Toughening mechanisms in commercial thermoplastic polyolefin blends

Impact fracture mechanisms in a variety of commercially available and experimental thermoplastic polyolefin (TPO) blends were studied using the double-notch four-point-bend Charpy impact test, followed by microscopy observations. It was shown that the failure mechanisms and the sizes of the subcritically formed crack-tip damage zone before fracture were quite different among the TPO systems investigated. The room temperature Izod impact strengths of the TPOs investigated were found to correlate qualitatively well with the sizes of the damage zone. At room temperature the main fracture mechanisms observed in TPOs include matrix crazing, particle–matrix debonding, rubber particle internal cavitation, and shear banding. At low temperature (−40°C), the operative fracture mechanisms in TPOs are limited only to crazing, particle cavitation, and debonding. A strategy for improving impact strength without sacrificing scratch/mar resistance of TPOs is discussed.