Melt mixing of polycarbonate/multi-wall carbon nanotube composites

Composites of polycarbonate (PC) with multi-wall carbon nanotubes (MWNT) of different concentrations are prepared by diluting a PC based masterbatch containing 15 wt% MWNT using melt mixing in a DACA-Micro Compounder (4 g scale). Electrical resistivity measurements indicate that the percolation of MWNT is reached between 1 and 1.5 wt%. In addition, melt rheology was applied as another sensitive method to detect the percolation of the nanotubes. Atomic Force Microscopy and visual observations of the composite dispersions in a PC-solvent were used to characterise the state of MWNT dispersion. Differential Scanning Calorimetry and Dynamic Mechanical Analysis were applied to detect changes in the glass transition temperature of PC as a result of processing and of MWNT interactions with the PC matrix including the state of dispersion. In addition, DMA confirmed the reinforcement effect of the nanotubes. The results show that the nanotube incorporation also influences the processing behaviour. Due to the enhancement in melt viscosity by adding nanotubes and the enhanced shear forces, the molecular weight of the PC in the composites is reduced as compared to PC extruded under the same conditions. This effect leads to changes in the glass transition temperature and modulus which counteracts the effects originating from the nanotube-polymer interaction.