Solid-state NMR provides data on the crystallinity and the allomorphicity of cellulosic samples.

It allows to exactly determine the ratio between crystalline and amorphous regions in a cellulose sample, the ratio between cellulose I and cellulose II allomorphs, and to address other structural parameters, such as crystallite sizes, pore systems, and accessibility. Also changes in these parameters over time can be followed by sample comparison. The solid-state NMR experiments are performed on a Bruker Avance III HD 400 spectrometer (resonance frequency of 1H of 400.13 MHz, and 13C of 100.61 MHz, respectively), equipped with a 4 mm dual broadband CP-MAS probe. The samples can be pretreated (swollen) before measurement.

The spectra obtained need to be deconvoluted to obtain the individual contributors. There are several approaches and theories how to do this, which can be chosen upon request. For instance, peak fitting of the C-4 signal for estimating the crystallinity index is performed with the Dmfit program (Massiot, 2002) according to the model of Zuckerstätter et al. (2013), see Fig.1), left.

The solid-state NMR technique is also used to determine the degree of substitution and to clarify structural issues of solid cellulose derivatives, such as cellulose ethers (e.g., methyl, hydroxypropyl or carboxylmethyl celluloses) and cellulose esters (e.g., acetates, butyrates). In many cases, the information from solid-state measurements is most valuable when complemented by the corresponding solution NMR spectra (Karrasch et al. 2009).  

Sample amount generally required: 200 mg. If possible, please, provide information on the “chemical history” of the sample, which might assist spectral interpretation.

References

Massiot, D., Fayon, F., Capron, M., King, I., LeCalve, S., Alonso, B., Durad, J., Bujoli, B., Gan, Z., Hoatson, G.,
Modelling one- and two-dimensional solid state NMR spectra.
Magnetic Resonance in Chemistry, 40 (2002), 70-76:

Zuckerstätter, G., Terinte, N., Sixta, H., Schuster, K.C.
Novel insight into cellulose supramolecular structure through 13C CP-MAS NMR spectroscopy and paramagnetic relaxation enhancement.
Carbohydrate Polymers, 93 (2013), 122-128:

Karrasch, A.; Jäger, C.; Karakawa, M.; Nakatsubo, F.; Potthast, A.; Rosenau, T.
Solid-state NMR studies of methyl celluloses. Part 1: Regioselectively substituted celluloses as standards for establishing an NMR data basis.
Cellulose 2009, 16(1), 129-137.

Karrasch, A.; Jäger, C.; Saake, B.; Potthast, A.; Rosenau, T.
Solid-state NMR studies of methyl celluloses. Part 2: Determination of degree of substitution and O-6 vs. O-2/O-3 substituent distribution in commercial methyl cellulose samples.
Cellulose 2009, 16(6), 1159–1166. DOI 10.1007/s10570-009-9304-2.