The kinetics of nonisothermal melting and the crystallization of polypropylene (PP) in polypropylene/carbon-fiber (C/PP) composites were studied by differential scanning calorimetry with the Nedkov and Atanasov method. Characteristic parameters such as the lamellar thickness, the transport energy through the phase boundary, and the surface free energy were determined and analyzed. In nonisothermal melting, the nucleation effect of carbon fibers was confirmed by decreasing transport energy (79 and 41 kJ/mol for PP and C/PP, respectively) and surface free energy (8 x 10(-4) and 7.9 x 10(-5) J/m(2) for PP and C/PP, respectively). Depending on the carbon-fiber content, the lamellar thickness changed from 6.7 x 10(-9) m to 9.05 x 10(-9) m. (C) 2004 Wiley Periodicals, Inc.