Mechanical functions: the mechanical functions of TPU elastomers mainly include: hardness, tensile strength, tightening function, tear strength, resilience and wear resistance function, resistance to flexion, etc., while the mechanical functions of TPU elastomers include, in addition to these functions, higher shear strength and impact work, etc.
1.Hardness: hardness is the ability of data to resist deformation, scratches and scratches. The hardness of TPU is usually measured by Shore A (Shore A) and Shore D (Shore D) durometers. A is used for soft TPU and Shore D for hard TPU. After hardness increases, other functions of TPU will also be changed, such as tensile modulus and tear strength increase, rigidity and tightening stress (load ability) increase, elongation decrease, density and dynamic heating increase, and environmental resistance increase. The hardness of TPU must be related to the temperature. From room temperature cooling to sudden temperature (-4~-12℃C), the hardness did not change significantly. At variable temperature, the hardness of TPU increases and becomes hard and elastic, which is due to the effect of soft crystallization.
2.Connection between hardness and tensile stress and elongation, and between hardness and tear strength. With the increase of TPU hardness, the stress at 100% and 300% constant elongation increased rapidly, and the elongation rate decreased. This is because the increase in hardness is primarily due to the increased content of the hard section. The higher the content of the hard segment, the easier it is to form sub-crystal or crystalline structure. If it is necessary to make the data deformation forward stress, then forward the constant elongation stress, together with the elongation rate decreases. The reason for the connection between TPU hardness and tear strength is the same as the explanation of modulus.
The formula and functions of TPU can be arranged and combined in many beautiful ways. However, it is very difficult to plan the formulation and industrial production in reality, because the original data (polyols and polyisocyanates and chain extenders) will bind each other, and then make the development of a practical application for a very high end.