Isothermal crystallization experiments generally confirm the
conclusions of the nonisothermal experiments: the addition of
carbon nanotubes significantly speeds the formation and growth
of crystallites. One cannot separate nucleation effects from
possible increases in crystal growth rate using isothermal
crystallization experiments. However, given the amount of filler
present, coupled with the fact that other studies have shown
that the rate of crystallite growth front movement is unaffected
by fiber nucleation, by far the most likely interpretation is that
increased nucleation by the nanotubes caused faster crystallization.
Figure 6 shows that nanotubes reduce the crystallization
halftime t1/2; the halftime is defined as the point where the
relative crystallinity reaches 50%. The top graph is simply the
halftime determined with t ) 0 as the time at which cooling
began, while the bottom graph assumes t ) 0 is ôo. Adding
nanotubes reduces the crystallization time at a given temperature
by roughly a factor of 2.