Summary of Investigations in Regard to the Kinetics of Absorbed Water Dehydration from Different Hydrogels

Abstract

A review of novel kinetics models of dehydration (DH) of equilibrium swollen hydrogels: poly(acrylic acid) hydrogel (PAAH), poly(acrylic-co-methacrylic acid) (PAMAH), and poly(acrylic acid)-g-gelatin (PAAGH), is presented. Kinetic curves of isothermal and non-isothermal dehydration of hydrogels were measured using thermogravimetric methods. The kinetic complexity of the dehydration process was analyzed by different methods: integral, differential, Kissinger-Assakura-Sanura (KAS), and Vyzovkin’s method. The complex kinetics of dehydration of hydrogels was described by a series of new kinetic models: distribution apparent energy activation model (DAEM), Webull’s distribution of reaction times, the dependence of the degree of conversion (α) on the temperature which is defined by the logistic function, coupled single step-approximation and iso conversion curve. Procedures were developed for calculating the function of the density distribution of probability (g(Ea)) of apparent activation energy (Ea). The relationship between the phase state of the absorbed water in hydrogel and the form of function of distribution of apparent Ea and kinetic parameters of dehydration was analyzed.