Mechanical properties: The mechanical properties of TPU elastomers mainly include: hardness, tensile strength, compression properties, tear strength, resilience and wear resistance, and resistance to fuss. The mechanical properties of TPU elastomers, in addition to these properties, There are also high shear strength and impact work.
1. Hardness: Hardness is an indicator of the ability of a material to resist deformation, nicking and scratching. The TPU hardness is usually measured using a Shore A and Shore D hardness tester, with Shore A for a softer TPU and Shore D for a harder TPU. The hardness is mainly determined by the hard segment content in the TPU structure. The higher the hardness of the hard segment, the higher the hardness of the TPU. After the hardness increases, the other properties of the TPU also change, the tensile modulus and the tear strength increase, the rigidity and compressive stress (load capacity) increase, the elongation decreases, the density and dynamic heat generation increase, and the environmental resistance increases. The hardness of TPU has a certain relationship with temperature. From the cooling at room temperature to the abrupt temperature (-4~-12 °C), the hardness did not change significantly; at the abrupt temperature, the hardness of the TPU suddenly increased and became very hard and lost elasticity, which was due to the crystallization of the soft segment.
2. Relationship between hardness and tensile stress and elongation, and hardness versus tear strength. As the hardness of TPU increases, the 100% modulus and 300% modulus increase rapidly, and the elongation decreases. This is because the increase in hardness is mainly due to the increase in the hard segment content. The high hard segment content, the easier the hard segment phase formed to form a sub-crystalline or crystalline structure increases the amount of physical cross-linking and limits material deformation. If the material is deformed, the stress must be increased, thereby increasing the modulus and the elongation is lowered. The relationship between TPU hardness and tear strength, as the hardness increases, the tear strength increases rapidly, the reason is also the same as the interpretation of the modulus.
The formulation and performance of the TPU can be arranged in a wide variety of ways. However, in the realistic design and industrial production, the raw materials (polyols and polyisocyanates and chain extenders) are mutually restricted, making it extremely difficult to develop applications that are really useful for high-end applications.