Comparison of cast films and hydrogels based on chitin nanofibers prepared using TEMPO/NaBr/NaClO and TEMPO/NaClO/NaClO₂ systems

Neutral TEMPO/NaClO/NaClO2 (TNN) oxidation, with NaClO2 as the primary oxidant under aqueous conditions at pH 6.8 was applied to selectively oxidize surface C6 primary hydroxyl groups of alpha-chitin to carboxylate groups. When 0.1 mmol TEMPO, 1 mmol NaClO and 20 mmol NaClO2 were added to 1 g alpha-chitin, the yield of water-insoluble oxidized chitin was 91.93 %, and the carboxylate content was 0.695 mmol/g. The TNN oxidized chitin (TNN-Ch) was mostly converted to individual nanofibrils by mechanical disintegration in water, with mostly widths of 20-24 nm and average lengths of 1 mu m. Compared to chitin nanofibers produced by TEMPO/NaBr/NaClO system (TBN-ChNs), with average widths of 16.67 +/- 7.9 nm and average lengths of 770 +/- 170 nm, TNN-ChNs were wider, longer and had a higher aspect ratio; its films and hydrogels also showed better mechanical properties, which indicated the size effect on the nanofiber-based materials resulted from different oxidation process.