Chemistry Reference
In-Depth Information
Fig. 3.10
DSC curves of pure and amylopectin-rich starch grafted with poly(propylene oxide)
diisocyanate [
81
]
extent of grafting onto PE [
19
]. The heat of fusion has also decreased considerably
with increase in the degree of grafting, which has indicated that grafted PE is less
stable in comparison with the virgin PE. DSC studies of amylopectin-rich starch
samples grafted with poly(propylene oxide) was carried out [
81
]. The DSC curves
of the pure and grafted amylopectins showed that the glass transition temperature
for pure amylopectin was about 50
C and after grafting reaction
T
g
value dropped
to
11
C (Fig.
3.10
). This
T
g
in grafted samples, which is lower than room
temperature, is a highly relevant factor for the potential application of this material
as solid electrolytes, since low
T
g
allows for greater chain mobility and, hence,
improves solvation and ion conduction. The presence of a second endotherm in the
DSC curves around 250
C for the copolymers synthesised from acrylamide was
reported earlier and this was attributed to the fusion of the crystallites [
82
].
The thermal transition and crystallisation of starch-g-poly(1,4-dioxan-2-one)
copolymers were studied by means of DSC [
83
]. It was found that the graft
structures of copolymers have obvious effects on the thermal and crystallisation
behaviours. Because there were more defect sites in the crystalline phase
originating from the short grafted chains of poly(1,4-dioxan-2-one) (PPDO), the
crystal structure of the copolymers was much less perfect than that of PPDO.
3.4.2.2 ThermoGravimetric Analysis of Starch-Graft-Polymers
The grafting of vinyl monomers alters the thermal stability of starch and in most
cases enhances it [
13
]. The thermal stability of graft copolymer can be compared at
the onset temperature of decomposition and the percentage of weight loss for
different stages of the decomposition. Pure starch shows a two-step characteristic
thermogram, wherein the major weight loss (75 %) takes place in the second step
within the temperature range of 233-368
C; the temperature for a maximum
