Destruction and formation of a conductive carbon nanotube network in polymer melts: In-line experiments

Investigations on electric conductivity and dielectric permittivity have been performed during melt processing of polycarbonate (PC) and polyamide 6 (PA6) containing different amounts of multi-walled carbon nanotubes (MWNT). For the experiments a measurement slit die containing two electrodes in capacitor geometry was flanged to the outlet of a twin-screw extruder. AC conductivity and the related complex permittivity were measured in the frequency range from 21.5 to 106 Hz for different processing conditions (melt temperature and throughput) and after stopping the extruder. It was found that the conductivity dropped down to values typical for the matrix polymer when the extrusion started. After the extruder was stopped the conductivity shows an increase of up to eight orders of magnitude with time. This conductivity recovery in the rest time after mechanical deformation was found to be faster for increasing melt temperature or samples with higher CNT concentration. The increase of the conductivity in the quiescent melt is explained by reorganization of the conductive network-like filler structure, which was - at least partially - destroyed under mechanical deformation. The reformation kinetics of the conductive network after mechanical deformation is considered to be an agglomeration process, which can be approximated by a combination of cluster aggregation and percolation theory.