Toughening mechanisms in commercial thermoplastic polyolefin blends

Impact fracture mechanisms in a variety of commercially available and exper imental thermoplastic polyolefin (TPO) blends were studied using the double -notch four-point-bend Charpy impact test, followed by microscopy observati ons. It was shown that the failure mechanisms and the sizes of the subcriti cally formed crack-tip damage zone before fracture were quite different amo ng the TPO systems investigated. The room temperature Izod impact strengths of the TPOs investigated were found to correlate qualitatively well with t he sizes of the damage zone. At room temperature the main fracture mechanis ms observed in TPOs include matrix crazing, particle-matrix debonding, rubb er particle internal cavitation, and shear banding. At low temperature (-40 degrees C), the operative fracture mechanisms in TPOs are limited only to crazing, particle cavitation, and debonding. A strategy for improving impac t strength without sacrificing scratch/mar resistance of TPOs is discussed. (C) 2000 John Wiley & Sons, Inc.