Chemistry Reference
In-Depth Information
gel-formation reactions. This effect led to
an even lower value for R
a
. Considering R
a
and MFR of LDPE-
tend to form aggregates dispersed in the
LDPE matrix.
[14]
Furthermore, the AA
would tend to homopolymerize noticeably.
So the optimum AA concentration is about
5.0 wt%.
-(AA-St), a suitable
DCP concentration was 0.2 wt%.
g
Effect of AA Concentration on MFR and
R
a
of LDPE-
g
-(AA-St)
Figure 5 shows the MFR and
Rheographs of LDPE-
g
-(AA-St)
Torque rheometry has frequently been
used to monitor chemical reactions during
reactive melt mixing. The torque-time
behavior of LDPE-g-(AA-St) (St/AA
¼
1)
were measured to further investigate the
effect of DCP concentration (from
0.05 wt% to 0.3 wt%) on the equilibrium
torque. From the rheographs in Figure 6,
we notice that when the DCP concentration
is below 0.1 wt%, the maximum torque
peak is absent. Increasing the DCP con-
centration caused the torque peak of the
reaction to rise dramatically. When the
DCP concentration was 0.2 wt% (Figure 6,
curve c), not only the torque peak of the
reaction increased dramatically, but also
the values of the equilibrium torque were
almost equal to that of curve b in Figure 6.
This indicates that under this condition, the
grafting reaction occurred to a suitable
degree and that the crosslinking reactions
were limited to a minimum degree.
[16]
However, when the 0.3 wt% DCP was
added to the system,
R
a
of LDPE-
g-(AA-St) versus comonomer (AA) con-
centration (St/AA
¼
1). The MFR of
LDPE-g-(AA-St) was the lowest when
the AA concentration was 1.0 wt%. This
was due to the severe crosslinking reactions
for the higher amount of DCP. MFR
reaches a maximum value when the AA
concentration is equal to 2.0 wt% and then
decreases gradually. A reasonable explana-
tion for this behavior is that the gel content
decreases under these conditions. On the
other hand, R
a
was still smaller. When the
AA concentration increases, crosslinking
reactions become more important than
grafting reaction. As a result, higher
R
a
values correlate with lower MFRs. There-
fore,
R
a
initially increases and reaches a
maximum when the AA concentration is
about 5.0 wt%. At higher AA concentra-
tions, the value of
R
a
starts decreasing
slightly. This behavior is probably a result
of the incompatibility between LDPE and
AA. The polar AA monomer molecules
the crosslinking
Figure 5.
Effect on monomer concentration on MFR and
R
a
of LDPE-
g
-(AA-St), DCP: 0.2 wt%.
