Synthesis, characterization, and swelling kinetics of pH-responsive and temperature-responsive carboxymethyl chitosan/polyacrylamide hydrogels

摘要

A novel pH- and temperature-responsive hydrogel composed of carboxymethyl chitosan (CMC) and polyacrylamide (PAM) semi-interpenetrating polymer networks (semi-IPNs) was synthesized by a crosslinking copolymerization route in the presence of N,N-methylene bisacrylamide and potassium persulfate. The structure of the CMC/PAM hydrogels was characterized by Fourier transform infrared spectroscopy, and the morphologies were observed by scanning electron microscopy. The swelling kinetics investigations demonstrated that the equilibrium swelling ratios (ESRs) of the semi-IPN hydrogels depended on the compositional ratios, pH values of the buffer solutions, and temperature. The ESR values increased with increasing CMC contents and pH values; this was in agreement with the maximum theoretical water contents fitted by the swelling kinetic data. The CMC/PAM hydrogels complied with Fickian behavior at pH 1.4 and non-Fickian behavior at pH 11.7 in the buffer solutions. These hydrogels displayed thermosensitivities that were different from those of common thermoresponsive gels. The swelling was enhanced when the temperature of the media was increased up to 40°C; this was followed by a reduction. Therefore, the swelling behavior of the CMC/PAM hydrogels could be controlled and modulated by means of the compositional ratios of CMC to acrylamide, pH values of the buffer solutions, and temperature.