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. 2017 May 18;10(5):545.
doi: 10.3390/ma10050545.

Effect of Graphite Nanoplate Morphology on the Dispersion and Physical Properties of Polycarbonate Based Composites

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Free PMC article

Effect of Graphite Nanoplate Morphology on the Dispersion and Physical Properties of Polycarbonate Based Composites

Michael Thomas Müller et al. Materials (Basel). .
Free PMC article

Abstract

The influence of the morphology of industrial graphite nanoplate (GNP) materials on their dispersion in polycarbonate (PC) is studied. Three GNP morphology types were identified, namely lamellar, fragmented or compact structure. The dispersion evolution of all GNP types in PC is similar with varying melt temperature, screw speed, or mixing time during melt mixing. Increased shear stress reduces the size of GNP primary structures, whereby the GNP aspect ratio decreases. A significant GNP exfoliation to individual or few graphene layers could not be achieved under the selected melt mixing conditions. The resulting GNP macrodispersion depends on the individual GNP morphology, particle sizes and bulk density and is clearly reflected in the composite's electrical, thermal, mechanical, and gas barrier properties. Based on a comparison with carbon nanotubes (CNT) and carbon black (CB), CNT are recommended in regard to electrical conductivity, whereas, for thermal conductive or gas barrier application, GNP is preferred.

Keywords: dispersion; electrical; graphite nanoplates; melt compounding; polymer-matrix composites (PMCs); thermal and mechanical properties.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
SEM images of different as-received commercially available GNP powders with compact platelet structure.
Figure 2
Figure 2
SEM images of different as-received commercially available GNP powders with lamellar worm-like structure.
Figure 3
Figure 3
SEM images of as-received commercially available GNP powder with a fragmented plate structure.
Figure 4
Figure 4
SEM images of as-received commercially available reference carbon filler powders.
Figure 5
Figure 5
Comparison of the shapes of the different used carbon filler after embedding in polycarbonate (TEM images).
Figure 5
Figure 5
Comparison of the shapes of the different used carbon filler after embedding in polycarbonate (TEM images).
Figure 6
Figure 6
Orientation of graphite platelet structures in extruded strands: (left) schematic figure of platelet orientation along strand flow direction by extrusion out of the die; and (right) transmission light microscopy pictures of samples cut perpendicular to the strand direction (shows mainly the layer thickness) and cut parallel to the long-axis of the strand (shows the lateral dimension of visible GNP structures), here shown for 1 wt % Graphene nanopowder AO-3 in PC.
Figure 7
Figure 7
Anisotropy effect in the evaluation of the area fraction of GNP structures (PC with 1 wt % GNP), based on light microscopy images: perpendicular to the strand direction (a) after 5 min and (c) after 30 min mixing; parallel to the strand direction (b) after 5 min and (d) after 30 min mixing; particle size distributions based on circle equivalent particle diameters.
Figure 8
Figure 8
Comparison of the area ratio Ar of microscopically visible GNP structures of different GNP morphologies in PC as a function of screw speed and melt temperature (a) Graphene nanopowder AO-3, (b) Cheap Tubes GNP Grade 3 and (c) ACS-Single Layer Graphene (filler content 1 wt %, mixing time 5 min) together with light microscopy images indicating the state of dispersion for selected processing parameters (cuts performed perpendicular to the strand direction).
Figure 8
Figure 8
Comparison of the area ratio Ar of microscopically visible GNP structures of different GNP morphologies in PC as a function of screw speed and melt temperature (a) Graphene nanopowder AO-3, (b) Cheap Tubes GNP Grade 3 and (c) ACS-Single Layer Graphene (filler content 1 wt %, mixing time 5 min) together with light microscopy images indicating the state of dispersion for selected processing parameters (cuts performed perpendicular to the strand direction).
Figure 9
Figure 9
Area ratio of the microscopically visible GNP structures as a function of the specific mechanical energy SME; small numbers indicating the mixing time (cuts performed perpendicular).
Figure 10
Figure 10
Electrical percolation behavior of various commercially available carbon fillers in polycarbonate (dispersion optimized processing parameters are used), measured through the thickness direction of compression molded plates (Keithley 8009 Resistivity Test Fixture; plate configuration).
Figure 11
Figure 11
Electrical percolation behavior of compact structure GNPs with different initial particle sizes in polycarbonate (dispersion optimized processing parameters are used; 280 °C, 250 rpm, 5 min), measured through the thickness direction of compression molded plates (Keithley 8009 Resistivity Test Fixture plate configuration).
Figure 12
Figure 12
Electrical percolation behavior of different types of lamellar structure GNPs in polycarbonate (dispersion optimized processing parameters are used), measured through the thickness direction of compression molded plates (Keithley 8009 Resistivity Test Fixture plate configuration).
Figure 13
Figure 13
Stress–strain behavior of various commercially available carbon fillers in polycarbonate (optimized processing parameters), measured on bars punched from compression molded plates.
Figure 14
Figure 14
Relative shear modulus (DMTA measurements) of GNP, CNT and CB based PC composites.
Figure 15
Figure 15
Thermal conductivity of different commercially available carbon fillers in polycarbonate (dispersion-optimized processing parameters), measured on a compression molded plates (using a HotDisc device) at a filler content of 10 wt %.
Figure 16
Figure 16
Glass transition temperature Tg (measured by DSC) of various commercially available carbon fillers in polycarbonate (dispersion-optimized processing parameters).
Figure 17
Figure 17
Relative oxygen permeability of commercially available carbon fillers in polycarbonate (dispersion optimized processing parameters); measured on compression molded plates.

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