AUTHORS: Fiona McKenzie, Rodney Andrews and Frank Derbyshire
Center for Applied Energy Research, University of Kentucky, Lexington, KY 40511-8410
Recent developments have shown that the production of multiwalled carbon nanotubes (MWNTs), both cheaply and in large quantities, is a distinct possibility. We anticipate that the main challenge in bringing nanotube materials into the marketplace will not be production, but rather the problems in synthesizing these advanced nanotube-containing materials. In recent work, we have focused on the development of nanotube-polymer composites. To prepare thin polymer films containing MWNTs, an ultrasonic wand was used to disperse the nanotubes and solvents were employed to reduce viscosity as an aid to enhancing dispersion. This work has shown that the presence of MWNTs in polymers can produce dramatic improvements in conductivity and changes in mechanical properties.
Industrial processing of MWNT-polymer mixtures would probably involve shear mixing followed by extrusion to form geometric shapes. Preliminary work suggests that the inclusion of relatively small quantities of MWNTs produces substantial changes in viscosity in both polymer and pitch systems and that these changes are very pronounced at low mixing speeds.
In this study the viscosity of polypropylene compounded with MWNTs is measured for a range of die aspect ratios using a Haake Polylab conical twin screw extruder with capillary rheometer. The rheological properties are studied as a function of temperature, MWNT concentration and the properties of the nanotubes (aspect ratio, length and diameter distribution) and the viscoelastic behavior of the mixtures described.