shows the exothermic peak at 400 °C due to the decomposition of acetyl (GlcNAc) units that predominates in this structure. For the polysaccharide obtained after alkaline deacetylation up to 60 min, Fig. 5b, two exothermic peaks are observed at 296 and 404 °C related to the thermal decomposition for amine (GlcN) and acetyl (GlcNAc) residues, respectively, characteristic for chitin/chitosan sample. Thus, the amine residues are termally less stable than acetyl ones. Similar thermal behavior has been showed for chitin/chitosan samples obtained between 90 and 180 min, Fig. 5b–f. With higher deacetylation reaction time, such as 240 and 360 min, the DSC curves are typical for chitosan samples with exothermic peaks at 299 and 298 °C, respectively, Fig. 5g and h. The exothermic peak at higher temperature is practically not observed due to the low acetyl content in these samples.
It is notorious that the peak area and peak height ascribed to the amine (GlcN) groups increase and the acetyl (GlcNAc) residues decrease while the thermochemical alkaline deacetylation proceeds. The values and temperatures for peak area and height of the exothermic event regarding to the amine (GlcN) groups decomposition are presented in Table 3. The temperature intervals used to integrate the peak areas in defined in this table.