Chemistry Reference
In-Depth Information
Fig. 3.5
Scanning electron micrographs of semi-IPN hydrogels prepared with (
a
) 0.013 mM, (
b
)
0.052 mM and (
c
) 0.097 mM of MBA [
28
]
The grafting of acrylic acid (AA) onto granular maize starch in aqueous medium
initiated by ceric ion has been studied [
6
,
7
]. XRD showed that the crystallinity of
starch decreased owing to grafting.
Starch granules are semicrystalline in nature. The crystallinity is essentially due
to amylopectin fraction. The areas of crystallinity comprise about 20-25 % of the
total volume of the starch granule [
5
]. The wide angle X-ray diffraction pattern of
pure granular maize starch comprises four more or less sharp peaks with low counts
merely up to 800 between 2
values of 10-30
, which on drying and grafting
appears to have compressed into abroad smoothened peak, thereby altering the
crystallinity of pure granular starch. Therefore, along with the amorphous region,
crystalline region of the granular starch is also involved in grafting.
There were five peaks around 19.798 on the XRD pattern of starch, while only
two peaks exhibited near 16.938 on that of starch-g-PVA [
62
]. The XRD profiles
suggested that both starch and starch-g-PVA were semicrystalline (Fig.
3.7
). It
could be calculated that the crystallinity of starch and starch-g-PVA was approxi-
mately 8.03 % and 7.74 %, respectively.
The XRD pattern of pure starch shows four crystal peaks, indicating low
crystallinity, but after the starch was grafted with methacrylamide (176.3 %
grafting), the four crystal peaks were merged into a smooth peak, suggesting that
the crystal phase was also involved [
33
]. The crystalline region increases on
θ
