Comparison of sample crystallinity determination methods by X-ray diffraction for challenging cellulose I materials

Abstract

Cellulose crystallinity assessment is important for optimizing the yield of cellulose products, such as bioethanol. X-ray diffraction is often used for this purpose for its perceived robustness and availability. In this work, the five most common analysis methods (the Segal peak height method and those based on peak fitting and/or amorphous standards) are critically reviewed and compared to two-dimensional Rietveld refinement. A larger (n ¼ 16) and more varied collection of samples than previous studies have presented is used. In particular, samples (n ¼ 6) with low crystallinity and small crystallite sizes are included. A good linear correlation (r 2 ! 0:90) between the five most common methods suggests that they agree on large-scale crystallinity differences between samples. For small crystallinity differences, however, correlation was not seen for samples that were from distinct sample sets. The least-squares fitting using an amorphous standard shows the smallest crystallite size dependence and this method combined with perpendicular transmission geometry also yielded values closest to independently obtained cellulose crystallinity values. On the other hand, these values are too low according to the Rietveld refinement. All analysis methods have weaknesses that should be considered when assessing differences in sample crystallinity.

Supercritical water hydrolysis: a green pathway for producing low-molecular-weight cellulose

“…The degree of crystallinity was determined by using a modified version of the amorphous fitting method. 34 Diffraction peaks of both cellulose Iβ 7 (n = 18) and cellulose II 35 (n = 17) were fitted to the radial integrals along with the amorphous model (sulphate lignin). To reduce the number of free fitting parameters, the positions of the cellulose II peaks were fixed to those obtained from the WI-LMWC and the relative height and the peak width were limited to be within 5% of the corresponding values of the precipitate.…”

13C NMR assignments of regenerated cellulose from solid-state 2D NMR spectroscopy

“…For native cellulose, solid-state nuclear magnetic resonance (NMR) spectroscopy studies (Foston, 2014;Larsson, Wickholm, & Iversen, 1997;Newman & Hemmingson, 1995;Wickholm, Larsson, & Iversen, 1998) have, together with other methods, such as XRD (Ahvenainen, Kontro, & Svedström, 2016;Terinte, Ibbett, & Schuster, 2011), been able to clarify the constitution of the elementary fibrils and the fibril aggregates in cellulose fibers. These findings have been key to increasing the value of native cellulose products (O'Sullivan, 1997).…”

Effect of ultrasonication on physicochemical properties of apple based nanocellulose-calcium carbonate composites

“…The intensity of reflections was measured over the angular 5°-90°2h with step intervals of 0.05°. The duration of the reflection count was 10 s. The crystalline phase composition and degree of crystallinity was calculated due to the Polish Standard PN-EN 13925-1:2007 based on amorphous subtraction method (Ahvenainen et al 2016). Briefly, the CI [%] of a sample is defined by the intensity ratio of the diffraction peaks and of the sum of all measured intensity.…”