Influence of the injection moulding conditions on the in-line measured electrical conductivity of polymer-carbon nanotube composites

Time resolved electrical conductivities of polycarbonate and polyamide-multiwalled carbon nanotube composites were measured inline in an injection moulding machine. During the first few seconds of an injection moulding cycle, the electrical conductivity varies with melt temperature and pressure, but then stays nearly constant for some seconds, until the part vitrifies and breaks off of the conductivity sensor, The conductivity values extracted from the time section of constant conductivity are shown in dependence of different injection moulding conditions: injection velocity, melt temperature and mould temperature. It turns out that the conductivity varied by 7 orders of magnitude by only small variations of the processing parameters. Injection velocity and melt temperature showed the largest influence, whereas the mould temperature has only minor importance. The inline measured values were compared to offline measured conductivity values, and good correlation was found. The observed behaviour of the electrical conductivity is explained in the framework of destruction/rebuilding of a conductive carbon nanotube network, where the actual state of destruction is frustrated by vitrification and crystallization. (C) 2008 WILEY-NCH Verlag GmbH & Co. KGaA, Weinheim