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. 2020 Feb 5;12(2):342.
doi: 10.3390/polym12020342.

Revisiting the Dissolution of Cellulose in NaOH as "Seen" by X-rays

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Free PMC article

Revisiting the Dissolution of Cellulose in NaOH as "Seen" by X-rays

Birte Martin-Bertelsen et al. Polymers (Basel). .
Free PMC article

Abstract

Cotton production is reaching a global limit, leading to a growing demand for bio-based textile fibers produced by other means. Textile fibers based on regenerated cellulose from wood holds great potential, but in order to produce fibers, the components need to be dissolved in suitable solvents. Furthermore, the dissolution process of cellulose is not yet fully understood. In this study, we investigated the dissolution state of microcrystalline cellulose in aqueous NaOH by using primarily scattering methods. Contrary to previous findings, this study indicated that cellulose concentrations of up to 2 wt % are completely molecularly dissolved in 8 wt % NaOH. Scattering data furthermore revealed the presence of semi-flexible cylinders with stiff segments. In order to improve the dissolution capability of NaOH, the effects of different additives have been of interest. In this study, scattering data indicated that the addition of ZnO decreased the formation of aggregates, while the addition of PEG did not improve the dissolution properties significantly, although preliminary NMR data did suggest a weak attraction between PEG and cellulose. Overall, this study sheds further light on the dissolution of cellulose in NaOH and highlights the use of scattering methods to assess solvent quality.

Keywords: ZnO; cellulose dissolution; cold alkali (NaOH); microcrystalline cellulose (MCC); poly(ethylene glycole) (PEG); small-angle X-ray-scattering (SAXS); static light scattering (SLS).

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Molecular structure of cellulose.
Figure 2
Figure 2
SAXS curves of microcrystalline cellulose (MCC) dissolved in 8 wt % (2 M) NaOH for MCC concentrations of 1, 2, 3 and 4 wt % MCC. The scattered intensity was scaled with the respective MCC weight fractions to facilitate comparisons of the different scattering curves.
Figure 3
Figure 3
Experimental data for 2 wt % MCC in 8 wt % NaOH (black dots) together with the theoretical scattering profile of semi-flexible cylinders (red curve). The model parameters used for the semi-flexible cylinder scattering profile were a radius of 4.1 Å, a persistence length of 100 Å and a total contour length of 600 Å.
Figure 4
Figure 4
Static light scattering data for MCC dissolved in 8 wt % NaOH for MCC concentrations of 1, 2 and 3 wt %. The scattered intensity is displayed as original light scattering contrast (y-axis, left-hand side) versus scaled to SAXS contrast (y-axis, right-hand side). The intensity was, furthermore, scaled with the respective MCC weight fractions to facilitate comparisons of the different scattering curves.
Figure 5
Figure 5
Different concentrations of ZnO in 8 wt % NaOH.
Figure 6
Figure 6
SAXS patterns for 4 wt % MCC dissolved in 8 wt % NaOH with/without a varying content of ZnO.
Figure 7
Figure 7
SAXS patterns for 4 wt % MCC dissolved in 8 wt % NaOH with/without a varying content of PEG with an average molecular weight of 200 g/mol.
Figure 8
Figure 8
Diffusion coefficients DH2O and DPEG for H2O and PEG, respectively. The diffusion coefficients were measured at different MCC concentrations and divided by the diffusion in the neat solvent, D0. Measurements were performed for 0.1 and 1 wt % PEG-200 (blue versus green data points).

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References

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