Deformation of polypropylene-EPDM blends in toughening of plastics

Polypropylene-EPDM rubber blends with rubber content varying between 0 - 30 vol. %, were made on a twin screw extruder and their mechanical properties studied. These included the measurement of the notched Izod fracture energy and the notched tensile behavior as function of strain rate (0.003 - 300 s-1) and also as a function of temperature (-40° - 140°C). During high speed testing, the deformation zone of the sample, warm up, and temperature development were followed using an infrared camera. The structure of the deformation zone was studied by scanning electron microscopy.

The blends were found to exhibit a sharp brittle-ductile transitionand have high fracture energies in the ductile region. By increasing the rubber content, the brittle ductile transition shifted strongly towards the lower temperatures. The deformation process changed with temperature and test speed, the test speed effect possibly being due to a strong adiabatic heating in the fracture plane and therefore a thermal blunting mechanism is proposed.