Chemistry Reference
In-Depth Information
samples was much stronger than that for
LDPE-g-AA, although the molar ratio of St
to AAwas equal to 0.1. The spectra showed
that the addition of St could significantly
increase the grafting degree of AA.
would produce a greater amount of primary
radicals. According to the grafting mechan-
ism,
[11]
an increase in the amount of
macroradicals leads to severe crosslinking
of LDPE. Entanglements between poly
(acrylic acid) and LDPE backbones also
become severe. However, the gel content
decreased gradually when the St concen-
tration increased, especially at high St con-
centrations. As was reported previously,
[13]
St can easily react with the primary radicals
produced by the initiator, stabilizing the
radicals on the LDPE backbone and hinder-
ing the crosslinking reactions.
As shown in Figure 3, the gel content of
LDPE-g-(AA-St)
Effect of St/AA on the Gel Content and
MFR of LDPE-
g
-(AA-St)
The effect of St/AA on the gel content and
MFR of LDPE-
-(AA-St) is shown in
Figure 2. The AA and DCP concentration
were fixed at 5.0 wt% and 0.1 wt%based on
LDPE, respectively. The MFR increased
with increasing St/AA ratio and reached a
maximum when St/AA was approximately
equal to 1:1. This was because the addition
of St could effectively decrease crosslinking
reactions and prolong the life of the
macroradicals. MFR changed only slightly
when the St/AA ratio was higher than 1
because formed St radicals were enough to
stabilize the produced macroradicals when
St/AA was bigger than 1. As shown in
Figure 2, the gel content is higher than
30 wt% in the absence of St although the
initiator concentration is comparatively
lower. This was because AA can easily
auto-polymerize at high temperatures and
auto-polymerization of AA decreases the
consumption of DCP; consequently DCP
g
(St/AA
¼
1)
is much
lower than that of LDPE-
-(AA-St) (St/
AA
¼
1/2). This is in agreement with the
results shown in Figure 2, although there
was difference in AA content in the grafting
systems. Apparently, the addition of St can
reduce the gel content of the LDPE-
g-(AA-St) when the St/AA is equal to 1.
The gel content in the lower curve of
Figure 3 is almost independent of the DCP
concentration, when the DCP concentra-
tion is greater than 0.10 wt% because the
grafting reactions under these conditions
are dominating in the melt system. As
shown in the upper curve of Figure 3, the
g
Figure 2.
Effect of the St concentration on the gel content and MFR value of the LDPE-
g
-(AA-St), AA: 5 wt%, DCP: 0.1 wt%.
