Multiwalled carbon nanotube (MWCNT)/polyethylene terephthalate (PET) composites were prepared by three processing methods: direct extrusion (DE), melt compounding followed by extrusion (MCE), and dispersion of the MWCNTs in a solvent by sonication followed by extrusion (SSE). The mechanical properties of the MWCNT/PET composites processed by MCE increased with 0.1？wt% MWCNTs with respect to the neat PET. The electrical percolation threshold of MWCNT/PET composites processed by DE and MCE was ？wt% and the conductivity was higher for composites processed by MCE. Raman spectroscopy and scanning electron microscopy showed that mixing the MWCNTs by melt compounding before extruding yields better dispersion of the MWCNTs within the PET matrix. The processing method assisted by a solvent resulted in matrix plasticization. 1. Introduction Polyethylene terephthalate (PET) is a thermoplastic of major industrial importance due to its high performance, low cost, and good physical properties. It has a variety of applications such as textiles, fibers, films, bottle containers, and food packaging and is also used in the automobile and electronic industries [1, 2]. On the other hand, the discovery of carbon nanotubes (CNTs) has attracted much attention in different areas of science and technology, from fundamental science to materials engineering. The excellent electrical, thermal, and mechanical properties of CNTs, together with their high aspect ratios and large surface areas, make them ideal candidates as reinforcements for thermoplastic polymer composites [3–6]. The most challenging tasks in the fabrication of CNT/polymer composites are a homogeneous dispersion of CNTs in the polymeric matrices and achieving good interfacial interactions between the CNTs and the matrix [7]. Currently, three processing techniques are in common use for fabrication of CNT/polymer composites: in situ polymerization, solution mixing, and melt compounding. Among these three processing techniques, melt compounding has been accepted as a simple and efficient method for processing thermoplastics, especially from an industrial perspective. This method allows the fabrication of high-performance thermoplastic nanocomposites at low cost, facilitating large scale-up for commercial applications. Furthermore, the combination of an inexpensive nonconductive thermoplastic polymer with a very small amount of electrically conductive CNTs is of great technological interest, since this may provide attractive possibilities for improving the mechanical and electrical properties of polymer nanocomposites
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