, which forms more physical cross-links, limiting material deformation. To deform the material, higher stress is required, thus increasing tensile stress and reducing elongation.
Relationship Between Hardness and Tear Strength: As hardness increases, tear strength rapidly increases for similar reasons as the increase in modulus. TPU formulations and properties can be varied in many ways, but in practical design and industrial production, the mutual limitations of raw materials (polyols, diisocyanates, and chain extenders) make it challenging to develop high-end applications.
In summary, TPU is a versatile and high-performance material with a wide range of applications due to its unique combination of properties.
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