TEMPO-mediated Oxidation of Cellulose in Carbonate Buffer Solution

The reaction stability is a challenge in the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of cellulose. Carbonate buffer solution (Na2CO3/NaHCO3) was used to study pH effects on stability of the oxidation reaction in this work. The structure and morphology of cellulose fibers were characterized by XRD and SEM techniques, respectively. It was found that the carboxyl content of oxidized cellulose was changed with different composition ratio of buffer solutions. The highest carboxyl content was obtained at the molar ratio of 7:3. The NaClO addition, as well as reaction temperature, affected the process of the oxidation reaction. The carboxylate content of the oxidized cellulose was increased as the temperature and NaClO consumption increased. However, both temperature and NaClO consumption have negative effect on yield. SEM results showed that the morphology of oxidized cellulose fibers was significantly changed at high reaction temperature. XRD showed that the oxidized cellulose fibers maintained the crystal structure of cellulose I. However, the crystallinity was decreased from 56.4 to 40.8 % with increasing oxidation temperature from 25 to 40 degrees C.