Chemistry Reference
In-Depth Information
in nature and this could be the reason for the high water absorption capacity of
starch-g-ethyl methacrylate/sodium acrylate/sodium silicate.
X-ray diffractograms of virgin low-density polyethylene (LDPE) and starch-
graft-LDPE samples have shown that there was a decrease in percent crystallinity
with the increase in percent graft yields of starch from 61.5 % to 80.68 % [
19
]. This
was attributed to the formation of cross-links by starch molecules on the backbone
of PE. It was also envisaged that, in addition to the decrease in percent crystallinity
of PE, there was trapped amorphous starch between the PE chains, which also had
contributed towards the decrease in crystallinity of the modified PE. The decrease
in crystallinity of PE has been due to the disruption of crystallites and the dilution of
inherent crystallinity of PE [
68
]. Singh et al. [
13
] reported that microwave-
accelerated grafting of potato starch with acrylamide resulted in loss of crystallinity
of the starch and showed halos typical for amorphous polymers in the XRD
patterns.
Comparison of XRD of starch, poly(acrylonitrile) (PAN) and starch-graft-PAN
was used to confirm grafting reaction [
47
]. XRD spectra of the grafted starch
showed increased crystallinity in the region of 2
28-32
due to the presence
θ ¼
18
originally present in the
starch has been significantly reduced after grafting (Fig.
3.8
). The XRD patterns of
graft copolymers of mixed monomers vinyl acetate and butyl acrylate onto corn
starch showed that there were several dispersion peaks; therefore, the graft
copolymerisation was the concomitant structure of a little crystalline state and
amorphous state [
30
].
Jyothi et al. [
20
] have done the powder X-ray diffraction analysis of native
cassava starch as well as starch-graft-poly(acrylamide) and observed that native
cassava starch showed C
A
-type X-ray diffraction pattern with major peaks at
diffraction angles, 2
of PAN grafts on starch backbone, while peak at 2
θ ¼
14.932
5.928), 17.141
5.169), 18.058
θ ¼
(
d ¼
(
d ¼
(
d ¼
4.908), 22.989
(
d ¼
3.866) and 23.408
(
d ¼
3.797). The graft copolymers
showed decreased peak intensity in comparison to native starch, which indicates
reduction in crystallinity, and with an increase in percentage graft yield, there was a
decrease in crystallinity.
The X-ray diffraction analysis of amylopectin-rich starch grafted with
polyethers revealed that the diffractograms of the amylopectin used for grafting
presented A-type pattern, whereas the peaks disappeared after the grafting reaction,
indicating a predominantly amorphous state.
3.3.4.4 NMR Spectra of Graft Copolymers
Cassava starch was chemically modified by radiation grafting with acrylic acid to
obtain cassava starch-graft-poly(acrylic acid), which was further modified by
esterification and etherification with poly(ethylene glycol) 4000 and propylene
oxide, respectively [
45
], and the product was characterised by NMR spectroscopy.
The hydroxypropyl groups on cassava starch were etherified with propylene oxide.
The presence of a peak at a chemical shift of 19.96 ppm is indicative of the presence
