he substitution is not complete. However the presence of cinnamic acid in chitosan modification caused an increase in the carbon and hydrogen content in the resulting material compared with the starting chitosan. A decrease in nitrogen/carbon ratio suggests that the substitution occurred.

3.2. Thermal Methods of Analysis

3.2.1. Thermogravimetry (TG)

TG curve of chitosan is shown in Figure 1. There are two degradation stages in chitosan polymer. In the first stage, weight loss starts at ~220˚C and continues to ~320˚C with ~50% weight loss. The maximum rate of weight loss, shown by derivative equipment associated with TG apparatus, occurs at ~295˚C. The second stage reaches a maximum at ~ 470˚C with a weight loss percentage of ~40%.

There are two degradation stages in NCC polymer as shown in Figure 2. The first stage starts at ~145˚C with a weight loss percentage of ~50%. The maximum rate of weight loss at ~360˚C with a weight loss percentage of ~44%. TG curves of NCC and chitosan polymers reveal that chitosan is more thermally stable than NCC polymer.

The effective activation energies of the thermal degradation of chitosan and NCC polymers were determined from the temperature dependence of the chain repture rate. The rate constant of the thermal degradation plotted according to the Arrhenius relationship (Figure 3). The activation energies of the chitosan and NCC polymers

Figure 1. TG curve of chitosan.

Figure 2. TG curve of NCC polymer.

Figure 3. Arrhinus plots of the rate constants of degradation of chitosan and NCC.

were found to be 52.2 and 32.7 KJ/mol, respectively. The smaller value of the activation energy of NCC than chitosan polymers indicates that the stabilities are in the same order of activation energies. Therefore, NCC polymer should undergo decomposition more readily than chitosan.

3.2.2. Thermal Degradation of NCC Polymer

The liquid fraction of the degradation of NCC polymer was injected into the GC-MS apparatus. Figures 4 (a) and (b) shows the GC trace of the liquid product of degradation of NCC polymer to 500˚C. Table 1 represents the results of degradation products which were identified by mass spectroscopy. From the degradation products it seems that the degradation of NCC polymer is characterized by the formation of low-molecular weight radicals,


Figure 4. GC curve of the degradation products of NCC polymer.

Table 1. GC-MS of the degradation products of NCC polymer

followed by random scission mechanism along the backbone chain.

The radical I may abstract H٠ to produce cinnamide (Peak 7).

The radical III may abstract 3 H٠ to produce 1-ethylbenzene as shown in peak 4 in Figure 4.

3-Phenylpropanoic acid was formed from the radical IV (Peak 8), which was confirmed by mass spectroscopy.

The aldehydic radical II may abstract H٠ to form 3,5,6-trihydroxyhexanol (Peak 6).

3,5,6-Ttrihydroxyherxanol may lose two molecules of water or formic acid forming 4,5-dihydroxypent-1-ene and 6-hydroxy-2,4-hexadienol (Peaks 3 and 5, respectively). 4,5-Dihydroxypent-1-ene may lose a molecule of water to form 5-hydroxy-1,3-pentadiene (Peak 1).

The enolic form of 3,5,6-trihydroxyhexanol may cyclized to form cyclohex-1-en-6-ol as shown in peak 2.

4. Conclusion

N-Cinnamoyl chitosan (NCC) polymer was synthesized via a Schiff reaction of chitosan with cinnamic acid. The formed modified polymer was characterized by elemental analysis (C, H, N), IR spectyroscopy and the thermal stability was compared with chitosan. Thermal degradation of the NCC polymer was studied and the degradation products were identified by GC-MS technique. 5-Hydroxy-1,3-pentadiene, cyclohex-1-en-6-ol, 4,5-dihydroxypent-1-ene, 1-ethylbenzene, 6-hydroxy-2, 4-hexadinol, 3, 5,6-trihydroxyhexanol, cinnamide and 3-phenylpronoic acid were the main degradation products. Accordingly, it seems that the mechanism of degradation of NCC polymer is characterized by elimination of low-molecular weight radicals. Combination of these radicals and random scission mechanism along the backbone chain are the main source of the degradation products.


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