Polypropylene-rubber blends 2: the effect of the rubber content and temperature on the fracture behaviour at low and high test speed

The effect of the rubber content on the deformation and impact behaviour of polypropylene–EPDM rubber blends is studied. The blends are made on a twin screw extruder. The rubber content ranged from 0 to 40 vol.%. The tensile modulus and the yield stress decrease linearly with increasing rubber content. The crystallinity of the PP phase as measured with differential scanning calorimetry did not change with rubber content. The fracture behaviour was studied with a notched Izod impact test and with an instrumented single edged notched tensile test at 1 m/s and 1 mm/s. The blends were studied in temperature range from −80 to 120°C. The brittle–ductile transition temperature (Tbd) decreases with increasing rubber content from 85°C for pure polypropylene to −50°C for a 40 vol.% blend, a shift of 135°C. The Tbd with the notched Izod test and the SEN at 1 m/s are very comparable. The Tbd for the SEN at 1 mm/s if compared to the 1 m/s are at a 30°C lower temperature. The brittle–ductile transition at the low test speed is gradual, while at high test speeds the transition is abrupt, discontinuous. A good criterion for the onset of ductility is the crack propagation displacement.