Chemistry Reference
In-Depth Information
Fig. 7.1
SEM of (
a
) psyllium and (
b
) cross-linked Psy-
g
-poly(AA) [
53
]
SEM micrograms of before and after graft copolymerization. Surface was found to
be less smooth, having caves and holes after graft copolymerization [
52
]. SEM
images of psyllium hydrogel showed marked differences before and after cross-
linking (Fig.
7.1
). Psyllium has smooth homogeneous surface, while cross-linked
psyllium with poly(acrylic acid) showed network structure with cross-linking in the
form of overlapped fibrils [
53
].
AFM is an important technique to study smooth gel surface with nanometer-
sized protrusions and provide quantitative information regarding topography. AFM
also provides information regarding mechanical properties and local elastic
properties of hydrogel surface [
54
].
Fourier transform infrared spectroscopy is used to determine the nature of
modification of hydrogels [
55
]. Introduction of acrylamide group in psyllium was
confirmed by FTIR spectrum which showed emergence of new bands at
1666.7 cm
-1
O stretch) and 1425.4 cm
1
(N-H in plane bending) and
1249.9 cm
1
(C-N stretching vibration) besides peaks obtained with that of psyl-
lium (Fig.
7.2
)[
56
]. Gum arabic showed peaks for O-H stretch at 3365.2 cm
1
and
C-O stretch at 1042.9 cm
1
. On the other hand, cross-linked gum arabic revealed
peaks at 1725.1 cm
1
and 1631.2 cm
1
due to C-O stretch which confirms the graft
copolymerization onto gum arabic [
57
].
TGA, DTA, DTG, and DSC are the different techniques to study the thermal
behavior and stability of hydrogels. Thermogravimetric analysis of polysaccharide
hydrogels is carried out as a function of weight loss versus temperature. Degrada-
tion of hydrogels that occurs in different stages corresponds to deacetylation,
dehydration, and decarboxylation which may result in single phase or two or
more phases of decomposition. TGA of gum ghatti as well as of cross-linked
hydrogel showed two stages of decomposition. However, final decomposition
temperature of cross-linked hydrogel was found to be higher than that of gum ghatti
itself. This could be accounted to the strengthening of amorphous region on cross-
linking which increased the stability of hydrogels [
58
]. Cross-linking of gum arabic
with methylmethacrylate enhanced the thermal stability of hydrogel. This is evident
from TGA and DTA studies. Cross-linked hydrogel shows high final decomposition
(C
ΒΌ
