Size effect of carboxymethyl chitin nanocrystals on the properties of foams in aqueous surfactant solutions

Abstract

Size effect of carboxymethyl chitin nanocrystals on foam stability and foaming ability in aqueous surfactant solutions was investigated. The chitin nanocrystals (CNC) were synthesized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidation of alpha-chitin at pH 10 similar to 11 with ultrasonic treatment. The sizes of chitin nanocrystal (CNC) were controlled by adding different amounts of NaClO during the TEMPO oxidation reaction. Since the surface of CNC was negatively charged, the aqueous foams prepared by cationic cetyltrimethylammonium bromide (CTAB) surfactant and CNC showed good foam properties. The CNC was also freeze-dried to confirm the effect of surface charge and hydrophobicity in foam. With the freeze-dried CNC, foamability was increased by lowering the size of CNC, but foam stability was decreased. On the other hand, with the non-freeze-dried CNC, foam stability was increased but foaming ability was decreased by lowering the size. The Cryo-SEM images demonstrated that CNCs were well adsorbed at air/water interface in foam, and improved foam stability.