title: 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.
authors.affiliation: Division of Physical Chemistry, Lund University , SE-22100 Lund, Sweden.
authors.forename: Marta
authors.initials: M
authors.lastname: Gubitosi
authors.affiliation: Faculty of Sciences and Technology (MeditBio), University of Algarve , Campus de Gambelas, Ed. 8, 8005-139 Faro, Portugal.
authors.forename: Hugo
authors.initials: H
authors.lastname: Duarte
authors.affiliation: Division of Physical Chemistry, Lund University , SE-22100 Lund, Sweden.
authors.forename: Luigi
authors.initials: L
authors.lastname: Gentile
authors.affiliation: Division of Physical Chemistry, Lund University , SE-22100 Lund, Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Olsson
authors.affiliation: Faculty of Sciences and Technology (MeditBio), University of Algarve , Campus de Gambelas, Ed. 8, 8005-139 Faro, Portugal.
authors.forename: Bruno
authors.initials: B
authors.lastname: Medronho
mesh_terms: D002482:Cellulose / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D053838:Scattering, Small Angle; D012995:Solubility; D013696:Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D000644:Quaternary Ammonium Compounds; D014867:Water; D002482:Cellulose; C009405:tetrabutylammonium