Comparison of rheological properties of carbon nanotube/polycarbonate and carbon black/polycarbonate composites

Abstract

Conductive fillers are often added to insulating polymers to increase the composite conductivity. Adding fillers often increases the viscosity, which can make the material more difficult to process. In this study, 2-8 wt % multiwalled carbon nanotubes or 2-8 wt % carbon black were added to polycarbonate. The effects on composites' viscosities were studied with small-amplitude oscillatory shear and capillary rheometer testing. The addition of carbon nanotubes and carbon black created yield-stress materials with the yield-stresses increasing with increased filler loadings. The addition of carbon black increased the steadyshear viscosity of the composite at all shear rates for all loadings. The addition of the carbon nanotubes reduced the steady-shear viscosity of the composite at high shear rates for all loadings. This is thought to be due to an internal lubrication of the flow (enhanced disentanglement) due to the presence of the carbon nanotubes. The lubrication effect saturates once 3 wt % carbon nanotubes has been reached. The observed rheological behavior of the carbon nanotube composites is markedly different than usually seen in filled systems. A yield-stress-modified Carreau-Yasuda model was used to interpret the effects of carbon nanotube and carbon black fillers on carbon nanotube/polycarbonate and carbon black/polycarbonate composite viscosity.

Shielding effectiveness of carbon‐filled polycarbonate composites

“…The materials used for this project were previously extruded by our research group using an American Leistritz Extruder Corporation 27 mm corotating intermeshing twin screw extruder. Additional information concerning extrusion conditions are found elsewhere . A Niigata single screw injection molding machine, model NE85UA 4 , was used to produce test specimens needed for this project.…”

Electrical conductivity modeling of carbon black/polycarbonate, carbon nanotube/polycarbonate, and exfoliated graphite nanoplatelet/polycarbonate composites

“…Both screw designs were chosen to obtain a minimum amount of filler degradation, while still dispersing the filler well in the polymers. The first screw design was used for the CB/PC composites and is shown elsewhere 37. The pure polycarbonate pellets were introduced in Zone 1.…”

Tensile modulus modeling of carbon black/polycarbonate, carbon nanotube/polycarbonate, and exfoliated graphite nanoplatelet/polycarbonate composites

“…Both screw designs were chosen to obtain a minimum amount of filler degradation, while still dispersing the filler well in the polymers. The first screw design was used for the CB/PC composites and is shown elsewhere 39. The pure PC pellets were introduced in Zone 1.…”

“…Ketjenblack EC‐600 JD was introduced in Zone 5. The second screw design was used for the CNT/PC and GNP/PC composites and is shown elsewhere 39. In this case, the pure PC pellets and the Hyperion FIBRIL™ masterbatch MB6015‐00 (containing 15 wt % CNT) or the Ovation Polymers Extima™ 15 wt % xGNP™ masterbatch MB PC1515A in PC were mixed at the appropriate weight ratio to yield the desired CNT or GNP concentration and introduced in Zone 1.…”