Electrically Conductive Polypropylene Nanocomposites with Negative Permittivity at Low Carbon Nanotube Loading Levels

Abstract

Polypropylene (PP)/carbon nanotubes (CNTs) nanocomposites were prepared by coating CNTs on the surface of gelated/swollen soft PP pellets. The electrical conductivity (σ) studies revealed a percolation threshold of only 0.3 wt %, and the electrical conductivity mechanism followed a 3-d variable range hopping (VRH) behavior. At lower processing temperature, the CNTs formed the network structure more easily, resulting in a higher σ. The fraction of γ-phase PP increased with increasing the pressing temperature. The CNTs at lower loading (0.1 wt %) served as nucleating sites and promoted the crystallization of PP. The CNTs favored the disentanglement of polymer chains and thus caused an even lower melt viscosity of nanocomposites than that of pure PP. The calculated optical band gap of CNTs was observed to increase with increasing the processing temperature, i.e., 1.55 eV for nanocomposites prepared at 120 °C and 1.70 eV prepared at 160 and 180 °C. Both the Drude model and interband transition phenomenon have been used for theoretical analysis of the real permittivity of the nanocomposites.

Effect of Carbon-Based Particles on the Mechanical Behavior of Isotactic Poly(propylene)s

“…[ 36 ] It therefore becomes independent of frequency in the percolation threshold, making lines connecting points measured at the same angular frequency cross. While this is true for homogeneous systems [ 83 ] and some heterogeneous composite systems, [ 49,58 ] our melt mixed samples showed a frequency-dependent values above the transition similar to that reported by Ratzsch et al [ 36 ] We chose to use the crossover of the 0.01 and 0.1 rad s −1 isolines, since it is the lower range of frequencies where the percolated zone was more easily observable experimentally.…”

“…[ 62 ] From this fi gure the strong effect of the carbon-based fi llers on the viscoelastic behavior of the poly(propylene) is evident. The pronounced effect is increasing G ′ by several orders of magnitude as reported for other iPP nanocomposites with CNTs, [ 7,44,45,51,[55][56][57][58] graphite, [ 61 ] and TrGO. [ 45,62 ] Figure 4 a shows a plateau in G ′ in composites with 10 wt% of CNTs at low frequencies, attributed to the formation of a percolated network within the nanocomposite limiting the polymer relaxations as above discussed.…”

“…[ 30 ] Moreover, rheology can detect the presence of complex morphologies, such as a percolated structure associated to the formation of a 3D network of nanoparticles along the nanocomposite, [ 42,43 ] This network changes the behavior of the melt matrix at low shear rates and low frequencies from a liquid-like Newtonian fl uid to a solid-like Hooke fl uid. The dependence of viscoelastic parameters on the concentration of carbon-based fi ller has been widely studied in the literature for polymer composites with CNTs, [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] but little has been addressed in composites with other fi llers such as graphite, [59][60][61] and/or TrGO. [ 36,45,60,62,63 ] Isotactic poly(propylene) nanocomposites with CNTs have a rheological percolation at concentrations between 0.3 and ≈ 3 wt%, [ 45,49,51,[56][57][58] while iPP/TrGO composites require concentration above 5 wt% to achieve rheological percolation, [ 45 ] showing that the size and aspect ratio of the carbon-based fi ller affect the melt rheology of the composite.…”

Magnetic negative permittivity with dielectric resonance in random Fe3O4@graphene-phenolic resin composites

“…It was found that the ɛ″ of the FGR-PR composites increased with increasing FGR content, indicating enhanced dielectric loss. Dielectric loss was mainly caused by interfacial polarization and conduction [45][46][47][48][49]. The interfacial polarization enhanced with the increasing FGR content, resulting in enhancement of interfacial polarization loss.…”

Introducing advanced composites and hybrid materials

“…For example, after introducing 0.7 wt% polyaniline (PANI) functionalized multi-walled carbon nanotubes (MWCNTs) into epoxy matrix, an 85% improvement in the tensile strength was obtained [24]. The electrical conductivity of polypropylene (PP) was increased by~7 orders of magnitudes after incorporating 0.3 wt% CNTs [25]. Adding 40 wt% functionalized graphite nanoplatelets (fGNPs) into polyphenylene sulfide (PPS) leads to a 20 times higher thermal conductivity as compared to pure PPS [26].…”