Melting Behavior and Isothermal Crystallization Kinetics of Polypropylene/Metallocene-Catalyzed Polyethylene Elastomer Blends

Polypropylene (PP)/metallocene-catalyzed polyethylene elastomer (mPE) blends were prepared in a twin-screw extruder. The melting behavior, crystallization behavior, and isothermal crystallization kinetics of the blends were studied with differential scanning calorimetry. The results showed that PP and mPE were partially miscible and that the addition of mPE shifted the melting peak of PP to a lower temperature but the crystallization temperature to a higher temperature, demonstrating a dilution effect of mPE on PP. The isothermal crystallization kinetics of the blends were described with the Avrami equation. The values of the Avrami exponent indicated that the nucleation mechanism of the blends was heterogeneous, the growth of spherulites was almost three-dimensional, and the crystallization mechanism of PP was not affected much by mPE. At the same time, the Avrami exponents of the blends were higher than that of pure PP, and this showed that the addition of mPE helped PP to form more perfect spherulites. The crystallization rate of PP was increased by mPE because the dilution effect of mPE on PP increased the mobility of PP chains. The crystallization activation energy was estimated with the Arrhenius equation, and the nucleation constant was determined by the Hoffman-Lauritzen theory. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 2615-2622, 2008