Impact toughening behaviour of quaternary PP/HDPE/EPDM/EP blends

Quaternary blends of polypropylene (PP), high-density polyethylene (HDPE), ethylene-propylene diene terpolymer (EPDM) and ethylene-propylene block copolymer (EP) were prepared in a twin-screw extruder followed by injection moulding. Izod impact tests were used to determine the impact behaviour of the blends. The results showed that the quaternary blends with EPDM content greater than or equal to 30 wt% exhibit superior impact strengths at 25 and -30 degrees C. This was due to shear yielding of the matrix in the stress whitening zone of the blends containing 30 wt% EPDM. However, Izod impact tests showed that the impact energies of the blends with 25 wt% EPDM content are dependent on the HDPE concentration at 25 degrees C. With a higher concentration of HDPE (greater than or equal to 15 wt%), the impact strengths at 25 degrees C were comparable to those of the blends containing EPDM content greater than or equal to 30 wt%. The blends with EPDM less than or equal to 25 wt% exhibited low-impact toughness at -30 degrees C as featureless fracture surface and cavitation around the rubber particles were observed in the induction zone ahead of the notch tip. The measured impact strengths generally correlated well with the SEM surface morphologies. (C) 1998 Elsevier Science Ltd. All rights reserved.