Chemistry Reference
In-Depth Information
Figure 6.
Rheographs of LDPE as a function of DCP concentration, a: 0.05%; b: 0.1%; c: 0.2%; d: 0.3% DCP based on LDPE,
AA: 6 wt%.
became severe for higher values of equili-
brium torque. This is not desirable for
processing with twin-screw or single-screw
extruders.
It was observed from the rheographs
that the torque is stabilized after approxi-
mately five minutes of mixing, suggesting
that mixing and grafting reactions had
occurred within these five minutes. In all,
the suitable value of the DCP was about
0.2 wt% from both Figure 4 and Figure 6.
the samples tend to decrease when com-
pared with 121
8
, the water contact angle of
the control LDPE film. The contact angle of
LDPE-g-(AA-St) is the smallest when St/
AA is equal to 1:10. However, when St/AA
is equal to 1:1, the contact angle increases
again. When small amounts of St are added
to the grafting system, there is an obvious
increase of R
a
of AA.
[15]
On the other hand,
the St groups located on the surface of the
film are comparatively lower. Both factors
improve the surface polarity of the film and
reduce the contact angle. When the St/AA
ratio increases, the amount of St introduced
onto the LDPE film increases and the
hydrophobic benzene ring reduces the
surface polarity of the film. However, as
we can see from the Table 1, when the St/
AA ratio is higher than 1:1, the grafting
degree of AA is elevated concomitantly,
but the St groups located on the surface
severely hinder the hydrophibility of the
grafted film. Therefore, the contact angle
began to increase again. These results can
be seen clearly in Figure 7.
Hydrophilicity Characterization of the
Grafted Films
The contact angles of water on the films of
LDPE-
-(AA-St)
are presented in Table 1. The data shows
that all the equilibrium contact angles of
g
-AA and various LDPE-
g
Table 1.
Relationship between the contact angle of water, R
a
and the feed molar composition.
St/AA
u
e
(Degree
2)
R
a
LDPE
121
0
0/1
108
0.2650
0.1/1
82
0.3843
Rheological Properties
Capillary rheometry was used to character-
ize the control LDPE (St/AA
ΒΌ
0/0) and the
0.5/1
90
0.4502
1/1
94
0.5705
1.5/1
101
0.5568
