OCSiAl in the Magazine Compounding World September 2016: Flow Key to CNT Dispersion
Carbon nanotubes (CNTs) have attracted considerable interest as a conductive additive for polymers due to their very high aspect ratio compared to commercially available carbon-based fillers such as carbon black, carbon fibre and graphite. This high aspect ratio results in a reduction in the percolation threshold for electrical conductivity (the minimum level where a connected network is established). The loading level of carbon black to achieve percolation, for example, is in the range from 5-10 wt%. Multi wall carbon nanotubes (MWCNTs) start to percolate at a loading level of around 1 wt%. Single wall carbon nanotubes (SWCNT) can achieve percolation at a loading level of just 0.001 wt%.
The ultralow percolation threshold of SWCNTs opens up new possibilities for the design of conductive polymer materials. For example, it is possible to produce coloured plastics filled with SWCNTs while still retaining antistatic properties. This makes SWCNTs a promising option for designing conductive plastics and for improving the physico-mechanical properties of these composites. However, the incorporation of SWCNTs into the polymer matrix remains a challenge.
It is well known that SWCNTs occur as bundles. Dispersion of the SWCNTs and the quality of that dispersion in the polymer matrix are the key parameters in achieving an optimum composite.
For thermoplastic materials, there are three main approaches to incorporating SWCNTs into a polymer matrix: in situ polymerisation; solvent-based methods; and melt mixing. The first two approaches allow preparation of a high quality SWCNT dispersion but are difficult to use at an industrial scale. Melt mixing is widely used in the polymer industry and, as a readily scalable and solvent-free method, seems well suited to SWCNT incorporation into thermoplastic matrixes.
Read the entire article in the Compounding World September 2016