Characterization of cellulose microfibrils, cellulose molecules, and hemicelluloses in buckwheat and rice husks

• Published in: Cellulose (London) Vol. 26; no. 11; pp. 6529 - 6541
• Main Authors: Nakamura, Yasutaka, Ono, Yuko, Saito, Tsuguyuki, Isogai, Akira
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 30.07.2019; Springer Nature B.V
• Subjects: Ashes; Atomic force microscopy; Atomic properties; Bioorganic Chemistry; Buckwheat; Cellulose; Ceramics; Chemistry; Chemistry and Materials Science; Comminution; Composites; Crystal structure; Dewaxing; Disintegration; Drying ovens; Glass; Leveling; Morphology; Natural Materials; Organic Chemistry; Original Research; Physical Chemistry; Polymer Sciences; Sustainable Development; Rice husk; Buckwheat husk; Neutral sugar composition; Molar mass; Nanofibril; Levelling-off DP
• ISSN: 0969-0239; 1572-882X
• DOI: 10.1007/s10570-019-02560-4

Holocelluloses, TEMPO-oxidized holocelluloses, and TEMPO-oxidized cellulose nanofibrils were prepared from buckwheat and rice husks to characterize the cellulose microfibril morphologies and holocellulose molar masses. The buckwheat and rice husks had ash contents of 0.8% and 23%, respectively. All TEMPO-oxidized holocelluloses had cellulose I crystal structures. TEMPO-oxidized cellulose nanofibrils prepared from the two husks were both ~ 3 nm wide. As significant amounts of xylan remained in the TEMPO-oxidized buckwheat and rice husk holocelluloses, the TEMPO-oxidized cellulose nanofibrils prepared from them by mechanical disintegration in water gave yields as low as 14–17% (based on dry weight of dewaxed husk samples). Atomic force microscopy images of TEMPO-oxidized cellulose nanofibrils prepared from buckwheat husks showed that individual nanofibrils with widths of ~ 3 nm were quite flexible, while nanofibril bundles had rigid and needle-like morphologies. Rice husks had a high ash content, with part of the ash remaining in the corresponding holocellulose, TEMPO-oxidized holocellulose, and TEMPO-oxidized cellulose nanofibrils. Never-dried buckwheat husk cellulose (prepared by removal of hemicelluloses from holocellulose) and oven-dried buckwheat husk holocellulose containing a significant amount of hemicelluloses had leveling-off degrees of polymerization (DPs) of 650 and 810, respectively, after dilute acid hydrolysis. In contrast, oven-dried buckwheat husk cellulose had a leveling-off DP of 270. Graphic abstract