Melt mixed Carbon Nanotube / Polymer Composites
Petra Pötschke, Arup R. Bhattacharyya
Institute of Polymer Research Dresden, Department of Polymer Reactions and Blends
Germany
Keywords: multiwalled carbon nanotubes, melt compounding, electrical percolation
Composites of carbon nanotubes (CNT) with polymer matrices possess high stiffness, high strength, and good electrical conductivity at relatively low concentrations of CNT filler. This is caused by the distinct properties of the CNTs and their very large aspect ratio which is as high as 100-1000 for multi-wall carbon nanotubes (MWNT).
During melt mixing, which is the preferred method of composite formation in many cases, the tendency of MWNT to form aggregates may be minimized by appropriate application of shear during melt mixing. This contribution presents composites of polycarbonate (PC) with MWNT produced by diluting a masterbatch using melt mixing in a DACA-Micro Compounder (4g scale). The influence of processing conditions, e. g. screw speed and mixing time, on electrical resistivity of the composites (as a measure for the percolation state of the sample) is discussed. In these composites, conductivity was achieved starting from 1.5 wt.% MWNT content.
In addition, melt rheology was applied as another sensitive method to detect the percolation of the nanotubes. Light microscopy, atomic force microscopy and photographs of the composite dispersions in tetrahydrofuran were used to characterize the state of MWNT dispersion. Differential scanning calorimetry and dynamic mechanical analysis (DMA) were applied to detect changes in the glass transition behavior of PC with extrusion and with varying levels of MWNT. In addition, DMA showed the reinforcement effect of the nanotubes. The molecular weight of the PC in the composites is reduced as compared to the pure PC extruded under the same conditions due to the enhanced shear forces which is a result of enhanced melt viscosity in presence of nanotubes. Thus, the molecular weight reduction leads to changes in glass transition temperature and moduli which is counteracting to the effects originating from the nanotube addition.