NaBr-free TEMPO-catalyzed oxidation of cellulose with sodium dichloroisocyanurate in water at pH 9

The conventional TEMPO/NaBr/NaOCl oxidation of cellulose in water at pH ~10 is an established method for preparing TEMPO-oxidized cellulose nanofibrils (TEMPO: 2,2,6,6-tetramethylpiperidine-1-oxyl radical). However, significant depolymerization, the formation of sodium polyglucuronate homopolymers, and other side reactions are unavoidable, resulting in the formation of oxidation products with heterogeneous chemical structures or low mass-recovery ratios. In this study, NaBr-free TEMPO/sodium dichloroisocyanurate (NaDCC) oxidation of cellulose in water at pH 9 was developed, which is advantageous in terms of process controls, mass recovery ratios, constant carboxy group contents, and maintenance of the original fiber morphologies, even under harsh oxidation conditions. This is probably because the oxidation of C6-OH groups into sodium C6-carboxylate groups occurred selectively on the cellulose microfibril surfaces, with less depolymerization or side reactions. TEMPO/NaDCC-oxidized microcrystalline cellulose and cotton linters cellulose were converted into cellulose nanocrystals and microfibrillated cellulose, respectively, by mechanical disintegration in water. In water at pH 9, the new TEMPO/NaDCC oxidation system can be used to oxidize various cellulose, pulp, and plant samples, or to produce TEMPO-oxidized cellulose fibers and nanomaterials with the benefits of lower cost, ease of handling, less depolymerization or fewer side reactions, higher mass recoveries, and lower environmental impact.