- K. Saalwächter, W. Burchard, P. Klüfers, G. Kettenbach,
P. Mayer, D. Klemm, S. Dugarmaa.
Cellulose Solutions in Water Containing Metal Complexes.
Macromolecules 33, 4094-4107 (2000).
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 a wavelength of 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 (DPw=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 nm for Cd-tren, lK=10.2 nm for Ni-tren, and lK=13.1 nm for cuoxam, corresponding to characteristic
ratios of C∞ = 24.6, 15.4, and 19.4, respectively. The problem
of preferential adsorption is discussed.