Measuring the crystallinity index of cellulose by solid state 13C nuclear magnetic resonance

Abstract

The crystallinity index of cellulose is an important parameter to establish because of the effect this property has on the utilization of cellulose as a material and as a feedstock for biofuels production. However, it has been found that the crystallinity index varies significantly depending on the choice of instrument and data analysis technique applied to the measurement. We introduce in this study a simple and straightforward method to evaluate the crystallinity index of cellulose. This novel method was developed using solid state 13 C NMR and subtraction of the spectrum of a standard amorphous cellulose. The crystallinity indexes of twelve different celluloses were measured and the values from this method were compared with the values obtained by other existing methods, including methods based on X-ray diffraction. An interesting observation was that the hydration of the celluloses increased their crystallinity indexes by about 5%, suggesting that addition of water increased cellulose order for all the cellulose samples studied.

Cellulose I crystallinity determination using FT–Raman spectroscopy: univariate and multivariate methods

“…Considering that in WAXS the peak-height crystallinity calculation method gave significantly higher values compared to other X-ray and NMR methods (Park et al 2009) the authors make the following suggestion based on the findings of the present investigation. It is proposed that, in the simple peak height method, the amorphous contribution be measured at *21°instead of *18°.…”

“…Higher crystallinity by WAXS methods has been reported in the literature. For example, Park et al (2009) used three X-ray methods (peak height, peak deconvolution, and amorphous contribution subtraction) to calculate the crystallinity index of 11 cellulose samples. The three methods produced significantly different crystallinity indexes.…”

Structural factors affecting 13C NMR chemical shifts of cellulose: a computational study

“…However, monosaccharide and disaccharide models differ greatly from a cellulose microfibril and as a result there were significant differences (* 10 ppm) between the calculated and observed d 13 C values. For example, compared to the cellulose experimental d 13 C4 values of 79-93 ppm (Park et al 2009), their calculated d 13 C4 were between * 65 and * 75 ppm. To improve the agreement between observation and calculation, in the work presented here, we utilized an Ib cellulose model system containing 12 cellotetraose chains with three different conformations of the C6 exocyclic group (tg, gt and gg) as shown in Fig.…”

“…4 Top row, relative potential energies of cellotetramers with respect to different torsion angle HO3-O3/C4-H4 when the exocyclic group at C6 taking tg, gt and gg conformations, respectively; Middle row, distances between H4 and HO3 (shown as circle, primary y-axis) and C4 NMR chemical shifts (shown as black dots, secondary y-axis) in relation to torsion angle HO3-O3/C4-H4. ; Bottom row, representative structures of cellulose tetramer of tg conformation at the max d 13 C4 (conformation A), plateau/energy minimum (conformation B), and min d 13 C4 (conformation C) Cellulose (2018) 25:23-36 31 (Park et al 2009), which varied from 77 to 90 ppm. Due to the small size of the model from the previous work, their calculated d 13 C4 varied from 70 to 75 ppm, * 10 ppm lower than the experiment values.…”

“…Solid-state NMR spectroscopy of cellulose produces doublet d 13 C4 peaks that have been used to estimate the degree of crystallinity of cellulose as well as the number of glucan chains in elementary cellulose microfibrils (Kennedy et al 2007;Newman et al 1994Newman et al , 1996Park et al 2009;Teeäär et al 1987;Wang et al 2015). Two d 13 C4 peaks, centered at * 89 and * 85 ppm, have been assigned to ordered (crystalline) and disordered (amorphous) regions, respectively (Atalla et al 1980;Earl and VanderHart 1980).…”