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) over bar) were analyzed for the first time by thermogravimetry coupled to infrared spectroscopy TG-FTIR in order to evaluate the effect of (DD) over bar on the thermal decomposition process. (DD) over bar values of chitins and chitosans were determined by H-1-NMR and structural difference were investigated by FTIR, SEM and XRD. Thermal stability of chitosan with 98, 87, 71% (DD) over bar, chitins with 47 and 27% (DD) over bar and commercial alpha-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) over bar.