TEMPO-MEDIATED OXIDATION OF CELLULOSE AND PREPARATION OF CELLULOSE NANOFIBRILS

摘要

Hard wood Kraft pulp was oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) using sodium hypochlorite as the primary oxidant and catalytic amount of sodium bromide at pH 10.0. The effect of the amount of primary oxidant on the degree of oxidation was studied. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were applied to study morphology and crystal structure of the oxidized cellulose. Carboxylate content and water retention value (WRV) of the oxidized cellulose were also analyzed. The results showed that the recovery of oxidation was more than 90%, and that the carboxylate content reached a maximum of 0.81mmol/g (cellulose) when the sodium hypochlorite added was 3mmol/g (cellulose). WRV was significantly increased from 106% to 224%. Cellulose nanofibrils of 5-20nm in width were obtained by homogenization of oxidized cellulose using an ultrasound wave generator. A stable homogeneous suspension of cellulose nanofibrils was also formed. After the oxidation the cellulose crystallinity increased from 61.10% to 63.84%, but the crystallinity of the nanofibrils was reduced to 55.89%, which can not be ignored.