PH and thermo-responsive hybrid hydrogels based on PNIPAAM and keratin

Abstract

This study investigated PNIPAAM/keratin hybrids that were prepared by free radical polymerization of NIPAMM in the presence of functionalized keratin with vinyl group. Functionalized keratin presented functionality greater than 2, therefore, it acted as a crosslinker and a pH-responsive segment in the polymer network. Preparation occurred in an aqueous medium at room temperature or 60 °C, using H2O2/ascorbic acid and ammonium persulfate redox initiators, respectively. Polymerization at 60 °C led to phase segregation due to the lower critical solution temperature (LCST) behavior of the PNIPAAM aqueous solution. However, this phenomenon had little influence on the global composition of the hybrids, and the incorporation of functionalized keratin into the hybrids was slightly higher for those prepared at room temperature. Keratin had no influence on the critical temperature of the PNIPAAM/keratin hydrogels. However, the extent of hydrogel contraction at LCST was proportional to the keratin amount and functionalization degree. The charge balance of the polymeric network determined the swelling behavior in solutions at different pH. The mechanical properties of the hydrogels, evaluated by compression tests, showed that the resistance of the hydrogels was proportional to the keratin concentration and functionalization degree. The hydrogels presented a foam-like structure with interconnected pores, a configuration that allowed the transport and adsorption of Cu2+ from aqueous solutions. These characteristics make the hybrids and their hydrogels potential candidates as cation adsorbent materials.