Cellulose organic solutions: A nuclear magnetic resonance investigation

Abstract

Four solvents of cellulose have been studied by using 13C‐NMR spectroscopy. All these solvents, N‐methyl morpholine‐N‐oxide, methylamine, hydrazine, and paraformaldehyde (PF), contained dimethyl sulfoxide (DMSO) as a cosolvent. Oligomers of cellulose of DP = 10 soluble in hot DMSO have been used as model compounds. 13C chemical shifts and line shapes show that three of the mentioned solvents are “true solvents” of cellulose. On the other hand, dissolution of cellulose in DMSO‐PF system occurs by the formation of a statistical derivative of cellulose. Enriched 13C bacterial cellulose on C‐1 and C‐6 positions have been used to identify the 13C positions mainly in DMSO‐N‐methyl morpholine‐N‐oxide system. This solvent has been found to be degradative for the macromolecule when the solution is kept at 100°C over a long period. Viscosity measurements show a reduction of the molecular weight in these conditions. Polarimetry indicates that no glucose is present in solution and hence there is a statistical break of the chain. Enriched cellulose solution in DMSO–N‐methyl morpholine‐N‐oxide has been also used for relaxation time (T1) determination both of the solvent and of the enriched carbons of the polymer. Nuclear Overhauser enhancement (NOE) was found to be 1.8 for C‐1 and 2.1 for C‐6 showing that relaxation phenomenon is not purely dipolar. T1 values of 97 and 65 msec are found for C‐1 and C‐6 of cellulose, in good agreement with the values known for polysaccharides. Determination of T1 for the different carbon atoms of the solvent DMSO‐N‐methyl morpholine‐N‐oxide with and without cellulose shows a large reduction of T1 for N‐methyl morpholine‐N‐oxide molecule. This denotes a slower molecular motion of this molecule and a preferential interaction with the cellulose macromolecule.

Two-Dimensional Nuclear Magnetic Resonance Spectra of Cellulose and Cellulose Triacetate

“…A peak at 81.8 ppm and a doublet peak at 78.3 ppm (in total three carbon peaks) cannot be assigned .explicitly due to the heavy overlapping of the proton peaks at 3.57 ppm which are directly correlated with the above three carbon peaks. The above assignment carried out here for 13 C peak is, as far as C 1 , C 2 , and C 6 carbon peaks are concerned, in good coincidence with those by Gagnaire et al 2 for cellulose oligomer/ DMSO-d 6 system and by Nardin and Vincendon 15 for cellulose/DMAC/LiCl system. Figure 7(a) shows the 1 H 1D-NMR spectrum of CT A/TCM-d system.…”

“…The assignment given by Gagnaire et al 2 for cellulose can be considered reasonable in DMSO-d6 ; however, mention should be made of the assignment of peaks in other solvents: it could not always be done, by referring to their assignment straightly, because Cs, C 3 , and C 2 peaks of cellulose oligomer in DMSO-d 6 were located very close to each other and the order of the peak positions may possibly to change in other solvents. In addition, note that the positions of the ring carbon peaks are significantly influenced by substitution of hydroxyl groups in cellulose derivatives, for which the assignment for cellulose by Gagnaire et al cannot be straightforwardly applied as it is and the methods proposed hithertofor in analysis of NMR spectra of cellulose derivatives are without exception too elaborate and timeconsuming and additionally they are not sufficiently accurate.…”

“…Peak assignment of 13 C NMR spectrum is generally more difficult than that of 1 H NMR, needing rather considerably complicated, and skillful techniques. For example, by applying the selective heteronuclear spin decoupling technique in measurement of 13 C NMR of cellulose oligomer with DP= 10 in DMSO, and also by taking into account an isotope effect of deuterated compounds, Gagnaire et al 2 assigned, from lower magnetic field, the peaks of cellulose oligomer, to C 1 , C 4 , C 5 , C 3 , C 2 , and C 6 carbons, respectively. Kowsaka and his coworkers,6 assigned, by applying low-power ~elective spin decoupling technique, the peaks of carbonyl carbon of acetyl group directly combined with C 2 , C 3 , and C 6 positions of CA and assigned also, 9 with the help of distortionless enhancement by polarization transfer (DEPT) technique, C 6 peak of CX.…”

Synthesis and Characterizations of Graft Copolymer of Ethylcellulose with Poly(caprolactone monoacrylate)

“…From Figure 2A, PCLA shows hydrocarbon around 1.38-2.32 and 4.01-4.35 ppm, methylene around 5.89-5.91 and 6.34-6.38 ppm and hypo-methylene around 6.12-6.19 ppm. The proton spectrum of EC-g-PCLA ( Figure 2D) shows the peaks of EC 16 ( Figure 2B) and shows methylene and hypo-methylene of PCLA. 17 It also shows methyl of TDI resonance at 2.19 ppm, and benzene ring resonance at 7.04-7.47 ppm from NCOPCLA in Figure 2C.…”

Effect of Ionic Liquids on Oil Palm Biomass Fiber Dissolution

“…The NMMO dissolution technique is well established for producing regenerated cellulose, with an output of 220 kilotons/year of Lyocell fibers. NMR analyses have shown that neither cellulose derivation nor cellulose complex formation takes place with NMMO (Gagnaire et al 1980). Fink et al (2001) has reviewed the structure formation of regenerated cellulose materials from NMMO solutions.…”