Cellulose solutions in water containing metal complexes

Aqueous solutions of a number of metal complexes have been found to dissolv e cellulose. Recently, a number of new metal complexes have been developed that completely dissolve cellulose by deprotonating and coordinative bindin g the hydroxyl groups in the C2 and C3 position of the anhydro glucose. A d etailed comparative light scattering study is given for cellulose in Schwei zer's reagent (cuoxam), Ni-tren, and Cd-tren. Cuoxam is the well-known solu tion of cupric hydroxide in aqueous ammonia, and the abbreviation tren stan ds 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 lambda(0) = 457.9 nm, and the data from thes e solvents required an absorption Correction according to the Lambert-Beer law. Cd-tren is almost colorless, and the data could be used without correc tion. Because of traces of colloid particles, possibly originating from the metal hydroxides, a special treatment for optical clarification became nec essary. 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 hi ghest degrees of polymerization of cotton linters and bacterial cellulose ( DPw = 9700). The limits for the two other solvents were DPw < 6300 for Ni-t ren and DPw < 5300 for cuoxam. A fairly high chain stiffness was found with Kuhn segment lengths of l(K) = 15.8 +/- 1.4 nm for Cd-tren, l(K) = 10.2 +/ - 0.8 nm for Ni-tren, and l(K) = 13.1 +/- 1.2 nm for cuoxam, corresponding to characteristic ratios of C infinity = 24.6, 15.4, and 19.4, respectively . The problem of preferential adsorption is discussed.