Solid-state CP/MAS carbon-13 NMR study of cellulose polymorphs

Abstract

Highly crystalline cellulose samples, which also have a high purity of crystal form, were used or prepared as models of cellulose polymorphs, cellulose I, III,, IV,, II, IIIn, and IVn, for solid-state 13C NMR and X-ray diffraction analyses. Differences between cellulose I, II, and III in the 13C NMR spectra appear at the chemical shifts of C6 in the anhydroglucose units; they have signals at 65.5-66.2, 63.5-64.1, and 62.1-62.8 ppm, respectively. Cellulose IV has a doublet signal for C4 at 83.6-84.6 ppm and a signal for C6 at 63.3-63.8 ppm, which is identical with that of cellulose II. Thus the mechanisms for the formation of cellulose polymorphs are primarily ascribed to some conformational and/or environmental transformations of C4 and C6. So-called cellulose IV, is likely to be a mixture of cellulose I and real cellulose IV,. The differences between cellulose III, and III,, were not detected clearly at the chemical shifts of C4 and C6 but at the chemical shift of Cl and the signal pattern of C2, C3, and C5.

Solid-State 13C Nuclear Magnetic Resonance Characterization of Cellulose in the Cell Walls of Arabidopsis thaliana Leaves

“…Cellulose IV contributes peaks at chemical shifts similar to those for cellulose I, although the patterns of relative signal strengths are different (Isogai et al, 1989). The published data for cellulose IV cannot account for a peak at 62.0 ppm in Figure 9a.…”

“…10a) also showed a peak at 86.2 ppm, which was not present in the spectrum of apple cell walls (Newman et al, 1994). The narrow lineshape is consistent with a wellordered (crystalline) environment, but the chemical shift is not consistent with known crystalline forms of cellulose (Isogai et al, 1989). The peak is therefore tentatively assigned to well-ordered chains of noncellulosic substances, e.g.…”

“…Cellulose 111 can be distinguished by its relatively simple spectrum (Isogai et al, 1989). In particular, it shows no peaks in the range 63 to 70 ppm and can therefore not account for peaks observed at 65.4 and 66.4 ppm in Figure 9a.…”

“…9b). This particular brand of microcrystalline cellulose was chosen because it was used as an example of cellulose I in a particularly thorough NMR and diffraction study of cellulose polymorphs (Isogai et al, 1989). We therefore interpreted our spectrum of the A. thaliana cell walls in terms of cellulose I as the dominant form of cellulose.…”

Rapid Dissolution of Cellulose in Ionic Liquid with Different Methods

“…Spectrum 1 gave strong crystalline peak at 22.3° for (002) crystal plane and at 16.1° merged from peaks of (110) and (11 0) crystal plane, indicating a cellulose Ι crystalline structure for native cellulose (Focher et al, 2001;Oh et al, 2005). After dissolution with ultrasonic irradiation and regeneration, cellulose sample comprised mainly amorphous structure and little cellulose ΙΙ crystalline structure, suggested by a broad peak at 19.8° in the diffratogram (Isogai et al, 1989), as shown in spectrum 2. However, spectrum of sample 31 and 34 displayed three obvious crystalline peaks at 12.2°, 20.2° and 22.0°.…”