The kinetics of isothermal dehydration of equilibrium swollen hydrogel of poly(acrylic-co-methacrylic acid)

Abstract

The isothermal dehydration of equilibrium swollen hydrogel of poly(acrylic-co-methacrylic acid) (PAM) was investigated. Thermogravimetric dehydration curves of equilibrium swollen PAM hydrogel at temperatures 293, 303 and 313 K were recorded. Applying model-fitting method, it was established that kinetic of isothermal dehydration of equilibrium swollen PAM hydrogel was controlled with the rate of contracting area of hydrogel network. Based on the results of differential isoconversional method it was evaluated that the kinetic parameters of the dehydration process linearly decrease with the increase of dehydration degree. Both the kinetic complexity of the dehydration process and the change in the kinetic parameters with the change in the dehydration degree is explained by energetical distribution of the dehydration centers where there are two clearly distinguishable most probable distributions of the values of activation energies, Ea, of 60.4 and 64 kJ/mol.