A new process was used to foam polypropylene (PP) with batch foaming technique with supercritical carbon dioxide (scCO(2)) as the blowing agent. Comparing with the conventional process, the new one takes less time to foam and the foaming temperature range is much broader, which is about 2.5 h and 55 degrees C, respectively. An activation model was established on the basis of mass equilibrium, this model was combined with classical nucleation theory and S-L EOS model to explain foaming behaviors of PP and simulate the cell nucleation and cell diameter. A satisfactory agreement between calculated and experimental values was obtained. (c) 2013 Wiley Periodicals, Inc.