Polypropylene-rubber blends: 4. The effect of the rubber particle size on the fracture behaviour at low and high test speed

The effect of the rubber particle size and rubber content on the fracture behaviour of polypropylene-EPR blends was studied at low and high test speeds. The particle size was varied by changing the molecular weight of the EPR phase, and ranged from about 0.5 to around 4.0 mu m. The fracture behaviour was determined as a function of temperature by the notched Izod impact test (high test speed) and by a tensile test on notched Izod bars at 1 mm/s (low test speed). At high test speed the brittle-ductile transition temperature (T-bd) increases with increasing particle size. At low test speed the T-bd decreases slightly with increasing particle size. The weight average particle size gave a better correlation with the notched Izod results than the number average particle size. This suggests that the larger particles initiate the fracture more easily. (C) 1999 Elsevier Science Ltd. All rights reserved.