Characterization of cellulose nanofibrils prepared by direct TEMPO-mediated oxidation of hemp bast

被引:0
作者
Buapan Puangsin
Hiroto Soeta
Tsuguyuki Saito
Akira Isogai
机构
[1] The University of Tokyo,Department of Biomaterial Sciences
[2] Kasetsart University,Department of Forest Products, Faculty of Forestry
来源
Cellulose | 2017年 / 24卷
关键词
2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO); Hemp bast; Direct oxidation; Cellulose nanofibrils; Delignification;
D O I
暂无
中图分类号
学科分类号
摘要
Hemp bast (α-cellulose 79.4%, Klason lignin 4.9%) was directly oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation in water at pH 10 and room temperature for 2 h. The level of added NaClO in oxidation varied from 5 to 30 mmol/g (based on dry weight of hemp bast). Weight recovery ratios of the TEMPO-oxidized hemp bast celluloses were in the range of 81–91%, and their carboxylate contents increased up to 1.2 mmol/g with the increased NaClO addition level. The lignin contents decreased to 0.5–0.9% after oxidation, and the viscosity-average degrees of polymerization decreased from 1100 to 560 because of depolymerization during oxidation. Thus, direct TEMPO-mediated oxidation of hemp bast introduced a significant number of carboxylate groups and simultaneously achieved sufficient delignification. Small amounts of xylose, mannose, and rhamnose originating from hemicelluloses remained in the TEMPO-oxidized hemp bast samples prepared by oxidation with 5–20 mmol/g NaClO. However, oxidation with 30 mmol/g NaClO completely removed these hemicellulose-originating sugars, and produced almost pure TEMPO-oxidized cellulose. When TEMPO-oxidized hemp bast samples were mechanically disintegrated in water, their nanofibrillation yields were 58–65%. After removal of unfibrillated fractions by centrifugation, transparent dispersions showed birefringence when observed between cross-polarizers, while atomic force microscopy images showed near-individually dispersed nanofibril elements with widths of ~2 nm.
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页码:3767 / 3775
页数:8
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