Composites of polymers with carbon nanotubes (CNTs) combine the excellent electrical and mechanical properties of CNTs with the properties and the flexible shaping of polymers. Electrical percolation at low filling grades is connected with the very high aspect ratio of CNTs requiring that the high initial CNT length is preserved to large extent after melt mixing. As shown before, shortening happens during melt mixing [1-3]. In this work, composites of polycarbonate and 0.25-2.0 wt% multiwalled CNT (Nanocyl NC7000) were melt mixed in a small-scale microcompounder by varying the mixing conditions (time, rotation speed). The electrical properties were measured and the CNT macrodispersion was examined by light microscopy. Furthermore, the length shortening and the changes in the curling state of the CNTs due to melt mixing were investigated in comparison to the as-grown nanotubes [1]. For these investigations composites containing 0.75 wt% CNTs were dissolved in chloroform and the single tubes were imaged using transmission electron microscopy. On such images, the length and the curling value of CNTs were quantified and correlated to the mixing conditions. The curling value was defined as the ratio of total to effective length of the individual nanotube. It was found that the CNT macrodispersion improved with increasing specific mechanical energy (SME) input. Additionally, the electrical percolation threshold increased with increasing SME input which correlated well with the more pronounced CNT shortening. Comparing the mean curling value at different mixing conditions, a decrease of the curling with increasing SME can be seen. Generally, the curling value lowered with decreasing CNT length. It is assumed that the nanotubes break at the defect sites and the remaining nanotube parts have a lower defect density and are straighter and more similar to an ideal nanotube. [1] Carbon 2011, 49: 1243-1247 [2] Comp Sci Technol 2011, 71(8): 1145-1153 [3] Polymer 2012, 53(2): 495-5