One-shot TEMPO-periodate oxidation of native cellulose.

TEMPO/NaClO/NaBr and sodium periodate were combined in a one-shot reaction to oxidise cellulose from bleached pulp. Oxidation of cellulose forms two fractions: a highly-carboxylated water-insoluble (up to 1.9 mmol COO-/g, DS = 0.39) and a water-soluble fraction (up to 4 mmol COO-/g, DS = 1.1). Results show that these regioselective oxidants work in synergy to produce fully-oxidised 2,3,6-tricarboxycellulose. Increasing the periodate concentration results in fibrillation and extensive depolymerisation of the pulp cellulose as more residual aldehyde groups participate in the depolymerisation process. X-ray diffraction (XRD) reveals that the addition of periodate increases cellulose crystallinity, retains crystal size but slightly alters the XRD pattern. The degree of substitution (DS), which governs the solubility of carboxylated cellulose, can be controlled by varying the periodate concentration. Combining TEMPO/NaBr/NaClO with sodium periodate simultaneously in a one-shot reaction produces low-cost cellulose with controlled level of carboxylation and unique properties.