Swelling studies of chitosan/cashew nut gum physical gels

Gels from chitosan/cashew nut gum (CH/CNG) were prepared with different chitosan to cashew nut gum ratio and their swelling behaviour was investigated as a function of pH and salt. Infrared and Carbon-13 nuclear magnetic resonance spectroscopy were used to elucidate the gel structure. Swelling in water diminishes sharply when the ratio CH/CNG increases. In the presence of Na+ counterions the degree of swelling (Q) remains fairly constant, whereas in presence of Ca2+ counterions Q increases with the CH/CNG ratio. It was found that swelling is maximal at pH 2 and at pH 10, where the gel can absorb water up to 44 times its own weight. Chitosan amine and cashew nut carboxylate groups seem to play a major role in the swelling mechanism, being the polysaccharide gum the major factor responsible for water absorption.