Dispersion and Alignment of Carbon Nanotubes in Polycarbonate
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Dispersion and Alignment of Carbon Nanotubes in Polycarbonate Michael Sennett, Elizabeth Welsh, J. B. Wright U.S. Army Soldier and Biological Chemical Command Natick Soldier Center Materials Science Team Natick, MA 01760 W. Z. Li, J. G. Wen, Z. F. Ren Department of Physics Boston College Chestnut Hill, MA 02467
ABSTRACT Dispersion and alignment of carbon nanotubes in thermoplastic polymers such as polycarbonate have been studied. Dispersion was accomplished by mixing in a conical twinscrew extruder and alignment was carried out using a fiber spinning apparatus. The effects of mixing time and fiber draw ratios on dispersion and alignment were investigated. Uniform dispersions were produced with relatively short residence times in the extruder. Excellent alignment of carbon nanotubes in nanocomposite filaments was obtained when the fiber draw ratio was greater than 7. The ability to closely control the dispersion and alignment of carbon nanotubes in polymers is expected to lead to the development of nanocomposites with desirable electronic and structural properties.
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Introduction The fabrication and characterization of polymer-matrix composite materials containing
carbon nanotubes (CNTs) including single wall carbon nanotubes (SWNTs) and multi wall carbon nanotubes (MWNTs) is an active field of research. These studies are motivated in large part by the potential that exists to achieve high levels of composite performance, based on the desirable physical properties of carbon nanotubes. These include tensile moduli of over 1 TPa and strengths up to 600 GPa. The need to obtain well-dispersed and aligned nanotubes in polymer matrices has been the subject of several recent reports, as this condition is anticipated to give rise to the best composite performance. High-energy sonication of solutions of polymers with dispersed nanotubes followed by solvent evaporation has been used successfully to achieve homogeneous nanocomposites.1,2 Recently, a solvent casting method coupled with a melt mixing procedure was used to make homogeneous SWNTs-PMMA films with enhanced electrical conductivity.3 Melt spinning of the homogeneous nanocomposite films at high draw ratios produced SWNTsPMMA fibers with substantial alignment of the nanotubes giving overall improved mechanical properties. Another study investigated the properties of MWNTs-PMMA films fabricated by melt blending and concluded that melt blending does not destroy the nanotubes, produces homogeneous films and increases the storage modulus of PMMA.4 We report herein, the first report to our knowledge, the direct mixing of MWNTs and SWNTs with molten polycarbonate via a twin-screw extruder to produce nanocomposites with excellent dispersion of nanotubes, followed by melt spinning of fiber to achieve a high degree of nanotube alignment.
2.
Experimental The MWNTs were produced by chemical vapor decomposition of acetylene on a
supported metal catalyst with the assistance of ammonia.5 The tubes were washed with aqueous HF to remove residual catalyst, rinsed with w
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