Figure 4. Raman spectra of the multi-walled carbon nanotubes for the
preparation of epoxy matrix composite materials.
The scanning electron micrographs of the epoxy matrix composite
materials are illustrated in Figure 5 which are reinforced with
single-walled carbon nanotubes. The fracture surface is relatively
smooth and absent of any structural features. The single-walled carbon
nanotube-reinforced fracture surfaces express substantial increases in
the micron-level surface roughness. This increase in surface roughness
is the likely reason that the nanocomposites express enhanced fracture
toughness. In the resultant polymer carbon nanotube composites, the
carbon nanotubes are an integral part of polymer chains rather than
separate fillers within a polymer matrix. Polymer-carbon nanotube
composites where the carbon nanotube is chemically associated with the
polymer has the advantage that load can be transferred to the nanotubes
which provides enhanced mechanical properties to the composite and also
helps prevent separation between the polymer surface and the carbon
nanotubes. The thermal and electrical properties of the carbon nanotubes
can also be exploited in this way. The at least one oxygen moiety of the
carbon nanotubes are reacted with a suitable molecule to form a carbon
nanotube macromer before being reacted with the at least one monomer to
attach polymer chains to the sidewalls of the carbon nanotubes. The
reaction between the carbon nanotube-molecule complex and the at least
one monomer may be activated or initiated through the application of
energy in the form of heat or by the presence of a suitable chemical
initiator. However, individual carbon nanotubes tend to agglomerate,
which tends to complicate subsequent processing. For example,
agglomeration of individual carbon nanotubes tends to clog nozzles used
in fused deposition modeling. More specifically, fused deposition
modeling works by laying down material in layers from a polymer filament
to form the shape of the article having final or near-final dimensions.
However, as individual carbon nanotubes tend to agglomerate, processing
becomes complicated due to clogging of a nozzle used to lay down the
layers of a polymer incorporated with individual carbon nanotubes. Also,
individual carbon nanotubes may become airborne, raising concerns with
handling of the carbon nanotubes. The dimensions of the carbon nanotube
sheetlets are not limited and may depend upon the application of the
carbon nanotube enhanced polymer. If the dimensions of the carbon
nanotube sheetlets are too small, then concerns with handling of the
carbon nanotubes may be raised. A width of the carbon nanotube sheetlets
is not limited and may depend upon the application of the carbon
nanotube enhanced polymer.