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 temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, 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 15 wt% conductive fillers, respectively, were in the range −22 to −20 dB, indicating that these composites are promising candidates for shielding applications.

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In this work, thermoplastic polyurethane-filled montmorillonite-polypyrrole (TPU/Mt-PPy) was prepared through melt mixing process for using in electromagnetic shielding applications. The effect of conducting filler content and type, sample thickness, and X-band frequency range on the electromagnetic interference shielding effectiveness (EMI SE) and EMI attenuation mechanism was investigated. A comparative study of electrical and microwave absorption properties of TPU/Mt-PPy nanocomposites and TPU/PPy blends was also reported. The total EMI SE average and electrical conductivity of all Mt-PPy.Cl or Mt-PPy.DBSA nanocomposites are higher than those found for TPU/PPy.Cl and TPU/PPy.DBSA blends. This behavior was attributed to the higher aspect ratio and better dispersion of the nanostructured Mt-PPy when compared with neat PPy. Moreover, the presence of Mt-PPy into TPU matrix increases absorption loss (SE A ) mechanism, contributing to increase EMI SE. The total EMI SE values of nanocomposites containing 30 wt% of Mt-PPy.DBSA with 2 and 5 mm thickness were approximately 16.6 and approximately 36.5 dB, respectively, corresponding to the total EMI of 98% (75% by absorption) and 99.9% (88% by absorption). These results highlight that the nanocomposites studied are promising materials for electromagnetic shielding applications. KEYWORDS montmorillonite, polypyrrole, shielding effectiveness, thermoplastic polyurethane 1 | INTRODUCTION Electromagnetic interference (EMI) has become a technical problem in the modern world because of the rapid proliferation of electronic and telecommunication systems, which emit electromagnetic radiation and may perturb the performance of electronic devices. To prevent EMI and increase the device efficiency and lifetime, many studies have been focused in producing electromagnetic radiation shielding or absorbing materials. In this context, electrically conducting polymer composites composed of intrinsically conducting polymer (ICP), such as polypyrrole (PPy) and polyaniline (PAni), dispersed in an insulating polymer matrix have attracted much interest for EMI shielding applications. 1-12 The scientific and technological interest for producing these materials is due to their lightweight, corrosion resistance, design flexibility, good processability, physical properties of polymeric materials, high electromagnetic interference shielding effectiveness (EMI SE), and good microwave absorption properties. 3,13-22 For many applications, the EMI SE value of 15 to 30 dB is considered satisfactory and corresponds to 99.9% attenuation of the EMI radiation. 13,23 Electromagnetic interference shielding effectiveness is influenced by 3 mechanisms: reflection (SE R ), absorption (SE A ), and multiple reflections (SE M ) of the electromagnetic waves. The attenuation of EMI by absorption has been preferred instead of reflection because of the increase demand of microwave absorbing materials. 24,25 Usually, microwave absorbing materials must display an electrical conductivity in the range of 10 −4 and 10 −1 S/...

Graphene nanoplatelets (xGnP), expanded graphite (EG), multiwall carbon nanotubes (MWCNTs), and carbon black (CB) were dispersed in various amounts in a thermosetting polyurethane (PU) matrix derived from castor oil and composite plaques were obtained by compression molding. The electrical percolation threshold was found to be 0.1 vol% for MWCNT, 0.5 vol% for xGnP, 2.8 vol% for CB, and 2.7 vol% for EGfilled systems. The relation between electrical conductivity, morphology, and electromagnetic interference shielding effectiveness (EMI SE) of the resulting composites was studied to understand how the EMI SE is influenced by morphology and electrical conductivity of each filler. The composites display significantly distinct EMI SE values, depending on the type of carbon filler and its volume fraction. Composite based in PU/ EG and PU/xGnP exhibited the highest EMI SE values (70 and 47 2dB, respectively); however, PU/MWCNT composites showed higher EMI SE (24 2dB) value at the same filler content (3 vol%) than the other composite system. POLYM. COMPOS., 00:000-000,

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Electrically conducting fibers were prepared through in situ oxidative polymerization of pyrrole (Py) in the presence of peach palm fibers (PPF) using iron (III) chloride hexahydrate (FeCl 3. 6H 2 O) as oxidant. The polypyrrole (PPy) coated PPF displayed a PPy layer on the fibers surface, which was responsible for an electrical conductivity of (2.2 6 0.3) 3 10 21 S cm 21 , similar to the neat PPy. Electrically conductive composites were prepared by dispersing various amounts of PPy-coated PPF in a polyurethane matrix derived from castor oil. The polyurethane/PPy-coated PPF composites (PU/ PPF-PPy) exhibited an electrical conductivity higher than PU/PPy blends with similar filler content. This behavior is attributed to the higher aspect ratio of PPF-PPy when compared with PPy particles, inducing a denser conductive network formation in the PU matrix. Electromagnetic interference shielding effectiveness (EMI SE) value in the X-band (8.2-12.4 GHz) found for PU/PPF-PPy composites containing 25 wt% of PPF-PPy were in the range 212 dB, which corresponds to 93.2% of attenuation, indicating that these composites are promising candidates for EMI shielding applications. POLYM. COMPOS., 00:000-000, 2015.