Cationization of kappa- and iota-carrageenan – Characterization and properties of amphoteric polysaccharides

• Amphoteric derivatives were obtained by cationization of kappa and iota carrageenan.
• Reaction was carried out with 3-chloro-2-hydroxypropyltrimethylammonium chloride.
• Products were characterized by elemental analysis, FT-IR, NMR, and ESI MS.
• Mechanical and rheological behavior showed interesting properties.
• Modified carrageenans improved flocculation of kaolin compared to controls.

Commercial kappa- and iota carrageenans were cationized with 3-chloro-2-hydroxypropyltrimethylammonium chloride in aqueous sodium hydroxide solution. For kappa-carrageenan three derivatives with different degrees of substitution were obtained. Native and amphoteric kappa-carrageenans were characterized by NMR and infrared spectroscopy, scanning electron and atomic force microscopy; methanolysis products were studied by electrospray ionization mass spectrometry. Young moduli and the strain at break of films, differential scanning calorimetry, rheological and flocculation behavior were also evaluated; the native and the amphoteric derivatives showed different and interesting properties. Cationization of iota-carrageenan was more difficult, indicating as it was previously observed for agarose, that substitution starts preferentially on the 2-position of 3,6-anhydrogalactose residues; in iota-carrageenan this latter unit is sulfated.