Understanding the Effect of Silica Nanoparticles and Exfoliated Graphite Nanoplatelets on the Crystallization Behavior of Isotactic Polypropylene

This study explores how the presence of nanofillers with different structural and chemical characteristics, specifi-cally silica nanoparticles and exfoliated graphite nanopla-telets (GNP), alters the crystallization behavior and polymorphism of a semicrystalline polymer, such as poly-propylene (PP). The main focus of this research is to investigate how silica and GNP affect the nucleation and growth of PP crystals during isothermal crystallization. The nonisothermal crystallization behavior, including crys-tal structures, crystallization temperature, and rate, is also determined. PP composites with nanomaterial con-tent up to 7 wt % were produced by melt mixing and injec-tion molding. Both silica and graphite were found to be effective nucleating agents, significantly increasing the crystallization rate during isothermal crystallization, with greater changes observed in case of GNP composites. The effect of filler type and amount on the PP polymor-phism and lamella thickness was studied by X-ray diffrac-tion and modulated differential scanning calorimetry. Both silica and graphite were found to be effective nucleating agents for the less common b-phase of PP crystals even at low nanomaterial concentration. a-2crystal perfection and the recrystallization of the b-form in the a-form and/ or at the transcrystalline regime were found to be respon-sible for the recrystallization occurring upon melting in nanocomposites at high silica or medium GNP content