Nanocomposites of isotactic polypropylene with carbon nanoparticles exhibiting enhanced stiffness, thermal stability and gas barrier properties

Carbon nanoparticles (CN), synthesized by a shock wave propagation method from the free carbon of the explosive, were dispersed in isotactic polypropylene (iPP) using a twin screw co-rotating extruder. These materials were analyzed for their tensile properties, crystallization morphology, thermal stability under N2, O2 and air, as well as their permeability rates for N2, O2 and CO2. Young’s modulus was significantly enhanced, as was the tensile strength at the yield point, although at a smaller extent. However, the tensile strength and elongation at the break point slightly deteriorated with the increase of the Filler’s concentration. This behaviour was attributed to the increase tendency of CN to form aggregates into iPP matrix by increasing its content. The size of aggregates, as was evaluated by extended micro-Raman mapping, is ranged from 1 up to 5 μm. The nanoparticles caused a significant reduction of the iPP chain’s mobility leading to smaller and less ordered crystallites, with the appearance of γ-phase crystallites at CN content 5 wt.%. In inert atmosphere (N2) the presence of the nanoparticles caused a shift of the starting decomposition temperature (Td), from 368 up to 418.6 °C, while, under oxygen, thermal decomposition was more complex, displaying more than two stages. The Td was slightly lowered, up to a filler content of 2.5 wt.%, with the nanoparticles exhibiting a catalytic role at the beginning of the polymer’s decomposition. Under air, the degradation behaviour was between those exhibited in inert and O2 atmospheres. Permeability rates for the gases measured were substantially lowered with increasing filler content.