Crystallization behavior of polypropylene/graphene nanoplatelets nanocomposite fibersII. Non-isothermal crystallization kinetics

Both physical and mechanical properties of a semi-crystalline polymer are highly related to the crystallization behavior and morphology development during processing. In the present work, non-isothermal crystallization of polypropylene/graphene nanoplatelets (PP/GnPs) nanocomposite fibers containing 0.1, 0.5, and 1% GnPs was investigated by differential scanning calorimetry (DSC). The Ozawa and Mo methods were used to fit the primary stage of non-isothermal crystallization of the samples. Moreover, the nucleation activity and the crystallization activation energy of GnPs in the PP matrix were calculated by Dobreva’s approach and Friedman’s method, respectively. The results show that the crystallization peak shifted to the lower temperatures with increasing cooling rate. Contrary to Ozawa method, it was observed that Mo approach could describe the non-isothermal crystallization process of PP and PP/GnPs nanocomposite fibers satisfactory. Furthermore, the maximum and minimum nucleation activity was observed for PP/G-0.1 and PP/G-1 nanocomposite fibers, respectively. Crystallization activation energy decreased in the presence of GnPs, indicating that it is easier for the PP/GnPs to crystallize. Although GnPs work as a nucleating agent, they also act as a barrier to molecular mobility and reduce the growth rate, resulting in a more depressed crystallization for PP/GnPs nanocomposite fibers.