Chemistry Reference
In-Depth Information
Figure 4.
Estimated Gibbs-Thomson parameters for the Crystaf model as a function of average comonomer content (The
dashed lines are to aid the eye only).
and Raiande and Fatou
[13-14]
showed that
the closest integer for parameter n for
polyethylene in several solvents was 4. This
agrees very well with an average n value of
3.96 obtained from our parameter estima-
tion. Our average value of parameter A
(90.45
8
C) is also close to the values for
the crystallization temperature of ethylene
homopolymers in several solvents (85-
90
to 10
15
min
n
.
[12-14]
It has also been
reported that the parameter k increases as
crystallization temperature decreases. This
observation agrees well with our results
since we show that
increases with incre-
asing Crystaf cooling rates (the faster the
cooling rate, the lower the crystallization
temperature.)
For ethylene/1-hexene copolymers, the
estimated values of the parameter
k
C) reported earlier by Jackson and
Mandelkern.
[15]
Our estimated value for the parameter
8
are
relatively constant, as expected; however,
the average value of the parameter
n
k
is in the range of 2
10
8
to 16
10
5
min
n
. To the best of our knowledge, no
values have been reported for the para-
meter
of
ethylene/1-hexene copolymers (n
¼
4.49) is
slightly higher than the one for polyethy-
lene (n
¼
3.96). The value of parameter k
was found to increase with a cooling rate as
we had also observed for the polyethylene
samples. Moreover, the k value of ethylene/
n
k
values for polyethylene crystallized in seve-
ral other solvents are in the range of 10
5
k
for polyethylene in TCB, but
