Materials 2011, 4(11), 1985-2002; doi:10.3390/ma4111985
Article

Cellulose Isolation Methodology for NMR Analysis of Cellulose Ultrastructure

Received: 26 September 2011; Accepted: 17 October 2011 / Published: 7 November 2011
(This article belongs to the Special Issue Carbohydrate Polymers)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract: In order to obtain accurate information about the ultrastructure of cellulose from native biomass by 13C cross polarization magic angle spinning (CP/MAS) NMR spectroscopy the cellulose component must be isolated due to overlapping resonances from both lignin and hemicellulose. Typically, cellulose isolation has been achieved via holocellulose pulping to remove lignin followed by an acid hydrolysis procedure to remove the hemicellulose components. Using 13C CP/MAS NMR and non-linear line-fitting of the cellulose C4 region, it was observed that the standard acid hydrolysis procedure caused an apparent increase in crystallinity of ~10% or less on the cellulose isolated from Populus holocellulose. We have examined the effect of the cellulose isolation method, particularly the acid treatment time for hemicellulose removal, on cellulose ultrastructural characteristics by studying these effects on cotton, microcrystalline cellulose (MCC) and holocellulose pulped Populus. 13C CP/MAS NMR of MCC indicated that holocellulose pulping and acid hydrolysis has little effect on the crystalline ultrastructural components of cellulose. Although any chemical method to isolate cellulose from native biomass will invariably alter substrate characteristics, especially those related to regions accessible to solvents, we found those changes to be minimal and consistent in samples of typical crystallinity and lignin/hemicellulose content. Based on the rate of the hemicellulose removal, as determined by HPLC-carbohydrate analysis and magnitude of cellulose ultrastructural alteration, the most suitable cellulose isolation methodology utilizes a treatment of 2.5 M HCl at 100 °C for a standard residence time between 1.5 and 4 h. However, for the most accurate crystallinity results this residence time should be determined empirically for a particular sample.
Keywords: acid hydrolysis; cellulose; crystallinity; isolation method; solid-state NMR; 13C CP/MAS
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MDPI and ACS Style

Foston, M.B.; Hubbell, C.A.; Ragauskas, A.J. Cellulose Isolation Methodology for NMR Analysis of Cellulose Ultrastructure. Materials 2011, 4, 1985-2002.

AMA Style

Foston MB, Hubbell CA, Ragauskas AJ. Cellulose Isolation Methodology for NMR Analysis of Cellulose Ultrastructure. Materials. 2011; 4(11):1985-2002.

Chicago/Turabian Style

Foston, Marcus B.; Hubbell, Chistopher A.; Ragauskas, Art J. 2011. "Cellulose Isolation Methodology for NMR Analysis of Cellulose Ultrastructure." Materials 4, no. 11: 1985-2002.

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