Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 6, Issue 9, Pages 6127-6138Publisher
AMER CHEMICAL SOC
DOI: 10.1021/am500359f
Keywords
nanocellulose; AFM; TEM; NMR; IGC; Raman; fluorescence
Funding
- AFOSR [MIPR F1ATA03239G001 A1]
- Swiss National Science Foundation (NRP 62: Smart Materials) [406240_126046]
- Lars-Erik Thunholms Foundation
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This work describes the measurement and comparison of several important properties of native cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), such as crystallinity, morphology, aspect ratio, and surface chemistry. Measurement of the fundamental properties of seven different CNCs/CNFs, from raw material sources (bacterial, tunicate, and wood) using typical hydrolysis conditions (acid, enzymatic, mechanical, and 2,2,6,6-tetramethylpiperidiny1-1-oxyl (TEMPO)-mediated oxidation), was accomplished using a variety of measurement methods. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and C-13 cross-polarization magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy were used to conclude that CNCs, which are rodlike in appearance, have a higher crystallinity than CNFs, which are fibrillar in appearance. CNC aspect ratio distributions were measured and ranged from 148 +/- 147 for tunicate-CNCs to 23 +/- 12 for wood-CNCs. Hydrophobic interactions, measured using inverse gas chromatography (IGC), were found to be an important contribution to the total surface energy of both types of cellulose. In all cases, a trace amount of naturally occurring fluorescent compounds was observed after hydrolysis. Confocal and Raman microscopy were used to confirm that the fluorescent species were unique for each cellulose source, and demonstrated that such methods can be useful for monitoring purity during CNC/CNF processing. This study reveals the broad, tunable, multidimensional material space in which CNCs and CNFs exist.
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