Fracture of polypropylene: 1. The effect of molecular weight and temperature at low and high test speed

The fracture behaviour of polypropylene was studied as a function of the molecular weight and the temperature. The molecular weight (Mw) ranged from 164 to 657 kg/mol. The fracture behaviour was studied by the notched Izod impact test and by a tensile test on notched Izod bars at low (1 mm/s) and high (1 m/s) test speed. The process of strong energy absorption during crack propagation, referred to as ductile deformation, is associated with the formation of shearlips. At 1 mm/s, the ductile deformation is initiated by necking during crack initiation; at 1 m/s ductile deformation precedes necking. The brittle/ductile transition temperature (Tbd) decreases with increasing molecular weight. The Tbd–molecular weight curve shifts by about 40°C towards higher temperatures if the test speed is increased from 1 mm/s to 1 m/s.