IMPACT TOUGHENING BEHAVIOR OF QUATERNARY PP HDPE/EPDM/EP BLENDS/

Quaternary blends of polypropylene (PP), high-density polyethylene (HD PE), 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 im pact behaviour of the blends. The results showed that the quaternary b lends with EPDM content greater than or equal to 30 wt% exhibit superi or impact strengths at 25 and -30 degrees C. This was due to shear yie lding of the matrix in the stress whitening zone of the blends contain ing 30 wt% EPDM. However, Izod impact tests showed that the impact ene rgies of the blends with 25 wt% EPDM content are dependent on the HDPE concentration at 25 degrees C. With a higher concentration of HDPE (g reater 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 2 5 wt% exhibited low-impact toughness at -30 degrees C as featureless f racture surface and cavitation around the rubber particles were observ ed in the induction zone ahead of the notch tip. The measured impact s trengths generally correlated well with the SEM surface morphologies. (C) 1998 Elsevier Science Ltd. All rights reserved.