Analyses of Radical Behavior in TEMPO-Mediated Oxidation of Cotton Fabric under Neutral Conditions, Using Electron Spin Resonance

Cotton fabric was oxidized with 2,2,6,6-tetramethylmpiperidine-1-oxyl radical (TEMPO) or 4- acetoamido-TEMPO (4-AcNH-TEMPO) and sodium hypochlorite (NaClO) as catalysts and sodium chlorite (NaClO2) as a primary oxidant in a phosphate buffer at pH 6.8. The reaction temperature was increased from room temperature to 80 ̊C for the initial 43 min and then maintained at 80 ̊C for ~120 min. Portions were taken from the reaction mixtures at various reaction times, and their radical concentrations owing to TEMPO or 4-AcNH-TEMPO were determined using an electron spin resonance apparatus. The concentrations of 4- AcNH-TEMPO and TEMPO during oxidation of cotton fabric with 4-AcNH-TEMPO/NaClO/NaClO2 and TEMPO/NaClO/NaClO2 systems, respectively, were determined to study oxidation mechanisms/processes. As a result, the relationships between radical concentration and reaction time during heating from room temperature to 80 ̊C and during a constant temperature at 80 ̊C were successfully obtained. The results provided fundamental information concerning oxidation mechanisms/processes of cotton fabric under the reaction conditions used in this study. Moreover, the changing patterns of carboxylate content and viscosityaverage degree of polymerization of the oxidized cotton fabrics were studied in terms of reaction times,temperatures, radical concentrations, and oxidation mechanism/processes.