Highlights
• Coupling of the degradation of acetylated and deacetilated units in chitosan with varying deacetylation degree.
• Model fitting of degradation in overlapped degradation mechanisms.
• Previous activation energy determination by applying “free model” methods allows subsequent model fitting of TGA traces.
• Sestack-Berggren model yields the best fit to the experimental data in chitosan.
Abstract
Thermal degradation of chitosan with varying deacetylation degree (DD) ranging between 50 and 85% was analyzed by dynamic thermogravimetric analysis at different heating rates. The present study focused on the temperature range between 500 and 800
K, above water evaporation. Thermal degradation showed a main degradation stage in this temperature interval with a second stage that appeared in the weight derivative curves as a shoulder in the high temperature side of the main peak with increasing intensity as the DD decreased. The Kissinger and isoconversional Ozawa-Flynn-Wall models were employed to evaluate the Ea of both thermal degradation processes. Different kinetic models were tested to computer simulate the thermogravimetric traces calculating the model parameters with a non-linear least squares fitting routine. The Sestack-Berggren model allowed reproducing accurately the overlapping of the two degradation mechanisms and calculating the mass fraction lost in each of them revealing the coupling between the two degradation mechanisms.
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