Physical characterization of commercial polyolefinic thermoplastic elastomers

In this work, a systematic study of physical characterization on a series of commercial polyolefinic thermoplastic elastomers (TPEs), is reported. Formulations from different manufacturers, having a wide range of Shore hardness values (from A45 to D51), were examined using simple, inexpensive and standard laboratory methods. From this analysis, the TPE chemical composition and its relationship with hardness and tensile set—the key parameters that define the TPE performance in most of the applications—could be established. It was found that the strategy followed by the manufacturers to design TPEs is very similar. The EPDMs used for the different formulations look similar in ethylene content and thermal properties. Therefore, the TPE bulk modulus (or hardness) is mainly controlled by the PP content. Nice elastomeric behavior was observed only in grades with a dominant proportion of EPDM, in agreement with the deformation mechanism generally accepted for this type of materials. Grades with higher hardness values—and a dominant proportion of PP—showed a mechanical response corresponding to a toughened thermoplastic, even when these grades are marketed by the producers as “thermoplastic elastomers”. Differently from conventional crosslinked elastomers, where hardness and ability to recover from highly deformed states can be simultaneously controlled by changing the degree of crosslinking, the results of this work indicate that it is very difficult to increase TPE hardness without sacrificing elastomeric properties.