Chemistry Reference
In-Depth Information
experimental Crystaf profiles (
), Equa-
lization temperatures and the broadening
of the distributions as the comonomer
content increases.
Optimummodel parameters (n, k, A, and
B) were obtained by minimizing the func-
tion
F
tion (10).
Results and Discussion
in Equation (10). Figure 3 and 4
shows the Avrami and modified Gibb-
Thomson parameters estimated for the
polyethylene samples at several cooling
rates. As expected, the values of
F
Figure 1 and 2 compare experimental and
modeled Crystaf profiles polyethylene and
ethylene/1-hexene copolymers measured at
several cooling rates. The proposed model
adequately describes the effect of cooling
rate on Crystaf profiles for all samples
and correctly follows the broadening of the
distributions due to crystallization kinetic
effects. The model also captures well the
comonomer content effect by predicting
the shift of Crystaf profiles to lower crystal-
B
are practically independent of cooling rate
(or crystallization temperature). For poly-
ethylene, the average values for these three
parameters are
n
,
A
, and
C, and
B
¼
654.75
8
C
(number of repeating unit).
Previous investigations on polymer crystal-
lization from solution by Devoy et al.
[12]
n
¼
3.96,
A
¼
90.45
8
Figure 3.
Estimated Avrami parameters for the Crystaf model. The parameter k is an apparent or average value. (The
dashed line is the average value for the estimated parameters).
