Carbon Nanotubes (CNTs), first discovered by Sumio Ijima[1] of NEC, are large fullerene molecules made up of sheets of carbon atoms, coaxially arranged in a cylindrical shape. They have been found to improve the mechanical properties[2-3] and thermal stability[4] of certain materials with which it is combined. It was hypothesized that if combined with PMMA, the nanotubes would serve to enhance the thermal and mechanical properties. The composite was prepared by melt mixing various concentrations (between 1% -.01%) of multi-walled carbon nanotubes with poly methyl methacrylate (PMMA). Dynamic Mechanical Analysis (DMA) revealed an increase in the glass transition temperature (Tg, The temperature at which a polymer changes phase from glassy to a rubber-like state) of 11-13oC regardless of concentration (i.e. Even the addition of .01% nanotubes results in a greater than 10.7% increase in Tg over pure PMMA)(see figures 1 and 2). Differential Scanning Calorimetry (DSC) confirmed these results. Additionally further DMA results demonstrated an interesting trend, that is when nanotube concentrations were above .5% the modulus of the nanocomposite was lower than that of pure PMMA, whereas at a concentration of .1% the modulus increases by nearly one order of magnitude. We believe that there is a critical loading value for CNTs with regards to their dispersion characteristics, that is above a certain concentration the nanotubes tend to clump together forming aggregates thus lowering the modulus of a given polymer, however loading less than that value will result in either not changing the modulus or possibly even increase it.

[1]"Helical microtubules of graphitic carbon", S Iijima Nature, vol.354, p56 (1991)
[2] "Exceptionally high Young's modulus observed for individual carbon nanotubes", M M J Treacy, T W Ebbesen and J M Gibson Nature, vol.381, p678 (1996).
[3] Bucking and collapse of embedded carbon nanotubes. O. Laurie, D.E. Cox, and H.D. Wagner. Appl Phys. Lett., 81(8):1638-1641,. 1998.
[4] "Thermal Degradation and Flammability Properties of\Poly(propylene)/Carbon Nanotube Composites", Takashi Kashiwagi, Eric Grulke, Jenny Hilding, Richard Harris, Walid Awad, Jack Douglas, Macromol.Rapid Commun. 23, 764 (2002)