Preparation and properties of cationic starch-carrageenan­sodium alginate hydrogels with pH and temperature sensitivity.

ABSTRACT

In this study, cationic starch-carrageenan­sodium alginate (CAS/CR/SA) hydrogels with different weight ratios of carrageenan and sodium alginate were prepared and their properties such as scanning electron microscopy (SEM), rheological properties, Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance (1H NMR), X-ray diffraction (XRD), and methylene blue adsorption test were measured. The results showed that the viscosity and the shear strain resistance of the CAS/CR/SA hybrid hydrogels positively correlated with their sodium alginate contents. The hybrid hydrogels with high carrageenan contents exhibited a high energy storage modulus (G') and a high loss modulus (G"). The swelling and methylene blue adsorption experiments showed that the CAS/CR/SA hydrogels had pH and temperature sensitivity. The hydrogels reached adsorption equilibrium in 12 h (alkaline conditions) and 24-36 h (acidic conditions). The adsorption kinetics of the hybrid hydrogels showed that their adsorption process was mainly controlled by chemisorption and that adsorption was exothermic (ΔH° < 0).