Cellulose Solutions in Water Containing Metal Complexes

Abstract

Aqueous solutions of a number of metal complexes have been found to dissolve cellulose. Recently, a number of new metal complexes have been developed that completely dissolve cellulose by deprotonating and coordinative binding the hydroxyl groups in the C2 and C3 position of the anhydro glucose. A detailed comparative light scattering study is given for cellulose in Schweizer's reagent (cuoxam), Ni-tren, and Cd-tren. Cuoxam is the well-known solution of cupric hydroxide in aqueous ammonia, and the abbreviation tren stands for tris(2-aminoethyl)amine. Cuoxam and Ni-tren are deep blue solvents. The light scattering measurements were carried out with the blue line of an argon ion laser at wavelength λ 0) 457.9 nm, and the data from these solvents required an absorption correction according to the Lambert-Beer law. Cd-tren is almost colorless, and the data could be used without correction. Because of traces of colloid particles, possibly originating from the metal hydroxides, a special treatment for optical clarification became necessary. A large number of samples, cotton linters, various pulp celluloses, and bacterial celluloses, were studied. All three solvents exhibited good solution properties, but only Cd-tren was capable of dissolving also the highest degrees of polymerization of cotton linters and bacterial cellulose (DP w) 9700). The limits for the two other solvents were DPw < 6300 for Ni-tren and DPw < 5300 for cuoxam. A fairly high chain stiffness was found with Kuhn segment lengths of lK) 15.8 (1.4 nm for Cd-tren, lK) 10.2 (0.8 nm for Ni-tren, and lK) 13.1 (1.2 nm for cuoxam, corresponding to characteristic ratios of C∝) 24.6, 15.4, and 19.4, respectively. The problem of preferential adsorption is discussed.

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

“…96 For cellulose dissolution in an aqueous metal complex based system, it has been realized that the deprotonation of OH-groups (C2 and C3) is necessary before the complex can be established at those positions. [97][98][99][100] Recently, more conclusive evidence for ionization at high pH has been obtained by Bialik et al in studies on model systems. 101 To elucidate the dissolution mechanism, these authors performed electrophoretic NMR on cellobiose, a subunit of cellulose, showing that cellobiose acts as an acid with two dissociation steps at pH 12 and 13.5 (Fig.…”

Spherical nanocomposite particles prepared from mixed cellulose–chitosan solutions

“…Today, commercial production is either carried out via the viscose (Huber et al 2011;Klemm et al 2004) or the Lyocell processes (Rosenau et al 2002), using derivatizing and non-derivatizing solvents, respectively; these processes involve toxic derivatization steps or toxic and expensive chemicals. There are other known routes for cellulose dissolution with inorganic complexes (Miyamoto et al 1995;Saalwächter et al 2000), or certain exotic organic solvents (Philipp 1993), which, however, cannot be considered sustainable for large scale production. In the early 1990s, alkali-based aqueous solvents started to gain more academic and technical attention for the reasons of being more environmental benign than other protocols (Isogai and Atalla 1998;Kamide et al 1992;Zhou and Zhang 2000).…”

Direct Dissolution of Cellulose: Background, Means and Applications

“…This is true for example with Cuoxam, Nitren and Cuen which all are deep blue, while Pden only displays a weak yellow color. The color of the solvent or in some cases the cellulose -metal complex in itself may cause problems in analytical applications where light scattering or refractive index is used [68]. Aqueous inorganic salts or metal complexes can also be used for dissolution and regeneration of cellulose.…”