A new method is proposed, which can be used to analyze the influence of different additives and fillers on the nonisothermal crystallization of polymers. The composites of talc in isotactic polypropylene (i-PP) were prepared using a corotating twin-screw extruder. The compounds were subsequently dried and injection molded. PP morphology and talc dispersion were visualized using optical microscopy and computed tomography. Wide-angle X-ray scattering and small-angle X-ray scattering measurements provided an insight into the crystal structure of PP. The data obtained from nonisothermal DSC measurements were fitted to the Avrami model for the nonisothermal case. The calculated Avrami's exponent (n), which takes into account the influence of talc on the nucleation and growth of the PP crystals, was used in the combination of LauritzenHoffman and Ozawa models to calculate the nucleation parameter (Kg). A good agreement was found between the model predictions and literature values. The examination shows that the developed model extension gives an expected trend in the case of i-PP filled with talcs from the same origin but with different particle sizes. Furthermore, it is shown that delaminated talc with a higher specific surface is more efficient in nucleation of i-PP. Thus, the introduced model extension could be a useful tool for comparing of nucleation ability of different additives in the crystallization of polymers. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012