Studies on structure of cuprammonium cellulose i. A circular dichroism study on the dissolved state of cellulose in cuprammonium solution

Abstract

An attempt was made to clarify the dissolved state of cellulose in aq cuprammonium hydroxide solution using ultraviolet (UV) and circular dichroism (CD) spectrophotometry on cellulose and its oligomers in the solution. Negative Cotton effect and positive Cotton effect for the cellulose-cuprammonium solution are observed at 300—350nm and ca. 600 nm. The former Cotton effect seems to originate from charge transfer (CT) excitation and the latter from d-d excitation of cupric ion due to coordination of cuprammonium complex to hydroxyl group of cellulose. The experimental fact that intensity of CD for almost C2-C3 substituted methyl cellulose in cuprammonium hydroxide is nearly zero leads us to an conclusion that cuprammonium complex coordinates preferentially to hydroxyl groups at C2 and C3, giving 5 chelate form. As a dissolved state of cellulose in aq cuprammonium hydroxide, an equilibrium state between cellulose-cuprammonium complex, cellulose and cuprammonium hydroxide was predicted where copper-cellulose molar ratio of ca. 0.6—0.8 is stable for the cellulose-cuprammonium complex. © 1995, The Society of Polymer Science, Japan. All rights reserved.