Electrical, rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)-filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator-conductor transition was very sharp and the electrical percolation threshold at room temperaturewas at CNT and CB contents of about 1.0 and 1.7wt%, respectively. The EMI SE over the X-band frequency range (8-12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15wt% conductive fillers, respectively, were in the range -22 to -20 dB, indicating that these composites are promising candidates for shielding applications. (C) 2013 Society of Chemical Industry