Optimizing the balance between impact strength and stiffness in polypropylene/elastomer blends by incorporation of a nucleating agent

Isotactic polypropylene (iPP) blends were prepared with two different thermoplastic elastomers, a triblock copolymer styrene–ethylene butylene–styrene (SEBS) and a metallocenic ethylene‐octene copolymer (EO). The mechanical properties and morphology of blends with 0–50 wt% elastomer were studied to determine the influence of the presence of the elastomer on the improvement of toughness. The addition of a nucleating agent as a third component exerted a significant effect on the overall properties. Dynamic mechanical properties, flexural modulus, and impact strength as well as morphology were studied for nucleated and nonnucleated iPP/SEBS and iPP/EO blends. The improvement of impact properties found in binary blends was accompanied by a decrease in stiffness. However, the addition of the nucleating agent provided a good balance between impact strength and stiffness. From the results, SEBS was determined to be a better impact modifier for iPP than EO. The nucleated iPP/SEBS blends demonstrated improved mechanical properties compared with both the nucleated iPP/EO blends and the nonnucleated blends. POLYM. ENG. SCI., 48:80–87, 2008. © 2007 Society of Plastics Engineers