Kinetics of isothermal dehydration of equilibrium swollen PAAG hydrogel under the microwave heating conditions

Abstract

The isothermal dehydration kinetics under microwave heating (MWH) of the equilibrium swollen poly(acrylic acid)-g-gelatin hydrogel (PAAG) was investigated. Dehydration kinetics curves have been measured for this recently synthesized and structurally defined hydrogel using a microwave thermogravimetric analyzer, within the temperature range from 323 to 353 K. It was found that the isothermal dehydration of the PAAG hydrogel was 15–17 times faster under the MWH than under the conventional heating (CH). We have established that the investigated dehydration is an elementary kinetics process. By applying the model-fitting method, it was found that the kinetics of isothermal dehydration under the microwave heating is mathematically best described by the Polanyi–Winger’s equation. The model rate constant values of the PAAG hydrogel isothermal microwave dehydration have been calculated. In accordance with the Arrhenius equation, the values of kinetics parameters have been obtained: Ea = 52.0 kJ mol−1 and ln(A/min−1) = 12.1. The higher values of dehydration rate under MWH, than under CH, are a consequence of the increase in the preexponential factor value caused by the change in the activated-state entropy of water molecules.