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 temperat ures. In addition, a cutting technique developed recently was adopted to me asure 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 re latively high tear strength of 10.40 +/- 0.94 kJ/m(2) at room temperature. Furthermore, good tear strength is still preserved, about 1.87 +/- 0.38 kJ/ m(2), at 150 degrees C, where some PP crystals are melted and start to flow . In contrast, the intrinsic strength of EPDM/PP TPEs determined from a cut ting test is varied slightly, 700-1000 J/m(2), over a wide range of tempera tures and rates. A comparison of the fracture energy measured by tearing an d cutting tests is provided and discussed. The energy density per unit volu me of EPDM/PP TPEs determined from the cutting test is 9.7 GJ/m(3), which i s about twice larger than that for the rupture of C-C bonds at room tempera ture. It is suggested that plastic yielding is a more effective process to enhance the toughness than is simply viscoelastic motion. (C) 2000 John Wil ey & Sons, Inc.