The effect of a rigid additive (nano-SiO2 filler) and a flexible additive [poly(dimethylsiloxane) elastomer] on the crystallization of polypropylene was studied under non-isothermal conditions with differential scanning calorimetry. Crystallization parameters were evaluated with standard equations, and the results were interpreted on the basis of the rate of nucleation, crystallization, and activation energy of crystallization. The observed effect of polydimethylsiloxane of increasing the crystallization rate and lowering the activation energy of crystallization was attributed to the effect of polydimethylsiloxane chain mobility at the interface, which facilitated the molecular mobility of polypropylene. Nano-SiO2, on the other hand, acted as a nucleating agent, and the nucleation effect was dependent on the cooling rate. (c) 2008 Wiley Periodicals, Inc.