The works of this thesis have helped contribute to the understanding and development of the physics and chemistry of materials. In this study, new high-performance thermoplastic polymer nanocomposites with enhanced structural, thermal and mechanical properties have been fabricated by using graphene, graphene oxide and modified carbon nanotubes as reinforcing nanofillers or nucleating agents. In the first time, Graphene nanosheets (GNs) have been obtained throughout the exfoliation of natural graphite by using an efficiency chemical route. Several characterizations techniques have confirmed that the GNs have been successfully formed in large quantity. The obtained graphene derivatives exhibit high structural quality with nanoscale thickness ranging between 0.95 and 1 nm and lateral dimensions of 0.1 to 1 μm. In the second time, we describe the fabrication by extrusion process of graphene-based nanocomposites by using the PP, HDPE and PVDF matrices. The effects of graphene content on the structural, thermal, mechanical and rheological properties were reported, and the obtained results were discussed in terms of morphology and state of dispersion and distribution of the graphene nanomaterial within the polymer matrices. Morphological characterizations of the nanocomposites have shown the graphene is well dispersed within the polymer matrices, with the presence of only few aggregates. Increasing GNs content resulted in a significant increase in both mechanical and thermal properties with only few percent of GNs loading. Rheological behavior of the as-prepared nanocomposites showed a Maxwellian-like behavior for low GNs concentrations and a viscoelastic solid-like behavior for GNs content exceeding the concentration of the percolation threshold (~1 %). The improvements obtained for selected properties of nanocomposites can broaden the scope of thermoplastic polymers Finally, two different fillers were separately used as nucleating agents of the peiezoelectricly active β-polymorph in the PVDF polymer. the first is the exfoliated graphene oxide nanosheets (GOn) that were obtained by exfoliation of bulk graphite oxide in DMF solvent via a sonication treatement and the second is the multi walled carbon nanotubes (CNTs) coated by a polymeric surfactant (Polyvinylpyrrolidone, PVP) that were obtained by sonification of CNTs in a aqueous solution in presence of PVP surfactant (CNTs-PVP). These nanomaterials (GOn and CNTs-PVP) exhibit high compatibility with the PVDF polymer due to the strong and specific interaction between carbonyl group (C=O) in GOn and CNTs-PVP surfaces and fluorine group (CF2) in PVDF. Nanocomposite films of PVDF/GOn and PVDF/CNTs-PVP were prepared via the solution casting method with various filler contents. Several techniques show that the both PVDF nanocomposite films exhibit a purely piezoelectric β-phase at low content of filler (0.1 wt%). Mechanical properties of the studied PVDF nanocomposite films were also largely affected by addition either GOn or CNTs-PVP. The flexible nanocomposite films obtained in this study at very low content of external nucleating agents can be used as active materials in the field of piezoelectric applications.
