Characterization of cellulose microfibrils, cellulose molecules, and hemicelluloses in buckwheat and rice husks
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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.
KeywordsBuckwheat husk Rice husk Molar mass Nanofibril Neutral sugar composition Levelling-off DP
This research was supported by Core Research for Evolutional Science and Technology (CREST, Grant Number JPMJCR13B2) of the Japan Science and Technology Agency (JST). We thank Simon Partridge, PhD, from Edanz Group (www.edanzediting.com/ac) for editing a draft of this manuscript.
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