TEMPO-mediated oxidation of β-chitin to prepare individual nanofibrils

TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation was applied to beta-chitins, originating from tubeworm and squid pen, to prepare chitin nanofibrils. Water-insoluble fractions of the TEMPO-oxidized beta-chitins were obtained in various ratios by controlling the addition level of NaClO used as the primary oxidant in the oxidation. The water-insoluble fractions of the TEMPO-oxidized tubeworm beta-chitins, when they had carboxylate groups of 0.18-0.25 mmol/g, were successfully converted to highly viscous and translucent gels by disintegration in water. The gels consisted of mostly individual nanofibrils 20-50 nm in width and at least several microns in length. On the other hand, the water-insoluble fractions of the TEMPO-oxidized squid pen beta-chitins could be transformed to neither transparent nor translucent dispersions under any oxidation or disintegration conditions used. When sufficient amounts of NaClO were used, both beta-chitins were completely oxidized to the corresponding water-soluble polyuronic acids by oxidation of all C6 primary hydroxyls to carboxylate groups. (C) 2009 Elsevier Ltd. All rights reserved.