Various cellulose II samples, ball-milled native celluloses and ball-milled wood saw dust were subjected to 2,2,6,6-tetramethypyperidine-1-oxyl radical (TEMPO)-mediated oxidation to prepare cellouronic acid Na salts (CUAs). The TEMPO-oxidized products obtained were analyzed by 13 C-NMR and size-exclusion chromatography (SEC). When the cellulose II samples with degrees of polymerization (DP) of 220-680 were used as the starting materials, the CUAs obtained had weight-average DP (DPw) values of only 38-79. Thus, significant depolymerization occurs on cellulose chains during the TEMPO-mediated oxidation. These DP values of CUAs correspond to the cellulose II crystal sizes along the chain direction in the original cellulose II samples, but not necessarily to their leveling-off DP values. CUAs can be obtained also from ball-milled native celluloses in good yields by TEMPO-mediated oxidation, although their DPw values are lower than about 80. On the other hand, CUA with DPw of about 170 was obtained from ball-milled wood saw dust.

Curdlan, amylodextrin, and regenerated cellulose fiber were subjected to electromediated oxidation with a 4-acetamido-TEMPO catalyst in a buffer at pH 6.8 without NaClO or NaClO(2). More than 90% of the C6 primary hydroxyls of Curdlan and amylodextrin were converted to sodium carboxylate groups by this method. Molecular mass values of the oxidized products were much higher than those prepared by the TEMPO/NaBr/NaClO system at pH 10. When the regenerate cellulose fiber was treated by the TEMPO electromediated oxidation for 45 h, carboxylate and aldehyde groups of 1.1 and 0.6 mmol/g, respectively, were formed in the oxidized cellulose fiber. The original fibrous and fine surface morphologies were maintained, and nearly no weight losses by the oxidation were observed. Thus, the TEMPO electromediated oxidation is a characteristic and environmentally friendly chemical modification for regenerated cellulose fibers, films, and related forming materials, and ion-exchangeable carboxylate and reactive aldehyde groups can be efficiently introduced into regenerated celluloses.

A softwood bleached kraft pulp (SBKP) was subjected to electro-mediated oxidation in water with TEMPO or 4-acetamido-TEMPO without any chlorine-containing oxidant. Solid recovery ratios of water-insoluble fractions of the oxidized SBKPs were more than 80%, and C6-carboxylate contents increased up to approximately 1 mmol g -1 after oxidation for 48 h. Significant amounts of C6-aldehyde groups (0.17-0.38 mmol g -1 ) were also formed in the oxidized SBKPs. The degree of polymerization decreased from 2,200 to 520 and 1,400 by the oxidation for 48 h with TEMPO at pH 10 and 4-acetamido-TEMPO at pH 6.8, respectively. The original cellulose I crystal structure and crystallinity of SBKP were maintained after the oxidation, indicating that all C6-oxidized groups were selectively formed on crystalline cellulose microfibril surfaces. The oxidized SBKPs with carboxylate contents of more than 0.9 mmol g -1 were convertible to individual cellulose nanofibrils in yields of more than 80% by disintegration in water.

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Three groups of cellulose II samples, 20% NaOH-treated native celluloses (M-native celluloses), commercial regenerated celluloses and those treated with 20% NaOH (M-regenerated celluloses), were subjected to dilute acid hydrolysis at 105°C to obtain so-called leveling-off degrees of polymerization (LODP). Molecular mass parameters of the acidhydrolyzed products were analyzed by SEC-MALLS using 1% LiCl/DMAc as an eluent. The LODP values were in the order of M-native celluloses % M-regenerated celluloses [ regenerated celluloses. The LODP values of M-regenerated celluloses are 1.5-1.7 times as much as those of the regenerated celluloses; the cellulose II crystallites in regenerated celluloses increase in size to the longitudinal direction by the alkali treatment and the successive acid hydrolysis at 105°C. This increase in the longitudinal crystal sizes might primarily occur during acid hydrolysis. All the acid-hydrolyzed products had bimodal SEC elution patterns, i.e. the predominant high-molecular-mass and minor low-molecular-mass components, the latter of which corresponded to DP 20.