Liquid-State NMR Analysis of Nanocelluloses

Abstract

Recent developments in ionic liquid electrolytes for cellulose or biomass dissolution has also allowed for high-resolution H andC NMR on very high molecular weight cellulose. This permits the development of advanced liquid-state quantitative NMR methods for characterization of unsubstituted and low degree of substitution celluloses, for example, surface-modified nanocelluloses, which are insoluble in all molecular solvents. As such, we present the use of the tetrabutylphosphonium acetate ([P][OAc]):DMSO- d electrolyte in the 1D and 2D NMR characterization of poly(methyl methacrylate) (PMMA)-grafted cellulose nanocrystals (CNCs). PMMA- g-CNCs was chosen as a difficult model to study, to illustrate the potential of the technique. The chemical shift range of [P][OAc] is completely upfield of the cellulose backbone signals, avoiding signal overlap. In addition, application of diffusion-editing for H and HSQC was shown to be effective in the discrimination between PMMA polymer graft resonances and those from low molecular weight components arising from the solvent system. The bulk ratio of methyl methacrylate monomer to anhydroglucose unit was determined using a combination of HSQC and quantitativeC NMR. After detachment and recovery of the PMMA grafts, through methanolysis, DOSY NMR was used to determine the average self-diffusion coefficient and, hence, molecular weight of the grafts compared to self-diffusion coefficients for PMMA GPC standards. This finally led to a calculation of both graft length and graft density using liquid-state NMR techniques. In addition, it was possible to discriminate between triads and tetrads, associated with PMMA tacticity, of the PMMA still attached to the CNCs (before methanolysis). CNC reducing end and sulfate half ester resonances, from sulfuric acid hydrolysis, were also assignable. Furthermore, other biopolymers, such as hemicelluloses and proteins (silk and wool), were found to be soluble in the electrolyte media, allowing for wider application of this method beyond just cellulose analytics.

Solvent Welding and Imprinting Cellulose Nanofiber Films Using Ionic Liquids

“…Therefore, it is necessary to apply suitable analytical methods to monitor the removal of the IL. In this case, the CNFF chemical compositions were assessed using FTIR, as a rapid technique and a novel liquid-state NMR method involving the dissolution of the films into IL electrolyte solution 49 , and XRD measurements. Figure 2 shows the FTIR spectra of the untreated and IL welded sample.…”

Enhanced Reactivity in Surface-Confined Water of Hierarchically Structured Polymers

“…Increasing the water content in the cellulose sample further to higher numbers (20 wt% and 30 wt% of water) than the equilibrated moisture content of 7 wt%, did not significantly influence the kinetics of the reactions ( Figure S3) but reduced the degree of substitution (DS) of the acetylated fibers and hence the reaction efficiency (Table S2). Our results, based on diffusion-edited 1 H-NMR spectra of the acetylated fibers ( Figure 3A) in the ionic liquid [P4444][OAc] 40 (more details can be found in Supplemental Methods 1.8 and Figure S4), showed that that smaller amounts of secondary hydroxyl groups were modified under these conditions, i.e., increasing selectivity for the primary 6-OH.…”

A comparative study of water-immiscible organic solvents in the production of furfural from xylose and birch hydrolysate

“…When a diffusion-edited 1 H experiment for the same sample is measured, compared to the standard 1 H experiment ( Figure A9), it is clear to see that there is polymeric material in the DMSO-d6 solution. Diffusion-editing has the effect of removal of the low molecular weight resonances and retention of the polymeric resonances [68]. The retained signals in the soluble organic fraction from the FUR:isophorone reaction correspond to both polymerised FUR and isophorone.…”