Non-isothermal dehydration kinetic study of a new swollen biopolymer silver nanocomposite hydrogel

Thermal dehydration kinetic of a novel swollen silver nanocomposite hydrogel (SNH), prepared based on poly(acrylic acid) grafted onto salep as a water soluble polysaccharide backbone, was studied by thermogravimetry under non-isothermal conditions. The values of apparent activation energies (E-a) and pre-exponential factors (A) for a set of reaction models at 5, 10, 15, and 20 K min(-1) heating rates were determined. The dependence of the activation energy on the extent of conversion was obtained by the model-free methods. Apparent activation energy (E-a) of the process was calculated from Kissinger-Akahira-Sunose and Tang isoconversional methods. From the strong dependence of the E-a value on the extent of conversion (alpha) for the investigated process, it was found that the dehydration process of SNH is complex and we cannot explain the whole process by a single mechanism. In the low extent of conversion (alpha), E-a rapidly decreases and the dehydration process is complex and probably involving a combination of several processes. In the range of alpha = 0.40-0.90, E-a is nearly constant and the dehydration process can be assumed to follow a single-step reaction. The results obtained from Criado and Invariant kinetic methods, in the constant-E-a region, confirmed that probable model for the dehydration process agreed with R3 model.