Influence of mixing conditions on rheological behavior and electrical conductivity of polyamides filled with carbon black

The introduction of carbon black in a polyamide matrix allows one to obtain conductive materials because of the formation of a filler network. Resulting electrical properties depend, among others, on the processing conditions. In a first part, we investigate the influence of mixing conditions (rotor speed, temperature, mixing time) on electrical conductivity. Then, in a second part, we try to characterize the conducting network by rheological measurements and to establish relationships between rheological parameters and electrical properties. For that purpose, we propose to perform successive strain sweep experiments at constant frequency, from 0.5 to 100%, then from 100 to 0.5%, and finally, again, from 0.5 to 100%. Between two successive strain sweeps, we observe a drop in the moduli values that can be attributed to the breakdown of the carbon black network. A clear relationship is established between rheological and electrical properties of the compounds. Moreover, we propose a presentation of the rheological data that permits to rank the samples according to the strength of the carbon black network.