146
7 Use of Diethylenetriamine Grafted onto Glyoxal Cross-Linked …
oxidizing and still conditions show either exothermic, endothermic or both peaks as
reported by [31]. Figure 7.5a, b and c demonstrates the TGA/DTA graphs for the CS,
DCS and GDCS from room temperature to 1000 °C under nitrogen atmosphere. Onset
temperature (T onset ), final decomposition temperature (T final ) and weight loss at the
end of each stage of decay were calculated from TGA graphs, while maximum decay
temperature (T max ) was obtained from DTA graphs [32]. The TGA/DTA variables
for the set of beads are given in Table 7.1. Thermal decline for CS was within the
range of 248.54–295.76 °C with optimum decline temperature at 278.44 °C. The
evolving shoulder agrees with the decay of glycosidic bonds, while the optimum
peak implies spontaneous cleavage of the chitosan glycosidic bond. Chitosan is a
biological substance comprising units β-(14)-2-acetamido-d-glucose and β-(14)-2amino-d-glucose, and the heat resistance is improved by the crystalline nature of the
material. Consequently, the beads’ chemical transformation process decreases their
thermal strength due to the disintegration of hydrogen bonds in their composition,
and heat degradation can occur in different stages.
When glyoxal was interlinked with chitosan beads, heat decline occurred in two
stages; the first stage was 190.23–294.68 °C due to the separation of the interlinked chitosan contact. The second stage is 349.59–458.77 °C, which is due to
0
200 400 600 800 1000
20
40
60
80
100
TGA thermogram
DTA thermogram
Temperature (
o
C)
% weight
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
Derivative weight loss (% o C)
0
200 400 600 800 1000
20
40
60
80
100
TGA thermogram
DTA thermogram
Temperature (
o
C)
% weight
-0.6
-0.4
-0.2
0.0
0.2
0.4
Derivative weight loss (% o C)
(a)
(b)
(c)
0
200 400 600 800 1000
20
40
60
80
100
TGA thermogram
DTA thermogram
Temperature (
o
C)
% Weight
-7
-6
-5
-4
-3
-2
-1
0
1
Derivative weight loss (% o C)
Fig. 7.5 CS, DCS and GDCS TGA, respectively