Fracture energies and tensile strength of an EPDM/PP thermoplastic elastomer

Measurements of the tear strength of EPDM/PP thermoplastic elastomers (EPDM/PP TPEs, Santoprene 201-87) were carried out at various rates and temperatures. In addition, a cutting technique developed recently was adopted to measure the fracture energy in a process where a well-controlled geometry of the crack tip was obtained. Results show that the EPDM/PP TPEs possess a relatively high tear strength of 10.40 ± 0.94 kJ/m2 at room temperature. Furthermore, good tear strength is still preserved, about 1.87 ± 0.38 kJ/m2, at 150°C, where some PP crystals are melted and start to flow. In contrast, the intrinsic strength of EPDM/PP TPEs determined from a cutting test is varied slightly, 700–1000 J/m2, over a wide range of temperatures and rates. A comparison of the fracture energy measured by tearing and cutting tests is provided and discussed. The energy density per unit volume of EPDM/PP TPEs determined from the cutting test is 9.7 GJ/m3, which is about twice larger than that for the rupture of CC bonds at room temperature. It is suggested that plastic yielding is a more effective process to enhance the toughness than is simply viscoelastic motion.