Thermal Analysis and Degradation Kinetics of Dextran and Highly Substituted Dextran Acetates

Dextran acetates were synthesized to study their thermal behavior in comparison with pure dextran. The results have indicated that dextran is significantly stabilized after acetylation. Dextran acetates are thermally 65-74 °C more stable as compared to pure dextran in terms of maximum decomposition temperature (Tdm). Likewise, degradation of dextran acetates also starts and ends later than dextran as shown by relatively higher initial (Tdi) 3-33 °C and final decomposition temperature (Tdf) 55-69 °C. The dextran acetates can be arranged in increasing order of thermal stability: dextran acetate DS 2.91 < dextran DS 2.98 < dextran acetate DS 3. The activation energy (Ea) of dextran and dextran acetates was calculated with the help of Friedman, Broido and Chang kinetic models while order of reaction (n) was calculated from thermal data using Chang and Kissinger models. Several other important parameters were also calculated including frequency factor (Z), enthalpy (∆H), Gibbs free energy (∆G) and entropy (∆S). The integral procedural decomposition temperature (IPDT) and comprehensive index of intrinsic thermal stability (ITS) was also drawn from TG curves using Doyle’s method. The dependence of IPDT, ITS and Ea on DS of the acetylation of dextran is also discussed.

Muhammad Amin, Muhammad Ajaz Hussain, Dure Shahwar and Mazhar Hussain