Morphology and properties of melt-spun polycarbonate fibers containing single- and multi-wall carbon nanotubes
Introduction
Carbon nanotubes (CNTs) are a new class of lightweight materials that posses extraordinary mechanical, electrical, and thermal properties. For example, the tensile modulus and strength of single and multiwalled nanotubes (SWNT and MWNT) have been estimated experimentally and theoretically to be of the order of 1 TPa and 30 GPa, respectively [1], [2], [3], [4]. The combination of CNTs' low density, mechanical performance, and high aspect ratio make them excellent candidates for their use as fillers in high performance polymer nanocomposites. Such nanocomposites are attractive for their potential uses in aerospace and defense-related applications as well as in more conventional applications, e.g. automotive parts. However, full exploitation of the mechanical properties of CNTs in polymer composite applications will require exceptional control of dispersion and attainment of high degrees of alignment of individual tubes within the polymer matrix.
Significant progress is being made to address the issues of CNT dispersion and alignment. For example, surfactants and amphiphilic polymers, e.g. sodium dodecyl sulfate [5], sodium dodecylbenzene sulfonate [6], [7], octylphenolethoxylate [8], poly(vinyl pryrollidone) [9], and Gum Arabic [10], are capable of dispersing low concentrations of SWNTs in solvents. Unfortunately, the low concentrations (≪1%) and difficultly in removing the surfactant from the final product inhibit commercialization of this approach. More recent efforts in our laboratories [11], [12] and elsewhere [13] have used moderately to highly acidic solutions, respectively, to disperse relatively high concentrations of SWNTs (∼1–10 wt%) without the need of surfactants. A downside to strong acids is the tendency to degrade the nanotubes. The need for a more practical and environmentally conducive means of dispersing CNT within polymers have led researchers to evaluate direct melt processing of CNT–polymer mixtures, e.g. via twin screw extrusion, which has yielded promising results [14], [15], [16], [17], [18]. With regard to alignment, a number of approaches ranging from external magnetic fields [19], [20] to electrospinning [21], [22], [23], [24] to more conventional fiber spinning techniques [16], [25], [26], [27], [28], [29] have been used to orient CNTs. Specifically, Hagenmuller et al. [25], [30], Sennett et al. [16], and Sreekumar et al. [27] reported high degrees of orientation of CNTs in melt-spun PMMA and PC fibers and dry–wet spun PAN fibers, respectively, as determined by polarized Raman spectroscopy, infrared spectroscopy, and transmission electron microscopy (TEM).
The aim of the present work is (i) to achieve good nanotube dispersion throughout the polymer matrix using solution and melt compounding methodologies, (ii) to promote nanotube alignment using the technique of fiber melt spinning, and (iii) to develop an understanding of the relationship between nanocomposite morphology and properties. Commercially available grades of SWNTs and multi-wall carbon nanotubes (MWNTs) have been incorporated into polycarbonate. Polycarbonate was chosen because of its good combination of stiffness and ductility, its ability to disperse CNTs via melt compounding, and because of its amorphous structure. An amorphous polymer was desired since fillers are well known to alter the crystalline morphology in semi-crystalline polymers which can complicate the interpretation of nanocomposite structure–property relationships.
Section snippets
Materials
Table 1 lists the materials used in this work. A high molecular weight grade of PC was chosen to generate high shear forces that could aid in the breakup and dispersion of the carbon nanotube bundles during melt compounding and to facilitate alignment during melt spinning of fibers. The higher molecular weight material also provides good melt strength and high levels of ductility which are needed when drawing fibers during melt spinning.
Melt processing
Fig. 1 shows the different processing routes used to form
Nanocomposite morphology
Various analytical methods can be used to determine the microstructure of the composites. For SWNTs, polarized Raman spectroscopy works well, while wide angle X-ray scattering can be used only on the MWCNTs. TEM is a challenge for both types of samples. Fig. 2 shows polarized Raman spectra for PC fibers containing SWNT-soln and SWNT-dry obtained at various fiber angles, ψ, relative to the polarization direction. Each set of spectra exhibits peaks at frequencies between ∼160–265 cm−1 and at ∼1310
Discussion
The above results indicate that reasonable levels of CNT dispersion and alignment can be achieved using solution and melt compounding methodologies combined with fiber melt spinning. With regard to nanotube alignment, analyses on Raman spectra and WAXD patterns confirm quantitatively that intermediate levels of CNT orientation are achieved along the fiber axis. However, because SWNTs do not give a recognizable wide angle X-ray signal, and MWNTs do not provide useful Raman data for determining
Conclusions
Polycarbonate composite fibers containing SWNT and MWNT were fabricated by first dispersing the nanotubes by solvent blending and/or melt extrusion followed by melt spinning the composites to promote tube alignment along the fiber axis. MWNT were found to more readily disperse within the PC matrix and have larger particle aspect ratios than SWNT as determined by transmission electron microscopy; careful extraction of the PC matrix prior to TEM investigations helped circumvent the issue of poor
Acknowledgements
The authors Dr Vaughn Samuelson and James O'Connor of DuPont for their assistance with the initial setup of the melt press spinner, and Prof Robert E. Cohen of MIT for the use of the Haake Mini-Lab extruder. This material is based upon work supported by, or in part by, the US Army Research Laboratory and the US Army Research Office under contract DAAD-19-02-D-0002.
References (41)
- et al.
Chem Phys Lett
(2001) - et al.
Polymer
(2002) - et al.
Chem Phys Lett
(2000) - et al.
Polymer
(2004) - et al.
Polymer
(1981) - et al.
Polymer
(2003) - et al.
Mater Today
(2004) - et al.
Nature (London)
(1996) - et al.
Phys Rev Lett
(2000) - et al.
Science
(1997)
Top Appl Phys
Science
Nano Lett
Langmuir
Nano Lett
Nano Lett
Macromolecules
Macromolecules
Macromolecules
Eur Polym J
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Present address: Lord Corporation, Chemical R&D, 110 Lord Dr., Cary NC 27512, USA.