CP/MASS 13C NMR Spectra of Cellulose Solids: An Explanation by the Intramolecular Hydrogen Bond Concept

Abstract

ABSTRACT:CPIMASS 13 C NMR spectra of wood pulp with the crystal form of cellulose I (referred to as cellulose I), cellulose regenerated from mercerized wood pulp with crystal form of cellulose II (cellulose II), and cellulose powder ground in ball mill were investigated. The spectrum of ball milled cellulose powder had broad carbon peaks at almost the same positions as those in solution, suggesting that there is no strong intramolecular hydrogen bonds of specific bond length. For cellulose I and II, one or two sharp components, in addition to broad component, were observed for each carbon and the former component was assigned to a strong intramolecular hydrogen bond. Among three possible intramolecular hydrogen bonds, 0 3-H · · · 0 2-H · · · and 0 6 -H · · · simultaneous hydrogen bonds of the former two can explain consistently all the peaks of the NMR spectrum of cellulose I experimentally observed. To explain the NMR spectrum of cellulose II, the three intramolecular hydrogen bonds are necessary.KEY WORDS CPIMASS 13 C NMR I Cellulose I Cellulose I I Cellulose II/ Intramolecular Hydrogen Bond I Recently, solid state high resolution 13 C NMR spectra were observed, using the crosspolarization/magic angle sample spinning (CP/ MASS) technique, for various cellulose samples of different crystalline form, crystallinity and super-molecular structure, revealing the usefulness of CP/MASS NMR method for analyzing the crystalline and non crystalline solid structure of celluloses. 1 -9 Each peak, assigned to C 1 , C 4 , and C 6 carbons in anhydroglucopyranose ring, was observed to consist of one or two sharp resonance(s) and a broad one, respectively. The relative content of the sharp and broad components, estimated from integral, depended significantly on crystal structure, crystallinity and morphology.5 In particular, the remarkable variation in the shape of the c4 carbon peak at 80-90 ppm (tetramethylsilane was used as a reference standard) has attracted the attention of many investigators. On the basis of a linear relationship between the integrated fraction of the downfield sharp component of C 4 carbon peaks, obtained in CP/MASS 13 C NMR spectra and the crystallinity determined by X-ray diffraction for regenerated cellulose sample with different crystallinity and cotton, Horii et a/. 4 concluded that the downfield sharp and upfield broad components are contributions from the crystalline and non-crystalline components, respectively. Earl and VanderHart 5 concluded from an analysis of the CP /MASS 13 C NMR spectra of native cellulose from several origins that the broad peaks of the c4 and c6 carbons are attributed to anhydroglucose on the surface of cellulose elementary fibrils in addition to non-crystalline and narrow C 4 and C 6 peaks (at 66 and 90 ppm) are due to anhydroglucose underneath the elementary 701

Determination of Intramolecular Hydrogen Bonds and Selective Coordination of Sodium Cation in Alkalicellulose by CP/MASS 13C NMR

“…10 Unexpectedly, the C 1 carbon peak of alkalicellulose is sharp at 108 ppm and significantly outside the possible variation of the C 1 carbon peak of cellulose. This must be explained on a basis other than the intramolecular hydrogen bonding.…”

“…Figure 1 shows the CP/MASS NMR spectra of cellulose sample C-1 (Figure 1a), cited from the previous paper 10 and of its alkali cell uloses 100 80 60ppm AC-1 and AC-la (Figures lb and c, respectively). Table I shows the peak positions (TMS as reference material) and integrated peak intensity (in blanket) of NMR spectra in Figure 1.…”

Structural Changes in Wood Pulp Treated by 55 wt% Aqueous Calcium Thiocyanate Solution

“…22 indicated that Xam(C3) is a measure of the degree of break down of intramolecular hydrogen bonds between C(3)-0H · · ·0(5') and the peak at 73 ppm is due to C(3) and C(2) carbon when the intermolecular hydrogen bonds, such as C(2)0-H · · · 0(6') for the natural cellulose and C(6)0H · · · 0(2') for regenerated cellulose were formed, respectively. From these facts, the intra-and intermolecular hydrogen bonds in the recovered cellulose at td = 1440 min are expected to develop in the order of methanol, water, and acetone.…”

13C NMR Study on the Distribution of Substituent Groups on Trihydric Alcohol Units in Cellulose Xanthate

“…For the latter case, we employed an alkali-soluble cellulose, reported by Kamide et a/. 16 25°C) and having the low degree of intramolecular hydrogen bond 17 (crystal form: cellulose I) was used as a starting material for the preparation of ex in the liquid-liquid reaction. The liquid-liquid reaction was carried out as follows: A 0.5 g of the cellulose was immersed into 5 g of 2.5 N sodium hydroxide (NaOH)jdeuterium oxide (0 2 0) solution at ooe, stirred vigorously.…”