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

Abstract

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 (Ea) 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 (Ea) of the process was calculated from Kissinger–Akahira–Sunose and Tang isoconversional methods. From the strong dependence of the Ea value on the extent of conversion (α) 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 (α), Ea rapidly decreases and the dehydration process is complex and probably involving a combination of several processes. In the range of α = 0.40–0.90, Ea 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-Ea region, confirmed that probable model for the dehydration process agreed with R3 model.