Swelling kinetic of hydrogels from methyl cellulose and poly(acrylamide)

The poly (acrylamide) (PAAm) and methyl cellulose (MC) hydrogels were prepared with a crosslinker using N, N'-methylene bisacrylamide (NNMBA) and glutaraldehyde (GA). In order to do this, it was necessary to modify the percentages of catalyst (potassium persulfate, KPS) and crosslinker (NNMBA) for poly (acrylamide). To evaluate their maximum degree of swelling and to determine the swelling kinetics, the quantity of fluids absorbed by films was measured at different temperatures (20, 30, and 40 degrees C and pH's (acidic, basic, and neutral). According to the results obtained from the experiment, the most suitable temperature and pH were 30 degrees C and neutral, conditions under which the highest swelling values were obtained. In the kinetic study, during the first hours, a first order kinetic (Fick Model) was observed. The results were non-Fickian, revealing that the chain's diffusion and relaxation processes occur at the same time during the absorption of the solution. For longer periods of time, with the exception of a 40 degrees C temperature (where the first order kinetic was identified), a second order kinetic was observed (Schott Model), indicating that there is no polymeric chain relaxation, but rather, contraction and collapse of the material. The relaxations of the polymer chain were observed after swelling via SEM pictures.