Rheological behavior of pH responsive composite hydrogels of chitosan and alginate: Characterization and its use in encapsulation of citral

The pure and composite hydrogels of chitosan with sodium alginate were synthesized at various pH values and characterized by rheology and 1R-spectroscopy. Chitosan shows gelation at neutral and basic pH while sodium alginate remains in solution form at all pH values. By careful adjustment of mixing weight fraction ratio and pH, an array of hydrogels with modulated structural dynamics and viscoelasticity, mechanical strength and encapsulation capacity were obtained. At acidic pH, a higher weight fraction of alginate increased the elasticity of the hydrogels while at basic pH more percentage of chitosan stabilized the hydrogel. Strongest composite hydrogels were obtained at acidic pH and gel strength decreased on increasing pH of the synthetic medium. The synthesized hydrogels were studied for their encapsulation capability towards Citral. The pure chitosan hydrogels showed maximum encapsulation capacity followed by the composite hydrogels prepared at neutral pH. This study highlights that a range of composite hydrogels with modified properties can be obtained by simple changes in experimental conditions exploiting physical interactions and can help in better understanding of niche of its applicability in research and industry. (C) 2018 Elsevier B.V. All rights reserved.