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Composite materials of polypropylene, graphene nanoplatelets (GNP) or fullerene C60 were synthesized by in situ polymerization. GNP particles consist of 3-5 graphene layers and have aspect ratio 40. In composites with pristine GNP particles their aspect ratio is 110, whereas ultrasonic processing reduces it to 40-50. This change of aspect ratio of filler particles and their aggregates results in different properties of composites with pristine and sonicated GNP. Percolation threshold for composites with pristine GNP is 0.25% vol. In composites with sonicated GNP it is 2-3% vol. This is due to reduction in the size of filler particles aggregates and more uniform distribution of particles in polymer matrix after ultrasonic treatment. The presence of nanocarbon filler (GNP or fullerene) makes α-transition, associated with the glass transition of the amorphous phase of polypropylene, clearly resolved. Its intensity increases with the concentration of nanofiller, which acts as a dielectric probe. POLYM. COMPOS., 36:1006-1011, 2015. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Nanocomposites of polypropylene and graphene nanoplatelets were synthesized by in situ polymerization in liquid monomer in the presence of highly effective isospecific homogeneous metallocene catalyst. Microstructure, mechanical, dielectric, and thermal properties of composites are presented. X-ray phase analysis data indicate that graphene nanoplatelets are present in composites as thin flaky particles aggregates, with aspect ratio affected by sonication of reaction mixture. Crystallization temperature of polypropylene increases in composites. Nanocomposites are characterized by high rigidity, thermal stability, and crystallization temperature, low conductivity, and high dielectric losses in the microwave range. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]