A new look towards the thermal decomposition of chitins and chitosans with different degrees of deacetylation by coupled TG-FTIR.

Chitins and Chitosans with different degrees of deacetylation (DD¯) were analyzed for the first time by thermogravimetry coupled to infrared spectroscopy TG-FTIR in order to evaluate the effect of DD¯ on the thermal decomposition process. DD¯ values of chitins and chitosans were determined by 1H-NMR and structural difference were investigated by FTIR, SEM and XRD. Thermal stability of chitosan with 98, 87, 71% DD¯, chitins with 47 and 27% DD¯ and commercial α-chitin were evaluated. Thermal decomposition of chitosans occurs in two steps, while for chitins occurs predominantly in first stage under air atmosphere. Commercial chitin thermally decomposed at lower temperatures than highly deacetylated chitosan. A faster thermal degradation process was found for chitins, except for commercial sample. TG-FTIR of evolved gas evidenced a complex gaseous mixture mainly composed by ammonia, acetic acid, acetamide, water, monoxide and carbon dioxide in proportions that are deeply dependent on the DD¯.