On cellulose dissolution and aggregation in aqueous tetrabutylammonium hydroxide

Abstract

Aqueous tetrabutylammonium hydroxide, TBAH(aq), has been found to dissolve cellulose and to be a potential solvent for chemical processing or fiber spinning. In this paper, we have investigated the dissolution state of cellulose in 40 wt % TBAH(aq) solvent, and present an extensive study of rheology, combined with static light and small-angle X-ray scattering, to correlate cellulose aggregation with changes in the rheological parameters. Two cellulose molecular weights are compared. Microcrystalline cellulose (MCC), with a degree of polymerization of ca. 260, and a dissolving pulp with an approximately ten times higher molecular weight. Scattering data demonstrate that cellulose is molecularly dissolved at lower cellulose concentrations, while aggregates are present when the concentration exceeds a certain value. The onset of the aggregate formation is marked by a pronounced increase in the scattering intensity at low q, shear thinning behavior and violation of the empirical Cox-Merz rule. Additionally, the SAXS data suggest the presence of a solvation shell enriched in TBA(+) ions, compared to the bulk solvent. The results are consistent with the recent suggestion that while native cellulose I may still dissolve, solutions are, above a particular concentration, becoming supersaturated with respect to the more stable crystal form cellulose II.

On the dissolution of cellulose in tetrabutylammonium acetate/dimethyl sulfoxide: a frustrated solvent

“…For lower q-values, the scattered intensity is significantly higher compared to what is predicted by the PSM. This shows that the cellulose molecules form aggregates, again similar to what was previously observed in aqueous tetrabutylammonium hydroxide solvent (Behrens et al 2016;Gubitosi et al 2016). The green curve in Fig.…”

“…8 and previously published scattering curves for the TBAH/water system (Behrens et al 2016;Gubitosi et al 2016). Essentially, the solvation sheath of TBA þ ions around the cellulose molecules is found in both systems, which indicates the presence of charge on the cellulose chains.…”

“…Finally, we discuss the dissolution mechanism in comparison to that in aqueous ''onium'' hydroxides, a class of cellulose solvents that has attracted recent attention (Ema et al 2014;Abe et al 2015). We have recently investigated cellulose solutions in the tetrabutylammonium hydroxide (TBAH)/water solvent system using similar methods (Behrens et al 2016;Gubitosi et al 2016;Gentile and Olsson 2016).…”

The relevance of structural features of cellulose and its interactions to dissolution, regeneration, gelation and plasticization phenomena

“…[41][42][43][44] -After dissolution of native cellulose (cellulose I), which is metastable, one typically observes gelation, which is due to cellulose aggregation and the onset of precipitation of (stable) cellulose II. 45,46 The fact that gelation is significantly reduced in the presence of surfactants points to the presence of hydrophobic parts.…”

On the dissolution state of cellulose in cold alkali solutions

“…Recently we have characterized the dissolution state of microcrystalline cellulose, MCC, in the related solvent, 40 wt% tetrabutyl ammonium hydroxide in water, TBAH(aq) (Gubitosi et al 2016;Gentile and Olsson 2016;Behrens et al 2016). It was found that the cellulose was molecularly dissolved, with effectively repulsive cellulose-cellulose interactions at concentrations lower than ca.…”