Melt mixing as method to disperse carbon nanotubes into thermoplastic polymers

This paper presents melt mixed composites where two ways of introducing nanotubes in polymer matrices were used. In the first case, commercially available masterbatches of nanotube/polymer composites are used as the starting materials that are diluted by the pure polymer in a subsequent melt mixing process (masterbatch dilution method) while in the other case nanotubes are directly incorporated into the polymer matrix. As an example of the masterbatch dilution method, composites of polycarbonate with MWNT are presented which are produced using a Brabender PL-19 single screw. extruder. In this system, electrical percolation was found at about 0.5 wt% MWNT. The nanotube dispersion as observed by TEM investigations is quite homogeneous. The direct incorporation method is discussed in composites of polycarbonate with MWNT and SWNT. For commercial MWNT percolation was found between 1.0 and 3.0 wt% depending on the aspect ratio and purity of the materials. For HiPCO-SWNT from CNI percolation occurred between 0.25 wt% and 0.5 wt% SWNT. The incorporation of nanotubes significantly changes the stress-strain behavior of the composites: modulus and stress are enhanced; however, the elongation at break is reduced especially above the percolation concentration.