The following will mainly explain the mechanical properties of TPU from the aspects of tensile strength and elongation, resilience, hardness, etc.
① High tensile strength and high elongation
TPU has excellent tensile strength and elongation. From the data in the figure below, we can see that the tensile strength and elongation of polyether TPU are far superior to polyvinyl chloride plastics and rubber.
In addition, TPU does not add or adds very little additives during the processing process, which can meet the requirements of the food industry, which is also difficult for other materials such as PVC and rubber.
② Resilience is very sensitive to temperature
The resilience of the elastomer TPU refers to the degree to which it quickly recovers to its original state after the deformation stress is released, which is expressed by recovery energy, that is, the ratio of the deformation retraction work to the work required to produce the deformation. It is a function of the dynamic modulus and internal friction of the elastomer and is very sensitive to temperature.
The soft segment of TPU is PTMG, PCL, and PBA, with relative molecular weights of 1000 and 2000 respectively; the hard segment is MDI-BDO, with hard segment contents of 48.2% (PCL-1250 is 42.7%) and 31.7% respectively, and r0=1.05 prepolymerization synthesis.
As expected, the rebound decreases with the decrease of temperature until a certain temperature, when the elasticity increases rapidly. This temperature is the crystallization temperature of the soft segment, which is determined by the structure of the macromolecular diol, and is lower for polyether TPU than polyester TPU. At temperatures below the crystallization temperature, the elastomer becomes very hard and loses its elasticity, so the rebound is similar to the rebound from leaving the hard metal surface.
③Hardness range is Shore 60A--80D
Hardness is an indicator of the material's ability to resist deformation, notches and scratches.
TPU hardness is usually measured by Shore A and Shore D durometers, Shore A is used for softer TPU, and Shore D is used for harder TPU.
Since the hardness of TPU can be adjusted by adjusting the ratio of soft and hard segments, TPU has a relatively wide hardness range, from Shore 60A--80D, spanning the hardness of rubber and plastic, and has high elasticity throughout the hardness range.
With the change of hardness, some properties of TPU will change. For example, increasing the hardness of TPU will result in performance changes such as increased tensile modulus and tear strength, increased rigidity and compressive stress (load capacity), reduced elongation, increased density and dynamic heat generation, and increased environmental resistance.