Humic acid embedded chitosan/poly (vinyl alcohol) pH-sensitive hydrogel: Synthesis, characterization, swelling kinetic and diffusion coefficient

In the present research, humic acid (HA) embedded chitosan (CHT)-poly (vinyl alcohol) (PVA) pH-sensitive hydrogels have been synthesized using glutaraldehyde as a crosslinker. The hydrogels were characterized by Fourier-transform infrared (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) analysis. The effect of HA content, pH, and temperature on the equilibrium solvent uptake has been investigated. With higher HA contents, the equilibrium swelling capacity increases while lower concentrations of acid cause a decrease in the degree of the swelling. The hydrogels have been found to undergo a number of swelling/deswelling cycles when pH of the swelling medium changes from 1.5 to 11.0. Fick's law, first-order, and second-order kinetic models were applied to the swelling ratio of hydrogels to explain the mass transfer mechanism and specify swelling kinetic parameters. The swelling parameters such as equilibrium swelling capacity, swelling rate constant, swelling exponent, initial swelling rate, diffusion coefficient, etc., have been evaluated.