Institution: | aGraduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan bResearch & Development Division, Nippon Paper Industries Co. Ltd, 5-21-1 Oji, Kita-ku, Tokyo 114-0002, Japan |
Abstract: | The 2,2,6,6-tetramethylpiperidine-1-oxy radial (TEMPO)-mediated oxidation was applied to aqueous slurries of cotton linters. The water-insoluble fibrous fractions thus obtained in the yields of more than 78% were characterized by solid-state 13C-NMR, X-ray diffraction and scanning electron microscopic analyses for evaluation of distribution of carboxylate groups formed in the TEMPO-oxidized celluloses. The patterns of solid-state 13C-NMR spectra revealed that the oxidation occurred at the C6 primary hydroxyl groups of cellulose. X-ray diffraction and scanning electron microscopic analyses showed that such C6 oxidation took place at the surfaces of cellulose I crystallites without any oxidation at the C6 of inside cellulose I crystallites. Thus, carboxylate and aldehyde groups introduced into the TEMPO-oxidized celluloses are densely present on the surfaces of cellulose I crystallites. In addition, the obtained results revealed that the shoulder signal due to non-crystalline C6 carbons at about 63 ppm in solid-state 13C-NMR spectra of native celluloses is ascribed to those of surfaces of cellulose I crystallites or those of cellulose microfibrils. |