Comparative analyses on isothermal kinetics of water evaporation and PAAG hydrogel dehydration under the microwave heating conditions

Abstract

The isothermal kinetic of water evaporation and poly(acrylic-g-gelatin) hydrogel (PAAG) dehydration in temperature range from 333 K to 363 K was investigated under microwave heating conditions (MWH). The isothermal kinetic curves of water evaporation and hydrogel dehydration could be entirely mathematically described by the Polanyi–Winger equation. The values of the rate constant for water evaporation and hydrogel dehydration and their kinetics parameters were calculated. Both the value of activation energy (Ea) and pre-exponential factor (lnA) for hydrogel dehydration under MWH is higher than those for water evaporation. The existence of a linear correlation relationship — compensation effect was established between the values of kinetics parameters for water evaporation and hydrogel dehydration. The values of thermodynamic parameters of activated complex formation for water evaporation and hydrogel dehydration (standard enthalpy of activation (ΔH*), standard entropy activation (ΔS*), and standard free Gibbs energy of activation (ΔG*)) were calculated. The mechanism of water molecules activation, both for evaporation and dehydration, by the resonant transfer of certain energy amount from the reaction system to the libration vibration of molecules of water is suggested.