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

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.

Probing Interactions in Combined Hydroxide Base Solvents for Improving Dissolution of Cellulose

“…It has also been suggested that the cellulose might not be molecularly dissolved in NaOH, but that it aggregates in solution already at low concentrations, as investigated by scattering methods [3]. There are however conflicting reports about the state of the cellulose in NaOH (aq), which suggests that the cellulose is sensitive to the preparation method and handling of the solutions [4].…”

Preparation and characterization of self-reinforced paper using NaOH/thiourea aqueous solution at room temperature

“…It can be found that NaOH alone can increase the stress at break of the paper. It is known from the literature that NaOH alone can dissolve a small amount of cellulose (Martin-Bertelsen et al 2020). Therefore, we speculate that the increase in the stress at break of paper may be related to the partial dissolution of cellulose.…”

Cellulose dissolution and gelation in NaOH(aq) under controlled CO2 atmosphere: supramolecular structure and flow properties

“…With this as a starting point, SAXS results revealed that in the dissolved state, prior to gelation (sample S1), the cellulose chains were dissolved in a rather stiff conformation, as reported previously. 60 Fitting a cylinder model 61 to sample S1 (Figure 3d) yielded a radius of 0.28 nm and length of 16 nm, indicating individually dissolved cellulose chains with straight segments of (approximately 30 glucose units). The gelation showed up in the SAXS intensities as an increased contribution of low values of the scattering vector q (Figure 3d).…”