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 λ0 = 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 ± 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.