Preparation of oxidized celluloses in a TEMPO/NaBr system using different chlorine reagents in water

Three chlorine reagents (NaClO solution, solid sodium dichloroisocyanurate (NaDCC), and solid NaClO·5H₂O) were used as primary oxidants in the TEMPO/NaBr oxidation of wood cellulose in water. The active chlorine content of NaDCC was stable during storage, while that of NaClO solution decreased by 20% after storage in a tightly closed bottle for 1 year. As NaClO·5H₂O has a melting point of ~ 25 °C, solid NaDCC was favored for use in laboratory experiments among the three chlorine reagents. TEMPO-oxidized celluloses prepared from wood cellulose using the three different chlorine reagents (10 mmol/g-cellulose) in water at pH 10 showed no significant differences in weight recovery ratio, carboxylate content, or viscosity-average degree of polymerization (DP_v). When TEMPO/NaBr/NaDCC oxidation was applied to wood cellulose in water at pH 9, the weight recovery ratio and DP_v of the oxidized cellulose were clearly higher than those prepared with the three chlorine reagents in water at pH 10, and the carboxylate content was 1.6 mmol/g when the amount of NaDCC added was 5 mmol/g-cellulose. Therefore, it was possible to prepare TEMPO-oxidized celluloses with higher weight recovery ratios, higher DP_v values, and similar carboxylate contents using NaDCC. Furthermore, adding NaDCC to the wood cellulose slurry in one portion did not increase the reaction mixture pH. These results showed that using NaDCC as primary oxidant in the TEMPO/NaBr oxidation of wood cellulose in water at pH 9 was advantageous compared using all three chlorine reagents in water at pH 10.