Multiwall nanotubes that have undergone acidic treatment of varying duration were melt-compounded with poly(ethylene terephthalate) (PET) in a batch-mixer in order to create nanocomposite structures. The samples were pressed into films and annealed above the crystallization temperature of the polymer. Fourier Transform infrared (FT-IR) as well as Raman spectroscopies were utilized to monitor the gauche to trans transformations due to the annealing process with respect to the duration of the treatment of nanotubes. In addition, differential scanning calorimetry (DSC) measurements were performed to study the crystallinity changes due to the presence of the tubes. Acid-treated nanotubes were found not only to increase PET's crystallinity but also lead to a much better crystalline formation of the polymeric chains. The spectroscopic measurements in correlation with the DSC findings showed that neat PET has relatively more trans conformers in the noncrystalline phase than the PET−MWNT nanocomposite samples. Therefore, the presence of the nanotubes transforms the trans conformers of the noncrystalline phase into crystalline domains with the nanotubes acting as moderate nucleation agents.

PET‐nanotube composite samples were manufactured by mixing neat PET with a PET‐multiwall carbon nanotube masterbatch. Fourier transform infrared (FTIR) spectroscopy was utilized to monitor the gauche and trans conformations of the polymeric chains with respect to the nanotube content. The crystallinity as well as the crystallization behavior of the polymer were studied via differential scanning calorimetry (DSC). An increase of the trans conformations and crystallinity was recorded at low NT contents followed by a sharp decrease at 1 wt % of nanotubes, further addition of nanotubes led once again to increase of the trans conformations and crystallinity. This behavior was attributed to the aggregations formation which as shown via transmission electron microscopy (TEM) was initiated at concentrations above 0.5 wt %. Discordance between the FTIR and DSC results in the case of the PET sample showed that the later bears relatively more trans non‐crystalline conformers than the nanocomposite samples. Thus it appears that the nanotubes incorporate the trans non‐crystalline segments into the crystalline phase. This work has shown that even a minor addition of carbon nanotubes (even 0.1 wt %) alters the crystallization behavior of the polymer dramatically, yielding a novel nanocomposite material rather than a simple mixture of two ingredients. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 668–676, 2008