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The rigid-rigid polymer toughening concept, i.e., utilization of an engineering polymer to toughen another engineering polymer, was employed to improve the fracture toughness of isotactic polypropylene (iPP) and to maintain the rigidity and heat deflection temperature of iPP. Noryl Poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) is chosen as the toughener phase to toughen PP. The fracture toughness of PP can be significantly improved by adding rigid thermoplastics PPO without causing any reduction in modulus. Incorporation of a small amount of styrene-ethylene-propylene (SEP) rubber compatibilizer, which helps reduce the size of PPO particles from 15 μm down to about 0.5 μm, further improves the toughness of iPP/PPO blends. Detailed fracture mechanism investigation reveals that Noryl PPO particles help trigger massive crazing in the PP matrix and serve to stabilize the growing crazes.

Fundamental knowledge concerning how thermoplastic polyolefins (TPOs) fail under impact fracture conditions is lacking. Approaches for gaining such knowledge are proposed. The fracture mechanisms in a variety of experimental and commercially available thermoplastic olefins (TPO) blends are investigated using the double-notch four-point-bend Charpy impact test. It is shown that the operative impact fracture mechanisms and the size of the damage zone in TPO blends depend strongly on the impact modifiers utilized. Strategy for improving low temperature impact strength of TPOs is discussed.