Instrumented tensile and falling weight impact response of injection-molded alpha- and beta-phase polypropylene homopolymers with various melt flow indices

In this study the instrumented tensile (ITI) and falling weight impact (IFW I) behavior of injection-molded alpha- and beta-phase polypropylene (PP) ho mopolymers were compared at ambient temperature in a broad melt flow index (MFI = 0.7-13 dg/min) range. It was found that the toughness of beta-PP is superior to the alpha-PP: the difference between them increased with decrea sing MFI or increasing molecular weight (MW). As expected, the injection mo lding induced skin layer thickness increased with increasing MW. Effects of the skin-core morphology were deduced indirectly by considering the result s achieved on specimens molded at low and high injection speeds (upsilon(in j) = 6 and 150 mm/s), respectively. It was found that the effect of the ski n-core structure is markedly stronger under uniaxial in-plane (i.e., ITI) t han in biaxial out-of-plane type loading (i.e., IFWI). (C) 1999 John Wiley & Sons, Inc.