Wood cellulose nanofibrils prepared by TEMPO electro-mediated oxidation
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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.
KeywordsElectro-mediated oxidation TEMPO 4-acetamido-TEMPO Cellulose nanofibril Carboxyl
This research was supported by the Japan Society for the Promotion of Science (JSPS), Grant-in-Aid for Scientific Research (S) and Research Fellowship for Young Scientist (Grant numbers 21228007 and 20-6499, respectively).
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